From bc70de7b3302d5a81515b901cae376b8b51d2004 Mon Sep 17 00:00:00 2001 From: "Arnold D. Robbins" Date: Fri, 16 Jul 2010 13:09:56 +0300 Subject: Move to gawk-3.1.0. --- doc/ChangeLog | 43 +- doc/Makefile.am | 80 + doc/Makefile.in | 480 +- doc/ad.block | 7 +- doc/awkcard.in | 919 +- doc/cardfonts | 2 +- doc/gawk.1 | 1475 ++- doc/gawk.info | 25095 ++++++++++++++++++++++++------------------- doc/gawk.texi | 28949 +++++++++++++++++++++++++++++--------------------- doc/gawkinet.info | 4246 ++++++++ doc/gawkinet.texi | 5075 +++++++++ doc/lflashlight.eps | 135 + doc/no.colors | 2 +- doc/rflashlight.eps | 141 + doc/statist.eps | 557 + doc/statist.jpg | Bin 0 -> 20400 bytes doc/texinfo.tex | 368 +- doc/uf002331.eps | 1155 ++ doc/uf002331.jpg | Bin 0 -> 36796 bytes 19 files changed, 45349 insertions(+), 23380 deletions(-) create mode 100644 doc/Makefile.am create mode 100644 doc/gawkinet.info create mode 100644 doc/gawkinet.texi create mode 100644 doc/lflashlight.eps create mode 100644 doc/rflashlight.eps create mode 100644 doc/statist.eps create mode 100644 doc/statist.jpg create mode 100644 doc/uf002331.eps create mode 100644 doc/uf002331.jpg (limited to 'doc') diff --git a/doc/ChangeLog b/doc/ChangeLog index 2d8e5208..79dac766 100644 --- a/doc/ChangeLog +++ b/doc/ChangeLog @@ -1,3 +1,44 @@ +Sun Jun 3 13:04:44 2001 Arnold D. Robbins + + * Release 3.1.0: Release tar file made. And there was + rejoicing. + +Mon May 14 19:57:31 2001 Arnold D. Robbins + + * gawk.texi, gawkinet.texi: Versions for distribution + put in place. + * gawk.1, awkcard.in: Minor edits for consistency of + usage, formatting. + +Wed Nov 22 14:57:59 2000 Arnold D. Robbins + + * gawk.texi, gawk.1, awkcard.in: Removed all documentation + of abort. + +Sun Aug 13 11:23:50 2000 Arnold D. Robbins + + * gawk.texi, gawk.1, awkcard.in: documented sort function + and optional third argument to match. + +Sun Aug 13 00:40:41 2000 Arnold D. Robbins + + * gawk.texi: hardwired publisher info. + * publisher.texi: Removed. Not needed any more. + * gawkinet.texi: Added title page stuff. + +Thu Jul 5 21:05:57 2000 Arnold D. Robbins + + * gawk.texi: moved to use of @command, @option everywhere + appropriate. Removed all @page and @group in anticipation + of re-page breaking. Updated stuff for install-info. + Added FDL. + +Tue Nov 10 11:42:26 1998 Arnold D. Robbins + + * publisher.texi: new file with publisher related info. + * Makefile.in: updated dvi and postscript targets to make + them lots smarter about not reformatting if need be. + Mon Aug 7 15:23:00 2000 Arnold D. Robbins * Release 3.0.6: Release tar file made. @@ -52,7 +93,7 @@ Thu Jul 29 23:15:34 1999 Arnold D. Robbins install it directly. Wed Jun 30 16:14:36 1999 Arnold D. Robbins - + * Release 3.0.4: Release tar file made. This time for sure. Wed Oct 7 21:59:33 1998 Arnold D. Robbins diff --git a/doc/Makefile.am b/doc/Makefile.am new file mode 100644 index 00000000..3a9e4b44 --- /dev/null +++ b/doc/Makefile.am @@ -0,0 +1,80 @@ +# +# doc/Makefile.am --- automake input file for gawk +# +# Copyright (C) 2000, 2001 the Free Software Foundation, Inc. +# +# This file is part of GAWK, the GNU implementation of the +# AWK Programming Language. +# +# GAWK is free software; you can redistribute it and/or modify +# it under the terms of the GNU General Public License as published by +# the Free Software Foundation; either version 2 of the License, or +# (at your option) any later version. +# +# GAWK is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY; without even the implied warranty of +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +# GNU General Public License for more details. +# +# You should have received a copy of the GNU General Public License +# along with this program; if not, write to the Free Software +# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA +# + +## process this file with automake to produce Makefile.in + +info_TEXINFOS = gawk.texi gawkinet.texi + +man_MANS = gawk.1 igawk.1 + +EXTRA_DIST = ChangeLog README.card ad.block setter.outline \ + awkcard.in awkforai.txt texinfo.tex cardfonts \ + macros colors no.colors $(man_MANS) \ + uf002331.eps uf002331.jpg lflashlight.eps rflashlight.eps \ + statist.jpg statist.eps + +MAKEINFO = @MAKEINFO@ --no-split + +TROFF = groff -t -Tps +SEDME = sed -e "s/^level0 restore/level0 restore flashme 100 72 moveto (Copyright `date '+%m-%d-%y %T'`, FSF, Inc. (all)) show/" \ + -e "s/^\/level0 save def/\/level0 save def 30 -48 translate/" + +CARDSRC = $(srcdir)/macros $(srcdir)/cardfonts $(srcdir)/colors awkcard.tr +CARDSRC_N = $(srcdir)/macros $(srcdir)/cardfonts $(srcdir)/no.colors awkcard.tr +CARDFILES= $(CARDSRC) ad.block awkcard.in setter.outline + +# Use this if your troff can correctly handle macros from 'colors' file +AWKCARD = awkcard.ps + +# Uncomment the following definition of AWKCARD if your troff can produce +# Postscript but still has troubles with macros from 'colors'. As this +# is not groff you will have to change TROFF macro as well. Do not forget +# to ensure that awkcard.tr is processed by tbl. +#AWKCARD = awkcard.nc + +postscript: gawk.ps gawkinet.ps gawk.1.ps igawk.1.ps $(AWKCARD) + +gawk.ps: gawk.dvi + dvips -o gawk.ps gawk.dvi + +gawkinet.ps: gawkinet.dvi + dvips -o gawkinet.ps gawkinet.dvi + +gawk.1.ps: gawk.1 + -groff -man $(srcdir)/gawk.1 > gawk.1.ps + +igawk.1.ps: igawk.1 + -groff -man $(srcdir)/igawk.1 > igawk.1.ps + +awkcard.tr: awkcard.in + sed 's:SRCDIR:$(srcdir):' < $(srcdir)/awkcard.in > awkcard.tr + +awkcard.ps: $(CARDFILES) + $(TROFF) $(CARDSRC) | $(SEDME) | cat $(srcdir)/setter.outline - > awkcard.ps + +awkcard.nc: $(CARDFILES) + $(TROFF) $(CARDSRC_N) | $(SEDME) | cat $(srcdir)/setter.outline - > awkcard.ps && touch awkcard.nc + +clean: + rm -f *.ps *~ awkcard.nc + diff --git a/doc/Makefile.in b/doc/Makefile.in index edcf4046..555450d2 100644 --- a/doc/Makefile.in +++ b/doc/Makefile.in @@ -1,112 +1,450 @@ -# Makefile for GNU Awk documentation. +# Makefile.in generated automatically by automake 1.4a from Makefile.am + +# Copyright 1994, 1995, 1996, 1997, 1998, 1999, 2000 +# Free Software Foundation, Inc. +# This Makefile.in is free software; the Free Software Foundation +# gives unlimited permission to copy and/or distribute it, +# with or without modifications, as long as this notice is preserved. + +# This program is distributed in the hope that it will be useful, +# but WITHOUT ANY WARRANTY, to the extent permitted by law; without +# even the implied warranty of MERCHANTABILITY or FITNESS FOR A +# PARTICULAR PURPOSE. + +SHELL = @SHELL@ + +srcdir = @srcdir@ +top_srcdir = @top_srcdir@ +VPATH = @srcdir@ +prefix = @prefix@ +exec_prefix = @exec_prefix@ + +bindir = @bindir@ +sbindir = @sbindir@ +libexecdir = @libexecdir@ +datadir = @datadir@ +sysconfdir = @sysconfdir@ +sharedstatedir = @sharedstatedir@ +localstatedir = @localstatedir@ +libdir = @libdir@ +infodir = @infodir@ +mandir = @mandir@ +includedir = @includedir@ +oldincludedir = /usr/include + +pkgdatadir = $(datadir)/@PACKAGE@ +pkglibdir = $(libdir)/@PACKAGE@ +pkgincludedir = $(includedir)/@PACKAGE@ + +top_builddir = .. + +ACLOCAL = @ACLOCAL@ +AUTOCONF = @AUTOCONF@ +AUTOMAKE = @AUTOMAKE@ +AUTOHEADER = @AUTOHEADER@ + +INSTALL = @INSTALL@ +INSTALL_PROGRAM = @INSTALL_PROGRAM@ +INSTALL_DATA = @INSTALL_DATA@ +INSTALL_SCRIPT = @INSTALL_SCRIPT@ +INSTALL_STRIP_FLAG = +transform = @program_transform_name@ + +NORMAL_INSTALL = : +PRE_INSTALL = : +POST_INSTALL = : +NORMAL_UNINSTALL = : +PRE_UNINSTALL = : +POST_UNINSTALL = : + +@SET_MAKE@ +AMDEP = @AMDEP@ +AMTAR = @AMTAR@ +AWK = @AWK@ +CATALOGS = @CATALOGS@ +CATOBJEXT = @CATOBJEXT@ +CC = @CC@ +CFLAGS = @CFLAGS@ +CPP = @CPP@ +CXX = @CXX@ +CXXCPP = @CXXCPP@ +DATADIRNAME = @DATADIRNAME@ +DEPDIR = @DEPDIR@ +GENCAT = @GENCAT@ +GMOFILES = @GMOFILES@ +GMSGFMT = @GMSGFMT@ +GT_NO = @GT_NO@ +GT_YES = @GT_YES@ +INCLUDE_LOCALE_H = @INCLUDE_LOCALE_H@ +INSTOBJEXT = @INSTOBJEXT@ +INTLDEPS = @INTLDEPS@ +INTLLIBS = @INTLLIBS@ +INTLOBJS = @INTLOBJS@ +LN_S = @LN_S@ +MKINSTALLDIRS = @MKINSTALLDIRS@ +MSGFMT = @MSGFMT@ +PACKAGE = @PACKAGE@ +POFILES = @POFILES@ +POSUB = @POSUB@ +RANLIB = @RANLIB@ +SOCKET_LIBS = @SOCKET_LIBS@ +U = @U@ +USE_INCLUDED_LIBINTL = @USE_INCLUDED_LIBINTL@ +USE_NLS = @USE_NLS@ +VERSION = @VERSION@ +YACC = @YACC@ +install_sh = @install_sh@ +l = @l@ + +# +# doc/Makefile.am --- automake input file for gawk +# +# Copyright (C) 2000, 2001 the Free Software Foundation, Inc. # -# Copyright (C) 1993-2000 the Free Software Foundation, Inc. -# # This file is part of GAWK, the GNU implementation of the # AWK Programming Language. -# +# # GAWK is free software; you can redistribute it and/or modify # it under the terms of the GNU General Public License as published by # the Free Software Foundation; either version 2 of the License, or # (at your option) any later version. -# +# # GAWK is distributed in the hope that it will be useful, # but WITHOUT ANY WARRANTY; without even the implied warranty of # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the # GNU General Public License for more details. -# +# # You should have received a copy of the GNU General Public License # along with this program; if not, write to the Free Software # Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA +# -SHELL = /bin/sh -srcdir = @srcdir@ -VPATH = @srcdir@ +info_TEXINFOS = gawk.texi gawkinet.texi -INSTALL = @INSTALL@ -INSTALL_PROGRAM = @INSTALL_PROGRAM@ -INSTALL_DATA = @INSTALL_DATA@ +man_MANS = gawk.1 igawk.1 -prefix = @prefix@ -exec_prefix = @exec_prefix@ -binprefix = -manprefix = +EXTRA_DIST = ChangeLog README.card ad.block setter.outline \ + awkcard.in awkforai.txt texinfo.tex cardfonts \ + macros colors no.colors $(man_MANS) \ + uf002331.eps uf002331.jpg lflashlight.eps rflashlight.eps \ + statist.jpg statist.eps -bindir = @bindir@ -libdir = @libdir@ -mandir = @mandir@/man1 -manext = .1 -infodir = @infodir@ -datadir = @datadir@/awk -TEXI2DVI = texi2dvi -TEX = tex -MAKEINFO = makeinfo --no-split +MAKEINFO = @MAKEINFO@ --no-split + TROFF = groff -t -Tps SEDME = sed -e "s/^level0 restore/level0 restore flashme 100 72 moveto (Copyright `date '+%m-%d-%y %T'`, FSF, Inc. (all)) show/" \ -e "s/^\/level0 save def/\/level0 save def 30 -48 translate/" -DOCS= gawk.1 igawk.1 gawk.texi - -TEXFILES= gawk.aux gawk.cp gawk.cps gawk.fn gawk.fns gawk.ky gawk.kys \ - gawk.pg gawk.pgs gawk.toc gawk.tp gawk.tps gawk.vr gawk.vrs - -ALLDOC= gawk.dvi $(TEXFILES) gawk.log awkcard.tr CARDSRC = $(srcdir)/macros $(srcdir)/cardfonts $(srcdir)/colors awkcard.tr CARDSRC_N = $(srcdir)/macros $(srcdir)/cardfonts $(srcdir)/no.colors awkcard.tr -CARDFILES= $(CARDSRC) ad.block awkcard.in setter.outline +CARDFILES = $(CARDSRC) ad.block awkcard.in setter.outline # Use this if your troff can correctly handle macros from 'colors' file AWKCARD = awkcard.ps +subdir = doc +mkinstalldirs = $(SHELL) $(top_srcdir)/mkinstalldirs +CONFIG_HEADER = ../config.h +CONFIG_CLEAN_FILES = +DIST_SOURCES = +TEXI2DVI = texi2dvi +INFO_DEPS = gawk.info gawkinet.info +DVIS = gawk.dvi gawkinet.dvi +TEXINFOS = gawk.texi gawkinet.texi +man1dir = $(mandir)/man1 +MANS = $(man_MANS) -# Uncomment the following definition of AWKCARD if your troff can produce -# Postscript but still has troubles with macros from 'colors'. As this -# is not groff you will have to change TROFF macro as well. Do not forget -# to ensure that awkcard.tr is processed by tbl. -#AWKCARD = awkcard.nc +NROFF = nroff +DIST_COMMON = ChangeLog Makefile.am Makefile.in texinfo.tex -all: $(DOCS) info -install: $(mandir)/gawk$(manext) $(mandir)/igawk$(manext) $(infodir)/gawk.info +DISTFILES = $(DIST_COMMON) $(DIST_SOURCES) $(TEXINFOS) $(EXTRA_DIST) -$(infodir)/gawk.info:: - -if test -f gawk.info; then d=.; \ - else d=$(srcdir); fi; \ - if [ -f $(infodir)/dir -a -f $(infodir)/gawk.info ] \ - && cmp $$d/gawk.info $(infodir)/gawk.info > /dev/null \ - && grep '(gawk)' $(infodir)/dir > /dev/null; then \ - exit 0; \ - fi; \ - $(INSTALL_DATA) $$d/gawk.info $(infodir)/gawk.info ; \ - if $(SHELL) -c 'install-info --version' > /dev/null 2>&1 ; \ - then install-info --info-dir=$(infodir) gawk.info ; \ - else true ; fi; exit 0 +GZIP_ENV = --best +all: all-redirect +.SUFFIXES: +.SUFFIXES: .dvi .info .ps .texi .texinfo .txi +$(srcdir)/Makefile.in: Makefile.am $(top_srcdir)/configure.in $(ACLOCAL_M4) + cd $(top_srcdir) && $(AUTOMAKE) --gnu doc/Makefile -$(mandir)/gawk$(manext):: gawk.1 - $(INSTALL_DATA) $(srcdir)/gawk.1 $(mandir)/gawk$(manext) +Makefile: $(srcdir)/Makefile.in $(top_builddir)/config.status + cd $(top_builddir) \ + && CONFIG_FILES=$(subdir)/$@ CONFIG_HEADERS= $(SHELL) ./config.status -$(mandir)/igawk$(manext):: igawk.1 - $(INSTALL_DATA) $(srcdir)/igawk.1 $(mandir)/igawk$(manext) -uninstall: - rm -f $(mandir)/gawk$(manext) $(mandir)/igawk$(manext) $(infodir)/gawk.info* +gawk.info: gawk.texi +gawk.dvi: gawk.texi -dvi: gawk.dvi -gawk.dvi: gawk.texi - -TEXINPUTS=$(srcdir):$$TEXINPUTS $(TEXI2DVI) $(srcdir)/gawk.texi +gawkinet.info: gawkinet.texi +gawkinet.dvi: gawkinet.texi -info: gawk.info -gawk.info: gawk.texi - $(MAKEINFO) $(srcdir)/gawk.texi +DVIPS = dvips + +.texi.info: + @cd $(srcdir) && rm -f $@ $@-[0-9] $@-[0-9][0-9] + cd $(srcdir) \ + && $(MAKEINFO) `echo $< | sed 's,.*/,,'` + +.texi.dvi: + TEXINPUTS=$(srcdir):$$TEXINPUTS \ + MAKEINFO='$(MAKEINFO) -I $(srcdir)' $(TEXI2DVI) $< + +.texi: + @cd $(srcdir) && rm -f $@ $@-[0-9] $@-[0-9][0-9] + cd $(srcdir) \ + && $(MAKEINFO) `echo $< | sed 's,.*/,,'` + +.texinfo.info: + @cd $(srcdir) && rm -f $@ $@-[0-9] $@-[0-9][0-9] + cd $(srcdir) \ + && $(MAKEINFO) `echo $< | sed 's,.*/,,'` + +.texinfo: + @cd $(srcdir) && rm -f $@ $@-[0-9] $@-[0-9][0-9] + cd $(srcdir) \ + && $(MAKEINFO) `echo $< | sed 's,.*/,,'` + +.texinfo.dvi: + TEXINPUTS=$(srcdir):$$TEXINPUTS \ + MAKEINFO='$(MAKEINFO) -I $(srcdir)' $(TEXI2DVI) $< + +.txi.info: + @cd $(srcdir) && rm -f $@ $@-[0-9] $@-[0-9][0-9] + cd $(srcdir) \ + && $(MAKEINFO) `echo $< | sed 's,.*/,,'` + +.txi.dvi: + TEXINPUTS=$(srcdir):$$TEXINPUTS \ + MAKEINFO='$(MAKEINFO) -I $(srcdir)' $(TEXI2DVI) $< + +.txi: + @cd $(srcdir) && rm -f $@ $@-[0-9] $@-[0-9][0-9] + cd $(srcdir) \ + && $(MAKEINFO) `echo $< | sed 's,.*/,,'` +.dvi.ps: + $(DVIPS) $< -o $@ + +install-info-am: $(INFO_DEPS) + @$(NORMAL_INSTALL) + $(mkinstalldirs) $(DESTDIR)$(infodir) + @list='$(INFO_DEPS)'; 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\ + inst=`echo $$inst | sed '$(transform)'`.$$ext; \ + echo " rm -f $(DESTDIR)$(man1dir)/$$inst"; \ + rm -f $(DESTDIR)$(man1dir)/$$inst; \ + done +install-man: $(MANS) + @$(NORMAL_INSTALL) + $(MAKE) $(AM_MAKEFLAGS) install-man1 +uninstall-man: + @$(NORMAL_UNINSTALL) + $(MAKE) $(AM_MAKEFLAGS) uninstall-man1 +tags: TAGS +TAGS: + + +distdir = $(top_builddir)/$(PACKAGE)-$(VERSION)/$(subdir) + +distdir: $(DISTFILES) + @for file in $(DISTFILES); do \ + d=$(srcdir); \ + if test -d $$d/$$file; then \ + cp -pR $$d/$$file $(distdir) \ + || exit 1; \ + else \ + test -f $(distdir)/$$file \ + || cp -p $$d/$$file $(distdir)/$$file \ + || exit 1; \ + fi; \ + done + $(MAKE) $(AM_MAKEFLAGS) top_distdir="$(top_distdir)" distdir="$(distdir)" dist-info +info-am: $(INFO_DEPS) +info: info-am +dvi-am: $(DVIS) +dvi: dvi-am +check-am: all-am +check: check-am +installcheck-am: +installcheck: installcheck-am +install-exec-am: +install-exec: install-exec-am + +install-data-am: install-info-am install-man +install-data: install-data-am + +install-am: all-am + @$(MAKE) $(AM_MAKEFLAGS) install-exec-am install-data-am +install: install-am +uninstall-am: uninstall-info uninstall-man +uninstall: uninstall-am +all-am: Makefile $(INFO_DEPS) $(MANS) +all-redirect: all-am +install-strip: + $(MAKE) $(AM_MAKEFLAGS) INSTALL_STRIP_FLAG=-s install +installdirs: + $(mkinstalldirs) $(DESTDIR)$(infodir) $(DESTDIR)$(mandir)/man1 + + +mostlyclean-generic: -postscript: dvi gawk.1 igawk.1 $(AWKCARD) +clean-generic: + +distclean-generic: + -rm -f Makefile $(CONFIG_CLEAN_FILES) + -rm -f config.cache config.log stamp-h stamp-h[0-9]* + +maintainer-clean-generic: + -rm -f Makefile.in +mostlyclean-am: mostlyclean-aminfo mostlyclean-generic + +mostlyclean: mostlyclean-am + +clean-am: clean-aminfo clean-generic mostlyclean-am + +clean: clean-am + +distclean-am: distclean-aminfo distclean-generic clean-am + +distclean: distclean-am + +maintainer-clean-am: maintainer-clean-aminfo maintainer-clean-generic \ + distclean-am + @echo "This command is intended for maintainers to use;" + @echo "it deletes files that may require special tools to rebuild." + +maintainer-clean: maintainer-clean-am + +.PHONY: install-info-am uninstall-info mostlyclean-aminfo \ +distclean-aminfo clean-aminfo maintainer-clean-aminfo install-man1 \ +uninstall-man1 install-man uninstall-man tags distdir info-am info \ +dvi-am dvi check check-am installcheck-am installcheck install-exec-am \ +install-exec install-data-am install-data install-am install \ +uninstall-am uninstall all-redirect all-am all install-strip \ +installdirs mostlyclean-generic distclean-generic clean-generic \ +maintainer-clean-generic clean mostlyclean distclean maintainer-clean + + +# Uncomment the following definition of AWKCARD if your troff can produce +# Postscript but still has troubles with macros from 'colors'. As this +# is not groff you will have to change TROFF macro as well. Do not forget +# to ensure that awkcard.tr is processed by tbl. +#AWKCARD = awkcard.nc + +postscript: gawk.ps gawkinet.ps gawk.1.ps igawk.1.ps $(AWKCARD) + +gawk.ps: gawk.dvi + dvips -o gawk.ps gawk.dvi + +gawkinet.ps: gawkinet.dvi + dvips -o gawkinet.ps gawkinet.dvi + +gawk.1.ps: gawk.1 -groff -man $(srcdir)/gawk.1 > gawk.1.ps + +igawk.1.ps: igawk.1 -groff -man $(srcdir)/igawk.1 > igawk.1.ps - dvips -o gawk.ps gawk.dvi awkcard.tr: awkcard.in sed 's:SRCDIR:$(srcdir):' < $(srcdir)/awkcard.in > awkcard.tr @@ -118,12 +456,8 @@ awkcard.nc: $(CARDFILES) $(TROFF) $(CARDSRC_N) | $(SEDME) | cat $(srcdir)/setter.outline - > awkcard.ps && touch awkcard.nc clean: - rm -f *.ps $(ALLDOC) *~ awkcard.nc - -distclean: clean - rm -f Makefile + rm -f *.ps *~ awkcard.nc -maintainer-clean: distclean - @echo "This command is intended for maintainers to use; it" - @echo "deletes files that may require special tools to rebuild." - rm -f gawk.info +# Tell versions [3.59,3.63) of GNU make to not export all variables. +# Otherwise a system limit (for SysV at least) may be exceeded. +.NOEXPORT: diff --git a/doc/ad.block b/doc/ad.block index d31f5d50..ee99a5a9 100644 --- a/doc/ad.block +++ b/doc/ad.block @@ -1,7 +1,7 @@ .\" AWK Reference Card --- Arnold Robbins, arnold@gnu.org .\" This file is the Ad block (included in cover) .\" -.\" Copyright (C) 1996, 98 Free Software Foundation, Inc. +.\" Copyright (C) 1996, 1998, 2000, 2001 Free Software Foundation, Inc. .\" .\" Permission is granted to make and distribute verbatim copies of .\" this reference card provided the copyright notice and this permission @@ -37,10 +37,9 @@ Fax (including Japan): +1-617-542-2652 E-mail: gnu@gnu.org URL: http://www.gnu.org -.ce 7 +.ce 5 .ft HB -\*(CGFree Software -Source Distributions on CD-ROM +\*(CGSource Distributions on CD-ROM Deluxe Distributions Emacs, Gawk, Make and GDB Manuals Emacs and GDB References\*(CX diff --git a/doc/awkcard.in b/doc/awkcard.in index ac1e8e56..43f73fb8 100644 --- a/doc/awkcard.in +++ b/doc/awkcard.in @@ -1,6 +1,6 @@ .\" AWK Reference Card --- Arnold Robbins, arnold@gnu.org .\" -.\" Copyright (C) 1996, 1997, 1998, 1999, 2000 Free Software Foundation, Inc. +.\" Copyright (C) 1996-2001 Free Software Foundation, Inc. .\" .\" Permission is granted to make and distribute verbatim copies of .\" this reference card provided the copyright notice and this permission @@ -45,57 +45,59 @@ .ES .in +.2i .nf -\*(FRAWK Program Execution 4 -Action Statements 7 -Arrays 9 -Bug Reports 15 +\*(FRAction Statements 7 +Arrays 11 +Awk Program Execution 4 +Bit Manipulation Functions (\*(GK) 16 +Bug Reports 2 +Closing Redirections 12 Command Line Arguments (standard) 2 Command Line Arguments (\*(GK) 3 Command Line Arguments (\*(MK) 4 -Conversions And Comparisons 10 -Copying Permissions 16 +Conversions And Comparisons 9 +Copying Permissions 18 Definitions 2 -Environment Variables 16 -Escape Sequences 7 -Expressions 9 +Dynamic Extensions (\*(GK) 18 +Environment Variables (\*(GK) 18 +Escape Sequences 8 +Expressions 11 Fields 6 -FTP Information 16 -Historical Features (\*(GK) 16 -Input Control 11 +FTP/HTTP Information 18 +Historical Features (\*(GK) 18 +Input Control 12 +Internationalization (\*(GK) 16 Lines And Statements 5 -.ig -Localization 10 -.. -Numeric Functions 13 -Output Control 11 +Localization (\*(GK) 17 +Numeric Functions 14 +Output Control 12 Pattern Elements 7 POSIX Character Classes (\*(GK) 6 -Printf Formats 12 +Printf Formats 13 Records 6 Regular Expressions 5 -Special Filenames 13 -String Functions 14 -Time Functions (\*(GK) 15 -User-defined Functions 15 +Special Filenames 14 +String Functions 15 +Time Functions (\*(GK) 16 +User-defined Functions 17 Variables 8\*(CX .in -.2i .EB "\s+2\f(HBCONTENTS\*(FR\s0" -.sp +.sp .4 .TD .fi -\*(CD\*(FRThis reference card was written by Arnold Robbins. -Brian Kernighan and Michael Brennan reviewed it; we thank them -for their help. -.sp +\*(CD\*(FRArnold Robbins wrote this reference card. +We thank +Brian Kernighan and Michael Brennan who reviewed it. +.sp .4 .SL -.sp +.sp .4 .so SRCDIR/ad.block .\" a subtlety here; this line changes color. We rely on it .\" also to provide a blank line. \*(CD .SL .nf -\*(FR\(co Copyright 1996-2000, Free Software Foundation +\*(FR\(co Copyright 1996-2001, Free Software Foundation 59 Temple Place \(em Suite 330 Boston, MA 02111-1307 USA .nf @@ -124,7 +126,7 @@ Several type faces are used to clarify the meaning: .fi .in +\n(INu .ti -\n(INu -\(bu\|\^\*(FI\*(IN\fP is used to indicate user input and for syntactic +\(bu\|\^\*(FI\*(IN\fP is used for emphasis, to indicate user input and for syntactic placeholders, such as \*(FIvariable\fP or \*(FIaction\fP. .in -\n(INu .br @@ -137,6 +139,8 @@ placeholders, such as \*(FIvariable\fP or \*(FIaction\fP. \*(FC1.4e2\*(FR or \*(FC4.1E5\*(FR. +\*(CBNumbers may also be given in octal or hexadecimal: e.g., +\*(FC011\*(FR or \*(FC0x11\*(FR.\*(CD .sp .5 \*(FIescape sequences\fP \- a special sequence of characters beginning with a backslash, used to describe otherwise unprintable characters. @@ -160,8 +164,10 @@ UNIX reference manual. .sp .5 \*(FIrule\fP \- a pattern-action pair, where the pattern or action may be missing.\*(CX -.EB \s+2\f(HBDEFINITIONS\*(FR\s0 +.EB "\s+2\f(HBDEFINITIONS\*(FR\s0" +.\" +.\" .\" --- Command Line Arguments .ES .fi @@ -176,7 +182,7 @@ expand; l lw(2.2i). \*(FC\-F \*(FIfs\*(FR use \*(FIfs\fP for the input field separator. \*(FC\-v\*(FI var\*(FC\^=\^\*(FIval\*(FR T{ -assign the value \*(FIval\*(FR, to the variable \*(FIvar\*(FR, +assign the value \*(FIval\*(FR to the variable \*(FIvar\*(FR before execution of the program begins. Such variable values are available to the \*(FCBEGIN\fP rule. T} @@ -201,79 +207,145 @@ l lw(2.2i). .TE .EB "\s+2\f(HBCOMMAND LINE ARGUMENTS (standard)\*(FR\s0" +.\" --- Bug Reports +.ES +.fi +\*(CDIf you find a bug in this reference card, please report it via electronic +mail to \*(FCbug-gawk@gnu.org\*(FR.\*(CX +.EB "\s+2\f(HBBUG REPORTS\*(FR\s0" + .BT +.\" +.\" +.\" --- Command Line Arguments (gawk) .ES .fi -\*(CDThe following options are specific to \*(GK. The \*(FC\-W\*(FR -forms are for full POSIX compliance. +\*(CDThe following options are specific to \*(GK. +You may also use ``\*(FC\-W \*(FIoption\*(FR'' +for full POSIX compliance. +Long options may abbreviated as long as the abbreviation +remains unique. .sp .5 .ig .\" This option is left undocumented, on purpose. -\*(FC\-\^\-nostalgia\*(FR -\*(FC\-W nostalgia\*(FR%T{ +\*(FC\-\^\-nostalgia\*(FR%T{ provide a moment of nostalgia for long time \*(AK users. T} .. .TS expand, tab(%); +l lw(1.3i). +\*(FC\-\^\-assign \*(FIvar\*(FC\^=\^\*(FIval\*(FR%just like \*(FC\-v\fP. +\*(FC\-\^\-field-separator \*(FIfs\*(FR%just like \*(FC\-F\fP. +\*(FC\-\^\-file \*(FIprog-file%\*(FRjust like \*(FC\-f\fP. +.TE +.TS +expand, tab(%); ls -l lw(1.8i). -\*(FC\-\^\-field-separator \*(FIfs\*(FR -%just like \*(FC\-F\fP -\*(FC\-\^\-assign \*(FIvar\*(FC\^=\^\*(FIval\*(FR%just like \*(FC\-v\fP -\*(FC\-\^\-file \*(FIprog-file%\*(FRjust like \*(FC\-f\fP -\*(FC\-\^\-traditional\*(FR -\*(FC\-\^\-compat\*(FR -\*(FC\-W compat\*(FR -\*(FC\-W traditional\*(FR%T{ -turn off \*(GK-specific extensions -(\*(FC\-\^\-traditional\*(FR preferred). -T} -\*(FC\-\^\-copyleft\*(FR -\*(FC\-\^\-copyright\*(FR -\*(FC\-W copyleft\*(FR -\*(FC\-W copyright\*(FR%T{ +l lw(2.2i). +\*(FC\-\^\-compat\*(FR, \*(FC\-\^\-traditional\*(FR +%T{ +disable \*(GK-specific extensions +(the use of \*(FC\-\^\-traditional\*(FR is preferred). +T} +.T& +ls +l lw(2.2i). +\*(FC\-\^\-copyleft\*(FR, \*(FC\-\^\-copyright\*(FR +%T{ print the short version of the GNU copyright information on \*(FCstdout\*(FR. T} -\*(FC\-\^\-help\*(FR -\*(FC\-\^\-usage\*(FR -\*(FC\-W help\*(FR -\*(FC\-W usage\*(FR%T{ +.T& +ls +l lw(2.2i). +\*(FC\-\^\-dump-variables\*(FR[\*(FC=\*(FIfile\*(FR] +%T{ +Print a sorted list of global variables, +their types and final values to +\*(FIfile\*(FR. +If no \*(FIfile\*(FR +is provided, \*(FCgawk\*(FR +uses \*(FCawkvars.out\*(FR. +T} +\*(FC\-\^\-gen\-po\*(FR%T{ +process the program and print a GNU \*(FCgettext\*(FR +format \*(FC\&.po\*(FR format file on standard output, +containing the text of all strings that were marked +for localization. +T} +.T& +ls +l lw(2.2i). +\*(FC\-\^\-help\*(FR, \*(FC\-\^\-usage\*(FR +%T{ print a short summary of the available options on \*(FCstdout\*(FR, then exit zero. T} -\*(FC\-\^\-lint\*(FR -\*(FC\-W lint\*(FR%T{ +.T& +ls +l lw(2.2i). +\*(FC\-\^\-lint\*(FR[\*(FC=fatal\*(FR] +%T{ warn about constructs that are dubious or non-portable to other \*(AKs. +With an optional argument of \*(FCfatal\*(FR, +lint warnings become fatal errors. T} -\*(FC\-\^\-lint\-old\*(FR -\*(FC\-W lint\-old\*(FR%T{ +.T& +l lw(2.2i). +\*(FC\-\^\-lint\-old\*(FR%T{ warn about constructs that are not portable to the original version of Unix \*(AK. T} -\*(FC\-\^\-posix\*(FR -\*(FC\-W posix\*(FR%T{ +.T& +ls +l lw(2.2i). +\*(FC\-\^\-non\-decimal\-data\*(FR +%T{ +recognize octal and hexadecimal values in input data. +\*(FIUse this option with great caution!\*(FR +T} +.T& +l lw(2.2i). +\*(FC\-\^\-posix\*(FR%T{ disable common and GNU extensions. Enable \*(FIinterval expressions\*(FR in regular expression matching (see \fHRegular Expressions\fP below). T} +.T& +ls +l lw(2.2i). +\*(FC\-\^\-profile\*(FR[\*(FC=\*(FIprof_file\*(FR] +%T{ +send profiling data to \*(FIprof_file\*(FR +(default: \*(FCawkprof.out\*(FR). +With \*(FIgawk\*(FR, +the profile is just a ``pretty printed'' version of the program. +With \*(FIpgawk\*(FR, +the profile contains execution counts in the left margin +of each statement in the program. +T} +.T& +ls +l lw(2.2i). \*(FC\-\^\-re\-interval\*(FR -\*(FC\-W re\-interval\*(FR%T{ +%T{ enable \*(FIinterval expressions\*(FR in regular expression matching (see \fHRegular Expressions\fP below). Useful if \*(FC\-\^\-posix\*(FR is not specified. T} +.T& +ls +l lw(2.2i). \*(FC\-\^\-source '\*(FItext\*(FC'\*(FR -\*(FC\-W source '\*(FItext\*(FC'\*(FR%use \*(FItext\*(FR as AWK program source code. -\*(FC\-\^\-version\*(FR -\*(FC\-W version\*(FR%T{ +%use \*(FItext\*(FR as AWK program source code. +\*(FC\-\^\-version\*(FR%T{ print version information on \*(FCstdout\fP and exit zero. T} @@ -281,16 +353,25 @@ T} .sp .5 .fi In compatibility mode, -any other options are flagged as illegal, but are otherwise ignored. +any other options are flagged as invalid, but are otherwise ignored. In normal operation, as long as program text has been supplied, unknown options are passed on to the AWK program in \*(FCARGV\*(FR for processing. This is most useful for running AWK -programs via the \*(FC#!\*(FR executable interpreter mechanism.\*(CB +programs via the \*(FC#!\*(FR executable interpreter mechanism. +.sp .5 +\*(FIpgawk\fP accepts two signals. +\*(FCSIGUSR1\fP causes it to dump a profile and function call stack to the +profile file. It then continues to run. +\*(FCSIGHUP\fP +causes it to dump the profile and function call stack and then exit.\*(CB .EB "\s+2\f(HBCOMMAND LINE ARGUMENTS (\*(GK\f(HB)\*(FR\s0" .BT +.\" +.\" +.\" --- Command Line Arguments (mawk) .ES .fi \*(CDThe following options are specific to \*(MK. @@ -309,7 +390,7 @@ options are processed. Useful with \*(FC#!\fP. T} \*(FC\-W interactive\*(FR T{ unbuffer \*(FCstdout\fP and line buffer \*(FCstdin\fP. -Lines are always records, ignoring \*(FCRS\fP +Lines are always records, ignoring \*(FCRS\fP. T} \*(FC\-W posix_space\*(FR T{ \*(FC\en\*(FR separates fields when \*(FCRS = "\^"\fP. @@ -396,10 +477,10 @@ If a program only has an \*(FCEND\fP rule, the input will be read. .\" --- Lines And Statements .ES .fi -\*(CDAWK is a line oriented language. The pattern comes first, and then the +\*(CDAWK is a line-oriented language. The pattern comes first, and then the action. Action statements are enclosed in \*(FC{\fP and \*(FC}\*(FR. Either the pattern or the action may be missing, but -not both. If the pattern is missing, the action will be +not both. If the pattern is missing, the action is executed for every input record. A missing action is equivalent to .sp .5 @@ -421,7 +502,7 @@ are automatically continued. Lines ending in \*(FCdo\fP or \*(FCelse\fP also have their statements automatically continued on the following line. In other cases, a line can be continued by ending it with a ``\e'', -in which case the newline will be ignored. However, a ``\e'' after a +in which case the newline is ignored. However, a ``\e'' after a \*(FC#\*(FR is not special. .sp .5 Multiple statements may be put on one line by separating them with a ``;''. @@ -465,8 +546,8 @@ _ \*(FC\e>\*(FR~end of a word \*(FC\ew\*(FR~any word-constituent character \*(FC\eW\*(FR~any non-word-constituent character -\*(FC\e`\*(FR~beginning of a buffer (string) -\*(FC\e'\*(FR~end of a buffer (string)\*(CD +\*(FC\e`\*(FR~beginning of a string +\*(FC\e'\*(FR~end of a string\*(CD \*(FIr\*(FC*\*(FR~zero or more occurrences of \*(FIr\*(FR \*(FIr\*(FC+\*(FR~one or more occurrences of \*(FIr\*(FR \*(FIr\*(FC?\*(FR~zero or one occurrences of \*(FIr\*(FR @@ -490,7 +571,7 @@ this feature in \*(GK.\*(CX .fi \*(CDIn regular expressions, within character ranges (\*(FC[\*(FR...\*(FC]\*(FR), -the notation \*(FC[[:\*(FIclass\*(FC:]]\*(FR defines characters classes: +the notation \*(FC[[:\*(FIclass\*(FC:]]\*(FR defines character classes: .sp .5 .TS center, tab(~); @@ -500,9 +581,12 @@ lp8 lp8 lp8 lp8. \*(FCblank\*(FR~space or tab~\*(FCpunct\*(FR~punctuation \*(FCcntrl\*(FR~control~\*(FCspace\*(FR~whitespace \*(FCdigit\*(FR~decimal~\*(FCupper\*(FR~upper-case -\*(FCgraph\*(FR~non-spaces~\*(FCxdigit\*(FR~hexadecimal\*(CB +\*(FCgraph\*(FR~non-spaces~\*(FCxdigit\*(FR~hexadecimal .TE .fi +.sp .5 +Recognition of these character classes is disabled +when \*(FC\-\-traditional\*(FR is supplied.\*(CB .EB "\s+2\f(HBPOSIX CHARACTER CLASSES (\*(GK\f(HB)\*(FR\s0" .\" --- Records @@ -515,11 +599,11 @@ If \*(FCRS\fP is any single character, that character separates records. \*(CLOtherwise, \*(FCRS\fP is a regular expression. \*(CR(Not \*(NK.)\*(CL Text in the input that matches this -regular expression will separate the record. +regular expression separates the record. \*(CB\*(GK sets \*(FCRT\*(FR to the value of the input text that matched the regular expression. The value of \*(FCIGNORECASE\fP -will also affect how records are separated when +also affects how records are separated when \*(FCRS\fP is a regular expression.\*(CD If \*(FCRS\fP is set to the null string, then records are separated by one or more blank lines. @@ -529,7 +613,7 @@ a field separator, in addition to whatever value \*(FCFS\fP may have. \*(CB\*(MK does not apply exceptional rules to \*(FCFS\fP when \*(FCRS = "\^"\fP.\*(CX -.EB \s+2\f(HBRECORDS\*(FR\s0 +.EB "\s+2\f(HBRECORDS\*(FR\s0" .\" --- Fields .ES @@ -548,13 +632,13 @@ by runs of spaces and/or tabs \*(CLand/or newlines\*(CD. Leading and trailing whitespace are ignored. \*(CBThe value of \*(FCIGNORECASE\fP -will also affect how fields are split when +also affects how fields are split when \*(FCFS\fP is a regular expression.\*(CD .sp .5 \*(CBIf the \*(FCFIELDWIDTHS\fP -variable is set to a space separated list of numbers, each field is +variable is set to a space-separated list of numbers, each field is expected to have a fixed width, and \*(GK -will split up the record using the specified widths. +splits up the record using the specified widths. The value of \*(FCFS\fP is ignored. Assigning a new value to \*(FCFS\fP overrides the use of \*(FCFIELDWIDTHS\*(FR, @@ -570,15 +654,15 @@ is set to the total number of fields in the input record. .sp .5 References to non-existent fields (i.e., fields after \*(FC$NF\*(FR) produce the null-string. However, assigning to a non-existent field -(e.g., \*(FC$(NF+2) = 5\*(FR) will increase the value of -\*(FCNF\*(FR, create any intervening fields with the null string as their value, -and cause the value of \*(FC$0\fP +(e.g., \*(FC$(NF+2) = 5\*(FR) increases the value of +\*(FCNF\*(FR, creates any intervening fields with the null string as their value, +and causes the value of \*(FC$0\fP to be recomputed with the fields being separated by the value of \*(FCOFS\*(FR. References to negative numbered fields cause a fatal error. Decreasing the value of \*(FCNF\fP causes the trailing fields to be lost \*(CR(not \*(NK).\*(CX -.EB \s+2\f(HBFIELDS\*(FR\s0 +.EB "\s+2\f(HBFIELDS\*(FR\s0" .BT @@ -614,26 +698,79 @@ It does not combine with any other pattern expression.\*(CX .\" --- Action Statements .ES -.nf -\*(CD\*(FCif (\*(FIcondition\*(FC) \*(FIstatement\*(FR [ \*(FCelse\*(FI statement \*(FR] -\*(FCwhile (\*(FIcondition\*(FC) \*(FIstatement \*(FR -\*(FCdo \*(FIstatement \*(FCwhile (\*(FIcondition\*(FC)\*(FR -\*(FCfor (\*(FIexpr1\*(FC; \*(FIexpr2\*(FC; \*(FIexpr3\*(FC) \*(FIstatement\*(FR -\*(FCfor (\*(FIvar \*(FCin\*(FI array\*(FC) \*(FIstatement\*(FR -.ig -\*(CB\*(FCabort\*(FR [ \*(FIexpression\*(FR ]\*(CD -.. -\*(FCbreak\*(FR +.fi +.in +.2i +.ti -.2i +\*(CD\*(FCbreak\*(FR +.br +break out of the nearest enclosing \*(FCdo\*(FR, \*(FCfor\*(FR, +or \*(FCwhile\*(FR loop. +.ti -.2i \*(FCcontinue\*(FR +.br +skip the rest of the loop body. +Evaluate the \*(FIcondition\*(FR +part of the nearest enclosing \*(FCdo\*(FR or \*(FCwhile\*(FR loop, +or go to the \*(FIincr\*(FR part of a \*(FCfor\*(FR loop. +.ti -.2i \*(FCdelete \*(FIarray\^\*(FC[\^\*(FIindex\^\*(FC]\*(FR -\*(CL\*(FCdelete \*(FIarray\^\*(FR\*(CD +.br +delete element \*(FIindex\*(FR from array \*(FIarray\*(FR. +.ti -.2i +\*(CL\*(FCdelete \*(FIarray\^\*(FR +.br +delete all elements from array \*(FIarray\*(FR.\*(CD +.ti -.2i +\*(FCdo \*(FIstatement \*(FCwhile (\*(FIcondition\*(FC)\*(FR +.br +execute \*(FIstatement\*(FR while \*(FIcondition\*(FR is true. +The \*(FIstatement\*(FR is always executed at least once. +.ti -.2i \*(FCexit\*(FR [ \*(FIexpression\*(FR ] -\*(FCnext\*(FR -\*(CL\*(FCnextfile\*(FR \*(CR(not \*(MK)\*(CD -\*(FC{ \*(FIstatements \*(FC}\*(CX +.br +terminate input record processing. +Execute the \*(FCEND\*(FR rule(s) if present. +If present, \*(FIexpression\*(FR becomes \*(AK's return value. +.ti -.2i +\*(FCfor (\*(FIinit\*(FC; \*(FIcond\*(FC; \*(FIincr\*(FC) \*(FIstatement\*(FR +.br +execute \*(FIinit\*(FR. +Evaluate \*(FIcond\*(FR. +If it is true, execute \*(FIstatement\*(FR. +Execute \*(FIincr\*(FR before going back to the top to +re-evaluate \*(FIcond\*(FR. +Any of the three may be omitted. +A missing \*(FIcond\*(FR is considered to be true. +.ti -.2i +\*(FCfor (\*(FIvar \*(FCin\*(FI array\*(FC) \*(FIstatement\*(FR +.br +execute \*(FIstatement\*(FR once for each subscript in \*(FIarray\*(FR, +with \*(FIvar\*(FR set to a different subscript each time through +the loop. +.ti -.2i +\*(CD\*(FCif (\*(FIcondition\*(FC) \*(FIstatement1\*(FR [ \*(FCelse\*(FI statement2\*(FR ] +.br +if \*(FIcondition\*(FR is true, execute \*(FIstatement1\*(FR, +otherwise execute \*(FIstatement2\*(FR. Each \*(FCelse\*(FR +matches the closest \*(FCif\*(FR. +.ti -.2i +\*(FCnext\*(FR see \fHInput Control.\fP +.ti -.2i +\*(CL\*(FCnextfile\*(FR \*(CR(not \*(MK) \*(CLsee \fHInput Control.\fP\*(CD +.ti -.2i +\*(FCwhile (\*(FIcondition\*(FC) \*(FIstatement \*(FR +.br +while \*(FIcondition\*(FR is true, execute \*(FIstatement\*(FR. +.ti -.2i +\*(FC{ \*(FIstatements \*(FC}\*(FR +.br +a list of statements enclosed in braces can be used anywhere +that a single statement would otherwise be used.\*(CX +.in -.2i .EB "\s+2\f(HBACTION STATEMENTS\*(FR\s0" +.BT .\" --- Escape Sequences .ES @@ -643,13 +780,6 @@ constants (\*(FC/.../\fP), escape sequences may be used to generate otherwise unprintable characters. This table lists the available escape sequences. .sp .5 -.ig -\*(CB\*(FCPROCINFO\fP T{ -elements of this array provide access to info -about the running AWK program. See -\*(AM for details.\*(CD -T} -.. .TS center, tab(~); lp8 lp8 lp8 lp8. @@ -661,17 +791,14 @@ lp8 lp8 lp8 lp8. \*(FC\e"\fP~double quote~\*(FC\e/\fP~forward slash\*(CX .TE .EB "\s+2\f(HBESCAPE SEQUENCES\*(FR\s0" - - -.BT - +.sp .7 .\" --- Variables .ES .fi .TS expand; l lw(2i). -\*(FCARGC\fP T{ +\*(CD\*(FCARGC\fP T{ number of command line arguments. T} \*(CB\*(FCARGIND\fP T{ @@ -683,19 +810,31 @@ array of command line arguments. Indexed from contents of \*(FCARGV\fP can control the files used for data. T} +\*(CL\*(FCBINMODE\fP T{ +controls ``binary'' mode for all file I/O. Values of 1, 2, or 3, +indicate input, output, or all files, respectively, should use binary +I/O. \*(CR(Not \*(NK.) \*(CLApplies only to non-POSIX systems. +\*(CBFor \*(GK, string values of \*(FC"r"\fP, or \*(FC"w"\fP specify +that input files, or output files, respectively, should use binary I/O. +String values of \*(FC"rw"\fP or \*(FC"wr"\fP specify that all files +should use binary I/O. Any other string value is treated as \*(FC"rw"\fP, +but generates a warning message.\*(CD +T} \*(FCCONVFMT\fP T{ conversion format for numbers, default value is \*(FC"%.6g"\*(FR. T} \*(FCENVIRON\fP T{ -array containing the the current environment. +array containing the current environment. The array is indexed by the environment variables, each element being the value of that variable. T} \*(CB\*(FCERRNO\fP T{ -contains a string describing the error when a -redirection or read for \*(FCgetline\*(FR fails, or if +string describing the error if a +\*(FCgetline\*(FR +redirection or read +fails, or if \*(FCclose()\*(FR fails. T} \*(FCFIELDWIDTHS\fP T{ @@ -710,7 +849,7 @@ on the command line, \*(FCFILENAME\fP is ``\-''. (unless set by \*(FCgetline\fP). T} \*(FCFNR\fP T{ -number of the input record in current input file. +record number in current input file. T} \*(FCFS\fP T{ input field separator, a space by default @@ -718,9 +857,18 @@ input field separator, a space by default T} \*(CB\*(FCIGNORECASE\fP T{ if non-zero, all regular expression and string -operations ignore case. \*(CRIn versions of \*(GK -prior to 3.0, \*(FCIGNORECASE\fP only affected -regular expression operations and \*(FCindex()\*(FR.\*(CD +operations ignore case. +Array subscripting and \*(FCasort()\*(FR are \*(FInot\*(FR affected. +T} +\*(CB\*(FCLINT\fP T{ +provides dynamic control of the \*(FC\-\^\-lint\fP +option from within an AWK program. +When true, \*(GK +prints lint warnings. +When assigned the string value \*(FC"fatal"\*(FR, +lint warnings become fatal errors, exactly like +\*(FC\-\-lint=fatal\*(FR. +Any other true value just prints warnings.\*(CD T} \*(FCNF\fP T{ number of fields in the current input record. @@ -730,49 +878,123 @@ total number of input records seen so far. T} \*(FCOFMT\fP T{ output format for numbers, \*(FC"%.6g"\*(FR, by default. -\*(CROld versions of \*(AK also used this for number -to string conversion instead of \*(FCCONVFMT\fP.\*(CD +\*(CROld versions of \*(AK used this for number +to string conversion.\*(CX T} -\*(FCOFS\fP T{ +.TE +.EB "\s+2\f(HBVARIABLES\*(FR\s0" +.BT + +.\" --- Variables (continued) +.ES +.fi +.TS +expand; +l lw(2i). +\*(CD\*(FCOFS\fP T{ output field separator, a space by default. T} \*(FCORS\fP T{ output record separator, a newline by default. T} +\*(CB\*(FCPROCINFO\fP T{ +elements of this array provide access to info +about the running AWK program. See +\*(AM for details.\*(CD +T} +\*(FCRLENGTH\fP T{ +length of the string matched by \*(FCmatch()\*(FR; +\-1 if no match. +T} \*(FCRS\fP T{ input record separator, a newline by default (see \fHRecords\fP above). T} -\*(CB\*(FCRT\fP T{ -record terminator. \*(GK sets \*(FCRT\fP to the input -text that matched the character or regular -expression specified by \*(FCRS\*(FR.\*(CD -T} \*(FCRSTART\fP T{ index of the first character matched by \*(FCmatch()\*(FR; 0 if no match. T} -\*(FCRLENGTH\fP T{ -length of the string matched by \*(FCmatch()\*(FR; -\-1 if no match. +\*(CB\*(FCRT\fP T{ +record terminator. \*(GK sets \*(FCRT\fP to the input +text that matched the character or regular +expression specified by \*(FCRS\*(FR.\*(CD T} \*(FCSUBSEP\fP T{ character(s) used to separate multiple subscripts -in array elements, by default \*(FC"\e034"\*(FR. (see -\fHArrays\fP below).\*(CX +in array elements, by default \*(FC"\e034"\*(FR. (See +\fHArrays\fP below). +T} +\*(CB\*(FCTEXTDOMAIN\fP T{ +the application's text domain for internationalization; +used to find the localized +translations for the program's strings.\*(CX T} .TE -.EB \s+2\f(HBVARIABLES\*(FR\s0 +.EB "\s+2\f(HBVARIABLES (continued)\*(FR\s0" + +.\" --- Conversions and Comparisons +.ES +.fi +\*(CDVariables and fields may be (floating point) numbers, strings or both. +Context determines how the value of a variable is interpreted. If used in +a numeric expression, it will be treated as a number, if used as a string +it will be treated as a string. +.sp .5 +To force a variable to be treated as a number, add 0 to it; to force it +to be treated as a string, concatenate it with the null string. +.sp .5 +When a string must be converted to a number, the conversion is accomplished +using \*(FIstrtod\*(FR(3). +A number is converted to a string by using the value of \*(FCCONVFMT\fP +as a format string for \*(FIsprintf\*(FR(3), +with the numeric value of the variable as the argument. +However, even though all numbers in AWK are floating-point, +integral values are \*(FIalways\fP converted as integers. +.sp .5 +Comparisons are performed as follows: +If two variables are numeric, they are compared numerically. +If one value is numeric and the other has a string value that is a +``numeric string,'' then comparisons are also done numerically. +Otherwise, the numeric value is converted to a string, and a string +comparison is performed. +Two strings are compared, of course, as strings. +.sp .5 +Note that string constants, such as \*(FC"57"\fP, are \*(FInot\fP +numeric strings, they are string constants. The idea of ``numeric string'' +only applies to fields, \*(FCgetline\fP input, +\*(FCFILENAME\*(FR, \*(FCARGV\fP elements, \*(FCENVIRON\fP +elements and the elements of an array created by +\*(FCsplit()\fP that are numeric strings. +The basic idea is that \*(FIuser input\*(FR, +and only user input, that looks numeric, +should be treated that way. +\*(CRNote that the POSIX standard applies the concept of +``numeric string'' everywhere, even to string constants. +However, this is +clearly incorrect, and none of the three free \*(AK\*(FRs do this.\*(CD +(Fortunately, this is fixed in the next version of the standard.) +.sp .5 +Uninitialized variables have the numeric value 0 and the string value +\*(FC"\^"\fP +(the null, or empty, string).\*(CX +.EB "\s+2\f(HBCONVERSIONS AND COMPARISONS\*(FR\s0" + +.BT + +.ES +\*(CX +.sp 61 +.EB "\s+2\f(HBNOTES\*(FR\s0" .BT .\" --- Arrays .ES .fi -\*(CDAn arrays subscript is an expression between square brackets +\*(CDAn array subscript is an expression between square brackets (\*(FC[ \*(FRand \*(FC]\*(FR). If the expression is a list -\*(FC(\*(FIexpr\*(FC, \*(FIexpr \*(FC...)\*(FR, +(\*(FIexpr\*(FC, \*(FIexpr \*(FR...), then the subscript is a string consisting of the concatenation of the (string) value of each expression, separated by the value of the \*(FCSUBSEP\fP variable. @@ -809,7 +1031,7 @@ element from an array. \*(CLSpecifying just the array name without a subscript in the \*(FCdelete\fP statement deletes the entire contents of an array.\*(CX -.EB \s+2\f(HBARRAYS\*(FR\s0 +.EB "\s+2\f(HBARRAYS\*(FR\s0" .\" --- Expressions .ES @@ -833,7 +1055,7 @@ and \*(FCsub()\fP, functions, mean \*(FC$0 ~ /\*(FIpat\*(FC/\*(FR. .sp .5 -The AWK operators, in order of decreasing precedence, are +The AWK operators, in order of decreasing precedence, are: .sp .5 .fi .TS @@ -864,95 +1086,18 @@ l lw(1.8i). \*(FC=\0+=\0\-=\0*=\0/=\0%=\0^=\0\*(CL**=\*(CD\fP assignment operators\*(CX .TE -.EB \s+2\f(HBEXPRESSIONS\*(FR\s0 - - -.BT - -.\" --- Conversions and Comparisons -.ES -.fi -\*(CDVariables and fields may be (floating point) numbers, strings or both. -Context determines how the value of a variable is interpreted. If used in -a numeric expression, it will be treated as a number, if used as a string -it will be treated as a string. -.sp .5 -To force a variable to be treated as a number, add 0 to it; to force it -to be treated as a string, concatenate it with the null string. -.sp .5 -When a string must be converted to a number, the conversion is accomplished -using \*(FIatof\*(FR(3). -A number is converted to a string by using the value of \*(FCCONVFMT\fP -as a format string for \*(FIsprintf\*(FR(3), -with the numeric value of the variable as the argument. -However, even though all numbers in AWK are floating-point, -integral values are \*(FIalways\fP converted as integers. -.sp .5 -Comparisons are performed as follows: -If two variables are numeric, they are compared numerically. -If one value is numeric and the other has a string value that is a -``numeric string,'' then comparisons are also done numerically. -Otherwise, the numeric value is converted to a string, and a string -comparison is performed. -Two strings are compared, of course, as strings. -\*(CRAccording to the POSIX standard, even if two strings are -numeric strings, a numeric comparison is performed. However, this is -clearly incorrect, and none of the three free \*(AK\*(FRs do this.\*(CD -.sp .5 -Note that string constants, such as \*(FC"57"\fP, are \*(FInot\fP -numeric strings, they are string constants. The idea of ``numeric string'' -only applies to fields, \*(FCgetline\fP input, -\*(FCFILENAME\*(FR, \*(FCARGV\fP elements, \*(FCENVIRON\fP -elements and the elements of an array created by -\*(FCsplit()\fP that are numeric strings. -The basic idea is that \*(FIuser input\*(FR, -and only user input, that looks numeric, -should be treated that way. -.sp .5 -Uninitialized variables have the numeric value 0 and the string value -\*(FC"\^"\fP -(the null, or empty, string).\*(CX -.EB "\s+2\f(HBCONVERSIONS AND COMPARISONS\*(FR\s0" - -.ig -.\" --- Localization -.ES -.nf -.ce 100 -\*(CDThis -section -is -under -construction. -.sp .5 -This -section -is -under -construction.\*(CB -.ce 0 -.EB "\s+2\f(HBLOCALIZATION\*(FR\s0" -.. - -.ig -.ps +2 -.ce 1 -\*(CD\fHISBN: 0-916151-97-2\*(FR -.ps -2 -.. +.EB "\s+2\f(HBEXPRESSIONS\*(FR\s0" .BT - .\" --- Input Control .ES .fi .TS expand; l lw(1.8i). -\*(CD\*(FCclose(\*(FIfile\*(FC)\*(FR close input file or pipe. \*(FCgetline\fP T{ -set \*(FC$0\fP from next input record; +set \*(FC$0\fP from next record; set \*(FCNF\*(FR, \*(FCNR\*(FR, \*(FCFNR\*(FR. T} \*(FCgetline < \*(FIfile\*(FR set \*(FC$0\fP from next record of \*(FIfile\*(FR; set \*(FCNF\*(FR. @@ -963,10 +1108,15 @@ T} \*(FCgetline \*(FIv \*(FC< \*(FIfile\*(FR set \*(FIv\fP from next record of \*(FIfile\*(FR. \*(FIcmd \*(FC| getline\*(FR pipe into \*(FCgetline\*(FR; set \*(FC$0\*(FR, \*(FCNF\*(FR. \*(FIcmd \*(FC| getline \*(FIv\*(FR pipe into \*(FCgetline\*(FR; set \*(FIv\*(FR. +\*(CB\*(FIcmd \*(FC|& getline\*(FR co-process pipe into \*(FCgetline\*(FR; set \*(FC$0\*(FR, \*(FCNF\*(FR. .TE .fi .in +.2i .ti -.2i +\*(FIcmd \*(FC|& getline \*(FIv\*(FR +.br +co-process pipe into \*(FCgetline\*(FR; set \*(FIv\*(FR. +.ti -.2i \*(FCnext\fP .br stop processing the current input @@ -986,15 +1136,15 @@ and processing starts over with the first pattern in the AWK program. Upon end of input data, execute any \*(FCEND\fP rule(s). \*(CREarlier versions of \*(GK used -\*(FCnext file\*(FR, as two words. This -generates a warning message and will -eventually be removed. \*(CR\*(MK does not -currently support \*(FCnextfile\*(FR.\*(CD +\*(FCnext file\*(FR, as two words. +This usage is no longer supported. +\*(CR\*(MK does not currently support \*(FCnextfile\*(FR.\*(CD .in -.2i .sp .5 .fi -\*(FCgetline\*(FR returns 0 on end of file, and \-1 on an -error.\*(CX +\*(FCgetline\*(FR returns 0 on end of file and \-1 on an error. +\*(CBUpon an error, \*(FCERRNO\*(FR contains a string describing +the problem.\*(CX .EB "\s+2\f(HBINPUT CONTROL\*(FR\s0" .\" --- Output Control @@ -1002,28 +1152,24 @@ error.\*(CX .fi .in +.2i .ti -.2i -\*(CD\*(FCclose(\*(FIfile\*(FC)\*(FR -.br -close output file or pipe. -.ti -.2i \*(CL\*(FCfflush(\*(FR[\*(FIfile\^\*(FR]\*(FC)\*(FR .br flush any buffers associated with the open output file or pipe \*(FIfile\*(FR.\*(CD -\*(CBIf \*(FIfile\fP is missing, then standard output is flushed. -If \*(FIfile\fP is the null string, then all open output files and pipes -are flushed \*(CR(not \*(NK)\*(CD. +\*(CBIf no \*(FIfile\fP, then flush standard output. +If \*(FIfile\fP is null, then flush all open output files and pipes +\*(CR(not \*(NK)\*(CD. .ti -.2i \*(FCprint\fP .br -print the current record. The output record is terminated -with the value of \*(FCORS\fP. +print the current record. Terminate output record +with \*(FCORS\fP. .ti -.2i \*(FCprint \*(FIexpr-list\*(FR .br print expressions. Each expression is separated -by the value of \*(FCOFS\fP. The output record is -terminated with the value of \*(FCORS\fP. +by the value of \*(FCOFS\fP. Terminate the output record +with \*(FCORS\fP. .ti -.2i \*(FCprintf \*(FIfmt\*(FC, \*(FIexpr-list\*(FR .br @@ -1042,21 +1188,47 @@ I/O redirections may be used with both \*(FCprint\fP and \*(FCprintf\fP. .ti -.2i \*(CD\*(FCprint "hello" > \*(FIfile\*(FR .br -Print data to \*(FIfile\fP. The first time the file is written to, it -will be truncated. Subsequent commands append data. +print data to \*(FIfile\fP. The first time the file is written to, it +is truncated. Subsequent commands append data. .ti -.2i \*(FCprint "hello" >> \*(FIfile\*(FR .br -Append data to \*(FIfile\fP. The previous contents of the file are not lost. +append data to \*(FIfile\fP. The previous contents of \*(FIfile\*(FR are not lost. .ti -.2i \*(FCprint "hello" | \*(FIcmd\*(FR .br -Print data down a pipeline to \*(FIcmd\*(FR.\*(CX +print data down a pipeline to \*(FIcmd\*(FR. +.ti -.2i +\*(CB\*(FCprint "hello" |& \*(FIcmd\*(FR +.br +print data down a pipeline to co-process \*(FIcmd\*(FR.\*(CX .in -.2i .EB "\s+2\f(HBOUTPUT CONTROL\*(FR\s0" -.BT +.ES +.fi +.in +.2i +.ti -.2i +\*(CD\*(FCclose(\*(FIfile\*(FC)\*(FR +.br +close input or output file, pipe \*(CBor co-process.\*(CD +.ti -.2i +\*(CB\*(FCclose(\*(FIcommand\*(FC, \*(FIhow\*(FC)\*(FR +.br +close one end of co-process pipe. +Use \*(FC"to"\*(FR for the write end, or +\*(FC"from"\*(FR for the read end.\*(CD +.in -.2i +.sp .5 +On success, \*(FCclose()\*(FR returns zero for a file, or the exit status for a process. +It returns \-1 if \*(FIfile\*(FR +was never opened, or +if there was a system problem. +\*(CB\*(FCERRNO\*(FR describes +the error.\*(CX +.EB "\s+2\f(HBCLOSING REDIRECTIONS\*(FR\s0" +.BT .\" --- Printf Formats .ES @@ -1091,6 +1263,14 @@ and the control letter: .TS expand; l lw(2.2i). +\*(CB\*(FIcount\*(FC$\*(FR T{ +use the +\*(FIcount\*(FR'th +argument at this point in the formatting +(a \*(FIpositional specifier\*(FR). +Use in translated versions of +format strings, not in the original text of an AWK program.\*(CD +T} \*(FC\-\fP T{ left-justify the expression within its field. T} @@ -1122,7 +1302,7 @@ trailing zeros are not removed. T} \*(FC0\fP T{ a leading zero acts as a flag, indicating output -should be padded with zeroes instead of spaces. +should be padded with zeros instead of spaces. This applies even to non-numeric output formats. Only has an effect when the field width is wider than the value to be printed. @@ -1130,11 +1310,11 @@ T} \*(FIwidth\fP T{ pad the field to this width. The field is normally padded with spaces. If the \*(FC0\fP flag has been used, -pad with zeroes. +pad with zeros. T} -\*(FC.\fP\*(FIprec\fP T{ +\*(FC.\*(FIprec\*(FR T{ precision. -The meaning varies by control letter: +The meaning of the \*(FIprec\*(FR varies by control letter: T} \*(FC%d\*(FR, \*(FC%o\*(FR, \*(FC%i\*(FR, \*(FC%u\*(FR, \*(FC%x\*(FR, \*(FC%X\fP T{ @@ -1155,12 +1335,13 @@ T} The dynamic \*(FIwidth\fP and \*(FIprec\fP capabilities of the ANSI C \*(FCprintf()\fP routines are supported. A \*(FC*\fP in place of either the \*(FIwidth\fP or \*(FIprec\fP -specifications will cause their values to be taken from -the argument list to \*(FCprintf\fP or \*(FCsprintf()\*(FR.\*(CX +specifications causes their values to be taken from +the argument list to \*(FCprintf\fP or \*(FCsprintf()\*(FR. +\*(CBUse \*(FC*\*(FIn\*(FC$\*(FR to use positional specifiers +with a dynamic width or precision.\*(CX .EB "\s+2\f(HBPRINTF FORMATS\*(FR\s0" - .BT .\" --- Special Filenames @@ -1187,13 +1368,28 @@ l lw(2i). .fi \*(CBThe following names are specific to \*(GK. .sp .5 -.TS -expand; -l lw(2i). -\*(FC/dev/fd/\^\*(FIn\*(FR T{ -file associated with the open file descriptor \*(FIn\*(FR -T} -.TE +.in +.2i +.ti -.2i +\*(FC/dev/fd/\^\*(FIn\*(FR +.br +File associated with the open file descriptor \*(FIn\*(FR. +.ti -.2i +\*(FC/inet/tcp/\*(FIlport\*(FC/\*(FIrhost\*(FC/\*(FIrport\*(FR +.br +File for TCP/IP connection on local port \*(FIlport\*(FR to +remote host \*(FIrhost\*(FR on remote port \*(FIrport\*(FR. +Use a port of \*(FC0\*(FR to have the system pick a port. +Usable only with the \*(FC|&\*(FR two-way I/O operator. +.ti -.2i +\*(FC/inet/udp/\*(FIlport\*(FC/\*(FIrhost\*(FC/\*(FIrport\*(FR +.br +Similar, but use UDP/IP instead of TCP/IP. +.ti -.2i +\*(CR\*(FC/inet/raw/\*(FIlport\*(FC/\*(FIrhost\*(FC/\*(FIrport\*(FR +.br +.\" Similar, but use raw IP sockets. +Reserved for future use.\*(CB +.in -.2i .sp .5 .fi Other special filenames provide access to information about the running @@ -1223,19 +1419,10 @@ T} .TE .sp .5 .fi -.ig \*(CRThese filenames are now obsolete. Use the \*(FCPROCINFO\fP array to obtain the information they provide.\*(CL -.. -.\" BEGIN FOR 3.0.x -\*(CRThese filenames will become obsolete in \*(GK 3.1. -Be aware that you will have to change your programs.\*(CL -.\" END FOR 3.0.x .EB "\s+2\f(HBSPECIAL FILENAMES\*(FR\s0" - - - .\" --- Builtin Numeric Functions .ES .fi @@ -1262,20 +1449,27 @@ T} .BT - .\" --- Builtin String Functions .ES .fi .in +.2i .ti -.2i +\*(CB\*(FCasort(\*(FIs\*(FC \*(FR[\*(FC, \*(FId\*(FR]\*(FC)\*(FR +.br +sorts the source array \*(FIs\*(FR, replacing the indices with numeric +values 1 through \*(FIn\*(FR (the number of elements in the array), +and returns the number of elements. +If destination \*(FId\*(FR is supplied, \*(FIs\*(FR is copied to \*(FId\*(FR, +\*(FId\*(FR is sorted, and \*(FIs\*(FR is unchanged.\*(CD +.ti -.2i \*(CB\*(FCgensub(\*(FIr\*(FC, \*(FIs\*(FC, \*(FIh \*(FR[\*(FC, \*(FIt\*(FR]\*(FC)\*(FR .br search the target string \*(FIt\fP for matches of the regular expression \*(FIr\*(FR. If \*(FIh\fP is a string beginning with \*(FCg\fP or \*(FCG\*(FR, replace all matches of \*(FIr\fP with \*(FIs\*(FR. Otherwise, \*(FIh\fP -is a number indicating which match of \*(FIr\fP to replace. If no -\*(FIt\fP is supplied, \*(FC$0\fP is used instead. Within the +is a number indicating which match of \*(FIr\fP to replace. +If \*(FIt\fP is not supplied, \*(FC$0\fP is used instead. Within the replacement text \*(FIs\*(FR, the sequence \*(FC\e\*(FIn\*(FR, where \*(FIn\fP is a digit from 1 to 9, may be used to indicate just the text that matched the \*(FIn\*(FRth parenthesized subexpression. @@ -1306,13 +1500,17 @@ returns the index of the string returns the length of the string \*(FIs\*(FR, or the length of \*(FC$0\fP if \*(FIs\fP is not supplied. .ti -.2i -\*(FCmatch(\*(FIs\*(FC, \*(FIr\*(FC)\*(FR +\*(FCmatch(\*(FIs\*(FC, \*(FIr \*(CB\*(FR[\*(FC, \*(FIa\*(FR]\*(CD\*(FC)\*(FR .br returns the position in \*(FIs\fP where the regular expression \*(FIr\fP occurs, or 0 if \*(FIr\fP is not present, and sets the values of variables \*(FCRSTART\fP and \*(FCRLENGTH\*(FR. +\*(CBIf \*(FIa\*(FR is supplied, the text matching all of \*(FIr\*(FR +is placed in \*(FIa\*(FC[0]\*(FR. If there were parenthesized +subexpressions, the matching texts are placed +in \*(FIa\*(FC[1]\*(FR, \*(FIa\*(FC[2]\*(FR, and so on.\*(CD .ti -.2i \*(FCsplit(\*(FIs\*(FC, \*(FIa \*(FR[\*(FC, \*(FIr\*(FR]\*(FC)\*(FR .br @@ -1328,6 +1526,16 @@ Splitting behaves identically to field splitting. prints \*(FIexpr-list\fP according to \*(FIfmt\*(FR, and returns the resulting string. .ti -.2i +\*(CB\*(FCstrtonum(\*(FIs\*(FC)\*(FR +.br +examines \*(FIs\*(FR, and returns its numeric value. +If \*(FIs\*(FR begins with a leading \*(FC0\*(FR, +\*(FCstrtonum()\*(FR assumes that \*(FIs\*(FR +is an octal number. +If \*(FIs\*(FR begins with a leading \*(FC0x\*(FR +or \*(FC0X\*(FR, \*(FCstrtonum()\*(FR assumes that +\*(FIs\*(FR is a hexadecimal number.\*(CD +.ti -.2i \*(FCsub(\*(FIr\*(FC, \*(FIs \*(FR[\*(FC, \*(FIt\*(FR]\*(FC)\*(FR .br just like @@ -1344,21 +1552,25 @@ If \*(FIn\fP is omitted, the rest of \*(FIs\fP is used. returns a copy of the string \*(FIstr\*(FR, with all the upper-case characters in \*(FIstr\fP translated to their corresponding lower-case counterparts. Non-alphabetic characters are -left unchanged. +left unchanged.\*(CX +.in -.2i +.EB "\s+2\f(HBSTRING FUNCTIONS\*(FR\s0" + +.BT + +.\" --- Builtin String Functions +.ES +.fi +.in +.2i .ti -.2i -\*(FCtoupper(\*(FIstr\*(FC)\*(FR +\*(CD\*(FCtoupper(\*(FIstr\*(FC)\*(FR .br returns a copy of the string \*(FIstr\*(FR, with all the lower-case characters in \*(FIstr\fP translated to their corresponding upper-case counterparts. Non-alphabetic characters are left unchanged.\*(CX .in -.2i -.EB "\s+2\f(HBSTRING FUNCTIONS\*(FR\s0" - - - -.BT - +.EB "\s+2\f(HBSTRING FUNCTIONS (continued)\*(FR\s0" .\" --- Builtin Time Functions .ES @@ -1369,15 +1581,13 @@ formatting them. .sp .5 .fi .in +.2i -.ig .ti -.2i \*(FCmktime(\*(FIdatespec\*(FC)\*(FR .br turns \*(FIdatespec\fP into a time stamp of the same form as returned by \*(FCsystime()\*(FR. The \*(FIdatespec\fP is a string of the form -\*(FC"\*(FIYYYY MM DD HH MM SS\*(FC"\*(FR. -.. +\*(FC"\*(FIYYYY MM DD HH MM SS[ DST]\*(FC"\*(FR. .ti -.2i \*(FCstrftime(\*(FR[\*(FIformat \*(FR[\*(FC, \*(FItimestamp\*(FR]]\*(FC)\*(FR .br @@ -1387,7 +1597,7 @@ according to the specification in \*(FIformat\*(FR. The \*(FCsystime()\*(FR. If \*(FItimestamp\fP is missing, the current time of day is used. If \*(FIformat\fP is missing, a default format equivalent to the output -of \*(FIdate\*(FR(1) will be used. +of \*(FIdate\*(FR(1) is used. .ti -.2i \*(FCsystime()\fP .br @@ -1396,7 +1606,83 @@ seconds since the Epoch.\*(CB .in -.2i .EB "\s+2\f(HBTIME FUNCTIONS (\*(GK\f(HB)\*(FR\s0" +.\" --- Builtin Bit Manipulation Functions +.ES +.fi +\*(CD\*(GK +provides the following functions for doing bitwise operations. +.sp .5 +.fi +.in +.2i +.ti -.2i +\*(FCand(\*(FIv1\*(FC, \*(FIv2\*(FC)\*(FR +.br +returns the bitwise AND of the values provided by +\*(FIv1\*(FR and \*(FIv2\*(FR. +.ti -.2i +\*(FCcompl(\*(FIval\*(FC)\*(FR +.br +returns the bitwise complement of +\*(FIval\*(FR. +.ti -.2i +\*(FClshift(\*(FIval\*(FC, \*(FIcount\*(FC)\*(FR +.br +returns the value of \*(FIval\*(FR, +shifted left by \*(FIcount\*(FR bits. +.ti -.2i +\*(FCor(\*(FIv1\*(FC, \*(FIv2\*(FC)\*(FR +.br +returns the bitwise OR of the values provided by +\*(FIv1\*(FR and \*(FIv2\*(FR. +.ti -.2i +\*(FCrshift(\*(FIval\*(FC, \*(FIcount\*(FC)\*(FR +.br +returns the value of \*(FIval\*(FR, +shifted right by \*(FIcount\*(FR bits. +.ti -.2i +\*(FCxor(\*(FIv1\*(FC, \*(FIv2\*(FC)\*(FR +.br +teturns the bitwise XOR of the values provided by +\*(FIv1\*(FR and \*(FIv2\*(FR.\*(CB +.in -.2i +.EB "\s+2\f(HBBIT MANIPULATION FUNCTIONS (\*(GK\f(HB)\*(FR\s0" + +.\" --- Builtin Internationalizatin Functions +.ES +.fi +\*(CD\*(GK +provides the following functions for runtime message translation. +.in +.2i +.sp .5 +.ti -.2i +\*(FCbindtextdomain(\*(FIdirectory \*(FR[\*(FC, \*(FIdomain\*(FR]\*(FC)\*(FR +.br +specifies the directory where \*(GK looks for the \*(FC\&.mo\*(FR +files, in case they +will not or cannot be placed in the ``standard'' locations +(e.g., during testing.) +It returns the directory where \*(FIdomain\*(FR is ``bound.'' +.sp .5 +The default \*(FIdomain\*(FR is the value of \*(FCTEXTDOMAIN\*(FR. +When \*(FIdirectory\*(FR is the null string (\*(FC"\^"\*(FR), +\*(FCbindtextdomain()\*(FR returns the current binding for the +given \*(FIdomain\*(FR. +.ti -.2i +\*(FCdcgettext(\*(FIstring \*(FR[\*(FC, \*(FIdomain \*(FR[\*(FC, \*(FIcategory\*(FR]]\*(FC)\*(FR +.br +returns the translation of \*(FIstring\*(FR in text domain +\*(FIdomain\*(FR for locale category \*(FIcategory\*(FR. +The default value for \*(FIdomain\*(FR is the current value of \*(FCTEXTDOMAIN\*(FR. +The default value for \*(FIcategory\*(FR is \*(FC"LC_MESSAGES"\*(FR. +.sp .5 +If you supply a value for \*(FIcategory\*(FR, it must be a string equal to +one of the known locale categories. +You must also supply a text domain. Use \*(FCTEXTDOMAIN\*(FR +to use the current domain.\*(CB +.in -.2i +.EB "\s+2\f(HBINTERNATIONALIZATION (\*(GK\f(HB)\*(FR\s0" +.BT .\" --- User-defined Functions .ES @@ -1420,7 +1706,7 @@ in the parameter list. The convention is to separate local variables from real parameters by extra spaces in the parameter list. For example: .sp .5 .nf - \*(FC# a & b are local + \*(FC# a and b are local function f(p, q, a, b) { \&..... @@ -1450,17 +1736,65 @@ may be used in place of \*(CRNote: This usage is deprecated.\*(CX .EB "\s+2\f(HBUSER-DEFINED FUNCTIONS\*(FR\s0" - - -.\" --- Bug Reports +.\" --- Localization .ES .fi -\*(CDIf you find a bug in this reference card, please report it via electronic -mail to \*(FCarnold@gnu.org\*(FR.\*(CX -.EB "\s+2\f(HBBUG REPORTS\*(FR\s0" +\*(CDThere are several steps involved in producing and running a localizable +\*(AK program. +.sp .5 +1. Add a \*(FCBEGIN\*(FR action to assign a value to the +\*(FCTEXTDOMAIN\*(FR variable to set the text domain for +your program. +.sp .5 +.ti +5n +\*(FCBEGIN { TEXTDOMAIN = "myprog" }\*(FR +.sp .5 +This allows \*(GK to find the \*(FC\&.mo\*(FR +file associated with your program. +Without this step, \*(GK uses the \*(FCmessages\*(FR text domain, +which probably won't work. +.sp .5 +2. Mark all strings that should be translated with leading underscores. +.sp .5 +3. Use the \*(FCdcgettext()\*(FR +and/or \*(FCbindtextdomain()\*(FR +functions in your program, as necessary or appropriate. +.sp .5 +4. Run +.sp .5 +.ti +5n +\*(FCgawk \-\^\-gen\-po \-f myprog.awk > myprog.po\*(FR +.sp .5 +to generate a \*(FC\&.po\*(FR +file for your program. +.sp .5 +5. Provide appropriate translations, and build and install a corresponding +\*(FC\&.mo\*(FR file. +.sp .5 +The internationalization features are described in full detail in \*(AM.\*(CB +.EB "\s+2\f(HBLOCALIZATION (\*(GK\f(HB)\*(FR\s0" + .BT +.\" --- Extensions +.ES +.fi +.in +.2i +.ti -.2i +\*(CD\*(FCextension(\*(FIlib\*(FC, \*(FIfunc\*(FC)\*(FR +.br +dynamically load the shared library +\*(FIlib\*(FR +and call +\*(FIfunc\*(FR +in it to initialize the library. +This adds new built-in functions to \*(GK. +It returns the value returned by +\*(FIfunc\*(FR.\*(CB +.in -.2i +.EB "\s+2\f(HBDYNAMIC EXTENSIONS (\*(GK\f(HB)\*(FR\s0" + .\" --- Environment Variables .ES .fi @@ -1487,7 +1821,7 @@ command line.\*(CB First, it is possible to call the \*(FClength()\fP built-in function not only with no argument, but even without parentheses. This feature is marked as ``deprecated'' in the POSIX standard, and \*(GK -will issue a warning about its use if \*(FC\-\^\-lint\fP +issues a warning about its use if \*(FC\-\^\-lint\fP is specified on the command line. .sp .5 The other feature is the use of \*(FCcontinue\fP @@ -1495,8 +1829,8 @@ or \*(FCbreak\fP statements outside the body of a \*(FCwhile\*(FR, \*(FCfor\*(FR, or \*(FCdo\fP loop. Historical AWK implementations have treated such usage as equivalent to the \*(FCnext\fP statement. -\*(GK will support this usage if \*(FC\-\^\-traditional\fP -has been specified.\*(CB +\*(GK supports this usage if \*(FC\-\^\-traditional\fP +is specified.\*(CB .EB "\s+2\f(HBHISTORICAL FEATURES (\*(GK\f(HB)\*(FR\s0" @@ -1504,15 +1838,14 @@ has been specified.\*(CB .ES .nf \*(CDHost: \*(FCgnudist.gnu.org\*(FR -File: \*(FC/gnu/gawk/gawk-3.0.6.tar.gz\fP +File: \*(FC/gnu/gawk/gawk-3.1.0.tar.gz\fP .in +.2i .fi GNU \*(AK (\*(GK). There may be a later version. .in -.2i .nf .sp .5 -Host: \*(FCnetlib.bell-labs.com\*(FR -File: \*(FC/netlib/research/awk.bundle.gz\fP +\*(FChttp://cm.bell-labs.com/who/bwk/awk.tar.gz\fP .in +.2i .fi \*(NK. This version requires an ANSI C compiler; @@ -1526,12 +1859,12 @@ File: \*(FC/pub/brennan/mawk1.3.3.tar.gz\fP .fi Michael Brennan's \*(MK. There may be a newer version.\*(CX .in -.2i -.EB "\s+2\f(HBFTP INFORMATION\*(FR\s0" +.EB "\s+2\f(HBFTP/HTTP INFORMATION\*(FR\s0" .\" --- Copying Permissions .ES .fi -\*(CDCopyright \(co 1996-2000 Free Software Foundation, Inc. +\*(CDCopyright \(co 1996-2001 Free Software Foundation, Inc. .sp .5 Permission is granted to make and distribute verbatim copies of this reference card provided the copyright notice and this permission notice diff --git a/doc/cardfonts b/doc/cardfonts index 5529ba98..dc44ce1b 100644 --- a/doc/cardfonts +++ b/doc/cardfonts @@ -34,4 +34,4 @@ FC - font courier .ds RN Times Roman .ds IN Times Italic .ds CN Courier Bold -.ds AM \fIThe GNU Awk User's Guide\fP +.ds AM \fIGAWK: Effective AWK Programming\fP diff --git a/doc/gawk.1 b/doc/gawk.1 index 6f07cfab..3e3c62b3 100644 --- a/doc/gawk.1 +++ b/doc/gawk.1 @@ -3,6 +3,7 @@ .ds AN \s-1ANSI\s+1 .ds GN \s-1GNU\s+1 .ds AK \s-1AWK\s+1 +.ds EP \fIGAWK: Effective AWK Programming\fP .if !\n(.g \{\ . if !\w|\*(lq| \{\ . ds lq `` @@ -13,7 +14,7 @@ . if \w'\(rq' .ds rq "\(rq . \} .\} -.TH GAWK 1 "May 17 2000" "Free Software Foundation" "Utility Commands" +.TH GAWK 1 "May 29 2001" "Free Software Foundation" "Utility Commands" .SH NAME gawk \- pattern scanning and processing language .SH SYNOPSIS @@ -32,6 +33,22 @@ gawk \- pattern scanning and processing language ] .I program-text file .\|.\|. +.sp +.B pgawk +[ \*(PX or \*(GN style options ] +.B \-f +.I program-file +[ +.B \-\^\- +] file .\|.\|. +.br +.B pgawk +[ \*(PX or \*(GN style options ] +[ +.B \-\^\- +] +.I program-text +file .\|.\|. .SH DESCRIPTION .I Gawk is the \*(GN Project's implementation of the \*(AK programming language. @@ -44,9 +61,22 @@ with the additional features found in the System V Release 4 version of \*(UX .IR awk . .I Gawk -also provides more recent Bell Labs +also provides more recent Bell Laboratories .I awk -extensions, and some \*(GN-specific extensions. +extensions, and a number of \*(GN-specific extensions. +.PP +.I Pgawk +is the profiling version of +.IR gawk . +It is identical in every way to +.IR gawk , +except that programs run more slowly, +and it automatically produces an execution profile in the file +.B awkprof.out +when done. +See the +.B \-\^\-profile +option, below. .PP The command line consists of options to .I gawk @@ -63,11 +93,11 @@ pre-defined \*(AK variables. .SH OPTION FORMAT .PP .I Gawk -options may be either the traditional \*(PX one letter options, -or the \*(GN style long options. \*(PX options start with a single \*(lq\-\*(rq, +options may be either traditional \*(PX one letter options, +or \*(GN style long options. \*(PX options start with a single \*(lq\-\*(rq, while long options start with \*(lq\-\^\-\*(rq. Long options are provided for both \*(GN-specific features and -for \*(PX mandated features. +for \*(PX-mandated features. .PP Following the \*(PX standard, .IR gawk -specific @@ -89,7 +119,7 @@ remains unique. .SH OPTIONS .PP .I Gawk -accepts the following options. +accepts the following options, listed alphabetically. .TP .PD 0 .BI \-F " fs" @@ -109,7 +139,7 @@ variable). .PD \fB\-\^\-assign \fIvar\fB\^=\^\fIval\fR Assign the value -.IR val , +.I val to the variable .IR var , before execution of the program begins. @@ -144,7 +174,7 @@ flag sets the maximum number of fields, and the .B r flag sets the maximum record size. These two flags and the .B \-m -option are from the Bell Labs research version of \*(UX +option are from the Bell Laboratories research version of \*(UX .IR awk . They are ignored by .IR gawk , @@ -153,16 +183,16 @@ since has no pre-defined limits. .TP .PD 0 -.B "\-W traditional" +.B "\-W compat" .TP .PD 0 -.B "\-W compat" +.B "\-W traditional" .TP .PD 0 -.B \-\^\-traditional +.B \-\^\-compat .TP .PD -.B \-\^\-compat +.B \-\^\-traditional Run in .I compatibility mode. In compatibility mode, @@ -189,7 +219,33 @@ below, for more information. .PD .B \-\^\-copyright Print the short version of the \*(GN copyright information message on -the standard output, and exits successfully. +the standard output and exit successfully. +.TP +.PD 0 +\fB\-W dump-variables\fR[\fB=\fIfile\fR] +.TP +.PD +\fB\-\^\-dump-variables\fR[\fB=\fIfile\fR] +Print a sorted list of global variables, their types and final values to +.IR file . +If no +.I file +is provided, +.I gawk +uses a file named +.I awkvars.out +in the current directory. +.sp .5 +Having a list of all the global variables is a good way to look for +typographical errors in your programs. +You would also use this option if you have a large program with a lot of +functions, and you want to be sure that your functions don't +inadvertently use global variables that you meant to be local. +(This is a particularly easy mistake to make with simple variable +names like +.BR i , +.BR j , +and so on.) .TP .PD 0 .B "\-W help" @@ -209,12 +265,17 @@ the standard output. these options cause an immediate, successful exit.) .TP .PD 0 -.B "\-W lint" +.BR "\-W lint" [ =fatal ] .TP .PD -.B \-\^\-lint +.BR \-\^\-lint [ =fatal ] Provide warnings about constructs that are dubious or non-portable to other \*(AK implementations. +With an optional argument of +.BR fatal , +lint warnings become fatal errors. +This may be drastic, but its use will certainly encourage the +development of cleaner \*(AK programs. .TP .PD 0 .B "\-W lint\-old" @@ -224,6 +285,29 @@ dubious or non-portable to other \*(AK implementations. Provide warnings about constructs that are not portable to the original version of Unix .IR awk . +.TP +.PD 0 +.B "\-W gen\-po" +.TP +.PD +.B \-\^\-gen\-po +Scan and parse the \*(AK program, and generate a \*(GN +.B \&.po +format file on standard output with entries for all localizable +strings in the program. The program itself is not executed. +See the \*(GN +.I gettext +distribution for more information on +.B \&.po +files. +.TP +.PD 0 +.B "\-W non\-decimal\-data" +.TP +.PD +.B "\-\^\-non\-decimal\-data" +Recognize octal and hexadecimal values in input data. +.I "Use this option with great caution!" .ig .\" This option is left undocumented, on purpose. .TP @@ -246,7 +330,7 @@ This turns on .I compatibility mode, with the following additional restrictions: .RS -.TP \w'\(bu'u+1n +.TP "\w'\(bu'u+1n" \(bu .B \ex escape sequences are not recognized. @@ -257,6 +341,12 @@ Only space and tab act as field separators when is set to a single space, newline does not. .TP \(bu +You cannot continue lines after +.B ? +and +.BR : . +.TP +\(bu The synonym .B func for the keyword @@ -280,6 +370,23 @@ function is not available. .RE .TP .PD 0 +\fB\-W profile\fR[\fB=\fIprof_file\fR] +.TP +.PD +\fB\-\^\-profile\fR[\fB=\fIprof_file\fR] +Send profiling data to +.IR prof_file . +The default is +.BR awkprof.out . +When run with +.IR gawk , +the profile is just a \*(lqpretty printed\*(rq version of the program. +When run with +.IR pgawk , +the profile contains execution counts of each statement in the program +in the left margin and function call counts for each user-defined function. +.TP +.PD 0 .B "\-W re\-interval" .TP .PD @@ -337,14 +444,15 @@ This is also useful when reporting bugs. .IR "GNU Coding Standards" , these options cause an immediate, successful exit.) .TP +.PD 0 .B \-\^\- -Signal the end of options. This is useful to allow further arguments to the +Signal the end of options. This is useful to allow further arguments to the \*(AK program itself to start with a \*(lq\-\*(rq. This is mainly for consistency with the argument parsing convention used by most other \*(PX programs. .PP In compatibility mode, -any other options are flagged as illegal, but are otherwise ignored. +any other options are flagged as invalid, but are otherwise ignored. In normal operation, as long as program text has been supplied, unknown options are passed on to the \*(AK program in the .B ARGV @@ -374,7 +482,7 @@ and .B \-\^\-source options may be used multiple times on the command line. .I Gawk -will read the program text as if all the +reads the program text as if all the .IR program-file s and command line source texts had been concatenated together. This is useful for building libraries @@ -472,7 +580,7 @@ is any single character, that character separates records. Otherwise, .B RS is a regular expression. Text in the input that matches this -regular expression will separate the record. +regular expression separates the record. However, in compatibility mode, only the first character of its string value is used for separating records. @@ -512,9 +620,10 @@ by runs of spaces and/or tabs and/or newlines. (But see the discussion of .BR \-\^\-posix , below). -Note that the value of +.B NOTE: +The value of .B IGNORECASE -(see below) will also affect how fields are split when +(see below) also affects how fields are split when .B FS is a regular expression, and how records are separated when .B RS @@ -525,7 +634,7 @@ If the variable is set to a space separated list of numbers, each field is expected to have fixed width, and .I gawk -will split up the record using the specified widths. The value of +splits up the record using the specified widths. The value of .B FS is ignored. Assigning a new value to @@ -539,7 +648,7 @@ Each field in the input record may be referenced by its position, .BR $2 , and so on. .B $0 -is the whole record. The value of a field may be assigned to as well. +is the whole record. Fields need not be referenced by constants: .RS .PP @@ -551,6 +660,7 @@ print $n .RE .PP prints the fifth field in the input record. +.PP The variable .B NF is set to the total number of fields in the input record. @@ -560,10 +670,10 @@ References to non-existent fields (i.e. fields after produce the null-string. However, assigning to a non-existent field (e.g., .BR "$(NF+2) = 5" ) -will increase the value of +increases the value of .BR NF , -create any intervening fields with the null string as their value, and -cause the value of +creates any intervening fields with the null string as their value, and +causes the value of .B $0 to be recomputed, with the fields being separated by the value of .BR OFS . @@ -574,12 +684,21 @@ causes the values of fields past the new value to be lost, and the value of .B $0 to be recomputed, with the fields being separated by the value of .BR OFS . +.PP +Assigning a value to an existing field +causes the whole record to be rebuilt when +.B $0 +is referenced. +Similarly, assigning a value to +.B $0 +causes the record to be resplit, creating new +values for the fields. .SS Built-in Variables .PP -.IR Gawk 's +.IR Gawk\^ "'s" built-in variables are: .PP -.TP \w'\fBFIELDWIDTHS\fR'u+1n +.TP "\w'\fBFIELDWIDTHS\fR'u+1n" .B ARGC The number of command line arguments (does not include options to .IR gawk , @@ -599,6 +718,16 @@ Dynamically changing the contents of .B ARGV can control the files used for data. .TP +.B BINMODE +On non-POSIX systems, specifies use of \*(lqbinary\*(rq mode for all file I/O. +Numeric values of 1, 2, or 3, specify that input files, output files, or +all files, respectively, should use binary I/O. +String values of \fB"r"\fR, or \fB"w"\fR specify that input files, or output files, +respectively, should use binary I/O. +String values of \fB"rw"\fR or \fB"wr"\fR specify that all files +should use binary I/O. +Any other string value is treated as \fB"rw"\fR, but generates a warning message. +.TP .B CONVFMT The conversion format for numbers, \fB"%.6g"\fR, by default. .TP @@ -612,9 +741,6 @@ Changing this array does not affect the environment seen by programs which spawns via redirection or the .B system() function. -(This may change in a future version of -.IR gawk .) -.\" but don't hold your breath... .TP .B ERRNO If a system error occurs either doing a redirection for @@ -627,6 +753,7 @@ then .B ERRNO will contain a string describing the error. +The value is subject to translation in non-English locales. .TP .B FIELDWIDTHS A white-space separated list of fieldwidths. When set, @@ -635,10 +762,6 @@ parses the input into fields of fixed width, instead of using the value of the .B FS variable as the field separator. -The fixed field width facility is still experimental; the -semantics may change as -.I gawk -evolves over time. .TP .B FILENAME The name of the current input file. @@ -649,7 +772,9 @@ However, .B FILENAME is undefined inside the .B BEGIN -block. +block +(unless set by +.BR getline ). .TP .B FNR The input record number in the current input file. @@ -682,8 +807,16 @@ and the .BR split() , and .B sub() -pre-defined functions will all ignore case when doing regular expression -operations. Thus, if +built-in functions all ignore case when doing regular expression +operations. +.B NOTE: +Array subscripting is +.I not +affected, nor is the +.B asort() +function. +.sp .5 +Thus, if .B IGNORECASE is not equal to zero, .B /aB/ @@ -695,13 +828,18 @@ is zero, so all regular expression and string operations are normally case-sensitive. Under Unix, the full ISO 8859-1 Latin-1 character set is used when ignoring case. -.B NOTE: -In versions of +.TP +.B LINT +Provides dynamic control of the +.B \-\^\-lint +option from within an \*(AK program. +When true, .I gawk -prior to 3.0, -.B IGNORECASE -only affected regular expression operations. It now affects string -comparisons as well. +prints lint warnings. When false, it does not. +When assigned the string value \fB"fatal"\fP, +lint warnings become fatal errors, exactly like +.BR \-\^\-lint=fatal . +Any other true value just prints warnings. .TP .B NF The number of fields in the current input record. @@ -718,6 +856,57 @@ The output field separator, a space by default. .B ORS The output record separator, by default a newline. .TP +.B PROCINFO +The elements of this array provide access to information about the +running \*(AK program. +On some systems, +there may be elements in the array, \fB"group1"\fP through +\fB"group\fIn\fB"\fR for some +.IR n , +which is the number of supplementary groups that the process has. +Use the +.B in +operator to test for these elements. +The following elements are guaranteed to be available: +.RS +.TP \w'\fBPROCINFO["pgrpid"]\fR'u+1n +\fBPROCINFO["egid"]\fP +the value of the +.IR getegid (2) +system call. +.TP +\fBPROCINFO["euid"]\fP +the value of the +.IR geteuid (2) +system call. +.TP +\fBPROCINFO["FS"]\fP +\fB"FS"\fP if field splitting with +.B FS +is in effect, or \fB"FIELDWIDTHS"\fP if field splitting with +.B FIELDWIDTHS +is in effect. +.TP +\fBPROCINFO["gid"]\fP +the value of the +.IR getgid (2) +system call. +.TP +\fBPROCINFO["pgrpid"]\fP +the process group ID of the current process. +.TP +\fBPROCINFO["pid"]\fP +the process ID of the current process. +.TP +\fBPROCINFO["ppid"]\fP +the parent process ID of the current process. +.TP +\fBPROCINFO["uid"]\fP +the value of the +.IR getuid (2) +system call. +.RE +.TP .B RS The input record separator, by default a newline. .TP @@ -743,6 +932,10 @@ The length of the string matched by .B SUBSEP The character used to separate multiple subscripts in array elements, by default \fB"\e034"\fR. +.TP +.B TEXTDOMAIN +The text domain of the \*(AK program; used to find the localized +translations for the program's strings. .SS Arrays .PP Arrays are subscripted with an expression between square brackets @@ -817,7 +1010,7 @@ to be treated as a string, concatenate it with the null string. .PP When a string must be converted to a number, the conversion is accomplished using -.IR atof (3). +.IR strtod (3). A number is converted to a string by using the value of .B CONVFMT as a format string for @@ -850,11 +1043,13 @@ If one value is numeric and the other has a string value that is a Otherwise, the numeric value is converted to a string and a string comparison is performed. Two strings are compared, of course, as strings. -According to the \*(PX standard, even if two strings are -numeric strings, a numeric comparison is performed. However, this is +Note that the POSIX standard applies the concept of +\*(lqnumeric string\*(rq everywhere, even to string constants. +However, this is clearly incorrect, and .I gawk does not do this. +(Fortunately, this is fixed in the next version of the standard.) .PP Note that string constants, such as \fB"57"\fP, are .I not @@ -877,6 +1072,79 @@ should be treated that way. .PP Uninitialized variables have the numeric value 0 and the string value "" (the null, or empty, string). +.SS Octal and Hexadecimal Constants +Starting with version 3.1 of +.I gawk , +you may use C-style octal and hexadecimal constants in your AWK +program source code. +For example, the octal value +.B 011 +is equal to decimal +.BR 9 , +and the hexadecimal value +.B 0x11 +is equal to decimal 17. +.SS String Constants +.PP +String constants in \*(AK are sequences of characters enclosed +between double quotes (\fB"\fR). Within strings, certain +.I "escape sequences" +are recognized, as in C. These are: +.PP +.TP "\w'\fB\e\^\fIddd\fR'u+1n" +.B \e\e +A literal backslash. +.TP +.B \ea +The \*(lqalert\*(rq character; usually the \s-1ASCII\s+1 \s-1BEL\s+1 character. +.TP +.B \eb +backspace. +.TP +.B \ef +form-feed. +.TP +.B \en +newline. +.TP +.B \er +carriage return. +.TP +.B \et +horizontal tab. +.TP +.B \ev +vertical tab. +.TP +.BI \ex "\^hex digits" +The character represented by the string of hexadecimal digits following +the +.BR \ex . +As in \*(AN C, all following hexadecimal digits are considered part of +the escape sequence. +(This feature should tell us something about language design by committee.) +E.g., \fB"\ex1B"\fR is the \s-1ASCII\s+1 \s-1ESC\s+1 (escape) character. +.TP +.BI \e ddd +The character represented by the 1-, 2-, or 3-digit sequence of octal +digits. +E.g., \fB"\e033"\fR is the \s-1ASCII\s+1 \s-1ESC\s+1 (escape) character. +.TP +.BI \e c +The literal character +.IR c\^ . +.PP +The escape sequences may also be used inside constant regular expressions +(e.g., +.B "/[\ \et\ef\en\er\ev]/" +matches whitespace characters). +.PP +In compatibility mode, the characters represented by octal and +hexadecimal escape sequences are treated literally when used in +regular expression constants. Thus, +.B /a\e52b/ +is equivalent to +.BR /a\e*b/ . .SH PATTERNS AND ACTIONS \*(AK is a line-oriented language. The pattern comes first, and then the action. Action statements are enclosed in @@ -884,7 +1152,7 @@ action. Action statements are enclosed in and .BR } . Either the pattern may be missing, or the action may be missing, but, -of course, not both. If the pattern is missing, the action will be +of course, not both. If the pattern is missing, the action is executed for every single record of input. A missing action is equivalent to .RS @@ -1005,7 +1273,7 @@ inclusive. It does not combine with any other sort of pattern expression. Regular expressions are the extended kind found in .IR egrep . They are composed of characters as follows: -.TP \w'\fB[^\fIabc.\|.\|.\fB]\fR'u+2n +.TP "\w'\fB[^\fIabc.\|.\|.\fB]\fR'u+2n" .I c matches the non-metacharacter .IR c . @@ -1045,17 +1313,17 @@ concatenation: matches and then .IR r2 . .TP -.IB r + +.IB r\^ + matches one or more -.IR r 's. +.IR r\^ "'s." .TP .IB r * matches zero or more -.IR r 's. +.IR r\^ "'s." .TP -.IB r ? +.IB r\^ ? matches zero or one -.IR r 's. +.IR r\^ "'s." .TP .BI ( r ) grouping: matches @@ -1071,7 +1339,7 @@ grouping: matches .IB r { n , m } One or two numbers inside braces denote an .IR "interval expression" . -If there is one number in the braces, the preceding regexp +If there is one number in the braces, the preceding regular expression .I r is repeated .I n @@ -1120,7 +1388,7 @@ matches the empty string at the beginning of a buffer (string). matches the empty string at the end of a buffer. .PP The escape sequences that are valid in string constants (see below) -are also legal in regular expressions. +are also valid in regular expressions. .PP .I "Character classes" are a new feature introduced in the \*(PX standard. @@ -1130,15 +1398,15 @@ actual characters themselves can vary from country to country and/or from character set to character set. For example, the notion of what is an alphabetic character differs in the USA and in France. .PP -A character class is only valid in a regexp +A character class is only valid in a regular expression .I inside the brackets of a character list. Character classes consist of .BR [: , a keyword denoting the class, and .BR :] . -Here are the character -classes defined by the \*(PX standard. -.TP +The character +classes defined by the \*(PX standard are: +.TP "\w'\fB[:alnum:]\fR'u+2n" .B [:alnum:] Alphanumeric characters. .TP @@ -1183,14 +1451,16 @@ For example, before the \*(PX standard, to match alphanumeric characters, you would have had to write .BR /[A\-Za\-z0\-9]/ . If your character set had other alphabetic characters in it, this would not -match them. With the \*(PX character classes, you can write +match them, and if your character set collated differently from +\s-1ASCII\s+1, this might not even match the +\s-1ASCII\s+1 alphanumeric characters. +With the \*(PX character classes, you can write .BR /[[:alnum:]]/ , -and this will match -.I all +and this matches the alphabetic and numeric characters in your character set. .PP Two additional special sequences can appear in character lists. -These apply to non-ASCII character sets, which can have single symbols +These apply to non-\s-1ASCII\s+1 character sets, which can have single symbols (called .IR "collating elements" ) that are represented with more than one @@ -1200,7 +1470,7 @@ or sorting, purposes. (E.g., in French, a plain \*(lqe\*(rq and a grave-accented e\` are equivalent.) .TP Collating Symbols -A collating symbols is a multi-character collating element enclosed in +A collating symbol is a multi-character collating element enclosed in .B [. and .BR .] . @@ -1208,9 +1478,9 @@ For example, if .B ch is a collating element, then .B [[.ch.]] -is a regexp that matches this collating element, while +is a regular expression that matches this collating element, while .B [ch] -is a regexp that matches either +is a regular expression that matches either .B c or .BR h . @@ -1224,15 +1494,17 @@ and For example, the name .B e might be used to represent all of -\*(lqe,\*(rq \*(lqe\`,\*(rq and \*(lqe\`.\*(rq +\*(lqe,\*(rq \*(lqe\h'-\w:e:u'\`,\*(rq and \*(lqe\h'-\w:e:u'\`.\*(rq In this case, -.B [[=e]] -is a regexp +.B [[=e=]] +is a regular expression that matches any of - .BR e , - .BR e\' , +.BR e , +....BR "e\'" , +.BR "e\h'-\w:e:u'\'" , or - .BR e\` . +....BR "e\`" . +.BR "e\h'-\w:e:u'\`" . .PP These features are very valuable in non-English speaking locales. The library functions that @@ -1253,22 +1525,22 @@ and .B \e' operators are specific to .IR gawk ; -they are extensions based on facilities in the \*(GN regexp libraries. +they are extensions based on facilities in the \*(GN regular expression libraries. .PP The various command line options control how .I gawk -interprets characters in regexps. +interprets characters in regular expressions. .TP No options In the default case, .I gawk provide all the facilities of -\*(PX regexps and the \*(GN regexp operators described above. +\*(PX regular expressions and the \*(GN regular expression operators described above. However, interval expressions are not supported. .TP .B \-\^\-posix -Only \*(PX regexps are supported, the \*(GN operators are not special. +Only \*(PX regular expressions are supported, the \*(GN operators are not special. (E.g., .B \ew matches a literal @@ -1278,16 +1550,16 @@ Interval expressions are allowed. .B \-\^\-traditional Traditional Unix .I awk -regexps are matched. The \*(GN operators +regular expressions are matched. The \*(GN operators are not special, interval expressions are not available, and neither are the \*(PX character classes .RB ( [[:alnum:]] and so on). Characters described by octal and hexadecimal escape sequences are -treated literally, even if they represent regexp metacharacters. +treated literally, even if they represent regular expression metacharacters. .TP .B \-\^\-re\-interval -Allow interval expressions in regexps, even if +Allow interval expressions in regular expressions, even if .B \-\^\-traditional has been provided. .SS Actions @@ -1413,8 +1685,14 @@ as follows: The input/output statements are as follows: .PP .TP "\w'\fBprintf \fIfmt, expr-list\fR'u+1n" -.BI close( file ) -Close file (or pipe, see below). +\fBclose(\fIfile \fR[\fB, \fIhow\fR]\fB)\fR +Close file, pipe or co-process. +The optional +.I how +should only be used when closing one end of a +two-way pipe to a co-process. +It must be a string value, either +\fB"to"\fR or \fB"from"\fR. .TP .B getline Set @@ -1445,6 +1723,28 @@ Set from next record of .IR file . .TP +\fIcommand\fB | getline \fR[\fIvar\fR] +Run +.I command +piping the output either into +.B $0 +or +.IR var , +as above. +.TP +\fIcommand\fB |& getline \fR[\fIvar\fR] +Run +.I command +as a co-process +piping the output either into +.B $0 +or +.IR var , +as above. +Co-processes are a +.I gawk +extension. +.TP .B next Stop processing the current input record. The next input record is read and processing starts over with the first pattern in the @@ -1461,14 +1761,9 @@ and are updated, .B FNR is reset to 1, and processing starts over with the first pattern in the -\*(AK program. If the end of the input data is reached, the +\*(AK program. If the end of the input data is reached, the .B END block(s), if any, are executed. -.B NOTE: -Earlier versions of gawk used -.BR "next file" , -as two words. While this usage is still recognized, it generates a -warning message and will eventually be removed. .TP .B print Prints the current record. @@ -1519,36 +1814,41 @@ is the null string, then all open output files and pipes have their buffers flushed. .PP -Other input/output redirections are also allowed. For +Additional output redirections are allowed for .B print and -.BR printf , -.BI >> " file" +.BR printf . +.TP +.BI "print .\|.\|. >>" " file" appends output to the -.IR file , -while -.BI | " command" +.IR file . +.TP +.BI "print .\|.\|. |" " command" writes on a pipe. -In a similar fashion, -.IB command " | getline" -pipes into -.BR getline . +.TP +.BI "print .\|.\|. |&" " command" +sends data to a co-process. +.PP The .BR getline -command will return 0 on end of file, and \-1 on an error. +command returns 0 on end of file and \-1 on an error. +Upon an error, +.B ERRNO +contains a string describing the problem. .PP -NOTE: If using a pipe to +.B NOTE: +If using a pipe or co-process to .BR getline , or from .B print or -.BR printf +.B printf within a loop, you .I must use .B close() to create new instances of the command. -AWK does not automatically close pipes when +\*(AK does not automatically close pipes or co-processes when they return EOF. .SS The \fIprintf\fP\^ Statement .PP @@ -1559,7 +1859,7 @@ statement and function (see below) accept the following conversion specification formats: -.TP +.TP "\w'\fB%g\fR, \fB%G\fR'u+2n" .B %c An \s-1ASCII\s+1 character. If the argument used for @@ -1568,18 +1868,10 @@ is numeric, it is treated as a character and printed. Otherwise, the argument is assumed to be a string, and the only first character of that string is printed. .TP -.PD 0 -.B %d -.TP -.PD -.B %i +.BR "%d" "," " %i" A decimal number (the integer part). .TP -.PD 0 -.B %e -.TP -.PD -.B %E +.B %e , " %E" A floating point number of the form .BR [\-]d.dddddde[+\^\-]dd . The @@ -1593,11 +1885,7 @@ instead of A floating point number of the form .BR [\-]ddd.dddddd . .TP -.PD 0 -.B %g -.TP -.PD -.B %G +.B %g , " %G" Use .B %e or @@ -1620,11 +1908,7 @@ An unsigned decimal number (again, an integer). .B %s A character string. .TP -.PD 0 -.B %x -.TP -.PD -.B %X +.B %x , " %X" An unsigned hexadecimal number (an integer). The .B %X @@ -1638,10 +1922,23 @@ A single .B % character; no argument is converted. .PP -There are optional, additional parameters that may lie between the +Optional, additional parameters may lie between the .B % and the control letter: .TP +.IB count $ +Use the +.IR count "'th" +argument at this point in the formatting. +This is called a +.I "positional specifier" +and +is intended primarily for use in translated versions of +format strings, not in the original text of an AWK program. +It is a +.I gawk +extension. +.TP .B \- The expression should be left-justified within its field. .TP @@ -1676,7 +1973,7 @@ For .BR %E , and .BR %f , -the result will always contain a +the result always contains a decimal point. For .BR %g , @@ -1722,7 +2019,9 @@ of significant digits. For the and .B %X formats, it specifies the minimum number of -digits to print. For a string, it specifies the maximum number of +digits to print. For +.BR %s , +it specifies the maximum number of characters from the string that should be printed. .PP The dynamic @@ -1738,11 +2037,18 @@ in place of either the .B width or .B prec -specifications will cause their values to be taken from +specifications causes their values to be taken from the argument list to .B printf or .BR sprintf() . +To use a positional specifier with a dynamic width or precision, +supply the +.IB count $ +after the +.B * +in the format string. +For example, \fB"%3$*2$.*1$s"\fP. .SS Special File Names .PP When doing I/O redirection from either @@ -1756,13 +2062,72 @@ from a file, .I gawk recognizes certain special filenames internally. These filenames allow access to open file descriptors inherited from -.IR gawk 's +.IR gawk\^ "'s" parent process (usually the shell). +These file names may also be used on the command line to name data files. +The filenames are: +.TP "\w'\fB/dev/stdout\fR'u+1n" +.B /dev/stdin +The standard input. +.TP +.B /dev/stdout +The standard output. +.TP +.B /dev/stderr +The standard error output. +.TP +.BI /dev/fd/\^ n +The file associated with the open file descriptor +.IR n . +.PP +These are particularly useful for error messages. For example: +.PP +.RS +.ft B +print "You blew it!" > "/dev/stderr" +.ft R +.RE +.PP +whereas you would otherwise have to use +.PP +.RS +.ft B +print "You blew it!" | "cat 1>&2" +.ft R +.RE +.PP +The following special filenames may be used with the +.B |& +co-process operator for creating TCP/IP network connections. +.TP "\w'\fB/inet/tcp/\fIlport\fB/\fIrhost\fB/\fIrport\fR'u+2n" +.BI /inet/tcp/ lport / rhost / rport +File for TCP/IP connection on local port +.I lport +to +remote host +.I rhost +on remote port +.IR rport . +Use a port of +.B 0 +to have the system pick a port. +.TP +.BI /inet/udp/ lport / rhost / rport +Similar, but use UDP/IP instead of TCP/IP. +.TP +.BI /inet/raw/ lport / rhost / rport +.\" Similar, but use raw IP sockets. +Reserved for future use. +.PP Other special filenames provide access to information about the running -.B gawk +.I gawk process. +.B "These filenames are now obsolete." +Use the +.B PROCINFO +array to obtain the information they provide. The filenames are: -.TP \w'\fB/dev/stdout\fR'u+1n +.TP "\w'\fB/dev/stdout\fR'u+1n" .B /dev/pid Reading this file returns the process ID of the current process, in decimal, terminated with a newline. @@ -1797,88 +2162,84 @@ system call. If there are any additional fields, they are the group IDs returned by .IR getgroups (2). Multiple groups may not be supported on all systems. +.SS Numeric Functions +.PP +\*(AK has the following built-in arithmetic functions: +.PP +.TP "\w'\fBsrand(\fR[\fIexpr\^\fR]\fB)\fR'u+1n" +.BI atan2( y , " x" ) +Returns the arctangent of +.I y/x +in radians. .TP -.B /dev/stdin -The standard input. +.BI cos( expr ) +Returns the cosine of +.IR expr , +which is in radians. .TP -.B /dev/stdout -The standard output. +.BI exp( expr ) +The exponential function. .TP -.B /dev/stderr -The standard error output. -.TP -.BI /dev/fd/\^ n -The file associated with the open file descriptor -.IR n . -.PP -These are particularly useful for error messages. For example: -.PP -.RS -.ft B -print "You blew it!" > "/dev/stderr" -.ft R -.RE -.PP -whereas you would otherwise have to use -.PP -.RS -.ft B -print "You blew it!" | "cat 1>&2" -.ft R -.RE -.PP -These file names may also be used on the command line to name data files. -.SS Numeric Functions -.PP -\*(AK has the following pre-defined arithmetic functions: -.PP -.TP \w'\fBsrand(\fR[\fIexpr\^\fR]\fB)\fR'u+1n -.BI atan2( y , " x" ) -returns the arctangent of -.I y/x -in radians. -.TP -.BI cos( expr ) -returns the cosine of -.IR expr , -which is in radians. -.TP -.BI exp( expr ) -the exponential function. -.TP -.BI int( expr ) -truncates to integer. +.BI int( expr ) +Truncates to integer. .TP .BI log( expr ) -the natural logarithm function. +The natural logarithm function. .TP .B rand() -returns a random number between 0 and 1. +Returns a random number between 0 and 1. .TP .BI sin( expr ) -returns the sine of +Returns the sine of .IR expr , which is in radians. .TP .BI sqrt( expr ) -the square root function. +The square root function. .TP \&\fBsrand(\fR[\fIexpr\^\fR]\fB)\fR -uses +Uses .I expr as a new seed for the random number generator. If no .I expr -is provided, the time of day will be used. +is provided, the time of day is used. The return value is the previous seed for the random number generator. .SS String Functions .PP .I Gawk -has the following pre-defined string functions: +has the following built-in string functions: .PP .TP "\w'\fBsprintf(\^\fIfmt\fB\^, \fIexpr-list\^\fB)\fR'u+1n" +\fBasort(\fIs \fR[\fB, \fId\fR]\fB)\fR +Returns the number of elements in the source +array +.IR s . +The contents of +.I s +are sorted using +.IR gawk\^ "'s" +normal rules for +comparing values, and the indexes of the +sorted values of +.I s +are replaced with sequential +integers starting with 1. If the optional +destination array +.I d +is specified, then +.I s +is first duplicated into +.IR d , +and then +.I d +is sorted, leaving the indexes of the +source array +.I s +unchanged. +.TP \fBgensub(\fIr\fB, \fIs\fB, \fIh \fR[\fB, \fIt\fR]\fB)\fR -search the target string +Search the target string .I t for matches of the regular expression .IR r . @@ -1897,9 +2258,9 @@ Otherwise, is a number indicating which match of .I r to replace. -If no +If .I t -is supplied, +is not supplied, .B $0 is used instead. Within the replacement text @@ -1925,7 +2286,7 @@ and the original target string is changed. .TP "\w'\fBsprintf(\^\fIfmt\fB\^, \fIexpr-list\^\fB)\fR'u+1n" \fBgsub(\fIr\fB, \fIs \fR[\fB, \fIt\fR]\fB)\fR -for each substring matching the regular expression +For each substring matching the regular expression .I r in the string .IR t , @@ -1943,18 +2304,18 @@ Use .B \e& to get a literal .BR & . -See -.I "Effective AWK Programming" +(This must be typed as \fB"\e\e&"\fP; +see \*(EP for a fuller discussion of the rules for .BR &'s and backslashes in the replacement text of .BR sub() , .BR gsub() , and -.BR gensub() . +.BR gensub() .) .TP .BI index( s , " t" ) -returns the index of the string +Returns the index of the string .I t in the string .IR s , @@ -1963,7 +2324,7 @@ or 0 if is not present. .TP \fBlength(\fR[\fIs\fR]\fB) -returns the length of the string +Returns the length of the string .IR s , or the length of .B $0 @@ -1971,8 +2332,8 @@ if .I s is not supplied. .TP -.BI match( s , " r" ) -returns the position in +\fBmatch(\fIs\fB, \fIr \fR[\fB, \fIa\fR]\fB)\fR +Returns the position in .I s where the regular expression .I r @@ -1982,9 +2343,33 @@ is not present, and sets the values of .B RSTART and .BR RLENGTH . +Note that the argument order is the same as for the +.B ~ +operator: +.IB str " ~" +.IR re . +.ft R +If array +.I a +is provided, +.I a +is cleared and then elements 1 through +.I n +are filled with the portions of +.I s +that match the corresponding parenthesized +subexpression in +.IR r . +The 0'th element of +.I a +contains the portion +of +.I s +matched by the entire regular expression +.IR r . .TP \fBsplit(\fIs\fB, \fIa \fR[\fB, \fIr\fR]\fB)\fR -splits the string +Splits the string .I s into the array .I a @@ -2001,19 +2386,44 @@ is cleared first. Splitting behaves identically to field splitting, described above. .TP .BI sprintf( fmt , " expr-list" ) -prints +Prints .I expr-list according to .IR fmt , and returns the resulting string. .TP +.BI strtonum( str ) +Examines +.IR str , +and returns its numeric value. +If +.I str +begins +with a leading +.BR 0 , +.B strtonum() +assumes that +.I str +is an octal number. +If +.I str +begins +with a leading +.B 0x +or +.BR 0X , +.B strtonum() +assumes that +.I str +is a hexadecimal number. +.TP \fBsub(\fIr\fB, \fIs \fR[\fB, \fIt\fR]\fB)\fR -just like +Just like .BR gsub() , but only the first matching substring is replaced. .TP \fBsubstr(\fIs\fB, \fIi \fR[\fB, \fIn\fR]\fB)\fR -returns the at most +Returns the at most .IR n -character substring of .I s @@ -2026,7 +2436,7 @@ is omitted, the rest of is used. .TP .BI tolower( str ) -returns a copy of the string +Returns a copy of the string .IR str , with all the upper-case characters in .I str @@ -2034,27 +2444,58 @@ translated to their corresponding lower-case counterparts. Non-alphabetic characters are left unchanged. .TP .BI toupper( str ) -returns a copy of the string +Returns a copy of the string .IR str , with all the lower-case characters in .I str translated to their corresponding upper-case counterparts. Non-alphabetic characters are left unchanged. .SS Time Functions -.PP Since one of the primary uses of \*(AK programs is processing log files that contain time stamp information, .I gawk -provides the following two functions for obtaining time stamps and +provides the following functions for obtaining time stamps and formatting them. .PP .TP "\w'\fBsystime()\fR'u+1n" -.B systime() -returns the current time of day as the number of seconds since the Epoch -(Midnight UTC, January 1, 1970 on \*(PX systems). +\fBmktime(\fIdatespec\fB)\fR +Rurns +.I datespec +into a time stamp of the same form as returned by +.BR systime() . +The +.I datespec +is a string of the form +.IR "YYYY MM DD HH MM SS[ DST]" . +The contents of the string are six or seven numbers representing respectively +the full year including century, +the month from 1 to 12, +the day of the month from 1 to 31, +the hour of the day from 0 to 23, +the minute from 0 to 59, +and the second from 0 to 60, +and an optional daylight saving flag. +The values of these numbers need not be within the ranges specified; +for example, an hour of \-1 means 1 hour before midnight. +The origin-zero Gregorian calendar is assumed, +with year 0 preceding year 1 and year \-1 preceding year 0. +The time is assumed to be in the local timezone. +If the daylight saving flag is positive, +the time is assumed to be daylight saving time; +if zero, the time is assumed to be standard time; +and if negative (the default), +.B mktime() +attempts to determine whether daylight saving time is in effect +for the specified time. +If +.I datespec +does not contain enough elements or if the resulting time +is out of range, +.B mktime() +returns \-1. .TP \fBstrftime(\fR[\fIformat \fR[\fB, \fItimestamp\fR]]\fB)\fR -formats +Formats .I timestamp according to the specification in .IR format. @@ -2069,7 +2510,7 @@ If .I format is missing, a default format equivalent to the output of .IR date (1) -will be used. +is used. See the specification for the .B strftime() function in \*(AN C for the format conversions that are @@ -2082,68 +2523,113 @@ if that version was used to build .IR gawk , then all of the conversions described in that man page are available to .IR gawk. -.SS String Constants -.PP -String constants in \*(AK are sequences of characters enclosed -between double quotes (\fB"\fR). Within strings, certain -.I "escape sequences" -are recognized, as in C. These are: -.PP -.TP \w'\fB\e\^\fIddd\fR'u+1n -.B \e\e -A literal backslash. .TP -.B \ea -The \*(lqalert\*(rq character; usually the \s-1ASCII\s+1 \s-1BEL\s+1 character. -.TP -.B \eb -backspace. -.TP -.B \ef -form-feed. -.TP -.B \en -newline. -.TP -.B \er -carriage return. +.B systime() +Returns the current time of day as the number of seconds since the Epoch +(1970-01-01 00:00:00 UTC on \*(PX systems). +.SS Bit Manipulations Functions +Starting with version 3.1 of +.IR gawk , +the following bit manipulation functions are available. +They work by converting double-precision floating point +values to +.B "unsigned long" +integers, doing the operation, and then converting the +result back to floating point. +The functions are: +.TP "\w'\fBrshift(\fIval\fB, \fIcount\fB)\fR'u+2n" +\fBand(\fIv1\fB, \fIv2\fB)\fR +Return the bitwise AND of the values provided by +.I v1 +and +.IR v2 . .TP -.B \et -horizontal tab. +\fBcompl(\fIval\fB)\fR +Return the bitwise complement of +.IR val . .TP -.B \ev -vertical tab. +\fBlshift(\fIval\fB, \fIcount\fB)\fR +Return the value of +.IR val , +shifted left by +.I count +bits. .TP -.BI \ex "\^hex digits" -The character represented by the string of hexadecimal digits following -the -.BR \ex . -As in \*(AN C, all following hexadecimal digits are considered part of -the escape sequence. -(This feature should tell us something about language design by committee.) -E.g., \fB"\ex1B"\fR is the \s-1ASCII\s+1 \s-1ESC\s+1 (escape) character. +\fBor(\fIv1\fB, \fIv2\fB)\fR +Return the bitwise OR of the values provided by +.I v1 +and +.IR v2 . .TP -.BI \e ddd -The character represented by the 1-, 2-, or 3-digit sequence of octal -digits. -E.g., \fB"\e033"\fR is the \s-1ASCII\s+1 \s-1ESC\s+1 (escape) character. +\fBrshift(\fIval\fB, \fIcount\fB)\fR +Return the value of +.IR val , +shifted right by +.I count +bits. .TP -.BI \e c -The literal character -.IR c\^ . -.PP -The escape sequences may also be used inside constant regular expressions -(e.g., -.B "/[\ \et\ef\en\er\ev]/" -matches whitespace characters). +\fBxor(\fIv1\fB, \fIv2\fB)\fR +Return the bitwise XOR of the values provided by +.I v1 +and +.IR v2 . .PP -In compatibility mode, the characters represented by octal and -hexadecimal escape sequences are treated literally when used in -regexp constants. Thus, -.B /a\e52b/ -is equivalent to -.BR /a\e*b/ . -.SH FUNCTIONS +.SS Internationalization Functions +Starting with version 3.1 of +.IR gawk , +the following functions may be used from within your AWK program for +translating strings at run-time. +For full details, see \*(EP. +.TP +\fBbindtextdomain(\fIdirectory \fR[\fB, \fIdomain\fR]\fB)\fR +Specifies the directory where +.I gawk +looks for the +.B \&.mo +files, in case they +will not or cannot be placed in the ``standard'' locations +(e.g., during testing). +It returns the directory where +.I domain +is ``bound.'' +.sp .5 +The default +.I domain +is the value of +.BR TEXTDOMAIN . +If +.I directory +is the null string (\fB""\fR), then +.B bindtextdomain() +returns the current binding for the +given +.IR domain . +.TP +\fBdcgettext(\fIstring \fR[\fB, \fIdomain \fR[\fB, \fIcategory\fR]]\fB)\fR +Returns the translation of +.I string +in +text domain +.I domain +for locale category +.IR category . +The default value for +.I domain +is the current value of +.BR TEXTDOMAIN . +The default value for +.I category +is \fB"LC_MESSAGES"\fR. +.sp .5 +If you supply a value for +.IR category , +it must be a string equal to +one of the known locale categories described +in \*(EP. +You must also supply a text domain. Use +.B TEXTDOMAIN +if you want to use the current domain. +.SH USER-DEFINED FUNCTIONS Functions in \*(AK are defined as follows: .PP .RS @@ -2163,7 +2649,7 @@ real parameters by extra spaces in the parameter list. For example: .RS .ft B .nf -function f(p, q, a, b) # a & b are local +function f(p, q, a, b) # a and b are local { \&.\|.\|. } @@ -2193,7 +2679,7 @@ If .B \-\^\-lint has been provided, .I gawk -will warn about calls to undefined functions at parse time, +warns about calls to undefined functions at parse time, instead of at run time. Calling an undefined function at run time is a fatal error. .PP @@ -2201,6 +2687,45 @@ The word .B func may be used in place of .BR function . +.SH DYNAMICALLY LOADING NEW FUNCTIONS +Beginning with version 3.1 of +.IR gawk , +you can dynamically add new built-in functions to the running +.I gawk +interpreter. +The full details are beyond the scope of this manual page; +see \*(EP for the details. +.PP +.TP 8 +\fBextension(\fIobject\fB, \fIfunction\fB)\fR +Dynamically link the shared object file named by +.IR object , +and invoke +.I function +in that object, to perform initialization. +These should both be provided as strings. +Returns the value returned by +.IR function . +.PP +.ft B +This function is provided and documented in \*(EP, +but everything about this feature is likely to change +in the next release. +We STRONGLY recommend that you do not use this feature +for anything that you aren't willing to redo. +.ft R +.SH SIGNALS +.I pgawk +accepts two signals. +.B SIGUSR1 +causes it to dump a profile and function call stack to the +profile file, which is either +.BR awkprof.out , +or whatever file was named with the +.B \-\^\-profile +option. It then continues to run. +.B SIGHUP +causes it to dump the profile and function call stack and then exit. .SH EXAMPLES .nf Print and sort the login names of all users: @@ -2229,23 +2754,84 @@ Concatenate and line number (a variation on a theme): { print NR, $0 } .ft R .fi -.SH SEE ALSO -.IR egrep (1), -.IR getpid (2), -.IR getppid (2), -.IR getpgrp (2), -.IR getuid (2), -.IR geteuid (2), -.IR getgid (2), -.IR getegid (2), -.IR getgroups (2) -.PP -.IR "The AWK Programming Language" , -Alfred V. Aho, Brian W. Kernighan, Peter J. Weinberger, -Addison-Wesley, 1988. ISBN 0-201-07981-X. -.PP -.IR "Effective AWK Programming" , -Edition 1.0, published by the Free Software Foundation, 1995. +.SH INTERNATIONALIZATION +.PP +String constants are sequences of characters enclosed in double +quotes. In non-English speaking environments, it is possible to mark +strings in the \*(AK program as requiring translation to the native +natural language. Such strings are marked in the \*(AK program with +a leading underscore (\*(lq_\*(rq). For example, +.sp +.RS +.ft B +gawk 'BEGIN { print "hello, world" }' +.RE +.sp +.ft R +always prints +.BR "hello, world" . +But, +.sp +.RS +.ft B +gawk 'BEGIN { print _"hello, world" }' +.RE +.sp +.ft R +might print +.B "bonjour, monde" +in France. +.PP +There are several steps involved in producing and running a localizable +\*(AK program. +.TP "\w'4.'u+2n" +1. +Add a +.B BEGIN +action to assign a value to the +.B TEXTDOMAIN +variable to set the text domain to a name associated with your program. +.sp +.ti +5n +.ft B +BEGIN { TEXTDOMAIN = "myprog" } +.ft R +.sp +This allows +.I gawk +to find the +.B \&.mo +file associated with your program. +Without this step, +.I gawk +uses the +.B messages +text domain, +which likely does not contain translations for your program. +.TP +2. +Mark all strings that should be translated with leading underscores. +.TP +3. +If necessary, use the +.B dcgettext() +and/or +.B bindtextdomain() +functions in your program, as appropriate. +.TP +4. +Run +.B "gawk \-\^\-gen\-po \-f myprog.awk > myprog.po" +to generate a +.B \&.po +file for your program. +.TP +5. +Provide appropriate translations, and build and install a corresponding +.B \&.mo +file. +.PP +The internationalization features are described in full detail in \*(EP. .SH POSIX COMPATIBILITY A primary goal for .I gawk @@ -2256,13 +2842,10 @@ To this end, .I gawk incorporates the following user visible features which are not described in the \*(AK book, -but are part of the Bell Labs version of +but are part of the Bell Laboratories version of .IR awk , and are in the \*(PX standard. .PP -The -.B \-v -option for assigning variables before program execution starts is new. The book indicates that command line variable assignment happens when .I awk would otherwise open the argument as a file, which is after the @@ -2275,9 +2858,11 @@ the block was run. Applications came to depend on this \*(lqfeature.\*(rq When .I awk -was changed to match its documentation, this option was added to +was changed to match its documentation, the +.B \-v +option for assigning variables before program execution was added to accommodate applications that depended upon the old behavior. -(This feature was agreed upon by both the AT&T and \*(GN developers.) +(This feature was agreed upon by both the Bell Laboratories and the \*(GN developers.) .PP The .B \-W @@ -2287,7 +2872,7 @@ When processing arguments, .I gawk uses the special option \*(lq\-\^\-\*(rq to signal the end of arguments. -In compatibility mode, it will warn about, but otherwise ignore, +In compatibility mode, it warns about but otherwise ignores undefined options. In normal operation, such arguments are passed on to the \*(AK program for it to process. @@ -2315,13 +2900,61 @@ and .BR \ev escape sequences (done originally in .I gawk -and fed back into AT&T's); the +and fed back into the Bell Laboratories version); the .B tolower() and .B toupper() -built-in functions (from AT&T); and the \*(AN C conversion specifications in +built-in functions (from the Bell Laboratories version); and the \*(AN C conversion specifications in .B printf -(done first in AT&T's version). +(done first in the Bell Laboratories version). +.SH HISTORICAL FEATURES +There are two features of historical \*(AK implementations that +.I gawk +supports. +First, it is possible to call the +.B length() +built-in function not only with no argument, but even without parentheses! +Thus, +.RS +.PP +.ft B +a = length # Holy Algol 60, Batman! +.ft R +.RE +.PP +is the same as either of +.RS +.PP +.ft B +a = length() +.br +a = length($0) +.ft R +.RE +.PP +This feature is marked as \*(lqdeprecated\*(rq in the \*(PX standard, and +.I gawk +issues a warning about its use if +.B \-\^\-lint +is specified on the command line. +.PP +The other feature is the use of either the +.B continue +or the +.B break +statements outside the body of a +.BR while , +.BR for , +or +.B do +loop. Traditional \*(AK implementations have treated such usage as +equivalent to the +.B next +statement. +.I Gawk +supports this usage if +.B \-\^\-traditional +has been specified. .SH GNU EXTENSIONS .I Gawk has a number of extensions to \*(PX @@ -2339,15 +2972,23 @@ The following features of are not available in \*(PX .IR awk . -.RS -.TP \w'\(bu'u+1n +.\" Environment vars and startup stuff +.TP "\w'\(bu'u+1n" +\(bu +No path search is performed for files named via the +.B \-f +option. Therefore the +.B AWKPATH +environment variable is not special. +.\" POSIX and language recognition issues +.TP \(bu The .B \ex escape sequence. (Disabled with .BR \-\^\-posix .) -.TP \w'\(bu'u+1n +.TP \(bu The .B fflush() @@ -2356,22 +2997,26 @@ function. .BR \-\^\-posix .) .TP \(bu -The -.BR systime(), -.BR strftime(), +The ability to continue lines after +.B ? and -.B gensub() -functions. +.BR : . +(Disabled with +.BR \-\^\-posix .) .TP \(bu -The special file names available for I/O redirection are not recognized. +Octal and hexadecimal constants in AWK programs. +.\" Special variables .TP \(bu The .BR ARGIND , +.BR BINMODE , .BR ERRNO , +.BR LINT , +.B RT and -.B RT +.B TEXTDOMAIN variables are not special. .TP \(bu @@ -2385,11 +3030,26 @@ The variable and fixed-width field splitting. .TP \(bu +The +.B PROCINFO +array is not available. +.\" I/O stuff +.TP +\(bu The use of .B RS as a regular expression. .TP \(bu +The special file names available for I/O redirection are not recognized. +.TP +\(bu +The +.B |& +operator for creating co-processes. +.\" Changes to standard awk functions +.TP +\(bu The ability to split out individual characters using the null string as the value of .BR FS , @@ -2397,33 +3057,75 @@ and as the third argument to .BR split() . .TP \(bu -No path search is performed for files named via the -.B \-f -option. Therefore the -.B AWKPATH -environment variable is not special. +The optional second argument to the +.B close() +function. .TP \(bu -The use of -.B "nextfile" -to abandon processing of the current input file. +The optional third argument to the +.B match() +function. +.TP +\(bu +The ability to use positional specifiers with +.B printf +and +.BR sprintf() . +.\" New keywords or changes to keywords .TP \(bu The use of .BI delete " array" to delete the entire contents of an array. -.RE +.TP +\(bu +The use of +.B "nextfile" +to abandon processing of the current input file. +.\" New functions +.TP +\(bu +The +.BR and() , +.BR asort() , +.BR bindtextdomain() , +.BR compl() , +.BR dcgettext() , +.BR gensub() , +.BR lshift() , +.BR mktime() , +.BR or() , +.BR rshift() , +.BR strftime() , +.BR strtonum() , +.B systime() +and +.B xor() +functions. +.\" I18N stuff +.TP +\(bu +Localizable strings. +.\" Extending gawk +.TP +\(bu +Adding new built-in functions dynamically with the +.B extension() +function. .PP -The AWK book does not define the return value of the +The \*(AK book does not define the return value of the .B close() function. -.IR Gawk\^ 's +.IR Gawk\^ "'s" .B close() returns the value from .IR fclose (3), or .IR pclose (3), -when closing a file or pipe, respectively. +when closing an output file or pipe, respectively. +It returns the process's exit status when closing an input pipe. +The return value is \-1 if the named file, pipe +or co-process was not opened with a redirection. .PP When .I gawk @@ -2436,7 +3138,7 @@ argument to the .B \-F option is \*(lqt\*(rq, then .B FS -will be set to the tab character. +is set to the tab character. Note that typing .B "gawk \-F\et \&.\|.\|." simply causes the shell to quote the \*(lqt,\*(rq, and does not pass @@ -2448,14 +3150,14 @@ This behavior also does not occur if .B \-\^\-posix has been specified. To really get a tab character as the field separator, it is best to use -quotes: +single quotes: .BR "gawk \-F'\et' \&.\|.\|." . .ig .PP If .I gawk -was compiled for debugging, it will -accept the following additional options: +was compiled for debugging, it +accepts the following additional options: .TP .PD 0 .B \-Wparsedebug @@ -2472,55 +3174,17 @@ This option should only be of interest to the maintainers, and may not even be compiled into .IR gawk . .. -.SH HISTORICAL FEATURES -There are two features of historical \*(AK implementations that -.I gawk -supports. -First, it is possible to call the -.B length() -built-in function not only with no argument, but even without parentheses! -Thus, -.RS -.PP -.ft B -a = length # Holy Algol 60, Batman! -.ft R -.RE -.PP -is the same as either of -.RS -.PP -.ft B -a = length() -.br -a = length($0) -.ft R -.RE -.PP -This feature is marked as \*(lqdeprecated\*(rq in the \*(PX standard, and +.SH ENVIRONMENT VARIABLES +The +.B AWKPATH +environment variable can be used to provide a list of directories that .I gawk -will issue a warning about its use if -.B \-\^\-lint -is specified on the command line. +searches when looking for files named via the +.B \-f +and +.B \-\^\-file +options. .PP -The other feature is the use of either the -.B continue -or the -.B break -statements outside the body of a -.BR while , -.BR for , -or -.B do -loop. Traditional \*(AK implementations have treated such usage as -equivalent to the -.B next -statement. -.I Gawk -will support this usage if -.B \-\^\-traditional -has been specified. -.SH ENVIRONMENT VARIABLES If .B POSIXLY_CORRECT exists in the environment, then @@ -2532,54 +3196,47 @@ If .B \-\^\-lint has been specified, .I gawk -will issue a warning message to this effect. +issues a warning message to this effect. +.SH SEE ALSO +.IR egrep (1), +.IR getpid (2), +.IR getppid (2), +.IR getpgrp (2), +.IR getuid (2), +.IR geteuid (2), +.IR getgid (2), +.IR getegid (2), +.IR getgroups (2) .PP -The -.B AWKPATH -environment variable can be used to provide a list of directories that -.I gawk -will search when looking for files named via the -.B \-f -and -.B \-\^\-file -options. +.IR "The AWK Programming Language" , +Alfred V. Aho, Brian W. Kernighan, Peter J. Weinberger, +Addison-Wesley, 1988. ISBN 0-201-07981-X. +.PP +\*(EP, +Edition 3.0, published by the Free Software Foundation, 2001. .SH BUGS The .B \-F option is not necessary given the command line variable assignment feature; it remains only for backwards compatibility. .PP -If your system actually has support for -.B /dev/fd -and the associated -.BR /dev/stdin , -.BR /dev/stdout , -and -.B /dev/stderr -files, you may get different output from -.I gawk -than you would get on a system without those files. When -.I gawk -interprets these files internally, it synchronizes output to the standard -output with output to -.BR /dev/stdout , -while on a system with those files, the output is actually to different -open files. -Caveat Emptor. -.PP Syntactically invalid single character programs tend to overflow the parse stack, generating a rather unhelpful message. Such programs are surprisingly difficult to diagnose in the completely general case, and the effort to do so really is not worth it. -.SH VERSION INFORMATION -This man page documents -.IR gawk , -version 3.0.6. +.ig +.PP +.I Gawk +suffers from ``feeping creaturism.'' +It's too bad +.I perl +is so inelegant. +.. .SH AUTHORS The original version of \*(UX .I awk was designed and implemented by Alfred Aho, -Peter Weinberger, and Brian Kernighan of AT&T Bell Labs. Brian Kernighan +Peter Weinberger, and Brian Kernighan of Bell Laboratories. Brian Kernighan continues to maintain and enhance it. .PP Paul Rubin and Jay Fenlason, @@ -2600,14 +3257,22 @@ The initial DOS port was done by Conrad Kwok and Scott Garfinkle. Scott Deifik is the current DOS maintainer. Pat Rankin did the port to VMS, and Michal Jaegermann did the port to the Atari ST. The port to OS/2 was done by Kai Uwe Rommel, with contributions and -help from Darrel Hankerson. Fred Fish supplied support for the Amiga. +help from Darrel Hankerson. Fred Fish supplied support for the Amiga, +Stephen Davies provided the Tandem port, +and Martin Brown provided the BeOS port. +.SH VERSION INFORMATION +This man page documents +.IR gawk , +version 3.1.0. .SH BUG REPORTS If you find a bug in .IR gawk , please send electronic mail to .BR bug-gawk@gnu.org . Please include your operating system and its revision, the version of -.IR gawk , +.I gawk +(from +.BR "gawk \-\^\-version" ), what C compiler you used to compile it, and a test program and data that are as small as possible for reproducing the problem. .PP @@ -2630,11 +3295,11 @@ developers occasionally read this newsgroup, posting bug reports there is an unreliable way to report bugs. Instead, please use the electronic mail addresses given above. .SH ACKNOWLEDGEMENTS -Brian Kernighan of Bell Labs +Brian Kernighan of Bell Laboratories provided valuable assistance during testing and debugging. We thank him. .SH COPYING PERMISSIONS -Copyright \(co 1996\-2000 Free Software Foundation, Inc. +Copyright \(co 1989, 1991\-2001 Free Software Foundation, Inc. .PP Permission is granted to make and distribute verbatim copies of this manual page provided the copyright notice and this permission diff --git a/doc/gawk.info b/doc/gawk.info index 037522e9..075d4947 100644 --- a/doc/gawk.info +++ b/doc/gawk.info @@ -1,35 +1,40 @@ -This is gawk.info, produced by makeinfo version 4.0 from ./gawk.texi. +This is gawk.info, produced by makeinfo version 4.0 from gawk.texi. -INFO-DIR-SECTION Programming Languages +INFO-DIR-SECTION GNU Packages START-INFO-DIR-ENTRY -* Gawk: (gawk). A Text Scanning and Processing Language. +* Gawk: (gawk). A text scanning and processing language. +END-INFO-DIR-ENTRY +INFO-DIR-SECTION Individual utilities +START-INFO-DIR-ENTRY +* awk: (gawk)Invoking gawk. Text scanning and processing. END-INFO-DIR-ENTRY This file documents `awk', a program that you can use to select particular records in a file and perform operations upon them. - This is Edition 1.0.6 of `Effective AWK Programming', for the -3.0.6 version of the GNU implementation of AWK. + This is Edition 3 of `GAWK: Effective AWK Programming: A User's +Guide for GNU Awk', for the 3.1.0 version of the GNU implementation of +AWK. - Copyright (C) 1989, 1991, 1992, 1993, 1996-2000 Free Software + Copyright (C) 1989, 1991, 1992, 1993, 1996-2001 Free Software Foundation, Inc. - Permission is granted to make and distribute verbatim copies of this -manual provided the copyright notice and this permission notice are -preserved on all copies. + Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "GNU General Public License", the Front-Cover +texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +"GNU Free Documentation License". - Permission is granted to copy and distribute modified versions of -this manual under the conditions for verbatim copying, provided that -the entire resulting derived work is distributed under the terms of a -permission notice identical to this one. + a. "A GNU Manual" - Permission is granted to copy and distribute translations of this -manual into another language, under the above conditions for modified -versions, except that this permission notice may be stated in a -translation approved by the Foundation. + b. "You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development."  -File: gawk.info, Node: Top, Next: Preface, Prev: (dir), Up: (dir) +File: gawk.info, Node: Top, Next: Foreword, Prev: (dir), Up: (dir) General Introduction ******************** @@ -37,313 +42,386 @@ General Introduction This file documents `awk', a program that you can use to select particular records in a file and perform operations upon them. - This is Edition 1.0.6 of `Effective AWK Programming', -for the 3.0.6 version of the GNU implementation -of AWK. + This is Edition 3 of `GAWK: Effective AWK Programming: A User's +Guide for GNU Awk', for the 3.1.0 version of the GNU implementation of +AWK. * Menu: -* Preface:: What this Info file is about; brief - history and acknowledgements. -* What Is Awk:: What is the `awk' language; using this - Info file. -* Getting Started:: A basic introduction to using `awk'. How - to run an `awk' program. Command line - syntax. -* One-liners:: Short, sample `awk' programs. -* Regexp:: All about matching things using regular - expressions. -* Reading Files:: How to read files and manipulate fields. -* Printing:: How to print using `awk'. Describes the - `print' and `printf' statements. - Also describes redirection of output. -* Expressions:: Expressions are the basic building blocks of - statements. -* Patterns and Actions:: Overviews of patterns and actions. -* Statements:: The various control statements are described - in detail. -* Built-in Variables:: Built-in Variables -* Arrays:: The description and use of arrays. Also - includes array-oriented control statements. -* Built-in:: The built-in functions are summarized here. -* User-defined:: User-defined functions are described in - detail. -* Invoking Gawk:: How to run `gawk'. -* Library Functions:: A Library of `awk' Functions. -* Sample Programs:: Many `awk' programs with complete - explanations. -* Language History:: The evolution of the `awk' language. -* Gawk Summary:: `gawk' Options and Language Summary. -* Installation:: Installing `gawk' under various operating - systems. -* Notes:: Something about the implementation of - `gawk'. -* Glossary:: An explanation of some unfamiliar terms. -* Copying:: Your right to copy and distribute `gawk'. -* Index:: Concept and Variable Index. - -* History:: The history of `gawk' and `awk'. -* Manual History:: Brief history of the GNU project and this - Info file. -* Acknowledgements:: Acknowledgements. -* This Manual:: Using this Info file. Includes sample - input files that you can use. -* Conventions:: Typographical Conventions. -* Sample Data Files:: Sample data files for use in the `awk' - programs illustrated in this Info file. -* Names:: What name to use to find `awk'. -* Running gawk:: How to run `gawk' programs; includes - command line syntax. -* One-shot:: Running a short throw-away `awk' program. -* Read Terminal:: Using no input files (input from terminal - instead). -* Long:: Putting permanent `awk' programs in - files. -* Executable Scripts:: Making self-contained `awk' programs. -* Comments:: Adding documentation to `gawk' programs. -* Very Simple:: A very simple example. -* Two Rules:: A less simple one-line example with two rules. -* More Complex:: A more complex example. -* Statements/Lines:: Subdividing or combining statements into - lines. -* Other Features:: Other Features of `awk'. -* When:: When to use `gawk' and when to use other - things. -* Regexp Usage:: How to Use Regular Expressions. -* Escape Sequences:: How to write non-printing characters. -* Regexp Operators:: Regular Expression Operators. -* GNU Regexp Operators:: Operators specific to GNU software. -* Case-sensitivity:: How to do case-insensitive matching. -* Leftmost Longest:: How much text matches. -* Computed Regexps:: Using Dynamic Regexps. -* Records:: Controlling how data is split into records. -* Fields:: An introduction to fields. -* Non-Constant Fields:: Non-constant Field Numbers. -* Changing Fields:: Changing the Contents of a Field. -* Field Separators:: The field separator and how to change it. -* Basic Field Splitting:: How fields are split with single characters or - simple strings. -* Regexp Field Splitting:: Using regexps as the field separator. -* Single Character Fields:: Making each character a separate field. -* Command Line Field Separator:: Setting `FS' from the command line. -* Field Splitting Summary:: Some final points and a summary table. -* Constant Size:: Reading constant width data. -* Multiple Line:: Reading multi-line records. -* Getline:: Reading files under explicit program control - using the `getline' function. -* Getline Intro:: Introduction to the `getline' function. -* Plain Getline:: Using `getline' with no arguments. -* Getline/Variable:: Using `getline' into a variable. -* Getline/File:: Using `getline' from a file. -* Getline/Variable/File:: Using `getline' into a variable from a - file. -* Getline/Pipe:: Using `getline' from a pipe. -* Getline/Variable/Pipe:: Using `getline' into a variable from a - pipe. -* Getline Summary:: Summary Of `getline' Variants. -* Print:: The `print' statement. -* Print Examples:: Simple examples of `print' statements. -* Output Separators:: The output separators and how to change them. -* OFMT:: Controlling Numeric Output With `print'. -* Printf:: The `printf' statement. -* Basic Printf:: Syntax of the `printf' statement. -* Control Letters:: Format-control letters. -* Format Modifiers:: Format-specification modifiers. -* Printf Examples:: Several examples. -* Redirection:: How to redirect output to multiple files and - pipes. -* Special Files:: File name interpretation in `gawk'. - `gawk' allows access to inherited file - descriptors. -* Close Files And Pipes:: Closing Input and Output Files and Pipes. -* Constants:: String, numeric, and regexp constants. -* Scalar Constants:: Numeric and string constants. -* Regexp Constants:: Regular Expression constants. -* Using Constant Regexps:: When and how to use a regexp constant. -* Variables:: Variables give names to values for later use. -* Using Variables:: Using variables in your programs. -* Assignment Options:: Setting variables on the command line and a - summary of command line syntax. This is an - advanced method of input. -* Conversion:: The conversion of strings to numbers and vice - versa. -* Arithmetic Ops:: Arithmetic operations (`+', `-', - etc.) -* Concatenation:: Concatenating strings. -* Assignment Ops:: Changing the value of a variable or a field. -* Increment Ops:: Incrementing the numeric value of a variable. -* Truth Values:: What is ``true'' and what is ``false''. -* Typing and Comparison:: How variables acquire types, and how this - affects comparison of numbers and strings with - `<', etc. -* Boolean Ops:: Combining comparison expressions using boolean - operators `||' (``or''), `&&' - (``and'') and `!' (``not''). -* Conditional Exp:: Conditional expressions select between two - subexpressions under control of a third - subexpression. -* Function Calls:: A function call is an expression. -* Precedence:: How various operators nest. -* Pattern Overview:: What goes into a pattern. -* Kinds of Patterns:: A list of all kinds of patterns. -* Regexp Patterns:: Using regexps as patterns. -* Expression Patterns:: Any expression can be used as a pattern. -* Ranges:: Pairs of patterns specify record ranges. -* BEGIN/END:: Specifying initialization and cleanup rules. -* Using BEGIN/END:: How and why to use BEGIN/END rules. -* I/O And BEGIN/END:: I/O issues in BEGIN/END rules. -* Empty:: The empty pattern, which matches every record. -* Action Overview:: What goes into an action. -* If Statement:: Conditionally execute some `awk' - statements. -* While Statement:: Loop until some condition is satisfied. -* Do Statement:: Do specified action while looping until some - condition is satisfied. -* For Statement:: Another looping statement, that provides - initialization and increment clauses. -* Break Statement:: Immediately exit the innermost enclosing loop. -* Continue Statement:: Skip to the end of the innermost enclosing - loop. -* Next Statement:: Stop processing the current input record. -* Nextfile Statement:: Stop processing the current file. -* Exit Statement:: Stop execution of `awk'. -* User-modified:: Built-in variables that you change to control - `awk'. -* Auto-set:: Built-in variables where `awk' gives you - information. -* ARGC and ARGV:: Ways to use `ARGC' and `ARGV'. -* Array Intro:: Introduction to Arrays -* Reference to Elements:: How to examine one element of an array. -* Assigning Elements:: How to change an element of an array. -* Array Example:: Basic Example of an Array -* Scanning an Array:: A variation of the `for' statement. It - loops through the indices of an array's - existing elements. -* Delete:: The `delete' statement removes an element - from an array. -* Numeric Array Subscripts:: How to use numbers as subscripts in - `awk'. -* Uninitialized Subscripts:: Using Uninitialized variables as subscripts. -* Multi-dimensional:: Emulating multi-dimensional arrays in - `awk'. -* Multi-scanning:: Scanning multi-dimensional arrays. -* Calling Built-in:: How to call built-in functions. -* Numeric Functions:: Functions that work with numbers, including - `int', `sin' and `rand'. -* String Functions:: Functions for string manipulation, such as - `split', `match', and - `sprintf'. -* I/O Functions:: Functions for files and shell commands. -* Time Functions:: Functions for dealing with time stamps. -* Definition Syntax:: How to write definitions and what they mean. -* Function Example:: An example function definition and what it - does. -* Function Caveats:: Things to watch out for. -* Return Statement:: Specifying the value a function returns. -* Options:: Command line options and their meanings. -* Other Arguments:: Input file names and variable assignments. -* AWKPATH Variable:: Searching directories for `awk' programs. -* Obsolete:: Obsolete Options and/or features. -* Undocumented:: Undocumented Options and Features. -* Known Bugs:: Known Bugs in `gawk'. -* Portability Notes:: What to do if you don't have `gawk'. -* Nextfile Function:: Two implementations of a `nextfile' - function. -* Assert Function:: A function for assertions in `awk' - programs. -* Round Function:: A function for rounding if `sprintf' does - not do it correctly. -* Ordinal Functions:: Functions for using characters as numbers and - vice versa. -* Join Function:: A function to join an array into a string. -* Mktime Function:: A function to turn a date into a timestamp. -* Gettimeofday Function:: A function to get formatted times. -* Filetrans Function:: A function for handling data file transitions. -* Getopt Function:: A function for processing command line - arguments. -* Passwd Functions:: Functions for getting user information. -* Group Functions:: Functions for getting group information. -* Library Names:: How to best name private global variables in - library functions. -* Clones:: Clones of common utilities. -* Cut Program:: The `cut' utility. -* Egrep Program:: The `egrep' utility. -* Id Program:: The `id' utility. -* Split Program:: The `split' utility. -* Tee Program:: The `tee' utility. -* Uniq Program:: The `uniq' utility. -* Wc Program:: The `wc' utility. -* Miscellaneous Programs:: Some interesting `awk' programs. -* Dupword Program:: Finding duplicated words in a document. -* Alarm Program:: An alarm clock. -* Translate Program:: A program similar to the `tr' utility. -* Labels Program:: Printing mailing labels. -* Word Sorting:: A program to produce a word usage count. -* History Sorting:: Eliminating duplicate entries from a history - file. -* Extract Program:: Pulling out programs from Texinfo source - files. -* Simple Sed:: A Simple Stream Editor. -* Igawk Program:: A wrapper for `awk' that includes files. -* V7/SVR3.1:: The major changes between V7 and System V - Release 3.1. -* SVR4:: Minor changes between System V Releases 3.1 - and 4. -* POSIX:: New features from the POSIX standard. -* BTL:: New features from the Bell Laboratories - version of `awk'. -* POSIX/GNU:: The extensions in `gawk' not in POSIX - `awk'. -* Command Line Summary:: Recapitulation of the command line. -* Language Summary:: A terse review of the language. -* Variables/Fields:: Variables, fields, and arrays. -* Fields Summary:: Input field splitting. -* Built-in Summary:: `awk''s built-in variables. -* Arrays Summary:: Using arrays. -* Data Type Summary:: Values in `awk' are numbers or strings. -* Rules Summary:: Patterns and Actions, and their component - parts. -* Pattern Summary:: Quick overview of patterns. -* Regexp Summary:: Quick overview of regular expressions. -* Actions Summary:: Quick overview of actions. -* Operator Summary:: `awk' operators. -* Control Flow Summary:: The control statements. -* I/O Summary:: The I/O statements. -* Printf Summary:: A summary of `printf'. -* Special File Summary:: Special file names interpreted internally. -* Built-in Functions Summary:: Built-in numeric and string functions. -* Time Functions Summary:: Built-in time functions. -* String Constants Summary:: Escape sequences in strings. -* Functions Summary:: Defining and calling functions. -* Historical Features:: Some undocumented but supported ``features''. -* Gawk Distribution:: What is in the `gawk' distribution. -* Getting:: How to get the distribution. -* Extracting:: How to extract the distribution. -* Distribution contents:: What is in the distribution. -* Unix Installation:: Installing `gawk' under various versions - of Unix. -* Quick Installation:: Compiling `gawk' under Unix. -* Configuration Philosophy:: How it's all supposed to work. -* VMS Installation:: Installing `gawk' on VMS. -* VMS Compilation:: How to compile `gawk' under VMS. -* VMS Installation Details:: How to install `gawk' under VMS. -* VMS Running:: How to run `gawk' under VMS. -* VMS POSIX:: Alternate instructions for VMS POSIX. -* PC Installation:: Installing and Compiling `gawk' on MS-DOS - and OS/2 -* Atari Installation:: Installing `gawk' on the Atari ST. -* Atari Compiling:: Compiling `gawk' on Atari -* Atari Using:: Running `gawk' on Atari -* Amiga Installation:: Installing `gawk' on an Amiga. -* Bugs:: Reporting Problems and Bugs. -* Other Versions:: Other freely available `awk' - implementations. -* Compatibility Mode:: How to disable certain `gawk' extensions. -* Additions:: Making Additions To `gawk'. -* Adding Code:: Adding code to the main body of `gawk'. -* New Ports:: Porting `gawk' to a new operating system. -* Future Extensions:: New features that may be implemented one day. -* Improvements:: Suggestions for improvements by volunteers. +* Foreword:: Some nice words about this + Info file. +* Preface:: What this Info file is about; brief + history and acknowledgments. +* Getting Started:: A basic introduction to using + `awk'. How to run an `awk' + program. Command-line syntax. +* Regexp:: All about matching things using regular + expressions. +* Reading Files:: How to read files and manipulate fields. +* Printing:: How to print using `awk'. Describes + the `print' and `printf' + statements. Also describes redirection of + output. +* Expressions:: Expressions are the basic building blocks + of statements. +* Patterns and Actions:: Overviews of patterns and actions. +* Arrays:: The description and use of arrays. Also + includes array-oriented control statements. +* Functions:: Built-in and user-defined functions. +* Internationalization:: Getting `gawk' to speak your + language. +* Advanced Features:: Stuff for advanced users, specific to + `gawk'. +* Invoking Gawk:: How to run `gawk'. +* Library Functions:: A Library of `awk' Functions. +* Sample Programs:: Many `awk' programs with complete + explanations. +* Language History:: The evolution of the `awk' + language. +* Installation:: Installing `gawk' under various + operating systems. +* Notes:: Notes about `gawk' extensions and + possible future work. +* Basic Concepts:: A very quick intoduction to programming + concepts. +* Glossary:: An explanation of some unfamiliar terms. +* Copying:: Your right to copy and distribute + `gawk'. +* GNU Free Documentation License:: The license for this Info file. +* Index:: Concept and Variable Index. + +* History:: The history of `gawk' and + `awk'. +* Names:: What name to use to find `awk'. +* This Manual:: Using this Info file. Includes + sample input files that you can use. +* Conventions:: Typographical Conventions. +* Manual History:: Brief history of the GNU project and this + Info file. +* How To Contribute:: Helping to save the world. +* Acknowledgments:: Acknowledgments. +* Running gawk:: How to run `gawk' programs; + includes command-line syntax. +* One-shot:: Running a short throw-away `awk' + program. +* Read Terminal:: Using no input files (input from terminal + instead). +* Long:: Putting permanent `awk' programs in + files. +* Executable Scripts:: Making self-contained `awk' + programs. +* Comments:: Adding documentation to `gawk' + programs. +* Quoting:: More discussion of shell quoting issues. +* Sample Data Files:: Sample data files for use in the + `awk' programs illustrated in this + Info file. +* Very Simple:: A very simple example. +* Two Rules:: A less simple one-line example using two + rules. +* More Complex:: A more complex example. +* Statements/Lines:: Subdividing or combining statements into + lines. +* Other Features:: Other Features of `awk'. +* When:: When to use `gawk' and when to use + other things. +* Regexp Usage:: How to Use Regular Expressions. +* Escape Sequences:: How to write non-printing characters. +* Regexp Operators:: Regular Expression Operators. +* Character Lists:: What can go between `[...]'. +* GNU Regexp Operators:: Operators specific to GNU software. +* Case-sensitivity:: How to do case-insensitive matching. +* Leftmost Longest:: How much text matches. +* Computed Regexps:: Using Dynamic Regexps. +* Records:: Controlling how data is split into records. +* Fields:: An introduction to fields. +* Non-Constant Fields:: Non-constant Field Numbers. +* Changing Fields:: Changing the Contents of a Field. +* Field Separators:: The field separator and how to change it. +* Regexp Field Splitting:: Using regexps as the field separator. +* Single Character Fields:: Making each character a separate field. +* Command Line Field Separator:: Setting `FS' from the command-line. +* Field Splitting Summary:: Some final points and a summary table. +* Constant Size:: Reading constant width data. +* Multiple Line:: Reading multi-line records. +* Getline:: Reading files under explicit program + control using the `getline' function. +* Plain Getline:: Using `getline' with no arguments. +* Getline/Variable:: Using `getline' into a variable. +* Getline/File:: Using `getline' from a file. +* Getline/Variable/File:: Using `getline' into a variable from a + file. +* Getline/Pipe:: Using `getline' from a pipe. +* Getline/Variable/Pipe:: Using `getline' into a variable from a + pipe. +* Getline/Coprocess:: Using `getline' from a coprocess. +* Getline/Variable/Coprocess:: Using `getline' into a variable from a + coprocess. +* Getline Notes:: Important things to know about + `getline'. +* Getline Summary:: Summary of `getline' Variants. +* Print:: The `print' statement. +* Print Examples:: Simple examples of `print' statements. +* Output Separators:: The output separators and how to change + them. +* OFMT:: Controlling Numeric Output With + `print'. +* Printf:: The `printf' statement. +* Basic Printf:: Syntax of the `printf' statement. +* Control Letters:: Format-control letters. +* Format Modifiers:: Format-specification modifiers. +* Printf Examples:: Several examples. +* Redirection:: How to redirect output to multiple files + and pipes. +* Special Files:: File name interpretation in `gawk'. + `gawk' allows access to inherited + file descriptors. +* Special FD:: Special files for I/O. +* Special Process:: Special files for process information. +* Special Network:: Special files for network communications. +* Special Caveats:: Things to watch out for. +* Close Files And Pipes:: Closing Input and Output Files and Pipes. +* Constants:: String, numeric and regexp constants. +* Scalar Constants:: Numeric and string constants. +* Non-decimal-numbers:: What are octal and hex numbers. +* Regexp Constants:: Regular Expression constants. +* Using Constant Regexps:: When and how to use a regexp constant. +* Variables:: Variables give names to values for later + use. +* Using Variables:: Using variables in your programs. +* Assignment Options:: Setting variables on the command-line and a + summary of command-line syntax. This is an + advanced method of input. +* Conversion:: The conversion of strings to numbers and + vice versa. +* Arithmetic Ops:: Arithmetic operations (`+', `-', + etc.) +* Concatenation:: Concatenating strings. +* Assignment Ops:: Changing the value of a variable or a + field. +* Increment Ops:: Incrementing the numeric value of a + variable. +* Truth Values:: What is ``true'' and what is ``false''. +* Typing and Comparison:: How variables acquire types and how this + affects comparison of numbers and strings + with `<', etc. +* Boolean Ops:: Combining comparison expressions using + boolean operators `||' (``or''), + `&&' (``and'') and `!' (``not''). +* Conditional Exp:: Conditional expressions select between two + subexpressions under control of a third + subexpression. +* Function Calls:: A function call is an expression. +* Precedence:: How various operators nest. +* Pattern Overview:: What goes into a pattern. +* Regexp Patterns:: Using regexps as patterns. +* Expression Patterns:: Any expression can be used as a pattern. +* Ranges:: Pairs of patterns specify record ranges. +* BEGIN/END:: Specifying initialization and cleanup + rules. +* Using BEGIN/END:: How and why to use BEGIN/END rules. +* I/O And BEGIN/END:: I/O issues in BEGIN/END rules. +* Empty:: The empty pattern, which matches every + record. +* Using Shell Variables:: How to use shell variables with + `awk'. +* Action Overview:: What goes into an action. +* Statements:: Describes the various control statements in + detail. +* If Statement:: Conditionally execute some `awk' + statements. +* While Statement:: Loop until some condition is satisfied. +* Do Statement:: Do specified action while looping until + some condition is satisfied. +* For Statement:: Another looping statement, that provides + initialization and increment clauses. +* Break Statement:: Immediately exit the innermost enclosing + loop. +* Continue Statement:: Skip to the end of the innermost enclosing + loop. +* Next Statement:: Stop processing the current input record. +* Nextfile Statement:: Stop processing the current file. +* Exit Statement:: Stop execution of `awk'. +* Built-in Variables:: Summarizes the built-in variables. +* User-modified:: Built-in variables that you change to + control `awk'. +* Auto-set:: Built-in variables where `awk' + gives you information. +* ARGC and ARGV:: Ways to use `ARGC' and `ARGV'. +* Array Intro:: Introduction to Arrays +* Reference to Elements:: How to examine one element of an array. +* Assigning Elements:: How to change an element of an array. +* Array Example:: Basic Example of an Array +* Scanning an Array:: A variation of the `for' statement. It + loops through the indices of an array's + existing elements. +* Delete:: The `delete' statement removes an + element from an array. +* Numeric Array Subscripts:: How to use numbers as subscripts in + `awk'. +* Uninitialized Subscripts:: Using Uninitialized variables as + subscripts. +* Multi-dimensional:: Emulating multidimensional arrays in + `awk'. +* Multi-scanning:: Scanning multidimensional arrays. +* Array Sorting:: Sorting array values and indices. +* Built-in:: Summarizes the built-in functions. +* Calling Built-in:: How to call built-in functions. +* Numeric Functions:: Functions that work with numbers, including + `int', `sin' and `rand'. +* String Functions:: Functions for string manipulation, such as + `split', `match' and + `sprintf'. +* Gory Details:: More than you want to know about `\' + and `&' with `sub', `gsub', + and `gensub'. +* I/O Functions:: Functions for files and shell commands. +* Time Functions:: Functions for dealing with timestamps. +* Bitwise Functions:: Functions for bitwise operations. +* I18N Functions:: Functions for string translation. +* User-defined:: Describes User-defined functions in detail. +* Definition Syntax:: How to write definitions and what they + mean. +* Function Example:: An example function definition and what it + does. +* Function Caveats:: Things to watch out for. +* Return Statement:: Specifying the value a function returns. +* Dynamic Typing:: How variable types can change at runtime. +* I18N and L10N:: Internationalization and Localization. +* Explaining gettext:: How GNU `gettext' works. +* Programmer i18n:: Features for the programmer. +* Translator i18n:: Features for the translator. +* String Extraction:: Extracting marked strings. +* Printf Ordering:: Rearranging `printf' arguments. +* I18N Portability:: `awk'-level portability issues. +* I18N Example:: A simple i18n example. +* Gawk I18N:: `gawk' is also internationalized. +* Non-decimal Data:: Allowing non-decimal input data. +* Two-way I/O:: Two-way communications with another + process. +* TCP/IP Networking:: Using `gawk' for network + programming. +* Portal Files:: Using `gawk' with BSD portals. +* Profiling:: Profiling your `awk' programs. +* Command Line:: How to run `awk'. +* Options:: Command-line options and their meanings. +* Other Arguments:: Input file names and variable assignments. +* AWKPATH Variable:: Searching directories for `awk' + programs. +* Obsolete:: Obsolete Options and/or features. +* Undocumented:: Undocumented Options and Features. +* Known Bugs:: Known Bugs in `gawk'. +* Library Names:: How to best name private global variables + in library functions. +* General Functions:: Functions that are of general use. +* Nextfile Function:: Two implementations of a `nextfile' + function. +* Assert Function:: A function for assertions in `awk' + programs. +* Round Function:: A function for rounding if `sprintf' + does not do it correctly. +* Cliff Random Function:: The Cliff Random Number Generator. +* Ordinal Functions:: Functions for using characters as numbers + and vice versa. +* Join Function:: A function to join an array into a string. +* Gettimeofday Function:: A function to get formatted times. +* Data File Management:: Functions for managing command-line data + files. +* Filetrans Function:: A function for handling data file + transitions. +* Rewind Function:: A function for rereading the current file. +* File Checking:: Checking that data files are readable. +* Ignoring Assigns:: Treating assignments as file names. +* Getopt Function:: A function for processing command-line + arguments. +* Passwd Functions:: Functions for getting user information. +* Group Functions:: Functions for getting group information. +* Running Examples:: How to run these examples. +* Clones:: Clones of common utilities. +* Cut Program:: The `cut' utility. +* Egrep Program:: The `egrep' utility. +* Id Program:: The `id' utility. +* Split Program:: The `split' utility. +* Tee Program:: The `tee' utility. +* Uniq Program:: The `uniq' utility. +* Wc Program:: The `wc' utility. +* Miscellaneous Programs:: Some interesting `awk' programs. +* Dupword Program:: Finding duplicated words in a document. +* Alarm Program:: An alarm clock. +* Translate Program:: A program similar to the `tr' + utility. +* Labels Program:: Printing mailing labels. +* Word Sorting:: A program to produce a word usage count. +* History Sorting:: Eliminating duplicate entries from a + history file. +* Extract Program:: Pulling out programs from Texinfo source + files. +* Simple Sed:: A Simple Stream Editor. +* Igawk Program:: A wrapper for `awk' that includes + files. +* V7/SVR3.1:: The major changes between V7 and System V + Release 3.1. +* SVR4:: Minor changes between System V Releases 3.1 + and 4. +* POSIX:: New features from the POSIX standard. +* BTL:: New features from the Bell Laboratories + version of `awk'. +* POSIX/GNU:: The extensions in `gawk' not in + POSIX `awk'. +* Contributors:: The major contributors to `gawk'. +* Gawk Distribution:: What is in the `gawk' distribution. +* Getting:: How to get the distribution. +* Extracting:: How to extract the distribution. +* Distribution contents:: What is in the distribution. +* Unix Installation:: Installing `gawk' under various + versions of Unix. +* Quick Installation:: Compiling `gawk' under Unix. +* Additional Configuration Options:: Other compile-time options. +* Configuration Philosophy:: How it's all supposed to work. +* Non-Unix Installation:: Installation on Other Operating Systems. +* Amiga Installation:: Installing `gawk' on an Amiga. +* BeOS Installation:: Installing `gawk' on BeOS. +* PC Installation:: Installing and Compiling `gawk' on + MS-DOS and OS/2. +* PC Binary Installation:: Installing a prepared distribution. +* PC Compiling:: Compiling `gawk' for MS-DOS, Win32, + and OS/2. +* PC Using:: Running `gawk' on MS-DOS, Win32 and + OS/2. +* VMS Installation:: Installing `gawk' on VMS. +* VMS Compilation:: How to compile `gawk' under VMS. +* VMS Installation Details:: How to install `gawk' under VMS. +* VMS Running:: How to run `gawk' under VMS. +* VMS POSIX:: Alternate instructions for VMS POSIX. +* Unsupported:: Systems whose ports are no longer + supported. +* Atari Installation:: Installing `gawk' on the Atari ST. +* Atari Compiling:: Compiling `gawk' on Atari. +* Atari Using:: Running `gawk' on Atari. +* Tandem Installation:: Installing `gawk' on a Tandem. +* Bugs:: Reporting Problems and Bugs. +* Other Versions:: Other freely available `awk' + implementations. +* Compatibility Mode:: How to disable certain `gawk' + extensions. +* Additions:: Making Additions To `gawk'. +* Adding Code:: Adding code to the main body of + `gawk'. +* New Ports:: Porting `gawk' to a new operating + system. +* Dynamic Extensions:: Adding new built-in functions to + `gawk'. +* Internals:: A brief look at some `gawk' + internals. +* Sample Library:: A example of new functions. +* Internal File Description:: What the new functions will do. +* Internal File Ops:: The code for internal file operations. +* Using Internal File Ops:: How to use an external extension. +* Future Extensions:: New features that may be implemented one + day. +* Basic High Level:: The high level view. +* Basic Data Typing:: A very quick intro to data types. +* Floating Point Issues:: Stuff to know about floating-point numbers. To Miriam, for making me complete. @@ -360,331 +438,383 @@ of AWK. To Malka, for the new beginning.  -File: gawk.info, Node: Preface, Next: What Is Awk, Prev: Top, Up: Top +File: gawk.info, Node: Foreword, Next: Preface, Prev: Top, Up: Top + +Foreword +******** + + Arnold Robbins and I are good friends. We were introduced 11 years +ago by circumstances--and our favorite programming language, AWK. The +circumstances started a couple of years earlier. I was working at a new +job and noticed an unplugged Unix computer sitting in the corner. No +one knew how to use it, and neither did I. However, a couple of days +later it was running, and I was `root' and the one-and-only user. That +day, I began the transition from statistician to Unix programmer. + + On one of many trips to the library or bookstore in search of books +on Unix, I found the gray AWK book, a.k.a. Aho, Kernighan and +Weinberger, `The AWK Programming Language', Addison-Wesley, 1988. +AWK's simple programming paradigm--find a pattern in the input and then +perform an action--often reduced complex or tedious data manipulations +to few lines of code. I was excited to try my hand at programming in +AWK. + + Alas, the `awk' on my computer was a limited version of the +language described in the AWK book. I discovered that my computer had +"old `awk'" and the AWK book described "new `awk'." I learned that +this was typical; the old version refused to step aside or relinquish +its name. If a system had a new `awk', it was invariably called +`nawk', and few systems had it. The best way to get a new `awk' was to +`ftp' the source code for `gawk' from `prep.ai.mit.edu'. `gawk' was a +version of new `awk' written by David Trueman and Arnold, and available +under the GNU General Public License. + + (Incidentally, it's no longer difficult to find a new `awk'. `gawk' +ships with Linux, and you can download binaries or source code for +almost any system; my wife uses `gawk' on her VMS box.) + + My Unix system started out unplugged from the wall; it certainly was +not plugged into a network. So, oblivious to the existence of `gawk' +and the Unix community in general, and desiring a new `awk', I wrote my +own, called `mawk'. Before I was finished I knew about `gawk', but it +was too late to stop, so I eventually posted to a `comp.sources' +newsgroup. + + A few days after my posting, I got a friendly email from Arnold +introducing himself. He suggested we share design and algorithms and +attached a draft of the POSIX standard so that I could update `mawk' to +support language extensions added after publication of the AWK book. + + Frankly, if our roles had been reversed, I would not have been so +open and we probably would have never met. I'm glad we did meet. He +is an AWK expert's AWK expert and a genuinely nice person. Arnold +contributes significant amounts of his expertise and time to the Free +Software Foundation. + + This book is the `gawk' reference manual, but at its core it is a +book about AWK programming that will appeal to a wide audience. It is +a definitive reference to the AWK language as defined by the 1987 Bell +Labs release and codified in the 1992 POSIX Utilities standard. + + On the other hand, the novice AWK programmer can study a wealth of +practical programs that emphasize the power of AWK's basic idioms: data +driven control-flow, pattern matching with regular expressions, and +associative arrays. Those looking for something new can try out +`gawk''s interface to network protocols via special `/inet' files. + + The programs in this book make clear that an AWK program is +typically much smaller and faster to develop than a counterpart written +in C. Consequently, there is often a payoff to prototype an algorithm +or design in AWK to get it running quickly and expose problems early. +Often, the interpreted performance is adequate and the AWK prototype +becomes the product. + + The new `pgawk' (profiling `gawk'), produces program execution +counts. I recently experimented with an algorithm that for n lines of +input, exhibited ~ C n^2 performance, while theory predicted ~ C n log n +behavior. A few minutes poring over the `awkprof.out' profile +pinpointed the problem to a single line of code. `pgawk' is a welcome +addition to my programmer's toolbox. + + Arnold has distilled over a decade of experience writing and using +AWK programs, and developing `gawk', into this book. If you use AWK or +want to learn how, then read this book. + + Michael Brennan + Author of `mawk' + + +File: gawk.info, Node: Preface, Next: Getting Started, Prev: Foreword, Up: Top Preface ******* + Several kinds of tasks occur repeatedly when working with text files. +You might want to extract certain lines and discard the rest. Or you +may need to make changes wherever certain patterns appear, but leave +the rest of the file alone. Writing single-use programs for these +tasks in languages such as C, C++ or Pascal is time-consuming and +inconvenient. Such jobs are often easier with `awk'. The `awk' +utility interprets a special-purpose programming language that makes it +easy to handle simple data-reformatting jobs. + + The GNU implementation of `awk' is called `gawk'; it is fully +compatible with the System V Release 4 version of `awk'. `gawk' is +also compatible with the POSIX specification of the `awk' language. +This means that all properly written `awk' programs should work with +`gawk'. Thus, we usually don't distinguish between `gawk' and other +`awk' implementations. + + Using `awk' allows you to: + + * Manage small, personal databases + + * Generate reports + + * Validate data + + * Produce indexes and perform other document preparation tasks + + * Experiment with algorithms that you can adapt later to other + computer languages. + + In addition, `gawk' provides facilities that make it easy to: + + * Extract bits and pieces of data for processing + + * Sort data + + * Perform simple network communications. + This Info file teaches you about the `awk' language and how you can use it effectively. You should already be familiar with basic system -commands, such as `cat' and `ls',(1) and basic shell facilities, such -as Input/Output (I/O) redirection and pipes. +commands, such as `cat' and `ls',(1) as well as basic shell facilities, +such as Input/Output (I/O) redirection and pipes. Implementations of the `awk' language are available for many different computing environments. This Info file, while describing the -`awk' language in general, also describes a particular implementation -of `awk' called `gawk' (which stands for "GNU Awk"). `gawk' runs on a +`awk' language in general, also describes the particular implementation +of `awk' called `gawk' (which stands for "GNU awk"). `gawk' runs on a broad range of Unix systems, ranging from 80386 PC-based computers, up -through large scale systems, such as Crays. `gawk' has also been ported -to MS-DOS and OS/2 PC's, Atari and Amiga micro-computers, and VMS. +through large-scale systems, such as Crays. `gawk' has also been ported +to Mac OS X, MS-DOS, Microsoft Windows (all versions) and OS/2 PC's, +Atari and Amiga micro-computers, BeOS, Tandem D20, and VMS. * Menu: -* History:: The history of `gawk' and `awk'. +* History:: The history of `gawk' and + `awk'. +* Names:: What name to use to find `awk'. +* This Manual:: Using this Info file. Includes sample + input files that you can use. +* Conventions:: Typographical Conventions. * Manual History:: Brief history of the GNU project and this Info file. -* Acknowledgements:: Acknowledgements. +* How To Contribute:: Helping to save the world. +* Acknowledgments:: Acknowledgments. ---------- Footnotes ---------- - (1) These commands are available on POSIX compliant systems, as well + (1) These commands are available on POSIX-compliant systems, as well as on traditional Unix based systems. If you are using some other operating system, you still need to be familiar with the ideas of I/O redirection and pipes.  -File: gawk.info, Node: History, Next: Manual History, Prev: Preface, Up: Preface +File: gawk.info, Node: History, Next: Names, Prev: Preface, Up: Preface History of `awk' and `gawk' =========================== + Recipe For A Programming Language + + 1 part `egrep' 1 part `snobol' + 2 parts `ed' 3 parts C + + Blend all parts well using `lex' and `yacc'. Document minimally + and release. + + After eight years, add another part `egrep' and two more parts C. + Document very well and release. + The name `awk' comes from the initials of its designers: Alfred V. -Aho, Peter J. Weinberger, and Brian W. Kernighan. The original version -of `awk' was written in 1977 at AT&T Bell Laboratories. In 1985 a new +Aho, Peter J. Weinberger and Brian W. Kernighan. The original version +of `awk' was written in 1977 at AT&T Bell Laboratories. In 1985, a new version made the programming language more powerful, introducing user-defined functions, multiple input streams, and computed regular -expressions. This new version became generally available with Unix -System V Release 3.1. The version in System V Release 4 added some new -features and also cleaned up the behavior in some of the "dark corners" -of the language. The specification for `awk' in the POSIX Command -Language and Utilities standard further clarified the language based on -feedback from both the `gawk' designers, and the original Bell Labs -`awk' designers. - - The GNU implementation, `gawk', was written in 1986 by Paul Rubin -and Jay Fenlason, with advice from Richard Stallman. John Woods +expressions. This new version became widely available with Unix System +V Release 3.1 (SVR3.1). The version in SVR4 added some new features +and cleaned up the behavior in some of the "dark corners" of the +language. The specification for `awk' in the POSIX Command Language +and Utilities standard further clarified the language. Both the `gawk' +designers and the original Bell Laboratories `awk' designers provided +feedback for the POSIX specification. + + Paul Rubin wrote the GNU implementation, `gawk', in 1986. Jay +Fenlason completed it, with advice from Richard Stallman. John Woods contributed parts of the code as well. In 1988 and 1989, David -Trueman, with help from Arnold Robbins, thoroughly reworked `gawk' for -compatibility with the newer `awk'. Current development focuses on bug -fixes, performance improvements, standards compliance, and -occasionally, new features. - - -File: gawk.info, Node: Manual History, Next: Acknowledgements, Prev: History, Up: Preface +Trueman, with help from me, thoroughly reworked `gawk' for compatibility +with the newer `awk'. Circa 1995, I became the primary maintainer. +Current development focuses on bug fixes, performance improvements, +standards compliance, and occasionally, new features. -The GNU Project and This Book -============================= + In May of 1997, Ju"rgen Kahrs felt the need for network access from +`awk', and with a little help from me, set about adding features to do +this for `gawk'. At that time, he also wrote the bulk of `TCP/IP +Internetworking with `gawk'' (a separate document, available as part of +the `gawk' distribution). His code finally became part of the main +`gawk' distribution with `gawk' version 3.1. - The Free Software Foundation (FSF) is a non-profit organization -dedicated to the production and distribution of freely distributable -software. It was founded by Richard M. Stallman, the author of the -original Emacs editor. GNU Emacs is the most widely used version of -Emacs today. + *Note Major Contributors to `gawk': Contributors, for a complete +list of those who made important contributions to `gawk'. - The GNU project is an on-going effort on the part of the Free -Software Foundation to create a complete, freely distributable, POSIX -compliant computing environment. (GNU stands for "GNU's not Unix".) -The FSF uses the "GNU General Public License" (or GPL) to ensure that -source code for their software is always available to the end user. A -copy of the GPL is included for your reference (*note GNU GENERAL -PUBLIC LICENSE: Copying.). The GPL applies to the C language source -code for `gawk'. + +File: gawk.info, Node: Names, Next: This Manual, Prev: History, Up: Preface - A shell, an editor (Emacs), highly portable optimizing C, C++, and -Objective-C compilers, a symbolic debugger, and dozens of large and -small utilities (such as `gawk'), have all been completed and are -freely available. As of this writing (early 1997), the GNU operating -system kernel (the HURD), has been released, but is still in an early -stage of development. +A Rose by Any Other Name +======================== - Until the GNU operating system is more fully developed, you should -consider using Linux, a freely distributable, Unix-like operating -system for 80386, DEC Alpha, Sun SPARC and other systems. There are -many books on Linux. One freely available one is `Linux Installation -and Getting Started', by Matt Welsh. Many Linux distributions are -available, often in computer stores or bundled on CD-ROM with books -about Linux. (There are three other freely available, Unix-like -operating systems for 80386 and other systems, NetBSD, FreeBSD,and -OpenBSD. All are based on the 4.4-Lite Berkeley Software Distribution, -and they use recent versions of `gawk' for their versions of `awk'.) - - This Info file itself has gone through several previous, preliminary -editions. I started working on a preliminary draft of `The GAWK -Manual', by Diane Close, Paul Rubin, and Richard Stallman in the fall -of 1988. It was around 90 pages long, and barely described the -original, "old" version of `awk'. After substantial revision, the first -version of the `The GAWK Manual' to be released was Edition 0.11 Beta in -October of 1989. The manual then underwent more substantial revision -for Edition 0.13 of December 1991. David Trueman, Pat Rankin, and -Michal Jaegermann contributed sections of the manual for Edition 0.13. -That edition was published by the FSF as a bound book early in 1992. -Since then there have been several minor revisions, notably Edition -0.14 of November 1992 that was published by the FSF in January of 1993, -and Edition 0.16 of August 1993. - - Edition 1.0 of `Effective AWK Programming' represents a significant -re-working of `The GAWK Manual', with much additional material. The -FSF and I agree that I am now the primary author. I also felt that it -needed a more descriptive title. - - `Effective AWK Programming' will undoubtedly continue to evolve. An -electronic version comes with the `gawk' distribution from the FSF. If -you find an error in this Info file, please report it! *Note Reporting -Problems and Bugs: Bugs, for information on submitting problem reports -electronically, or write to me in care of the FSF. - - -File: gawk.info, Node: Acknowledgements, Prev: Manual History, Up: Preface - -Acknowledgements -================ + The `awk' language has evolved over the years. Full details are +provided in *Note The Evolution of the `awk' Language: Language History. +The language described in this Info file is often referred to as "new +`awk'" (`nawk'). - I would like to acknowledge Richard M. Stallman, for his vision of a -better world, and for his courage in founding the FSF and starting the -GNU project. + Because of this, many systems have multiple versions of `awk'. Some +systems have an `awk' utility that implements the original version of +the `awk' language and a `nawk' utility for the new version. Others +have an `oawk' for the "old `awk'" language and plain `awk' for the new +one. Still others only have one version, which is usually the new +one.(1) - The initial draft of `The GAWK Manual' had the following -acknowledgements: - - Many people need to be thanked for their assistance in producing - this manual. Jay Fenlason contributed many ideas and sample - programs. Richard Mlynarik and Robert Chassell gave helpful - comments on drafts of this manual. The paper `A Supplemental - Document for `awk'' by John W. Pierce of the Chemistry Department - at UC San Diego, pinpointed several issues relevant both to `awk' - implementation and to this manual, that would otherwise have - escaped us. - - The following people provided many helpful comments on Edition 0.13 -of `The GAWK Manual': Rick Adams, Michael Brennan, Rich Burridge, Diane -Close, Christopher ("Topher") Eliot, Michael Lijewski, Pat Rankin, -Miriam Robbins, and Michal Jaegermann. - - The following people provided many helpful comments for Edition 1.0 -of `Effective AWK Programming': Karl Berry, Michael Brennan, Darrel -Hankerson, Michal Jaegermann, Michael Lijewski, and Miriam Robbins. -Pat Rankin, Michal Jaegermann, Darrel Hankerson and Scott Deifik -updated their respective sections for Edition 1.0. - - Robert J. Chassell provided much valuable advice on the use of -Texinfo. He also deserves special thanks for convincing me _not_ to -title this Info file `How To Gawk Politely'. Karl Berry helped -significantly with the TeX part of Texinfo. - - David Trueman deserves special credit; he has done a yeoman job of -evolving `gawk' so that it performs well, and without bugs. Although -he is no longer involved with `gawk', working with him on this project -was a significant pleasure. - - Scott Deifik, Darrel Hankerson, Kai Uwe Rommel, Pat Rankin, and -Michal Jaegermann (in no particular order) are long time members of the -`gawk' "crack portability team." Without their hard work and help, -`gawk' would not be nearly the fine program it is today. It has been -and continues to be a pleasure working with this team of fine people. - - Jeffrey Friedl provided invaluable help in tracking down a number of -last minute problems with regular expressions in `gawk' 3.0. - - David and I would like to thank Brian Kernighan of Bell Labs for -invaluable assistance during the testing and debugging of `gawk', and -for help in clarifying numerous points about the language. We could -not have done nearly as good a job on either `gawk' or its -documentation without his help. - - I would like to thank Marshall and Elaine Hartholz of Seattle, and -Dr. Bert and Rita Schreiber of Detroit for large amounts of quiet -vacation time in their homes, which allowed me to make significant -progress on this Info file and on `gawk' itself. Phil Hughes of SSC -contributed in a very important way by loaning me his laptop Linux -system, not once, but twice, allowing me to do a lot of work while away -from home. - - Finally, I must thank my wonderful wife, Miriam, for her patience -through the many versions of this project, for her proof-reading, and -for sharing me with the computer. I would like to thank my parents for -their love, and for the grace with which they raised and educated me. -I also must acknowledge my gratitude to G-d, for the many opportunities -He has sent my way, as well as for the gifts He has given me with which -to take advantage of those opportunities. + All in all, this makes it difficult for you to know which version of +`awk' you should run when writing your programs. The best advice I can +give here is to check your local documentation. Look for `awk', `oawk', +and `nawk', as well as for `gawk'. It is likely that you already have +some version of new `awk' on your system, which is what you should use +when running your programs. (Of course, if you're reading this Info +file, chances are good that you have `gawk'!) + Throughout this Info file, whenever we refer to a language feature +that should be available in any complete implementation of POSIX `awk', +we simply use the term `awk'. When referring to a feature that is +specific to the GNU implementation, we use the term `gawk'. + ---------- Footnotes ---------- -Arnold Robbins -Atlanta, Georgia -February, 1997 + (1) Often, these systems use `gawk' for their `awk' implementation!  -File: gawk.info, Node: What Is Awk, Next: Getting Started, Prev: Preface, Up: Top - -Introduction -************ - - If you are like many computer users, you would frequently like to -make changes in various text files wherever certain patterns appear, or -extract data from parts of certain lines while discarding the rest. To -write a program to do this in a language such as C or Pascal is a -time-consuming inconvenience that may take many lines of code. The job -may be easier with `awk'. - - The `awk' utility interprets a special-purpose programming language -that makes it possible to handle simple data-reformatting jobs with -just a few lines of code. +File: gawk.info, Node: This Manual, Next: Conventions, Prev: Names, Up: Preface - The GNU implementation of `awk' is called `gawk'; it is fully upward -compatible with the System V Release 4 version of `awk'. `gawk' is -also upward compatible with the POSIX specification of the `awk' -language. This means that all properly written `awk' programs should -work with `gawk'. Thus, we usually don't distinguish between `gawk' -and other `awk' implementations. - - Using `awk' you can: - - * manage small, personal databases - - * generate reports +Using This Book +=============== - * validate data + Documentation is like sex: when it is good, it is very, very good; + and when it is bad, it is better than nothing. + Dick Brandon + + The term `awk' refers to a particular program as well as to the +language you use to tell this program what to do. When we need to be +careful, we call the program "the `awk' utility" and the language "the +`awk' language." This Info file explains both the `awk' language and +how to run the `awk' utility. The term "`awk' program" refers to a +program written by you in the `awk' programming language. + + Primarily, this Info file explains the features of `awk', as defined +in the POSIX standard. It does so in the context of the `gawk' +implementation. While doing so, it also attempts to describe important +differences between `gawk' and other `awk' implementations.(1) Finally, +any `gawk' features that are not in the POSIX standard for `awk' are +noted. + + There are subsections labelled as *Advanced Notes* scattered +throughout the Info file. They add a more complete explanation of +points that are relevant, but not likely to be of interest on first +reading. All appear in the index, under the heading "advanced notes." + + Most of the time, the examples use complete `awk' programs. In some +of the more advanced sections, only the part of the `awk' program that +illustrates the concept currently being described is shown. - * produce indexes, and perform other document preparation tasks + While this Info file is aimed principally at people who have not been +exposed to `awk', there is a lot of information here that even the `awk' +expert should find useful. In particular, the description of POSIX +`awk' and the example programs in *Note A Library of `awk' Functions: +Library Functions, and in *Note Practical `awk' Programs: Sample +Programs, should be of interest. - * even experiment with algorithms that can be adapted later to other - computer languages + *Note Getting Started with `awk': Getting Started, provides the +essentials you need to know to begin using `awk'. -* Menu: + *Note Regular Expressions: Regexp, introduces regular expressions in +general, and in particular the flavors supported by POSIX `awk' and +`gawk'. -* This Manual:: Using this Info file. Includes sample - input files that you can use. -* Conventions:: Typographical Conventions. -* Sample Data Files:: Sample data files for use in the `awk' - programs illustrated in this Info file. + *Note Reading Input Files: Reading Files, describes how `awk' reads +your data. It introduces the concepts of records and fields, as well +as the `getline' command. I/O redirection is first described here. - -File: gawk.info, Node: This Manual, Next: Conventions, Prev: What Is Awk, Up: What Is Awk + *Note Printing Output: Printing, describes how `awk' programs can +produce output with `print' and `printf'. -Using This Book -=============== + *Note Expressions::, describes expressions, which are the basic +building blocks for getting most things done in a program. - The term `awk' refers to a particular program, and to the language -you use to tell this program what to do. When we need to be careful, -we call the program "the `awk' utility" and the language "the `awk' -language." The term `gawk' refers to a version of `awk' developed as -part the GNU project. The purpose of this Info file is to explain both -the `awk' language and how to run the `awk' utility. + *Note Patterns Actions and Variables: Patterns and Actions, +describes how to write patterns for matching records, actions for doing +something when a record is matched, and the built-in variables `awk' +and `gawk' use. - The main purpose of the Info file is to explain the features of -`awk', as defined in the POSIX standard. It does so in the context of -one particular implementation, `gawk'. While doing so, it will also -attempt to describe important differences between `gawk' and other -`awk' implementations. Finally, any `gawk' features that are not in -the POSIX standard for `awk' will be noted. + *Note Arrays in `awk': Arrays, covers `awk''s one-and-only data +structure: associative arrays. Deleting array elements and whole +arrays is also described, as well as sorting arrays in `gawk'. - The term "`awk' program" refers to a program written by you in the -`awk' programming language. + *Note Functions::, describes the built-in functions `awk' and `gawk' +provide for you, as well as how to define your own functions. - *Note Getting Started with `awk': Getting Started, for the bare -essentials you need to know to start using `awk'. + *Note Internationalization with `gawk': Internationalization, +describes special features in `gawk' for translating program messages +into different languages at runtime. - Some useful "one-liners" are included to give you a feel for the -`awk' language (*note Useful One Line Programs: One-liners.). + *Note Advanced Features of `gawk': Advanced Features, describes a +number of `gawk'-specific advanced features. Of particular note are +the abilities to have two-way communications with another process, +perform TCP/IP networking, and profile your `awk' programs. - Many sample `awk' programs have been provided for you (*note A -Library of `awk' Functions: Library Functions.; also *note Practical -`awk' Programs: Sample Programs.). + *Note Running `awk' and `gawk': Invoking Gawk, describes how to run +`gawk', the meaning of its command-line options, and how it finds `awk' +program source files. - The entire `awk' language is summarized for quick reference in *Note -`gawk' Summary: Gawk Summary. Look there if you just need to refresh -your memory about a particular feature. + *Note A Library of `awk' Functions: Library Functions, and *Note +Practical `awk' Programs: Sample Programs, provide many sample `awk' +programs. Reading them allows you to see `awk' being used for solving +real problems. - If you find terms that you aren't familiar with, try looking them up -in the glossary (*note Glossary::). + *Note The Evolution of the `awk' Language: Language History, +describes how the `awk' language has evolved since it was first +released to present. It also describes how `gawk' has acquired +features over time. - Most of the time complete `awk' programs are used as examples, but in -some of the more advanced sections, only the part of the `awk' program -that illustrates the concept being described is shown. + *Note Installing `gawk': Installation, describes how to get `gawk', +how to compile it under Unix, and how to compile and use it on different +non-Unix systems. It also describes how to report bugs in `gawk' and +where to get three other freely available implementations of `awk'. - While this Info file is aimed principally at people who have not been -exposed to `awk', there is a lot of information here that even the `awk' -expert should find useful. In particular, the description of POSIX -`awk', and the example programs in *Note A Library of `awk' Functions: -Library Functions, and *Note Practical `awk' Programs: Sample Programs, -should be of interest. + *Note Implementation Notes: Notes, describes how to disable `gawk''s +extensions, as well as how to contribute new code to `gawk', how to +write extension libraries, and some possible future directions for +`gawk' development. -Dark Corners ------------- + *Note Basic Programming Concepts: Basic Concepts, provides some very +cursory background material for those who are completely unfamiliar +with computer programming. Also centralized there is a discussion of +some of the issues involved in using floating-point numbers. - Who opened that window shade?!? - Count Dracula + The *Note Glossary::, defines most, if not all, the significant +terms used throughout the book. If you find terms that you aren't +familiar with, try looking them up. + *Note GNU General Public License: Copying, and *Note GNU Free +Documentation License::, present the licenses that cover the `gawk' +source code, and this Info file, respectively. + ---------- Footnotes ---------- - Until the POSIX standard (and `The Gawk Manual'), many features of -`awk' were either poorly documented, or not documented at all. -Descriptions of such features (often called "dark corners") are noted -in this Info file with "(d.c.)". They also appear in the index under -the heading "dark corner." + (1) All such differences appear in the index under the heading +"differences between `gawk' and `awk'."  -File: gawk.info, Node: Conventions, Next: Sample Data Files, Prev: This Manual, Up: What Is Awk +File: gawk.info, Node: Conventions, Next: Manual History, Prev: This Manual, Up: Preface Typographical Conventions ========================= This Info file is written using Texinfo, the GNU documentation formatting language. A single Texinfo source file is used to produce -both the printed and on-line versions of the documentation. This -section briefly documents the typographical conventions used in Texinfo. +both the printed and online versions of the documentation. This minor +node briefly documents the typographical conventions used in Texinfo. - Examples you would type at the command line are preceded by the + Examples you would type at the command-line are preceded by the common shell primary and secondary prompts, `$' and `>'. Output from the command is preceded by the glyph "-|". This typically represents the command's standard output. Error messages, and other output on the @@ -699,84 +829,204 @@ example: Characters that you type at the keyboard look `like this'. In particular, there are special characters called "control characters." These are characters that you type by holding down both the `CONTROL' -key and another key, at the same time. For example, a `Control-d' is -typed by first pressing and holding the `CONTROL' key, next pressing -the `d' key, and finally releasing both keys. +key and another key, at the same time. For example, a `Ctrl-d' is typed +by first pressing and holding the `CONTROL' key, next pressing the `d' +key and finally releasing both keys. + +Dark Corners +............ + + Dark corners are basically fractal -- no matter how much you + illuminate, there's always a smaller but darker one. + Brian Kernighan + + Until the POSIX standard (and `The Gawk Manual'), many features of +`awk' were either poorly documented or not documented at all. +Descriptions of such features (often called "dark corners") are noted +in this Info file with "(d.c.)". They also appear in the index under +the heading "dark corner." + + As noted by the opening quote, though, any coverage of dark corners +is, by definition, something that is incomplete.  -File: gawk.info, Node: Sample Data Files, Prev: Conventions, Up: What Is Awk +File: gawk.info, Node: Manual History, Next: How To Contribute, Prev: Conventions, Up: Preface -Data Files for the Examples -=========================== +The GNU Project and This Book +============================= - Many of the examples in this Info file take their input from two -sample data files. The first, called `BBS-list', represents a list of -computer bulletin board systems together with information about those -systems. The second data file, called `inventory-shipped', contains -information about shipments on a monthly basis. In both files, each -line is considered to be one "record". + Software is like sex: it's better when it's free. + Linus Torvalds - In the file `BBS-list', each record contains the name of a computer -bulletin board, its phone number, the board's baud rate(s), and a code -for the number of hours it is operational. An `A' in the last column -means the board operates 24 hours a day. A `B' in the last column -means the board operates evening and weekend hours, only. A `C' means -the board operates only on weekends. + The Free Software Foundation (FSF) is a non-profit organization +dedicated to the production and distribution of freely distributable +software. It was founded by Richard M. Stallman, the author of the +original Emacs editor. GNU Emacs is the most widely used version of +Emacs today. - aardvark 555-5553 1200/300 B - alpo-net 555-3412 2400/1200/300 A - barfly 555-7685 1200/300 A - bites 555-1675 2400/1200/300 A - camelot 555-0542 300 C - core 555-2912 1200/300 C - fooey 555-1234 2400/1200/300 B - foot 555-6699 1200/300 B - macfoo 555-6480 1200/300 A - sdace 555-3430 2400/1200/300 A - sabafoo 555-2127 1200/300 C + The GNU(1) Project is an ongoing effort on the part of the Free +Software Foundation to create a complete, freely distributable, +POSIX-compliant computing environment. The FSF uses the "GNU General +Public License" (GPL) to ensure that their software's source code is +always available to the end user. A copy of the GPL is included for +your reference (*note GNU General Public License: Copying.). The GPL +applies to the C language source code for `gawk'. To find out more +about the FSF and the GNU Project online, see the GNU Project's home +page (http://www.gnu.org). This Info file may also be read from their +web site (http://www.gnu.org/manual/gawk/). - The second data file, called `inventory-shipped', represents -information about shipments during the year. Each record contains the -month of the year, the number of green crates shipped, the number of -red boxes shipped, the number of orange bags shipped, and the number of -blue packages shipped, respectively. There are 16 entries, covering -the 12 months of one year and four months of the next year. + A shell, an editor (Emacs), highly portable optimizing C, C++, and +Objective-C compilers, a symbolic debugger and dozens of large and +small utilities (such as `gawk'), have all been completed and are +freely available. The GNU operating system kernel (the HURD), has been +released but is still in an early stage of development. - Jan 13 25 15 115 - Feb 15 32 24 226 - Mar 15 24 34 228 - Apr 31 52 63 420 - May 16 34 29 208 - Jun 31 42 75 492 - Jul 24 34 67 436 - Aug 15 34 47 316 - Sep 13 55 37 277 - Oct 29 54 68 525 - Nov 20 87 82 577 - Dec 17 35 61 401 - - Jan 21 36 64 620 - Feb 26 58 80 652 - Mar 24 75 70 495 - Apr 21 70 74 514 + Until the GNU operating system is more fully developed, you should +consider using GNU/Linux, a freely distributable, Unix-like operating +system for Intel 80386, DEC Alpha, Sun SPARC, IBM S/390, and other +systems.(2) There are many books on GNU/Linux. One that is freely +available is `Linux Installation and Getting Started', by Matt Welsh. +Many GNU/Linux distributions are often available in computer stores or +bundled on CD-ROMs with books about Linux. (There are three other +freely available, Unix-like operating systems for 80386 and other +systems: NetBSD, FreeBSD, and OpenBSD. All are based on the 4.4-Lite +Berkeley Software Distribution, and they use recent versions of `gawk' +for their versions of `awk'.) + + The Info file itself has gone through a number of previous editions. +Paul Rubin wrote the very first draft of `The GAWK Manual'; it was +around 40 pages in size. Diane Close and Richard Stallman improved it, +yielding a version that was around 90 pages long and barely described +the original, "old" version of `awk'. + + I started working with that version in the fall of 1988. As work on +it progressed, the FSF published several preliminary versions (numbered +0.X). In 1996, Edition 1.0 was released with `gawk' 3.0.0. The FSF +published the first two editions under the title `The GNU Awk User's +Guide'. + + This edition maintains the basic structure of Edition 1.0, but with +significant additional material, reflecting the host of new features in +`gawk' version 3.1. Of particular note is *Note Sorting Array Values +and Indices with `gawk': Array Sorting, as well as *Note Using `gawk''s +Bit Manipulation Functions: Bitwise Functions, *Note +Internationalization with `gawk': Internationalization, and also *Note +Advanced Features of `gawk': Advanced Features, and *Note Adding New +Built-in Functions to `gawk': Dynamic Extensions. + + `GAWK: Effective AWK Programming' will undoubtedly continue to +evolve. An electronic version comes with the `gawk' distribution from +the FSF. If you find an error in this Info file, please report it! +*Note Reporting Problems and Bugs: Bugs, for information on submitting +problem reports electronically, or write to me in care of the publisher. - If you are reading this in GNU Emacs using Info, you can copy the -regions of text showing these sample files into your own test files. -This way you can try out the examples shown in the remainder of this -document. You do this by using the command `M-x write-region' to copy -text from the Info file into a file for use with `awk' (*Note -Miscellaneous File Operations: (emacs)Misc File Ops, for more -information). Using this information, create your own `BBS-list' and -`inventory-shipped' files, and practice what you learn in this Info -file. + ---------- Footnotes ---------- - If you are using the stand-alone version of Info, see *Note -Extracting Programs from Texinfo Source Files: Extract Program, for an -`awk' program that will extract these data files from `gawk.texi', the -Texinfo source file for this Info file. + (1) GNU stands for "GNU's not Unix." + + (2) The terminology "GNU/Linux" is explained in the *Note Glossary::. + + +File: gawk.info, Node: How To Contribute, Next: Acknowledgments, Prev: Manual History, Up: Preface + +How to Contribute +================= + + As the maintainer of GNU `awk', I am starting a collection of +publicly available `awk' programs. For more information, see +`ftp://ftp.freefriends.org/arnold/Awkstuff'. If you have written an +interesting `awk' program, or have written a `gawk' extension that you +would like to share with the rest of the world, please contact me +(). Making things available on the Internet helps keep +the `gawk' distribution down to manageable size. + + +File: gawk.info, Node: Acknowledgments, Prev: How To Contribute, Up: Preface + +Acknowledgments +=============== + + The initial draft of `The GAWK Manual' had the following +acknowledgments: + + Many people need to be thanked for their assistance in producing + this manual. Jay Fenlason contributed many ideas and sample + programs. Richard Mlynarik and Robert Chassell gave helpful + comments on drafts of this manual. The paper `A Supplemental + Document for `awk'' by John W. Pierce of the Chemistry Department + at UC San Diego, pinpointed several issues relevant both to `awk' + implementation and to this manual, that would otherwise have + escaped us. + + I would like to acknowledge Richard M. Stallman, for his vision of a +better world and for his courage in founding the FSF and starting the +GNU project. + + The following people (in alphabetical order) provided helpful +comments on various versions of this book, up to and including this +edition. Rick Adams, Nelson H.F. Beebe, Karl Berry, Dr. Michael +Brennan, Rich Burridge, Claire Coutier, Diane Close, Scott Deifik, +Christopher ("Topher") Eliot, Jeffrey Friedl, Dr. Darrel Hankerson, +Michal Jaegermann, Dr. Richard J. LeBlanc, Michael Lijewski, Pat Rankin, +Miriam Robbins, Mary Sheehan, and Chuck Toporek. + + Robert J. Chassell provided much valuable advice on the use of +Texinfo. He also deserves special thanks for convincing me _not_ to +title this Info file `How To Gawk Politely'. Karl Berry helped +significantly with the TeX part of Texinfo. + + I would like to thank Marshall and Elaine Hartholz of Seattle and +Dr. Bert and Rita Schreiber of Detroit for large amounts of quiet +vacation time in their homes, which allowed me to make significant +progress on this Info file and on `gawk' itself. + + Phil Hughes of SSC contributed in a very important way by loaning me +his laptop GNU/Linux system, not once, but twice, which allowed me to +do a lot of work while away from home. + + David Trueman deserves special credit; he has done a yeoman job of +evolving `gawk' so that it performs well and without bugs. Although he +is no longer involved with `gawk', working with him on this project was +a significant pleasure. + + The intrepid members of the GNITS mailing list, and most notably +Ulrich Drepper, provided invaluable help and feedback for the design of +the internationalization features. + + Nelson Beebe, Martin Brown, Scott Deifik, Darrel Hankerson, Michal +Jaegermann, Ju"rgen Kahrs, Pat Rankin, Kai Uwe Rommel, and Eli Zaretskii +(in alphabetical order) are long-time members of the `gawk' "crack +portability team." Without their hard work and help, `gawk' would not +be nearly the fine program it is today. It has been and continues to +be a pleasure working with this team of fine people. + + David and I would like to thank Brian Kernighan of Bell Laboratories +for invaluable assistance during the testing and debugging of `gawk', +and for help in clarifying numerous points about the language. We +could not have done nearly as good a job on either `gawk' or its +documentation without his help. + + Chuck Toporek, Mary Sheehan, and Claire Coutier of O'Reilly & +Associates contributed significant editorial help for this Info file +for the 3.1 release of `gawk'. + + I must thank my wonderful wife, Miriam, for her patience through the +many versions of this project, for her proof-reading, and for sharing +me with the computer. I would like to thank my parents for their love, +and for the grace with which they raised and educated me. Finally, I +also must acknowledge my gratitude to G-d, for the many opportunities +He has sent my way, as well as for the gifts He has given me with which +to take advantage of those opportunities. + + + +Arnold Robbins +Nof Ayalon +ISRAEL +March, 2001  -File: gawk.info, Node: Getting Started, Next: One-liners, Prev: What Is Awk, Up: Top +File: gawk.info, Node: Getting Started, Next: Regexp, Prev: Preface, Up: Top Getting Started with `awk' ************************** @@ -784,29 +1034,29 @@ Getting Started with `awk' The basic function of `awk' is to search files for lines (or other units of text) that contain certain patterns. When a line matches one of the patterns, `awk' performs specified actions on that line. `awk' -keeps processing input lines in this way until the end of the input -files are reached. +keeps processing input lines in this way until it reaches the end of +the input files. Programs in `awk' are different from programs in most other languages, because `awk' programs are "data-driven"; that is, you -describe the data you wish to work with, and then what to do when you +describe the data you want to work with and then what to do when you find it. Most other languages are "procedural"; you have to describe, in great detail, every step the program is to take. When working with procedural languages, it is usually much harder to clearly describe the data your program will process. For this reason, `awk' programs are -often refreshingly easy to both write and read. +often refreshingly easy to write and read. When you run `awk', you specify an `awk' "program" that tells `awk' what to do. The program consists of a series of "rules". (It may also -contain "function definitions", an advanced feature which we will -ignore for now. *Note User-defined Functions: User-defined.) Each -rule specifies one pattern to search for, and one action to perform -when that pattern is found. +contain "function definitions", an advanced feature that we will ignore +for now. *Note User-Defined Functions: User-defined.) Each rule +specifies one pattern to search for and one action to perform upon +finding the pattern. Syntactically, a rule consists of a pattern followed by an action. The action is enclosed in curly braces to separate it from the pattern. -Rules are usually separated by newlines. Therefore, an `awk' program -looks like this: +Newlines usually separate rules. Therefore, an `awk' program looks +like this: PATTERN { ACTION } PATTERN { ACTION } @@ -814,54 +1064,22 @@ looks like this: * Menu: -* Names:: What name to use to find `awk'. * Running gawk:: How to run `gawk' programs; includes - command line syntax. + command-line syntax. +* Sample Data Files:: Sample data files for use in the `awk' + programs illustrated in this Info file. * Very Simple:: A very simple example. -* Two Rules:: A less simple one-line example with two rules. +* Two Rules:: A less simple one-line example using two + rules. * More Complex:: A more complex example. * Statements/Lines:: Subdividing or combining statements into lines. * Other Features:: Other Features of `awk'. -* When:: When to use `gawk' and when to use other - things. - - -File: gawk.info, Node: Names, Next: Running gawk, Prev: Getting Started, Up: Getting Started - -A Rose By Any Other Name -======================== - - The `awk' language has evolved over the years. Full details are -provided in *Note The Evolution of the `awk' Language: Language History. -The language described in this Info file is often referred to as "new -`awk'." - - Because of this, many systems have multiple versions of `awk'. Some -systems have an `awk' utility that implements the original version of -the `awk' language, and a `nawk' utility for the new version. Others -have an `oawk' for the "old `awk'" language, and plain `awk' for the -new one. Still others only have one version, usually the new one.(1) - - All in all, this makes it difficult for you to know which version of -`awk' you should run when writing your programs. The best advice we -can give here is to check your local documentation. Look for `awk', -`oawk', and `nawk', as well as for `gawk'. Chances are, you will have -some version of new `awk' on your system, and that is what you should -use when running your programs. (Of course, if you're reading this -Info file, chances are good that you have `gawk'!) - - Throughout this Info file, whenever we refer to a language feature -that should be available in any complete implementation of POSIX `awk', -we simply use the term `awk'. When referring to a feature that is -specific to the GNU implementation, we use the term `gawk'. - - ---------- Footnotes ---------- - - (1) Often, these systems use `gawk' for their `awk' implementation! +* When:: When to use `gawk' and when to use + other things.  -File: gawk.info, Node: Running gawk, Next: Very Simple, Prev: Names, Up: Getting Started +File: gawk.info, Node: Running gawk, Next: Sample Data Files, Prev: Getting Started, Up: Getting Started How to Run `awk' Programs ========================= @@ -872,29 +1090,31 @@ this: awk 'PROGRAM' INPUT-FILE1 INPUT-FILE2 ... -where PROGRAM consists of a series of patterns and actions, as -described earlier. (The reason for the single quotes is described -below, in *Note One-shot Throw-away `awk' Programs: One-shot.) - When the program is long, it is usually more convenient to put it in a file and run it with a command like this: awk -f PROGRAM-FILE INPUT-FILE1 INPUT-FILE2 ... + This minor node discusses both mechanisms, along with several +variations of each. + * Menu: -* One-shot:: Running a short throw-away `awk' program. +* One-shot:: Running a short throw-away `awk' + program. * Read Terminal:: Using no input files (input from terminal instead). * Long:: Putting permanent `awk' programs in files. * Executable Scripts:: Making self-contained `awk' programs. -* Comments:: Adding documentation to `gawk' programs. +* Comments:: Adding documentation to `gawk' + programs. +* Quoting:: More discussion of shell quoting issues.  File: gawk.info, Node: One-shot, Next: Read Terminal, Prev: Running gawk, Up: Running gawk -One-shot Throw-away `awk' Programs +One-Shot Throw-Away `awk' Programs ---------------------------------- Once you are familiar with `awk', you will often type in simple @@ -908,55 +1128,48 @@ described earlier. This command format instructs the "shell", or command interpreter, to start `awk' and use the PROGRAM to process records in the input -file(s). There are single quotes around PROGRAM so that the shell -doesn't interpret any `awk' characters as special shell characters. -They also cause the shell to treat all of PROGRAM as a single argument -for `awk' and allow PROGRAM to be more than one line long. +file(s). There are single quotes around PROGRAM so the shell won't +interpret any `awk' characters as special shell characters. The quotes +also cause the shell to treat all of PROGRAM as a single argument for +`awk', and allow PROGRAM to be more than one line long. This format is also useful for running short or medium-sized `awk' programs from shell scripts, because it avoids the need for a separate file for the `awk' program. A self-contained shell script is more -reliable since there are no other files to misplace. +reliable because there are no other files to misplace. - *Note Useful One Line Programs: One-liners, presents several short, + *Note Some Simple Examples: Very Simple, presents several short, self-contained programs. - As an interesting side point, the command - - awk '/foo/' FILES ... - -is essentially the same as - - egrep foo FILES ... -  File: gawk.info, Node: Read Terminal, Next: Long, Prev: One-shot, Up: Running gawk -Running `awk' without Input Files +Running `awk' Without Input Files --------------------------------- You can also run `awk' without any input files. If you type the -command line: +following command line: awk 'PROGRAM' -then `awk' applies the PROGRAM to the "standard input", which usually -means whatever you type on the terminal. This continues until you -indicate end-of-file by typing `Control-d'. (On other operating -systems, the end-of-file character may be different. For example, on -OS/2 and MS-DOS, it is `Control-z'.) +`awk' applies the PROGRAM to the "standard input", which usually means +whatever you type on the terminal. This continues until you indicate +end-of-file by typing `Ctrl-d'. (On other operating systems, the +end-of-file character may be different. For example, on OS/2 and +MS-DOS, it is `Ctrl-z'.) - For example, the following program prints a friendly piece of advice -(from Douglas Adams' `The Hitchhiker's Guide to the Galaxy'), to keep -you from worrying about the complexities of computer programming -(`BEGIN' is a feature we haven't discussed yet). + As an example, the following program prints a friendly piece of +advice (from Douglas Adams's `The Hitchhiker's Guide to the Galaxy'), +to keep you from worrying about the complexities of computer +programming. (`BEGIN' is a feature we haven't discussed yet.): $ awk "BEGIN { print \"Don't Panic!\" }" -| Don't Panic! This program does not read any input. The `\' before each of the -inner double quotes is necessary because of the shell's quoting rules, -in particular because it mixes both single quotes and double quotes. +inner double quotes is necessary because of the shell's quoting +rules--in particular because it mixes both single quotes and double +quotes.(1) This next simple `awk' program emulates the `cat' utility; it copies whatever you type at the keyboard to its standard output. (Why this @@ -971,7 +1184,13 @@ works is explained shortly.) -| Four score and seven years ago, ... What, me worry? -| What, me worry? - Control-d + Ctrl-d + + ---------- Footnotes ---------- + + (1) Although we generally recommend the use of single quotes around +the program text, double quotes are needed here in order to put the +single quote into the message.  File: gawk.info, Node: Long, Next: Executable Scripts, Prev: Read Terminal, Up: Running gawk @@ -979,9 +1198,9 @@ File: gawk.info, Node: Long, Next: Executable Scripts, Prev: Read Terminal, Running Long Programs --------------------- - Sometimes your `awk' programs can be very long. In this case it is -more convenient to put the program into a separate file. To tell `awk' -to use that file for its program, you type: + Sometimes your `awk' programs can be very long. In this case, it is +more convenient to put the program into a separate file. In order to +tell `awk' to use that file for its program, you type: awk -f SOURCE-FILE INPUT-FILE1 INPUT-FILE2 ... @@ -999,7 +1218,7 @@ does the same thing as this one: awk "BEGIN { print \"Don't Panic!\" }" -which was explained earlier (*note Running `awk' without Input Files: +This was explained earlier (*note Running `awk' Without Input Files: Read Terminal.). Note that you don't usually need single quotes around the file name that you specify with `-f', because most file names don't contain any of the shell's special characters. Notice that in @@ -1009,7 +1228,7 @@ command line. If you want to identify your `awk' program files clearly as such, you can add the extension `.awk' to the file name. This doesn't affect -the execution of the `awk' program, but it does make "housekeeping" +the execution of the `awk' program but it does make "housekeeping" easier.  @@ -1020,76 +1239,71 @@ Executable `awk' Programs Once you have learned `awk', you may want to write self-contained `awk' scripts, using the `#!' script mechanism. You can do this on -many Unix systems(1) (and someday on the GNU system). - - For example, you could update the file `advice' to look like this: +many Unix systems(1) as well as on the GNU system. For example, you +could update the file `advice' to look like this: #! /bin/awk -f - BEGIN { print "Don't Panic!" } + BEGIN { print "Don't Panic!" } -After making this file executable (with the `chmod' utility), you can -simply type `advice' at the shell, and the system will arrange to run -`awk'(2) as if you had typed `awk -f advice'. +After making this file executable (with the `chmod' utility), simply +type `advice' at the shell and the system arranges to run `awk'(2) as +if you had typed `awk -f advice': + $ chmod +x advice $ advice -| Don't Panic! Self-contained `awk' scripts are useful when you want to write a -program which users can invoke without their having to know that the +program that users can invoke without their having to know that the program is written in `awk'. - *Caution:* You should not put more than one argument on the `#!' -line after the path to `awk'. This will not work. The operating system -treats the rest of the line as a single agument, and passes it to `awk'. -Doing this will lead to confusing behavior: most likely a usage -diagnostic of some sort from `awk'. - - Some older systems do not support the `#!' mechanism. You can get a -similar effect using a regular shell script. It would look something -like this: +Advanced Notes: Portability Issues with `#!' +-------------------------------------------- - : The colon ensures execution by the standard shell. - awk 'PROGRAM' "$@" + Some systems limit the length of the interpreter name to 32 +characters. Often, this can be dealt with by using a symbolic link. - Using this technique, it is _vital_ to enclose the PROGRAM in single -quotes to protect it from interpretation by the shell. If you omit the -quotes, only a shell wizard can predict the results. + You should not put more than one argument on the `#!' line after the +path to `awk'. It does not work. The operating system treats the rest +of the line as a single argument and passes it to `awk'. Doing this +leads to confusing behavior--most likely a usage diagnostic of some +sort from `awk'. - The `"$@"' causes the shell to forward all the command line -arguments to the `awk' program, without interpretation. The first -line, which starts with a colon, is used so that this shell script will -work even if invoked by a user who uses the C shell. (Not all older -systems obey this convention, but many do.) + Finally, the value of `ARGV[0]' (*note Built-in Variables::) varies +depending upon your operating system. Some systems put `awk' there, +some put the full pathname of `awk' (such as `/bin/awk'), and some put +the name of your script (`advice'). Don't rely on the value of +`ARGV[0]' to provide your script name. ---------- Footnotes ---------- - (1) The `#!' mechanism works on Linux systems, Unix systems derived -from Berkeley Unix, System V Release 4, and some System V Release 3 + (1) The `#!' mechanism works on Linux systems, systems derived from +the 4.4-Lite Berkeley Software Distribution, and most commercial Unix systems. (2) The line beginning with `#!' lists the full file name of an -interpreter to be run, and an optional initial command line argument to +interpreter to run and an optional initial command-line argument to pass to that interpreter. The operating system then runs the interpreter with the given argument and the full argument list of the executed program. The first argument in the list is the full file name -of the `awk' program. The rest of the argument list will either be -options to `awk', or data files, or both. +of the `awk' program. The rest of the argument list is either options +to `awk', or data files, or both.  -File: gawk.info, Node: Comments, Prev: Executable Scripts, Up: Running gawk +File: gawk.info, Node: Comments, Next: Quoting, Prev: Executable Scripts, Up: Running gawk Comments in `awk' Programs -------------------------- A "comment" is some text that is included in a program for the sake -of human readers; it is not really part of the program. Comments can -explain what the program does, and how it works. Nearly all -programming languages have provisions for comments, because programs are -typically hard to understand without their extra help. +of human readers; it is not really an executable part of the program. +Comments can explain what the program does and how it works. Nearly all +programming languages have provisions for comments, as programs are +typically hard to understand without them. In the `awk' language, a comment starts with the sharp sign -character, `#', and continues to the end of the line. The `#' does not +character (`#') and continues to the end of the line. The `#' does not have to be the first character on the line. The `awk' language ignores the rest of a line following a sharp sign. For example, we could have put the following into `advice': @@ -1099,107 +1313,361 @@ put the following into `advice': BEGIN { print "Don't Panic!" } You can put comment lines into keyboard-composed throw-away `awk' -programs also, but this usually isn't very useful; the purpose of a -comment is to help you or another person understand the program at a -later time. +programs, but this usually isn't very useful; the purpose of a comment +is to help you or another person understand the program when reading it +at a later time. - *Caution:* As mentioned in *Note One-shot Throw-away `awk' Programs: + *Caution:* As mentioned in *Note One-Shot Throw-Away `awk' Programs: One-shot, you can enclose small to medium programs in single quotes, in order to keep your shell scripts self-contained. When doing so, _don't_ put an apostrophe (i.e., a single quote) into a comment (or -anywhere else in your program). The shell will interpret the quote as -the closing quote for the entire program. As a result, usually the -shell will print a message about mismatched quotes, and if `awk' -actually runs, it will probably print strange messages about syntax -errors. For example: +anywhere else in your program). The shell interprets the quote as the +closing quote for the entire program. As a result, usually the shell +prints a message about mismatched quotes, and if `awk' actually runs, +it will probably print strange messages about syntax errors. For +example, look at the following: + + $ awk '{ print "hello" } # let's be cute' + > - awk 'BEGIN { print "hello" } # let's be cute' + The shell sees that the first two quotes match, and that a new +quoted object begins at the end of the command-line. It therefore +prompts with the secondary prompt, waiting for more input. With Unix +`awk', closing the quoted string produces this result: + + $ awk '{ print "hello" } # let's be cute' + > ' + error--> awk: can't open file be + error--> source line number 1 + + Putting a backslash before the single quote in `let's' wouldn't help, +since backslashes are not special inside single quotes. The next +node describes the shell's quoting rules.  -File: gawk.info, Node: Very Simple, Next: Two Rules, Prev: Running gawk, Up: Getting Started +File: gawk.info, Node: Quoting, Prev: Comments, Up: Running gawk -A Very Simple Example -===================== +Shell Quoting Issues +-------------------- - The following command runs a simple `awk' program that searches the -input file `BBS-list' for the string of characters: `foo'. (A string -of characters is usually called a "string". The term "string" is -perhaps based on similar usage in English, such as "a string of -pearls," or, "a string of cars in a train.") + For short to medium length `awk' programs, it is most convenient to +enter the program on the `awk' command line. This is best done by +enclosing the entire program in single quotes. This is true whether +you are entering the program interactively at the shell prompt, or +writing it as part of a larger shell script: - awk '/foo/ { print $0 }' BBS-list + awk 'PROGRAM TEXT' INPUT-FILE1 INPUT-FILE2 ... -When lines containing `foo' are found, they are printed, because -`print $0' means print the current line. (Just `print' by itself means -the same thing, so we could have written that instead.) + Once you are working with the shell, it is helpful to have a basic +knowledge of shell quoting rules. The following rules apply only to +POSIX-compliant, Bourne-style shells (such as `bash', the GNU +Bourne-Again Shell). If you use `csh', you're on your own. - You will notice that slashes, `/', surround the string `foo' in the -`awk' program. The slashes indicate that `foo' is a pattern to search -for. This type of pattern is called a "regular expression", and is -covered in more detail later (*note Regular Expressions: Regexp.). The -pattern is allowed to match parts of words. There are single-quotes -around the `awk' program so that the shell won't interpret any of it as -special shell characters. + * Quoted items can be concatenated with nonquoted items as well as + with other quoted items. The shell turns everything into one + argument for the command. - Here is what this program prints: + * Preceding any single character with a backslash (`\') quotes that + character. The shell removes the backslash and passes the quoted + character on to the command. - $ awk '/foo/ { print $0 }' BBS-list - -| fooey 555-1234 2400/1200/300 B - -| foot 555-6699 1200/300 B - -| macfoo 555-6480 1200/300 A - -| sabafoo 555-2127 1200/300 C + * Single quotes protect everything between the opening and closing + quotes. The shell does no interpretation of the quoted text, + passing it on verbatim to the command. It is _impossible_ to + embed a single quote inside single-quoted text. Refer back to + *Note Comments in `awk' Programs: Comments, for an example showing + what happens if you try. - In an `awk' rule, either the pattern or the action can be omitted, -but not both. If the pattern is omitted, then the action is performed -for _every_ input line. If the action is omitted, the default action -is to print all lines that match the pattern. + * Double quotes protect most things between the opening and closing + quotes. The shell does at least variable and command substitution + on the quoted text. Different shells may do additional kinds of + processing on double-quoted text. - Thus, we could leave out the action (the `print' statement and the -curly braces) in the above example, and the result would be the same: -all lines matching the pattern `foo' would be printed. By comparison, -omitting the `print' statement but retaining the curly braces makes an -empty action that does nothing; then no lines would be printed. + Since certain characters within double-quoted text are processed + by the shell, they must be "escaped" within the text. Of note are + the characters `$', ``', `\' and `"', all of which must be + preceded by a backslash within double-quoted text if they are to + be passed on literally to the program. (The leading backslash is + stripped first.) Thus, the example seen in *Note Running `awk' + Without Input Files: Read Terminal, is applicable: - -File: gawk.info, Node: Two Rules, Next: More Complex, Prev: Very Simple, Up: Getting Started + $ awk "BEGIN { print \"Don't Panic!\" }" + -| Don't Panic! -An Example with Two Rules -========================= + Note that the single quote is not special within double quotes. - The `awk' utility reads the input files one line at a time. For -each line, `awk' tries the patterns of each of the rules. If several -patterns match then several actions are run, in the order in which they -appear in the `awk' program. If no patterns match, then no actions are -run. + * Null strings are removed when they occur as part of a non-null + command-line argument, while explicit non-null objects are kept. + For example, to specify that the field separator `FS' should be + set to the null string, use: - After processing all the rules (perhaps none) that match the line, -`awk' reads the next line (however, *note The `next' Statement: Next -Statement., and also *note The `nextfile' Statement: Nextfile -Statement.). This continues until the end of the file is reached. + awk -F "" 'PROGRAM' FILES # correct - For example, the `awk' program: + Don't use this: - /12/ { print $0 } - /21/ { print $0 } + awk -F"" 'PROGRAM' FILES # wrong! -contains two rules. The first rule has the string `12' as the pattern -and `print $0' as the action. The second rule has the string `21' as -the pattern and also has `print $0' as the action. Each rule's action -is enclosed in its own pair of braces. + In the second case, `awk' will attempt to use the text of the + program as the value of `FS', and the first file name as the text + of the program! This results in syntax errors at best, and + confusing behavior at worst. - This `awk' program prints every line that contains the string `12' -_or_ the string `21'. If a line contains both strings, it is printed -twice, once by each rule. + Mixing single and double quotes is difficult. You have to resort to +shell quoting tricks, like this: - This is what happens if we run this program on our two sample data -files, `BBS-list' and `inventory-shipped', as shown here: + $ awk 'BEGIN { print "Here is a single quote <'"'"'>" }' + -| Here is a single quote <'> - $ awk '/12/ { print $0 } - > /21/ { print $0 }' BBS-list inventory-shipped - -| aardvark 555-5553 1200/300 B - -| alpo-net 555-3412 2400/1200/300 A - -| barfly 555-7685 1200/300 A - -| bites 555-1675 2400/1200/300 A +This program consists of three concatenated quoted strings. The first +and the third are single-quoted, the second is double-quoted. + + This can be "simplified" to: + + $ awk 'BEGIN { print "Here is a single quote <'\''>" }' + -| Here is a single quote <'> + +Judge for yourself which of these two is the more readable. + + Another option is to use double quotes, escaping the embedded, +`awk'-level double quotes: + + $ awk "BEGIN { print \"Here is a single quote <'>\" }" + -| Here is a single quote <'> + +This option is also painful, because double quotes, backslashes, and +dollar signs are very common in `awk' programs. + + If you really need both single and double quotes in your `awk' +program, it is probably best to move it into a separate file, where the +shell won't be part of the picture, and you can say what you mean. + + +File: gawk.info, Node: Sample Data Files, Next: Very Simple, Prev: Running gawk, Up: Getting Started + +Data Files for the Examples +=========================== + + Many of the examples in this Info file take their input from two +sample data files. The first, called `BBS-list', represents a list of +computer bulletin board systems together with information about those +systems. The second data file, called `inventory-shipped', contains +information about monthly shipments. In both files, each line is +considered to be one "record". + + In the file `BBS-list', each record contains the name of a computer +bulletin board, its phone number, the board's baud rate(s), and a code +for the number of hours it is operational. An `A' in the last column +means the board operates 24 hours a day. A `B' in the last column +means the board only operates on evening and weekend hours. A `C' +means the board operates only on weekends: + + aardvark 555-5553 1200/300 B + alpo-net 555-3412 2400/1200/300 A + barfly 555-7685 1200/300 A + bites 555-1675 2400/1200/300 A + camelot 555-0542 300 C + core 555-2912 1200/300 C + fooey 555-1234 2400/1200/300 B + foot 555-6699 1200/300 B + macfoo 555-6480 1200/300 A + sdace 555-3430 2400/1200/300 A + sabafoo 555-2127 1200/300 C + + The second data file, called `inventory-shipped', represents +information about shipments during the year. Each record contains the +month, the number of green crates shipped, the number of red boxes +shipped, the number of orange bags shipped, and the number of blue +packages shipped, respectively. There are 16 entries, covering the 12 +months of last year and the first four months of the current year. + + Jan 13 25 15 115 + Feb 15 32 24 226 + Mar 15 24 34 228 + Apr 31 52 63 420 + May 16 34 29 208 + Jun 31 42 75 492 + Jul 24 34 67 436 + Aug 15 34 47 316 + Sep 13 55 37 277 + Oct 29 54 68 525 + Nov 20 87 82 577 + Dec 17 35 61 401 + + Jan 21 36 64 620 + Feb 26 58 80 652 + Mar 24 75 70 495 + Apr 21 70 74 514 + + If you are reading this in GNU Emacs using Info, you can copy the +regions of text showing these sample files into your own test files. +This way you can try out the examples shown in the remainder of this +document. You do this by using the command `M-x write-region' to copy +text from the Info file into a file for use with `awk' (*Note +Miscellaneous File Operations: (emacs)Misc File Ops, for more +information). Using this information, create your own `BBS-list' and +`inventory-shipped' files and practice what you learn in this Info file. + + If you are using the stand-alone version of Info, see *Note +Extracting Programs from Texinfo Source Files: Extract Program, for an +`awk' program that extracts these data files from `gawk.texi', the +Texinfo source file for this Info file. + + +File: gawk.info, Node: Very Simple, Next: Two Rules, Prev: Sample Data Files, Up: Getting Started + +Some Simple Examples +==================== + + The following command runs a simple `awk' program that searches the +input file `BBS-list' for the character string `foo'. (A string of +characters is usually called a "string". The term "string" is based on +similar usage in English, such as "a string of pearls," or, "a string +of cars in a train."): + + awk '/foo/ { print $0 }' BBS-list + +When lines containing `foo' are found, they are printed because +`print $0' means print the current line. (Just `print' by itself means +the same thing, so we could have written that instead.) + + You will notice that slashes (`/') surround the string `foo' in the +`awk' program. The slashes indicate that `foo' is the pattern to +search for. This type of pattern is called a "regular expression", +which is covered in more detail later (*note Regular Expressions: +Regexp.). The pattern is allowed to match parts of words. There are +single quotes around the `awk' program so that the shell won't +interpret any of it as special shell characters. + + Here is what this program prints: + + $ awk '/foo/ { print $0 }' BBS-list + -| fooey 555-1234 2400/1200/300 B + -| foot 555-6699 1200/300 B + -| macfoo 555-6480 1200/300 A + -| sabafoo 555-2127 1200/300 C + + In an `awk' rule, either the pattern or the action can be omitted, +but not both. If the pattern is omitted, then the action is performed +for _every_ input line. If the action is omitted, the default action +is to print all lines that match the pattern. + + Thus, we could leave out the action (the `print' statement and the +curly braces) in the above example and the result would be the same: all +lines matching the pattern `foo' are printed. By comparison, omitting +the `print' statement but retaining the curly braces makes an empty +action that does nothing (i.e., no lines are printed). + + Many practical `awk' programs are just a line or two. Following is a +collection of useful, short programs to get you started. Some of these +programs contain constructs that haven't been covered yet. (The +description of the program will give you a good idea of what is going +on, but please read the rest of the Info file to become an `awk' +expert!) Most of the examples use a data file named `data'. This is +just a placeholder; if you use these programs yourself, substitute your +own file names for `data'. For future reference, note that there is +often more than one way to do things in `awk'. At some point, you may +want to look back at these examples and see if you can come up with +different ways to do the same things shown here: + + * Print the length of the longest input line: + + awk '{ if (length($0) > max) max = length($0) } + END { print max }' data + + * Print every line that is longer than 80 characters: + + awk 'length($0) > 80' data + + The sole rule has a relational expression as its pattern and it + has no action--so the default action, printing the record, is used. + + * Print the length of the longest line in `data': + + expand data | awk '{ if (x < length()) x = length() } + END { print "maximum line length is " x }' + + The input is processed by the `expand' utility to change tabs into + spaces, so the widths compared are actually the right-margin + columns. + + * Print every line that has at least one field: + + awk 'NF > 0' data + + This is an easy way to delete blank lines from a file (or rather, + to create a new file similar to the old file but from which the + blank lines have been removed). + + * Print seven random numbers from 0 to 100, inclusive: + + awk 'BEGIN { for (i = 1; i <= 7; i++) + print int(101 * rand()) }' + + * Print the total number of bytes used by FILES: + + ls -l FILES | awk '{ x += $5 } + END { print "total bytes: " x }' + + * Print the total number of kilobytes used by FILES: + + ls -l FILES | awk '{ x += $5 } + END { print "total K-bytes: " (x + 1023)/1024 }' + + * Print a sorted list of the login names of all users: + + awk -F: '{ print $1 }' /etc/passwd | sort + + * Count lines in a file: + + awk 'END { print NR }' data + + * Print the even-numbered lines in the data file: + + awk 'NR % 2 == 0' data + + If you use the expression `NR % 2 == 1' instead, it would print + the odd-numbered lines. + + +File: gawk.info, Node: Two Rules, Next: More Complex, Prev: Very Simple, Up: Getting Started + +An Example with Two Rules +========================= + + The `awk' utility reads the input files one line at a time. For +each line, `awk' tries the patterns of each of the rules. If several +patterns match, then several actions are run in the order in which they +appear in the `awk' program. If no patterns match, then no actions are +run. + + After processing all the rules that match the line (and perhaps +there are none), `awk' reads the next line. (However, *note The `next' +Statement: Next Statement., and also *note Using `gawk''s `nextfile' +Statement: Nextfile Statement.). This continues until the end of the +file is reached. For example, the following `awk' program contains two +rules: + + /12/ { print $0 } + /21/ { print $0 } + +The first rule has the string `12' as the pattern and `print $0' as the +action. The second rule has the string `21' as the pattern and also +has `print $0' as the action. Each rule's action is enclosed in its +own pair of braces. + + This program prints every line that contains the string `12' _or_ +the string `21'. If a line contains both strings, it is printed twice, +once by each rule. + + This is what happens if we run this program on our two sample data +files, `BBS-list' and `inventory-shipped', as shown here: + + $ awk '/12/ { print $0 } + > /21/ { print $0 }' BBS-list inventory-shipped + -| aardvark 555-5553 1200/300 B + -| alpo-net 555-3412 2400/1200/300 A + -| barfly 555-7685 1200/300 A + -| bites 555-1675 2400/1200/300 A -| core 555-2912 1200/300 C -| fooey 555-1234 2400/1200/300 B -| foot 555-6699 1200/300 B @@ -1210,7 +1678,7 @@ files, `BBS-list' and `inventory-shipped', as shown here: -| Jan 21 36 64 620 -| Apr 21 70 74 514 -Note how the line in `BBS-list' beginning with `sabafoo' was printed +Note how the line beginning with `sabafoo' in `BBS-list' was printed twice, once for each rule.  @@ -1219,34 +1687,29 @@ File: gawk.info, Node: More Complex, Next: Statements/Lines, Prev: Two Rules, A More Complex Example ====================== - Here is an example to give you an idea of what typical `awk' -programs do. This example shows how `awk' can be used to summarize, -select, and rearrange the output of another utility. It uses features -that haven't been covered yet, so don't worry if you don't understand -all the details. + Now that we've mastered some simple tasks, let's look at what +typical `awk' programs do. This example shows how `awk' can be used to +summarize, select, and rearrange the output of another utility. It uses +features that haven't been covered yet, so don't worry if you don't +understand all the details: - ls -lg | awk '$6 == "Nov" { sum += $5 } + ls -l | awk '$6 == "Nov" { sum += $5 } END { print sum }' This command prints the total number of bytes in all the files in the current directory that were last modified in November (of any year). -(In the C shell you would need to type a semicolon and then a backslash -at the end of the first line; in a POSIX-compliant shell, such as the -Bourne shell or Bash, the GNU Bourne-Again shell, you can type the -example as shown.) - - The `ls -lg' part of this example is a system command that gives you -a listing of the files in a directory, including file size and the date -the file was last modified. Its output looks like this: +(1) The `ls -l' part of this example is a system command that gives you +a listing of the files in a directory, including each file's size and +the date the file was last modified. Its output looks like this: -rw-r--r-- 1 arnold user 1933 Nov 7 13:05 Makefile - -rw-r--r-- 1 arnold user 10809 Nov 7 13:03 gawk.h - -rw-r--r-- 1 arnold user 983 Apr 13 12:14 gawk.tab.h - -rw-r--r-- 1 arnold user 31869 Jun 15 12:20 gawk.y - -rw-r--r-- 1 arnold user 22414 Nov 7 13:03 gawk1.c - -rw-r--r-- 1 arnold user 37455 Nov 7 13:03 gawk2.c - -rw-r--r-- 1 arnold user 27511 Dec 9 13:07 gawk3.c - -rw-r--r-- 1 arnold user 7989 Nov 7 13:03 gawk4.c + -rw-r--r-- 1 arnold user 10809 Nov 7 13:03 awk.h + -rw-r--r-- 1 arnold user 983 Apr 13 12:14 awk.tab.h + -rw-r--r-- 1 arnold user 31869 Jun 15 12:20 awk.y + -rw-r--r-- 1 arnold user 22414 Nov 7 13:03 awk1.c + -rw-r--r-- 1 arnold user 37455 Nov 7 13:03 awk2.c + -rw-r--r-- 1 arnold user 27511 Dec 9 13:07 awk3.c + -rw-r--r-- 1 arnold user 7989 Nov 7 13:03 awk4.c The first field contains read-write permissions, the second field contains the number of links to the file, and the third field @@ -1254,27 +1717,41 @@ identifies the owner of the file. The fourth field identifies the group of the file. The fifth field contains the size of the file in bytes. The sixth, seventh and eighth fields contain the month, day, and time, respectively, that the file was last modified. Finally, the ninth field -contains the name of the file. +contains the name of the file.(2) The `$6 == "Nov"' in our `awk' program is an expression that tests -whether the sixth field of the output from `ls -lg' matches the string +whether the sixth field of the output from `ls -l' matches the string `Nov'. Each time a line has the string `Nov' for its sixth field, the -action `sum += $5' is performed. This adds the fifth field (the file +action `sum += $5' is performed. This adds the fifth field (the file's size) to the variable `sum'. As a result, when `awk' has finished -reading all the input lines, `sum' is the sum of the sizes of files -whose lines matched the pattern. (This works because `awk' variables -are automatically initialized to zero.) +reading all the input lines, `sum' is the total of the sizes of the +files whose lines matched the pattern. (This works because `awk' +variables are automatically initialized to zero.) After the last line of output from `ls' has been processed, the -`END' rule is executed, and the value of `sum' is printed. In this -example, the value of `sum' would be 80600. +`END' rule executes and prints the value of `sum'. In this example, +the value of `sum' is 140963. These more advanced `awk' techniques are covered in later sections -(*note Overview of Actions: Action Overview.). Before you can move on -to more advanced `awk' programming, you have to know how `awk' -interprets your input and displays your output. By manipulating fields -and using `print' statements, you can produce some very useful and -impressive looking reports. +(*note Actions: Action Overview.). Before you can move on to more +advanced `awk' programming, you have to know how `awk' interprets your +input and displays your output. By manipulating fields and using +`print' statements, you can produce some very useful and impressive +looking reports. + + ---------- Footnotes ---------- + + (1) In the C shell (`csh'), you need to type a semicolon and then a +backslash at the end of the first line; see *Note `awk' Statements +Versus Lines: Statements/Lines, for an explanation as to why. In a +POSIX-compliant shell, such as the Bourne shell or `bash', you can type +the example as shown. If the command `echo $path' produces an empty +output line, you are most likely using a POSIX-compliant shell. +Otherwise, you are probably using the C shell or a shell derived from +it. + + (2) On some very old systems, you may need to use `ls -lg' to get +this output.  File: gawk.info, Node: Statements/Lines, Next: Other Features, Prev: More Complex, Up: Getting Started @@ -1288,20 +1765,18 @@ separate rule, like this: awk '/12/ { print $0 } /21/ { print $0 }' BBS-list inventory-shipped - However, `gawk' will ignore newlines after any of the following: + However, `gawk' ignores newlines after any of the following symbols +and keywords: , { ? : || && do else -A newline at any other point is considered the end of the statement. -(Splitting lines after `?' and `:' is a minor `gawk' extension. The -`?' and `:' referred to here is the three operand conditional -expression described in *Note Conditional Expressions: Conditional Exp.) +A newline at any other point is considered the end of the statement.(1) If you would like to split a single statement into two lines at a point where a newline would terminate it, you can "continue" it by -ending the first line with a backslash character, `\'. The backslash -must be the final character on the line to be recognized as a -continuation character. This is allowed absolutely anywhere in the +ending the first line with a backslash character (`\'). The backslash +must be the final character on the line in order to be recognized as a +continuation character. A backslash is allowed anywhere in the statement, even in the middle of a string or regular expression. For example: @@ -1309,27 +1784,26 @@ example: on the next line/ { print $1 }' We have generally not used backslash continuation in the sample programs -in this Info file. Since in `gawk' there is no limit on the length of -a line, it is never strictly necessary; it just makes programs more -readable. For this same reason, as well as for clarity, we have kept -most statements short in the sample programs presented throughout the -Info file. Backslash continuation is most useful when your `awk' -program is in a separate source file, instead of typed in on the -command line. You should also note that many `awk' implementations are -more particular about where you may use backslash continuation. For -example, they may not allow you to split a string constant using -backslash continuation. Thus, for maximal portability of your `awk' -programs, it is best not to split your lines in the middle of a regular -expression or a string. - - *Caution: backslash continuation does not work as described above -with the C shell.* Continuation with backslash works for `awk' -programs in files, and also for one-shot programs _provided_ you are -using a POSIX-compliant shell, such as the Bourne shell or Bash, the -GNU Bourne-Again shell. But the C shell (`csh') behaves differently! -There, you must use two backslashes in a row, followed by a newline. -Note also that when using the C shell, _every_ newline in your awk -program must be escaped with a backslash. To illustrate: +in this Info file. In `gawk', there is no limit on the length of a +line, so backslash continuation is never strictly necessary; it just +makes programs more readable. For this same reason, as well as for +clarity, we have kept most statements short in the sample programs +presented throughout the Info file. Backslash continuation is most +useful when your `awk' program is in a separate source file instead of +entered from the command line. You should also note that many `awk' +implementations are more particular about where you may use backslash +continuation. For example, they may not allow you to split a string +constant using backslash continuation. Thus, for maximum portability +of your `awk' programs, it is best not to split your lines in the +middle of a regular expression or a string. + + *Caution:* _Backslash continuation does not work as described above +with the C shell._ It works for `awk' programs in files and for +one-shot programs, _provided_ you are using a POSIX-compliant shell, +such as the Unix Bourne shell or `bash'. But the C shell behaves +differently! There, you must use two backslashes in a row, followed by +a newline. Note also that when using the C shell, _every_ newline in +your awk program must be escaped with a backslash. To illustrate: % awk 'BEGIN { \ ? print \\ @@ -1340,14 +1814,23 @@ program must be escaped with a backslash. To illustrate: Here, the `%' and `?' are the C shell's primary and secondary prompts, analogous to the standard shell's `$' and `>'. + Compare the previous example to how it is done with a +POSIX-compliant shell: + + $ awk 'BEGIN { + > print \ + > "hello, world" + > }' + -| hello, world + `awk' is a line-oriented language. Each rule's action has to begin on the same line as the pattern. To have the pattern and action on -separate lines, you _must_ use backslash continuation--there is no +separate lines, you _must_ use backslash continuation; there is no other way. - Note that backslash continuation and comments do not mix. As soon as -`awk' sees the `#' that starts a comment, it ignores _everything_ on -the rest of the line. For example: + Another thing to keep in mind is that backslash continuation and +comments do not mix. As soon as `awk' sees the `#' that starts a +comment, it ignores _everything_ on the rest of the line. For example: $ gawk 'BEGIN { print "dont panic" # a friendly \ > BEGIN rule @@ -1355,23 +1838,31 @@ the rest of the line. For example: error--> gawk: cmd. line:2: BEGIN rule error--> gawk: cmd. line:2: ^ parse error -Here, it looks like the backslash would continue the comment onto the -next line. However, the backslash-newline combination is never even -noticed, since it is "hidden" inside the comment. Thus, the `BEGIN' is -noted as a syntax error. +In this case, it looks like the backslash would continue the comment +onto the next line. However, the backslash-newline combination is never +even noticed because it is "hidden" inside the comment. Thus, the +`BEGIN' is noted as a syntax error. When `awk' statements within one rule are short, you might want to -put more than one of them on a line. You do this by separating the -statements with a semicolon, `;'. - - This also applies to the rules themselves. Thus, the previous -program could have been written: +put more than one of them on a line. This is accomplished by +separating the statements with a semicolon (`;'). This also applies to +the rules themselves. Thus, the program shown at the start of this +minor node could also be written this way: /12/ { print $0 } ; /21/ { print $0 } -*Note:* the requirement that rules on the same line must be separated -with a semicolon was not in the original `awk' language; it was added -for consistency with the treatment of statements within an action. +*Note:* The requirement that states that rules on the same line must be +separated with a semicolon was not in the original `awk' language; it +was added for consistency with the treatment of statements within an +action. + + ---------- Footnotes ---------- + + (1) The `?' and `:' referred to here is the three-operand +conditional expression described in *Note Conditional Expressions: +Conditional Exp. Splitting lines after `?' and `:' is a minor `gawk' +extension; if `--posix' is specified (*note Command-Line Options: +Options.), then this extension is disabled.  File: gawk.info, Node: Other Features, Next: When, Prev: Statements/Lines, Up: Getting Started @@ -1379,13 +1870,15 @@ File: gawk.info, Node: Other Features, Next: When, Prev: Statements/Lines, U Other Features of `awk' ======================= - The `awk' language provides a number of predefined, or built-in -variables, which your programs can use to get information from `awk'. -There are other variables your program can set to control how `awk' -processes your data. + The `awk' language provides a number of predefined, or "built-in", +variables that your programs can use to get information from `awk'. +There are other variables your program can set as well to control how +`awk' processes your data. In addition, `awk' provides a number of built-in functions for doing -common computational and string related operations. +common computational and string related operations. `gawk' provides +built-in functions for working with timestamps, performing bit +manipulation, and for runtime string translation. As we develop our presentation of the `awk' language, we introduce most of the variables and many of the functions. They are defined @@ -1398,24 +1891,24 @@ File: gawk.info, Node: When, Prev: Other Features, Up: Getting Started When to Use `awk' ================= - You might wonder how `awk' might be useful for you. Using utility -programs, advanced patterns, field separators, arithmetic statements, -and other selection criteria, you can produce much more complex output. -The `awk' language is very useful for producing reports from large -amounts of raw data, such as summarizing information from the output of -other utility programs like `ls'. (*Note A More Complex Example: More -Complex.) + Now that you've seen some of what `awk' can do, you might wonder how +`awk' could be useful for you. By using utility programs, advanced +patterns, field separators, arithmetic statements, and other selection +criteria, you can produce much more complex output. The `awk' language +is very useful for producing reports from large amounts of raw data, +such as summarizing information from the output of other utility +programs like `ls'. (*Note A More Complex Example: More Complex.) Programs written with `awk' are usually much smaller than they would be in other languages. This makes `awk' programs easy to compose and use. Often, `awk' programs can be quickly composed at your terminal, -used once, and thrown away. Since `awk' programs are interpreted, you +used once, and thrown away. Because `awk' programs are interpreted, you can avoid the (usually lengthy) compilation part of the typical edit-compile-test-debug cycle of software development. Complex programs have been written in `awk', including a complete retargetable assembler for eight-bit microprocessors (*note Glossary::, -for more information) and a microcode assembler for a special purpose +for more information), and a microcode assembler for a special purpose Prolog computer. However, `awk''s capabilities are strained by tasks of such complexity. @@ -1424,98 +1917,29 @@ hundred lines, you might consider using a different programming language. Emacs Lisp is a good choice if you need sophisticated string or pattern matching capabilities. The shell is also good at string and pattern matching; in addition, it allows powerful use of the system -utilities. More conventional languages, such as C, C++, and Lisp, offer +utilities. More conventional languages, such as C, C++, and Java, offer better facilities for system programming and for managing the complexity of large programs. Programs in these languages may require more lines of source code than the equivalent `awk' programs, but they are easier to maintain and usually run more efficiently.  -File: gawk.info, Node: One-liners, Next: Regexp, Prev: Getting Started, Up: Top - -Useful One Line Programs -************************ - - Many useful `awk' programs are short, just a line or two. Here is a -collection of useful, short programs to get you started. Some of these -programs contain constructs that haven't been covered yet. The -description of the program will give you a good idea of what is going -on, but please read the rest of the Info file to become an `awk' expert! - - Most of the examples use a data file named `data'. This is just a -placeholder; if you were to use these programs yourself, you would -substitute your own file names for `data'. - - Since you are reading this in Info, each line of the example code is -enclosed in quotes, to represent text that you would type literally. -The examples themselves represent shell commands that use single quotes -to keep the shell from interpreting the contents of the program. When -reading the examples, focus on the text between the open and close -quotes. - -`awk '{ if (length($0) > max) max = length($0) }' -` END { print max }' data' - This program prints the length of the longest input line. - -`awk 'length($0) > 80' data' - This program prints every line that is longer than 80 characters. - The sole rule has a relational expression as its pattern, and has - no action (so the default action, printing the record, is used). - -`expand data | awk '{ if (x < length()) x = length() }' -` END { print "maximum line length is " x }'' - This program prints the length of the longest line in `data'. The - input is processed by the `expand' program to change tabs into - spaces, so the widths compared are actually the right-margin - columns. - -`awk 'NF > 0' data' - This program prints every line that has at least one field. This - is an easy way to delete blank lines from a file (or rather, to - create a new file similar to the old file but from which the blank - lines have been deleted). - -`awk 'BEGIN { for (i = 1; i <= 7; i++)' -` print int(101 * rand()) }'' - This program prints seven random numbers from zero to 100, - inclusive. - -`ls -lg FILES | awk '{ x += $5 } ; END { print "total bytes: " x }'' - This program prints the total number of bytes used by FILES. - -`ls -lg FILES | awk '{ x += $5 }' -` END { print "total K-bytes: " (x + 1023)/1024 }'' - This program prints the total number of kilobytes used by FILES. - -`awk -F: '{ print $1 }' /etc/passwd | sort' - This program prints a sorted list of the login names of all users. - -`awk 'END { print NR }' data' - This program counts lines in a file. - -`awk 'NR % 2 == 0' data' - This program prints the even numbered lines in the data file. If - you were to use the expression `NR % 2 == 1' instead, it would - print the odd numbered lines. - - -File: gawk.info, Node: Regexp, Next: Reading Files, Prev: One-liners, Up: Top +File: gawk.info, Node: Regexp, Next: Reading Files, Prev: Getting Started, Up: Top Regular Expressions ******************* A "regular expression", or "regexp", is a way of describing a set of strings. Because regular expressions are such a fundamental part of -`awk' programming, their format and use deserve a separate chapter. +`awk' programming, their format and use deserve a separate major node. A regular expression enclosed in slashes (`/') is an `awk' pattern -that matches every input record whose text belongs to that set. - - The simplest regular expression is a sequence of letters, numbers, or -both. Such a regexp matches any string that contains that sequence. -Thus, the regexp `foo' matches any string containing `foo'. Therefore, -the pattern `/foo/' matches any input record containing the three -characters `foo', _anywhere_ in the record. Other kinds of regexps let +that matches every input record whose text belongs to that set. The +simplest regular expression is a sequence of letters, numbers, or both. +Such a regexp matches any string that contains that sequence. Thus, +the regexp `foo' matches any string containing `foo'. Therefore, the +pattern `/foo/' matches any input record containing the three +characters `foo' _anywhere_ in the record. Other kinds of regexps let you specify more complicated classes of strings. * Menu: @@ -1523,6 +1947,7 @@ you specify more complicated classes of strings. * Regexp Usage:: How to Use Regular Expressions. * Escape Sequences:: How to write non-printing characters. * Regexp Operators:: Regular Expression Operators. +* Character Lists:: What can go between `[...]'. * GNU Regexp Operators:: Operators specific to GNU software. * Case-sensitivity:: How to do case-insensitive matching. * Leftmost Longest:: How much text matches. @@ -1537,8 +1962,9 @@ How to Use Regular Expressions A regular expression can be used as a pattern by enclosing it in slashes. Then the regular expression is tested against the entire text of each record. (Normally, it only needs to match some part of the -text in order to succeed.) For example, this prints the second field -of each record that contains the three characters `foo' anywhere in it: +text in order to succeed.) For example, the following prints the +second field of each record that contains the string `foo' anywhere in +it: $ awk '/foo/ { print $2 }' BBS-list -| 555-1234 @@ -1548,43 +1974,46 @@ of each record that contains the three characters `foo' anywhere in it: Regular expressions can also be used in matching expressions. These expressions allow you to specify the string to match against; it need -not be the entire current input record. The two operators, `~' and -`!~', perform regular expression comparisons. Expressions using these -operators can be used as patterns or in `if', `while', `for', and `do' -statements. (*Note Control Statements in Actions: Statements.) - -`EXP ~ /REGEXP/' - This is true if the expression EXP (taken as a string) is matched - by REGEXP. The following example matches, or selects, all input - records with the upper-case letter `J' somewhere in the first - field: - - $ awk '$1 ~ /J/' inventory-shipped - -| Jan 13 25 15 115 - -| Jun 31 42 75 492 - -| Jul 24 34 67 436 - -| Jan 21 36 64 620 - - So does this: - - awk '{ if ($1 ~ /J/) print }' inventory-shipped - -`EXP !~ /REGEXP/' - This is true if the expression EXP (taken as a character string) - is _not_ matched by REGEXP. The following example matches, or - selects, all input records whose first field _does not_ contain - the upper-case letter `J': - - $ awk '$1 !~ /J/' inventory-shipped - -| Feb 15 32 24 226 - -| Mar 15 24 34 228 - -| Apr 31 52 63 420 - -| May 16 34 29 208 - ... +not be the entire current input record. The two operators `~' and `!~' +perform regular expression comparisons. Expressions using these +operators can be used as patterns, or in `if', `while', `for', and `do' +statements. (*Note Control Statements in Actions: Statements.) For +example: + + EXP ~ /REGEXP/ + +is true if the expression EXP (taken as a string) matches REGEXP. The +following example matches, or selects, all input records with the +uppercase letter `J' somewhere in the first field: + + $ awk '$1 ~ /J/' inventory-shipped + -| Jan 13 25 15 115 + -| Jun 31 42 75 492 + -| Jul 24 34 67 436 + -| Jan 21 36 64 620 + + So does this: + + awk '{ if ($1 ~ /J/) print }' inventory-shipped + + This next example is true if the expression EXP (taken as a +character string) does _not_ match REGEXP: + + EXP !~ /REGEXP/ - When a regexp is written enclosed in slashes, like `/foo/', we call -it a "regexp constant", much like `5.27' is a numeric constant, and -`"foo"' is a string constant. + The following example matches, or selects, all input records whose +first field _does not_ contain the uppercase letter `J': + + $ awk '$1 !~ /J/' inventory-shipped + -| Feb 15 32 24 226 + -| Mar 15 24 34 228 + -| Apr 31 52 63 420 + -| May 16 34 29 208 + ... + + When a regexp is enclosed in slashes, such as `/foo/', we call it a +"regexp constant", much like `5.27' is a numeric constant and `"foo"' +is a string constant.  File: gawk.info, Node: Escape Sequences, Next: Regexp Operators, Prev: Regexp Usage, Up: Regexp @@ -1593,393 +2022,259 @@ Escape Sequences ================ Some characters cannot be included literally in string constants -(`"foo"') or regexp constants (`/foo/'). You represent them instead -with "escape sequences", which are character sequences beginning with a -backslash (`\'). - - One use of an escape sequence is to include a double-quote character -in a string constant. Since a plain double-quote would end the string, -you must use `\"' to represent an actual double-quote character as a -part of the string. For example: +(`"foo"') or regexp constants (`/foo/'). Instead, they should be +represented with "escape sequences", which are character sequences +beginning with a backslash (`\'). One use of an escape sequence is to +include a double quote character in a string constant. Because a plain +double quote ends the string, you must use `\"' to represent an actual +double quote character as a part of the string. For example: $ awk 'BEGIN { print "He said \"hi!\" to her." }' -| He said "hi!" to her. The backslash character itself is another character that cannot be -included normally; you write `\\' to put one backslash in the string or -regexp. Thus, the string whose contents are the two characters `"' and -`\' must be written `"\"\\"'. +included normally; you must write `\\' to put one backslash in the +string or regexp. Thus, the string whose contents are the two +characters `"' and `\' must be written `"\"\\"'. Another use of backslash is to represent unprintable characters such as tab or newline. While there is nothing to stop you from entering most unprintable characters directly in a string constant or regexp constant, they may look ugly. - Here is a table of all the escape sequences used in `awk', and what -they represent. Unless noted otherwise, all of these escape sequences -apply to both string constants and regexp constants. + The following table lists all the escape sequences used in `awk' and +what they represent. Unless noted otherwise, all these escape sequences +apply to both string constants and regexp constants: `\\' A literal backslash, `\'. `\a' - The "alert" character, `Control-g', ASCII code 7 (BEL). + The "alert" character, `Ctrl-g', ASCII code 7 (BEL). (This + usually makes some sort of audible noise.) `\b' - Backspace, `Control-h', ASCII code 8 (BS). + Backspace, `Ctrl-h', ASCII code 8 (BS). `\f' - Formfeed, `Control-l', ASCII code 12 (FF). + Formfeed, `Ctrl-l', ASCII code 12 (FF). `\n' - Newline, `Control-j', ASCII code 10 (LF). + Newline, `Ctrl-j', ASCII code 10 (LF). `\r' - Carriage return, `Control-m', ASCII code 13 (CR). + Carriage return, `Ctrl-m', ASCII code 13 (CR). `\t' - Horizontal tab, `Control-i', ASCII code 9 (HT). + Horizontal tab, `Ctrl-i', ASCII code 9 (HT). `\v' - Vertical tab, `Control-k', ASCII code 11 (VT). + Vertical tab, `Ctrl-k', ASCII code 11 (VT). `\NNN' - The octal value NNN, where NNN are one to three digits between `0' - and `7'. For example, the code for the ASCII ESC (escape) + The octal value NNN, where NNN stands for 1 to 3 digits between + `0' and `7'. For example, the code for the ASCII ESC (escape) character is `\033'. `\xHH...' - The hexadecimal value HH, where HH are hexadecimal digits (`0' - through `9' and either `A' through `F' or `a' through `f'). Like - the same construct in ANSI C, the escape sequence continues until - the first non-hexadecimal digit is seen. However, using more than - two hexadecimal digits produces undefined results. (The `\x' - escape sequence is not allowed in POSIX `awk'.) + The hexadecimal value HH, where HH stands for a sequence of + hexadecimal digits (`0' through `9', and either `A' through `F' or + `a' through `f'). Like the same construct in ISO C, the escape + sequence continues until the first non-hexadecimal digit is seen. + However, using more than two hexadecimal digits produces undefined + results. (The `\x' escape sequence is not allowed in POSIX `awk'.) `\/' - A literal slash (necessary for regexp constants only). You use - this when you wish to write a regexp constant that contains a - slash. Since the regexp is delimited by slashes, you need to - escape the slash that is part of the pattern, in order to tell - `awk' to keep processing the rest of the regexp. + A literal slash (necessary for regexp constants only). This + expression is used when you want to write a regexp constant that + contains a slash. Because the regexp is delimited by slashes, you + need to escape the slash that is part of the pattern, in order to + tell `awk' to keep processing the rest of the regexp. `\"' - A literal double-quote (necessary for string constants only). You - use this when you wish to write a string constant that contains a - double-quote. Since the string is delimited by double-quotes, you - need to escape the quote that is part of the string, in order to - tell `awk' to keep processing the rest of the string. - - In `gawk', there are additional two character sequences that begin -with backslash that have special meaning in regexps. *Note Additional -Regexp Operators Only in `gawk': GNU Regexp Operators. - - In a string constant, what happens if you place a backslash before -something that is not one of the characters listed above? POSIX `awk' -purposely leaves this case undefined. There are two choices. - - * Strip the backslash out. This is what Unix `awk' and `gawk' both - do. For example, `"a\qc"' is the same as `"aqc"'. + A literal double quote (necessary for string constants only). + This expression is used when you want to write a string constant + that contains a double quote. Because the string is delimited by + double quotes, you need to escape the quote that is part of the + string, in order to tell `awk' to keep processing the rest of the + string. - * Leave the backslash alone. Some other `awk' implementations do - this. In such implementations, `"a\qc"' is the same as if you had - typed `"a\\qc"'. + In `gawk', a number of additional two-character sequences that begin +with a backslash have special meaning in regexps. *Note +`gawk'-Specific Regexp Operators: GNU Regexp Operators. In a regexp, a backslash before any character that is not in the -above table, and not listed in *Note Additional Regexp Operators Only -in `gawk': GNU Regexp Operators, means that the next character should -be taken literally, even if it would normally be a regexp operator. -E.g., `/a\+b/' matches the three characters `a+b'. +above table and not listed in *Note `gawk'-Specific Regexp Operators: +GNU Regexp Operators, means that the next character should be taken +literally, even if it would normally be a regexp operator. For +example, `/a\+b/' matches the three characters `a+b'. For complete portability, do not use a backslash before any -character not listed in the table above. - - Another interesting question arises. Suppose you use an octal or -hexadecimal escape to represent a regexp metacharacter (*note Regular -Expression Operators: Regexp Operators.). Does `awk' treat the -character as a literal character, or as a regexp operator? - - It turns out that historically, such characters were taken literally -(d.c.). However, the POSIX standard indicates that they should be -treated as real metacharacters, and this is what `gawk' does. However, -in compatibility mode (*note Command Line Options: Options.), `gawk' -treats the characters represented by octal and hexadecimal escape -sequences literally when used in regexp constants. Thus, `/a\52b/' is -equivalent to `/a\*b/'. +character not shown in the table above. To summarize: - 1. The escape sequences in the table above are always processed first, + * The escape sequences in the table above are always processed first, for both string constants and regexp constants. This happens very early, as soon as `awk' reads your program. - 2. `gawk' processes both regexp constants and dynamic regexps (*note + * `gawk' processes both regexp constants and dynamic regexps (*note Using Dynamic Regexps: Computed Regexps.), for the special - operators listed in *Note Additional Regexp Operators Only in - `gawk': GNU Regexp Operators. + operators listed in *Note `gawk'-Specific Regexp Operators: GNU + Regexp Operators. - 3. A backslash before any other character means to treat that + * A backslash before any other character means to treat that character literally. +Advanced Notes: Backslash Before Regular Characters +--------------------------------------------------- + + If you place a backslash in a string constant before something that +is not one of the characters listed above, POSIX `awk' purposely leaves +what happens as undefined. There are two choices: + +Strip the backslash out + This is what Unix `awk' and `gawk' both do. For example, `"a\qc"' + is the same as `"aqc"'. (Because this is such an easy bug to both + introduce and to miss, `gawk' warns you about it.) Consider `FS = + "[ \t]+\|[ \t]+"' to use vertical bars surrounded by whitespace as + the field separator. There should be two backslashes in the + string, `FS = "[ \t]+\\|[ \t]+"'.) + +Leave the backslash alone + Some other `awk' implementations do this. In such + implementations, `"a\qc"' is the same as if you had typed + `"a\\qc"'. + +Advanced Notes: Escape Sequences for Metacharacters +--------------------------------------------------- + + Suppose you use an octal or hexadecimal escape to represent a regexp +metacharacter (*note Regular Expression Operators: Regexp Operators.). +Does `awk' treat the character as a literal character or as a regexp +operator? + + Historically, such characters were taken literally. (d.c.) +However, the POSIX standard indicates that they should be treated as +real metacharacters, which is what `gawk' does. In compatibility mode +(*note Command-Line Options: Options.), `gawk' treats the characters +represented by octal and hexadecimal escape sequences literally when +used in regexp constants. Thus, `/a\52b/' is equivalent to `/a\*b/'. +  -File: gawk.info, Node: Regexp Operators, Next: GNU Regexp Operators, Prev: Escape Sequences, Up: Regexp +File: gawk.info, Node: Regexp Operators, Next: Character Lists, Prev: Escape Sequences, Up: Regexp Regular Expression Operators ============================ - You can combine regular expressions with the following characters, -called "regular expression operators", or "metacharacters", to increase -the power and versatility of regular expressions. + You can combine regular expressions with special characters, called +"regular expression operators" or "metacharacters", to increase the +power and versatility of regular expressions. The escape sequences described in *Note Escape Sequences::, are -valid inside a regexp. They are introduced by a `\'. They are +valid inside a regexp. They are introduced by a `\', and are recognized and converted into the corresponding real characters as the very first step in processing regexps. - Here is a table of metacharacters. All characters that are not -escape sequences and that are not listed in the table stand for -themselves. + Here is a list of metacharacters. All characters that are not escape +sequences and that are not listed in the table stand for themselves: `\' This is used to suppress the special meaning of a character when - matching. For example: - - \$ - - matches the character `$'. + matching. For example, `\$' matches the character `$'. `^' - This matches the beginning of a string. For example: - - ^@chapter - - matches the `@chapter' at the beginning of a string, and can be - used to identify chapter beginnings in Texinfo source files. The - `^' is known as an "anchor", since it anchors the pattern to - matching only at the beginning of the string. + This matches the beginning of a string. For example, `^@chapter' + matches `@chapter' at the beginning of a string, and can be used + to identify chapter beginnings in Texinfo source files. The `^' + is known as an "anchor", because it anchors the pattern to match + only at the beginning of the string. It is important to realize that `^' does not match the beginning of - a line embedded in a string. In this example the condition is not - true: + a line embedded in a string. The condition is not true in the + following example: if ("line1\nLINE 2" ~ /^L/) ... `$' - This is similar to `^', but it matches only at the end of a string. - For example: - - p$ - - matches a record that ends with a `p'. The `$' is also an anchor, - and also does not match the end of a line embedded in a string. - In this example the condition is not true: + This is similar to `^' but it matches only at the end of a string. + For example, `p$' matches a record that ends with a `p'. The `$' + is an anchor and does not match the end of a line embedded in a + string. The condition is not true in the following example: if ("line1\nLINE 2" ~ /1$/) ... `.' - The period, or dot, matches any single character, _including_ the - newline character. For example: - - .P - - matches any single character followed by a `P' in a string. Using - concatenation we can make a regular expression like `U.A', which - matches any three-character sequence that begins with `U' and ends - with `A'. + This matches any single character, _including_ the newline + character. For example, `.P' matches any single character + followed by a `P' in a string. Using concatenation, we can make a + regular expression such as `U.A', that matches any three-character + sequence that begins with `U' and ends with `A'. - In strict POSIX mode (*note Command Line Options: Options.), `.' + In strict POSIX mode (*note Command-Line Options: Options.), `.' does not match the NUL character, which is a character with all bits equal to zero. Otherwise, NUL is just another character. Other versions of `awk' may not be able to match the NUL character. `[...]' - This is called a "character list". It matches any _one_ of the - characters that are enclosed in the square brackets. For example: - - [MVX] - - matches any one of the characters `M', `V', or `X' in a string. - - Ranges of characters are indicated by using a hyphen between the - beginning and ending characters, and enclosing the whole thing in - brackets. For example: - - [0-9] - - matches any digit. Multiple ranges are allowed. E.g., the list - `[A-Za-z0-9]' is a common way to express the idea of "all - alphanumeric characters." - - To include one of the characters `\', `]', `-' or `^' in a - character list, put a `\' in front of it. For example: - - [d\]] - - matches either `d', or `]'. - - This treatment of `\' in character lists is compatible with other - `awk' implementations, and is also mandated by POSIX. The regular - expressions in `awk' are a superset of the POSIX specification for - Extended Regular Expressions (EREs). POSIX EREs are based on the - regular expressions accepted by the traditional `egrep' utility. - - "Character classes" are a new feature introduced in the POSIX - standard. A character class is a special notation for describing - lists of characters that have a specific attribute, but where the - actual characters themselves can vary from country to country - and/or from character set to character set. For example, the - notion of what is an alphabetic character differs in the USA and - in France. - - A character class is only valid in a regexp _inside_ the brackets - of a character list. Character classes consist of `[:', a keyword - denoting the class, and `:]'. Here are the character classes - defined by the POSIX standard. - - `[:alnum:]' - Alphanumeric characters. - - `[:alpha:]' - Alphabetic characters. - - `[:blank:]' - Space and tab characters. - - `[:cntrl:]' - Control characters. - - `[:digit:]' - Numeric characters. - - `[:graph:]' - Characters that are printable and are also visible. (A space - is printable, but not visible, while an `a' is both.) - - `[:lower:]' - Lower-case alphabetic characters. - - `[:print:]' - Printable characters (characters that are not control - characters.) - - `[:punct:]' - Punctuation characters (characters that are not letter, - digits, control characters, or space characters). - - `[:space:]' - Space characters (such as space, tab, and formfeed, to name a - few). - - `[:upper:]' - Upper-case alphabetic characters. - - `[:xdigit:]' - Characters that are hexadecimal digits. - - For example, before the POSIX standard, to match alphanumeric - characters, you had to write `/[A-Za-z0-9]/'. If your character - set had other alphabetic characters in it, this would not match - them. With the POSIX character classes, you can write - `/[[:alnum:]]/', and this will match _all_ the alphabetic and - numeric characters in your character set. - - Two additional special sequences can appear in character lists. - These apply to non-ASCII character sets, which can have single - symbols (called "collating elements") that are represented with - more than one character, as well as several characters that are - equivalent for "collating", or sorting, purposes. (E.g., in - French, a plain "e" and a grave-accented "e`" are equivalent.) - - Collating Symbols - A "collating symbol" is a multi-character collating element - enclosed in `[.' and `.]'. For example, if `ch' is a - collating element, then `[[.ch.]]' is a regexp that matches - this collating element, while `[ch]' is a regexp that matches - either `c' or `h'. - - Equivalence Classes - An "equivalence class" is a locale-specific name for a list of - characters that are equivalent. The name is enclosed in `[=' - and `=]'. For example, the name `e' might be used to - represent all of "e," "e`," and "e'." In this case, `[[=e]]' - is a regexp that matches any of `e', `e'', or `e`'. - - These features are very valuable in non-English speaking locales. - - *Caution:* The library functions that `gawk' uses for regular - expression matching currently only recognize POSIX character - classes; they do not recognize collating symbols or equivalence - classes. + This is called a "character list".(1) It matches any _one_ of the + characters that are enclosed in the square brackets. For example, + `[MVX]' matches any one of the characters `M', `V', or `X', in a + string. A full discussion of what can be inside the square + brackets of a character list is given in *Note Using Character + Lists: Character Lists. `[^ ...]' This is a "complemented character list". The first character after the `[' _must_ be a `^'. It matches any characters _except_ those - in the square brackets. For example: - - [^0-9] - - matches any character that is not a digit. + in the square brackets. For example, `[^awk]' matches any + character that is not an `a', a `w', or a `k'. `|' - This is the "alternation operator", and it is used to specify - alternatives. For example: - - ^P|[0-9] - - matches any string that matches either `^P' or `[0-9]'. This - means it matches any string that starts with `P' or contains a - digit. + This is the "alternation operator" and it is used to specify + alternatives. The `|' has the lowest precedence of all the regular + expression operators. For example, `^P|[[:digit:]]' matches any + string that matches either `^P' or `[[:digit:]]'. This means it + matches any string that starts with `P' or contains a digit. The alternation applies to the largest possible regexps on either - side. In other words, `|' has the lowest precedence of all the - regular expression operators. + side. `(...)' - Parentheses are used for grouping in regular expressions as in - arithmetic. They can be used to concatenate regular expressions + Parentheses are used for grouping in regular expressions, similar + to arithmetic. They can be used to concatenate regular expressions containing the alternation operator, `|'. For example, - `@(samp|code)\{[^}]+\}' matches both `@code{foo}' and - `@samp{bar}'. (These are Texinfo formatting control sequences.) + `@(samp|code)\{[^}]+\}' matches both `@code{foo}' and `@samp{bar}'. + (These are Texinfo formatting control sequences.) `*' - This symbol means that the preceding regular expression is to be - repeated as many times as necessary to find a match. For example: - - ph* - - applies the `*' symbol to the preceding `h' and looks for matches - of one `p' followed by any number of `h's. This will also match - just `p' if no `h's are present. + This symbol means that the preceding regular expression should be + repeated as many times as necessary to find a match. For example, + `ph*' applies the `*' symbol to the preceding `h' and looks for + matches of one `p' followed by any number of `h's. This also + matches just `p' if no `h's are present. The `*' repeats the _smallest_ possible preceding expression. - (Use parentheses if you wish to repeat a larger expression.) It - finds as many repetitions as possible. For example: - - awk '/\(c[ad][ad]*r x\)/ { print }' sample - - prints every record in `sample' containing a string of the form - `(car x)', `(cdr x)', `(cadr x)', and so on. Notice the escaping - of the parentheses by preceding them with backslashes. + (Use parentheses if you want to repeat a larger expression.) It + finds as many repetitions as possible. For example, `awk + '/\(c[ad][ad]*r x\)/ { print }' sample' prints every record in + `sample' containing a string of the form `(car x)', `(cdr x)', + `(cadr x)', and so on. Notice the escaping of the parentheses by + preceding them with backslashes. `+' - This symbol is similar to `*', but the preceding expression must be - matched at least once. This means that: - - wh+y - - would match `why' and `whhy' but not `wy', whereas `wh*y' would - match all three of these strings. This is a simpler way of - writing the last `*' example: + This symbol is similar to `*' except that the preceding expression + must be matched at least once. This means that `wh+y' would match + `why' and `whhy', but not `wy', whereas `wh*y' would match all + three of these strings. The following is a simpler way of writing + the last `*' example: awk '/\(c[ad]+r x\)/ { print }' sample `?' - This symbol is similar to `*', but the preceding expression can be - matched either once or not at all. For example: - - fe?d - - will match `fed' and `fd', but nothing else. + This symbol is similar to `*' except that the preceding expression + can be matched either once or not at all. For example, `fe?d' + matches `fed' and `fd', but nothing else. `{N}' `{N,}' @@ -1989,111 +2284,212 @@ themselves. repeated N times. If there are two numbers separated by a comma, the preceding regexp is repeated N to M times. If there is one number followed by a comma, then the preceding regexp is repeated - at least N times. + at least N times: `wh{3}y' - matches `whhhy' but not `why' or `whhhhy'. + Matches `whhhy', but not `why' or `whhhhy'. `wh{3,5}y' - matches `whhhy' or `whhhhy' or `whhhhhy', only. + Matches `whhhy', `whhhhy', or `whhhhhy', only. `wh{2,}y' - matches `whhy' or `whhhy', and so on. + Matches `whhy' or `whhhy', and so on. Interval expressions were not traditionally available in `awk'. - As part of the POSIX standard they were added, to make `awk' and + They were added as part of the POSIX standard to make `awk' and `egrep' consistent with each other. - However, since old programs may use `{' and `}' in regexp + However, because old programs may use `{' and `}' in regexp constants, by default `gawk' does _not_ match interval expressions in regexps. If either `--posix' or `--re-interval' are specified - (*note Command Line Options: Options.), then interval expressions + (*note Command-Line Options: Options.), then interval expressions are allowed in regexps. + For new programs that use `{' and `}' in regexp constants, it is + good practice to always escape them with a backslash. Then the + regexp constants are valid and work the way you want them to, using + any version of `awk'.(2) + In regular expressions, the `*', `+', and `?' operators, as well as the braces `{' and `}', have the highest precedence, followed by concatenation, and finally by `|'. As in arithmetic, parentheses can change how operators are grouped. - If `gawk' is in compatibility mode (*note Command Line Options: -Options.), character classes and interval expressions are not available -in regular expressions. + In POSIX `awk' and `gawk', the `*', `+', and `?' operators stand for +themselves when there is nothing in the regexp that precedes them. For +example, `/+/' matches a literal plus sign. However, many other +versions of `awk' treat such a usage as a syntax error. - The next node discusses the GNU-specific regexp operators, and -provides more detail concerning how command line options affect the way -`gawk' interprets the characters in regular expressions. + If `gawk' is in compatibility mode (*note Command-Line Options: +Options.), POSIX character classes and interval expressions are not +available in regular expressions. - -File: gawk.info, Node: GNU Regexp Operators, Next: Case-sensitivity, Prev: Regexp Operators, Up: Regexp + ---------- Footnotes ---------- -Additional Regexp Operators Only in `gawk' -========================================== + (1) In other literature, you may see a character list referred to as +either a "character set", a "character class" or a "bracket expression". + + (2) Use two backslashes if you're using a string constant with a +regexp operator or function. + + +File: gawk.info, Node: Character Lists, Next: GNU Regexp Operators, Prev: Regexp Operators, Up: Regexp + +Using Character Lists +===================== + + Within a character list, a "range expression" consists of two +characters separated by a hyphen. It matches any single character that +sorts between the two characters, using the locale's collating sequence +and character set. For example, in the default C locale, `[a-dx-z]' is +equivalent to `[abcdxyz]'. Many locales sort characters in dictionary +order, and in these locales, `[a-dx-z]' is typically not equivalent to +`[abcdxyz]'; instead it might be equivalent to `[aBbCcDdxXyYz]', for +example. To obtain the traditional interpretation of bracket +expressions, you can use the C locale by setting the `LC_ALL' +environment variable to the value `C'. + + To include one of the characters `\', `]', `-', or `^' in a +character list, put a `\' in front of it. For example: + + [d\]] + +matches either `d' or `]'. + + This treatment of `\' in character lists is compatible with other +`awk' implementations and is also mandated by POSIX. The regular +expressions in `awk' are a superset of the POSIX specification for +Extended Regular Expressions (EREs). POSIX EREs are based on the +regular expressions accepted by the traditional `egrep' utility. + + "Character classes" are a new feature introduced in the POSIX +standard. A character class is a special notation for describing lists +of characters that have a specific attribute, but the actual characters +can vary from country to country and/or from character set to character +set. For example, the notion of what is an alphabetic character +differs between the United States and France. + + A character class is only valid in a regexp _inside_ the brackets of +a character list. Character classes consist of `[:', a keyword +denoting the class, and `:]'. Here are the character classes defined +by the POSIX standard: + +`[:alnum:]' Alphanumeric characters. +`[:alpha:]' Alphabetic characters. +`[:blank:]' Space and tab characters. +`[:cntrl:]' Control characters. +`[:digit:]' Numeric characters. +`[:graph:]' Characters that are both printable and visible. (A space is + printable but not visible, whereas an `a' is both.) +`[:lower:]' Lowercase alphabetic characters. +`[:print:]' Printable characters (characters that are not control + characters). +`[:punct:]' Punctuation characters (characters that are not letters, + digits, control characters, or space characters). +`[:space:]' Space characters (such as space, tab, and formfeed, to name a + few). +`[:upper:]' Uppercase alphabetic characters. +`[:xdigit:]' Characters that are hexadecimal digits. + + For example, before the POSIX standard, you had to write +`/[A-Za-z0-9]/' to match alphanumeric characters. If your character +set had other alphabetic characters in it, this would not match them, +and if your character set collated differently from ASCII, this might +not even match the ASCII alphanumeric characters. With the POSIX +character classes, you can write `/[[:alnum:]]/' to match the alphabetic +and numeric characters in your character set. + + Two additional special sequences can appear in character lists. +These apply to non-ASCII character sets, which can have single symbols +(called "collating elements") that are represented with more than one +character. They can also have several characters that are equivalent for +"collating", or sorting, purposes. (For example, in French, a plain "e" +and a grave-accented "e`" are equivalent.) + +Collating Symbols + A "collating symbol" is a multicharacter collating element + enclosed between `[.' and `.]'. For example, if `ch' is a + collating element, then `[[.ch.]]' is a regexp that matches this + collating element, whereas `[ch]' is a regexp that matches either + `c' or `h'. + +Equivalence Classes + An "equivalence class" is a locale-specific name for a list of + characters that are equal. The name is enclosed between `[=' and + `=]'. For example, the name `e' might be used to represent all of + "e," "e`," and "e'." In this case, `[[=e=]]' is a regexp that + matches any of `e', `e'', or `e`'. + + These features are very valuable in non-English speaking locales. + + *Caution:* The library functions that `gawk' uses for regular +expression matching currently only recognize POSIX character classes; +they do not recognize collating symbols or equivalence classes. + + +File: gawk.info, Node: GNU Regexp Operators, Next: Case-sensitivity, Prev: Character Lists, Up: Regexp + +`gawk'-Specific Regexp Operators +================================ GNU software that deals with regular expressions provides a number of additional regexp operators. These operators are described in this -section, and are specific to `gawk'; they are not available in other -`awk' implementations. - - Most of the additional operators are for dealing with word matching. -For our purposes, a "word" is a sequence of one or more letters, digits, -or underscores (`_'). +minor node and are specific to `gawk'; they are not available in other +`awk' implementations. Most of the additional operators deal with word +matching. For our purposes, a "word" is a sequence of one or more +letters, digits, or underscores (`_'): `\w' - This operator matches any word-constituent character, i.e. any - letter, digit, or underscore. Think of it as a short-hand for + Matches any word-constituent character--that is, it matches any + letter, digit, or underscore. Think of it as short-hand for `[[:alnum:]_]'. `\W' - This operator matches any character that is not word-constituent. - Think of it as a short-hand for `[^[:alnum:]_]'. + Matches any character that is not word-constituent. Think of it + as short-hand for `[^[:alnum:]_]'. `\<' - This operator matches the empty string at the beginning of a word. - For example, `/\' - This operator matches the empty string at the end of a word. For - example, `/stow\>/' matches `stow', but not `stowaway'. + Matches the empty string at the end of a word. For example, + `/stow\>/' matches `stow' but not `stowaway'. `\y' - This operator matches the empty string at either the beginning or - the end of a word (the word boundar*y*). For example, `\yballs?\y' - matches either `ball' or `balls' as a separate word. + Matches the empty string at either the beginning or the end of a + word (i.e., the word boundar*y*). For example, `\yballs?\y' + matches either `ball' or `balls', as a separate word. `\B' - This operator matches the empty string within a word. In other - words, `\B' matches the empty string that occurs between two - word-constituent characters. For example, `/\Brat\B/' matches - `crate', but it does not match `dirty rat'. `\B' is essentially - the opposite of `\y'. + Matches the empty string that occurs between two word-constituent + characters. For example, `/\Brat\B/' matches `crate' but it does + not match `dirty rat'. `\B' is essentially the opposite of `\y'. There are two other operators that work on buffers. In Emacs, a -"buffer" is, naturally, an Emacs buffer. For other programs, the -regexp library routines that `gawk' uses consider the entire string to -be matched as the buffer. - - For `awk', since `^' and `$' always work in terms of the beginning -and end of strings, these operators don't add any new capabilities. -They are provided for compatibility with other GNU software. +"buffer" is, naturally, an Emacs buffer. For other programs, `gawk''s +regexp library routines consider the entire string to match as the +buffer. `\`' - This operator matches the empty string at the beginning of the - buffer. + Matches the empty string at the beginning of a buffer (string). `\'' - This operator matches the empty string at the end of the buffer. + Matches the empty string at the end of a buffer (string). - In other GNU software, the word boundary operator is `\b'. However, -that conflicts with the `awk' language's definition of `\b' as -backspace, so `gawk' uses a different letter. + Because `^' and `$' always work in terms of the beginning and end of +strings, these operators don't add any new capabilities for `awk'. +They are provided for compatibility with other GNU software. - An alternative method would have been to require two backslashes in -the GNU operators, but this was deemed to be too confusing, and the -current method of using `\y' for the GNU `\b' appears to be the lesser -of two evils. + In other GNU software, the word-boundary operator is `\b'. However, +that conflicts with the `awk' language's definition of `\b' as +backspace, so `gawk' uses a different letter. An alternative method +would have been to require two backslashes in the GNU operators, but +this was deemed too confusing. The current method of using `\y' for the +GNU `\b' appears to be the lesser of two evils. - The various command line options (*note Command Line Options: -Options.) control how `gawk' interprets characters in regexps. + The various command-line options (*note Command-Line Options: +Options.) control how `gawk' interprets characters in regexps: No options In the default case, `gawk' provides all the facilities of POSIX @@ -2102,16 +2498,16 @@ No options expressions are not supported. `--posix' - Only POSIX regexps are supported, the GNU operators are not special + Only POSIX regexps are supported; the GNU operators are not special (e.g., `\w' matches a literal `w'). Interval expressions are allowed. `--traditional' Traditional Unix `awk' regexps are matched. The GNU operators are - not special, interval expressions are not available, and neither - are the POSIX character classes (`[[:alnum:]]' and so on). - Characters described by octal and hexadecimal escape sequences are - treated literally, even if they represent regexp metacharacters. + not special, interval expressions are not available, nor are the + POSIX character classes (`[[:alnum:]]' and so on). Characters + described by octal and hexadecimal escape sequences are treated + literally, even if they represent regexp metacharacters. `--re-interval' Allow interval expressions in regexps, even if `--traditional' has @@ -2120,36 +2516,36 @@ No options  File: gawk.info, Node: Case-sensitivity, Next: Leftmost Longest, Prev: GNU Regexp Operators, Up: Regexp -Case-sensitivity in Matching +Case Sensitivity in Matching ============================ Case is normally significant in regular expressions, both when -matching ordinary characters (i.e. not metacharacters), and inside -character sets. Thus a `w' in a regular expression matches only a -lower-case `w' and not an upper-case `W'. +matching ordinary characters (i.e., not metacharacters) and inside +character sets. Thus, a `w' in a regular expression matches only a +lowercase `w' and not an uppercase `W'. The simplest way to do a case-independent match is to use a character -list: `[Ww]'. However, this can be cumbersome if you need to use it -often; and it can make the regular expressions harder to read. There -are two alternatives that you might prefer. - - One way to do a case-insensitive match at a particular point in the -program is to convert the data to a single case, using the `tolower' or -`toupper' built-in string functions (which we haven't discussed yet; -*note Built-in Functions for String Manipulation: String Functions.). +list--for example, `[Ww]'. However, this can be cumbersome if you need +to use it often and it can make the regular expressions harder to read. +There are two alternatives that you might prefer. + + One way to perform a case-insensitive match at a particular point in +the program is to convert the data to a single case, using the +`tolower' or `toupper' built-in string functions (which we haven't +discussed yet; *note String Manipulation Functions: String Functions.). For example: tolower($1) ~ /foo/ { ... } -converts the first field to lower-case before matching against it. -This will work in any POSIX-compliant implementation of `awk'. +converts the first field to lowercase before matching against it. This +works in any POSIX-compliant `awk'. Another method, specific to `gawk', is to set the variable -`IGNORECASE' to a non-zero value (*note Built-in Variables::). When +`IGNORECASE' to a nonzero value (*note Built-in Variables::). When `IGNORECASE' is not zero, _all_ regexp and string operations ignore case. Changing the value of `IGNORECASE' dynamically controls the case -sensitivity of your program as it runs. Case is significant by default -because `IGNORECASE' (like most variables) is initialized to zero. +sensitivity of the program as it runs. Case is significant by default +because `IGNORECASE' (like most variables) is initialized to zero: x = "aB" if (x ~ /ab/) ... # this test will fail @@ -2158,66 +2554,70 @@ because `IGNORECASE' (like most variables) is initialized to zero. if (x ~ /ab/) ... # now it will succeed In general, you cannot use `IGNORECASE' to make certain rules -case-insensitive and other rules case-sensitive, because there is no way -to set `IGNORECASE' just for the pattern of a particular rule. To do -this, you must use character lists or `tolower'. However, one thing -you can do only with `IGNORECASE' is turn case-sensitivity on or off -dynamically for all the rules at once. - - `IGNORECASE' can be set on the command line, or in a `BEGIN' rule -(*note Other Command Line Arguments: Other Arguments.; also *note +case-insensitive and other rules case-sensitive, because there is no +straightforward way to set `IGNORECASE' just for the pattern of a +particular rule.(1) To do this, use either character lists or +`tolower'. However, one thing you can do with `IGNORECASE' only is +dynamically turn case-sensitivity on or off for all the rules at once. + + `IGNORECASE' can be set on the command line or in a `BEGIN' rule +(*note Other Command-Line Arguments: Other Arguments.; also *note Startup and Cleanup Actions: Using BEGIN/END.). Setting `IGNORECASE' from the command line is a way to make a program case-insensitive without having to edit it. - Prior to version 3.0 of `gawk', the value of `IGNORECASE' only -affected regexp operations. It did not affect string comparison with -`==', `!=', and so on. Beginning with version 3.0, both regexp and -string comparison operations are affected by `IGNORECASE'. + Prior to `gawk' 3.0, the value of `IGNORECASE' affected regexp +operations only. It did not affect string comparison with `==', `!=', +and so on. Beginning with version 3.0, both regexp and string +comparison operations are also affected by `IGNORECASE'. - Beginning with version 3.0 of `gawk', the equivalences between -upper-case and lower-case characters are based on the ISO-8859-1 (ISO -Latin-1) character set. This character set is a superset of the -traditional 128 ASCII characters, that also provides a number of -characters suitable for use with European languages. + Beginning with `gawk' 3.0, the equivalences between upper- and +lowercase characters are based on the ISO-8859-1 (ISO Latin-1) +character set. This character set is a superset of the traditional 128 +ASCII characters, that also provides a number of characters suitable +for use with European languages. The value of `IGNORECASE' has no effect if `gawk' is in -compatibility mode (*note Command Line Options: Options.). Case is +compatibility mode (*note Command-Line Options: Options.). Case is always significant in compatibility mode. + ---------- Footnotes ---------- + + (1) Experienced C and C++ programmers will note that it is possible, +using something like `IGNORECASE = 1 && /foObAr/ { ... }' and +`IGNORECASE = 0 || /foobar/ { ... }'. However, this is somewhat +obscure and we don't recommend it. +  File: gawk.info, Node: Leftmost Longest, Next: Computed Regexps, Prev: Case-sensitivity, Up: Regexp How Much Text Matches? ====================== - Consider the following example: + Consider the following: echo aaaabcd | awk '{ sub(/a+/, ""); print }' - This example uses the `sub' function (which we haven't discussed yet, -*note Built-in Functions for String Manipulation: String Functions.) -to make a change to the input record. Here, the regexp `/a+/' indicates -"one or more `a' characters," and the replacement text is `'. - - The input contains four `a' characters. What will the output be? -In other words, how many is "one or more"--will `awk' match two, three, -or all four `a' characters? + This example uses the `sub' function (which we haven't discussed yet; +*note String Manipulation Functions: String Functions.) to make a +change to the input record. Here, the regexp `/a+/' indicates "one or +more `a' characters," and the replacement text is `'. - The answer is, `awk' (and POSIX) regular expressions always match -the leftmost, _longest_ sequence of input characters that can match. -Thus, in this example, all four `a' characters are replaced with `'. + The input contains four `a' characters. `awk' (and POSIX) regular +expressions always match the leftmost, _longest_ sequence of input +characters that can match. Thus, all four `a' characters are replaced +with `' in this example: $ echo aaaabcd | awk '{ sub(/a+/, ""); print }' -| bcd For simple match/no-match tests, this is not so important. But when doing text matching and substitutions with the `match', `sub', `gsub', -and `gensub' functions, it is very important. *Note Built-in Functions -for String Manipulation: String Functions, for more information on -these functions. Understanding this principle is also important for -regexp-based record and field splitting (*note How Input is Split into -Records: Records., and also *note Specifying How Fields are Separated: +and `gensub' functions, it is very important. *Note String +Manipulation Functions: String Functions, for more information on these +functions. Understanding this principle is also important for +regexp-based record and field splitting (*note How Input Is Split into +Records: Records., and also *note Specifying How Fields Are Separated: Field Separators.).  @@ -2226,27 +2626,27 @@ File: gawk.info, Node: Computed Regexps, Prev: Leftmost Longest, Up: Regexp Using Dynamic Regexps ===================== - The right hand side of a `~' or `!~' operator need not be a regexp -constant (i.e. a string of characters between slashes). It may be any -expression. The expression is evaluated, and converted if necessary to -a string; the contents of the string are used as the regexp. A regexp -that is computed in this way is called a "dynamic regexp". For example: + The righthand side of a `~' or `!~' operator need not be a regexp +constant (i.e., a string of characters between slashes). It may be any +expression. The expression is evaluated and converted to a string if +necessary; the contents of the string are used as the regexp. A regexp +that is computed in this way is called a "dynamic regexp": - BEGIN { identifier_regexp = "[A-Za-z_][A-Za-z_0-9]*" } - $0 ~ identifier_regexp { print } + BEGIN { digits_regexp = "[[:digit:]]+" } + $0 ~ digits_regexp { print } -sets `identifier_regexp' to a regexp that describes `awk' variable -names, and tests if the input record matches this regexp. +This sets `digits_regexp' to a regexp that describes one or more digits, +and tests whether the input record matches this regexp. - *Caution:* When using the `~' and `!~' operators, there is a -difference between a regexp constant enclosed in slashes, and a string -constant enclosed in double quotes. If you are going to use a string -constant, you have to understand that the string is in essence scanned -_twice_; the first time when `awk' reads your program, and the second -time when it goes to match the string on the left-hand side of the -operator with the pattern on the right. This is true of any string -valued expression (such as `identifier_regexp' above), not just string -constants. + When using the `~' and `!~' *Caution:* When using the `~' and `!~' +operators, there is a difference between a regexp constant enclosed in +slashes and a string constant enclosed in double quotes. If you are +going to use a string constant, you have to understand that the string +is, in essence, scanned _twice_: the first time when `awk' reads your +program, and the second time when it goes to match the string on the +lefthand side of the operator with the pattern on the right. This is +true of any string valued expression (such as `digits_regexp' shown +previously), not just string constants. What difference does it make if the string is scanned twice? The answer has to do with escape sequences, and particularly with @@ -2254,28 +2654,51 @@ backslashes. To get a backslash into a regular expression inside a string, you have to type two backslashes. For example, `/\*/' is a regexp constant for a literal `*'. Only -one backslash is needed. To do the same thing with a string, you would -have to type `"\\*"'. The first backslash escapes the second one, so -that the string actually contains the two characters `\' and `*'. +one backslash is needed. To do the same thing with a string, you have +to type `"\\*"'. The first backslash escapes the second one so that +the string actually contains the two characters `\' and `*'. Given that you can use both regexp and string constants to describe regular expressions, which should you use? The answer is "regexp -constants," for several reasons. +constants," for several reasons: - 1. String constants are more complicated to write, and more difficult + * String constants are more complicated to write and more difficult to read. Using regexp constants makes your programs less error-prone. Not understanding the difference between the two kinds of constants is a common source of errors. - 2. It is also more efficient to use regexp constants: `awk' can note - that you have supplied a regexp and store it internally in a form - that makes pattern matching more efficient. When using a string + * It is more efficient to use regexp constants. `awk' can note that + you have supplied a regexp, and store it internally in a form that + makes pattern matching more efficient. When using a string constant, `awk' must first convert the string into this internal - form, and then perform the pattern matching. + form and then perform the pattern matching. - 3. Using regexp constants is better style; it shows clearly that you + * Using regexp constants is better form; it shows clearly that you intend a regexp match. +Advanced Notes: Using `\n' in Character Lists of Dynamic Regexps +---------------------------------------------------------------- + + Some commercial versions of `awk' do not allow the newline character +to be used inside a character list for a dynamic regexp: + + $ awk '$0 ~ "[ \t\n]"' + error--> awk: newline in character class [ + error--> ]... + error--> source line number 1 + error--> context is + error--> >>> <<< + + But a newline in a regexp constant works with no problem: + + $ awk '$0 ~ /[ \t\n]/' + here is a sample line + -| here is a sample line + Ctrl-d + + `gawk' does not have this problem, and it isn't likely to occur +often in practice, but it's worth noting for future reference. +  File: gawk.info, Node: Reading Files, Next: Printing, Prev: Regexp, Up: Top @@ -2283,20 +2706,20 @@ Reading Input Files ******************* In the typical `awk' program, all input is read either from the -standard input (by default the keyboard, but often a pipe from another -command) or from files whose names you specify on the `awk' command -line. If you specify input files, `awk' reads them in order, reading -all the data from one before going on to the next. The name of the -current input file can be found in the built-in variable `FILENAME' -(*note Built-in Variables::). - - The input is read in units called "records", and processed by the +standard input (by default, this is the keyboard but often it is a pipe +from another command), or from files whose names you specify on the +`awk' command line. If you specify input files, `awk' reads them in +order, processing all the data from one before going on to the next. +The name of the current input file can be found in the built-in variable +`FILENAME' (*note Built-in Variables::). + + The input is read in units called "records", and is processed by the rules of your program one record at a time. By default, each record is one line. Each record is automatically split into chunks called "fields". This makes it more convenient for programs to work on the parts of a record. - On rare occasions you will need to use the `getline' command. The + On rare occasions, you may need to use the `getline' command. The `getline' command is valuable, both because it can do explicit input from any number of files, and because the files used with it do not have to be named on the `awk' command line (*note Explicit Input with @@ -2317,38 +2740,47 @@ have to be named on the `awk' command line (*note Explicit Input with  File: gawk.info, Node: Records, Next: Fields, Prev: Reading Files, Up: Reading Files -How Input is Split into Records +How Input Is Split into Records =============================== The `awk' utility divides the input for your `awk' program into -records and fields. Records are separated by a character called the -"record separator". By default, the record separator is the newline -character. This is why records are, by default, single lines. You can -use a different character for the record separator by assigning the -character to the built-in variable `RS'. - - You can change the value of `RS' in the `awk' program, like any -other variable, with the assignment operator, `=' (*note Assignment +records and fields. `awk' keeps track of the number of records that +have been read so far from the current input file. This value is +stored in a built-in variable called `FNR'. It is reset to zero when a +new file is started. Another built-in variable, `NR', is the total +number of input records read so far from all data files. It starts at +zero, but is never automatically reset to zero. + + Records are separated by a character called the "record separator". +By default, the record separator is the newline character. This is why +records are, by default, single lines. A different character can be +used for the record separator by assigning the character to the +built-in variable `RS'. + + Like any other variable, the value of `RS' can be changed in the +`awk' program with the assignment operator, `=' (*note Assignment Expressions: Assignment Ops.). The new record-separator character should be enclosed in quotation marks, which indicate a string constant. Often the right time to do this is at the beginning of -execution, before any input has been processed, so that the very first -record will be read with the proper separator. To do this, use the -special `BEGIN' pattern (*note The `BEGIN' and `END' Special Patterns: -BEGIN/END.). For example: +execution, before any input is processed, so that the very first record +is read with the proper separator. To do this, use the special `BEGIN' +pattern (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.). +For example: - awk 'BEGIN { RS = "/" } ; { print $0 }' BBS-list + awk 'BEGIN { RS = "/" } + { print $0 }' BBS-list changes the value of `RS' to `"/"', before reading any input. This is a string whose first character is a slash; as a result, records are separated by slashes. Then the input file is read, and the second rule in the `awk' program (the action with no pattern) prints each record. -Since each `print' statement adds a newline at the end of its output, +Because each `print' statement adds a newline at the end of its output, the effect of this `awk' program is to copy the input with each slash changed to a newline. Here are the results of running the program on `BBS-list': - $ awk 'BEGIN { RS = "/" } ; { print $0 }' BBS-list + $ awk 'BEGIN { RS = "/" } + > { print $0 }' BBS-list -| aardvark 555-5553 1200 -| 300 B -| alpo-net 555-3412 2400 @@ -2382,11 +2814,15 @@ Files.), the line looks like this: camelot 555-0542 300 C -It only has one baud rate; there are no slashes in the record. +It has one baud rate only, so there are no slashes in the record, +unlike the others which have two or more baud rates. In fact, this +record is treated as part of the record for the `core' BBS; the newline +separating them in the output is the original newline in the data file, +not the one added by `awk' when it printed the record! Another way to change the record separator is on the command line, -using the variable-assignment feature (*note Other Command Line -Arguments: Other Arguments.). +using the variable-assignment feature (*note Other Command-Line +Arguments: Other Arguments.): awk '{ print $0 }' RS="/" BBS-list @@ -2394,50 +2830,49 @@ This sets `RS' to `/' before processing `BBS-list'. Using an unusual character such as `/' for the record separator produces correct behavior in the vast majority of cases. However, the -following (extreme) pipeline prints a surprising `1'. There is one -field, consisting of a newline. The value of the built-in variable -`NF' is the number of fields in the current record. +following (extreme) pipeline prints a surprising `1': $ echo | awk 'BEGIN { RS = "a" } ; { print NF }' -| 1 -Reaching the end of an input file terminates the current input record, -even if the last character in the file is not the character in `RS' -(d.c.). + There is one field, consisting of a newline. The value of the +built-in variable `NF' is the number of fields in the current record. + + Reaching the end of an input file terminates the current input +record, even if the last character in the file is not the character in +`RS'. (d.c.) - The empty string, `""' (a string of no characters), has a special -meaning as the value of `RS': it means that records are separated by -one or more blank lines, and nothing else. *Note Multiple-Line -Records: Multiple Line, for more details. + The empty string `""' (a string without any characters) has a +special meaning as the value of `RS'. It means that records are +separated by one or more blank lines and nothing else. *Note +Multiple-Line Records: Multiple Line, for more details. If you change the value of `RS' in the middle of an `awk' run, the new value is used to delimit subsequent records, but the record -currently being processed (and records already processed) are not +currently being processed, as well as records already processed, are not affected. After the end of the record has been determined, `gawk' sets the -variable `RT' to the text in the input that matched `RS'. - - The value of `RS' is in fact not limited to a one-character string. -It can be any regular expression (*note Regular Expressions: Regexp.). -In general, each record ends at the next string that matches the -regular expression; the next record starts at the end of the matching -string. This general rule is actually at work in the usual case, where -`RS' contains just a newline: a record ends at the beginning of the -next matching string (the next newline in the input) and the following +variable `RT' to the text in the input that matched `RS'. When using +`gawk', the value of `RS' is not limited to a one-character string. It +can be any regular expression (*note Regular Expressions: Regexp.). In +general, each record ends at the next string that matches the regular +expression; the next record starts at the end of the matching string. +This general rule is actually at work in the usual case, where `RS' +contains just a newline: a record ends at the beginning of the next +matching string (the next newline in the input) and the following record starts just after the end of this string (at the first character -of the following line). The newline, since it matches `RS', is not +of the following line). The newline, because it matches `RS', is not part of either record. - When `RS' is a single character, `RT' will contain the same single -character. However, when `RS' is a regular expression, then `RT' -becomes more useful; it contains the actual input text that matched the -regular expression. + When `RS' is a single character, `RT' contains the same single +character. However, when `RS' is a regular expression, `RT' contains +the actual input text that matched the regular expression. The following example illustrates both of these features. It sets -`RS' equal to a regular expression that matches either a newline, or a -series of one or more upper-case letters with optional leading and/or -trailing white space (*note Regular Expressions: Regexp.). +`RS' equal to a regular expression that matches either a newline or a +series of one or more uppercase letters with optional leading and/or +trailing whitespace: $ echo record 1 AAAA record 2 BBBB record 3 | > gawk 'BEGIN { RS = "\n|( *[[:upper:]]+ *)" } @@ -2448,24 +2883,47 @@ trailing white space (*note Regular Expressions: Regexp.). -| The final line of output has an extra blank line. This is because the -value of `RT' is a newline, and then the `print' statement supplies its -own terminating newline. - - *Note A Simple Stream Editor: Simple Sed, for a more useful example -of `RS' as a regexp and `RT'. +value of `RT' is a newline, and the `print' statement supplies its own +terminating newline. *Note A Simple Stream Editor: Simple Sed, for a +more useful example of `RS' as a regexp and `RT'. The use of `RS' as a regular expression and the `RT' variable are `gawk' extensions; they are not available in compatibility mode (*note -Command Line Options: Options.). In compatibility mode, only the first +Command-Line Options: Options.). In compatibility mode, only the first character of the value of `RS' is used to determine the end of the record. - The `awk' utility keeps track of the number of records that have -been read so far from the current input file. This value is stored in a -built-in variable called `FNR'. It is reset to zero when a new file is -started. Another built-in variable, `NR', is the total number of input -records read so far from all data files. It starts at zero but is -never automatically reset to zero. +Advanced Notes: `RS = "\0"' Is Not Portable +------------------------------------------- + + There are times when you might want to treat an entire data file as a +single record. The only way to make this happen is to give `RS' a +value that you know doesn't occur in the input file. This is hard to +do in a general way, such that a program always works for arbitrary +input files. + + You might think that for text files, the NUL character, which +consists of a character with all bits equal to zero, is a good value to +use for `RS' in this case: + + BEGIN { RS = "\0" } # whole file becomes one record? + + `gawk' in fact accepts this, and uses the NUL character for the +record separator. However, this usage is _not_ portable to other `awk' +implementations. + + All other `awk' implementations(1) store strings internally as +C-style strings. C strings use the NUL character as the string +terminator. In effect, this means that `RS = "\0"' is the same as `RS += ""'. (d.c.) + + The best way to treat a whole file as a single record is to simply +read the file in, one record at a time, concatenating each record onto +the end of the previous ones. + + ---------- Footnotes ---------- + + (1) At least that we know about.  File: gawk.info, Node: Fields, Next: Non-Constant Fields, Prev: Records, Up: Reading Files @@ -2475,45 +2933,42 @@ Examining Fields When `awk' reads an input record, the record is automatically separated or "parsed" by the interpreter into chunks called "fields". -By default, fields are separated by whitespace, like words in a line. -Whitespace in `awk' means any string of one or more spaces, tabs or -newlines;(1) other characters such as formfeed, and so on, that are -considered whitespace by other languages are _not_ considered +By default, fields are separated by "whitespace", like words in a line. +Whitespace in `awk' means any string of one or more spaces, tabs, or +newlines;(1) other characters, such as formfeed, vertical tab, etc. +that are considered whitespace by other languages, are _not_ considered whitespace by `awk'. The purpose of fields is to make it more convenient for you to refer to these pieces of the record. You don't have to use them--you can -operate on the whole record if you wish--but fields are what make +operate on the whole record if you want--but fields are what make simple `awk' programs so powerful. - To refer to a field in an `awk' program, you use a dollar-sign, `$', + A dollar-sign (`$') is used to refer to a field in an `awk' program, followed by the number of the field you want. Thus, `$1' refers to the -first field, `$2' to the second, and so on. For example, suppose the -following is a line of input: +first field, `$2' to the second, and so on. (Unlike the Unix shells, +the field numbers are not limited to single digits. `$127' is the one +hundred and twenty-seventh field in the record.) For example, suppose +the following is a line of input: This seems like a pretty nice example. -Here the first field, or `$1', is `This'; the second field, or `$2', is -`seems'; and so on. Note that the last field, `$7', is `example.'. +Here the first field, or `$1', is `This', the second field, or `$2', is +`seems', and so on. Note that the last field, `$7', is `example.'. Because there is no space between the `e' and the `.', the period is considered part of the seventh field. `NF' is a built-in variable whose value is the number of fields in -the current record. `awk' updates the value of `NF' automatically, -each time a record is read. - - No matter how many fields there are, the last field in a record can -be represented by `$NF'. So, in the example above, `$NF' would be the -same as `$7', which is `example.'. Why this works is explained below -(*note Non-constant Field Numbers: Non-Constant Fields.). If you try -to reference a field beyond the last one, such as `$8' when the record -has only seven fields, you get the empty string. - - `$0', which looks like a reference to the "zeroth" field, is a -special case: it represents the whole input record. `$0' is used when -you are not interested in fields. +the current record. `awk' automatically updates the value of `NF' each +time it reads a record. No matter how many fields there are, the last +field in a record can be represented by `$NF'. So, `$NF' is the same +as `$7', which is `example.'. If you try to reference a field beyond +the last one (such as `$8' when the record has only seven fields), you +get the empty string. (If used in a numeric operation, you get zero.) - Here are some more examples: + The use of `$0', which looks like a reference to the "zeroth" field, +is a special case: it represents the whole input record when you are +not interested in specific fields. Here are some more examples: $ awk '$1 ~ /foo/ { print $0 }' BBS-list -| fooey 555-1234 2400/1200/300 B @@ -2528,8 +2983,8 @@ Usage.); it tests whether a string (here, the field `$1') matches a given regular expression. By contrast, the following example looks for `foo' in _the entire -record_ and prints the first field and the last field for each input -record containing a match. +record_ and prints the first field and the last field for each matching +input record: $ awk '/foo/ { print $1, $NF }' BBS-list -| fooey B @@ -2545,7 +3000,7 @@ separating fields.  File: gawk.info, Node: Non-Constant Fields, Next: Changing Fields, Prev: Fields, Up: Reading Files -Non-constant Field Numbers +Non-Constant Field Numbers ========================== The number of a field does not need to be a constant. Any @@ -2560,13 +3015,12 @@ Recall that `NR' is the number of records read so far: one in the first record, two in the second, etc. So this example prints the first field of the first record, the second field of the second record, and so on. For the twentieth record, field number 20 is printed; most likely, the -record has fewer than 20 fields, so this prints a blank line. - - Here is another example of using expressions as field numbers: +record has fewer than 20 fields, so this prints a blank line. Here is +another example of using expressions as field numbers: awk '{ print $(2*2) }' BBS-list - `awk' must evaluate the expression `(2*2)' and use its value as the + `awk' evaluates the expression `(2*2)' and uses its value as the number of the field to print. The `*' sign represents multiplication, so the expression `2*2' evaluates to four. The parentheses are used so that the multiplication is done before the `$' operation; they are @@ -2578,16 +3032,15 @@ Operator Precedence (How Operators Nest): Precedence.) If the field number you compute is zero, you get the entire record. Thus, `$(2-2)' has the same value as `$0'. Negative field numbers are -not allowed; trying to reference one will usually terminate your -running `awk' program. (The POSIX standard does not define what -happens when you reference a negative field number. `gawk' will notice -this and terminate your program. Other `awk' implementations may -behave differently.) - - As mentioned in *Note Examining Fields: Fields, the number of fields -in the current record is stored in the built-in variable `NF' (also +not allowed; trying to reference one usually terminates the program. +(The POSIX standard does not define what happens when you reference a +negative field number. `gawk' notices this and terminates your +program. Other `awk' implementations may behave differently.) + + As mentioned in *Note Examining Fields: Fields, `awk' stores the +current record's number of fields in the built-in variable `NF' (also *note Built-in Variables::). The expression `$NF' is not a special -feature: it is the direct consequence of evaluating `NF' and using its +feature--it is the direct consequence of evaluating `NF' and using its value as a field number.  @@ -2596,36 +3049,38 @@ File: gawk.info, Node: Changing Fields, Next: Field Separators, Prev: Non-Con Changing the Contents of a Field ================================ - You can change the contents of a field as seen by `awk' within an + The contents of a field, as seen by `awk', can be changed within an `awk' program; this changes what `awk' perceives as the current input record. (The actual input is untouched; `awk' _never_ modifies the -input file.) +input file.) Consider this example and its output: - Consider this example and its output: - - $ awk '{ $3 = $2 - 10; print $2, $3 }' inventory-shipped + $ awk '{ nboxes = $3 ; $3 = $3 - 10 + > print nboxes, $3 }' inventory-shipped -| 13 3 -| 15 5 -| 15 5 ... -The `-' sign represents subtraction, so this program reassigns field -three, `$3', to be the value of field two minus ten, `$2 - 10'. (*Note -Arithmetic Operators: Arithmetic Ops.) Then field two, and the new -value for field three, are printed. - - In order for this to work, the text in field `$2' must make sense as -a number; the string of characters must be converted to a number in -order for the computer to do arithmetic on it. The number resulting -from the subtraction is converted back to a string of characters which -then becomes field three. *Note Conversion of Strings and Numbers: +The program first saves the original value of field three in the +variable `nboxes'. The `-' sign represents subtraction, so this +program reassigns field three, `$3', as the original value of field +three minus ten: `$3 - 10'. (*Note Arithmetic Operators: Arithmetic +Ops.) Then it prints the original and new values for field three. +(Someone in the warehouse made a consistent mistake while inventorying +the red boxes.) + + For this to work, the text in field `$2' must make sense as a +number; the string of characters must be converted to a number for the +computer to do arithmetic on it. The number resulting from the +subtraction is converted back to a string of characters that then +becomes field three. *Note Conversion of Strings and Numbers: Conversion. - When you change the value of a field (as perceived by `awk'), the + When the value of a field is changed (as perceived by `awk'), the text of the input record is recalculated to contain the new field where -the old one was. Therefore, `$0' changes to reflect the altered field. -Thus, this program prints a copy of the input file, with 10 subtracted -from the second field of each line. +the old one was. In other words, `$0' changes to reflect the altered +field. Thus, this program prints a copy of the input file, with 10 +subtracted from the second field of each line: $ awk '{ $2 = $2 - 10; print $0 }' inventory-shipped -| Jan 3 25 15 115 @@ -2633,8 +3088,8 @@ from the second field of each line. -| Mar 5 24 34 228 ... - You can also assign contents to fields that are out of range. For -example: + It is also possible to also assign contents to fields that are out +of range. For example: $ awk '{ $6 = ($5 + $4 + $3 + $2) > print $6 }' inventory-shipped @@ -2649,16 +3104,17 @@ We've just created `$6', whose value is the sum of fields `$2', `$3', shipped for a particular month. Creating a new field changes `awk''s internal copy of the current -input record--the value of `$0'. Thus, if you do `print $0' after -adding a field, the record printed includes the new field, with the -appropriate number of field separators between it and the previously +input record, which is the value of `$0'. Thus, if you do `print $0' +after adding a field, the record printed includes the new field, with +the appropriate number of field separators between it and the previously existing fields. This recomputation affects and is affected by `NF' (the number of -fields; *note Examining Fields: Fields.), and by a feature that has not -been discussed yet, the "output field separator", `OFS', which is used -to separate the fields (*note Output Separators::). For example, the -value of `NF' is set to the number of the highest field you create. +fields; *note Examining Fields: Fields.). It is also affected by a +feature that has not been discussed yet: the "output field separator", +`OFS', used to separate the fields (*note Output Separators::). For +example, the value of `NF' is set to the number of the highest field +you create. Note, however, that merely _referencing_ an out-of-range field does _not_ change the value of either `$0' or `NF'. Referencing an @@ -2676,130 +3132,120 @@ and Comparison Expressions: Typing and Comparison, for more information about the `!=' operator.) It is important to note that making an assignment to an existing -field will change the value of `$0', but will not change the value of -`NF', even when you assign the empty string to a field. For example: +field changes the value of `$0' but does not change the value of `NF', +even when you assign the empty string to a field. For example: $ echo a b c d | awk '{ OFS = ":"; $2 = "" > print $0; print NF }' -| a::c:d -| 4 -The field is still there; it just has an empty value. You can tell -because there are two colons in a row. - - This example shows what happens if you create a new field. +The field is still there; it just has an empty value, denoted by the +two colons between `a' and `c'. This example shows what happens if you +create a new field: $ echo a b c d | awk '{ OFS = ":"; $2 = ""; $6 = "new" > print $0; print NF }' -| a::c:d::new -| 6 -The intervening field, `$5' is created with an empty value (indicated +The intervening field, `$5', is created with an empty value (indicated by the second pair of adjacent colons), and `NF' is updated with the value six. - Finally, decrementing `NF' will lose the values of the fields after -the new value of `NF', and `$0' will be recomputed. Here is an example: + Decrementing `NF' throws away the values of the fields after the new +value of `NF' and recomputes `$0'. (d.c.) Here is an example: - $ echo a b c d e f | ../gawk '{ print "NF =", NF; - > NF = 3; print $0 }' + $ echo a b c d e f | awk '{ print "NF =", NF; + > NF = 3; print $0 }' -| NF = 6 -| a b c + *Caution:* Some versions of `awk' don't rebuild `$0' when `NF' is +decremented. Caveat emptor. +  File: gawk.info, Node: Field Separators, Next: Constant Size, Prev: Changing Fields, Up: Reading Files -Specifying How Fields are Separated +Specifying How Fields Are Separated =================================== - This section is rather long; it describes one of the most fundamental -operations in `awk'. - * Menu: -* Basic Field Splitting:: How fields are split with single characters - or simple strings. * Regexp Field Splitting:: Using regexps as the field separator. * Single Character Fields:: Making each character a separate field. -* Command Line Field Separator:: Setting `FS' from the command line. +* Command Line Field Separator:: Setting `FS' from the command-line. * Field Splitting Summary:: Some final points and a summary table. - -File: gawk.info, Node: Basic Field Splitting, Next: Regexp Field Splitting, Prev: Field Separators, Up: Field Separators - -The Basics of Field Separating ------------------------------- - The "field separator", which is either a single character or a regular expression, controls the way `awk' splits an input record into fields. `awk' scans the input record for character sequences that match the separator; the fields themselves are the text between the matches. - In the examples below, we use the bullet symbol "*" to represent -spaces in the output. - - If the field separator is `oo', then the following line: + In the examples that follow, we use the bullet symbol (*) to +represent spaces in the output. If the field separator is `oo', then +the following line: moo goo gai pan -would be split into three fields: `m', `*g' and `*gai*pan'. Note the +is split into three fields: `m', `*g', and `*gai*pan'. Note the leading spaces in the values of the second and third fields. The field separator is represented by the built-in variable `FS'. -Shell programmers take note! `awk' does _not_ use the name `IFS' which -is used by the POSIX compatible shells (such as the Bourne shell, `sh', -or the GNU Bourne-Again Shell, Bash). +Shell programmers take note: `awk' does _not_ use the name `IFS' that +is used by the POSIX-compliant shells (such as the Unix Bourne shell, +`sh', or `bash'). - You can change the value of `FS' in the `awk' program with the + The value of `FS' can be changed in the `awk' program with the assignment operator, `=' (*note Assignment Expressions: Assignment -Ops.). Often the right time to do this is at the beginning of -execution, before any input has been processed, so that the very first -record will be read with the proper separator. To do this, use the -special `BEGIN' pattern (*note The `BEGIN' and `END' Special Patterns: -BEGIN/END.). For example, here we set the value of `FS' to the string -`","': +Ops.). Often the right time to do this is at the beginning of execution +before any input has been processed, so that the very first record is +read with the proper separator. To do this, use the special `BEGIN' +pattern (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.). +For example, here we set the value of `FS' to the string `","': awk 'BEGIN { FS = "," } ; { print $2 }' -Given the input line, +Given the input line: John Q. Smith, 29 Oak St., Walamazoo, MI 42139 this `awk' program extracts and prints the string `*29*Oak*St.'. - Sometimes your input data will contain separator characters that -don't separate fields the way you thought they would. For instance, the + Sometimes the input data contains separator characters that don't +separate fields the way you thought they would. For instance, the person's name in the example we just used might have a title or suffix -attached, such as `John Q. Smith, LXIX'. From input containing such a -name: +attached, such as: John Q. Smith, LXIX, 29 Oak St., Walamazoo, MI 42139 -the above program would extract `*LXIX', instead of `*29*Oak*St.'. If +The same program would extract `*LXIX', instead of `*29*Oak*St.'. If you were expecting the program to print the address, you would be -surprised. The moral is: choose your data layout and separator -characters carefully to prevent such problems. - - Normally, fields are separated by whitespace sequences (spaces, tabs -and newlines), not by single spaces: two spaces in a row do not delimit -an empty field. The default value of the field separator `FS' is a -string containing a single space, `" "'. If this value were -interpreted in the usual way, each space character would separate +surprised. The moral is to choose your data layout and separator +characters carefully to prevent such problems. (If the data is not in +a form that is easy to process, perhaps you can massage it first with a +separate `awk' program.) + + Fields are normally separated by whitespace sequences (spaces, tabs, +and newlines), not by single spaces. Two spaces in a row do not +delimit an empty field. The default value of the field separator `FS' +is a string containing a single space, `" "'. If `awk' interpreted +this value in the usual way, each space character would separate fields, so two spaces in a row would make an empty field between them. The reason this does not happen is that a single space as the value of -`FS' is a special case: it is taken to specify the default manner of +`FS' is a special case--it is taken to specify the default manner of delimiting fields. If `FS' is any other single character, such as `","', then each occurrence of that character separates two fields. Two consecutive occurrences delimit an empty field. If the character occurs at the beginning or the end of the line, that too delimits an empty field. The -space character is the only single character which does not follow these +space character is the only single character that does not follow these rules.  -File: gawk.info, Node: Regexp Field Splitting, Next: Single Character Fields, Prev: Basic Field Splitting, Up: Field Separators +File: gawk.info, Node: Regexp Field Splitting, Next: Single Character Fields, Prev: Field Separators, Up: Field Separators Using Regular Expressions to Separate Fields -------------------------------------------- @@ -2813,26 +3259,24 @@ example, the assignment: FS = ", \t" makes every area of an input line that consists of a comma followed by a -space and a tab, into a field separator. (`\t' is an "escape sequence" +space and a tab into a field separator. (`\t' is an "escape sequence" that stands for a tab; *note Escape Sequences::, for the complete list of similar escape sequences.) - For a less trivial example of a regular expression, suppose you want -single spaces to separate fields the way single commas were used above. -You can set `FS' to `"[ ]"' (left bracket, space, right bracket). This -regular expression matches a single space and nothing else (*note -Regular Expressions: Regexp.). + For a less trivial example of a regular expression, try using single +spaces to separate fields the way single commas are used. `FS' can be +set to `"[ ]"' (left bracket, space, right bracket). This regular +expression matches a single space and nothing else (*note Regular +Expressions: Regexp.). There is an important difference between the two cases of `FS = " "' -(a single space) and `FS = "[ \t\n]+"' (left bracket, space, backslash, -"t", backslash, "n", right bracket, which is a regular expression -matching one or more spaces, tabs, or newlines). For both values of -`FS', fields are separated by runs of spaces, tabs and/or newlines. -However, when the value of `FS' is `" "', `awk' will first strip -leading and trailing whitespace from the record, and then decide where -the fields are. - - For example, the following pipeline prints `b': +(a single space) and `FS = "[ \t\n]+"' (a regular expression matching +one or more spaces, tabs, or newlines). For both values of `FS', +fields are separated by "runs" (multiple adjacent occurrences) of +spaces, tabs, and/or newlines. However, when the value of `FS' is +`" "', `awk' first strips leading and trailing whitespace from the +record and then decides where the fields are. For example, the +following pipeline prints `b': $ echo ' a b c d ' | awk '{ print $2 }' -| b @@ -2840,11 +3284,11 @@ the fields are. However, this pipeline prints `a' (note the extra spaces around each letter): - $ echo ' a b c d ' | awk 'BEGIN { FS = "[ \t]+" } + $ echo ' a b c d ' | awk 'BEGIN { FS = "[ \t\n]+" } > { print $2 }' -| a -In this case, the first field is "null", or empty. +In this case, the first field is "null" or empty. The stripping of leading and trailing whitespace also comes into play whenever `$0' is recomputed. For instance, study this pipeline: @@ -2856,8 +3300,8 @@ play whenever `$0' is recomputed. For instance, study this pipeline: The first `print' statement prints the record as it was read, with leading whitespace intact. The assignment to `$2' rebuilds `$0' by concatenating `$1' through `$NF' together, separated by the value of -`OFS'. Since the leading whitespace was ignored when finding `$1', it -is not part of the new `$0'. Finally, the last `print' statement +`OFS'. Because the leading whitespace was ignored when finding `$1', +it is not part of the new `$0'. Finally, the last `print' statement prints the new `$0'.  @@ -2867,9 +3311,9 @@ Making Each Character a Separate Field -------------------------------------- There are times when you may want to examine each character of a -record separately. In `gawk', this is easy to do, you simply assign -the null string (`""') to `FS'. In this case, each individual character -in the record will become a separate field. Here is an example: +record separately. This can be done in `gawk' by simply assigning the +null string (`""') to `FS'. In this case, each individual character in +the record becomes a separate field. For example: $ echo a b | gawk 'BEGIN { FS = "" } > { @@ -2880,11 +3324,11 @@ in the record will become a separate field. Here is an example: -| Field 2 is -| Field 3 is b - Traditionally, the behavior for `FS' equal to `""' was not defined. -In this case, Unix `awk' would simply treat the entire record as only -having one field (d.c.). In compatibility mode (*note Command Line -Options: Options.), if `FS' is the null string, then `gawk' will also -behave this way. + Traditionally, the behavior of `FS' equal to `""' was not defined. +In this case, most versions of Unix `awk' simply treat the entire record +as only having one field. (d.c.) In compatibility mode (*note +Command-Line Options: Options.), if `FS' is the null string, then +`gawk' also behaves this way.  File: gawk.info, Node: Command Line Field Separator, Next: Field Splitting Summary, Prev: Single Character Fields, Up: Field Separators @@ -2892,47 +3336,46 @@ File: gawk.info, Node: Command Line Field Separator, Next: Field Splitting Sum Setting `FS' from the Command Line ---------------------------------- - `FS' can be set on the command line. You use the `-F' option to do -so. For example: + `FS' can be set on the command line. Use the `-F' option to do so. +For example: awk -F, 'PROGRAM' INPUT-FILES -sets `FS' to be the `,' character. Notice that the option uses a -capital `F'. Contrast this with `-f', which specifies a file -containing an `awk' program. Case is significant in command line -options: the `-F' and `-f' options have nothing to do with each other. -You can use both options at the same time to set the `FS' variable -_and_ get an `awk' program from a file. +sets `FS' to the `,' character. Notice that the option uses a capital +`F' instead of a lowercase `-f', which specifies a file containing an +`awk' program. Case is significant in command-line options: the `-F' +and `-f' options have nothing to do with each other. You can use both +options at the same time to set the `FS' variable _and_ get an `awk' +program from a file. The value used for the argument to `-F' is processed in exactly the -same way as assignments to the built-in variable `FS'. This means that -if the field separator contains special characters, they must be escaped -appropriately. For example, to use a `\' as the field separator, you +same way as assignments to the built-in variable `FS'. Any special +characters in the field separator must be escaped appropriately. For +example, to use a `\' as the field separator on the command line, you would have to type: # same as FS = "\\" awk -F\\\\ '...' files ... -Since `\' is used for quoting in the shell, `awk' will see `-F\\'. -Then `awk' processes the `\\' for escape characters (*note Escape -Sequences::), finally yielding a single `\' to be used for the field +Because `\' is used for quoting in the shell, `awk' sees `-F\\'. Then +`awk' processes the `\\' for escape characters (*note Escape +Sequences::), finally yielding a single `\' to use for the field separator. - As a special case, in compatibility mode (*note Command Line + As a special case, in compatibility mode (*note Command-Line Options: Options.), if the argument to `-F' is `t', then `FS' is set to -the tab character. This is because if you type `-F\t' at the shell, -without any quotes, the `\' gets deleted, so `awk' figures that you -really want your fields to be separated with tabs, and not `t's. Use -`-v FS="t"' on the command line if you really do want to separate your -fields with `t's (*note Command Line Options: Options.). +the tab character. If you type `-F\t' at the shell, without any +quotes, the `\' gets deleted, so `awk' figures that you really want +your fields to be separated with tabs and not `t's. Use `-v FS="t"' or +`-F"[t]"' on the command line if you really do want to separate your +fields with `t's. For example, let's use an `awk' program file called `baud.awk' that -contains the pattern `/300/', and the action `print $1'. Here is the -program: +contains the pattern `/300/' and the action `print $1': /300/ { print $1 } - Let's also set `FS' to be the `-' character, and run the program on + Let's also set `FS' to be the `-' character and run the program on the file `BBS-list'. The following command prints a list of the names of the bulletin boards that operate at 300 baud and the first three digits of their phone numbers: @@ -2941,10 +3384,17 @@ digits of their phone numbers: -| aardvark 555 -| alpo -| barfly 555 - ... - -Note the second line of output. In the original file (*note Data Files -for the Examples: Sample Data Files.), the second line looked like this: + -| bites 555 + -| camelot 555 + -| core 555 + -| fooey 555 + -| foot 555 + -| macfoo 555 + -| sdace 555 + -| sabafoo 555 + +Note the second line of output. The second line in the original file +looked like this: alpo-net 555-3412 2400/1200/300 A @@ -2953,15 +3403,17 @@ separator, instead of the `-' in the phone number that was originally intended. This demonstrates why you have to be careful in choosing your field and record separators. - On many Unix systems, each user has a separate entry in the system -password file, one line per user. The information in these lines is -separated by colons. The first field is the user's logon name, and the -second is the user's encrypted password. A password file entry might + Perhaps the most common use of a single character as the field +separator occurs when processing the Unix system password file. On +many Unix systems, each user has a separate entry in the system password +file, one line per user. The information in these lines is separated +by colons. The first field is the user's logon name and the second is +the user's (encrypted or shadow) password. A password file entry might look like this: - arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/sh + arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/bash - The following program searches the system password file, and prints + The following program searches the system password file and prints the entries for users who have no password: awk -F: '$2 == ""' /etc/passwd @@ -2972,30 +3424,6 @@ File: gawk.info, Node: Field Splitting Summary, Prev: Command Line Field Separ Field Splitting Summary ----------------------- - According to the POSIX standard, `awk' is supposed to behave as if -each record is split into fields at the time that it is read. In -particular, this means that you can change the value of `FS' after a -record is read, and the value of the fields (i.e. how they were split) -should reflect the old value of `FS', not the new one. - - However, many implementations of `awk' do not work this way. -Instead, they defer splitting the fields until a field is actually -referenced. The fields will be split using the _current_ value of -`FS'! (d.c.) This behavior can be difficult to diagnose. The following -example illustrates the difference between the two methods. (The -`sed'(1) command prints just the first line of `/etc/passwd'.) - - sed 1q /etc/passwd | awk '{ FS = ":" ; print $1 }' - -will usually print - - root - -on an incorrect implementation of `awk', while `gawk' will print -something like - - root:nSijPlPhZZwgE:0:0:Root:/: - The following table summarizes how fields are split, based on the value of `FS'. (`==' means "is equal to.") @@ -3016,6 +3444,35 @@ value of `FS'. (`==' means "is equal to.") `FS == ""' Each individual character in the record becomes a separate field. + (This is a `gawk' extension; it is not specified by the POSIX + standard.) + +Advanced Notes: Changing `FS' Does Not Affect the Fields +-------------------------------------------------------- + + According to the POSIX standard, `awk' is supposed to behave as if +each record is split into fields at the time it is read. In +particular, this means that if you change the value of `FS' after a +record is read, the value of the fields (i.e., how they were split) +should reflect the old value of `FS', not the new one. + + However, many implementations of `awk' do not work this way. +Instead, they defer splitting the fields until a field is actually +referenced. The fields are split using the _current_ value of `FS'! +(d.c.) This behavior can be difficult to diagnose. The following +example illustrates the difference between the two methods. (The +`sed'(1) command prints just the first line of `/etc/passwd'.) + + sed 1q /etc/passwd | awk '{ FS = ":" ; print $1 }' + +which usually prints: + + root + +on an incorrect implementation of `awk', while `gawk' prints something +like: + + root:nSijPlPhZZwgE:0:0:Root:/: ---------- Footnotes ---------- @@ -3025,35 +3482,35 @@ defined by the POSIX standard.  File: gawk.info, Node: Constant Size, Next: Multiple Line, Prev: Field Separators, Up: Reading Files -Reading Fixed-width Data +Reading Fixed-Width Data ======================== - (This section discusses an advanced, experimental feature. If you -are a novice `awk' user, you may wish to skip it on the first reading.) + (This minor node discusses an advanced feature of `awk'. If you are +a novice `awk' user, you might want to skip it on the first reading.) - `gawk' version 2.13 introduced a new facility for dealing with -fixed-width fields with no distinctive field separator. Data of this -nature arises, for example, in the input for old FORTRAN programs where -numbers are run together; or in the output of programs that did not + `gawk' version 2.13 introduced a facility for dealing with +fixed-width fields with no distinctive field separator. For example, +data of this nature arises in the input for old Fortran programs where +numbers are run together, or in the output of programs that did not anticipate the use of their output as input for other programs. An example of the latter is a table where all the columns are lined up by the use of a variable number of spaces and _empty fields are just -spaces_. Clearly, `awk''s normal field splitting based on `FS' will +spaces_. Clearly, `awk''s normal field splitting based on `FS' does not work well in this case. Although a portable `awk' program can use -a series of `substr' calls on `$0' (*note Built-in Functions for String -Manipulation: String Functions.), this is awkward and inefficient for a +a series of `substr' calls on `$0' (*note String Manipulation +Functions: String Functions.), this is awkward and inefficient for a large number of fields. The splitting of an input record into fixed-width fields is specified by assigning a string containing space-separated numbers to the built-in variable `FIELDWIDTHS'. Each number specifies the width -of the field _including_ columns between fields. If you want to ignore -the columns between fields, you can specify the width as a separate -field that is subsequently ignored. - - The following data is the output of the Unix `w' utility. It is -useful to illustrate the use of `FIELDWIDTHS'. +of the field, _including_ columns between fields. If you want to +ignore the columns between fields, you can specify the width as a +separate field that is subsequently ignored. It is a fatal error to +supply a field width that is not a positive number. The following data +is the output of the Unix `w' utility. It is useful to illustrate the +use of `FIELDWIDTHS': 10:06pm up 21 days, 14:04, 23 users User tty login idle JCPU PCPU what @@ -3067,9 +3524,11 @@ useful to illustrate the use of `FIELDWIDTHS'. dave ttyq4 26Jun9115days 46 46 wnewmail The following program takes the above input, converts the idle time -to number of seconds and prints out the first two fields and the -calculated idle time. (This program uses a number of `awk' features -that haven't been introduced yet.) +to number of seconds, and prints out the first two fields and the +calculated idle time. + + *Note:* This program uses a number of `awk' features that haven't +been introduced yet. BEGIN { FIELDWIDTHS = "9 6 10 6 7 7 35" } NR > 2 { @@ -3087,7 +3546,7 @@ that haven't been introduced yet.) print $1, $2, idle } - Here is the result of running the program on the data: + Running the program on the data produces the following results: hzuo ttyV0 0 hzang ttyV3 50 @@ -3099,10 +3558,10 @@ that haven't been introduced yet.) dave ttyq4 1296000 Another (possibly more practical) example of fixed-width input data -would be the input from a deck of balloting cards. In some parts of -the United States, voters mark their choices by punching holes in -computer cards. These cards are then processed to count the votes for -any particular candidate or on any particular issue. Since a voter may +is the input from a deck of balloting cards. In some parts of the +United States, voters mark their choices by punching holes in computer +cards. These cards are then processed to count the votes for any +particular candidate or on any particular issue. Because a voter may choose not to vote on some issue, any column on the card may be empty. An `awk' program for processing such data could use the `FIELDWIDTHS' feature to simplify reading the data. (Of course, getting `gawk' to @@ -3110,11 +3569,21 @@ run on a system with card readers is another story!) Assigning a value to `FS' causes `gawk' to return to using `FS' for field splitting. Use `FS = FS' to make this happen, without having to -know the current value of `FS'. +know the current value of `FS'. In order to tell which kind of field +splitting is in effect, use `PROCINFO["FS"]' (*note Built-in Variables +That Convey Information: Auto-set.). The value is `"FS"' if regular +field splitting is being used, or it is `"FIELDWIDTHS"' if fixed-width +field splitting is being used: + + if (PROCINFO["FS"] == "FS") + REGULAR FIELD SPLITTING ... + else + FIXED-WIDTH FIELD SPLITTING ... - This feature is still experimental, and may evolve over time. Note -that in particular, `gawk' does not attempt to verify the sanity of the -values used in the value of `FIELDWIDTHS'. + This information is useful when writing a function that needs to +temporarily change `FS' or `FIELDWIDTHS', read some records, and then +restore the original settings (*note Reading the User Database: Passwd +Functions., for an example of such a function).  File: gawk.info, Node: Multiple Line, Next: Getline, Prev: Constant Size, Up: Reading Files @@ -3122,13 +3591,9 @@ File: gawk.info, Node: Multiple Line, Next: Getline, Prev: Constant Size, Up Multiple-Line Records ===================== - In some data bases, a single line cannot conveniently hold all the -information in one entry. In such cases, you can use multi-line -records. - - The first step in doing this is to choose your data format: when -records are not defined as single lines, how do you want to define them? -What should separate records? + In some databases, a single line cannot conveniently hold all the +information in one entry. In such cases, you can use multiline +records. The first step in doing this is to choose your data format. One technique is to use an unusual character or string to separate records. For example, you could use the formfeed character (written @@ -3139,49 +3604,49 @@ well be used, as long as it won't be part of the data in a record. Another technique is to have blank lines separate records. By a special dispensation, an empty string as the value of `RS' indicates -that records are separated by one or more blank lines. If you set `RS' -to the empty string, a record always ends at the first blank line -encountered. And the next record doesn't start until the first -non-blank line that follows--no matter how many blank lines appear in a -row, they are considered one record-separator. +that records are separated by one or more blank lines. When `RS' is set +to the empty string, each record always ends at the first blank line +encountered. The next record doesn't start until the first non-blank +line that follows. No matter how many blank lines appear in a row, they +all act as one record separator. (Blank lines must be completely +empty; lines that contain only whitespace do not count.) You can achieve the same effect as `RS = ""' by assigning the string `"\n\n+"' to `RS'. This regexp matches the newline at the end of the -record, and one or more blank lines after the record. In addition, a +record and one or more blank lines after the record. In addition, a regular expression always matches the longest possible sequence when there is a choice (*note How Much Text Matches?: Leftmost Longest.). So the next record doesn't start until the first non-blank line that follows--no matter how many blank lines appear in a row, they are -considered one record-separator. +considered one record separator. There is an important difference between `RS = ""' and `RS = "\n\n+"'. In the first case, leading newlines in the input data file are ignored, and if a file ends without extra blank lines after the last record, the final newline is removed from the record. In the -second case, this special processing is not done (d.c.). +second case, this special processing is not done. (d.c.) Now that the input is separated into records, the second step is to separate the fields in the record. One way to do this is to divide each of the lines into fields in the normal manner. This happens by default -as the result of a special feature: when `RS' is set to the empty +as the result of a special feature. When `RS' is set to the empty string, the newline character _always_ acts as a field separator. This is in addition to whatever field separations result from `FS'. The original motivation for this special exception was probably to -provide useful behavior in the default case (i.e. `FS' is equal to +provide useful behavior in the default case (i.e., `FS' is equal to `" "'). This feature can be a problem if you really don't want the -newline character to separate fields, since there is no way to prevent -it. However, you can work around this by using the `split' function to -break up the record manually (*note Built-in Functions for String -Manipulation: String Functions.). +newline character to separate fields, because there is no way to +prevent it. However, you can work around this by using the `split' +function to break up the record manually (*note String Manipulation +Functions: String Functions.). Another way to separate fields is to put each field on a separate line: to do this, just set the variable `FS' to the string `"\n"'. -(This simple regular expression matches a single newline.) - - A practical example of a data file organized this way might be a -mailing list, where each entry is separated by blank lines. If we have -a mailing list in a file named `addresses', that looks like this: +(This simple regular expression matches a single newline.) A practical +example of a data file organized this way might be a mailing list, +where each entry is separated by blank lines. Consider a mailing list +in a file named `addresses', that looks like this: Jane Doe 123 Main Street @@ -3192,7 +3657,7 @@ a mailing list in a file named `addresses', that looks like this: Smallville, MW 98765-4321 ... -A simple program to process this file would look like this: +A simple program to process this file is as follows: # addrs.awk --- simple mailing list program @@ -3221,10 +3686,9 @@ A simple program to process this file would look like this: ... *Note Printing Mailing Labels: Labels Program, for a more realistic -program that deals with address lists. - - The following table summarizes how records are split, based on the -value of `RS'. (`==' means "is equal to.") +program that deals with address lists. The following table summarizes +how records are split, based on the value of `RS'. (`==' means "is +equal to.") `RS == "\n"' Records are separated by the newline character (`\n'). In effect, @@ -3244,7 +3708,8 @@ value of `RS'. (`==' means "is equal to.") `RS == REGEXP' Records are separated by occurrences of characters that match REGEXP. Leading and trailing matches of REGEXP delimit empty - records. + records. (This is a `gawk' extension, it is not specified by the + POSIX standard.) In all cases, `gawk' sets `RT' to the input text that matched the value specified by `RS'. @@ -3261,43 +3726,40 @@ output from another program) or from the files specified on the command line. The `awk' language has a special built-in command called `getline' that can be used to read input under your explicit control. -* Menu: - -* Getline Intro:: Introduction to the `getline' function. -* Plain Getline:: Using `getline' with no arguments. -* Getline/Variable:: Using `getline' into a variable. -* Getline/File:: Using `getline' from a file. -* Getline/Variable/File:: Using `getline' into a variable from a - file. -* Getline/Pipe:: Using `getline' from a pipe. -* Getline/Variable/Pipe:: Using `getline' into a variable from a - pipe. -* Getline Summary:: Summary Of `getline' Variants. - - -File: gawk.info, Node: Getline Intro, Next: Plain Getline, Prev: Getline, Up: Getline - -Introduction to `getline' -------------------------- - - This command is used in several different ways, and should _not_ be -used by beginners. It is covered here because this is the chapter on -input. The examples that follow the explanation of the `getline' -command include material that has not been covered yet. Therefore, -come back and study the `getline' command _after_ you have reviewed the -rest of this Info file and have a good knowledge of how `awk' works. + The `getline' command is used in several different ways and should +_not_ be used by beginners. The examples that follow the explanation +of the `getline' command include material that has not been covered +yet. Therefore, come back and study the `getline' command _after_ you +have reviewed the rest of this Info file and have a good knowledge of +how `awk' works. - `getline' returns one if it finds a record, and zero if the end of -the file is encountered. If there is some error in getting a record, -such as a file that cannot be opened, then `getline' returns -1. In -this case, `gawk' sets the variable `ERRNO' to a string describing the -error that occurred. + The `getline' command returns one if it finds a record and zero if +the end of the file is encountered. If there is some error in getting +a record, such as a file that cannot be opened, then `getline' returns +-1. In this case, `gawk' sets the variable `ERRNO' to a string +describing the error that occurred. In the following examples, COMMAND stands for a string value that represents a shell command. +* Menu: + +* Plain Getline:: Using `getline' with no arguments. +* Getline/Variable:: Using `getline' into a variable. +* Getline/File:: Using `getline' from a file. +* Getline/Variable/File:: Using `getline' into a variable from a + file. +* Getline/Pipe:: Using `getline' from a pipe. +* Getline/Variable/Pipe:: Using `getline' into a variable from a + pipe. +* Getline/Coprocess:: Using `getline' from a coprocess. +* Getline/Variable/Coprocess:: Using `getline' into a variable from a + coprocess. +* Getline Notes:: Important things to know about `getline'. +* Getline Summary:: Summary of `getline' Variants. +  -File: gawk.info, Node: Plain Getline, Next: Getline/Variable, Prev: Getline Intro, Up: Getline +File: gawk.info, Node: Plain Getline, Next: Getline/Variable, Prev: Getline, Up: Getline Using `getline' with No Arguments --------------------------------- @@ -3305,12 +3767,12 @@ Using `getline' with No Arguments The `getline' command can be used without arguments to read input from the current input file. All it does in this case is read the next input record and split it up into fields. This is useful if you've -finished processing the current record, but you want to do some special +finished processing the current record, but want to do some special processing _right now_ on the next record. Here's an example: - awk '{ + { if ((t = index($0, "/*")) != 0) { - # value will be "" if t is 1 + # value of `tmp' will be "" if t is 1 tmp = substr($0, 1, t - 1) u = index(substr($0, t + 2), "*/") while (u == 0) { @@ -3325,70 +3787,65 @@ processing _right now_ on the next record. Here's an example: } # substr expression will be "" if */ # occurred at end of line - $0 = tmp substr($0, t + u + 3) + $0 = tmp substr($0, u + 2) } print $0 - }' + } - This `awk' program deletes all C-style comments, `/* ... */', from + This `awk' program deletes all C-style comments (`/* ... */') from the input. By replacing the `print $0' with other statements, you could perform more complicated processing on the decommented input, -like searching for matches of a regular expression. This program has a -subtle problem--it does not work if one comment ends and another begins -on the same line. +such as searching for matches of a regular expression. (This program +has a subtle problem--it does not work if one comment ends and another +begins on the same line.) - This form of the `getline' command sets `NF' (the number of fields; -*note Examining Fields: Fields.), `NR' (the number of records read so -far; *note How Input is Split into Records: Records.), `FNR' (the -number of records read from this input file), and the value of `$0'. + This form of the `getline' command sets `NF', `NR', `FNR', and the +value of `$0'. - *Note:* the new value of `$0' is used in testing the patterns of any + *Note:* The new value of `$0' is used to test the patterns of any subsequent rules. The original value of `$0' that triggered the rule -which executed `getline' is lost (d.c.). By contrast, the `next' -statement reads a new record but immediately begins processing it -normally, starting with the first rule in the program. *Note The -`next' Statement: Next Statement. +that executed `getline' is lost. By contrast, the `next' statement +reads a new record but immediately begins processing it normally, +starting with the first rule in the program. *Note The `next' +Statement: Next Statement.  File: gawk.info, Node: Getline/Variable, Next: Getline/File, Prev: Plain Getline, Up: Getline -Using `getline' Into a Variable +Using `getline' into a Variable ------------------------------- You can use `getline VAR' to read the next record from `awk''s input -into the variable VAR. No other processing is done. +into the variable VAR. No other processing is done. For example, +suppose the next line is a comment or a special string, and you want to +read it without triggering any rules. This form of `getline' allows +you to read that line and store it in a variable so that the main +read-a-line-and-check-each-rule loop of `awk' never sees it. The +following example swaps every two lines of input. The program is as +follows: - For example, suppose the next line is a comment, or a special string, -and you want to read it, without triggering any rules. This form of -`getline' allows you to read that line and store it in a variable so -that the main read-a-line-and-check-each-rule loop of `awk' never sees -it. + { + if ((getline tmp) > 0) { + print tmp + print $0 + } else + print $0 + } - The following example swaps every two lines of input. For example, -given: +It takes the following list: wan tew free phore -it outputs: +and produces these results: tew wan phore free -Here's the program: - - awk '{ - if ((getline tmp) > 0) { - print tmp - print $0 - } else - print $0 - }' - The `getline' command used in this way sets only the variables `NR' and `FNR' (and of course, VAR). The record is not split into fields, so the values of the fields (including `$0') and the value of `NF' do @@ -3400,68 +3857,59 @@ File: gawk.info, Node: Getline/File, Next: Getline/Variable/File, Prev: Getli Using `getline' from a File --------------------------- - Use `getline < FILE' to read the next record from the file FILE. -Here FILE is a string-valued expression that specifies the file name. -`< FILE' is called a "redirection" since it directs input to come from -a different place. + Use `getline < FILE' to read the next record from FILE. Here FILE +is a string-valued expression that specifies the file name. `< FILE' +is called a "redirection" because it directs input to come from a +different place. For example, the following program reads its input +record from the file `secondary.input' when it encounters a first field +with a value equal to 10 in the current input file: - For example, the following program reads its input record from the -file `secondary.input' when it encounters a first field with a value -equal to 10 in the current input file. - - awk '{ + { if ($1 == 10) { getline < "secondary.input" print } else print - }' + } - Since the main input stream is not used, the values of `NR' and -`FNR' are not changed. But the record read is split into fields in the -normal manner, so the values of `$0' and other fields are changed. So -is the value of `NF'. + Because the main input stream is not used, the values of `NR' and +`FNR' are not changed. However, the record it reads is split into +fields in the normal manner, so the values of `$0' and the other fields +are changed, resulting in a new value of `NF'. According to POSIX, `getline < EXPRESSION' is ambiguous if EXPRESSION contains unparenthesized operators other than `$'; for example, `getline < dir "/" file' is ambiguous because the -concatenation operator is not parenthesized, and you should write it as +concatenation operator is not parenthesized. You should write it as `getline < (dir "/" file)' if you want your program to be portable to -other `awk' implementations. +other `awk' implementations. (It happens that `gawk' gets it right, +but you should not rely on this. Parentheses make it easier to read.)  File: gawk.info, Node: Getline/Variable/File, Next: Getline/Pipe, Prev: Getline/File, Up: Getline -Using `getline' Into a Variable from a File +Using `getline' into a Variable from a File ------------------------------------------- - Use `getline VAR < FILE' to read input the file FILE and put it in -the variable VAR. As above, FILE is a string-valued expression that -specifies the file from which to read. + Use `getline VAR < FILE' to read input from the file FILE, and put +it in the variable VAR. As above, FILE is a string-valued expression +that specifies the file from which to read. In this version of `getline', none of the built-in variables are -changed, and the record is not split into fields. The only variable -changed is VAR. - - According to POSIX, `getline VAR < EXPRESSION' is ambiguous if -EXPRESSION contains unparenthesized operators other than `$'; for -example, `getline < dir "/" file' is ambiguous because the -concatenation operator is not parenthesized, and you should write it as -`getline < (dir "/" file)' if you want your program to be portable to -other `awk' implementations. - - For example, the following program copies all the input files to the -output, except for records that say `@include FILENAME'. Such a record -is replaced by the contents of the file FILENAME. +changed and the record is not split into fields. The only variable +changed is VAR. For example, the following program copies all the +input files to the output, except for records that say +`@include FILENAME'. Such a record is replaced by the contents of the +file FILENAME: - awk '{ + { if (NF == 2 && $1 == "@include") { while ((getline line < $2) > 0) print line close($2) } else print - }' + } Note here how the name of the extra input file is not built into the program; it is taken directly from the data, from the second field on @@ -3469,13 +3917,13 @@ the `@include' line. The `close' function is called to ensure that if two identical `@include' lines appear in the input, the entire specified file is -included twice. *Note Closing Input and Output Files and Pipes: Close +included twice. *Note Closing Input and Output Redirections: Close Files And Pipes. One deficiency of this program is that it does not process nested -`@include' statements (`@include' statements in included files) the way -a true macro preprocessor would. *Note An Easy Way to Use Library -Functions: Igawk Program, for a program that does handle nested +`@include' statements (i.e., `@include' statements in included files) +the way a true macro preprocessor would. *Note An Easy Way to Use +Library Functions: Igawk Program, for a program that does handle nested `@include' statements.  @@ -3484,16 +3932,15 @@ File: gawk.info, Node: Getline/Pipe, Next: Getline/Variable/Pipe, Prev: Getli Using `getline' from a Pipe --------------------------- - You can pipe the output of a command into `getline', using `COMMAND -| getline'. In this case, the string COMMAND is run as a shell command -and its output is piped into `awk' to be used as input. This form of -`getline' reads one record at a time from the pipe. + The output of a command can also be piped into `getline', using +`COMMAND | getline'. In this case, the string COMMAND is run as a +shell command and its output is piped into `awk' to be used as input. +This form of `getline' reads one record at a time from the pipe. For +example, the following program copies its input to its output, except +for lines that begin with `@execute', which are replaced by the output +produced by running the rest of the line as a shell command: - For example, the following program copies its input to its output, -except for lines that begin with `@execute', which are replaced by the -output produced by running the rest of the line as a shell command: - - awk '{ + { if ($1 == "@execute") { tmp = substr($0, 10) while ((tmp | getline) > 0) @@ -3501,13 +3948,12 @@ output produced by running the rest of the line as a shell command: close(tmp) } else print - }' + } The `close' function is called to ensure that if two identical `@execute' lines appear in the input, the command is run for each one. -*Note Closing Input and Output Files and Pipes: Close Files And Pipes. - - Given the input: +*Note Closing Input and Output Redirections: Close Files And Pipes. +Given the input: foo bar @@ -3527,97 +3973,147 @@ the program might produce: Notice that this program ran the command `who' and printed the result. (If you try this program yourself, you will of course get different -results, showing you who is logged in on your system.) +results, depending upon who is logged in on your system.) This variation of `getline' splits the record into fields, sets the value of `NF' and recomputes the value of `$0'. The values of `NR' and `FNR' are not changed. According to POSIX, `EXPRESSION | getline' is ambiguous if -EXPRESSION contains unparenthesized operators other than `$'; for +EXPRESSION contains unparenthesized operators other than `$'--for example, `"echo " "date" | getline' is ambiguous because the -concatenation operator is not parenthesized, and you should write it as +concatenation operator is not parenthesized. You should write it as `("echo " "date") | getline' if you want your program to be portable to other `awk' implementations. (It happens that `gawk' gets it right, but you should not rely on this. Parentheses make it easier to read, anyway.)  -File: gawk.info, Node: Getline/Variable/Pipe, Next: Getline Summary, Prev: Getline/Pipe, Up: Getline +File: gawk.info, Node: Getline/Variable/Pipe, Next: Getline/Coprocess, Prev: Getline/Pipe, Up: Getline -Using `getline' Into a Variable from a Pipe +Using `getline' into a Variable from a Pipe ------------------------------------------- - When you use `COMMAND | getline VAR', the output of the command -COMMAND is sent through a pipe to `getline' and into the variable VAR. -For example, the following program reads the current date and time into -the variable `current_time', using the `date' utility, and then prints -it. + When you use `COMMAND | getline VAR', the output of COMMAND is sent +through a pipe to `getline' and into the variable VAR. For example, the +following program reads the current date and time into the variable +`current_time', using the `date' utility, and then prints it: - awk 'BEGIN { + BEGIN { "date" | getline current_time close("date") print "Report printed on " current_time - }' + } In this version of `getline', none of the built-in variables are -changed, and the record is not split into fields. +changed and the record is not split into fields. According to POSIX, `EXPRESSION | getline VAR' is ambiguous if EXPRESSION contains unparenthesized operators other than `$'; for example, `"echo " "date" | getline VAR' is ambiguous because the -concatenation operator is not parenthesized, and you should write it as +concatenation operator is not parenthesized. You should write it as `("echo " "date") | getline VAR' if you want your program to be portable to other `awk' implementations. (It happens that `gawk' gets it right, but you should not rely on this. Parentheses make it easier to read, anyway.)  -File: gawk.info, Node: Getline Summary, Prev: Getline/Variable/Pipe, Up: Getline +File: gawk.info, Node: Getline/Coprocess, Next: Getline/Variable/Coprocess, Prev: Getline/Variable/Pipe, Up: Getline -Summary of `getline' Variants ------------------------------ +Using `getline' from a Coprocess +-------------------------------- - With all the forms of `getline', even though `$0' and `NF', may be -updated, the record will not be tested against all the patterns in the -`awk' program, in the way that would happen if the record were read -normally by the main processing loop of `awk'. However the new record -is tested against any subsequent rules. - - Many `awk' implementations limit the number of pipelines an `awk' -program may have open to just one! In `gawk', there is no such limit. -You can open as many pipelines as the underlying operating system will -permit. - - An interesting side-effect occurs if you use `getline' (without a -redirection) inside a `BEGIN' rule. Since an unredirected `getline' -reads from the command line data files, the first `getline' command -causes `awk' to set the value of `FILENAME'. Normally, `FILENAME' does -not have a value inside `BEGIN' rules, since you have not yet started -to process the command line data files (d.c.). (*Note The `BEGIN' and -`END' Special Patterns: BEGIN/END, also *note Built-in Variables that -Convey Information: Auto-set..) - - The following table summarizes the six variants of `getline', -listing which built-in variables are set by each one. + Input into `getline' from a pipe is a one-way operation. The +command that is started with `COMMAND | getline' only sends data _to_ +your `awk' program. -`getline' - sets `$0', `NF', `FNR', and `NR'. + On occasion, you might want to send data to another program for +processing and then read the results back. `gawk' allows you start a +"coprocess", with which two-way communications are possible. This is +done with the `|&' operator. Typically, you write data to the +coprocess first, and then read results back, as shown in the following: -`getline VAR' - sets VAR, `FNR', and `NR'. + print "SOME QUERY" |& "db_server" + "db_server" |& getline -`getline < FILE' - sets `$0', and `NF'. +which sends a query to `db_server' and then reads the results. -`getline VAR < FILE' - sets VAR. + The values of `NR' and `FNR' are not changed, because the main input +stream is not used. However, the record is split into fields in the +normal manner, thus changing the values of `$0', the other fields, and +of `NF'. -`COMMAND | getline' - sets `$0', and `NF'. + Coprocesses are an advanced feature. They are discussed here only +because this is the minor node on `getline'. *Note Two-Way +Communications with Another Process: Two-way I/O, where coprocesses are +discussed in more detail. -`COMMAND | getline VAR' - sets VAR. + +File: gawk.info, Node: Getline/Variable/Coprocess, Next: Getline Notes, Prev: Getline/Coprocess, Up: Getline + +Using `getline' into a Variable from a Coprocess +------------------------------------------------ + + When you use `COMMAND |& getline VAR', the output from the coprocess +COMMAND is sent through a two-way pipe to `getline' and into the +variable VAR. + + In this version of `getline', none of the built-in variables are +changed and the record is not split into fields. The only variable +changed is VAR. + + Coprocesses are an advanced feature. They are discussed here only +because this is the minor node on `getline'. *Note Two-Way +Communications with Another Process: Two-way I/O, where coprocesses are +discussed in more detail. + + +File: gawk.info, Node: Getline Notes, Next: Getline Summary, Prev: Getline/Variable/Coprocess, Up: Getline + +Points About `getline' to Remember +---------------------------------- + + Here are some miscellaneous points about `getline' that you should +bear in mind: + + * When `getline' changes the value of `$0' and `NF', `awk' does + _not_ automatically jump to the start of the program and start + testing the new record against every pattern. However, the new + record is tested against any subsequent rules. + + * Many `awk' implementations limit the number of pipelines that an + `awk' program may have open to just one. In `gawk', there is no + such limit. You can open as many pipelines (and coprocesses) as + the underlying operating system permits. + + * An interesting side effect occurs if you use `getline' without a + redirection inside a `BEGIN' rule. Because an unredirected + `getline' reads from the command-line data files, the first + `getline' command causes `awk' to set the value of `FILENAME'. + Normally, `FILENAME' does not have a value inside `BEGIN' rules, + because you have not yet started to process the command-line data + files. (d.c.) (*Note The `BEGIN' and `END' Special Patterns: + BEGIN/END, also *note Built-in Variables That Convey Information: + Auto-set..) + + +File: gawk.info, Node: Getline Summary, Prev: Getline Notes, Up: Getline + +Summary of `getline' Variants +----------------------------- + + The following table summarizes the eight variants of `getline', +listing which built-in variables are set by each one. + +`getline' Sets `$0', `NF', `FNR' and `NR' +`getline' VAR Sets VAR, `FNR' and `NR' +`getline <' FILE Sets `$0' and `NF' +`getline VAR < FILE' Sets VAR +COMMAND `| getline' Sets `$0' and `NF' +COMMAND `| getline' VAR Sets VAR +COMMAND `|& getline' Sets `$0' and `NF' (this is a `gawk' + extension) +COMMAND `|& getline' VAR Sets VAR (this is a `gawk' extension)  File: gawk.info, Node: Printing, Next: Expressions, Prev: Reading Files, Up: Top @@ -3625,10 +4121,21 @@ File: gawk.info, Node: Printing, Next: Expressions, Prev: Reading Files, Up: Printing Output *************** - One of the most common actions is to "print", or output, some or all -of the input. You use the `print' statement for simple output. You -use the `printf' statement for fancier formatting. Both are described -in this chapter. + One of the most common programming actions is to "print" or output, +some or all of the input. Use the `print' statement for simple output, +and the `printf' statement for fancier formatting. The `print' +statement is not limited when computing _which_ values to print. +However, with two exceptions, you cannot specify _how_ to print +them--how many columns, whether to use exponential notation or not, and +so on. (For the exceptions, *note Output Separators::, and *Note +Controlling Numeric Output with `print': OFMT.) For that, you need the +`printf' statement (*note Using `printf' Statements for Fancier +Printing: Printf.). + + Besides basic and formatted printing, this major node also covers +I/O redirections to files and pipes, introduces the special file names +that `gawk' processes internally, and discusses the `close' built-in +function. * Menu: @@ -3650,44 +4157,29 @@ File: gawk.info, Node: Print, Next: Print Examples, Prev: Printing, Up: Prin The `print' Statement ===================== - The `print' statement does output with simple, standardized -formatting. You specify only the strings or numbers to be printed, in a -list separated by commas. They are output, separated by single spaces, -followed by a newline. The statement looks like this: + The `print' statement is used to produce output with simple, +standardized formatting. Specify only the strings or numbers to print, +in a list separated by commas. They are output, separated by single +spaces, followed by a newline. The statement looks like this: print ITEM1, ITEM2, ... -The entire list of items may optionally be enclosed in parentheses. The +The entire list of items may be optionally enclosed in parentheses. The parentheses are necessary if any of the item expressions uses the `>' relational operator; otherwise it could be confused with a redirection (*note Redirecting Output of `print' and `printf': Redirection.). - The items to be printed can be constant strings or numbers, fields -of the current record (such as `$1'), variables, or any `awk' -expressions. Numeric values are converted to strings, and then printed. - - The `print' statement is completely general for computing _what_ -values to print. However, with two exceptions, you cannot specify _how_ -to print them--how many columns, whether to use exponential notation or -not, and so on. (For the exceptions, *note Output Separators::, and -*Note Controlling Numeric Output with `print': OFMT.) For that, you -need the `printf' statement (*note Using `printf' Statements for -Fancier Printing: Printf.). + The items to print can be constant strings or numbers, fields of the +current record (such as `$1'), variables, or any `awk' expression. +Numeric values are converted to strings and then printed. The simple statement `print' with no items is equivalent to `print $0': it prints the entire current record. To print a blank line, use -`print ""', where `""' is the empty string. - - To print a fixed piece of text, use a string constant such as -`"Don't Panic"' as one item. If you forget to use the double-quote -characters, your text will be taken as an `awk' expression, and you -will probably get an error. Keep in mind that a space is printed -between any two items. - - Each `print' statement makes at least one line of output. But it -isn't limited to one line. If an item value is a string that contains a -newline, the newline is output along with the rest of the string. A -single `print' can make any number of lines this way. +`print ""', where `""' is the empty string. To print a fixed piece of +text, use a string constant, such as `"Don't Panic"', as one item. If +you forget to use the double quote characters, your text is taken as an +`awk' expression and you will probably get an error. Keep in mind that +a space is printed between any two items.  File: gawk.info, Node: Print Examples, Next: Output Separators, Prev: Print, Up: Printing @@ -3695,17 +4187,24 @@ File: gawk.info, Node: Print Examples, Next: Output Separators, Prev: Print, Examples of `print' Statements ============================== - Here is an example of printing a string that contains embedded -newlines (the `\n' is an escape sequence, used to represent the newline -character; *note Escape Sequences::): + Each `print' statement makes at least one line of output. However, +it isn't limited to only one line. If an item value is a string that +contains a newline, the newline is output along with the rest of the +string. A single `print' statement can make any number of lines this +way. + + The following is an example of printing a string that contains +embedded newlines (the `\n' is an escape sequence, used to represent +the newline character; *note Escape Sequences::): $ awk 'BEGIN { print "line one\nline two\nline three" }' -| line one -| line two -| line three - Here is an example that prints the first two fields of each input -record, with a space between them: + The next example, which is run on the `inventory-shipped' file, +prints the first two fields of each input record, with a space between +them: $ awk '{ print $1, $2 }' inventory-shipped -| Jan 13 @@ -3725,19 +4224,18 @@ Here is the same program, without the comma: -| Mar15 ... - To someone unfamiliar with the file `inventory-shipped', neither + To someone unfamiliar with the `inventory-shipped' file, neither example's output makes much sense. A heading line at the beginning would make it clearer. Let's add some headings to our table of months (`$1') and green crates shipped (`$2'). We do this using the `BEGIN' -pattern (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.) to -force the headings to be printed only once: +pattern (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.) so +that the headings are only printed once: awk 'BEGIN { print "Month Crates" print "----- ------" } { print $1, $2 }' inventory-shipped -Did you already guess what happens? When run, the program prints the -following: +When run, the program prints the following: Month Crates ----- ------ @@ -3746,23 +4244,24 @@ following: Mar 15 ... -The headings and the table data don't line up! We can fix this by -printing some spaces between the two fields: +The only problem, however, is that the headings and the table data +don't line up! We can fix this by printing some spaces between the two +fields: awk 'BEGIN { print "Month Crates" print "----- ------" } { print $1, " ", $2 }' inventory-shipped - You can imagine that this way of lining up columns can get pretty -complicated when you have many columns to fix. Counting spaces for two -or three columns can be simple, but more than this and you can get lost -quite easily. This is why the `printf' statement was created (*note -Using `printf' Statements for Fancier Printing: Printf.); one of its -specialties is lining up columns of data. + Lining up columns this way can get pretty complicated when there are +many columns to fix. Counting spaces for two or three columns is +simple, but any more than this can take up a lot of time. This is why +the `printf' statement was created (*note Using `printf' Statements for +Fancier Printing: Printf.); one of its specialties is lining up columns +of data. - As a side point, you can continue either a `print' or `printf' -statement simply by putting a newline after any comma (*note `awk' -Statements Versus Lines: Statements/Lines.). + *Note:* You can continue either a `print' or `printf' statement +simply by putting a newline after any comma (*note `awk' Statements +Versus Lines: Statements/Lines.).  File: gawk.info, Node: Output Separators, Next: OFMT, Prev: Print Examples, Up: Printing @@ -3771,31 +4270,28 @@ Output Separators ================= As mentioned previously, a `print' statement contains a list of -items, separated by commas. In the output, the items are normally -separated by single spaces. This need not be the case; a single space -is only the default. You can specify any string of characters to use -as the "output field separator" by setting the built-in variable `OFS'. -The initial value of this variable is the string `" "', that is, a -single space. +items separated by commas. In the output, the items are normally +separated by single spaces. However, this doesn't need to be the case; +a single space is only the default. Any string of characters may be +used as the "output field separator" by setting the built-in variable +`OFS'. The initial value of this variable is the string `" "'--that +is, a single space. The output from an entire `print' statement is called an "output -record". Each `print' statement outputs one output record and then -outputs a string called the "output record separator". The built-in -variable `ORS' specifies this string. The initial value of `ORS' is -the string `"\n"', i.e. a newline character; thus, normally each -`print' statement makes a separate line. - - You can change how output fields and records are separated by -assigning new values to the variables `OFS' and/or `ORS'. The usual -place to do this is in the `BEGIN' rule (*note The `BEGIN' and `END' -Special Patterns: BEGIN/END.), so that it happens before any input is -processed. You may also do this with assignments on the command line, -before the names of your input files, or using the `-v' command line -option (*note Command Line Options: Options.). - - The following example prints the first and second fields of each -input record separated by a semicolon, with a blank line added after -each line: +record". Each `print' statement outputs one output record, and then +outputs a string called the "output record separator" (or `ORS'). The +initial value of `ORS' is the string `"\n"'; i.e., a newline character. +Thus, each `print' statement normally makes a separate line. + + In order to change how output fields and records are separated, +assign new values to the variables `OFS' and `ORS'. The usual place to +do this is in the `BEGIN' rule (*note The `BEGIN' and `END' Special +Patterns: BEGIN/END.), so that it happens before any input is +processed. It can also be done with assignments on the command line, +before the names of the input files, or using the `-v' command-line +option (*note Command-Line Options: Options.). The following example +prints the first and second fields of each input record, separated by a +semicolon, with a blank line added after each newline: $ awk 'BEGIN { OFS = ";"; ORS = "\n\n" } > { print $1, $2 }' BBS-list @@ -3806,9 +4302,8 @@ each line: -| barfly;555-7685 ... - If the value of `ORS' does not contain a newline, all your output -will be run together on a single line, unless you output newlines some -other way. + If the value of `ORS' does not contain a newline, the program's +output is run together on a single line.  File: gawk.info, Node: OFMT, Next: Printf, Prev: Output Separators, Up: Printing @@ -3816,31 +4311,31 @@ File: gawk.info, Node: OFMT, Next: Printf, Prev: Output Separators, Up: Prin Controlling Numeric Output with `print' ======================================= - When you use the `print' statement to print numeric values, `awk' -internally converts the number to a string of characters, and prints + When the `print' statement is used to print numeric values, `awk' +internally converts the number to a string of characters and prints that string. `awk' uses the `sprintf' function to do this conversion -(*note Built-in Functions for String Manipulation: String Functions.). -For now, it suffices to say that the `sprintf' function accepts a -"format specification" that tells it how to format numbers (or -strings), and that there are a number of different ways in which -numbers can be formatted. The different format specifications are -discussed more fully in *Note Format-Control Letters: Control Letters. +(*note String Manipulation Functions: String Functions.). For now, it +suffices to say that the `sprintf' function accepts a "format +specification" that tells it how to format numbers (or strings), and +that there are a number of different ways in which numbers can be +formatted. The different format specifications are discussed more +fully in *Note Format-Control Letters: Control Letters. The built-in variable `OFMT' contains the default format specification that `print' uses with `sprintf' when it wants to convert a number to a string for printing. The default value of `OFMT' is -`"%.6g"'. By supplying different format specifications as the value of -`OFMT', you can change how `print' will print your numbers. As a brief -example: +`"%.6g"'. The way `print' prints numbers can be changed by supplying +different format specifications as the value of `OFMT', as shown in the +following example: $ awk 'BEGIN { > OFMT = "%.0f" # print numbers as integers (rounds) - > print 17.23 }' - -| 17 + > print 17.23, 17.54 }' + -| 17 18 -According to the POSIX standard, `awk''s behavior will be undefined if -`OFMT' contains anything but a floating point conversion specification -(d.c.). +According to the POSIX standard, `awk''s behavior is undefined if +`OFMT' contains anything but a floating-point conversion specification. +(d.c.)  File: gawk.info, Node: Printf, Next: Redirection, Prev: OFMT, Up: Printing @@ -3848,13 +4343,14 @@ File: gawk.info, Node: Printf, Next: Redirection, Prev: OFMT, Up: Printing Using `printf' Statements for Fancier Printing ============================================== - If you want more precise control over the output format than `print' -gives you, use `printf'. With `printf' you can specify the width to -use for each item, and you can specify various formatting choices for -numbers (such as what radix to use, whether to print an exponent, -whether to print a sign, and how many digits to print after the decimal -point). You do this by supplying a string, called the "format string", -which controls how and where to print the other arguments. + For more precise control over the output format than what is +normally provided by `print', use `printf'. `printf' can be used to +specify the width to use for each item, as well as various formatting +choices for numbers (such as what output base to use, whether to print +an exponent, whether to print a sign, and how many digits to print +after the decimal point). This is done by supplying a string, called +the "format string", that controls how and where to print the other +arguments. * Menu: @@ -3869,39 +4365,40 @@ File: gawk.info, Node: Basic Printf, Next: Control Letters, Prev: Printf, Up Introduction to the `printf' Statement -------------------------------------- - The `printf' statement looks like this: + A simple `printf' statement looks like this: printf FORMAT, ITEM1, ITEM2, ... The entire list of arguments may optionally be enclosed in parentheses. The parentheses are necessary if any of the item expressions use the -`>' relational operator; otherwise it could be confused with a -redirection (*note Redirecting Output of `print' and `printf': -Redirection.). +`>' relational operator; otherwise it can be confused with a redirection +(*note Redirecting Output of `print' and `printf': Redirection.). The difference between `printf' and `print' is the FORMAT argument. This is an expression whose value is taken as a string; it specifies how to output each of the other arguments. It is called the "format string". - The format string is very similar to that in the ANSI C library -function `printf'. Most of FORMAT is text to be output verbatim. -Scattered among this text are "format specifiers", one per item. Each + The format string is very similar to that in the ISO C library +function `printf'. Most of FORMAT is text to output verbatim. +Scattered among this text are "format specifiers"--one per item. Each format specifier says to output the next item in the argument list at that place in the format. - The `printf' statement does not automatically append a newline to its -output. It outputs only what the format string specifies. So if you -want a newline, you must include one in the format string. The output -separator variables `OFS' and `ORS' have no effect on `printf' + The `printf' statement does not automatically append a newline to +its output. It outputs only what the format string specifies. So if a +newline is needed, you must include one in the format string. The +output separator variables `OFS' and `ORS' have no effect on `printf' statements. For example: - BEGIN { - ORS = "\nOUCH!\n"; OFS = "!" - msg = "Don't Panic!"; printf "%s\n", msg - } + $ awk 'BEGIN { + > ORS = "\nOUCH!\n"; OFS = "+" + > msg = "Dont Panic!" + > printf "%s\n", msg + > }' + -| Dont Panic! - This program still prints the familiar `Don't Panic!' message. +Here, neither the `+' nor the `OUCH' appear when the message is printed.  File: gawk.info, Node: Control Letters, Next: Format Modifiers, Prev: Basic Printf, Up: Printf @@ -3910,79 +4407,71 @@ Format-Control Letters ---------------------- A format specifier starts with the character `%' and ends with a -"format-control letter"; it tells the `printf' statement how to output -one item. (If you actually want to output a `%', write `%%'.) The -format-control letter specifies what kind of value to print. The rest -of the format specifier is made up of optional "modifiers" which are -parameters to use, such as the field width. +"format-control letter"--it tells the `printf' statement how to output +one item. The format-control letter specifies what _kind_ of value to +print. The rest of the format specifier is made up of optional +"modifiers" that control _how_ to print the value, such as the field +width. Here is a list of the format-control letters: - Here is a list of the format-control letters: - -`c' - This prints a number as an ASCII character. Thus, `printf "%c", - 65' outputs the letter `A'. The output for a string value is the - first character of the string. +`%c' + This prints a number as an ASCII character; thus, `printf "%c", + 65' outputs the letter `A'. (The output for a string value is the + first character of the string.) -`d' -`i' - These are equivalent. They both print a decimal integer. The `%i' - specification is for compatibility with ANSI C. +`%d, %i' + These are equivalent; they both print a decimal integer. (The + `%i' specification is for compatibility with ISO C.) -`e' -`E' - This prints a number in scientific (exponential) notation. For - example, +`%e, %E' + These print a number in scientific (exponential) notation; for + example: printf "%4.3e\n", 1950 - prints `1.950e+03', with a total of four significant figures of - which three follow the decimal point. The `4.3' are modifiers, - discussed below. `%E' uses `E' instead of `e' in the output. + prints `1.950e+03', with a total of four significant figures, + three of which follow the decimal point. (The `4.3' represents + two modifiers, discussed in the next node.) `%E' uses `E' instead + of `e' in the output. -`f' - This prints a number in floating point notation. For example, +`%f' + This prints a number in floating-point notation. For example: printf "%4.3f", 1950 - prints `1950.000', with a total of four significant figures of - which three follow the decimal point. The `4.3' are modifiers, - discussed below. + prints `1950.000', with a total of four significant figures, three + of which follow the decimal point. (The `4.3' represents two + modifiers, discussed in the next node.) -`g' -`G' - This prints a number in either scientific notation or floating - point notation, whichever uses fewer characters. If the result is - printed in scientific notation, `%G' uses `E' instead of `e'. +`%g, %G' + These print a number in either scientific notation or in + floating-point notation, whichever uses fewer characters; if the + result is printed in scientific notation, `%G' uses `E' instead of + `e'. -`o' - This prints an unsigned octal integer. (In octal, or base-eight - notation, the digits run from `0' to `7'; the decimal number eight - is represented as `10' in octal.) +`%o' + This prints an unsigned octal integer. -`s' +`%s' This prints a string. -`u' - This prints an unsigned decimal number. (This format is of - marginal use, since all numbers in `awk' are floating point. It +`%u' + This prints an unsigned decimal integer. (This format is of + marginal use, because all numbers in `awk' are floating-point; it is provided primarily for compatibility with C.) -`x' -`X' - This prints an unsigned hexadecimal integer. (In hexadecimal, or - base-16 notation, the digits are `0' through `9' and `a' through - `f'. The hexadecimal digit `f' represents the decimal number 15.) - `%X' uses the letters `A' through `F' instead of `a' through `f'. +`%x, %X' + These print an unsigned hexadecimal integer; `%X' uses the letters + `A' through `F' instead of `a' through `f'. -`%' - This isn't really a format-control letter, but it does have a - meaning when used after a `%': the sequence `%%' outputs one `%'. - It does not consume an argument, and it ignores any modifiers. +`%%' + This isn't a format-control letter but it does have meaning--the + sequence `%%' outputs one `%'; it does not consume an argument and + it ignores any modifiers. - When using the integer format-control letters for values that are -outside the range of a C `long' integer, `gawk' will switch to the `%g' -format specifier. Other versions of `awk' may print invalid values, or -do something else entirely (d.c.). + *Note:* When using the integer format-control letters for values +that are outside the range of a C `long' integer, `gawk' switches to the +`%g' format specifier. Other versions of `awk' may print invalid values +or do something else entirely. (d.c.)  File: gawk.info, Node: Format Modifiers, Next: Printf Examples, Prev: Control Letters, Up: Printf @@ -3991,50 +4480,69 @@ Modifiers for `printf' Formats ------------------------------ A format specification can also include "modifiers" that can control -how much of the item's value is printed and how much space it gets. The -modifiers come between the `%' and the format-control letter. In the -examples below, we use the bullet symbol "*" to represent spaces in the -output. Here are the possible modifiers, in the order in which they may -appear: +how much of the item's value is printed, as well as how much space it +gets. The modifiers come between the `%' and the format-control letter. +We will use the bullet symbol "*" in the following examples to represent +spaces in the output. Here are the possible modifiers, in the order in +which they may appear: + +`N$' + An integer constant followed by a `$' is a "positional specifier". + Normally, format specifications are applied to arguments in the + order given in the format string. With a positional specifier, + the format specification is applied to a specific argument, + instead of what would be the next argument in the list. + Positional specifiers begin counting with one: + + printf "%s %s\n", "don't", "panic" + printf "%2$s %1$s\n", "panic", "don't" + + prints the famous friendly message twice. + + At first glance, this feature doesn't seem to be of much use. It + is in fact a `gawk' extension, intended for use in translating + messages at runtime. *Note Rearranging `printf' Arguments: Printf + Ordering, which describes how and why to use positional specifiers. + For now, we will not use them. `-' - The minus sign, used before the width modifier (see below), says - to left-justify the argument within its specified width. Normally - the argument is printed right-justified in the specified width. - Thus, + The minus sign, used before the width modifier (see further on in + this table), says to left-justify the argument within its + specified width. Normally, the argument is printed + right-justified in the specified width. Thus: printf "%-4s", "foo" prints `foo*'. `SPACE' - For numeric conversions, prefix positive values with a space, and + For numeric conversions, prefix positive values with a space and negative values with a minus sign. `+' - The plus sign, used before the width modifier (see below), says to - always supply a sign for numeric conversions, even if the data to - be formatted is positive. The `+' overrides the space modifier. + The plus sign, used before the width modifier (see further on in + this table), says to always supply a sign for numeric conversions, + even if the data to format is positive. The `+' overrides the + space modifier. `#' Use an "alternate form" for certain control letters. For `%o', - supply a leading zero. For `%x', and `%X', supply a leading `0x' - or `0X' for a non-zero result. For `%e', `%E', and `%f', the - result will always contain a decimal point. For `%g', and `%G', + supply a leading zero. For `%x' and `%X', supply a leading `0x' + or `0X' for a nonzero result. For `%e', `%E', and `%f', the + result always contains a decimal point. For `%g' and `%G', trailing zeros are not removed from the result. `0' - A leading `0' (zero) acts as a flag, that indicates output should - be padded with zeros instead of spaces. This applies even to - non-numeric output formats (d.c.). This flag only has an effect - when the field width is wider than the value to be printed. + A leading `0' (zero) acts as a flag that indicates that output + should be padded with zeros instead of spaces. This applies even + to non-numeric output formats. (d.c.) This flag only has an + effect when the field width is wider than the value to print. `WIDTH' This is a number specifying the desired minimum width of a field. - Inserting any number between the `%' sign and the format control - character forces the field to be expanded to this width. The - default way to do this is to pad with spaces on the left. For - example, + Inserting any number between the `%' sign and the format-control + character forces the field to expand to this width. The default + way to do this is to pad with spaces on the left. For example: printf "%4s", "foo" @@ -4042,7 +4550,7 @@ appear: The value of WIDTH is a minimum width, not a maximum. If the item value requires more than WIDTH characters, it can be as wide as - necessary. Thus, + necessary. Thus, the following: printf "%4s", "foobar" @@ -4052,14 +4560,24 @@ appear: padded with spaces on the right, instead of on the left. `.PREC' - This is a number that specifies the precision to use when printing. - For the `e', `E', and `f' formats, this specifies the number of - digits you want printed to the right of the decimal point. For - the `g', and `G' formats, it specifies the maximum number of - significant digits. For the `d', `o', `i', `u', `x', and `X' - formats, it specifies the minimum number of digits to print. For - a string, it specifies the maximum number of characters from the - string that should be printed. Thus, + A period followed by an integer constant specifies the precision + to use when printing. The meaning of the precision varies by + control letter: + + `%e', `%E', `%f' + Number of digits to the right of the decimal point. + + `%g', `%G' + Maximum number of significant digits. + + `%d', `%i', `%o', `%u', `%x', `%X' + Minimum number of digits to print. + + `%s' + Maximum number of characters from the string that should + print. + + Thus, the following: printf "%.4s", "foobar" @@ -4067,38 +4585,37 @@ appear: The C library `printf''s dynamic WIDTH and PREC capability (for example, `"%*.*s"') is supported. Instead of supplying explicit WIDTH -and/or PREC values in the format string, you pass them in the argument -list. For example: +and/or PREC values in the format string, they are passed in the +argument list. For example: w = 5 p = 3 s = "abcdefg" printf "%*.*s\n", w, p, s -is exactly equivalent to +is exactly equivalent to: s = "abcdefg" printf "%5.3s\n", s -Both programs output `**abc'. - - Earlier versions of `awk' did not support this capability. If you -must use such a version, you may simulate this feature by using -concatenation to build up the format string, like so: +Both programs output `**abc'. Earlier versions of `awk' did not +support this capability. If you must use such a version, you may +simulate this feature by using concatenation to build up the format +string, like so: w = 5 p = 3 s = "abcdefg" printf "%" w "." p "s\n", s -This is not particularly easy to read, but it does work. +This is not particularly easy to read but it does work. - C programmers may be used to supplying additional `l' and `h' flags -in `printf' format strings. These are not valid in `awk'. Most `awk' -implementations silently ignore these flags. If `--lint' is provided -on the command line (*note Command Line Options: Options.), `gawk' will -warn about their use. If `--posix' is supplied, their use is a fatal -error. + C programmers may be used to supplying additional `l', `L', and `h' +modifiers in `printf' format strings. These are not valid in `awk'. +Most `awk' implementations silently ignore these modifiers. If +`--lint' is provided on the command line (*note Command-Line Options: +Options.), `gawk' warns about their use. If `--posix' is supplied, +their use is a fatal error.  File: gawk.info, Node: Printf Examples, Prev: Format Modifiers, Up: Printf @@ -4106,14 +4623,15 @@ File: gawk.info, Node: Printf Examples, Prev: Format Modifiers, Up: Printf Examples Using `printf' ----------------------- - Here is how to use `printf' to make an aligned table: + The following is a simple example of how to use `printf' to make an +aligned table: awk '{ printf "%-10s %s\n", $1, $2 }' BBS-list -prints the names of bulletin boards (`$1') of the file `BBS-list' as a -string of 10 characters, left justified. It also prints the phone -numbers (`$2') afterward on the line. This produces an aligned -two-column table of names and phone numbers: +This command prints the names of the bulletin boards (`$1') in the file +`BBS-list' as a string of 10 characters that are left-justified. It +also prints the phone numbers (`$2') next on the line. This produces +an aligned two-column table of names and phone numbers, as shown here: $ awk '{ printf "%-10s %s\n", $1, $2 }' BBS-list -| aardvark 555-5553 @@ -4128,35 +4646,34 @@ two-column table of names and phone numbers: -| sdace 555-3430 -| sabafoo 555-2127 - Did you notice that we did not specify that the phone numbers be -printed as numbers? They had to be printed as strings because the -numbers are separated by a dash. If we had tried to print the phone -numbers as numbers, all we would have gotten would have been the first -three digits, `555'. This would have been pretty confusing. + In this case, the phone numbers had to be printed as strings because +the numbers are separated by a dash. Printing the phone numbers as +numbers would have produced just the first three digits: `555'. This +would have been pretty confusing. - We did not specify a width for the phone numbers because they are the -last things on their lines. We don't need to put spaces after them. + It wasn't necessary to specify a width for the phone numbers because +they are last on their lines. They don't need to have spaces after +them. - We could make our table look even nicer by adding headings to the -tops of the columns. To do this, we use the `BEGIN' pattern (*note The -`BEGIN' and `END' Special Patterns: BEGIN/END.) to force the header to -be printed only once, at the beginning of the `awk' program: + The table could be made to look even nicer by adding headings to the +tops of the columns. This is done using the `BEGIN' pattern (*note The +`BEGIN' and `END' Special Patterns: BEGIN/END.) so that the headers +are only printed once, at the beginning of the `awk' program: awk 'BEGIN { print "Name Number" print "---- ------" } { printf "%-10s %s\n", $1, $2 }' BBS-list - Did you notice that we mixed `print' and `printf' statements in the -above example? We could have used just `printf' statements to get the -same results: + The above example mixed `print' and `printf' statements in the same +program. Using just `printf' statements can produce the same results: awk 'BEGIN { printf "%-10s %s\n", "Name", "Number" printf "%-10s %s\n", "----", "------" } { printf "%-10s %s\n", $1, $2 }' BBS-list -By printing each column heading with the same format specification used -for the elements of the column, we have made sure that the headings are -aligned just like the columns. +Printing each column heading with the same format specification used +for the column elements ensures that the headings are aligned just like +the columns. The fact that the same format specification is used three times can be emphasized by storing it in a variable, like this: @@ -4166,9 +4683,10 @@ be emphasized by storing it in a variable, like this: printf format, "----", "------" } { printf format, $1, $2 }' BBS-list - See if you can use the `printf' statement to line up the headings and -table data for our `inventory-shipped' example covered earlier in the -section on the `print' statement (*note The `print' Statement: Print.). + At this point, it would be a worthwhile exercise to use the `printf' +statement to line up the headings and table data for the +`inventory-shipped' example that was covered earlier in the minor node +on the `print' statement (*note The `print' Statement: Print.).  File: gawk.info, Node: Redirection, Next: Special Files, Prev: Printf, Up: Printing @@ -4176,34 +4694,33 @@ File: gawk.info, Node: Redirection, Next: Special Files, Prev: Printf, Up: P Redirecting Output of `print' and `printf' ========================================== - So far we have been dealing only with output that prints to the -standard output, usually your terminal. Both `print' and `printf' can -also send their output to other places. This is called "redirection". + So far, the output from `print' and `printf' has gone to the standard +output, usually the terminal. Both `print' and `printf' can also send +their output to other places. This is called "redirection". A redirection appears after the `print' or `printf' statement. Redirections in `awk' are written just like redirections in shell commands, except that they are written inside the `awk' program. - There are three forms of output redirection: output to a file, -output appended to a file, and output through a pipe to another command. -They are all shown for the `print' statement, but they work identically -for `printf' also. + There are four forms of output redirection: output to a file, output +appended to a file, output through a pipe to another command, and output +to a coprocess. They are all shown for the `print' statement, but they +work identically for `printf': `print ITEMS > OUTPUT-FILE' This type of redirection prints the items into the output file - OUTPUT-FILE. The file name OUTPUT-FILE can be any expression. - Its value is changed to a string and then used as a file name - (*note Expressions::). + named OUTPUT-FILE. The file name OUTPUT-FILE can be any + expression. Its value is changed to a string and then used as a + file name (*note Expressions::). When this type of redirection is used, the OUTPUT-FILE is erased before the first output is written to it. Subsequent writes to the same OUTPUT-FILE do not erase OUTPUT-FILE, but append to it. - If OUTPUT-FILE does not exist, then it is created. - - For example, here is how an `awk' program can write a list of BBS - names to a file `name-list' and a list of phone numbers to a file - `phone-list'. Each output file contains one name or number per - line. + (This is different from how you use redirections in shell scripts.) + If OUTPUT-FILE does not exist, it is created. For example, here + is how an `awk' program can write a list of BBS names to one file + named `name-list', and a list of phone numbers to another file + named `phone-list': $ awk '{ print $2 > "phone-list" > print $1 > "name-list" }' BBS-list @@ -4216,9 +4733,11 @@ for `printf' also. -| alpo-net ... + Each output file contains one name or number per line. + `print ITEMS >> OUTPUT-FILE' This type of redirection prints the items into the pre-existing - output file OUTPUT-FILE. The difference between this and the + output file named OUTPUT-FILE. The difference between this and the single-`>' redirection is that the old contents (if any) of OUTPUT-FILE are not erased. Instead, the `awk' output is appended to the file. If OUTPUT-FILE does not exist, then it is created. @@ -4226,27 +4745,26 @@ for `printf' also. `print ITEMS | COMMAND' It is also possible to send output to another program through a pipe instead of into a file. This type of redirection opens a - pipe to COMMAND and writes the values of ITEMS through this pipe, + pipe to COMMAND, and writes the values of ITEMS through this pipe to another process created to execute COMMAND. The redirection argument COMMAND is actually an `awk' expression. - Its value is converted to a string, whose contents give the shell - command to be run. - - For example, this produces two files, one unsorted list of BBS - names and one list sorted in reverse alphabetical order: + Its value is converted to a string whose contents give the shell + command to be run. For example, the following produces two files, + one unsorted list of BBS names, and one list sorted in reverse + alphabetical order: awk '{ print $1 > "names.unsorted" command = "sort -r > names.sorted" print $1 | command }' BBS-list - Here the unsorted list is written with an ordinary redirection - while the sorted list is written by piping through the `sort' - utility. + The unsorted list is written with an ordinary redirection, while + the sorted list is written by piping through the `sort' utility. - This example uses redirection to mail a message to a mailing list - `bug-system'. This might be useful when trouble is encountered in - an `awk' script run periodically for system maintenance. + The next example uses redirection to mail a message to the mailing + list `bug-system'. This might be useful when trouble is + encountered in an `awk' script run periodically for system + maintenance: report = "mail bug-system" print "Awk script failed:", $0 | report @@ -4256,26 +4774,73 @@ for `printf' also. The message is built using string concatenation and saved in the variable `m'. It is then sent down the pipeline to the `mail' - program. + program. (The parentheses group the items to concatenate--see + *Note String Concatenation: Concatenation.) + + The `close' function is called here because it's a good idea to + close the pipe as soon as all the intended output has been sent to + it. *Note Closing Input and Output Redirections: Close Files And + Pipes, for more information on this. + + This example also illustrates the use of a variable to represent a + FILE or COMMAND--it is not necessary to always use a string + constant. Using a variable is generally a good idea, because + `awk' requires that the string value be spelled identically every + time. + +`print ITEMS |& COMMAND' + This type of redirection prints the items to the input of COMMAND. + The difference between this and the single-`|' redirection is that + the output from COMMAND can be read with `getline'. Thus COMMAND + is a "coprocess", that works together with, but subsidiary to, the + `awk' program. + + This feature is a `gawk' extension, and is not available in POSIX + `awk'. *Note Two-Way Communications with Another Process: Two-way + I/O, for a more complete discussion. + + Redirecting output using `>', `>>', `|', or `|&' asks the system to +open a file, pipe, or coprocess, only if the particular FILE or COMMAND +you specify has not already been written to by your program or if it +has been closed since it was last written to. + + It is a common error to use `>' redirection for the first `print' to +a file, and then to use `>>' for subsequent output: + + # clear the file + print "Don't panic" > "guide.txt" + ... + # append + print "Avoid improbability generators" >> "guide.txt" + +This is indeed how redirections must be used from the shell. But in +`awk', it isn't necessary. In this kind of case, a program should use +`>' for all the `print' statements, since the output file is only +opened once. + + Many `awk' implementations limit the number of pipelines that an +`awk' program may have open to just one! In `gawk', there is no such +limit. `gawk' allows a program to open as many pipelines as the +underlying operating system permits. - We call the `close' function here because it's a good idea to close - the pipe as soon as all the intended output has been sent to it. - *Note Closing Input and Output Files and Pipes: Close Files And - Pipes, for more information on this. This example also - illustrates the use of a variable to represent a FILE or COMMAND: - it is not necessary to always use a string constant. Using a - variable is generally a good idea, since `awk' requires you to - spell the string value identically every time. +Advanced Notes: Piping into `sh' +-------------------------------- + + A particularly powerful way to use redirection is to build command +lines, and pipe them into the shell, `sh'. For example, suppose you +have a list of files brought over from a system where all the file names +are stored in uppercase, and you wish to rename them to have names in +all lowercase. The following program is both simple and efficient: - Redirecting output using `>', `>>', or `|' asks the system to open a -file or pipe only if the particular FILE or COMMAND you've specified -has not already been written to by your program, or if it has been -closed since it was last written to. + { printf("mv %s %s\n", $0, tolower($0)) | "sh" } + + END { close("sh") } - Many `awk' implementations limit the number of pipelines an `awk' -program may have open to just one! In `gawk', there is no such limit. -You can open as many pipelines as the underlying operating system will -permit. + The `tolower' function returns its argument string with all +uppercase characters converted to lowercase (*note String Manipulation +Functions: String Functions.). The program builds up a list of command +lines, using the `mv' utility to rename the files. It then sends the +list to the shell for execution.  File: gawk.info, Node: Special Files, Next: Close Files And Pipes, Prev: Redirection, Up: Printing @@ -4283,38 +4848,57 @@ File: gawk.info, Node: Special Files, Next: Close Files And Pipes, Prev: Redi Special File Names in `gawk' ============================ + `gawk' provides a number of special file names that it interprets +internally. These file names provide access to standard file +descriptors, process-related information, and TCP/IP networking. + +* Menu: + +* Special FD:: Special files for I/O. +* Special Process:: Special files for process information. +* Special Network:: Special files for network communications. +* Special Caveats:: Things to watch out for. + + +File: gawk.info, Node: Special FD, Next: Special Process, Prev: Special Files, Up: Special Files + +Special Files for Standard Descriptors +-------------------------------------- + Running programs conventionally have three input and output streams already available to them for reading and writing. These are known as the "standard input", "standard output", and "standard error output". These streams are, by default, connected to your terminal, but they are -often redirected with the shell, via the `<', `<<', `>', `>>', `>&' and -`|' operators. Standard error is typically used for writing error -messages; the reason we have two separate streams, standard output and -standard error, is so that they can be redirected separately. +often redirected with the shell, via the `<', `<<', `>', `>>', `>&', +and `|' operators. Standard error is typically used for writing error +messages; the reason there are two separate streams, standard output, +and standard error, is so that they can be redirected separately. In other implementations of `awk', the only way to write an error message to standard error in an `awk' program is as follows: print "Serious error detected!" | "cat 1>&2" -This works by opening a pipeline to a shell command which can access the -standard error stream which it inherits from the `awk' process. This -is far from elegant, and is also inefficient, since it requires a -separate process. So people writing `awk' programs often neglect to do +This works by opening a pipeline to a shell command that can access the +standard error stream that it inherits from the `awk' process. This is +far from elegant, and it is also inefficient, because it requires a +separate process. So people writing `awk' programs often don't do this. Instead, they send the error messages to the terminal, like this: print "Serious error detected!" > "/dev/tty" -This usually has the same effect, but not always: although the standard -error stream is usually the terminal, it can be redirected, and when -that happens, writing to the terminal is not correct. In fact, if -`awk' is run from a background job, it may not have a terminal at all. -Then opening `/dev/tty' will fail. +This usually has the same effect but not always: although the standard +error stream is usually the terminal, it can be redirected; when that +happens, writing to the terminal is not correct. In fact, if `awk' is +run from a background job, it may not have a terminal at all. Then +opening `/dev/tty' fails. `gawk' provides special file names for accessing the three standard -streams. When you redirect input or output in `gawk', if the file name -matches one of these special names, then `gawk' directly uses the -stream it stands for. +streams, as well as any other inherited open files. If the file name +matches one of these special names when `gawk' redirects input or +output, then it directly uses the stream that the file name stands for. +(These special file names work for all operating systems that `gawk' +has been ported to, not just those that are POSIX-compliant.): `/dev/stdin' The standard input (file descriptor 0). @@ -4326,39 +4910,46 @@ stream it stands for. The standard error output (file descriptor 2). `/dev/fd/N' - The file associated with file descriptor N. Such a file must have - been opened by the program initiating the `awk' execution - (typically the shell). Unless you take special pains in the shell - from which you invoke `gawk', only descriptors 0, 1 and 2 are - available. + The file associated with file descriptor N. Such a file must be + opened by the program initiating the `awk' execution (typically + the shell). Unless special pains are taken in the shell from which + `gawk' is invoked, only descriptors 0, 1, and 2 are available. The file names `/dev/stdin', `/dev/stdout', and `/dev/stderr' are -aliases for `/dev/fd/0', `/dev/fd/1', and `/dev/fd/2', respectively, -but they are more self-explanatory. - - The proper way to write an error message in a `gawk' program is to -use `/dev/stderr', like this: +aliases for `/dev/fd/0', `/dev/fd/1', and `/dev/fd/2', respectively. +However, they are more self-explanatory. The proper way to write an +error message in a `gawk' program is to use `/dev/stderr', like this: print "Serious error detected!" > "/dev/stderr" + Note the use of quotes around the file name. Like any other +redirection, the value must be a string. It is a common error to omit +the quotes, which leads to confusing results. + + +File: gawk.info, Node: Special Process, Next: Special Network, Prev: Special FD, Up: Special Files + +Special Files for Process-Related Information +--------------------------------------------- + `gawk' also provides special file names that give access to information about the running `gawk' process. Each of these "files" provides a single record of information. To read them more than once, -you must first close them with the `close' function (*note Closing -Input and Output Files and Pipes: Close Files And Pipes.). The -filenames are: +they must first be closed with the `close' function (*note Closing +Input and Output Redirections: Close Files And Pipes.). The file names +are: `/dev/pid' Reading this file returns the process ID of the current process, - in decimal, terminated with a newline. + in decimal form, terminated with a newline. `/dev/ppid' Reading this file returns the parent process ID of the current - process, in decimal, terminated with a newline. + process, in decimal form, terminated with a newline. `/dev/pgrpid' Reading this file returns the process group ID of the current - process, in decimal, terminated with a newline. + process, in decimal form, terminated with a newline. `/dev/user' Reading this file returns a single record terminated with a @@ -4382,56 +4973,103 @@ filenames are: group ID number). If there are any additional fields, they are the group IDs - returned by `getgroups' system call. (Multiple groups may not be - supported on all systems.) + returned by the `getgroups' system call. (Multiple groups may not + be supported on all systems.) These special file names may be used on the command line as data files, as well as for I/O redirections within an `awk' program. They may not be used as source files with the `-f' option. - Recognition of these special file names is disabled if `gawk' is in -compatibility mode (*note Command Line Options: Options.). + *Note:* The special files that provide process-related information +are now considered obsolete and will disappear entirely in the next +release of `gawk'. `gawk' prints a warning message every time you use +one of these files. To obtain process-related information, use the +`PROCINFO' array. *Note Built-in Variables That Convey Information: +Auto-set. + + +File: gawk.info, Node: Special Network, Next: Special Caveats, Prev: Special Process, Up: Special Files + +Special Files for Network Communications +---------------------------------------- + + Starting with version 3.1 of `gawk', `awk' programs can open a +two-way TCP/IP connection, acting as either a client or server. This +is done using a special file name of the form: + + `/inet/PROTOCOL/LOCAL-PORT/REMOTE-HOST/REMOTE-PORT' + + The PROTOCOL is one of `tcp', `udp', or `raw', and the other fields +represent the other essential pieces of information for making a +networking connection. These file names are used with the `|&' +operator for communicating with a coprocess (*note Two-Way +Communications with Another Process: Two-way I/O.). This is an +advanced feature, mentioned here only for completeness. Full +discussion is delayed until *Note Using `gawk' for Network Programming: +TCP/IP Networking. - *Caution*: Unless your system actually has a `/dev/fd' directory -(or any of the other above listed special files), the interpretation of -these file names is done by `gawk' itself. For example, using -`/dev/fd/4' for output will actually write on file descriptor 4, and -not on a new file descriptor that was `dup''ed from file descriptor 4. -Most of the time this does not matter; however, it is important to -_not_ close any of the files related to file descriptors 0, 1, and 2. -If you do close one of these files, unpredictable behavior will result. + +File: gawk.info, Node: Special Caveats, Prev: Special Network, Up: Special Files + +Special File Name Caveats +------------------------- + + Here is a list of things to bear in mind when using the special file +names that `gawk' provides. + + * Recognition of these special file names is disabled if `gawk' is in + compatibility mode (*note Command-Line Options: Options.). + + * The special files that provide process-related information are now + considered obsolete and will disappear entirely in the next + release of `gawk'. `gawk' prints a warning message every time you + use one of these files. To obtain process-related information, + use the `PROCINFO' array. *Note Built-in Variables::. + + * Starting with version 3.1, `gawk' _always_ interprets these + special file names.(1) For example, using `/dev/fd/4' for output + actually writes on file descriptor 4, and not on a new file + descriptor that is `dup''ed from file descriptor 4. Most of the + time this does not matter; however, it is important to _not_ close + any of the files related to file descriptors 0, 1, and 2. Doing + so results in unpredictable behavior. + + ---------- Footnotes ---------- - The special files that provide process-related information will -disappear in a future version of `gawk'. *Note Probable Future -Extensions: Future Extensions. + (1) Older versions of `gawk' would only interpret these names +internally if the system did not actually have a a `/dev/fd' directory +or any of the other above listed special files. Usually this didn't +make a difference, but sometimes it did; thus, it was decided to make +`gawk''s behavior consistent on all systems and to have it always +interpret the special file names itself.  File: gawk.info, Node: Close Files And Pipes, Prev: Special Files, Up: Printing -Closing Input and Output Files and Pipes -======================================== +Closing Input and Output Redirections +===================================== If the same file name or the same shell command is used with -`getline' (*note Explicit Input with `getline': Getline.) more than -once during the execution of an `awk' program, the file is opened (or -the command is executed) only the first time. At that time, the first +`getline' more than once during the execution of an `awk' program +(*note Explicit Input with `getline': Getline.), the file is opened (or +the command is executed) the first time only. At that time, the first record of input is read from that file or command. The next time the -same file or command is used in `getline', another record is read from -it, and so on. +same file or command is used with `getline', another record is read +from it, and so on. - Similarly, when a file or pipe is opened for output, the file name -or command associated with it is remembered by `awk' and subsequent + Similarly, when a file or pipe is opened for output, the file name or +command associated with it is remembered by `awk', and subsequent writes to the same file or command are appended to the previous writes. The file or pipe stays open until `awk' exits. - This implies that if you want to start reading the same file again -from the beginning, or if you want to rerun a shell command (rather than -reading more output from the command), you must take special steps. -What you must do is use the `close' function, as follows: + This implies that special steps are necessary in order to read the +same file again from the beginning, or to rerun a shell command (rather +than reading more output from the same command). The `close' function +makes these things possible: close(FILENAME) -or +or: close(COMMAND) @@ -4448,12 +5086,11 @@ then you must close it with this: Once this function call is executed, the next `getline' from that file or command, or the next `print' or `printf' to that file or -command, will reopen the file or rerun the command. - - Because the expression that you use to close a file or pipeline must -exactly match the expression used to open the file or run the command, -it is good practice to use a variable to store the file name or command. -The previous example would become +command, reopens the file or reruns the command. Because the +expression that you use to close a file or pipeline must exactly match +the expression used to open the file or run the command, it is good +practice to use a variable to store the file name or command. The +previous example becomes the following: sortcom = "sort -r names" sortcom | getline foo @@ -4461,67 +5098,142 @@ The previous example would become close(sortcom) This helps avoid hard-to-find typographical errors in your `awk' -programs. - - Here are some reasons why you might need to close an output file: +programs. Here are some of the reasons for closing an output file: * To write a file and read it back later on in the same `awk' - program. Close the file when you are finished writing it; then - you can start reading it with `getline'. + program. Close the file after writing it, then begin reading it + with `getline'. * To write numerous files, successively, in the same `awk' program. - If you don't close the files, eventually you may exceed a system - limit on the number of open files in one process. So close each - one when you are finished writing it. + If the files aren't closed, eventually `awk' may exceed a system + limit on the number of open files in one process. It is best to + close each one when the program has finished writing it. - * To make a command finish. When you redirect output through a pipe, - the command reading the pipe normally continues to try to read - input as long as the pipe is open. Often this means the command - cannot really do its work until the pipe is closed. For example, - if you redirect output to the `mail' program, the message is not - actually sent until the pipe is closed. + * To make a command finish. When output is redirected through a + pipe, the command reading the pipe normally continues to try to + read input as long as the pipe is open. Often this means the + command cannot really do its work until the pipe is closed. For + example, if output is redirected to the `mail' program, the + message is not actually sent until the pipe is closed. * To run the same program a second time, with the same arguments. This is not the same thing as giving more input to the first run! - For example, suppose you pipe output to the `mail' program. If you - output several lines redirected to this pipe without closing it, - they make a single message of several lines. By contrast, if you - close the pipe after each line of output, then each line makes a - separate message. - - `close' returns a value of zero if the close succeeded. Otherwise, -the value will be non-zero. In this case, `gawk' sets the variable -`ERRNO' to a string describing the error that occurred. + For example, suppose a program pipes output to the `mail' program. + If it outputs several lines redirected to this pipe without closing + it, they make a single message of several lines. By contrast, if + the program closes the pipe after each line of output, then each + line makes a separate message. If you use more files than the system allows you to have open, -`gawk' will attempt to multiplex the available open files among your -data files. `gawk''s ability to do this depends upon the facilities of -your operating system: it may not always work. It is therefore both -good practice and good portability advice to always use `close' on your -files when you are done with them. +`gawk' attempts to multiplex the available open files among your data +files. `gawk''s ability to do this depends upon the facilities of your +operating system, so it may not always work. It is therefore both good +practice and good portability advice to always use `close' on your +files when you are done with them. In fact, if you are using a lot of +pipes, it is essential that you close commands when done. For example, +consider something like this: - -File: gawk.info, Node: Expressions, Next: Patterns and Actions, Prev: Printing, Up: Top + { + ... + command = ("grep " $1 " /some/file | my_prog -q " $3) + while ((command | getline) > 0) { + PROCESS OUTPUT OF command + } + # need close(command) here + } + + This example creates a new pipeline based on data in _each_ record. +Without the call to `close' indicated in the comment, `awk' creates +child processes to run the commands, until it eventually runs out of +file descriptors for more pipelines. + + Even though each command has finished (as indicated by the +end-of-file return status from `getline'), the child process is not +terminated;(1) more importantly, the file descriptor for the pipe is +not closed and released until `close' is called or `awk' exits. + + `close' will silently do nothing if given an argument that does not +represent a file, pipe or coprocess that was opened with a redirection. + + When using the `|&' operator to communicate with a coprocess, it is +occasionally useful to be able to close one end of the two-way pipe +without closing the other. This is done by supplying a second argument +to `close'. As in any other call to `close', the first argument is the +name of the command or special file used to start the coprocess. The +second argument should be a string, with either of the values `"to"' or +`"from"'. Case does not matter. As this is an advanced feature, a +more complete discussion is delayed until *Note Two-Way Communications +with Another Process: Two-way I/O, which discusses it in more detail +and gives an example. + +Advanced Notes: Using `close''s Return Value +-------------------------------------------- + + In many versions of Unix `awk', the `close' function is actually a +statement. It is a syntax error to try and use the return value from +`close': (d.c.) + + command = "..." + command | getline info + retval = close(command) # syntax error in most Unix awks + + `gawk' treats `close' as a function. The return value is -1 if the +argument names something that was never opened with a redirection, or +if there is a system problem closing the file or process. In these +cases, `gawk' sets the built-in variable `ERRNO' to a string describing +the problem. + + In `gawk', when closing a pipe or coprocess, the return value is the +exit status of the command. Otherwise, it is the return value from the +system's `close' or `fclose' C functions when closing input or output +files, respectively. This value is zero if the close succeeds, or -1 if +it fails. + + The return value for closing a pipeline is particularly useful. It +allows you to get the output from a command as well as its exit status. + + For POSIX-compliant systems, if the exit status is a number above +128, then the program was terminated by a signal. Subtract 128 to get +the signal number: + + exit_val = close(command) + if (exit_val > 128) + print command, "died with signal", exit_val - 128 + else + print command, "exited with code", exit_val + + Currently, in `gawk', this only works for commands piping into +`getline'. For commands piped into from `print' or `printf', the +return value from `close' is that of the library's `pclose' function. + + ---------- Footnotes ---------- + + (1) The technical terminology is rather morbid. The finished child +is called a "zombie," and cleaning up after it is referred to as +"reaping." + + +File: gawk.info, Node: Expressions, Next: Patterns and Actions, Prev: Printing, Up: Top Expressions *********** Expressions are the basic building blocks of `awk' patterns and -actions. An expression evaluates to a value, which you can print, test, -store in a variable or pass to a function. Additionally, an expression -can assign a new value to a variable or a field, with an assignment -operator. +actions. An expression evaluates to a value that you can print, test, +or pass to a function. Additionally, an expression can assign a new +value to a variable or a field by using an assignment operator. An expression can serve as a pattern or action statement on its own. -Most other kinds of statements contain one or more expressions which -specify data on which to operate. As in other languages, expressions -in `awk' include variables, array references, constants, and function -calls, as well as combinations of these with various operators. +Most other kinds of statements contain one or more expressions that +specify the data on which to operate. As in other languages, +expressions in `awk' include variables, array references, constants, +and function calls, as well as combinations of these with various +operators. * Menu: -* Constants:: String, numeric, and regexp constants. +* Constants:: String, numeric and regexp constants. * Using Constant Regexps:: When and how to use a regexp constant. * Variables:: Variables give names to values for later use. * Conversion:: The conversion of strings to numbers and vice @@ -4532,7 +5244,7 @@ calls, as well as combinations of these with various operators. * Assignment Ops:: Changing the value of a variable or a field. * Increment Ops:: Incrementing the numeric value of a variable. * Truth Values:: What is ``true'' and what is ``false''. -* Typing and Comparison:: How variables acquire types, and how this +* Typing and Comparison:: How variables acquire types and how this affects comparison of numbers and strings with `<', etc. * Boolean Ops:: Combining comparison expressions using boolean @@ -4551,46 +5263,129 @@ Constant Expressions ==================== The simplest type of expression is the "constant", which always has -the same value. There are three types of constants: numeric constants, -string constants, and regular expression constants. +the same value. There are three types of constants: numeric, string, +and regular expression. + + Each is used in the appropriate context when you need a data value +that isn't going to change. Numeric constants can have different +forms, but are stored identically internally. * Menu: * Scalar Constants:: Numeric and string constants. +* Non-decimal-numbers:: What are octal and hex numbers. * Regexp Constants:: Regular Expression constants.  -File: gawk.info, Node: Scalar Constants, Next: Regexp Constants, Prev: Constants, Up: Constants +File: gawk.info, Node: Scalar Constants, Next: Non-decimal-numbers, Prev: Constants, Up: Constants Numeric and String Constants ---------------------------- A "numeric constant" stands for a number. This number can be an integer, a decimal fraction, or a number in scientific (exponential) -notation.(1) Here are some examples of numeric constants, which all -have the same value: +notation.(1) Here are some examples of numeric constants that all have +the same value: 105 1.05e+2 1050e-1 A string constant consists of a sequence of characters enclosed in -double-quote marks. For example: +double quote marks. For example: "parrot" represents the string whose contents are `parrot'. Strings in `gawk' -can be of any length and they can contain any of the possible eight-bit -ASCII characters including ASCII NUL (character code zero). Other `awk' -implementations may have difficulty with some character codes. +can be of any length, and they can contain any of the possible +eight-bit ASCII characters including ASCII NUL (character code zero). +Other `awk' implementations may have difficulty with some character +codes. ---------- Footnotes ---------- - (1) The internal representation uses double-precision floating point -numbers. If you don't know what that means, then don't worry about it. + (1) The internal representation of all numbers, including integers, +uses double-precision floating-point numbers. On most modern systems, +these are in IEEE 754 standard format. + + +File: gawk.info, Node: Non-decimal-numbers, Next: Regexp Constants, Prev: Scalar Constants, Up: Constants + +Octal and Hexadecimal Numbers +----------------------------- + + In `awk', all numbers are in decimal; i.e., base 10. Many other +programming languages allow you to specify numbers in other bases, often +octal (base 8) and hexadecimal (base 16). In octal, the numbers go 0, +1, 2, 3, 4, 5, 6, 7, 10, 11, 12, etc.. Just as `11' in decimal is 1 +times 10 plus 1, so `11' in octal is 1 times 8, plus 1. This equals +nine in decimal. In hexadecimal, there are 16 digits. Since the +everyday decimal number system only has ten digits (`0'--`9'), the +letters `a' through `f' are used to represent the rest. (Case in the +letters is usually irrelevant; hexadecimal `a' and `A' have the same +value.) Thus, `11' in hexadecimal is 1 times 16 plus 1, which equals +17 in decimal. + + Just by looking at plain `11', you can't tell what base it's in. +So, in C, C++, and other languages derived from C, there is a special +notation to help signify the base. Octal numbers start with a leading +`0', and hexadecimal numbers start with a leading `0x' or `0X': + +`11' + Decimal 11. + +`011' + Octal 11, decimal value 9. + +`0x11' + Hexadecimal 11, decimal value 17. + + This example shows the difference: + + $ gawk 'BEGIN { printf "%d, %d, %d\n", 011, 11, 0x11 }' + -| 9, 11, 17 + + Being able to use octal and hexadecimal constants in your programs +is most useful when working with data that cannot be represented +conveniently as characters or as regular numbers, such as binary data +of various sorts. + + `gawk' allows the use of octal and hexadecimal constants in your +program text. However, such numbers in the input data are not treated +differently; doing so by default would break old programs. (If you +really need to do this, use the `--non-decimal-data' command-line +option, *note Allowing Non-Decimal Input Data: Non-decimal Data..) If +you have octal or hexadecimal data, you can use the `strtonum' function +(*note String Manipulation Functions: String Functions.) to convert +the data into a number. Most of the time, you will want to use octal +or hexadecimal constants when working with the built-in bit +manipulation functions; see *Note Using `gawk''s Bit Manipulation +Functions: Bitwise Functions, for more information. + + Unlike some early C implementations, `8' and `9' are not valid in +octal constants; e.g., `gawk' treats `018' as decimal 18. + + $ gawk 'BEGIN { print "021 is", 021 ; print 018 }' + -| 021 is 17 + -| 18 + + Octal and hexadecimal source code constants are a `gawk' extension. +If `gawk' is in compatibility mode (*note Command-Line Options: +Options.), they are not available. + +Advanced Notes: A Constant's Base Does Not Affect Its Value +----------------------------------------------------------- + + Once a numeric constant has been converted internally into a number, +`gawk' no longer remembers what the original form of the constant was; +the internal value is always used. This has particular consequences +for conversion of numbers to strings: + + $ gawk 'BEGIN { printf "0x11 is <%s>\n", 0x11 }' + -| 0x11 is <17>  -File: gawk.info, Node: Regexp Constants, Prev: Scalar Constants, Up: Constants +File: gawk.info, Node: Regexp Constants, Prev: Non-decimal-numbers, Up: Constants Regular Expression Constants ---------------------------- @@ -4607,28 +5402,25 @@ File: gawk.info, Node: Using Constant Regexps, Next: Variables, Prev: Constan Using Regular Expression Constants ================================== - When used on the right hand side of the `~' or `!~' operators, a + When used on the righthand side of the `~' or `!~' operators, a regexp constant merely stands for the regexp that is to be matched. - - Regexp constants (such as `/foo/') may be used like simple +However, regexp constants (such as `/foo/') may be used like simple expressions. When a regexp constant appears by itself, it has the same -meaning as if it appeared in a pattern, i.e. `($0 ~ /foo/)' (d.c.) -(*note Expressions as Patterns: Expression Patterns.). This means that -the two code segments, +meaning as if it appeared in a pattern, i.e.; `($0 ~ /foo/)' (d.c.) +*Note Expressions as Patterns: Expression Patterns. This means that +the following two code segments: if ($0 ~ /barfly/ || $0 ~ /camelot/) print "found" -and +and: if (/barfly/ || /camelot/) print "found" -are exactly equivalent. - - One rather bizarre consequence of this rule is that the following -boolean expression is valid, but does not do what the user probably -intended: +are exactly equivalent. One rather bizarre consequence of this rule is +that the following Boolean expression is valid, but does not do what +the user probably intended: # note that /foo/ is on the left of the ~ if (/foo/ ~ $1) print "found foo" @@ -4636,34 +5428,27 @@ intended: This code is "obviously" testing `$1' for a match against the regexp `/foo/'. But in fact, the expression `/foo/ ~ $1' actually means `($0 ~ /foo/) ~ $1'. In other words, first match the input record against -the regexp `/foo/'. The result will be either zero or one, depending -upon the success or failure of the match. Then match that result -against the first field in the record. - - Since it is unlikely that you would ever really wish to make this -kind of test, `gawk' will issue a warning when it sees this construct in -a program. - - Another consequence of this rule is that the assignment statement +the regexp `/foo/'. The result is either zero or one, depending upon +the success or failure of the match. That result is then matched +against the first field in the record. Because it is unlikely that you +would ever really want to make this kind of test, `gawk' issues a +warning when it sees this construct in a program. Another consequence +of this rule is that the assignment statement: matches = /foo/ -will assign either zero or one to the variable `matches', depending -upon the contents of the current input record. - - This feature of the language was never well documented until the -POSIX specification. +assigns either zero or one to the variable `matches', depending upon +the contents of the current input record. This feature of the language +has never been well documented until the POSIX specification. Constant regular expressions are also used as the first argument for -the `gensub', `sub' and `gsub' functions, and as the second argument of -the `match' function (*note Built-in Functions for String Manipulation: -String Functions.). Modern implementations of `awk', including `gawk', -allow the third argument of `split' to be a regexp constant, while some -older implementations do not (d.c.). - - This can lead to confusion when attempting to use regexp constants -as arguments to user defined functions (*note User-defined Functions: -User-defined.). For example: +the `gensub', `sub', and `gsub' functions, and as the second argument +of the `match' function (*note String Manipulation Functions: String +Functions.). Modern implementations of `awk', including `gawk', allow +the third argument of `split' to be a regexp constant, but some older +implementations do not. (d.c.) This can lead to confusion when +attempting to use regexp constants as arguments to user defined +functions (*note User-Defined Functions: User-defined.). For example: function mysub(pat, repl, str, global) { @@ -4681,15 +5466,13 @@ User-defined.). For example: ... } - In this example, the programmer wishes to pass a regexp constant to -the user-defined function `mysub', which will in turn pass it on to -either `sub' or `gsub'. However, what really happens is that the `pat' -parameter will be either one or zero, depending upon whether or not -`$0' matches `/hi/'. - - As it is unlikely that you would ever really wish to pass a truth -value in this way, `gawk' will issue a warning when it sees a regexp -constant used as a parameter to a user-defined function. + In this example, the programmer wants to pass a regexp constant to +the user-defined function `mysub', which in turn passes it on to either +`sub' or `gsub'. However, what really happens is that the `pat' +parameter is either one or zero, depending upon whether or not `$0' +matches `/hi/'. `gawk' issues a warning when it sees a regexp constant +used as a parameter to a user-defined function, since passing a truth +value in this way is probably not what was intended.  File: gawk.info, Node: Variables, Next: Conversion, Prev: Using Constant Regexps, Up: Expressions @@ -4698,15 +5481,15 @@ Variables ========= Variables are ways of storing values at one point in your program for -use later in another part of your program. You can manipulate them -entirely within your program text, and you can also assign values to -them on the `awk' command line. +use later in another part of your program. They can be manipulated +entirely within the program text, and they can also be assigned values +on the `awk' command line. * Menu: * Using Variables:: Using variables in your programs. -* Assignment Options:: Setting variables on the command line and a - summary of command line syntax. This is an +* Assignment Options:: Setting variables on the command-line and a + summary of command-line syntax. This is an advanced method of input.  @@ -4715,29 +5498,31 @@ File: gawk.info, Node: Using Variables, Next: Assignment Options, Prev: Varia Using Variables in a Program ---------------------------- - Variables let you give names to values and refer to them later. You -have already seen variables in many of the examples. The name of a -variable must be a sequence of letters, digits and underscores, but it -may not begin with a digit. Case is significant in variable names; `a' -and `A' are distinct variables. + Variables let you give names to values and refer to them later. +Variables have already been used in many of the examples. The name of +a variable must be a sequence of letters, digits, or underscores, and +it may not begin with a digit. Case is significant in variable names; +`a' and `A' are distinct variables. A variable name is a valid expression by itself; it represents the variable's current value. Variables are given new values with -"assignment operators", "increment operators" and "decrement operators". -*Note Assignment Expressions: Assignment Ops. +"assignment operators", "increment operators", and "decrement +operators". *Note Assignment Expressions: Assignment Ops. - A few variables have special built-in meanings, such as `FS', the -field separator, and `NF', the number of fields in the current input -record. *Note Built-in Variables::, for a list of them. These -built-in variables can be used and assigned just like all other -variables, but their values are also used or changed automatically by -`awk'. All built-in variables names are entirely upper-case. + A few variables have special built-in meanings, such as `FS' (the +field separator), and `NF' (the number of fields in the current input +record). *Note Built-in Variables::, for a list of the built-in +variables. These built-in variables can be used and assigned just like +all other variables, but their values are also used or changed +automatically by `awk'. All built-in variables' names are entirely +uppercase. Variables in `awk' can be assigned either numeric or string values. -By default, variables are initialized to the empty string, which is -zero if converted to a number. There is no need to "initialize" each -variable explicitly in `awk', the way you would in C and in most other -traditional languages. +The kind of value a variable holds can change over the life of a +program. By default, variables are initialized to the empty string, +which is zero if converted to a number. There is no need to +"initialize" each variable explicitly in `awk', which is what you would +do in C and in most other traditional languages.  File: gawk.info, Node: Assignment Options, Prev: Using Variables, Up: Variables @@ -4745,28 +5530,26 @@ File: gawk.info, Node: Assignment Options, Prev: Using Variables, Up: Variabl Assigning Variables on the Command Line --------------------------------------- - You can set any `awk' variable by including a "variable assignment" -among the arguments on the command line when you invoke `awk' (*note -Other Command Line Arguments: Other Arguments.). Such an assignment has -this form: + Any `awk' variable can be set by including a "variable assignment" +among the arguments on the command line when `awk' is invoked (*note +Other Command-Line Arguments: Other Arguments.). Such an assignment +has the following form: VARIABLE=TEXT -With it, you can set a variable either at the beginning of the `awk' -run or in between input files. - - If you precede the assignment with the `-v' option, like this: +With it, a variable is set either at the beginning of the `awk' run or +in between input files. When the assignment is preceded with the `-v' +option, as in the following: -v VARIABLE=TEXT -then the variable is set at the very beginning, before even the `BEGIN' +the variable is set at the very beginning, even before the `BEGIN' rules are run. The `-v' option and its assignment must precede all the -file name arguments, as well as the program text. (*Note Command Line +file name arguments, as well as the program text. (*Note Command-Line Options: Options, for more information about the `-v' option.) - - Otherwise, the variable assignment is performed at a time determined -by its position among the input file arguments: after the processing of -the preceding input file argument. For example: +Otherwise, the variable assignment is performed at a time determined by +its position among the input file arguments--after the processing of the +preceding input file argument. For example: awk '{ print $n }' n=4 inventory-shipped n=2 BBS-list @@ -4775,7 +5558,7 @@ first file is read, the command line sets the variable `n' equal to four. This causes the fourth field to be printed in lines from the file `inventory-shipped'. After the first file has finished, but before the second file is started, `n' is set to two, so that the -second field is printed in lines from `BBS-list'. +second field is printed in lines from `BBS-list': $ awk '{ print $n }' n=4 inventory-shipped n=2 BBS-list -| 15 @@ -4785,12 +5568,10 @@ second field is printed in lines from `BBS-list'. -| 555-3412 ... - Command line arguments are made available for explicit examination by + Command-line arguments are made available for explicit examination by the `awk' program in an array named `ARGV' (*note Using `ARGC' and -`ARGV': ARGC and ARGV.). - - `awk' processes the values of command line assignments for escape -sequences (d.c.) (*note Escape Sequences::). +`ARGV': ARGC and ARGV.). `awk' processes the values of command-line +assignments for escape sequences (d.c.) (*note Escape Sequences::).  File: gawk.info, Node: Conversion, Next: Arithmetic Ops, Prev: Variables, Up: Expressions @@ -4798,68 +5579,72 @@ File: gawk.info, Node: Conversion, Next: Arithmetic Ops, Prev: Variables, Up Conversion of Strings and Numbers ================================= - Strings are converted to numbers, and numbers to strings, if the -context of the `awk' program demands it. For example, if the value of -either `foo' or `bar' in the expression `foo + bar' happens to be a -string, it is converted to a number before the addition is performed. -If numeric values appear in string concatenation, they are converted to -strings. Consider this: + Strings are converted to numbers and numbers are converted to +strings, if the context of the `awk' program demands it. For example, +if the value of either `foo' or `bar' in the expression `foo + bar' +happens to be a string, it is converted to a number before the addition +is performed. If numeric values appear in string concatenation, they +are converted to strings. Consider the following: two = 2; three = 3 print (two three) + 4 This prints the (numeric) value 27. The numeric values of the variables `two' and `three' are converted to strings and concatenated -together, and the resulting string is converted back to the number 23, -to which four is then added. +together. The resulting string is converted back to the number 23, to +which four is then added. If, for some reason, you need to force a number to be converted to a string, concatenate the empty string, `""', with that number. To force -a string to be converted to a number, add zero to that string. - - A string is converted to a number by interpreting any numeric prefix -of the string as numerals: `"2.5"' converts to 2.5, `"1e3"' converts to +a string to be converted to a number, add zero to that string. A +string is converted to a number by interpreting any numeric prefix of +the string as numerals: `"2.5"' converts to 2.5, `"1e3"' converts to 1000, and `"25fix"' has a numeric value of 25. Strings that can't be -interpreted as valid numbers are converted to zero. +interpreted as valid numbers convert to zero. The exact manner in which numbers are converted into strings is controlled by the `awk' built-in variable `CONVFMT' (*note Built-in -Variables::). Numbers are converted using the `sprintf' function -(*note Built-in Functions for String Manipulation: String Functions.) -with `CONVFMT' as the format specifier. +Variables::). Numbers are converted using the `sprintf' function with +`CONVFMT' as the format specifier (*note String Manipulation Functions: +String Functions.). `CONVFMT''s default value is `"%.6g"', which prints a value with at -least six significant digits. For some applications you will want to -change it to specify more precision. On most modern machines, you must -print 17 digits to capture a floating point number's value exactly. - - Strange results can happen if you set `CONVFMT' to a string that -doesn't tell `sprintf' how to format floating point numbers in a useful -way. For example, if you forget the `%' in the format, all numbers -will be converted to the same constant string. - - As a special case, if a number is an integer, then the result of -converting it to a string is _always_ an integer, no matter what the -value of `CONVFMT' may be. Given the following code fragment: +least six significant digits. For some applications, you might want to +change it to specify more precision. On most modern machines, 17 +digits is enough to capture a floating-point number's value exactly, +most of the time.(1) + + Strange results can occur if you set `CONVFMT' to a string that +doesn't tell `sprintf' how to format floating-point numbers in a useful +way. For example, if you forget the `%' in the format, `awk' converts +all numbers to the same constant string. As a special case, if a +number is an integer, then the result of converting it to a string is +_always_ an integer, no matter what the value of `CONVFMT' may be. +Given the following code fragment: CONVFMT = "%2.2f" a = 12 b = a "" -`b' has the value `"12"', not `"12.00"' (d.c.). - - Prior to the POSIX standard, `awk' specified that the value of -`OFMT' was used for converting numbers to strings. `OFMT' specifies -the output format to use when printing numbers with `print'. `CONVFMT' -was introduced in order to separate the semantics of conversion from -the semantics of printing. Both `CONVFMT' and `OFMT' have the same -default value: `"%.6g"'. In the vast majority of cases, old `awk' -programs will not change their behavior. However, this use of `OFMT' -is something to keep in mind if you must port your program to other -implementations of `awk'; we recommend that instead of changing your -programs, you just port `gawk' itself! *Note The `print' Statement: +`b' has the value `"12"', not `"12.00"'. (d.c.) + + Prior to the POSIX standard, `awk' used the value of `OFMT' for +converting numbers to strings. `OFMT' specifies the output format to +use when printing numbers with `print'. `CONVFMT' was introduced in +order to separate the semantics of conversion from the semantics of +printing. Both `CONVFMT' and `OFMT' have the same default value: +`"%.6g"'. In the vast majority of cases, old `awk' programs do not +change their behavior. However, these semantics for `OFMT' are +something to keep in mind if you must port your new style program to +older implementations of `awk'. We recommend that instead of changing +your programs, just port `gawk' itself. *Note The `print' Statement: Print, for more information on the `print' statement. + ---------- Footnotes ---------- + + (1) Pathological cases can require up to 752 digits (!), but we +doubt that you need to worry about this. +  File: gawk.info, Node: Arithmetic Ops, Next: Concatenation, Prev: Conversion, Up: Expressions @@ -4868,19 +5653,18 @@ Arithmetic Operators The `awk' language uses the common arithmetic operators when evaluating expressions. All of these arithmetic operators follow normal -precedence rules, and work as you would expect them to. Arithmetic -operations are evaluated using double precision floating point, which -has the usual problems of inexactness and exceptions.(1) +precedence rules and work as you would expect them to. - Here is a file `grades' containing a list of student names and three -test scores per student (it's a small class): + The following example uses a file named `grades', which contains a +list of student names as well as three test scores per student (it's a +small class): Pat 100 97 58 Sandy 84 72 93 Chris 72 92 89 -This programs takes the file `grades', and prints the average of the -scores. +This programs takes the file `grades' and prints the average of the +scores: $ awk '{ sum = $2 + $3 + $4 ; avg = sum / 3 > print $1, avg }' grades @@ -4888,44 +5672,34 @@ scores. -| Sandy 83 -| Chris 84.3333 - This table lists the arithmetic operators in `awk', in order from -highest precedence to lowest: + The following list provides the arithmetic operators in `awk', in +order from the highest precedence to the lowest: `- X' Negation. `+ X' - Unary plus. The expression is converted to a number. + Unary plus; the expression is converted to a number. `X ^ Y' `X ** Y' - Exponentiation: X raised to the Y power. `2 ^ 3' has the value - eight. The character sequence `**' is equivalent to `^'. (The - POSIX standard only specifies the use of `^' for exponentiation.) + Exponentiation; X raised to the Y power. `2 ^ 3' has the value + eight; the character sequence `**' is equivalent to `^'. `X * Y' Multiplication. `X / Y' - Division. Since all numbers in `awk' are floating point numbers, - the result is not rounded to an integer: `3 / 4' has the value - 0.75. + Division; because all numbers in `awk' are floating-point + numbers, the result is _not_ rounded to an integer--`3 / 4' has + the value 0.75. (It is a common mistake, especially for C + programmers, to forget that _all_ numbers in `awk' are + floating-point, and that division of integer-looking constants + produces a real number, not an integer.) `X % Y' - Remainder. The quotient is rounded toward zero to an integer, - multiplied by Y and this result is subtracted from X. This - operation is sometimes known as "trunc-mod." The following - relation always holds: - - b * int(a / b) + (a % b) == a - - One possibly undesirable effect of this definition of remainder is - that `X % Y' is negative if X is negative. Thus, - - -17 % 8 = -1 - - In other `awk' implementations, the signedness of the remainder - may be machine dependent. + Remainder; further discussion is provided in the text, just after + this list. `X + Y' Addition. @@ -4933,17 +5707,27 @@ highest precedence to lowest: `X - Y' Subtraction. - For maximum portability, do not use the `**' operator. - Unary plus and minus have the same precedence, the multiplication operators all have the same precedence, and addition and subtraction have the same precedence. - ---------- Footnotes ---------- + When computing the remainder of `X % Y', the quotient is rounded +toward zero to an integer and multiplied by Y. This result is +subtracted from X; this operation is sometimes known as "trunc-mod." +The following relation always holds: - (1) David Goldberg, `What Every Computer Scientist Should Know About -Floating-point Arithmetic' (http://www.validgh.com/goldberg/paper.ps), -`ACM Computing Surveys' *23*, 1 (1991-03), 5-48. + b * int(a / b) + (a % b) == a + + One possibly undesirable effect of this definition of remainder is +that `X % Y' is negative if X is negative. Thus: + + -17 % 8 = -1 + + In other `awk' implementations, the signedness of the remainder may +be machine dependent. + + *Note:* The POSIX standard only specifies the use of `^' for +exponentiation. For maximum portability, do not use the `**' operator.  File: gawk.info, Node: Concatenation, Next: Assignment Ops, Prev: Arithmetic Ops, Up: Expressions @@ -4954,8 +5738,6 @@ String Concatenation It seemed like a good idea at the time. Brian Kernighan - - There is only one string operation: concatenation. It does not have a specific operator to represent it. Instead, concatenation is performed by writing expressions next to one another, with no operator. @@ -4967,16 +5749,16 @@ For example: ... Without the space in the string constant after the `:', the line -would run together. For example: +runs together. For example: $ awk '{ print "Field number one:" $1 }' BBS-list -| Field number one:aardvark -| Field number one:alpo-net ... - Since string concatenation does not have an explicit operator, it is -often necessary to insure that it happens where you want it to by using -parentheses to enclose the items to be concatenated. For example, the + Because string concatenation does not have an explicit operator, it +is often necessary to insure that it happens at the right time by using +parentheses to enclose the items to concatenate. For example, the following code fragment does not concatenate `file' and `name' as you might expect: @@ -4988,8 +5770,45 @@ It is necessary to use the following: print "something meaningful" > (file name) - We recommend that you use parentheses around concatenation in all -but the most common contexts (such as on the right-hand side of `='). + Parentheses should be used around concatenation in all but the most +common contexts, such as on the righthand side of `='. Be careful +about the kinds of expressions used in string concatenation. In +particular, the order of evaluation of expressions used for +concatenation is undefined in the `awk' language. Consider this +example: + + BEGIN { + a = "don't" + print (a " " (a = "panic")) + } + +It is not defined whether the assignment to `a' happens before or after +the value of `a' is retrieved for producing the concatenated value. +The result could be either `don't panic', or `panic panic'. The +precedence of concatenation, when mixed with other operators, is often +counter-intuitive. Consider this example: + + $ awk 'BEGIN { print -12 " " -24 }' + -| -12-24 + + This "obviously" is concatenating -12, a space, and -24. But where +did the space disappear to? The answer lies in the combination of +operator precedences and `awk''s automatic conversion rules. To get +the desired result, write the program in the following manner: + + $ awk 'BEGIN { print -12 " " (-24) }' + -| -12 -24 + + This forces `awk' to treat the `-' on the `-24' as unary. +Otherwise, it's parsed as follows: + + -12 (`" "' - 24) + => -12 (0 - 24) + => -12 (-24) + => -12-24 + + As mentioned earlier, when doing concatenation, _parenthesize_. +Otherwise, you're never quite sure what you'll get.  File: gawk.info, Node: Assignment Ops, Next: Increment Ops, Prev: Concatenation, Up: Expressions @@ -4997,46 +5816,44 @@ File: gawk.info, Node: Assignment Ops, Next: Increment Ops, Prev: Concatenati Assignment Expressions ====================== - An "assignment" is an expression that stores a new value into a -variable. For example, let's assign the value one to the variable `z': + An "assignment" is an expression that stores a (usually different) +value into a variable. For example, let's assign the value one to the +variable `z': z = 1 After this expression is executed, the variable `z' has the value one. Whatever old value `z' had before the assignment is forgotten. - Assignments can store string values also. For example, this would -store the value `"this food is good"' in the variable `message': + Assignments can also store string values. For example, the +following stores the value `"this food is good"' in the variable +`message': thing = "food" predicate = "good" message = "this " thing " is " predicate -(This also illustrates string concatenation.) - - The `=' sign is called an "assignment operator". It is the simplest -assignment operator because the value of the right-hand operand is -stored unchanged. +This also illustrates string concatenation. The `=' sign is called an +"assignment operator". It is the simplest assignment operator because +the value of the righthand operand is stored unchanged. Most operators +(addition, concatenation, and so on) have no effect except to compute a +value. If the value isn't used, there's no reason to use the operator. +An assignment operator is different; it does produce a value, but even +if you ignore it, the assignment still makes itself felt through the +alteration of the variable. We call this a "side effect". - Most operators (addition, concatenation, and so on) have no effect -except to compute a value. If you ignore the value, you might as well -not use the operator. An assignment operator is different; it does -produce a value, but even if you ignore the value, the assignment still -makes itself felt through the alteration of the variable. We call this -a "side effect". - - The left-hand operand of an assignment need not be a variable (*note + The lefthand operand of an assignment need not be a variable (*note Variables::); it can also be a field (*note Changing the Contents of a Field: Changing Fields.) or an array element (*note Arrays in `awk': Arrays.). These are all called "lvalues", which means they can appear -on the left-hand side of an assignment operator. The right-hand -operand may be any expression; it produces the new value which the -assignment stores in the specified variable, field or array element. -(Such values are called "rvalues"). +on the lefthand side of an assignment operator. The righthand operand +may be any expression; it produces the new value that the assignment +stores in the specified variable, field, or array element. (Such values +are called "rvalues"). It is important to note that variables do _not_ have permanent types. -The type of a variable is simply the type of whatever value it happens -to hold at the moment. In the following program fragment, the variable +A variable's type is simply the type of whatever value it happens to +hold at the moment. In the following program fragment, the variable `foo' has a numeric value at first, and a string value later on: foo = 1 @@ -5048,38 +5865,39 @@ When the second assignment gives `foo' a string value, the fact that it previously had a numeric value is forgotten. String values that do not begin with a digit have a numeric value of -zero. After executing this code, the value of `foo' is five: +zero. After executing the following code, the value of `foo' is five: foo = "a string" foo = foo + 5 -(Note that using a variable as a number and then later as a string can -be confusing and is poor programming style. The above examples +*Note:* Using a variable as a number and then later as a string can be +confusing and is poor programming style. The previous two examples illustrate how `awk' works, _not_ how you should write your own -programs!) +programs! - An assignment is an expression, so it has a value: the same value -that is assigned. Thus, `z = 1' as an expression has the value one. + An assignment is an expression, so it has a value--the same value +that is assigned. Thus, `z = 1' is an expression with the value one. One consequence of this is that you can write multiple assignments -together: +together, such as: - x = y = z = 0 + x = y = z = 5 -stores the value zero in all three variables. It does this because the -value of `z = 0', which is zero, is stored into `y', and then the value -of `y = z = 0', which is zero, is stored into `x'. +This example stores the value five in all three variables (`x', `y', +and `z'). It does so because the value of `z = 5', which is five, is +stored into `y' and then the value of `y = z = 5', which is five, is +stored into `x'. - You can use an assignment anywhere an expression is called for. For -example, it is valid to write `x != (y = 1)' to set `y' to one and then -test whether `x' equals one. But this style tends to make programs -hard to read; except in a one-shot program, you should not use such -nesting of assignments. + Assignments may be used anywhere an expression is called for. For +example, it is valid to write `x != (y = 1)' to set `y' to one, and +then test whether `x' equals one. But this style tends to make +programs hard to read; such nesting of assignments should be avoided, +except perhaps in a one-shot program. Aside from `=', there are several other assignment operators that do arithmetic with the old value of the variable. For example, the -operator `+=' computes a new value by adding the right-hand value to -the old value of the variable. Thus, the following assignment adds -five to the value of `foo': +operator `+=' computes a new value by adding the righthand value to the +old value of the variable. Thus, the following assignment adds five to +the value of `foo': foo += 5 @@ -5087,11 +5905,11 @@ This is equivalent to the following: foo = foo + 5 -Use whichever one makes the meaning of your program clearer. +Use whichever makes the meaning of your program clearer. There are situations where using `+=' (or any assignment operator) -is _not_ the same as simply repeating the left-hand operand in the -right-hand expression. For example: +is _not_ the same as simply repeating the lefthand operand in the +righthand expression. For example: # Thanks to Pat Rankin for this example BEGIN { @@ -5104,17 +5922,14 @@ right-hand expression. For example: print x, bar[x] } -The indices of `bar' are guaranteed to be different, because `rand' -will return different values each time it is called. (Arrays and the -`rand' function haven't been covered yet. *Note Arrays in `awk': -Arrays, and see *Note Numeric Built-in Functions: Numeric Functions, -for more information). This example illustrates an important fact -about the assignment operators: the left-hand expression is only -evaluated _once_. - - It is also up to the implementation as to which expression is -evaluated first, the left-hand one or the right-hand one. Consider -this example: +The indices of `bar' are practically guaranteed to be different, because +`rand' returns different values each time it is called. (Arrays and +the `rand' function haven't been covered yet. *Note Arrays in `awk': +Arrays, and see *Note Numeric Functions::, for more information). This +example illustrates an important fact about assignment operators: the +lefthand expression is only evaluated _once_. It is up to the +implementation as to which expression is evaluated first, the lefthand +or the righthand. Consider this example: i = 1 a[i += 2] = i + 1 @@ -5122,31 +5937,41 @@ this example: The value of `a[3]' could be either two or four. Here is a table of the arithmetic assignment operators. In each -case, the right-hand operand is an expression whose value is converted +case, the righthand operand is an expression whose value is converted to a number. -`LVALUE += INCREMENT' - Adds INCREMENT to the value of LVALUE to make the new value of - LVALUE. +LVALUE `+=' INCREMENT Adds INCREMENT to the value of LVALUE. +LVALUE `-=' DECREMENT Subtracts DECREMENT from the value of LVALUE. +LVALUE `*=' Multiplies the value of LVALUE by COEFFICIENT. +COEFFICIENT +LVALUE `/=' DIVISOR Divides the value of LVALUE by DIVISOR. +LVALUE `%=' MODULUS Sets LVALUE to its remainder by MODULUS. +LVALUE `^=' POWER +LVALUE `**=' POWER Raises LVALUE to the power POWER. + + *Note:* Only the `^=' operator is specified by POSIX. For maximum +portability, do not use the `**=' operator. -`LVALUE -= DECREMENT' - Subtracts DECREMENT from the value of LVALUE. +Advanced Notes: Syntactic Ambiguities Between `/=' and Regular Expressions +-------------------------------------------------------------------------- -`LVALUE *= COEFFICIENT' - Multiplies the value of LVALUE by COEFFICIENT. + There is a syntactic ambiguity between the `/=' assignment operator +and regexp constants whose first character is an `='. (d.c.) This is +most notable in commercial `awk' versions. For example: -`LVALUE /= DIVISOR' - Divides the value of LVALUE by DIVISOR. + $ awk /==/ /dev/null + error--> awk: syntax error at source line 1 + error--> context is + error--> >>> /= <<< + error--> awk: bailing out at source line 1 -`LVALUE %= MODULUS' - Sets LVALUE to its remainder by MODULUS. +A workaround is: -`LVALUE ^= POWER' -`LVALUE **= POWER' - Raises LVALUE to the power POWER. (Only the `^=' operator is - specified by POSIX.) + awk '/[=]=/' /dev/null - For maximum portability, do not use the `**=' operator. + `gawk' does not have this problem, nor do the other freely-available +versions described in *Note Other Freely Available `awk' +Implementations: Other Versions.  File: gawk.info, Node: Increment Ops, Next: Truth Values, Prev: Assignment Ops, Up: Expressions @@ -5155,44 +5980,41 @@ Increment and Decrement Operators ================================= "Increment" and "decrement operators" increase or decrease the value -of a variable by one. You could do the same thing with an assignment -operator, so the increment operators add no power to the `awk' -language; but they are convenient abbreviations for very common -operations. - - The operator to add one is written `++'. It can be used to increment -a variable either before or after taking its value. - - To pre-increment a variable V, write `++V'. This adds one to the -value of V and that new value is also the value of this expression. -The assignment expression `V += 1' is completely equivalent. - - Writing the `++' after the variable specifies post-increment. This -increments the variable value just the same; the difference is that the -value of the increment expression itself is the variable's _old_ value. -Thus, if `foo' has the value four, then the expression `foo++' has the -value four, but it changes the value of `foo' to five. - - The post-increment `foo++' is nearly equivalent to writing `(foo += -1) - 1'. It is not perfectly equivalent because all numbers in `awk' -are floating point: in floating point, `foo + 1 - 1' does not -necessarily equal `foo'. But the difference is minute as long as you -stick to numbers that are fairly small (less than 10e12). - - Any lvalue can be incremented. Fields and array elements are -incremented just like variables. (Use `$(i++)' when you wish to do a -field reference and a variable increment at the same time. The -parentheses are necessary because of the precedence of the field -reference operator, `$'.) - - The decrement operator `--' works just like `++' except that it -subtracts one instead of adding. Like `++', it can be used before the -lvalue to pre-decrement or after it to post-decrement. - - Here is a summary of increment and decrement expressions. +of a variable by one. An assignment operator can do the same thing, so +the increment operators add no power to the `awk' language; however they +are convenient abbreviations for very common operations. + + The operator used for adding one is written `++'. It can be used to +increment a variable either before or after taking its value. To +pre-increment a variable `v', write `++v'. This adds one to the value +of `v'--that new value is also the value of the expression. (The +assignment expression `v += 1' is completely equivalent.) Writing the +`++' after the variable specifies post-increment. This increments the +variable value just the same; the difference is that the value of the +increment expression itself is the variable's _old_ value. Thus, if +`foo' has the value four, then the expression `foo++' has the value +four, but it changes the value of `foo' to five. In other words, the +operator returns the old value of the variable, but with the side +effect of incrementing it. + + The post-increment `foo++' is nearly the same as writing `(foo += 1) +- 1'. It is not perfectly equivalent because all numbers in `awk' are +floating-point--in floating-point, `foo + 1 - 1' does not necessarily +equal `foo'. But the difference is minute as long as you stick to +numbers that are fairly small (less than 10e12). + + Fields and array elements are incremented just like variables. (Use +`$(i++)' when you want to do a field reference and a variable increment +at the same time. The parentheses are necessary because of the +precedence of the field reference operator `$'.) + + The decrement operator `--' works just like `++', except that it +subtracts one instead of adding it. As with `++', it can be used before +the lvalue to pre-decrement or after it to post-decrement. Following +is a summary of increment and decrement expressions: `++LVALUE' - This expression increments LVALUE and the new value becomes the + This expression increments LVALUE, and the new value becomes the value of the expression. `LVALUE++' @@ -5200,13 +6022,42 @@ lvalue to pre-decrement or after it to post-decrement. is the _old_ value of LVALUE. `--LVALUE' - Like `++LVALUE', but instead of adding, it subtracts. It - decrements LVALUE and delivers the value that results. + This expression is like `++LVALUE', but instead of adding, it + subtracts. It decrements LVALUE and delivers the value that is + the result. `LVALUE--' - Like `LVALUE++', but instead of adding, it subtracts. It - decrements LVALUE. The value of the expression is the _old_ value - of LVALUE. + This expression is like `LVALUE++', but instead of adding, it + subtracts. It decrements LVALUE. The value of the expression is + the _old_ value of LVALUE. + +Advanced Notes: Operator Evaluation Order +----------------------------------------- + + Doctor, doctor! It hurts when I do this! + So don't do that! + Groucho Marx + +What happens for something like the following? + + b = 6 + print b += b++ + +Or something even stranger? + + b = 6 + b += ++b + b++ + print b + + In other words, when do the various side effects prescribed by the +postfix operators (`b++') take effect? When side effects happen is +"implementation defined". In other words, it is up to the particular +version of `awk'. The result for the first example may be 12 or 13, +and for the second, it may be 22 or 23. + + In short, doing things like this is not recommended and definitely +not anything that you can rely upon for portability. You should avoid +such things in your own programs.  File: gawk.info, Node: Truth Values, Next: Typing and Comparison, Prev: Increment Ops, Up: Expressions @@ -5216,13 +6067,12 @@ True and False in `awk' Many programming languages have a special representation for the concepts of "true" and "false." Such languages usually use the special -constants `true' and `false', or perhaps their upper-case equivalents. - - `awk' is different. It borrows a very simple concept of true and -false from C. In `awk', any non-zero numeric value, _or_ any non-empty -string value is true. Any other value (zero or the null string, `""') -is false. The following program will print `A strange truth value' -three times: +constants `true' and `false', or perhaps their uppercase equivalents. +However, `awk' is different. It borrows a very simple concept of true +and false from C. In `awk', any nonzero numeric value _or_ any +non-empty string value is true. Any other value (zero or the null +string `""') is false. The following program prints `A strange truth +value' three times: BEGIN { if (3.1415927) @@ -5233,8 +6083,9 @@ three times: print "A strange truth value" } - There is a surprising consequence of the "non-zero or non-null" rule: -The string constant `"0"' is actually true, since it is non-null (d.c.). + There is a surprising consequence of the "nonzero or non-null" rule: +the string constant `"0"' is actually true, because it is non-null. +(d.c.)  File: gawk.info, Node: Typing and Comparison, Next: Boolean Ops, Prev: Truth Values, Up: Expressions @@ -5245,40 +6096,35 @@ Variable Typing and Comparison Expressions The Guide is definitive. Reality is frequently inaccurate. The Hitchhiker's Guide to the Galaxy - - Unlike other programming languages, `awk' variables do not have a fixed type. Instead, they can be either a number or a string, depending upon the value that is assigned to them. The 1992 POSIX standard introduced the concept of a "numeric -string", which is simply a string that looks like a number, for +string", which is simply a string that looks like a number--for example, `" +2"'. This concept is used for determining the type of a -variable. - - The type of the variable is important, since the types of two -variables determine how they are compared. - - In `gawk', variable typing follows these rules. +variable. The type of the variable is important because the types of +two variables determine how they are compared. In `gawk', variable +typing follows these rules: - 1. A numeric literal or the result of a numeric operation has the + * A numeric constant or the result of a numeric operation has the NUMERIC attribute. - 2. A string literal or the result of a string operation has the STRING - attribute. + * A string constant or the result of a string operation has the + STRING attribute. - 3. Fields, `getline' input, `FILENAME', `ARGV' elements, `ENVIRON' - elements and the elements of an array created by `split' that are + * Fields, `getline' input, `FILENAME', `ARGV' elements, `ENVIRON' + elements, and the elements of an array created by `split' that are numeric strings have the STRNUM attribute. Otherwise, they have the STRING attribute. Uninitialized variables also have the STRNUM attribute. - 4. Attributes propagate across assignments, but are not changed by - any use. + * Attributes propagate across assignments but are not changed by any + use. The last rule is particularly important. In the following program, `a' has numeric type, even though it is later used in a string -operation. +operation: BEGIN { a = 12.345 @@ -5287,23 +6133,29 @@ operation. } When two operands are compared, either string comparison or numeric -comparison may be used, depending on the attributes of the operands, -according to the following, symmetric, matrix: +comparison may be used. This depends upon the attributes of the +operands, according to the following symmetric matrix: - +---------------------------------------------- - | STRING NUMERIC STRNUM + +---------------------------------------------- + | STRING NUMERIC STRNUM --------+---------------------------------------------- - | - STRING | string string string - | - NUMERIC | string numeric numeric - | - STRNUM | string numeric numeric + | + STRING | string string string + | + NUMERIC | string numeric numeric + | + STRNUM | string numeric numeric --------+---------------------------------------------- - The basic idea is that user input that looks numeric, and _only_ -user input, should be treated as numeric, even though it is actually -made of characters, and is therefore also a string. + The basic idea is that user input that looks numeric--and _only_ +user input--should be treated as numeric, even though it is actually +made of characters and is therefore also a string. Thus, for example, +the string constant `" +3.14"' is a string, even though it looks +numeric, and is _never_ treated as number for comparison purposes. + + In short, when one operand is a "pure" string, such as a string +constant, then a string comparison is performed. Otherwise, a numeric +comparison is performed.(1) "Comparison expressions" compare strings or numbers for relationships such as equality. They are written using "relational @@ -5339,20 +6191,19 @@ them: SUBSCRIPT. Comparison expressions have the value one if true and zero if false. - - When comparing operands of mixed types, numeric operands are -converted to strings using the value of `CONVFMT' (*note Conversion of -Strings and Numbers: Conversion.). +When comparing operands of mixed types, numeric operands are converted +to strings using the value of `CONVFMT' (*note Conversion of Strings +and Numbers: Conversion.). Strings are compared by comparing the first character of each, then -the second character of each, and so on. Thus `"10"' is less than +the second character of each, and so on. Thus, `"10"' is less than `"9"'. If there are two strings where one is a prefix of the other, -the shorter string is less than the longer one. Thus `"abc"' is less +the shorter string is less than the longer one. Thus, `"abc"' is less than `"abcd"'. - It is very easy to accidentally mistype the `==' operator, and leave -off one of the `='s. The result is still valid `awk' code, but the -program will not do what you mean: + It is very easy to accidentally mistype the `==' operator and leave +off one of the `=' characters. The result is still valid `awk' code, +but the program does not do what is intended: if (a = b) # oops! should be a == b ... @@ -5360,11 +6211,11 @@ program will not do what you mean: ... Unless `b' happens to be zero or the null string, the `if' part of the -test will always succeed. Because the operators are so similar, this -kind of error is very difficult to spot when scanning the source code. +test always succeeds. Because the operators are so similar, this kind +of error is very difficult to spot when scanning the source code. - Here are some sample expressions, how `gawk' compares them, and what -the result of the comparison is. + The following table of expressions illustrates the kind of comparison +`gawk' performs, as well as what the result of the comparison is: `1.5 <= 2.0' numeric comparison (true) @@ -5383,50 +6234,55 @@ the result of the comparison is. string comparison (true) `a = 2; b = " +2"' + `a == b' string comparison (false) - In this example, + In the next example: $ echo 1e2 3 | awk '{ print ($1 < $2) ? "true" : "false" }' -| false -the result is `false' since both `$1' and `$2' are numeric strings and -thus both have the STRNUM attribute, dictating a numeric comparison. - - The purpose of the comparison rules and the use of numeric strings is -to attempt to produce the behavior that is "least surprising," while -still "doing the right thing." - - String comparisons and regular expression comparisons are very -different. For example, +the result is `false' because both `$1' and `$2' are user input. They +are numeric strings--therefore both have the STRNUM attribute, +dictating a numeric comparison. The purpose of the comparison rules +and the use of numeric strings is to attempt to produce the behavior +that is "least surprising," while still "doing the right thing." +String comparisons and regular expression comparisons are very +different. For example: x == "foo" -has the value of one, or is true, if the variable `x' is precisely -`foo'. By contrast, +has the value one, or is true if the variable `x' is precisely `foo'. +By contrast: x ~ /foo/ has the value one if `x' contains `foo', such as `"Oh, what a fool am I!"'. - The right hand operand of the `~' and `!~' operators may be either a -regexp constant (`/.../'), or an ordinary expression, in which case the -value of the expression as a string is used as a dynamic regexp (*note -How to Use Regular Expressions: Regexp Usage.; also *note Using Dynamic -Regexps: Computed Regexps.). + The righthand operand of the `~' and `!~' operators may be either a +regexp constant (`/.../') or an ordinary expression. In the latter +case, the value of the expression as a string is used as a dynamic +regexp (*note How to Use Regular Expressions: Regexp Usage.; also *note +Using Dynamic Regexps: Computed Regexps.). - In recent implementations of `awk', a constant regular expression in + In modern implementations of `awk', a constant regular expression in slashes by itself is also an expression. The regexp `/REGEXP/' is an -abbreviation for this comparison expression: +abbreviation for the following comparison expression: $0 ~ /REGEXP/ One special place where `/foo/' is _not_ an abbreviation for `$0 ~ -/foo/' is when it is the right-hand operand of `~' or `!~'! *Note -Using Regular Expression Constants: Using Constant Regexps, where this -is discussed in more detail. +/foo/' is when it is the righthand operand of `~' or `!~'. *Note Using +Regular Expression Constants: Using Constant Regexps, where this is +discussed in more detail. + + ---------- Footnotes ---------- + + (1) The POSIX standard is under revision. The revised standard's +rules for typing and comparison are the same as just described for +`gawk'.  File: gawk.info, Node: Boolean Ops, Next: Conditional Exp, Prev: Typing and Comparison, Up: Expressions @@ -5434,42 +6290,41 @@ File: gawk.info, Node: Boolean Ops, Next: Conditional Exp, Prev: Typing and C Boolean Expressions =================== - A "boolean expression" is a combination of comparison expressions or -matching expressions, using the boolean operators "or" (`||'), "and" + A "Boolean expression" is a combination of comparison expressions or +matching expressions, using the Boolean operators "or" (`||'), "and" (`&&'), and "not" (`!'), along with parentheses to control nesting. -The truth value of the boolean expression is computed by combining the +The truth value of the Boolean expression is computed by combining the truth values of the component expressions. Boolean expressions are also referred to as "logical expressions". The terms are equivalent. Boolean expressions can be used wherever comparison and matching -expressions can be used. They can be used in `if', `while', `do' and +expressions can be used. They can be used in `if', `while', `do', and `for' statements (*note Control Statements in Actions: Statements.). -They have numeric values (one if true, zero if false), which come into -play if the result of the boolean expression is stored in a variable, or +They have numeric values (one if true, zero if false), that come into +play if the result of the Boolean expression is stored in a variable or used in arithmetic. - In addition, every boolean expression is also a valid pattern, so -you can use one as a pattern to control the execution of rules. - - Here are descriptions of the three boolean operators, with examples. + In addition, every Boolean expression is also a valid pattern, so +you can use one as a pattern to control the execution of rules. The +Boolean operators are: `BOOLEAN1 && BOOLEAN2' True if both BOOLEAN1 and BOOLEAN2 are true. For example, the following statement prints the current input record if it contains - both `2400' and `foo'. + both `2400' and `foo': if ($0 ~ /2400/ && $0 ~ /foo/) print The subexpression BOOLEAN2 is evaluated only if BOOLEAN1 is true. This can make a difference when BOOLEAN2 contains expressions that - have side effects: in the case of `$0 ~ /foo/ && ($2 == bar++)', - the variable `bar' is not incremented if there is no `foo' in the - record. + have side effects. In the case of `$0 ~ /foo/ && ($2 == bar++)', + the variable `bar' is not incremented if there is no substring + `foo' in the record. `BOOLEAN1 || BOOLEAN2' True if at least one of BOOLEAN1 or BOOLEAN2 is true. For example, the following statement prints all records in the input - that contain _either_ `2400' or `foo', or both. + that contain _either_ `2400' or `foo' or both: if ($0 ~ /2400/ || $0 ~ /foo/) print @@ -5479,81 +6334,88 @@ you can use one as a pattern to control the execution of rules. `! BOOLEAN' True if BOOLEAN is false. For example, the following program - prints all records in the input file `BBS-list' that do _not_ - contain the string `foo'. + prints `no home!' in the unusual event that the `HOME' environment + variable is not defined: - awk '{ if (! ($0 ~ /foo/)) print }' BBS-list + BEGIN { if (! ("HOME" in ENVIRON)) + print "no home!" } + + (The `in' operator is described in *Note Referring to an Array + Element: Reference to Elements.) The `&&' and `||' operators are called "short-circuit" operators because of the way they work. Evaluation of the full expression is "short-circuited" if the result can be determined part way through its evaluation. - You can continue a statement that uses `&&' or `||' simply by -putting a newline after them. But you cannot put a newline in front of -either of these operators without using backslash continuation (*note -`awk' Statements Versus Lines: Statements/Lines.). - - The actual value of an expression using the `!' operator will be -either one or zero, depending upon the truth value of the expression it -is applied to. + Statements that use `&&' or `||' can be continued simply by putting +a newline after them. But you cannot put a newline in front of either +of these operators without using backslash continuation (*note `awk' +Statements Versus Lines: Statements/Lines.). - The `!' operator is often useful for changing the sense of a flag -variable from false to true and back again. For example, the following -program is one way to print lines in between special bracketing lines: + The actual value of an expression using the `!' operator is either +one or zero, depending upon the truth value of the expression it is +applied to. The `!' operator is often useful for changing the sense of +a flag variable from false to true and back again. For example, the +following program is one way to print lines in between special +bracketing lines: - $1 == "START" { interested = ! interested } + $1 == "START" { interested = ! interested; next } interested == 1 { print } - $1 == "END" { interested = ! interested } + $1 == "END" { interested = ! interested; next } -The variable `interested', like all `awk' variables, starts out +The variable `interested', as with all `awk' variables, starts out initialized to zero, which is also false. When a line is seen whose first field is `START', the value of `interested' is toggled to true, using `!'. The next rule prints lines as long as `interested' is true. When a line is seen whose first field is `END', `interested' is toggled back to false. + *Note:* The `next' statement is discussed in *Note The `next' +Statement: Next Statement. `next' tells `awk' to skip the rest of the +rules, get the next record, and start processing the rules over again +at the top. The reason it's there is to avoid printing the bracketing +`START' and `END' lines. +  File: gawk.info, Node: Conditional Exp, Next: Function Calls, Prev: Boolean Ops, Up: Expressions Conditional Expressions ======================= - A "conditional expression" is a special kind of expression with + A "conditional expression" is a special kind of expression that has three operands. It allows you to use one expression's value to select -one of two other expressions. - - The conditional expression is the same as in the C language: +one of two other expressions. The conditional expression is the same +as in the C language, as shown here: SELECTOR ? IF-TRUE-EXP : IF-FALSE-EXP There are three subexpressions. The first, SELECTOR, is always -computed first. If it is "true" (not zero and not null) then +computed first. If it is "true" (not zero or not null), then IF-TRUE-EXP is computed next and its value becomes the value of the whole expression. Otherwise, IF-FALSE-EXP is computed next and its -value becomes the value of the whole expression. - - For example, this expression produces the absolute value of `x': +value becomes the value of the whole expression. For example, the +following expression produces the absolute value of `x': - x > 0 ? x : -x + x >= 0 ? x : -x - Each time the conditional expression is computed, exactly one of + Each time the conditional expression is computed, only one of IF-TRUE-EXP and IF-FALSE-EXP is used; the other is ignored. This is important when the expressions have side effects. For example, this conditional expression examines element `i' of either array `a' or -array `b', and increments `i'. +array `b', and increments `i': x == y ? a[i++] : b[i++] This is guaranteed to increment `i' exactly once, because each time -only one of the two increment expressions is executed, and the other is +only one of the two increment expressions is executed and the other is not. *Note Arrays in `awk': Arrays, for more information about arrays. - As a minor `gawk' extension, you can continue a statement that uses -`?:' simply by putting a newline after either character. However, you -cannot put a newline in front of either character without using -backslash continuation (*note `awk' Statements Versus Lines: -Statements/Lines.). If `--posix' is specified (*note Command Line + As a minor `gawk' extension, a statement that uses `?:' can be +continued simply by putting a newline after either character. However, +putting a newline in front of either character does not work without +using backslash continuation (*note `awk' Statements Versus Lines: +Statements/Lines.). If `--posix' is specified (*note Command-Line Options: Options.), then this extension is disabled.  @@ -5562,58 +6424,55 @@ File: gawk.info, Node: Function Calls, Next: Precedence, Prev: Conditional Ex Function Calls ============== - A "function" is a name for a particular calculation. Because it has -a name, you can ask for it by name at any point in the program. For -example, the function `sqrt' computes the square root of a number. + A "function" is a name for a particular calculation. This enables +you to ask for it by name at any point in the program. For example, +the function `sqrt' computes the square root of a number. A fixed set of functions are "built-in", which means they are available in every `awk' program. The `sqrt' function is one of these. *Note Built-in Functions: Built-in, for a list of built-in functions -and their descriptions. In addition, you can define your own functions -for use in your program. *Note User-defined Functions: User-defined, -for how to do this. +and their descriptions. In addition, you can define functions for use +in your program. *Note User-Defined Functions: User-defined, for +instructions on how to do this. The way to use a function is with a "function call" expression, which consists of the function name followed immediately by a list of -"arguments" in parentheses. The arguments are expressions which -provide the raw materials for the function's calculations. When there -is more than one argument, they are separated by commas. If there are -no arguments, write just `()' after the function name. Here are some -examples: +"arguments" in parentheses. The arguments are expressions that provide +the raw materials for the function's calculations. When there is more +than one argument, they are separated by commas. If there are no +arguments, just write `()' after the function name. The following +examples show function calls with and without arguments: sqrt(x^2 + y^2) one argument atan2(y, x) two arguments rand() no arguments - *Do not put any space between the function name and the -open-parenthesis!* A user-defined function name looks just like the -name of a variable, and space would make the expression look like + *Caution:* Do not put any space between the function name and the +open-parenthesis! A user-defined function name looks just like the +name of a variable--a space would make the expression look like concatenation of a variable with an expression inside parentheses. -Space before the parenthesis is harmless with built-in functions, but -it is best not to get into the habit of using space to avoid mistakes -with user-defined functions. - Each function expects a particular number of arguments. For -example, the `sqrt' function must be called with a single argument, the -number to take the square root of: + With built-in functions, space before the parenthesis is harmless, +but it is best not to get into the habit of using space to avoid +mistakes with user-defined functions. Each function expects a +particular number of arguments. For example, the `sqrt' function must +be called with a single argument: the number to take the square root of: sqrt(ARGUMENT) - Some of the built-in functions allow you to omit the final argument. -If you do so, they use a reasonable default. *Note Built-in Functions: -Built-in, for full details. If arguments are omitted in calls to -user-defined functions, then those arguments are treated as local -variables, initialized to the empty string (*note User-defined -Functions: User-defined.). + Some of the built-in functions have one or more optional arguments. +If those arguments are not supplied, the functions use a reasonable +default value. *Note Built-in Functions: Built-in, for full details. +If arguments are omitted in calls to user-defined functions, then those +arguments are treated as local variables and initialized to the empty +string (*note User-Defined Functions: User-defined.). Like every other expression, the function call has a value, which is computed by the function based on the arguments you give it. In this example, the value of `sqrt(ARGUMENT)' is the square root of ARGUMENT. A function can also have side effects, such as assigning values to -certain variables or doing I/O. - - Here is a command to read numbers, one number per line, and print the -square root of each one: +certain variables or doing I/O. The following program reads numbers, +one number per line, and prints the square root of each one: $ awk '{ print "The square root of", $1, "is", sqrt($1) }' 1 @@ -5622,7 +6481,7 @@ square root of each one: -| The square root of 3 is 1.73205 5 -| The square root of 5 is 2.23607 - Control-d + Ctrl-d  File: gawk.info, Node: Precedence, Prev: Function Calls, Up: Expressions @@ -5630,36 +6489,34 @@ File: gawk.info, Node: Precedence, Prev: Function Calls, Up: Expressions Operator Precedence (How Operators Nest) ======================================== - "Operator precedence" determines how operators are grouped, when + "Operator precedence" determines how operators are grouped when different operators appear close by in one expression. For example, `*' has higher precedence than `+'; thus, `a + b * c' means to multiply -`b' and `c', and then add `a' to the product (i.e. `a + (b * c)'). +`b' and `c', and then add `a' to the product (i.e., `a + (b * c)'). - You can overrule the precedence of the operators by using -parentheses. You can think of the precedence rules as saying where the -parentheses are assumed to be if you do not write parentheses yourself. -In fact, it is wise to always use parentheses whenever you have an -unusual combination of operators, because other people who read the -program may not remember what the precedence is in this case. You -might forget, too; then you could make a mistake. Explicit parentheses -will help prevent any such mistake. + The normal precedence of the operators can be overruled by using +parentheses. Think of the precedence rules as saying where the +parentheses are assumed to be. In fact, it is wise to always use +parentheses whenever there is an unusual combination of operators, +because other people who read the program may not remember what the +precedence is in this case. Even experienced programmers occasionally +forget the exact rules, which leads to mistakes. Explicit parentheses +help prevent any such mistakes. When operators of equal precedence are used together, the leftmost -operator groups first, except for the assignment, conditional and +operator groups first, except for the assignment, conditional, and exponentiation operators, which group in the opposite order. Thus, `a -- b + c' groups as `(a - b) + c', and `a = b = c' groups as `a = (b = +- b + c' groups as `(a - b) + c' and `a = b = c' groups as `a = (b = c)'. The precedence of prefix unary operators does not matter as long as only unary operators are involved, because there is only one way to -interpret them--innermost first. Thus, `$++i' means `$(++i)' and +interpret them: innermost first. Thus, `$++i' means `$(++i)' and `++$x' means `++($x)'. However, when another operator follows the -operand, then the precedence of the unary operators can matter. Thus, -`$x^2' means `($x)^2', but `-x^2' means `-(x^2)', because `-' has lower -precedence than `^' while `$' has higher precedence. - - Here is a table of `awk''s operators, in order from highest -precedence to lowest: +operand, then the precedence of the unary operators can matter. `$x^2' +means `($x)^2', but `-x^2' means `-(x^2)', because `-' has lower +precedence than `^', whereas `$' has higher precedence. This table +presents `awk''s operators, in order of highest precedence to lowest: `(...)' Grouping. @@ -5671,11 +6528,10 @@ precedence to lowest: Increment, decrement. `^ **' - Exponentiation. These operators group right-to-left. (The `**' - operator is not specified by POSIX.) + Exponentiation. These operators group right-to-left. `+ - !' - Unary plus, minus, logical "not". + Unary plus, minus, logical "not." `* / %' Multiplication, division, modulus. @@ -5683,25 +6539,26 @@ precedence to lowest: `+ -' Addition, subtraction. -`Concatenation' - No special token is used to indicate concatenation. The operands - are simply written side by side. +`String Concatenation' + No special symbol is used to indicate concatenation. The operands + are simply written side by side (*note String Concatenation: + Concatenation.). `< <= == !=' -`> >= >> |' - Relational, and redirection. The relational operators and the +`> >= >> | |&' + Relational and redirection. The relational operators and the redirections have the same precedence level. Characters such as `>' serve both as relationals and as redirections; the context distinguishes between the two meanings. Note that the I/O redirection operators in `print' and `printf' statements belong to the statement level, not to expressions. The - redirection does not produce an expression which could be the + redirection does not produce an expression that could be the operand of another operator. As a result, it does not make sense to use a redirection operator near another operator of lower - precedence, without parentheses. Such combinations, for example - `print foo > a ? b : c', result in syntax errors. The correct way - to write this statement is `print foo > (a ? b : c)'. + precedence without parentheses. Such combinations (for example + `print foo > a ? b : c'), result in syntax errors. The correct + way to write this statement is `print foo > (a ? b : c)'. `~ !~' Matching, non-matching. @@ -5720,71 +6577,73 @@ precedence to lowest: `= += -= *=' `/= %= ^= **=' - Assignment. These operators group right-to-left. (The `**=' - operator is not specified by POSIX.) + Assignment. These operators group right-to-left. + + *Note:* The `|&', `**', and `**=' operators are not specified by +POSIX. For maximum portability, do not use them.  -File: gawk.info, Node: Patterns and Actions, Next: Statements, Prev: Expressions, Up: Top +File: gawk.info, Node: Patterns and Actions, Next: Arrays, Prev: Expressions, Up: Top -Patterns and Actions -******************** +Patterns, Actions, and Variables +******************************** As you have already seen, each `awk' statement consists of a pattern -with an associated action. This chapter describes how you build -patterns and actions. +with an associated action. This major node describes how you build +patterns and actions, what kinds of things you can do within actions, +and `awk''s built-in variables. + + The pattern-action rules and the statements available for use within +actions form the core of `awk' programming. In a sense, everything +covered up to here has been the foundation that programs are built on +top of. Now it's time to start building something useful. * Menu: * Pattern Overview:: What goes into a pattern. +* Using Shell Variables:: How to use shell variables with `awk'. * Action Overview:: What goes into an action. +* Statements:: Describes the various control statements in + detail. +* Built-in Variables:: Summarizes the built-in variables.  -File: gawk.info, Node: Pattern Overview, Next: Action Overview, Prev: Patterns and Actions, Up: Patterns and Actions +File: gawk.info, Node: Pattern Overview, Next: Using Shell Variables, Prev: Patterns and Actions, Up: Patterns and Actions Pattern Elements ================ - Patterns in `awk' control the execution of rules: a rule is executed -when its pattern matches the current input record. This section -explains all about how to write patterns. - * Menu: -* Kinds of Patterns:: A list of all kinds of patterns. * Regexp Patterns:: Using regexps as patterns. * Expression Patterns:: Any expression can be used as a pattern. * Ranges:: Pairs of patterns specify record ranges. * BEGIN/END:: Specifying initialization and cleanup rules. * Empty:: The empty pattern, which matches every record. - -File: gawk.info, Node: Kinds of Patterns, Next: Regexp Patterns, Prev: Pattern Overview, Up: Pattern Overview - -Kinds of Patterns ------------------ - - Here is a summary of the types of patterns supported in `awk'. + Patterns in `awk' control the execution of rules--a rule is executed +when its pattern matches the current input record. The following is a +summary of the types of patterns in `awk': `/REGULAR EXPRESSION/' - A regular expression as a pattern. It matches when the text of the - input record fits the regular expression. (*Note Regular - Expressions: Regexp.) + A regular expression. It matches when the text of the input record + fits the regular expression. (*Note Regular Expressions: Regexp.) `EXPRESSION' - A single expression. It matches when its value is non-zero (if a + A single expression. It matches when its value is nonzero (if a number) or non-null (if a string). (*Note Expressions as Patterns: Expression Patterns.) `PAT1, PAT2' A pair of patterns separated by a comma, specifying a range of records. The range includes both the initial record that matches - PAT1, and the final record that matches PAT2. (*Note Specifying + PAT1 and the final record that matches PAT2. (*Note Specifying Record Ranges with Patterns: Ranges.) `BEGIN' `END' - Special patterns for you to supply start-up or clean-up actions - for your `awk' program. (*Note The `BEGIN' and `END' Special + Special patterns for you to supply startup or cleanup actions for + your `awk' program. (*Note The `BEGIN' and `END' Special Patterns: BEGIN/END.) `EMPTY' @@ -5792,13 +6651,13 @@ Kinds of Patterns Pattern: Empty.)  -File: gawk.info, Node: Regexp Patterns, Next: Expression Patterns, Prev: Kinds of Patterns, Up: Pattern Overview +File: gawk.info, Node: Regexp Patterns, Next: Expression Patterns, Prev: Pattern Overview, Up: Pattern Overview Regular Expressions as Patterns ------------------------------- - We have been using regular expressions as patterns since our early -examples. This kind of pattern is simply a regexp constant in the + Regular expressions are one of the first kinds of patterns presented +in this book. This kind of pattern is simply a regexp constant in the pattern part of a rule. Its meaning is `$0 ~ /PATTERN/'. The pattern matches when the input record matches the regexp. For example: @@ -5811,35 +6670,29 @@ File: gawk.info, Node: Expression Patterns, Next: Ranges, Prev: Regexp Patter Expressions as Patterns ----------------------- - Any `awk' expression is valid as an `awk' pattern. Then the pattern -matches if the expression's value is non-zero (if a number) or non-null -(if a string). - - The expression is reevaluated each time the rule is tested against a -new input record. If the expression uses fields such as `$1', the -value depends directly on the new input record's text; otherwise, it -depends only on what has happened so far in the execution of the `awk' -program, but that may still be useful. - - A very common kind of expression used as a pattern is the comparison -expression, using the comparison operators described in *Note Variable -Typing and Comparison Expressions: Typing and Comparison. - - Regexp matching and non-matching are also very common expressions. -The left operand of the `~' and `!~' operators is a string. The right -operand is either a constant regular expression enclosed in slashes -(`/REGEXP/'), or any expression, whose string value is used as a -dynamic regular expression (*note Using Dynamic Regexps: Computed -Regexps.). - - The following example prints the second field of each input record -whose first field is precisely `foo'. + Any `awk' expression is valid as an `awk' pattern. The pattern +matches if the expression's value is nonzero (if a number) or non-null +(if a string). The expression is reevaluated each time the rule is +tested against a new input record. If the expression uses fields such +as `$1', the value depends directly on the new input record's text; +otherwise it depends on only what has happened so far in the execution +of the `awk' program. + + Comparison expressions, using the comparison operators described in +*Note Variable Typing and Comparison Expressions: Typing and Comparison, +are a very common kind of pattern. Regexp matching and non-matching +are also very common expressions. The left operand of the `~' and `!~' +operators is a string. The right operand is either a constant regular +expression enclosed in slashes (`/REGEXP/'), or any expression whose +string value is used as a dynamic regular expression (*note Using +Dynamic Regexps: Computed Regexps.). The following example prints the +second field of each input record whose first field is precisely `foo': $ awk '$1 == "foo" { print $2 }' BBS-list -(There is no output, since there is no BBS site named "foo".) Contrast -this with the following regular expression match, which would accept -any record with a first field that contains `foo': +(There is no output, because there is no BBS site with the exact name +`foo'.) Contrast this with the following regular expression match, +which accepts any record with a first field that contains `foo': $ awk '$1 ~ /foo/ { print $2 }' BBS-list -| 555-1234 @@ -5847,18 +6700,21 @@ any record with a first field that contains `foo': -| 555-6480 -| 555-2127 + A regexp constant as a pattern is also a special case of an +expression pattern. The expression `/foo/' has the value one if `foo' +appears in the current input record. Thus, as a pattern, `/foo/' +matches any record containing `foo'. + Boolean expressions are also commonly used as patterns. Whether the pattern matches an input record depends on whether its subexpressions -match. - - For example, the following command prints all records in `BBS-list' -that contain both `2400' and `foo'. +match. For example, the following command prints all the records in +`BBS-list' that contain both `2400' and `foo': $ awk '/2400/ && /foo/' BBS-list -| fooey 555-1234 2400/1200/300 B The following command prints all records in `BBS-list' that contain -_either_ `2400' or `foo', or both. +_either_ `2400' or `foo' (or both, of course): $ awk '/2400/ || /foo/' BBS-list -| alpo-net 555-3412 2400/1200/300 A @@ -5870,7 +6726,7 @@ _either_ `2400' or `foo', or both. -| sabafoo 555-2127 1200/300 C The following command prints all records in `BBS-list' that do _not_ -contain the string `foo'. +contain the string `foo': $ awk '! /foo/' BBS-list -| aardvark 555-5553 1200/300 B @@ -5881,17 +6737,12 @@ contain the string `foo'. -| core 555-2912 1200/300 C -| sdace 555-3430 2400/1200/300 A - The subexpressions of a boolean operator in a pattern can be + The subexpressions of a Boolean operator in a pattern can be constant regular expressions, comparisons, or any other `awk' expressions. Range patterns are not expressions, so they cannot appear -inside boolean patterns. Likewise, the special patterns `BEGIN' and +inside Boolean patterns. Likewise, the special patterns `BEGIN' and `END', which never match any input record, are not expressions and -cannot appear inside boolean patterns. - - A regexp constant as a pattern is also a special case of an -expression pattern. `/foo/' as an expression has the value one if `foo' -appears in the current input record; thus, as a pattern, `/foo/' -matches any record containing `foo'. +cannot appear inside Boolean patterns.  File: gawk.info, Node: Ranges, Next: BEGIN/END, Prev: Expression Patterns, Up: Pattern Overview @@ -5899,60 +6750,67 @@ File: gawk.info, Node: Ranges, Next: BEGIN/END, Prev: Expression Patterns, U Specifying Record Ranges with Patterns -------------------------------------- - A "range pattern" is made of two patterns separated by a comma, of -the form `BEGPAT, ENDPAT'. It matches ranges of consecutive input -records. The first pattern, BEGPAT, controls where the range begins, -and the second one, ENDPAT, controls where it ends. For example, + A "range pattern" is made of two patterns separated by a comma, in +the form `BEGPAT, ENDPAT'. It is used to match ranges of consecutive +input records. The first pattern, BEGPAT, controls where the range +begins, while ENDPAT controls where the pattern ends. For example, the +following: - awk '$1 == "on", $1 == "off"' + awk '$1 == "on", $1 == "off"' myfile -prints every record between `on'/`off' pairs, inclusive. +prints every record in `myfile' between `on'/`off' pairs, inclusive. A range pattern starts out by matching BEGPAT against every input -record; when a record matches BEGPAT, the range pattern becomes "turned -on". The range pattern matches this record. As long as it stays -turned on, it automatically matches every input record read. It also -matches ENDPAT against every input record; when that succeeds, the -range pattern is turned off again for the following record. Then it -goes back to checking BEGPAT against each record. +record. When a record matches BEGPAT, the range pattern is "turned on" +and the range pattern matches this record as well. As long as the +range pattern stays turned on, it automatically matches every input +record read. The range pattern also matches ENDPAT against every input +record; when this succeeds, the range pattern is turned off again for +the following record. Then the range pattern goes back to checking +BEGPAT against each record. The record that turns on the range pattern and the one that turns it off both match the range pattern. If you don't want to operate on these records, you can write `if' statements in the rule's action to distinguish them from the records you are interested in. - It is possible for a pattern to be turned both on and off by the same -record, if the record satisfies both conditions. Then the action is -executed for just that record. - - For example, suppose you have text between two identical markers (say -the `%' symbol) that you wish to ignore. You might try to combine a + It is possible for a pattern to be turned on and off by the same +record. If the record satisfies both conditions, then the action is +executed for just that record. For example, suppose there is text +between two identical markers (say the `%' symbol), each on its own +line, that should be ignored. A first attempt would be to combine a range pattern that describes the delimited text with the `next' statement (not discussed yet, *note The `next' Statement: Next -Statement.), which causes `awk' to skip any further processing of the +Statement.). This causes `awk' to skip any further processing of the current record and start over again with the next input record. Such a -program would look like this: +program looks like this: /^%$/,/^%$/ { next } { print } This program fails because the range pattern is both turned on and -turned off by the first line with just a `%' on it. To accomplish this -task, you must write the program this way, using a flag: +turned off by the first line, which just has a `%' on it. To +accomplish this task, write the program in the following manner, using +a flag: /^%$/ { skip = ! skip; next } skip == 1 { next } # skip lines with `skip' set - Note that in a range pattern, the `,' has the lowest precedence (is -evaluated last) of all the operators. Thus, for example, the following -program attempts to combine a range pattern with another, simpler test. + In a range pattern, the comma (`,') has the lowest precedence of all +the operators (i.e., it is evaluated last). Thus, the following +program attempts to combine a range pattern with another simpler test: echo Yes | awk '/1/,/2/ || /Yes/' - The author of this program intended it to mean `(/1/,/2/) || /Yes/'. -However, `awk' interprets this as `/1/, (/2/ || /Yes/)'. This cannot -be changed or worked around; range patterns do not combine with other -patterns. + The intent of this program is `(/1/,/2/) || /Yes/'. However, `awk' +interprets this as `/1/, (/2/ || /Yes/)'. This cannot be changed or +worked around; range patterns do not combine with other patterns: + + $ echo yes | gawk '(/1/,/2/) || /Yes/' + error--> gawk: cmd. line:1: (/1/,/2/) || /Yes/ + error--> gawk: cmd. line:1: ^ parse error + error--> gawk: cmd. line:2: (/1/,/2/) || /Yes/ + error--> gawk: cmd. line:2: ^ unexpected newline  File: gawk.info, Node: BEGIN/END, Next: Empty, Prev: Ranges, Up: Pattern Overview @@ -5960,9 +6818,13 @@ File: gawk.info, Node: BEGIN/END, Next: Empty, Prev: Ranges, Up: Pattern Ove The `BEGIN' and `END' Special Patterns -------------------------------------- - `BEGIN' and `END' are special patterns. They are not used to match -input records. Rather, they supply start-up or clean-up actions for -your `awk' script. + All the patterns described so far are for matching input records. +The `BEGIN' and `END' special patterns are different. They supply +startup and cleanup actions for `awk' programs. `BEGIN' and `END' +rules must have actions; there is no default action for these rules +because there is no current record when they run. `BEGIN' and `END' +rules are often referred to as "`BEGIN' and `END' blocks" by long-time +`awk' programmers. * Menu: @@ -5975,61 +6837,59 @@ File: gawk.info, Node: Using BEGIN/END, Next: I/O And BEGIN/END, Prev: BEGIN/ Startup and Cleanup Actions ........................... - A `BEGIN' rule is executed, once, before the first input record has -been read. An `END' rule is executed, once, after all the input has -been read. For example: + A `BEGIN' rule is executed once only, before the first input record +is read. Likewise, an `END' rule is executed once only, after all the +input is read. For example: $ awk ' > BEGIN { print "Analysis of \"foo\"" } > /foo/ { ++n } - > END { print "\"foo\" appears " n " times." }' BBS-list + > END { print "\"foo\" appears", n, "times." }' BBS-list -| Analysis of "foo" -| "foo" appears 4 times. This program finds the number of records in the input file `BBS-list' that contain the string `foo'. The `BEGIN' rule prints a title for the report. There is no need to use the `BEGIN' rule to initialize the -counter `n' to zero, as `awk' does this automatically (*note -Variables::). - - The second rule increments the variable `n' every time a record -containing the pattern `foo' is read. The `END' rule prints the value -of `n' at the end of the run. +counter `n' to zero, since `awk' does this automatically (*note +Variables::). The second rule increments the variable `n' every time a +record containing the pattern `foo' is read. The `END' rule prints the +value of `n' at the end of the run. The special patterns `BEGIN' and `END' cannot be used in ranges or -with boolean operators (indeed, they cannot be used with any operators). - - An `awk' program may have multiple `BEGIN' and/or `END' rules. They -are executed in the order they appear, all the `BEGIN' rules at -start-up and all the `END' rules at termination. `BEGIN' and `END' +with Boolean operators (indeed, they cannot be used with any operators). +An `awk' program may have multiple `BEGIN' and/or `END' rules. They +are executed in the order in which they appear: all the `BEGIN' rules +at startup and all the `END' rules at termination. `BEGIN' and `END' rules may be intermixed with other rules. This feature was added in -the 1987 version of `awk', and is included in the POSIX standard. The -original (1978) version of `awk' required you to put the `BEGIN' rule -at the beginning of the program, and the `END' rule at the end, and -only allowed one of each. This is no longer required, but it is a good -idea in terms of program organization and readability. +the 1987 version of `awk' and is included in the POSIX standard. The +original (1978) version of `awk' required the `BEGIN' rule to be placed +at the beginning of the program, the `END' rule to be placed at the +end, and only allowed one of each. This is no longer required, but it +is a good idea to follow this template in terms of program organization +and readability. Multiple `BEGIN' and `END' rules are useful for writing library -functions, since each library file can have its own `BEGIN' and/or -`END' rule to do its own initialization and/or cleanup. Note that the -order in which library functions are named on the command line controls -the order in which their `BEGIN' and `END' rules are executed. -Therefore you have to be careful to write such rules in library files -so that the order in which they are executed doesn't matter. *Note -Command Line Options: Options, for more information on using library +functions, because each library file can have its own `BEGIN' and/or +`END' rule to do its own initialization and/or cleanup. The order in +which library functions are named on the command line controls the +order in which their `BEGIN' and `END' rules are executed. Therefore +you have to be careful when writing such rules in library files so that +the order in which they are executed doesn't matter. *Note +Command-Line Options: Options, for more information on using library functions. *Note A Library of `awk' Functions: Library Functions, for a number of useful library functions. - If an `awk' program only has a `BEGIN' rule, and no other rules, -then the program exits after the `BEGIN' rule has been run. (The -original version of `awk' used to keep reading and ignoring input until -end of file was seen.) However, if an `END' rule exists, then the -input will be read, even if there are no other rules in the program. -This is necessary in case the `END' rule checks the `FNR' and `NR' -variables (d.c.). + If an `awk' program only has a `BEGIN' rule and no other rules, then +the program exits after the `BEGIN' rule is run.(1) However, if an +`END' rule exists, then the input is read, even if there are no other +rules in the program. This is necessary in case the `END' rule checks +the `FNR' and `NR' variables. + + ---------- Footnotes ---------- - `BEGIN' and `END' rules must have actions; there is no default -action for these rules since there is no current record when they run. + (1) The original version of `awk' used to keep reading and ignoring +input until end of file was seen.  File: gawk.info, Node: I/O And BEGIN/END, Prev: Using BEGIN/END, Up: BEGIN/END @@ -6037,38 +6897,42 @@ File: gawk.info, Node: I/O And BEGIN/END, Prev: Using BEGIN/END, Up: BEGIN/EN Input/Output from `BEGIN' and `END' Rules ......................................... - There are several (sometimes subtle) issues involved when doing I/O -from a `BEGIN' or `END' rule. - - The first has to do with the value of `$0' in a `BEGIN' rule. Since -`BEGIN' rules are executed before any input is read, there simply is no -input record, and therefore no fields, when executing `BEGIN' rules. -References to `$0' and the fields yield a null string or zero, -depending upon the context. One way to give `$0' a real value is to -execute a `getline' command without a variable (*note Explicit Input -with `getline': Getline.). Another way is to simply assign a value to -it. - - The second point is similar to the first, but from the other -direction. Inside an `END' rule, what is the value of `$0' and `NF'? -Traditionally, due largely to implementation issues, `$0' and `NF' were -_undefined_ inside an `END' rule. The POSIX standard specified that -`NF' was available in an `END' rule, containing the number of fields -from the last input record. Due most probably to an oversight, the -standard does not say that `$0' is also preserved, although logically -one would think that it should be. In fact, `gawk' does preserve the -value of `$0' for use in `END' rules. Be aware, however, that Unix -`awk', and possibly other implementations, do not. - - The third point follows from the first two. What is the meaning of -`print' inside a `BEGIN' or `END' rule? The meaning is the same as -always, `print $0'. If `$0' is the null string, then this prints an -empty line. Many long time `awk' programmers use `print' in `BEGIN' -and `END' rules, to mean `print ""', relying on `$0' being null. While -you might generally get away with this in `BEGIN' rules, in `gawk' at -least, it is a very bad idea in `END' rules. It is also poor style, -since if you want an empty line in the output, you should say so -explicitly in your program. + There are several (sometimes subtle) points to remember when doing +I/O from a `BEGIN' or `END' rule. The first has to do with the value +of `$0' in a `BEGIN' rule. Because `BEGIN' rules are executed before +any input is read, there simply is no input record, and therefore no +fields, when executing `BEGIN' rules. References to `$0' and the fields +yield a null string or zero, depending upon the context. One way to +give `$0' a real value is to execute a `getline' command without a +variable (*note Explicit Input with `getline': Getline.). Another way +is to simply assign a value to `$0'. + + The second point is similar to the first but from the other +direction. Traditionally, due largely to implementation issues, `$0' +and `NF' were _undefined_ inside an `END' rule. The POSIX standard +specifies that `NF' is available in an `END' rule. It contains the +number of fields from the last input record. Most probably due to an +oversight, the standard does not say that `$0' is also preserved, +although logically one would think that it should be. In fact, `gawk' +does preserve the value of `$0' for use in `END' rules. Be aware, +however, that Unix `awk', and possibly other implementations, do not. + + The third point follows from the first two. The meaning of `print' +inside a `BEGIN' or `END' rule is the same as always: `print $0'. If +`$0' is the null string, then this prints an empty line. Many long +time `awk' programmers use an unadorned `print' in `BEGIN' and `END' +rules, to mean `print ""', relying on `$0' being null. Although one +might generally get away with this in `BEGIN' rules, it is a very bad +idea in `END' rules, at least in `gawk'. It is also poor style, since +if an empty line is needed in the output, the program should print one +explicitly. + + Finally, the `next' and `nextfile' statements are not allowed in a +`BEGIN' rule, because the implicit +read-a-record-and-match-against-the-rules loop has not started yet. +Similarly, those statements are not valid in an `END' rule, since all +the input has been read. (*Note The `next' Statement: Next Statement, +and see *Note Using `gawk''s `nextfile' Statement: Nextfile Statement.)  File: gawk.info, Node: Empty, Prev: BEGIN/END, Up: Pattern Overview @@ -6076,7 +6940,7 @@ File: gawk.info, Node: Empty, Prev: BEGIN/END, Up: Pattern Overview The Empty Pattern ----------------- - An empty (i.e. non-existent) pattern is considered to match _every_ + An empty (i.e., non-existent) pattern is considered to match _every_ input record. For example, the program: awk '{ print $1 }' BBS-list @@ -6084,19 +6948,70 @@ input record. For example, the program: prints the first field of every record.  -File: gawk.info, Node: Action Overview, Prev: Pattern Overview, Up: Patterns and Actions +File: gawk.info, Node: Using Shell Variables, Next: Action Overview, Prev: Pattern Overview, Up: Patterns and Actions -Overview of Actions -=================== +Using Shell Variables in Programs +================================= - An `awk' program or script consists of a series of rules and -function definitions, interspersed. (Functions are described later. -*Note User-defined Functions: User-defined.) + `awk' programs are often used as components in larger programs +written in shell. For example, it is very common to use a shell +variable to hold a pattern that the `awk' program searches for. There +are two ways to get the value of the shell variable into the body of +the `awk' program. + + The most common method is to use shell quoting to substitute the +variable's value into the program inside the script. For example, in +the following program: + + echo -n "Enter search pattern: " + read pattern + awk "/$pattern/ "'{ nmatches++ } + END { print nmatches, "found" }' /path/to/data + +the `awk' program consists of two pieces of quoted text that are +concatenated together to form the program. The first part is +double-quoted, which allows substitution of the `pattern' variable +inside the quotes. The second part is single-quoted. + + Variable substitution via quoting works, but can be potentially +messy. It requires a good understanding of the shell's quoting rules +(*note Shell Quoting Issues: Quoting.), and it's often difficult to +correctly match up the quotes when reading the program. + + A better method is to use `awk''s variable assignment feature (*note +Assigning Variables on the Command Line: Assignment Options.) to +assign the shell variable's value to an `awk' variable's value. Then +use dynamic regexps to match the pattern (*note Using Dynamic Regexps: +Computed Regexps.). The following shows how to redo the previous +example using this technique: + + echo -n "Enter search pattern: " + read pattern + awk -v pat="$pattern" '$0 ~ pat { nmatches++ } + END { print nmatches, "found" }' /path/to/data + +Now, the `awk' program is just one single-quoted string. The +assignment `-v pat="$pattern"' still requires double quotes, in case +there is whitespace in the value of `$pattern'. The `awk' variable +`pat' could be named `pattern' too, but that would be more confusing. +Using a variable also provides more flexibility, since the variable can +be used anywhere inside the program--for printing, as an array +subscript, or for any other use--without requiring the quoting tricks +at every point in the program. + + +File: gawk.info, Node: Action Overview, Next: Statements, Prev: Using Shell Variables, Up: Patterns and Actions + +Actions +======= - A rule contains a pattern and an action, either of which (but not -both) may be omitted. The purpose of the "action" is to tell `awk' -what to do once a match for the pattern is found. Thus, in outline, an -`awk' program generally looks like this: + An `awk' program or script consists of a series of rules and +function definitions interspersed. (Functions are described later. +*Note User-Defined Functions: User-defined.) A rule contains a pattern +and an action, either of which (but not both) may be omitted. The +purpose of the "action" is to tell `awk' what to do once a match for +the pattern is found. Thus, in outline, an `awk' program generally +looks like this: [PATTERN] [{ ACTION }] [PATTERN] [{ ACTION }] @@ -6105,18 +7020,17 @@ what to do once a match for the pattern is found. Thus, in outline, an ... An action consists of one or more `awk' "statements", enclosed in -curly braces (`{' and `}'). Each statement specifies one thing to be -done. The statements are separated by newlines or semicolons. +curly braces (`{' and `}'). Each statement specifies one thing to do. +The statements are separated by newlines or semicolons. The curly +braces around an action must be used even if the action contains only +one statement, or if it contains no statements at all. However, if you +omit the action entirely, omit the curly braces as well. An omitted +action is equivalent to `{ print $0 }': - The curly braces around an action must be used even if the action -contains only one statement, or even if it contains no statements at -all. However, if you omit the action entirely, omit the curly braces as -well. An omitted action is equivalent to `{ print $0 }'. + /foo/ { } match `foo', do nothing -- empty action + /foo/ match `foo', print the record -- omitted action - /foo/ { } # match foo, do nothing - empty action - /foo/ # match foo, print the record - omitted action - - Here are the kinds of statements supported in `awk': + The following types of statements are supported in `awk': * Expressions, which can call functions or assign values to variables (*note Expressions::). Executing this kind of statement simply @@ -6132,38 +7046,36 @@ well. An omitted action is equivalent to `{ print $0 }'. * Compound statements, which consist of one or more statements enclosed in curly braces. A compound statement is used in order to put several statements together in the body of an `if', - `while', `do' or `for' statement. + `while', `do', or `for' statement. - * Input statements, using the `getline' command (*note Explicit - Input with `getline': Getline.), the `next' statement (*note The - `next' Statement: Next Statement.), and the `nextfile' statement - (*note The `nextfile' Statement: Nextfile Statement.). + * Input statements using the `getline' command (*note Explicit Input + with `getline': Getline.), the `next' statement (*note The `next' + Statement: Next Statement.), and the `nextfile' statement (*note + Using `gawk''s `nextfile' Statement: Nextfile Statement.). - * Output statements, `print' and `printf'. *Note Printing Output: - Printing. + * Output statements, such as `print' and `printf'. *Note Printing + Output: Printing. - * Deletion statements, for deleting array elements. *Note The + * Deletion statements for deleting array elements. *Note The `delete' Statement: Delete.  -File: gawk.info, Node: Statements, Next: Built-in Variables, Prev: Patterns and Actions, Up: Top +File: gawk.info, Node: Statements, Next: Built-in Variables, Prev: Action Overview, Up: Patterns and Actions Control Statements in Actions -***************************** +============================= - "Control statements" such as `if', `while', and so on control the + "Control statements", such as `if', `while', and so on, control the flow of execution in `awk' programs. Most of the control statements in `awk' are patterned on similar statements in C. - All the control statements start with special keywords such as `if' -and `while', to distinguish them from simple expressions. - - Many control statements contain other statements; for example, the -`if' statement contains another statement which may or may not be -executed. The contained statement is called the "body". If you want -to include more than one statement in the body, group them into a -single "compound statement" with curly braces, separating them with -newlines or semicolons. + All the control statements start with special keywords, such as `if' +and `while', to distinguish them from simple expressions. Many control +statements contain other statements. For example, the `if' statement +contains another statement that may or may not be executed. The +contained statement is called the "body". To include more than one +statement in the body, group them into a single "compound statement" +with curly braces, separating them with newlines or semicolons. * Menu: @@ -6185,7 +7097,7 @@ newlines or semicolons. File: gawk.info, Node: If Statement, Next: While Statement, Prev: Statements, Up: Statements The `if'-`else' Statement -========================= +------------------------- The `if'-`else' statement is `awk''s decision-making statement. It looks like this: @@ -6193,68 +7105,58 @@ looks like this: if (CONDITION) THEN-BODY [else ELSE-BODY] The CONDITION is an expression that controls what the rest of the -statement will do. If CONDITION is true, THEN-BODY is executed; +statement does. If the CONDITION is true, THEN-BODY is executed; otherwise, ELSE-BODY is executed. The `else' part of the statement is optional. The condition is considered false if its value is zero or -the null string, and true otherwise. - - Here is an example: +the null string; otherwise the condition is true. Refer to the +following: if (x % 2 == 0) print "x is even" else print "x is odd" - In this example, if the expression `x % 2 == 0' is true (that is, + In this example, if the expression `x % 2 == 0' is true (that is, if the value of `x' is evenly divisible by two), then the first `print' -statement is executed, otherwise the second `print' statement is -executed. - - If the `else' appears on the same line as THEN-BODY, and THEN-BODY -is not a compound statement (i.e. not surrounded by curly braces), then -a semicolon must separate THEN-BODY from `else'. To illustrate this, -let's rewrite the previous example: +statement is executed; otherwise the second `print' statement is +executed. If the `else' keyword appears on the same line as THEN-BODY +and THEN-BODY is not a compound statement (i.e., not surrounded by +curly braces), then a semicolon must separate THEN-BODY from the `else'. +To illustrate this, the previous example can be rewritten as: if (x % 2 == 0) print "x is even"; else print "x is odd" -If you forget the `;', `awk' won't be able to interpret the statement, -and you will get a syntax error. - - We would not actually write this example this way, because a human -reader might fail to see the `else' if it were not the first thing on -its line. +If the `;' is left out, `awk' can't interpret the statement and it +produces a syntax error. Don't actually write programs this way, +because a human reader might fail to see the `else' if it is not the +first thing on its line.  File: gawk.info, Node: While Statement, Next: Do Statement, Prev: If Statement, Up: Statements The `while' Statement -===================== - - In programming, a "loop" means a part of a program that can be -executed two or more times in succession. +--------------------- - The `while' statement is the simplest looping statement in `awk'. -It repeatedly executes a statement as long as a condition is true. It -looks like this: + In programming, a "loop" is a part of a program that can be executed +two or more times in succession. The `while' statement is the simplest +looping statement in `awk'. It repeatedly executes a statement as long +as a condition is true. For example: while (CONDITION) BODY -Here BODY is a statement that we call the "body" of the loop, and -CONDITION is an expression that controls how long the loop keeps -running. - - The first thing the `while' statement does is test CONDITION. If +BODY is a statement called the "body" of the loop, and CONDITION is an +expression that controls how long the loop keeps running. The first +thing the `while' statement does is test the CONDITION. If the CONDITION is true, it executes the statement BODY. (The CONDITION is true when the value is not zero and not a null string.) After BODY has been executed, CONDITION is tested again, and if it is still true, BODY -is executed again. This process repeats until CONDITION is no longer -true. If CONDITION is initially false, the body of the loop is never -executed, and `awk' continues with the statement following the loop. - - This example prints the first three fields of each record, one per -line. +is executed again. This process repeats until the CONDITION is no +longer true. If the CONDITION is initially false, the body of the loop +is never executed and `awk' continues with the statement following the +loop. This example prints the first three fields of each record, one +per line: awk '{ i = 1 while (i <= 3) { @@ -6263,64 +7165,61 @@ line. } }' inventory-shipped -Here the body of the loop is a compound statement enclosed in braces, -containing two statements. - - The loop works like this: first, the value of `i' is set to one. -Then, the `while' tests whether `i' is less than or equal to three. -This is true when `i' equals one, so the `i'-th field is printed. Then -the `i++' increments the value of `i' and the loop repeats. The loop -terminates when `i' reaches four. +The body of this loop is a compound statement enclosed in braces, +containing two statements. The loop works in the following manner: +first, the value of `i' is set to one. Then, the `while' statement +tests whether `i' is less than or equal to three. This is true when +`i' equals one, so the `i'-th field is printed. Then the `i++' +increments the value of `i' and the loop repeats. The loop terminates +when `i' reaches four. - As you can see, a newline is not required between the condition and -the body; but using one makes the program clearer unless the body is a -compound statement or is very simple. The newline after the open-brace -that begins the compound statement is not required either, but the -program would be harder to read without it. + A newline is not required between the condition and the body; +however using one makes the program clearer unless the body is a +compound statement or else is very simple. The newline after the +open-brace that begins the compound statement is not required either, +but the program is harder to read without it.  File: gawk.info, Node: Do Statement, Next: For Statement, Prev: While Statement, Up: Statements The `do'-`while' Statement -========================== +-------------------------- The `do' loop is a variation of the `while' looping statement. The -`do' loop executes the BODY once, and then repeats BODY as long as -CONDITION is true. It looks like this: +`do' loop executes the BODY once and then repeats the BODY as long as +the CONDITION is true. It looks like this: do BODY while (CONDITION) - Even if CONDITION is false at the start, BODY is executed at least -once (and only once, unless executing BODY makes CONDITION true). + Even if the CONDITION is false at the start, the BODY is executed at +least once (and only once, unless executing BODY makes CONDITION true). Contrast this with the corresponding `while' statement: while (CONDITION) BODY -This statement does not execute BODY even once if CONDITION is false to -begin with. +This statement does not execute BODY even once if the CONDITION is +false to begin with. The following is an example of a `do' statement: - Here is an example of a `do' statement: - - awk '{ i = 1 + { i = 1 do { print $0 i++ } while (i <= 10) - }' + } -This program prints each input record ten times. It isn't a very -realistic example, since in this case an ordinary `while' would do just -as well. But this reflects actual experience; there is only -occasionally a real use for a `do' statement. +This program prints each input record ten times. However, it isn't a +very realistic example, since in this case an ordinary `while' would do +just as well. This situation reflects actual experience; only +occasionally is there a real use for a `do' statement.  File: gawk.info, Node: For Statement, Next: Break Statement, Prev: Do Statement, Up: Statements The `for' Statement -=================== +------------------- The `for' statement makes it more convenient to count iterations of a loop. The general form of the `for' statement looks like this: @@ -6328,48 +7227,47 @@ loop. The general form of the `for' statement looks like this: for (INITIALIZATION; CONDITION; INCREMENT) BODY -The INITIALIZATION, CONDITION and INCREMENT parts are arbitrary `awk' +The INITIALIZATION, CONDITION, and INCREMENT parts are arbitrary `awk' expressions, and BODY stands for any `awk' statement. The `for' statement starts by executing INITIALIZATION. Then, as -long as CONDITION is true, it repeatedly executes BODY and then -INCREMENT. Typically INITIALIZATION sets a variable to either zero or +long as the CONDITION is true, it repeatedly executes BODY and then +INCREMENT. Typically, INITIALIZATION sets a variable to either zero or one, INCREMENT adds one to it, and CONDITION compares it against the -desired number of iterations. - - Here is an example of a `for' statement: +desired number of iterations. For example: awk '{ for (i = 1; i <= 3; i++) print $i }' inventory-shipped -This prints the first three fields of each input record, one field per -line. +This prints the first three fields of each input record, with one field +per line. - You cannot set more than one variable in the INITIALIZATION part -unless you use a multiple assignment statement such as `x = y = 0', -which is possible only if all the initial values are equal. (But you -can initialize additional variables by writing their assignments as -separate statements preceding the `for' loop.) + It isn't possible to set more than one variable in the +INITIALIZATION part without using a multiple assignment statement such +as `x = y = 0'. This makes sense only if all the initial values are +equal. (But it is possible to initialize additional variables by +writing their assignments as separate statements preceding the `for' +loop.) - The same is true of the INCREMENT part; to increment additional -variables, you must write separate statements at the end of the loop. -The C compound expression, using C's comma operator, would be useful in -this context, but it is not supported in `awk'. + The same is true of the INCREMENT part. Incrementing additional +variables requires separate statements at the end of the loop. The C +compound expression, using C's comma operator, is useful in this +context but it is not supported in `awk'. - Most often, INCREMENT is an increment expression, as in the example -above. But this is not required; it can be any expression whatever. -For example, this statement prints all the powers of two between one -and 100: + Most often, INCREMENT is an increment expression, as in the previous +example. But this is not required; it can be any expression +whatsoever. For example, the following statement prints all the powers +of two between 1 and 100: for (i = 1; i <= 100; i *= 2) print i - Any of the three expressions in the parentheses following the `for' -may be omitted if there is nothing to be done there. Thus, + If there is nothing to be done, any of the three expressions in the +parentheses following the `for' keyword may be omitted. Thus, `for (; x > 0;)' is equivalent to `while (x > 0)'. If the CONDITION is -omitted, it is treated as TRUE, effectively yielding an "infinite loop" -(i.e. a loop that will never terminate). +omitted, it is treated as true, effectively yielding an "infinite loop" +(i.e., a loop that never terminates). In most cases, a `for' loop is an abbreviation for a `while' loop, as shown here: @@ -6381,10 +7279,16 @@ as shown here: } The only exception is when the `continue' statement (*note The -`continue' Statement: Continue Statement.) is used inside the loop; -changing a `for' statement to a `while' statement in this way can +`continue' Statement: Continue Statement.) is used inside the loop. +Changing a `for' statement to a `while' statement in this way can change the effect of the `continue' statement inside the loop. + The `awk' language has a `for' statement in addition to a `while' +statement because a `for' loop is often both less work to type and more +natural to think of. Counting the number of iterations is very common +in loops. It can be easier to think of this counting as part of +looping rather than as something to do inside the loop. + There is an alternate version of the `for' loop, for iterating over all the indices of an array: @@ -6394,102 +7298,95 @@ all the indices of an array: *Note Scanning All Elements of an Array: Scanning an Array, for more information on this version of the `for' loop. - The `awk' language has a `for' statement in addition to a `while' -statement because often a `for' loop is both less work to type and more -natural to think of. Counting the number of iterations is very common -in loops. It can be easier to think of this counting as part of -looping rather than as something to do inside the loop. - - The next section has more complicated examples of `for' loops. -  File: gawk.info, Node: Break Statement, Next: Continue Statement, Prev: For Statement, Up: Statements The `break' Statement -===================== +--------------------- The `break' statement jumps out of the innermost `for', `while', or `do' loop that encloses it. The following example finds the smallest divisor of any integer, and also identifies prime numbers: - awk '# find smallest divisor of num - { num = $1 - for (div = 2; div*div <= num; div++) - if (num % div == 0) - break - if (num % div == 0) - printf "Smallest divisor of %d is %d\n", num, div - else - printf "%d is prime\n", num - }' + # find smallest divisor of num + { + num = $1 + for (div = 2; div*div <= num; div++) + if (num % div == 0) + break + if (num % div == 0) + printf "Smallest divisor of %d is %d\n", num, div + else + printf "%d is prime\n", num + } When the remainder is zero in the first `if' statement, `awk' immediately "breaks out" of the containing `for' loop. This means that `awk' proceeds immediately to the statement following the loop and continues processing. (This is very different from the `exit' -statement which stops the entire `awk' program. *Note The `exit' +statement, which stops the entire `awk' program. *Note The `exit' Statement: Exit Statement.) - Here is another program equivalent to the previous one. It -illustrates how the CONDITION of a `for' or `while' could just as well -be replaced with a `break' inside an `if': - - awk '# find smallest divisor of num - { num = $1 - for (div = 2; ; div++) { - if (num % div == 0) { - printf "Smallest divisor of %d is %d\n", num, div - break - } - if (div*div > num) { - printf "%d is prime\n", num - break - } - } - }' + Th following program illustrates how the CONDITION of a `for' or +`while' statement could be replaced with a `break' inside an `if': + + # find smallest divisor of num + { + num = $1 + for (div = 2; ; div++) { + if (num % div == 0) { + printf "Smallest divisor of %d is %d\n", num, div + break + } + if (div*div > num) { + printf "%d is prime\n", num + break + } + } + } - As described above, the `break' statement has no meaning when used -outside the body of a loop. However, although it was never documented, -historical implementations of `awk' have treated the `break' statement -outside of a loop as if it were a `next' statement (*note The `next' -Statement: Next Statement.). Recent versions of Unix `awk' no longer -allow this usage. `gawk' will support this use of `break' only if -`--traditional' has been specified on the command line (*note Command -Line Options: Options.). Otherwise, it will be treated as an error, -since the POSIX standard specifies that `break' should only be used -inside the body of a loop (d.c.). + The `break' statement has no meaning when used outside the body of a +loop. However, although it was never documented, historical +implementations of `awk' treated the `break' statement outside of a +loop as if it were a `next' statement (*note The `next' Statement: Next +Statement.). Recent versions of Unix `awk' no longer allow this usage. +`gawk' supports this use of `break' only if `--traditional' has been +specified on the command line (*note Command-Line Options: Options.). +Otherwise, it is treated as an error, since the POSIX standard +specifies that `break' should only be used inside the body of a loop. +(d.c.)  File: gawk.info, Node: Continue Statement, Next: Next Statement, Prev: Break Statement, Up: Statements The `continue' Statement -======================== +------------------------ - The `continue' statement, like `break', is used only inside `for', + As with `break', the `continue' statement is used only inside `for', `while', and `do' loops. It skips over the rest of the loop body, causing the next cycle around the loop to begin immediately. Contrast this with `break', which jumps out of the loop altogether. The `continue' statement in a `for' loop directs `awk' to skip the -rest of the body of the loop, and resume execution with the +rest of the body of the loop and resume execution with the increment-expression of the `for' statement. The following program illustrates this fact: - awk 'BEGIN { + BEGIN { for (x = 0; x <= 20; x++) { if (x == 5) continue printf "%d ", x } print "" - }' + } -This program prints all the numbers from zero to 20, except for five, -for which the `printf' is skipped. Since the increment `x++' is not +This program prints all the numbers from 0 to 20--except for five, for +which the `printf' is skipped. Because the increment `x++' is not skipped, `x' does not remain stuck at five. Contrast the `for' loop -above with this `while' loop: +from the previous example with the following `while' loop: - awk 'BEGIN { + BEGIN { x = 0 while (x <= 20) { if (x == 5) @@ -6498,48 +7395,48 @@ above with this `while' loop: x++ } print "" - }' + } -This program loops forever once `x' gets to five. +This program loops forever once `x' reaches five. - As described above, the `continue' statement has no meaning when -used outside the body of a loop. However, although it was never -documented, historical implementations of `awk' have treated the -`continue' statement outside of a loop as if it were a `next' statement -(*note The `next' Statement: Next Statement.). Recent versions of Unix -`awk' no longer allow this usage. `gawk' will support this use of -`continue' only if `--traditional' has been specified on the command -line (*note Command Line Options: Options.). Otherwise, it will be -treated as an error, since the POSIX standard specifies that `continue' -should only be used inside the body of a loop (d.c.). + The `continue' statement has no meaning when used outside the body of +a loop. Historical versions of `awk' treated a `continue' statement +outside a loop the same way they treated a `break' statement outside a +loop: as if it were a `next' statement (*note The `next' Statement: +Next Statement.). Recent versions of Unix `awk' no longer work this +way, and `gawk' allows it only if `--traditional' is specified on the +command line (*note Command-Line Options: Options.). Just like the +`break' statement, the POSIX standard specifies that `continue' should +only be used inside the body of a loop. (d.c.)  File: gawk.info, Node: Next Statement, Next: Nextfile Statement, Prev: Continue Statement, Up: Statements The `next' Statement -==================== +-------------------- The `next' statement forces `awk' to immediately stop processing the current record and go on to the next record. This means that no -further rules are executed for the current record. The rest of the -current rule's action is not executed either. +further rules are executed for the current record, and the rest of the +current rule's action isn't executed. Contrast this with the effect of the `getline' function (*note -Explicit Input with `getline': Getline.). That too causes `awk' to +Explicit Input with `getline': Getline.). That also causes `awk' to read the next record immediately, but it does not alter the flow of -control in any way. So the rest of the current action executes with a -new input record. +control in any way (i.e., the rest of the current action executes with +a new input record). At the highest level, `awk' program execution is a loop that reads an input record and then tests each rule's pattern against it. If you think of this loop as a `for' statement whose body contains the rules, -then the `next' statement is analogous to a `continue' statement: it -skips to the end of the body of this implicit loop, and executes the +then the `next' statement is analogous to a `continue' statement. It +skips to the end of the body of this implicit loop and executes the increment (which reads another record). - For example, if your `awk' program works only on records with four -fields, and you don't want it to fail when given bad input, you might -use this rule near the beginning of the program: + For example, suppose an `awk' program works only on records with +four fields, and it shouldn't fail when given bad input. To avoid +complicating the rest of the program, write a "weed out" rule near the +beginning, in the following manner: NF != 4 { err = sprintf("%s:%d: skipped: NF != 4\n", FILENAME, FNR) @@ -6547,107 +7444,117 @@ use this rule near the beginning of the program: next } -so that the following rules will not see the bad record. The error -message is redirected to the standard error output stream, as error -messages should be. *Note Special File Names in `gawk': Special Files. +Because of the `next' statement, the program's subsequent rules won't +see the bad record. The error message is redirected to the standard +error output stream, as error messages should be. *Note Special File +Names in `gawk': Special Files. According to the POSIX standard, the behavior is undefined if the -`next' statement is used in a `BEGIN' or `END' rule. `gawk' will treat -it as a syntax error. Although POSIX permits it, some other `awk' +`next' statement is used in a `BEGIN' or `END' rule. `gawk' treats it +as a syntax error. Although POSIX permits it, some other `awk' implementations don't allow the `next' statement inside function bodies -(*note User-defined Functions: User-defined.). Just as any other -`next' statement, a `next' inside a function body reads the next record -and starts processing it with the first rule in the program. - - If the `next' statement causes the end of the input to be reached, -then the code in any `END' rules will be executed. *Note The `BEGIN' -and `END' Special Patterns: BEGIN/END. - - *Caution:* Some `awk' implementations generate a run-time error if -you use the `next' statement inside a user-defined function (*note -User-defined Functions: User-defined.). `gawk' does not have this -problem. +(*note User-Defined Functions: User-defined.). Just as with any other +`next' statement, a `next' statement inside a function body reads the +next record and starts processing it with the first rule in the program. +If the `next' statement causes the end of the input to be reached, then +the code in any `END' rules is executed. *Note The `BEGIN' and `END' +Special Patterns: BEGIN/END.  File: gawk.info, Node: Nextfile Statement, Next: Exit Statement, Prev: Next Statement, Up: Statements -The `nextfile' Statement -======================== +Using `gawk''s `nextfile' Statement +----------------------------------- `gawk' provides the `nextfile' statement, which is similar to the `next' statement. However, instead of abandoning processing of the current record, the `nextfile' statement instructs `gawk' to stop processing the current data file. + The `nextfile' statement is a `gawk' extension. In most other `awk' +implementations, or if `gawk' is in compatibility mode (*note +Command-Line Options: Options.), `nextfile' is not special. + Upon execution of the `nextfile' statement, `FILENAME' is updated to the name of the next data file listed on the command line, `FNR' is reset to one, `ARGIND' is incremented, and processing starts over with -the first rule in the progam. *Note Built-in Variables::. - - If the `nextfile' statement causes the end of the input to be -reached, then the code in any `END' rules will be executed. *Note The -`BEGIN' and `END' Special Patterns: BEGIN/END. - - The `nextfile' statement is a `gawk' extension; it is not -(currently) available in any other `awk' implementation. *Note -Implementing `nextfile' as a Function: Nextfile Function, for a -user-defined function you can use to simulate the `nextfile' statement. - - The `nextfile' statement would be useful if you have many data files -to process, and you expect that you would not want to process every -record in every file. Normally, in order to move on to the next data -file, you would have to continue scanning the unwanted records. The -`nextfile' statement accomplishes this much more efficiently. +the first rule in the program. (`ARGIND' hasn't been introduced yet. +*Note Built-in Variables::.) If the `nextfile' statement causes the +end of the input to be reached, then the code in any `END' rules is +executed. *Note The `BEGIN' and `END' Special Patterns: BEGIN/END. + + The `nextfile' statement is useful when there are many data files to +process but it isn't necessary to process every record in every file. +Normally, in order to move on to the next data file, a program has to +continue scanning the unwanted records. The `nextfile' statement +accomplishes this much more efficiently. + + While one might think that `close(FILENAME)' would accomplish the +same as `nextfile', this isn't true. `close' is reserved for closing +files, pipes, and coprocesses that are opened with redirections. It is +not related to the main processing that `awk' does with the files +listed in `ARGV'. + + If it's necessary to use an `awk' version that doesn't support +`nextfile', see *Note Implementing `nextfile' as a Function: Nextfile +Function, for a user-defined function that simulates the `nextfile' +statement. + + The current version of the Bell Laboratories `awk' (*note Other +Freely Available `awk' Implementations: Other Versions.) also supports +`nextfile'. However, it doesn't allow the `nextfile' statement inside +function bodies (*note User-Defined Functions: User-defined.). `gawk' +does; a `nextfile' inside a function body reads the next record and +starts processing it with the first rule in the program, just as any +other `nextfile' statement. *Caution:* Versions of `gawk' prior to 3.0 used two words (`next -file') for the `nextfile' statement. This was changed in 3.0 to one -word, since the treatment of `file' was inconsistent. When it appeared -after `next', it was a keyword. Otherwise, it was a regular -identifier. The old usage is still accepted. However, `gawk' will -generate a warning message, and support for `next file' will eventually -be discontinued in a future version of `gawk'. +file') for the `nextfile' statement. In version 3.0, this was changed +to one word, because the treatment of `file' was inconsistent. When it +appeared after `next', `file' was a keyword; otherwise, it was a +regular identifier. The old usage is no longer accepted; `next file' +generates a syntax error.  File: gawk.info, Node: Exit Statement, Prev: Nextfile Statement, Up: Statements The `exit' Statement -==================== +-------------------- The `exit' statement causes `awk' to immediately stop executing the current rule and to stop processing input; any remaining input is -ignored. It looks like this: +ignored. The `exit' statement is written as follows: exit [RETURN CODE] - If an `exit' statement is executed from a `BEGIN' rule the program -stops processing everything immediately. No input records are read. -However, if an `END' rule is present, it is executed (*note The `BEGIN' -and `END' Special Patterns: BEGIN/END.). - - If `exit' is used as part of an `END' rule, it causes the program to -stop immediately. + When an `exit' statement is executed from a `BEGIN' rule, the +program stops processing everything immediately. No input records are +read. However, if an `END' rule is present, as part of executing the +`exit' statement, the `END' rule is executed (*note The `BEGIN' and +`END' Special Patterns: BEGIN/END.). If `exit' is used as part of an +`END' rule, it causes the program to stop immediately. An `exit' statement that is not part of a `BEGIN' or `END' rule stops the execution of any further automatic rules for the current record, skips reading any remaining input records, and executes the `END' rule if there is one. - If you do not want the `END' rule to do its job in this case, you -can set a variable to non-zero before the `exit' statement, and check -that variable in the `END' rule. *Note Assertions: Assert Function, -for an example that does this. + In such a case, if you don't want the `END' rule to do its job, set +a variable to nonzero before the `exit' statement and check that +variable in the `END' rule. *Note Assertions: Assert Function, for an +example that does this. If an argument is supplied to `exit', its value is used as the exit status code for the `awk' process. If no argument is supplied, `exit' returns status zero (success). In the case where an argument is supplied to a first `exit' statement, and then `exit' is called a -second time with no argument, the previously supplied exit value is -used (d.c.). +second time from an `END' rule with no argument, `awk' uses the +previously supplied exit value. (d.c.) - For example, let's say you've discovered an error condition you -really don't know how to handle. Conventionally, programs report this -by exiting with a non-zero status. Your `awk' program can do this -using an `exit' statement with a non-zero argument. Here is an example: + For example, suppose an error condition occurs that is difficult or +impossible to handle. Conventionally, programs report this by exiting +with a nonzero status. An `awk' program can do this using an `exit' +statement with a nonzero argument, as shown in the following example: BEGIN { if (("date" | getline date_now) <= 0) { @@ -6659,69 +7566,88 @@ using an `exit' statement with a non-zero argument. Here is an example: }  -File: gawk.info, Node: Built-in Variables, Next: Arrays, Prev: Statements, Up: Top +File: gawk.info, Node: Built-in Variables, Prev: Statements, Up: Patterns and Actions Built-in Variables -****************** +================== Most `awk' variables are available for you to use for your own -purposes; they never change except when your program assigns values to -them, and never affect anything except when your program examines them. -However, a few variables in `awk' have special built-in meanings. Some -of them `awk' examines automatically, so that they enable you to tell -`awk' how to do certain things. Others are set automatically by `awk', -so that they carry information from the internal workings of `awk' to -your program. - - This chapter documents all the built-in variables of `gawk'. Most -of them are also documented in the chapters describing their areas of +purposes; they never change unless your program assigns values to them, +and they never affect anything unless your program examines them. +However, a few variables in `awk' have special built-in meanings. +`awk' examines some of these automatically, so that they enable you to +tell `awk' how to do certain things. Others are set automatically by +`awk', so that they carry information from the internal workings of +`awk' to your program. + + This minor node documents all the built-in variables of `gawk', most +of which are also documented in the chapters describing their areas of activity. * Menu: * User-modified:: Built-in variables that you change to control `awk'. -* Auto-set:: Built-in variables where `awk' gives you - information. +* Auto-set:: Built-in variables where `awk' gives + you information. * ARGC and ARGV:: Ways to use `ARGC' and `ARGV'.  File: gawk.info, Node: User-modified, Next: Auto-set, Prev: Built-in Variables, Up: Built-in Variables -Built-in Variables that Control `awk' -===================================== +Built-in Variables That Control `awk' +------------------------------------- - This is an alphabetical list of the variables which you can change to -control how `awk' does certain things. Those variables that are -specific to `gawk' are marked with an asterisk, `*'. + The following is an alphabetical list of variables that you can +change to control how `awk' does certain things. The variables that are +specific to `gawk' are marked with a pound sign (`#'). + +`BINMODE #' + On non-POSIX systems, this variable specifies use of "binary" mode + for all I/O. Numeric values of one, two, or three, specify that + input files, output files, or all files, respectively, should use + binary I/O. Alternatively, string values of `"r"' or `"w"' + specify that input files and output files, respectively, should + use binary I/O. A string value of `"rw"' or `"wr"' indicates that + all files should use binary I/O. Any other string value is + equivalent to `"rw"', but `gawk' generates a warning message. + `BINMODE' is described in more detail in *Note Using `gawk' on PC + Operating Systems: PC Using. + + This variable is a `gawk' extension. In other `awk' + implementations (except `mawk', *note Other Freely Available `awk' + Implementations: Other Versions.), or if `gawk' is in + compatibility mode (*note Command-Line Options: Options.), it is + not special. `CONVFMT' This string controls conversion of numbers to strings (*note Conversion of Strings and Numbers: Conversion.). It works by being passed, in effect, as the first argument to the `sprintf' - function (*note Built-in Functions for String Manipulation: String - Functions.). Its default value is `"%.6g"'. `CONVFMT' was - introduced by the POSIX standard. - -`FIELDWIDTHS *' - This is a space separated list of columns that tells `gawk' how to - split input with fixed, columnar boundaries. It is an - experimental feature. Assigning to `FIELDWIDTHS' overrides the - use of `FS' for field splitting. *Note Reading Fixed-width Data: - Constant Size, for more information. - - If `gawk' is in compatibility mode (*note Command Line Options: - Options.), then `FIELDWIDTHS' has no special meaning, and field - splitting operations are done based exclusively on the value of + function (*note String Manipulation Functions: String Functions.). + Its default value is `"%.6g"'. `CONVFMT' was introduced by the + POSIX standard. + +`FIELDWIDTHS #' + This is a space-separated list of columns that tells `gawk' how to + split input with fixed columnar boundaries. Assigning a value to + `FIELDWIDTHS' overrides the use of `FS' for field splitting. + *Note Reading Fixed-Width Data: Constant Size, for more + information. + + If `gawk' is in compatibility mode (*note Command-Line Options: + Options.), then `FIELDWIDTHS' has no special meaning, and + field-splitting operations occur based exclusively on the value of `FS'. `FS' - `FS' is the input field separator (*note Specifying How Fields are + This is the input field separator (*note Specifying How Fields Are Separated: Field Separators.). The value is a single-character string or a multi-character regular expression that matches the separations between fields in an input record. If the value is the null string (`""'), then each character in the record becomes - a separate field. + a separate field. (This behavior is a `gawk' extension. POSIX + `awk' does not specify the behavior when `FS' is the null string.) The default value is `" "', a string consisting of a single space. As a special exception, this value means that any sequence of @@ -6734,61 +7660,94 @@ specific to `gawk' are marked with an asterisk, `*'. awk -F, 'PROGRAM' INPUT-FILES - If `gawk' is using `FIELDWIDTHS' for field-splitting, assigning a - value to `FS' will cause `gawk' to return to the normal, - `FS'-based, field splitting. An easy way to do this is to simply - say `FS = FS', perhaps with an explanatory comment. - -`IGNORECASE *' - If `IGNORECASE' is non-zero or non-null, then all string - comparisons, and all regular expression matching are - case-independent. Thus, regexp matching with `~' and `!~', and - the `gensub', `gsub', `index', `match', `split' and `sub' - functions, record termination with `RS', and field splitting with - `FS' all ignore case when doing their particular regexp operations. - The value of `IGNORECASE' does _not_ affect array subscripting. - *Note Case-sensitivity in Matching: Case-sensitivity. - - If `gawk' is in compatibility mode (*note Command Line Options: - Options.), then `IGNORECASE' has no special meaning, and string + If `gawk' is using `FIELDWIDTHS' for field splitting, assigning a + value to `FS' causes `gawk' to return to the normal, `FS'-based + field splitting. An easy way to do this is to simply say `FS = + FS', perhaps with an explanatory comment. + +`IGNORECASE #' + If `IGNORECASE' is nonzero or non-null, then all string comparisons + and all regular expression matching are case-independent. Thus, + regexp matching with `~' and `!~', as well as the `gensub', + `gsub', `index', `match', `split', and `sub' functions, record + termination with `RS', and field splitting with `FS', all ignore + case when doing their particular regexp operations. However, the + value of `IGNORECASE' does _not_ affect array subscripting. *Note + Case Sensitivity in Matching: Case-sensitivity. + + If `gawk' is in compatibility mode (*note Command-Line Options: + Options.), then `IGNORECASE' has no special meaning. Thus, string and regexp operations are always case-sensitive. +`LINT #' + When this variable is true (nonzero or non-null), `gawk' behaves + as if the `--lint' command-line option is in effect. (*note + Command-Line Options: Options.). With a value of `"fatal"', lint + warnings become fatal errors. Any other true value prints + non-fatal warnings. Assigning a false value to `LINT' turns off + the lint warnings. + + This variable is a `gawk' extension. It is not special in other + `awk' implementations. Unlike the other special variables, + changing `LINT' does affect the production of lint warnings, even + if `gawk' is in compatibility mode. Much as the `--lint' and + `--traditional' options independently control different aspects of + `gawk''s behavior, the control of lint warnings during program + execution is independent of the flavor of `awk' being executed. + `OFMT' This string controls conversion of numbers to strings (*note Conversion of Strings and Numbers: Conversion.) for printing with - the `print' statement. It works by being passed, in effect, as - the first argument to the `sprintf' function (*note Built-in - Functions for String Manipulation: String Functions.). Its - default value is `"%.6g"'. Earlier versions of `awk' also used - `OFMT' to specify the format for converting numbers to strings in - general expressions; this is now done by `CONVFMT'. + the `print' statement. It works by being passed as the first + argument to the `sprintf' function (*note String Manipulation + Functions: String Functions.). Its default value is `"%.6g"'. + Earlier versions of `awk' also used `OFMT' to specify the format + for converting numbers to strings in general expressions; this is + now done by `CONVFMT'. `OFS' This is the output field separator (*note Output Separators::). - It is output between the fields output by a `print' statement. Its - default value is `" "', a string consisting of a single space. + It is output between the fields printed by a `print' statement. + Its default value is `" "', a string consisting of a single space. `ORS' This is the output record separator. It is output at the end of - every `print' statement. Its default value is `"\n"'. (*Note - Output Separators::.) + every `print' statement. Its default value is `"\n"', the newline + character. (*Note Output Separators::.) `RS' This is `awk''s input record separator. Its default value is a string containing a single newline character, which means that an input record consists of a single line of text. It can also be the null string, in which case records are separated by runs of - blank lines, or a regexp, in which case records are separated by - matches of the regexp in the input text. (*Note How Input is - Split into Records: Records.) + blank lines. If it is a regexp, records are separated by matches + of the regexp in the input text. (*Note How Input Is Split into + Records: Records.) + + The ability for `RS' to be a regular expression is a `gawk' + extension. In most other `awk' implementations, or if `gawk' is + in compatibility mode (*note Command-Line Options: Options.), just + the first character of `RS''s value is used. `SUBSEP' - `SUBSEP' is the subscript separator. It has the default value of - `"\034"', and is used to separate the parts of the indices of a - multi-dimensional array. Thus, the expression `foo["A", "B"]' - really accesses `foo["A\034B"]' (*note Multi-dimensional Arrays: + This is the subscript separator. It has the default value of + `"\034"' and is used to separate the parts of the indices of a + multidimensional array. Thus, the expression `foo["A", "B"]' + really accesses `foo["A\034B"]' (*note Multidimensional Arrays: Multi-dimensional.). +`TEXTDOMAIN #' + This variable is used for internationalization of programs at the + `awk' level. It sets the default text domain for specially marked + string constants in the source text, as well as for the + `dcgettext' and `bindtextdomain' functions (*note + Internationalization with `gawk': Internationalization.). The + default value of `TEXTDOMAIN' is `"messages"'. + + This variable is a `gawk' extension. In other `awk' + implementations, or if `gawk' is in compatibility mode (*note + Command-Line Options: Options.), it is not special. + ---------- Footnotes ---------- (1) In POSIX `awk', newline does not count as whitespace. @@ -6796,136 +7755,184 @@ specific to `gawk' are marked with an asterisk, `*'.  File: gawk.info, Node: Auto-set, Next: ARGC and ARGV, Prev: User-modified, Up: Built-in Variables -Built-in Variables that Convey Information -========================================== +Built-in Variables That Convey Information +------------------------------------------ - This is an alphabetical list of the variables that are set -automatically by `awk' on certain occasions in order to provide -information to your program. Those variables that are specific to -`gawk' are marked with an asterisk, `*'. + The following is an alphabetical list of variables that `awk' sets +automatically on certain occasions in order to provide information to +your program. The variables that are specific to `gawk' are marked +with an asterisk (`*'). -`ARGC' -`ARGV' +`ARGC, ARGV' The command-line arguments available to `awk' programs are stored in an array called `ARGV'. `ARGC' is the number of command-line - arguments present. *Note Other Command Line Arguments: Other - Arguments. Unlike most `awk' arrays, `ARGV' is indexed from zero - to `ARGC' - 1. For example: + arguments present. *Note Other Command-Line Arguments: Other + Arguments. Unlike most `awk' arrays, `ARGV' is indexed from 0 to + `ARGC' - 1. In the following example: $ awk 'BEGIN { - > for (i = 0; i < ARGC; i++) - > print ARGV[i] + > for (i = 0; i < ARGC; i++) + > print ARGV[i] > }' inventory-shipped BBS-list -| awk -| inventory-shipped -| BBS-list - In this example, `ARGV[0]' contains `"awk"', `ARGV[1]' contains - `"inventory-shipped"', and `ARGV[2]' contains `"BBS-list"'. The + `ARGV[0]' contains `"awk"', `ARGV[1]' contains + `"inventory-shipped"' and `ARGV[2]' contains `"BBS-list"'. The value of `ARGC' is three, one more than the index of the last - element in `ARGV', since the elements are numbered from zero. + element in `ARGV', because the elements are numbered from zero. The names `ARGC' and `ARGV', as well as the convention of indexing - the array from zero to `ARGC' - 1, are derived from the C - language's method of accessing command line arguments. *Note - Using `ARGC' and `ARGV': ARGC and ARGV, for information about how - `awk' uses these variables. - -`ARGIND *' - The index in `ARGV' of the current file being processed. Every - time `gawk' opens a new data file for processing, it sets `ARGIND' - to the index in `ARGV' of the file name. When `gawk' is - processing the input files, it is always true that `FILENAME == - ARGV[ARGIND]'. + the array from 0 to `ARGC' - 1, are derived from the C language's + method of accessing command-line arguments. + + The value of `ARGV[0]' can vary from system to system. Also, you + should note that the program text is _not_ included in `ARGV', nor + are any of `awk''s command-line options. *Note Using `ARGC' and + `ARGV': ARGC and ARGV, for information about how `awk' uses these + variables. + +`ARGIND #' + This is the index in `ARGV' of the current file being processed. + Every time `gawk' opens a new data file for processing, it sets + `ARGIND' to the index in `ARGV' of the file name. When `gawk' is + processing the input files, `FILENAME == ARGV[ARGIND]' is always + true. This variable is useful in file processing; it allows you to tell - how far along you are in the list of data files, and to - distinguish between successive instances of the same filename on + how far along you are in the list of data files as well as to + distinguish between successive instances of the same file name on the command line. While you can change the value of `ARGIND' within your `awk' - program, `gawk' will automatically set it to a new value when the - next file is opened. + program, `gawk' automatically sets it to a new value when the next + file is opened. - This variable is a `gawk' extension. In other `awk' + This variable is a `gawk' extension. In other `awk' implementations, or if `gawk' is in compatibility mode (*note - Command Line Options: Options.), it is not special. + Command-Line Options: Options.), it is not special. `ENVIRON' An associative array that contains the values of the environment. - The array indices are the environment variable names; the values + The array indices are the environment variable names; the elements are the values of the particular environment variables. For example, `ENVIRON["HOME"]' might be `/home/arnold'. Changing this array does not affect the environment passed on to any programs that `awk' may spawn via redirection or the `system' function. - (In a future version of `gawk', it may do so.) Some operating systems may not have environment variables. On such systems, the `ENVIRON' array is empty (except for - `ENVIRON["AWKPATH"]'). + `ENVIRON["AWKPATH"]', *note The `AWKPATH' Environment Variable: + AWKPATH Variable.). -`ERRNO *' - If a system error occurs either doing a redirection for `getline', +`ERRNO #' + If a system error occurs during a redirection for `getline', during a read for `getline', or during a `close' operation, then - `ERRNO' will contain a string describing the error. + `ERRNO' contains a string describing the error. - This variable is a `gawk' extension. In other `awk' + This variable is a `gawk' extension. In other `awk' implementations, or if `gawk' is in compatibility mode (*note - Command Line Options: Options.), it is not special. + Command-Line Options: Options.), it is not special. `FILENAME' This is the name of the file that `awk' is currently reading. When no data files are listed on the command line, `awk' reads - from the standard input, and `FILENAME' is set to `"-"'. + from the standard input and `FILENAME' is set to `"-"'. `FILENAME' is changed each time a new file is read (*note Reading Input Files: Reading Files.). Inside a `BEGIN' rule, the value of `FILENAME' is `""', since there are no input files being processed - yet.(1) (d.c.) + yet.(1) (d.c.) Note though, that using `getline' (*note Explicit + Input with `getline': Getline.) inside a `BEGIN' rule can give + `FILENAME' a value. `FNR' - `FNR' is the current record number in the current file. `FNR' is + This is the current record number in the current file. `FNR' is incremented each time a new record is read (*note Explicit Input with `getline': Getline.). It is reinitialized to zero each time a new input file is started. `NF' - `NF' is the number of fields in the current input record. `NF' is - set each time a new record is read, when a new field is created, - or when `$0' changes (*note Examining Fields: Fields.). + This is the number of fields in the current input record. `NF' is + set each time a new record is read, when a new field is created or + when `$0' changes (*note Examining Fields: Fields.). `NR' This is the number of input records `awk' has processed since the - beginning of the program's execution (*note How Input is Split - into Records: Records.). `NR' is set each time a new record is - read. + beginning of the program's execution (*note How Input Is Split + into Records: Records.). `NR' is incremented each time a new + record is read. + +`PROCINFO #' + The elements of this array provide access to information about the + running `awk' program. The following elements (listed + alphabetically) are guaranteed to be available: + + `PROCINFO["egid"]' + The value of the `getegid' system call. + + `PROCINFO["euid"]' + The value of the `geteuid' system call. + + `PROCINFO["FS"]' + This is `"FS"' if field splitting with `FS' is in effect, or + it is `"FIELDWIDTHS"' if field splitting with `FIELDWIDTHS' + is in effect. + + `PROCINFO["gid"]' + The value of the `getgid' system call. + + `PROCINFO["pgrpid"]' + The process group ID of the current process. + + `PROCINFO["pid"]' + The process ID of the current process. + + `PROCINFO["ppid"]' + The parent process ID of the current process. + + `PROCINFO["uid"]' + The value of the `getuid' system call. + + On some systems, there may be elements in the array, `"group1"' + through `"groupN"' for some N. N is the number of supplementary + groups that the process has. Use the `in' operator to test for + these elements (*note Referring to an Array Element: Reference to + Elements.). + + This array is a `gawk' extension. In other `awk' implementations, + or if `gawk' is in compatibility mode (*note Command-Line Options: + Options.), it is not special. `RLENGTH' - `RLENGTH' is the length of the substring matched by the `match' - function (*note Built-in Functions for String Manipulation: String - Functions.). `RLENGTH' is set by invoking the `match' function. - Its value is the length of the matched string, or -1 if no match - was found. + This is the length of the substring matched by the `match' function + (*note String Manipulation Functions: String Functions.). + `RLENGTH' is set by invoking the `match' function. Its value is + the length of the matched string, or -1 if no match is found. `RSTART' - `RSTART' is the start-index in characters of the substring matched - by the `match' function (*note Built-in Functions for String - Manipulation: String Functions.). `RSTART' is set by invoking the + This is the start-index in characters of the substring that is + matched by the `match' function (*note String Manipulation + Functions: String Functions.). `RSTART' is set by invoking the `match' function. Its value is the position of the string where the matched substring starts, or zero if no match was found. -`RT *' - `RT' is set each time a record is read. It contains the input text +`RT #' + This is set each time a record is read. It contains the input text that matched the text denoted by `RS', the record separator. - This variable is a `gawk' extension. In other `awk' + This variable is a `gawk' extension. In other `awk' implementations, or if `gawk' is in compatibility mode (*note - Command Line Options: Options.), it is not special. + Command-Line Options: Options.), it is not special. + +Advanced Notes: Changing `NR' and `FNR' +--------------------------------------- - A side note about `NR' and `FNR'. `awk' simply increments both of -these variables each time it reads a record, instead of setting them to -the absolute value of the number of records read. This means that your -program can change these variables, and their new values will be -incremented for each record (d.c.). For example: + `awk' increments `NR' and `FNR' each time it reads a record, instead +of setting them to the absolute value of the number of records read. +This means that a program can change these variables and their new +values are incremented for each record. (d.c.) This is demonstrated +in the following example: $ echo '1 > 2 @@ -6938,7 +7945,7 @@ incremented for each record (d.c.). For example: -| 19 Before `FNR' was added to the `awk' language (*note Major Changes -between V7 and SVR3.1: V7/SVR3.1.), many `awk' programs used this +Between V7 and SVR3.1: V7/SVR3.1.), many `awk' programs used this feature to track the number of records in a file by resetting `NR' to zero when `FILENAME' changed. @@ -6946,17 +7953,17 @@ zero when `FILENAME' changed. (1) Some early implementations of Unix `awk' initialized `FILENAME' to `"-"', even if there were data files to be processed. This behavior -was incorrect, and should not be relied upon in your programs. +was incorrect and should not be relied upon in your programs.  File: gawk.info, Node: ARGC and ARGV, Prev: Auto-set, Up: Built-in Variables Using `ARGC' and `ARGV' -======================= +----------------------- - In *Note Built-in Variables that Convey Information: Auto-set, you -saw this program describing the information contained in `ARGC' and -`ARGV': + *Note Built-in Variables That Convey Information: Auto-set, +presented the following program describing the information contained in +`ARGC' and `ARGV': $ awk 'BEGIN { > for (i = 0; i < ARGC; i++) @@ -6966,15 +7973,14 @@ saw this program describing the information contained in `ARGC' and -| inventory-shipped -| BBS-list -In this example, `ARGV[0]' contains `"awk"', `ARGV[1]' contains -`"inventory-shipped"', and `ARGV[2]' contains `"BBS-list"'. - - Notice that the `awk' program is not entered in `ARGV'. The other -special command line options, with their arguments, are also not -entered. This includes variable assignments done with the `-v' option -(*note Command Line Options: Options.). Normal variable assignments on -the command line _are_ treated as arguments, and do show up in the -`ARGV' array. +In this example, `ARGV[0]' contains `awk', `ARGV[1]' contains +`inventory-shipped', and `ARGV[2]' contains `BBS-list'. Notice that +the `awk' program is not entered in `ARGV'. The other special +command-line options, with their arguments, are also not entered. This +includes variable assignments done with the `-v' option (*note +Command-Line Options: Options.). Normal variable assignments on the +command line _are_ treated as arguments and do show up in the `ARGV' +array: $ cat showargs.awk -| BEGIN { @@ -6985,38 +7991,35 @@ the command line _are_ treated as arguments, and do show up in the -| END { printf "A=%d, B=%d\n", A, B } $ awk -v A=1 -f showargs.awk B=2 /dev/null -| A=1, B=0 - -| ARGV[0] = awk - -| ARGV[1] = B=2 - -| ARGV[2] = /dev/null + -| ARGV[0] = awk + -| ARGV[1] = B=2 + -| ARGV[2] = /dev/null -| A=1, B=2 - Your program can alter `ARGC' and the elements of `ARGV'. Each time + A program can alter `ARGC' and the elements of `ARGV'. Each time `awk' reaches the end of an input file, it uses the next element of `ARGV' as the name of the next input file. By storing a different -string there, your program can change which files are read. You can -use `"-"' to represent the standard input. By storing additional -elements and incrementing `ARGC' you can cause additional files to be -read. +string there, a program can change which files are read. Use `"-"' to +represent the standard input. Storing additional elements and +incrementing `ARGC' causes additional files to be read. - If you decrease the value of `ARGC', that eliminates input files + If the value of `ARGC' is decreased, that eliminates input files from the end of the list. By recording the old value of `ARGC' -elsewhere, your program can treat the eliminated arguments as something +elsewhere, a program can treat the eliminated arguments as something other than file names. To eliminate a file from the middle of the list, store the null string (`""') into `ARGV' in place of the file's name. As a special feature, `awk' ignores file names that have been replaced with the null -string. You may also use the `delete' statement to remove elements from -`ARGV' (*note The `delete' Statement: Delete.). - - All of these actions are typically done from the `BEGIN' rule, -before actual processing of the input begins. *Note Splitting a Large -File Into Pieces: Split Program, and see *Note Duplicating Output Into -Multiple Files: Tee Program, for an example of each way of removing -elements from `ARGV'. +string. Another option is to use the `delete' statement to remove +elements from `ARGV' (*note The `delete' Statement: Delete.). - The following fragment processes `ARGV' in order to examine, and -then remove, command line options. + All of these actions are typically done in the `BEGIN' rule, before +actual processing of the input begins. *Note Splitting a Large File +into Pieces: Split Program, and see *Note Duplicating Output into +Multiple Files: Tee Program, for examples of each way of removing +elements from `ARGV'. The following fragment processes `ARGV' in order +to examine, and then remove, command-line options: BEGIN { for (i = 1; i < ARGC; i++) { @@ -7034,36 +8037,44 @@ then remove, command line options. } } - To actually get the options into the `awk' program, you have to end -the `awk' options with `--', and then supply your options, like so: + To actually get the options into the `awk' program, end the `awk' +options with `--' and then supply the `awk' program's options, in the +following manner: awk -f myprog -- -v -d file1 file2 ... - This is not necessary in `gawk': Unless `--posix' has been + This is not necessary in `gawk'. Unless `--posix' has been specified, `gawk' silently puts any unrecognized options into `ARGV' -for the `awk' program to deal with. - - As soon as it sees an unknown option, `gawk' stops looking for other -options it might otherwise recognize. The above example with `gawk' -would be: +for the `awk' program to deal with. As soon as it sees an unknown +option, `gawk' stops looking for other options that it might otherwise +recognize. The previous example with `gawk' would be: gawk -f myprog -d -v file1 file2 ... -Since `-d' is not a valid `gawk' option, the following `-v' is passed -on to the `awk' program. +Because `-d' is not a valid `gawk' option, it and the following `-v' +are passed on to the `awk' program.  -File: gawk.info, Node: Arrays, Next: Built-in, Prev: Built-in Variables, Up: Top +File: gawk.info, Node: Arrays, Next: Functions, Prev: Patterns and Actions, Up: Top Arrays in `awk' *************** - An "array" is a table of values, called "elements". The elements of + An "array" is a table of values called "elements". The elements of an array are distinguished by their indices. "Indices" may be either -numbers or strings. `awk' maintains a single set of names that may be -used for naming variables, arrays and functions (*note User-defined -Functions: User-defined.). Thus, you cannot have a variable and an -array with the same name in the same `awk' program. +numbers or strings. + + This major node describes how arrays work in `awk', how to use array +elements, how to scan through every element in an array, and how to +remove array elements. It also describes how `awk' simulates +multidimensional arrays, as well as some of the less obvious points +about array usage. The major node finishes with a discussion of +`gawk''s facility for sorting an array based on its indices. + + `awk' maintains a single set of names that may be used for naming +variables, arrays, and functions (*note User-Defined Functions: +User-defined.). Thus, you cannot have a variable and an array with the +same name in the same `awk' program. * Menu: @@ -7079,10 +8090,10 @@ array with the same name in the same `awk' program. * Numeric Array Subscripts:: How to use numbers as subscripts in `awk'. * Uninitialized Subscripts:: Using Uninitialized variables as subscripts. -* Multi-dimensional:: Emulating multi-dimensional arrays in +* Multi-dimensional:: Emulating multidimensional arrays in `awk'. -* Multi-scanning:: Scanning multi-dimensional arrays. -* Array Efficiency:: Implementation-specific tips. +* Multi-scanning:: Scanning multidimensional arrays. +* Array Sorting:: Sorting array values and indices.  File: gawk.info, Node: Array Intro, Next: Reference to Elements, Prev: Arrays, Up: Arrays @@ -7090,74 +8101,75 @@ File: gawk.info, Node: Array Intro, Next: Reference to Elements, Prev: Arrays Introduction to Arrays ====================== - The `awk' language provides one-dimensional "arrays" for storing -groups of related strings or numbers. - - Every `awk' array must have a name. Array names have the same -syntax as variable names; any valid variable name would also be a valid -array name. But you cannot use one name in both ways (as an array and -as a variable) in one `awk' program. + The `awk' language provides one-dimensional arrays for storing +groups of related strings or numbers. Every `awk' array must have a +name. Array names have the same syntax as variable names; any valid +variable name would also be a valid array name. But one name cannot be +used in both ways (as an array and as a variable) in the same `awk' +program. Arrays in `awk' superficially resemble arrays in other programming -languages; but there are fundamental differences. In `awk', you don't -need to specify the size of an array before you start to use it. -Additionally, any number or string in `awk' may be used as an array -index, not just consecutive integers. - - In most other languages, you have to "declare" an array and specify -how many elements or components it contains. In such languages, the -declaration causes a contiguous block of memory to be allocated for that -many elements. An index in the array usually must be a positive -integer; for example, the index zero specifies the first element in the -array, which is actually stored at the beginning of the block of -memory. Index one specifies the second element, which is stored in -memory right after the first element, and so on. It is impossible to -add more elements to the array, because it has room for only as many -elements as you declared. (Some languages allow arbitrary starting and -ending indices, e.g., `15 .. 27', but the size of the array is still -fixed when the array is declared.) - - A contiguous array of four elements might look like this, -conceptually, if the element values are eight, `"foo"', `""' and 30: +languages, but there are fundamental differences. In `awk', it isn't +necessary to specify the size of an array before starting to use it. +Additionally, any number or string in `awk', not just consecutive +integers, may be used as an array index. + + In most other languages, arrays must be "declared" before use, +including a specification of how many elements or components they +contain. In such languages, the declaration causes a contiguous block +of memory to be allocated for that many elements. Usually, an index in +the array must be a positive integer. For example, the index zero +specifies the first element in the array, which is actually stored at +the beginning of the block of memory. Index one specifies the second +element, which is stored in memory right after the first element, and +so on. It is impossible to add more elements to the array, because it +has room only for as many elements as given in the declaration. (Some +languages allow arbitrary starting and ending indices--e.g., `15 .. +27'--but the size of the array is still fixed when the array is +declared.) + + A contiguous array of four elements might look like the following +example, conceptually, if the element values are 8, `"foo"', `""', and +30: +---------+---------+--------+---------+ - | 8 | "foo" | "" | 30 | value + | 8 | "foo" | "" | 30 | Value +---------+---------+--------+---------+ - 0 1 2 3 index + 0 1 2 3 Index Only the values are stored; the indices are implicit from the order of -the values. Eight is the value at index zero, because eight appears in -the position with zero elements before it. +the values. 8 is the value at index zero, because 8 appears in the +position with zero elements before it. - Arrays in `awk' are different: they are "associative". This means + Arrays in `awk' are different--they are "associative". This means that each array is a collection of pairs: an index, and its corresponding array element value: - Element 4 Value 30 - Element 2 Value "foo" - Element 1 Value 8 - Element 3 Value "" + Element 3 Value 30 + Element 1 Value "foo" + Element 0 Value 8 + Element 2 Value "" -We have shown the pairs in jumbled order because their order is -irrelevant. +The pairs are shown in jumbled order because their order is irrelevant. One advantage of associative arrays is that new pairs can be added -at any time. For example, suppose we add to the above array a tenth -element whose value is `"number ten"'. The result is this: +at any time. For example, suppose a tenth element is added to the array +whose value is `"number ten"'. The result is: Element 10 Value "number ten" - Element 4 Value 30 - Element 2 Value "foo" - Element 1 Value 8 - Element 3 Value "" + Element 3 Value 30 + Element 1 Value "foo" + Element 0 Value 8 + Element 2 Value "" -Now the array is "sparse", which just means some indices are missing: -it has elements 1-4 and 10, but doesn't have elements 5, 6, 7, 8, or 9. +Now the array is "sparse", which just means some indices are missing. +It has elements 0-3 and 10, but doesn't have elements 4, 5, 6, 7, 8, or +9. Another consequence of associative arrays is that the indices don't have to be positive integers. Any number, or even a string, can be an -index. For example, here is an array which translates words from -English into French: +index. For example, the following is an array that translates words +from English into French: Element "dog" Value "chien" Element "cat" Value "chat" @@ -7166,17 +8178,20 @@ English into French: Here we decided to translate the number one in both spelled-out and numeric form--thus illustrating that a single array can have both -numbers and strings as indices. (In fact, array subscripts are always +numbers and strings as indices. In fact, array subscripts are always strings; this is discussed in more detail in *Note Using Numbers to -Subscript Arrays: Numeric Array Subscripts.) +Subscript Arrays: Numeric Array Subscripts. Here, the number `1' isn't +double-quoted, since `awk' automatically converts it to a string. The value of `IGNORECASE' has no effect upon array subscripting. -You must use the exact same string value to retrieve an array element -as you used to store it. +The identical string value used to store an array element must be used +to retrieve it. When `awk' creates an array (e.g., with the `split' +built-in function), that array's indices are consecutive integers +starting at one. (*Note String Manipulation Functions: String +Functions.) - When `awk' creates an array for you, e.g., with the `split' built-in -function, that array's indices are consecutive integers starting at one. -(*Note Built-in Functions for String Manipulation: String Functions.) + `awk''s arrays are efficient--the time to access an element is +independent of the number of elements in the array.  File: gawk.info, Node: Reference to Elements, Next: Assigning Elements, Prev: Array Intro, Up: Arrays @@ -7184,47 +8199,44 @@ File: gawk.info, Node: Reference to Elements, Next: Assigning Elements, Prev: Referring to an Array Element ============================= - The principal way of using an array is to refer to one of its -elements. An array reference is an expression which looks like this: + The principal way to use an array is to refer to one of its elements. +An array reference is an expression as follows: ARRAY[INDEX] Here, ARRAY is the name of an array. The expression INDEX is the index -of the element of the array that you want. +of the desired element of the array. The value of the array reference is the current value of that array element. For example, `foo[4.3]' is an expression for the element of array `foo' at index `4.3'. - If you refer to an array element that has no recorded value, the -value of the reference is `""', the null string. This includes elements -to which you have not assigned any value, and elements that have been -deleted (*note The `delete' Statement: Delete.). Such a reference + A reference to an array element that has no recorded value yields a +value of `""', the null string. This includes elements that have not +been assigned any value as well as elements that have been deleted +(*note The `delete' Statement: Delete.). Such a reference automatically creates that array element, with the null string as its value. (In some cases, this is unfortunate, because it might waste memory inside `awk'.) - You can find out if an element exists in an array at a certain index -with the expression: + To determine whether an element exists in an array at a certain +index, use the following expression: INDEX in ARRAY This expression tests whether or not the particular index exists, without the side effect of creating that element if it is not present. -The expression has the value one (true) if `ARRAY[INDEX]' exists, and -zero (false) if it does not exist. - - For example, to test whether the array `frequencies' contains the -index `2', you could write this statement: +The expression has the value one (true) if `ARRAY[INDEX]' exists and +zero (false) if it does not exist. For example, this statement tests +whether the array `frequencies' contains the index `2': if (2 in frequencies) print "Subscript 2 is present." - Note that this is _not_ a test of whether or not the array -`frequencies' contains an element whose _value_ is two. (There is no -way to do that except to scan all the elements.) Also, this _does not_ -create `frequencies[2]', while the following (incorrect) alternative -would do so: + Note that this is _not_ a test of whether the array `frequencies' +contains an element whose _value_ is two. There is no way to do that +except to scan all the elements. Also, this _does not_ create +`frequencies[2]', while the following (incorrect) alternative does: if (frequencies[2] != "") print "Subscript 2 is present." @@ -7235,15 +8247,13 @@ File: gawk.info, Node: Assigning Elements, Next: Array Example, Prev: Referen Assigning Array Elements ======================== - Array elements are lvalues: they can be assigned values just like -`awk' variables: + Array elements can be assigned values just like `awk' variables: ARRAY[SUBSCRIPT] = VALUE -Here ARRAY is the name of your array. The expression SUBSCRIPT is the -index of the element of the array that you want to assign a value. The -expression VALUE is the value you are assigning to that element of the -array. +ARRAY is the name of an array. The expression SUBSCRIPT is the index +of the element of the array that is assigned a value. The expression +VALUE is the value to assign to that element of the array.  File: gawk.info, Node: Array Example, Next: Scanning an Array, Prev: Assigning Elements, Up: Arrays @@ -7253,12 +8263,12 @@ Basic Array Example The following program takes a list of lines, each beginning with a line number, and prints them out in order of line number. The line -numbers are not in order, however, when they are first read: they are +numbers are not in order when they are first read--instead they are scrambled. This program sorts the lines by making an array using the -line numbers as subscripts. It then prints out the lines in sorted -order of their numbers. It is a very simple program, and gets confused -if it encounters repeated numbers, gaps, or lines that don't begin with -a number. +line numbers as subscripts. The program then prints out the lines in +sorted order of their numbers. It is a very simple program and gets +confused upon encountering repeated numbers, gaps, or lines that don't +begin with a number: { if ($1 > max) @@ -7273,12 +8283,9 @@ a number. The first rule keeps track of the largest line number seen so far; it also stores each line into the array `arr', at an index that is the -line's number. - - The second rule runs after all the input has been read, to print out -all the lines. - - When this program is run with the following input: +line's number. The second rule runs after all the input has been read, +to print out all the lines. When this program is run with the +following input: 5 I am the Five man 2 Who are you? The new number two! @@ -7286,7 +8293,7 @@ all the lines. 1 Who is number one? 3 I three you. -its output is this: +its output is: 1 Who is number one? 2 Who are you? The new number two! @@ -7295,10 +8302,8 @@ its output is this: 5 I am the Five man If a line number is repeated, the last line with a given number -overrides the others. - - Gaps in the line numbers can be handled with an easy improvement to -the program's `END' rule: +overrides the others. Gaps in the line numbers can be handled with an +easy improvement to the program's `END' rule, as follows: END { for (x = 1; x <= max; x++) @@ -7312,36 +8317,36 @@ File: gawk.info, Node: Scanning an Array, Next: Delete, Prev: Array Example, Scanning All Elements of an Array ================================= - In programs that use arrays, you often need a loop that executes -once for each element of an array. In other languages, where arrays are -contiguous and indices are limited to positive integers, this is easy: -you can find all the valid indices by counting from the lowest index up -to the highest. This technique won't do the job in `awk', since any -number or string can be an array index. So `awk' has a special kind of -`for' statement for scanning an array: + In programs that use arrays, it is often necessary to use a loop that +executes once for each element of an array. In other languages, where +arrays are contiguous and indices are limited to positive integers, +this is easy: all the valid indices can be found by counting from the +lowest index up to the highest. This technique won't do the job in +`awk', because any number or string can be an array index. So `awk' +has a special kind of `for' statement for scanning an array: for (VAR in ARRAY) BODY -This loop executes BODY once for each index in ARRAY that your program +This loop executes BODY once for each index in ARRAY that the program has previously used, with the variable VAR set to that index. - Here is a program that uses this form of the `for' statement. The + The following program uses this form of the `for' statement. The first rule scans the input records and notes which words appear (at least once) in the input, by storing a one into the array `used' with the word as index. The second rule scans the elements of `used' to find all the distinct words that appear in the input. It prints each -word that is more than 10 characters long, and also prints the number of -such words. *Note Built-in Functions for String Manipulation: String -Functions, for more information on the built-in function `length'. +word that is more than 10 characters long and also prints the number of +such words. *Note String Manipulation Functions: String Functions, for +more information on the built-in function `length'. - # Record a 1 for each word that is used at least once. + # Record a 1 for each word that is used at least once { for (i = 1; i <= NF; i++) used[$i] = 1 } - # Find number of distinct words more than 10 characters long. + # Find number of distinct words more than 10 characters long END { for (x in used) if (length(x) > 10) { @@ -7358,7 +8363,7 @@ example of this type. statement is determined by the internal arrangement of the array elements within `awk' and cannot be controlled or changed. This can lead to problems if new elements are added to ARRAY by statements in -the loop body; you cannot predict whether or not the `for' loop will +the loop body; it is not predictable whether or not the `for' loop will reach them. Similarly, changing VAR inside the loop may produce strange results. It is best to avoid such things. @@ -7368,83 +8373,84 @@ File: gawk.info, Node: Delete, Next: Numeric Array Subscripts, Prev: Scanning The `delete' Statement ====================== - You can remove an individual element of an array using the `delete' + To remove an individual element of an array, use the `delete' statement: delete ARRAY[INDEX] - Once you have deleted an array element, you can no longer obtain any -value the element once had. It is as if you had never referred to it -and had never given it any value. - - Here is an example of deleting elements in an array: + Once an array element has been deleted, any value the element once +had is no longer available. It is as if the element had never been +referred to or had been given a value. The following is an example of +deleting elements in an array: for (i in frequencies) delete frequencies[i] This example removes all the elements from the array `frequencies'. - - If you delete an element, a subsequent `for' statement to scan the -array will not report that element, and the `in' operator to check for -the presence of that element will return zero (i.e. false): +Once an element is deleted, a subsequent `for' statement to scan the +array does not report that element and the `in' operator to check for +the presence of that element returns zero (i.e., false): delete foo[4] if (4 in foo) print "This will never be printed" It is important to note that deleting an element is _not_ the same -as assigning it a null value (the empty string, `""'). +as assigning it a null value (the empty string, `""'). For example: foo[4] = "" if (4 in foo) print "This is printed, even though foo[4] is empty" - It is not an error to delete an element that does not exist. + It is not an error to delete an element that does not exist. If +`--lint' is provided on the command line (*note Command-Line Options: +Options.), `gawk' issues a warning message when an element that is not +in the array is deleted. - You can delete all the elements of an array with a single statement, -by leaving off the subscript in the `delete' statement. + All the elements of an array may be deleted with a single statement +by leaving off the subscript in the `delete' statement, as follows: delete ARRAY This ability is a `gawk' extension; it is not available in -compatibility mode (*note Command Line Options: Options.). +compatibility mode (*note Command-Line Options: Options.). Using this version of the `delete' statement is about three times more efficient than the equivalent loop that deletes each element one at a time. - The following statement provides a portable, but non-obvious way to -clear out an array. + The following statement provides a portable but non-obvious way to +clear out an array:(1) - # thanks to Michael Brennan for pointing this out split("", array) - The `split' function (*note Built-in Functions for String -Manipulation: String Functions.) clears out the target array first. -This call asks it to split apart the null string. Since there is no -data to split out, the function simply clears the array and then -returns. + The `split' function (*note String Manipulation Functions: String +Functions.) clears out the target array first. This call asks it to +split apart the null string. Because there is no data to split out, the +function simply clears the array and then returns. *Caution:* Deleting an array does not change its type; you cannot -delete an array and then use the array's name as a scalar. For example, -this will not work: +delete an array and then use the array's name as a scalar (i.e., a +regular variable). For example, the following does not work: a[1] = 3; delete a; a = 3 + ---------- Footnotes ---------- + + (1) Thanks to Michael Brennan for pointing this out. +  File: gawk.info, Node: Numeric Array Subscripts, Next: Uninitialized Subscripts, Prev: Delete, Up: Arrays Using Numbers to Subscript Arrays ================================= - An important aspect of arrays to remember is that _array subscripts -are always strings_. If you use a numeric value as a subscript, it -will be converted to a string value before it is used for subscripting -(*note Conversion of Strings and Numbers: Conversion.). - - This means that the value of the built-in variable `CONVFMT' can -potentially affect how your program accesses elements of an array. For -example: + An important aspect about arrays to remember is that _array +subscripts are always strings_. When a numeric value is used as a +subscript, it is converted to a string value before being used for +subscripting (*note Conversion of Strings and Numbers: Conversion.). +This means that the value of the built-in variable `CONVFMT' can affect +how your program accesses elements of an array. For example: xyz = 12.153 data[xyz] = 1 @@ -7457,26 +8463,32 @@ example: This prints `12.15 is not in data'. The first statement gives `xyz' a numeric value. Assigning to `data[xyz]' subscripts `data' with the string value `"12.153"' (using the default conversion value of -`CONVFMT', `"%.6g"'), and assigns one to `data["12.153"]'. The program -then changes the value of `CONVFMT'. The test `(xyz in data)' -generates a new string value from `xyz', this time `"12.15"', since the -value of `CONVFMT' only allows two significant digits. This test fails, -since `"12.15"' is a different string from `"12.153"'. +`CONVFMT', `"%.6g"'). Thus, the array element `data["12.153"]' is +assigned the value one. The program then changes the value of +`CONVFMT'. The test `(xyz in data)' generates a new string value from +`xyz'--this time `"12.15"'--because the value of `CONVFMT' only allows +two significant digits. This test fails, since `"12.15"' is a +different string from `"12.153"'. According to the rules for conversions (*note Conversion of Strings and Numbers: Conversion.), integer values are always converted to strings as integers, no matter what the value of `CONVFMT' may happen -to be. So the usual case of: +to be. So the usual case of the following works: for (i = 1; i <= maxsub; i++) do something with array[i] -will work, no matter what the value of `CONVFMT'. + The "integer values always convert to strings as integers" rule has +an additional consequence for array indexing. Octal and hexadecimal +constants (*note Octal and Hexadecimal Numbers: Non-decimal-numbers.) +are converted internally into numbers and their original form is +forgotten. This means, for example, that `array[17]', `array[021]', and +`array[0x11]' all refer to the same element! - Like many things in `awk', the majority of the time things work as -you would expect them to work. But it is useful to have a precise -knowledge of the actual rules, since sometimes they can have a subtle -effect on your programs. + As with many things in `awk', the majority of the time things work +as one would expect them to. But it is useful to have a precise +knowledge of the actual rules which sometimes can have a subtle effect +on your programs.  File: gawk.info, Node: Uninitialized Subscripts, Next: Multi-dimensional, Prev: Numeric Array Subscripts, Up: Arrays @@ -7484,9 +8496,9 @@ File: gawk.info, Node: Uninitialized Subscripts, Next: Multi-dimensional, Pre Using Uninitialized Variables as Subscripts =========================================== - Suppose you want to print your input data in reverse order. A -reasonable attempt at a program to do so (with some test data) might -look like this: + Suppose it's necessary to write a program to print the input data in +reverse order. A reasonable attempt to do so (with some test data) +might look like this: $ echo 'line 1 > line 2 @@ -7505,11 +8517,10 @@ the output! `lines' is uninitialized, and uninitialized variables have the numeric value zero. So, `awk' should have printed the value of `l[0]'. - The issue here is that subscripts for `awk' arrays are *always* -strings. And uninitialized variables, when used as strings, have the -value `""', not zero. Thus, `line 1' ended up stored in `l[""]'. - - The following version of the program works correctly: + The issue here is that subscripts for `awk' arrays are _always_ +strings. Uninitialized variables, when used as strings, have the value +`""', not zero. Thus, `line 1' ends up stored in `l[""]'. The +following version of the program works correctly: { l[lines++] = $0 } END { @@ -7518,37 +8529,37 @@ value `""', not zero. Thus, `line 1' ended up stored in `l[""]'. } Here, the `++' forces `lines' to be numeric, thus making the "old -value" numeric zero, which is then converted to `"0"' as the array +value" numeric zero. This is then converted to `"0"' as the array subscript. - As we have just seen, even though it is somewhat unusual, the null -string (`""') is a valid array subscript (d.c.). If `--lint' is provided -on the command line (*note Command Line Options: Options.), `gawk' will -warn about the use of the null string as a subscript. + Even though it is somewhat unusual, the null string (`""') is a +valid array subscript. (d.c.) `gawk' warns about the use of the null +string as a subscript if `--lint' is provided on the command line +(*note Command-Line Options: Options.).  File: gawk.info, Node: Multi-dimensional, Next: Multi-scanning, Prev: Uninitialized Subscripts, Up: Arrays -Multi-dimensional Arrays -======================== +Multidimensional Arrays +======================= - A multi-dimensional array is an array in which an element is -identified by a sequence of indices, instead of a single index. For + A multidimensional array is an array in which an element is +identified by a sequence of indices instead of a single index. For example, a two-dimensional array requires two indices. The usual way (in most languages, including `awk') to refer to an element of a two-dimensional array named `grid' is with `grid[X,Y]'. - Multi-dimensional arrays are supported in `awk' through -concatenation of indices into one string. What happens is that `awk' -converts the indices into strings (*note Conversion of Strings and -Numbers: Conversion.) and concatenates them together, with a separator -between them. This creates a single string that describes the values -of the separate indices. The combined string is used as a single index -into an ordinary, one-dimensional array. The separator used is the -value of the built-in variable `SUBSEP'. + Multidimensional arrays are supported in `awk' through concatenation +of indices into one string. `awk' converts the indices into strings +(*note Conversion of Strings and Numbers: Conversion.) and concatenates +them together, with a separator between them. This creates a single +string that describes the values of the separate indices. The combined +string is used as a single index into an ordinary, one-dimensional +array. The separator used is the value of the built-in variable +`SUBSEP'. For example, suppose we evaluate the expression `foo[5,12] = "value"' -when the value of `SUBSEP' is `"@"'. The numbers five and 12 are +when the value of `SUBSEP' is `"@"'. The numbers 5 and 12 are converted to strings and concatenated with an `@' between them, yielding `"5@12"'; thus, the array element `foo["5@12"]' is set to `"value"'. @@ -7559,19 +8570,17 @@ expressions `foo[5,12]' and `foo[5 SUBSEP 12]' are always equivalent. The default value of `SUBSEP' is the string `"\034"', which contains a non-printing character that is unlikely to appear in an `awk' program -or in most input data. - - The usefulness of choosing an unlikely character comes from the fact -that index values that contain a string matching `SUBSEP' lead to -combined strings that are ambiguous. Suppose that `SUBSEP' were `"@"'; -then `foo["a@b", "c"]' and `foo["a", "b@c"]' would be indistinguishable -because both would actually be stored as `foo["a@b@c"]'. - - You can test whether a particular index-sequence exists in a -"multi-dimensional" array with the same operator `in' used for single -dimensional arrays. Instead of a single index as the left-hand operand, -write the whole sequence of indices, separated by commas, in -parentheses: +or in most input data. The usefulness of choosing an unlikely +character comes from the fact that index values that contain a string +matching `SUBSEP' can lead to combined strings that are ambiguous. +Suppose that `SUBSEP' is `"@"'; then `foo["a@b", "c"]' and +`foo["a", "b@c"]' are indistinguishable because both are actually +stored as `foo["a@b@c"]'. + + To test whether a particular index sequence exists in a +"multidimensional" array, use the same operator (`in') that is used for +single dimensional arrays. Write the whole sequence of indices in +parentheses, separated by commas, as the left operand: (SUBSCRIPT1, SUBSCRIPT2, ...) in ARRAY @@ -7579,7 +8588,7 @@ parentheses: fields; it rotates this array 90 degrees clockwise and prints the result. It assumes that all lines have the same number of elements. - awk '{ + { if (max_nf < NF) max_nf = NF max_nr = NR @@ -7593,7 +8602,7 @@ result. It assumes that all lines have the same number of elements. printf("%s ", vector[x, y]) printf("\n") } - }' + } When given the input: @@ -7602,7 +8611,7 @@ When given the input: 3 4 5 6 1 2 4 5 6 1 2 3 -it produces: +the program produces the following output: 4 3 2 1 5 4 3 2 @@ -7612,85 +8621,146 @@ it produces: 3 2 1 6  -File: gawk.info, Node: Multi-scanning, Next: Array Efficiency, Prev: Multi-dimensional, Up: Arrays +File: gawk.info, Node: Multi-scanning, Next: Array Sorting, Prev: Multi-dimensional, Up: Arrays -Scanning Multi-dimensional Arrays -================================= +Scanning Multidimensional Arrays +================================ There is no special `for' statement for scanning a -"multi-dimensional" array; there cannot be one, because in truth there -are no multi-dimensional arrays or elements; there is only a -multi-dimensional _way of accessing_ an array. +"multidimensional" array. There cannot be one, because in truth there +are no multidimensional arrays or elements--there is only a +multidimensional _way of accessing_ an array. However, if your program has an array that is always accessed as -multi-dimensional, you can get the effect of scanning it by combining +multidimensional, you can get the effect of scanning it by combining the scanning `for' statement (*note Scanning All Elements of an Array: -Scanning an Array.) with the `split' built-in function (*note Built-in -Functions for String Manipulation: String Functions.). It works like -this: +Scanning an Array.) with the built-in `split' function (*note String +Manipulation Functions: String Functions.). It works in the following +manner: for (combined in array) { - split(combined, separate, SUBSEP) - ... + split(combined, separate, SUBSEP) + ... } -This sets `combined' to each concatenated, combined index in the array, -and splits it into the individual indices by breaking it apart where -the value of `SUBSEP' appears. The split-out indices become the -elements of the array `separate'. +This sets the variable `combined' to each concatenated combined index +in the array, and splits it into the individual indices by breaking it +apart where the value of `SUBSEP' appears. The individual indices then +become the elements of the array `separate'. - Thus, suppose you have previously stored a value in `array[1, -"foo"]'; then an element with index `"1\034foo"' exists in `array'. -(Recall that the default value of `SUBSEP' is the character with code -034.) Sooner or later the `for' statement will find that index and do -an iteration with `combined' set to `"1\034foo"'. Then the `split' -function is called as follows: + Thus, if a value is previously stored in `array[1, "foo"]'; then an +element with index `"1\034foo"' exists in `array'. (Recall that the +default value of `SUBSEP' is the character with code 034.) Sooner or +later, the `for' statement finds that index and does an iteration with +the variable `combined' set to `"1\034foo"'. Then the `split' function +is called as follows: split("1\034foo", separate, "\034") -The result of this is to set `separate[1]' to `"1"' and `separate[2]' -to `"foo"'. Presto, the original sequence of separate indices has been +The result is to set `separate[1]' to `"1"' and `separate[2]' to +`"foo"'. Presto! The original sequence of separate indices is recovered.  -File: gawk.info, Node: Array Efficiency, Prev: Multi-scanning, Up: Arrays +File: gawk.info, Node: Array Sorting, Prev: Multi-scanning, Up: Arrays -Using Array Memory Efficiently -============================== +Sorting Array Values and Indices with `gawk' +============================================ - This section applies just to `gawk'. + The order in which an array is scanned with a `for (i in array)' +loop is essentially arbitrary. In most `awk' implementations, sorting +an array requires writing a `sort' function. While this can be +educational for exploring different sorting algorithms, usually that's +not the point of the program. `gawk' provides the built-in `asort' +function (*note String Manipulation Functions: String Functions.) that +sorts an array. For example: + + POPULATE THE ARRAY data + n = asort(data) + for (i = 1; i <= n; i++) + DO SOMETHING WITH data[i] + + After the call to `asort', the array `data' is indexed from 1 to +some number N, the total number of elements in `data'. (This count is +`asort''s return value.) `data[1]' <= `data[2]' <= `data[3]', and so +on. The comparison of array elements is done using `gawk''s usual +comparison rules (*note Variable Typing and Comparison Expressions: +Typing and Comparison.). + + An important side effect of calling `asort' is that _the array's +original indices are irrevocably lost_. As this isn't always +desirable, `asort' accepts a second argument: + + POPULATE THE ARRAY source + n = asort(source, dest) + for (i = 1; i <= n; i++) + DO SOMETHING WITH dest[i] + + In this case, `gawk' copies the `source' array into the `dest' array +and then sorts `dest', destroying its indices. However, the `source' +array is not affected. + + Often, what's needed is to sort on the values of the _indices_ +instead of the values of the elements. To do this, use a helper array +to hold the sorted index values, and then access the original array's +elements. It works in the following way: + + POPULATE THE ARRAY data + # copy indices + j = 1 + for (i in data) { + ind[j] = i # index value becomes element value + j++ + } + n = asort(ind) # index values are now sorted + for (i = 1; i <= n; i++) + DO SOMETHING WITH data[ind[i]] - It is often useful to use the same bit of data as an index into -multiple arrays. Due to the way `gawk' implements associative arrays, -when you need to use input data as an index for multiple arrays, it is -much more effecient to assign the input field to a separate variable, -and then use that variable as the index. + Sorting the array by replacing the indices provides maximal +flexibility. To traverse the elements in decreasing order, use a loop +that goes from N down to 1, either over the elements or over the +indices. - { - name = $1 - ssn = $2 - nkids = $3 - ... - seniority[name]++ # better than seniority[$1]++ - kids[name] = nkids # better than kids[$1] = nkids - } + Copying array indices and elements isn't expensive in terms of +memory. Internally, `gawk' maintains "reference counts" to data. For +example, when `asort' copies the first array to the second one, there +is only one copy of the original array elements' data, even though both +arrays use the values. Similarly, when copying the indices from `data' +to `ind', there is only one copy of the actual index strings. + + As with array subscripts, the value of `IGNORECASE' does not affect +array sorting. + + +File: gawk.info, Node: Functions, Next: Internationalization, Prev: Arrays, Up: Top + +Functions +********* + + This major node describes `awk''s built-in functions, which fall +into three categories: numeric, string, and I/O. `gawk' provides +additional groups of functions to work with values that represent time, +do bit manipulation, and to internationalize and localize programs. - Using separate variables with mnemonic names for the input fields -makes programs more readable, in any case. It is an eventual goal to -make `gawk''s array indexing as efficient as possible, no matter what -the source of the index value. + Besides the built-in functions, `awk' has provisions for writing new +functions that the rest of a program can use. The second half of this +major node describes these "user-defined" functions. + +* Menu: + +* Built-in:: Summarizes the built-in functions. +* User-defined:: Describes User-defined functions in detail.  -File: gawk.info, Node: Built-in, Next: User-defined, Prev: Arrays, Up: Top +File: gawk.info, Node: Built-in, Next: User-defined, Prev: Functions, Up: Functions Built-in Functions -****************** +================== - "Built-in" functions are functions that are always available for -your `awk' program to call. This chapter defines all the built-in -functions in `awk'; some of them are mentioned in other sections, but -they are summarized here for your convenience. (You can also define -new functions yourself. *Note User-defined Functions: User-defined.) + "Built-in" functions are always available for your `awk' program to +call. This minor node defines all the built-in functions in `awk'; +some of these are mentioned in other sections but are summarized here +for your convenience. * Menu: @@ -7698,26 +8768,27 @@ new functions yourself. *Note User-defined Functions: User-defined.) * Numeric Functions:: Functions that work with numbers, including `int', `sin' and `rand'. * String Functions:: Functions for string manipulation, such as - `split', `match', and - `sprintf'. + `split', `match' and `sprintf'. * I/O Functions:: Functions for files and shell commands. -* Time Functions:: Functions for dealing with time stamps. +* Time Functions:: Functions for dealing with timestamps. +* Bitwise Functions:: Functions for bitwise operations. +* I18N Functions:: Functions for string translation.  File: gawk.info, Node: Calling Built-in, Next: Numeric Functions, Prev: Built-in, Up: Built-in Calling Built-in Functions -========================== +-------------------------- - To call a built-in function, write the name of the function followed -by arguments in parentheses. For example, `atan2(y + z, 1)' is a call -to the function `atan2', with two arguments. + To call one of `awk''s built-in functions, write the name of the +function followed by arguments in parentheses. For example, `atan2(y + +z, 1)' is a call to the function `atan2', and has two arguments. Whitespace is ignored between the built-in function name and the -open-parenthesis, but we recommend that you avoid using whitespace +open parenthesis, and it is good practice to avoid using whitespace there. User-defined functions do not permit whitespace in this way, and -you will find it easier to avoid mistakes by following a simple -convention which always works: no whitespace after a function name. +it is easier to avoid mistakes by following a simple convention that +always works--no whitespace after a function name. Each built-in function accepts a certain number of arguments. In some cases, arguments can be omitted. The defaults for omitted @@ -7727,88 +8798,86 @@ given to built-in functions are ignored. However, in `gawk', it is a fatal error to give extra arguments to a built-in function. When a function is called, expressions that create the function's -actual parameters are evaluated completely before the function call is -performed. For example, in the code fragment: +actual parameters are evaluated completely before the call is performed. +For example, in the following code fragment: i = 4 j = sqrt(i++) -the variable `i' is set to five before `sqrt' is called with a value of -four for its actual parameter. - - The order of evaluation of the expressions used for the function's -parameters is undefined. Thus, you should not write programs that -assume that parameters are evaluated from left to right or from right -to left. For example, +the variable `i' is incremented to the value five before `sqrt' is +called with a value of four for its actual parameter. The order of +evaluation of the expressions used for the function's parameters is +undefined. Thus, avoid writing programs that assume that parameters +are evaluated from left to right or from right to left. For example: i = 5 j = atan2(i++, i *= 2) If the order of evaluation is left to right, then `i' first becomes -six, and then 12, and `atan2' is called with the two arguments six and +six, and then 12, and `atan2' is called with the two arguments 6 and 12. But if the order of evaluation is right to left, `i' first becomes -10, and then 11, and `atan2' is called with the two arguments 11 and 10. +10, then 11, and `atan2' is called with the two arguments 11 and 10.  File: gawk.info, Node: Numeric Functions, Next: String Functions, Prev: Calling Built-in, Up: Built-in -Numeric Built-in Functions -========================== +Numeric Functions +----------------- - Here is a full list of built-in functions that work with numbers. -Optional parameters are enclosed in square brackets ("[" and "]"). + The following list describes all of the built-in functions that work +with numbers. Optional parameters are enclosed in square brackets ([ +and ]): `int(X)' - This produces the nearest integer to X, located between X and zero, - truncated toward zero. + This returns the nearest integer to X, located between X and zero + and truncated toward zero. For example, `int(3)' is three, `int(3.9)' is three, `int(-3.9)' is -3, and `int(-3)' is -3 as well. `sqrt(X)' - This gives you the positive square root of X. It reports an error - if X is negative. Thus, `sqrt(4)' is two. + This returns the positive square root of X. `gawk' reports an + error if X is negative. Thus, `sqrt(4)' is two. `exp(X)' - This gives you the exponential of X (`e ^ X'), or reports an error - if X is out of range. The range of values X can have depends on - your machine's floating point representation. + This returns the exponential of X (`e ^ X') or reports an error if + X is out of range. The range of values X can have depends on your + machine's floating-point representation. `log(X)' - This gives you the natural logarithm of X, if X is positive; + This returns the natural logarithm of X, if X is positive; otherwise, it reports an error. `sin(X)' - This gives you the sine of X, with X in radians. + This returns the sine of X, with X in radians. `cos(X)' - This gives you the cosine of X, with X in radians. + This returns the cosine of X, with X in radians. `atan2(Y, X)' - This gives you the arctangent of `Y / X' in radians. + This returns the arctangent of `Y / X' in radians. `rand()' - This gives you a random number. The values of `rand' are - uniformly-distributed between zero and one. The value is never - zero and never one. + This returns a random number. The values of `rand' are uniformly + distributed between zero and one. The value is never zero and + never one.(1) - Often you want random integers instead. Here is a user-defined - function you can use to obtain a random non-negative integer less - than N: + Often random integers are needed instead. Following is a + user-defined function that can be used to obtain a random + non-negative integer less than N: function randint(n) { return int(n * rand()) } The multiplication produces a random number greater than zero and - less than `n'. We then make it an integer (using `int') between - zero and `n' - 1, inclusive. + less than `n'. Using `int', this result is made into an integer + between zero and `n' - 1, inclusive. - Here is an example where a similar function is used to produce - random integers between one and N. This program prints a new - random number for each input record. + The following example uses a similar function to produce random + integers between one and N. This program prints a new random + number for each input record. - awk ' # Function to roll a simulated die. function roll(n) { return 1 + int(rand() * n) } @@ -7817,37 +8886,47 @@ Optional parameters are enclosed in square brackets ("[" and "]"). { printf("%d points\n", roll(6)+roll(6)+roll(6)) - }' + } *Caution:* In most `awk' implementations, including `gawk', `rand' starts generating numbers from the same starting number, or - "seed", each time you run `awk'. Thus, a program will generate - the same results each time you run it. The numbers are random - within one `awk' run, but predictable from run to run. This is - convenient for debugging, but if you want a program to do - different things each time it is used, you must change the seed to - a value that will be different in each run. To do this, use - `srand'. + "seed", each time you run `awk'. Thus, a program generates the + same results each time you run it. The numbers are random within + one `awk' run but predictable from run to run. This is convenient + for debugging, but if you want a program to do different things + each time it is used, you must change the seed to a value that is + different in each run. To do this, use `srand'. `srand([X])' The function `srand' sets the starting point, or seed, for generating random numbers to the value X. Each seed value leads to a particular sequence of random - numbers.(1) Thus, if you set the seed to the same value a second - time, you will get the same sequence of random numbers again. + numbers.(2) Thus, if the seed is set to the same value a second + time, the same sequence of random numbers is produced again. + + Different `awk' implementations use different random number + generators internally. Don't expect the same `awk' program to + produce the same series of random numbers when executed by + different versions of `awk'. - If you omit the argument X, as in `srand()', then the current date - and time of day are used for a seed. This is the way to get random - numbers that are truly unpredictable. + If the argument X is omitted, as in `srand()', then the current + date and time of day are used for a seed. This is the way to get + random numbers that are truly unpredictable. The return value of `srand' is the previous seed. This makes it - easy to keep track of the seeds for use in consistently reproducing - sequences of random numbers. + easy to keep track of the seeds in case you need to consistently + reproduce sequences of random numbers. ---------- Footnotes ---------- - (1) Computer generated random numbers really are not truly random. + (1) The C version of `rand' is known to produce fairly poor +sequences of random numbers. However, nothing requires that an `awk' +implementation use the C `rand' to implement the `awk' version of +`rand'. In fact, `gawk' uses the BSD `random' function, which is +considerably better than `rand', to produce random numbers. + + (2) Computer generated random numbers really are not truly random. They are technically known as "pseudo-random." This means that while the numbers in a sequence appear to be random, you can in fact generate the same sequence of random numbers over and over again. @@ -7855,17 +8934,53 @@ the same sequence of random numbers over and over again.  File: gawk.info, Node: String Functions, Next: I/O Functions, Prev: Numeric Functions, Up: Built-in -Built-in Functions for String Manipulation -========================================== +String Manipulation Functions +----------------------------- + + The functions in this minor node look at or change the text of one +or more strings. Optional parameters are enclosed in square brackets +([ and ]). Those functions that are specific to `gawk' are marked with +a pound sign (`#'): + +* Menu: + +* Gory Details:: More than you want to know about `\' and + `&' with `sub', `gsub', and + `gensub'. + +`asort(SOURCE [, DEST]) #' + `asort' is a `gawk'-specific extension, returning the number of + elements in the array SOURCE. The contents of SOURCE are sorted + using `gawk''s normal rules for comparing values, and the indices + of the sorted values of SOURCE are replaced with sequential + integers starting with one. If the optional array DEST is + specified, then SOURCE is duplicated into DEST. DEST is then + sorted, leaving the indices of SOURCE unchanged. For example, if + the contents of `a' are as follows: + + a["last"] = "de" + a["first"] = "sac" + a["middle"] = "cul" + + A call to `asort': + + asort(a) + + results in the following contents of `a': + + a[1] = "cul" + a[2] = "de" + a[3] = "sac" - The functions in this section look at or change the text of one or -more strings. Optional parameters are enclosed in square brackets ("[" -and "]"). + The `asort' function is described in more detail in *Note Sorting + Array Values and Indices with `gawk': Array Sorting. `asort' is a + `gawk' extension; it is not available in compatibility mode (*note + Command-Line Options: Options.). `index(IN, FIND)' This searches the string IN for the first occurrence of the string FIND, and returns the position in characters where that occurrence - begins in the string IN. For example: + begins in the string IN. Consider the following example: $ awk 'BEGIN { print index("peanut", "an") }' -| 3 @@ -7874,29 +8989,33 @@ and "]"). indices in `awk' start at one.) `length([STRING])' - This gives you the number of characters in STRING. If STRING is a + This returns the number of characters in STRING. If STRING is a number, the length of the digit string representing that number is - returned. For example, `length("abcde")' is five. By contrast, - `length(15 * 35)' works out to three. How? Well, 15 * 35 = 525, + returned. For example, `length("abcde")' is 5. By contrast, + `length(15 * 35)' works out to 3. In this example, 15 * 35 = 525, and 525 is then converted to the string `"525"', which has three characters. If no argument is supplied, `length' returns the length of `$0'. - In older versions of `awk', you could call the `length' function - without any parentheses. Doing so is marked as "deprecated" in the - POSIX standard. This means that while you can do this in your - programs, it is a feature that can eventually be removed from a - future version of the standard. Therefore, for maximal - portability of your `awk' programs, you should always supply the - parentheses. - -`match(STRING, REGEXP)' - The `match' function searches the string, STRING, for the longest, - leftmost substring matched by the regular expression, REGEXP. It - returns the character position, or "index", of where that - substring begins (one, if it starts at the beginning of STRING). - If no match is found, it returns zero. + *Note:* In older versions of `awk', the `length' function could be + called without any parentheses. Doing so is marked as + "deprecated" in the POSIX standard. This means that while a + program can do this, it is a feature that can eventually be + removed from a future version of the standard. Therefore, for + programs to be maximally portable, always supply the parentheses. + +`match(STRING, REGEXP [, ARRAY])' + The `match' function searches STRING for the longest leftmost + substring matched by the regular expression, REGEXP. It returns + the character position, or "index", where that substring begins + (one, if it starts at the beginning of STRING). If no match is + found, it returns zero. + + The order of the first two arguments is backwards from most other + string functions that work with regular expressions, such as `sub' + and `gsub'. It might help to remember that for `match', the order + is the same as for the `~' operator: `STRING ~ REGEXP'. The `match' function sets the built-in variable `RSTART' to the index. It also sets the built-in variable `RLENGTH' to the length @@ -7905,21 +9024,21 @@ and "]"). For example: - awk '{ + { if ($1 == "FIND") regex = $2 else { where = match($0, regex) if (where != 0) - print "Match of", regex, "found at", \ + print "Match of", regex, "found at", where, "in", $0 } - }' + } This program looks for lines that match the regular expression stored in the variable `regex'. This regular expression can be changed. If the first word on a line is `FIND', `regex' is - changed to be the second word on that line. Therefore, given: + changed to be the second word on that line. Therefore, if given: FIND ru+n My program runs @@ -7934,14 +9053,31 @@ and "]"). Match of ru+n found at 12 in My program runs Match of Melvin found at 1 in Melvin was here. + If ARRAY is present, it is cleared, and then the 0'th element of + ARRAY is set to the entire portion of STRING matched by REGEXP. + If REGEXP contains parentheses, the integer-indexed elements of + ARRAY are set to contain the portion of STRING matching the + corresponding parenthesized sub-expression. For example: + + $ echo foooobazbarrrrr | + > gawk '{ match($0, /(fo+).+(ba*r)/, arr) + > print arr[1], arr[2] }' + -| foooo barrrrr + + The ARRAY argument to `match' is a `gawk' extension. In + compatibility mode (*note Command-Line Options: Options.), using a + third argument is a fatal error. + `split(STRING, ARRAY [, FIELDSEP])' - This divides STRING into pieces separated by FIELDSEP, and stores - the pieces in ARRAY. The first piece is stored in `ARRAY[1]', the - second piece in `ARRAY[2]', and so forth. The string value of the - third argument, FIELDSEP, is a regexp describing where to split - STRING (much as `FS' can be a regexp describing where to split - input records). If the FIELDSEP is omitted, the value of `FS' is - used. `split' returns the number of elements created. + This function divides STRING into pieces separated by FIELDSEP, + and stores the pieces in ARRAY. The first piece is stored in + `ARRAY[1]', the second piece in `ARRAY[2]', and so forth. The + string value of the third argument, FIELDSEP, is a regexp + describing where to split STRING (much as `FS' can be a regexp + describing where to split input records). If the FIELDSEP is + omitted, the value of `FS' is used. `split' returns the number of + elements created. If STRING does not match FIELDSEP, ARRAY is + empty and `split' returns zero. The `split' function splits strings into pieces in a manner similar to the way input lines are split into fields. For example: @@ -7958,53 +9094,65 @@ and "]"). The value returned by this call to `split' is three. As with input field-splitting, when the value of FIELDSEP is - `" "', leading and trailing whitespace is ignored, and the elements - are separated by runs of whitespace. - - Also as with input field-splitting, if FIELDSEP is the null - string, each individual character in the string is split into its - own array element. (This is a `gawk'-specific extension.) + `" "', leading and trailing whitespace is ignored and the elements + are separated by runs of whitespace. Also as with input + field-splitting, if FIELDSEP is the null string, each individual + character in the string is split into its own array element. + (This is a `gawk'-specific extension.) - Recent implementations of `awk', including `gawk', allow the third - argument to be a regexp constant (`/abc/'), as well as a string - (d.c.). The POSIX standard allows this as well. + Modern implementations of `awk', including `gawk', allow the third + argument to be a regexp constant (`/abc/') as well as a string. + (d.c.) The POSIX standard allows this as well. Before splitting the string, `split' deletes any previously - existing elements in the array ARRAY (d.c.). + existing elements in the array ARRAY. If STRING does not match + FIELDSEP at all, ARRAY has one element only. The value of that + element is the original STRING. - If STRING does not match FIELDSEP at all, ARRAY will have one - element. The value of that element will be the original STRING. - -`sprintf(FORMAT, EXPRESSION1,...)' +`sprintf(FORMAT, EXPRESSION1, ...)' This returns (without printing) the string that `printf' would have printed out with the same arguments (*note Using `printf' Statements for Fancier Printing: Printf.). For example: - sprintf("pi = %.2f (approx.)", 22/7) + pival = sprintf("pi = %.2f (approx.)", 22/7) + + assigns the string `"pi = 3.14 (approx.)"' to the variable `pival'. + +`strtonum(STR) #' + Examines STR and returns its numeric value. If STR begins with a + leading `0', `strtonum' assumes that STR is an octal number. If + STR begins with a leading `0x' or `0X', `strtonum' assumes that + STR is a hexadecimal number. For example: + + $ echo 0x11 | + > gawk '{ printf "%d\n", strtonum($1) }' + -| 17 - returns the string `"pi = 3.14 (approx.)"'. + Using the `strtonum' function is _not_ the same as adding zero to + a string value; the automatic coercion of strings to numbers works + only for decimal data, not for octal or hexadecimal.(1) + + `strtonum' is a `gawk' extension; it is not available in + compatibility mode (*note Command-Line Options: Options.). `sub(REGEXP, REPLACEMENT [, TARGET])' The `sub' function alters the value of TARGET. It searches this value, which is treated as a string, for the leftmost longest - substring matched by the regular expression, REGEXP, extending - this match as far as possible. Then the entire string is changed - by replacing the matched text with REPLACEMENT. The modified - string becomes the new value of TARGET. + substring matched by the regular expression REGEXP. Then the + entire string is changed by replacing the matched text with + REPLACEMENT. The modified string becomes the new value of TARGET. This function is peculiar because TARGET is not simply used to - compute a value, and not just any expression will do: it must be a - variable, field or array element, so that `sub' can store a + compute a value, and not just any expression will do--it must be a + variable, field, or array element so that `sub' can store a modified value there. If this argument is omitted, then the - default is to use and alter `$0'. - - For example: + default is to use and alter `$0'. For example: str = "water, water, everywhere" sub(/at/, "ith", str) sets `str' to `"wither, water, everywhere"', by replacing the - leftmost, longest occurrence of `at' with `ith'. + leftmost longest occurrence of `at' with `ith'. The `sub' function returns the number of substitutions made (either one or zero). @@ -8014,21 +9162,19 @@ and "]"). can match more than one string, then this precise substring may vary.) For example: - awk '{ sub(/candidate/, "& and his wife"); print }' + { sub(/candidate/, "& and his wife"); print } changes the first occurrence of `candidate' to `candidate and his - wife' on each input line. - - Here is another example: + wife' on each input line. Here is another example: - awk 'BEGIN { - str = "daabaaa" - sub(/a+/, "C&C", str) - print str - }' + $ awk 'BEGIN { + > str = "daabaaa" + > sub(/a+/, "C&C", str) + > print str + > }' -| dCaaCbaaa - This shows how `&' can represent a non-constant string, and also + This shows how `&' can represent a non-constant string and also illustrates the "leftmost, longest" rule in regexp matching (*note How Much Text Matches?: Leftmost Longest.). @@ -8036,28 +9182,28 @@ and "]"). putting a backslash before it in the string. As usual, to insert one backslash in the string, you must write two backslashes. Therefore, write `\\&' in a string constant to include a literal - `&' in the replacement. For example, here is how to replace the - first `|' on each line with an `&': + `&' in the replacement. For example, following is shown how to + replace the first `|' on each line with an `&': - awk '{ sub(/\|/, "\\&"); print }' + { sub(/\|/, "\\&"); print } - *Note:* As mentioned above, the third argument to `sub' must be a - variable, field or array reference. Some versions of `awk' allow - the third argument to be an expression which is not an lvalue. In - such a case, `sub' would still search for the pattern and return - zero or one, but the result of the substitution (if any) would be - thrown away because there is no place to put it. Such versions of - `awk' accept expressions like this: + As mentioned, the third argument to `sub' must be a variable, + field or array reference. Some versions of `awk' allow the third + argument to be an expression that is not an lvalue. In such a + case, `sub' still searches for the pattern and returns zero or + one, but the result of the substitution (if any) is thrown away + because there is no place to put it. Such versions of `awk' + accept expressions such as the following: sub(/USA/, "United States", "the USA and Canada") - For historical compatibility, `gawk' will accept erroneous code, - such as in the above example. However, using any other - non-changeable object as the third parameter will cause a fatal - error, and your program will not run. + For historical compatibility, `gawk' accepts erroneous code, such + as in the previous example. However, using any other non-changeable + object as the third parameter causes a fatal error and your program + will not run. Finally, if the REGEXP is not a regexp constant, it is converted - into a string and then the value of that string is treated as the + into a string, and then the value of that string is treated as the regexp to match. `gsub(REGEXP, REPLACEMENT [, TARGET])' @@ -8066,34 +9212,32 @@ and "]"). substrings it can find. The `g' in `gsub' stands for "global," which means replace everywhere. For example: - awk '{ gsub(/Britain/, "United Kingdom"); print }' + { gsub(/Britain/, "United Kingdom"); print } replaces all occurrences of the string `Britain' with `United Kingdom' for all input records. The `gsub' function returns the number of substitutions made. If - the variable to be searched and altered, TARGET, is omitted, then - the entire input record, `$0', is used. + the variable to search and alter (TARGET) is omitted, then the + entire input record (`$0') is used. As in `sub', the characters + `&' and `\' are special, and the third argument must be assignable. - As in `sub', the characters `&' and `\' are special, and the third - argument must be an lvalue. - -`gensub(REGEXP, REPLACEMENT, HOW [, TARGET])' +`gensub(REGEXP, REPLACEMENT, HOW [, TARGET]) #' `gensub' is a general substitution function. Like `sub' and `gsub', it searches the target string TARGET for matches of the regular expression REGEXP. Unlike `sub' and `gsub', the modified - string is returned as the result of the function, and the original + string is returned as the result of the function and the original target string is _not_ changed. If HOW is a string beginning with `g' or `G', then it replaces all matches of REGEXP with - REPLACEMENT. Otherwise, HOW is a number indicating which match of - REGEXP to replace. If no TARGET is supplied, `$0' is used instead. + REPLACEMENT. Otherwise, HOW is treated as a number that indicates + which match of REGEXP to replace. If no TARGET is supplied, `$0' + is used. `gensub' provides an additional feature that is not available in `sub' or `gsub': the ability to specify components of a regexp in the replacement text. This is done by using parentheses in the - regexp to mark the components, and then specifying `\N' in the - replacement text, where N is a digit from one to nine. For - example: + regexp to mark the components and then specifying `\N' in the + replacement text, where N is a digit from 1 to 9. For example: $ gawk ' > BEGIN { @@ -8103,14 +9247,14 @@ and "]"). > }' -| def abc - As described above for `sub', you must type two backslashes in - order to get one into the string. + As with `sub', you must type two backslashes in order to get one + into the string. In the replacement text, the sequence `\0' represents the entire matched text, as does the character `&'. - This example shows how you can use the third argument to control - which match of the regexp should be changed. + The following example shows how you can use the third argument to + control which match of the regexp should be changed: $ echo a b c a b c | > gawk '{ print gensub(/a/, "AA", 2) }' @@ -8121,19 +9265,20 @@ and "]"). `print' for printing. If the HOW argument is a string that does not begin with `g' or - `G', or if it is a number that is less than zero, only one - substitution is performed. + `G', or if it is a number that is less than or equal to zero, only + one substitution is performed. If HOW is zero, `gawk' issues a + warning message. If REGEXP does not match TARGET, `gensub''s return value is the - original, unchanged value of TARGET. + original unchanged value of TARGET. `gensub' is a `gawk' extension; it is not available in - compatibility mode (*note Command Line Options: Options.). + compatibility mode (*note Command-Line Options: Options.). `substr(STRING, START [, LENGTH])' This returns a LENGTH-character-long substring of STRING, starting at character number START. The first character of a string is - character number one. For example, `substr("washington", 5, 3)' + character number one.(2) For example, `substr("washington", 5, 3)' returns `"ing"'. If LENGTH is not present, this function returns the whole suffix of @@ -8142,60 +9287,80 @@ and "]"). also returned if LENGTH is greater than the number of characters remaining in the string, counting from character number START. - *Note:* The string returned by `substr' _cannot_ be assigned to. - Thus, it is a mistake to attempt to change a portion of a string, - like this: + The string returned by `substr' _cannot_ be assigned. Thus, it is + a mistake to attempt to change a portion of a string, as shown in + the following example: string = "abcdef" # try to get "abCDEf", won't work substr(string, 3, 3) = "CDE" - or to use `substr' as the third agument of `sub' or `gsub': + It is also a mistake to use `substr' as the third argument of + `sub' or `gsub': gsub(/xyz/, "pdq", substr($0, 5, 20)) # WRONG + (Some commercial versions of `awk' do in fact let you use `substr' + this way, but doing so is not portable.) + + If you need to replace bits and pieces of a string, combine + `substr' with string concatenation, in the following manner: + + string = "abcdef" + ... + string = substr(string, 1, 2) "CDE" substr(string, 6) + `tolower(STRING)' - This returns a copy of STRING, with each upper-case character in - the string replaced with its corresponding lower-case character. + This returns a copy of STRING, with each uppercase character in + the string replaced with its corresponding lowercase character. Non-alphabetic characters are left unchanged. For example, `tolower("MiXeD cAsE 123")' returns `"mixed case 123"'. `toupper(STRING)' - This returns a copy of STRING, with each lower-case character in - the string replaced with its corresponding upper-case character. + This returns a copy of STRING, with each lowercase character in + the string replaced with its corresponding uppercase character. Non-alphabetic characters are left unchanged. For example, `toupper("MiXeD cAsE 123")' returns `"MIXED CASE 123"'. -More About `\' and `&' with `sub', `gsub' and `gensub' ------------------------------------------------------- + ---------- Footnotes ---------- + + (1) Unless you use the `--non-decimal-data' option, which isn't +recommended. *Note Allowing Non-Decimal Input Data: Non-decimal Data, +for more information. + + (2) This is different from C and C++, where the first character is +number zero. - When using `sub', `gsub' or `gensub', and trying to get literal + +File: gawk.info, Node: Gory Details, Prev: String Functions, Up: String Functions + +More About `\' and `&' with `sub', `gsub', and `gensub' +....................................................... + + When using `sub', `gsub', or `gensub', and trying to get literal backslashes and ampersands into the replacement text, you need to remember that there are several levels of "escape processing" going on. First, there is the "lexical" level, which is when `awk' reads your -program, and builds an internal copy of your program that can be -executed. - - Then there is the run-time level, when `awk' actually scans the +program and builds an internal copy of it that can be executed. Then +there is the runtime level, which is when `awk' actually scans the replacement string to determine what to generate. At both levels, `awk' looks for a defined set of characters that can come after a backslash. At the lexical level, it looks for the escape sequences listed in *Note Escape Sequences::. Thus, for every `\' that -`awk' will process at the run-time level, you type two `\'s at the +`awk' processes at the runtime level, type two backslashes at the lexical level. When a character that is not valid for an escape sequence follows the `\', Unix `awk' and `gawk' both simply remove the -initial `\', and put the following character into the string. Thus, for +initial `\' and put the next character into the string. Thus, for example, `"a\qb"' is treated as `"aqb"'. - At the run-time level, the various functions handle sequences of `\' + At the runtime level, the various functions handle sequences of `\' and `&' differently. The situation is (sadly) somewhat complex. - - Historically, the `sub' and `gsub' functions treated the two -character sequence `\&' specially; this sequence was replaced in the -generated text with a single `&'. Any other `\' within the REPLACEMENT -string that did not precede an `&' was passed through unchanged. To +Historically, the `sub' and `gsub' functions treated the two character +sequence `\&' specially; this sequence was replaced in the generated +text with a single `&'. Any other `\' within the REPLACEMENT string +that did not precede an `&' was passed through unchanged. To illustrate with a table: You type `sub' sees `sub' generates @@ -8208,11 +9373,11 @@ illustrate with a table: `\\\\\\&' `\\\&' a literal `\\&' `\\q' `\q' a literal `\q' -This table shows both the lexical level processing, where an odd number -of backslashes becomes an even number at the run time level, and the -run-time processing done by `sub'. (For the sake of simplicity, the -rest of the tables below only show the case of even numbers of `\'s -entered at the lexical level.) +This table shows both the lexical-level processing, where an odd number +of backslashes becomes an even number at the runtime level, as well as +the runtime processing done by `sub'. (For the sake of simplicity, the +rest of the tables below only show the case of even numbers of +backslashes entered at the lexical level.) The problem with the historical approach is that there is no way to get a literal `\' followed by the matched text. @@ -8220,7 +9385,7 @@ get a literal `\' followed by the matched text. The 1992 POSIX standard attempted to fix this problem. The standard says that `sub' and `gsub' look for either a `\' or an `&' after the `\'. If either one follows a `\', that character is output literally. -The interpretation of `\' and `&' then becomes like this: +The interpretation of `\' and `&' then becomes: You type `sub' sees `sub' generates -------- ---------- --------------- @@ -8229,23 +9394,23 @@ The interpretation of `\' and `&' then becomes like this: `\\\\&' `\\&' a literal `\', then the matched text `\\\\\\&' `\\\&' a literal `\&' -This would appear to solve the problem. Unfortunately, the phrasing of -the standard is unusual. It says, in effect, that `\' turns off the -special meaning of any following character, but that for anything other -than `\' and `&', such special meaning is undefined. This wording -leads to two problems. +This appears to solve the problem. Unfortunately, the phrasing of the +standard is unusual. It says, in effect, that `\' turns off the special +meaning of any following character, but for anything other than `\' and +`&', such special meaning is undefined. This wording leads to two +problems: - 1. Backslashes must now be doubled in the REPLACEMENT string, breaking + * Backslashes must now be doubled in the REPLACEMENT string, breaking historical `awk' programs. - 2. To make sure that an `awk' program is portable, _every_ character + * To make sure that an `awk' program is portable, _every_ character in the REPLACEMENT string must be preceded with a backslash.(1) - The POSIX standard is under revision.(2) Because of the above -problems, proposed text for the revised standard reverts to rules that + The POSIX standard is under revision. Because of the problems just +listed, proposed text for the revised standard reverts to rules that correspond more closely to the original existing practice. The proposed rules have special cases that make it possible to produce a `\' -preceding the matched text. +preceding the matched text: You type `sub' sees `sub' generates -------- ---------- --------------- @@ -8254,24 +9419,24 @@ preceding the matched text. `\\&' `\&' a literal `&' `\\q' `\q' a literal `\q' - In a nutshell, at the run-time level, there are now three special -sequences of characters, `\\\&', `\\&' and `\&', whereas historically, + In a nutshell, at the runtime level, there are now three special +sequences of characters (`\\\&', `\\&' and `\&') whereas historically there was only one. However, as in the historical case, any `\' that -is not part of one of these three sequences is not special, and appears +is not part of one of these three sequences is not special and appears in the output literally. - `gawk' 3.0 follows these proposed POSIX rules for `sub' and `gsub'. -Whether these proposed rules will actually become codified into the -standard is unknown at this point. Subsequent `gawk' releases will -track the standard and implement whatever the final version specifies; -this Info file will be updated as well. + `gawk' 3.0 and 3.1 follow these proposed POSIX rules for `sub' and +`gsub'. Whether these proposed rules will actually become codified +into the standard is unknown at this point. Subsequent `gawk' releases +will track the standard and implement whatever the final version +specifies; this Info file will be updated as well.(2) - The rules for `gensub' are considerably simpler. At the run-time + The rules for `gensub' are considerably simpler. At the runtime level, whenever `gawk' sees a `\', if the following character is a digit, then the text that matched the corresponding parenthesized subexpression is placed in the generated output. Otherwise, no matter -what the character after the `\' is, that character will appear in the -generated text, and the `\' will not. +what the character after the `\' is, it appears in the generated text +and the `\' does not: You type `gensub' sees `gensub' generates -------- ------------- ------------------ @@ -8282,69 +9447,99 @@ generated text, and the `\' will not. `\\\\\\&' `\\\&' a literal `\&' `\\q' `\q' a literal `q' - Because of the complexity of the lexical and run-time level -processing, and the special cases for `sub' and `gsub', we recommend -the use of `gawk' and `gensub' for when you have to do substitutions. + Because of the complexity of the lexical and runtime level processing +and the special cases for `sub' and `gsub', we recommend the use of +`gawk' and `gensub' when you have to do substitutions. + +Advanced Notes: Matching the Null String +---------------------------------------- + + In `awk', the `*' operator can match the null string. This is +particularly important for the `sub', `gsub', and `gensub' functions. +For example: + + $ echo abc | awk '{ gsub(/m*/, "X"); print }' + -| XaXbXcX + +Although this makes a certain amount of sense, it can be surprising. ---------- Footnotes ---------- (1) This consequence was certainly unintended. - (2) As of July, 2000, with final approval and publication as part of -the Austin Group Standards hopefully sometime in 2001. + (2) As this Info file was being finalized, we learned that the POSIX +standard will not use these rules. However, it was too late to change +`gawk' for the 3.1 release. `gawk' behaves as described here.  File: gawk.info, Node: I/O Functions, Next: Time Functions, Prev: String Functions, Up: Built-in -Built-in Functions for Input/Output -=================================== - - The following functions are related to Input/Output (I/O). Optional -parameters are enclosed in square brackets ("[" and "]"). +Input/Output Functions +---------------------- -`close(FILENAME)' - Close the file FILENAME, for input or output. The argument may - alternatively be a shell command that was used for redirecting to - or from a pipe; then the pipe is closed. *Note Closing Input and - Output Files and Pipes: Close Files And Pipes, for more - information. + The following functions relate to Input/Output (I/O). Optional +parameters are enclosed in square brackets ([ and ]): + +`close(FILENAME [, HOW])' + Close the file FILENAME for input or output. Alternatively, the + argument may be a shell command that was used for creating a + coprocess, or for redirecting to or from a pipe; then the + coprocess or pipe is closed. *Note Closing Input and Output + Redirections: Close Files And Pipes, for more information. + + When closing a coprocess, it is occasionally useful to first close + one end of the two-way pipe, and then to close the other. This is + done by providing a second argument to `close'. This second + argument should be one of the two string values `"to"' or `"from"', + indicating which end of the pipe to close. Case in the string does + not matter. *Note Two-Way Communications with Another Process: + Two-way I/O, which discusses this feature in more detail and gives + an example. `fflush([FILENAME])' - Flush any buffered output associated FILENAME, which is either a - file opened for writing, or a shell command for redirecting output - to a pipe. - - Many utility programs will "buffer" their output; they save - information to be written to a disk file or terminal in memory, - until there is enough for it to be worthwhile to send the data to - the ouput device. This is often more efficient than writing every + Flush any buffered output associated with FILENAME, which is + either a file opened for writing or a shell command for + redirecting output to a pipe or coprocess. + + Many utility programs "buffer" their output; i.e., they save + information to write to a disk file or terminal in memory, until + there is enough for it to be worthwhile to send the data to the + output device. This is often more efficient than writing every little bit of information as soon as it is ready. However, sometimes it is necessary to force a program to "flush" its buffers; that is, write the information to its destination, even if a buffer is not full. This is the purpose of the `fflush' - function; `gawk' too buffers its output, and the `fflush' function - can be used to force `gawk' to flush its buffers. + function--`gawk' also buffers its output and the `fflush' function + forces `gawk' to flush its buffers. - `fflush' is a recent (1994) addition to the Bell Labs research - version of `awk'; it is not part of the POSIX standard, and will - not be available if `--posix' has been specified on the command - line (*note Command Line Options: Options.). + `fflush' was added to the Bell Laboratories research version of + `awk' in 1994; it is not part of the POSIX standard and is not + available if `--posix' has been specified on the command line + (*note Command-Line Options: Options.). `gawk' extends the `fflush' function in two ways. The first is to allow no argument at all. In this case, the buffer for the - standard output is flushed. The second way is to allow the null - string (`""') as the argument. In this case, the buffers for _all_ - open output files and pipes are flushed. + standard output is flushed. The second is to allow the null string + (`""') as the argument. In this case, the buffers for _all_ open + output files and pipes are flushed. + + `fflush' returns zero if the buffer is successfully flushed; + otherwise it returns -1. In the case where all buffers are + flushed, the return value is zero only if all buffers were flushed + successfully. Otherwise, it is -1, and `gawk' warns about the + FILENAME that had the problem. - `fflush' returns zero if the buffer was successfully flushed, and - nonzero otherwise. + `gawk' also issues a warning message if you attempt to flush a + file or pipe that was opened for reading (such as with `getline'), + or if FILENAME is not an open file, pipe, or coprocess. In such a + case, `fflush' returns -1 as well. `system(COMMAND)' The `system' function allows the user to execute operating system commands and then return to the `awk' program. The `system' function executes the command given by the string COMMAND. It - returns, as its value, the status returned by the command that was - executed. + returns the status returned by the command that was executed as + its value. For example, if the following fragment of code is put in your `awk' program: @@ -8353,12 +9548,12 @@ parameters are enclosed in square brackets ("[" and "]"). system("date | mail -s 'awk run done' root") } - the system administrator will be sent mail when the `awk' program + the system administrator is sent mail when the `awk' program finishes processing input and begins its end-of-input processing. Note that redirecting `print' or `printf' into a pipe is often enough to accomplish your task. If you need to run many commands, - it will be more efficient to simply print them to a pipe to the + it is more efficient to simply print them down a pipeline to the shell: while (MORE STUFF TO DO) @@ -8367,62 +9562,59 @@ parameters are enclosed in square brackets ("[" and "]"). However, if your `awk' program is interactive, `system' is useful for cranking up large self-contained programs, such as a shell or - an editor. + an editor. Some operating systems cannot implement the `system' + function. `system' causes a fatal error if it is not supported. - Some operating systems cannot implement the `system' function. - `system' causes a fatal error if it is not supported. +Advanced Notes: Interactive Versus Non-Interactive Buffering +------------------------------------------------------------ -Interactive vs. Non-Interactive Buffering ------------------------------------------ - - As a side point, buffering issues can be even more confusing -depending upon whether or not your program is "interactive", i.e., + As a side point, buffering issues can be even more confusing, +depending upon whether your program is "interactive"; i.e., communicating with a user sitting at a keyboard.(1) - Interactive programs generally "line buffer" their output; they + Interactive programs generally "line buffer" their output; i.e., they write out every line. Non-interactive programs wait until they have a -full buffer, which may be many lines of output. - - Here is an example of the difference. +full buffer, which may be many lines of output. Here is an example of +the difference: $ awk '{ print $1 + $2 }' 1 1 -| 2 2 3 -| 5 - Control-d + Ctrl-d Each line of output is printed immediately. Compare that behavior with -this example. +this example: $ awk '{ print $1 + $2 }' | cat 1 1 2 3 - Control-d + Ctrl-d -| 2 -| 5 -Here, no output is printed until after the `Control-d' is typed, since -it is all buffered, and sent down the pipe to `cat' in one shot. +Here, no output is printed until after the `Ctrl-d' is typed, because +it is all buffered and sent down the pipe to `cat' in one shot. -Controlling Output Buffering with `system' ------------------------------------------- +Advanced Notes: Controlling Output Buffering with `system' +---------------------------------------------------------- The `fflush' function provides explicit control over output buffering for individual files and pipes. However, its use is not portable to many other `awk' implementations. An alternative method to -flush output buffers is by calling `system' with a null string as its +flush output buffers is to call `system' with a null string as its argument: system("") # flush output -`gawk' treats this use of the `system' function as a special case, and +`gawk' treats this use of the `system' function as a special case and is smart enough not to run a shell (or other command interpreter) with the empty command. Therefore, with `gawk', this idiom is not only -useful, it is efficient. While this method should work with other -`awk' implementations, it will not necessarily avoid starting an +useful, it is also efficient. While this method should work with other +`awk' implementations, it does not necessarily avoid starting an unnecessary shell. (Other implementations may only flush the buffer -associated with the standard output, and not necessarily all buffered +associated with the standard output and not necessarily all buffered output.) If you think about what a programmer expects, it makes sense that @@ -8434,20 +9626,20 @@ output.) print "second print" } -must print +must print: first print system echo second print -and not +and not: system echo first print second print If `awk' did not flush its buffers before calling `system', the -latter (undesirable) output is what you would see. +latter (undesirable) output is what you see. ---------- Footnotes ---------- @@ -8455,57 +9647,89 @@ latter (undesirable) output is what you would see. a terminal device.  -File: gawk.info, Node: Time Functions, Prev: I/O Functions, Up: Built-in +File: gawk.info, Node: Time Functions, Next: Bitwise Functions, Prev: I/O Functions, Up: Built-in -Functions for Dealing with Time Stamps -====================================== +Using `gawk''s Timestamp Functions +---------------------------------- A common use for `awk' programs is the processing of log files -containing time stamp information, indicating when a particular log -record was written. Many programs log their time stamp in the form +containing timestamp information, indicating when a particular log +record was written. Many programs log their timestamp in the form returned by the `time' system call, which is the number of seconds -since a particular epoch. On POSIX systems, it is the number of -seconds since Midnight, January 1, 1970, UTC. - - In order to make it easier to process such log files, and to produce -useful reports, `gawk' provides two functions for working with time -stamps. Both of these are `gawk' extensions; they are not specified in -the POSIX standard, nor are they in any other known version of `awk'. - - Optional parameters are enclosed in square brackets ("[" and "]"). +since a particular epoch. On POSIX-compliant systems, it is the number +of seconds since 1970-01-01 00:00:00 UTC, not counting leap seconds.(1) +All known POSIX-compliant systems support timestamps from 0 through +2^31 - 1, which is sufficient to represent times through 2038-01-19 +03:14:07 UTC. Many systems support a wider range of timestamps, +including negative timestamps that represent times before the epoch. + + In order to make it easier to process such log files and to produce +useful reports, `gawk' provides the following functions for working +with timestamps. They are `gawk' extensions; they are not specified in +the POSIX standard, nor are they in any other known version of `awk'.(2) +Optional parameters are enclosed in square brackets ([ and ]): `systime()' This function returns the current time as the number of seconds since the system epoch. On POSIX systems, this is the number of - seconds since Midnight, January 1, 1970, UTC. It may be a - different number on other systems. + seconds since 1970-01-01 00:00:00 UTC, not counting leap seconds. + It may be a different number on other systems. + +`mktime(DATESPEC)' + This function turns DATESPEC into a timestamp in the same form as + is returned by `systime'. It is similar to the function of the + same name in ISO C. The argument, DATESPEC, is a string of the + form `"YYYY MM DD HH MM SS [DST]"'. The string consists of six or + seven numbers representing, respectively, the full year including + century, the month from 1 to 12, the day of the month from 1 to + 31, the hour of the day from 0 to 23, the minute from 0 to 59, the + second from 0 to 60,(3) and an optional daylight savings flag. + + The values of these numbers need not be within the ranges + specified; for example, an hour of -1 means 1 hour before midnight. + The origin-zero Gregorian calendar is assumed, with year 0 + preceding year 1 and year -1 preceding year 0. The time is + assumed to be in the local timezone. If the daylight savings flag + is positive, the time is assumed to be daylight savings time; if + zero, the time is assumed to be standard time; and if negative + (the default), `mktime' attempts to determine whether daylight + savings time is in effect for the specified time. + + If DATESPEC does not contain enough elements or if the resulting + time is out of range, `mktime' returns -1. `strftime([FORMAT [, TIMESTAMP]])' This function returns a string. It is similar to the function of - the same name in ANSI C. The time specified by TIMESTAMP is used - to produce a string, based on the contents of the FORMAT string. - The TIMESTAMP is in the same format as the value returned by the + the same name in ISO C. The time specified by TIMESTAMP is used to + produce a string, based on the contents of the FORMAT string. The + TIMESTAMP is in the same format as the value returned by the `systime' function. If no TIMESTAMP argument is supplied, `gawk' - will use the current time of day as the time stamp. If no FORMAT + uses the current time of day as the timestamp. If no FORMAT argument is supplied, `strftime' uses `"%a %b %d %H:%M:%S %Z %Y"'. - This format string produces output (almost) equivalent to that of - the `date' utility. (Versions of `gawk' prior to 3.0 require the - FORMAT argument.) + This format string produces output that is (almost) equivalent to + that of the `date' utility. (Versions of `gawk' prior to 3.0 + require the FORMAT argument.) - The `systime' function allows you to compare a time stamp from a log + The `systime' function allows you to compare a timestamp from a log file with the current time of day. In particular, it is easy to determine how long ago a particular record was logged. It also allows you to produce log records using the "seconds since the epoch" format. - The `strftime' function allows you to easily turn a time stamp into + The `mktime' function allows you to convert a textual representation +of a date and time into a timestamp. This makes it easy to do +before/after comparisons of dates and times, particularly when dealing +with date and time data coming from an external source, such as a log +file. + + The `strftime' function allows you to easily turn a timestamp into human-readable information. It is similar in nature to the `sprintf' -function (*note Built-in Functions for String Manipulation: String -Functions.), in that it copies non-format specification characters -verbatim to the returned string, while substituting date and time -values for format specifications in the FORMAT string. +function (*note String Manipulation Functions: String Functions.), in +that it copies non-format specification characters verbatim to the +returned string, while substituting date and time values for format +specifications in the FORMAT string. - `strftime' is guaranteed by the ANSI C standard to support the -following date format specifications: + `strftime' is guaranteed by the 1999 ISO C standard(4) to support +the following date format specifications: `%a' The locale's abbreviated weekday name. @@ -8520,11 +9744,40 @@ following date format specifications: The locale's full month name. `%c' - The locale's "appropriate" date and time representation. + The locale's "appropriate" date and time representation. (This is + `%A %B %d %T %Y' in the `"C"' locale.) + +`%C' + The century. This is the year divided by 100 and truncated to the + next lower integer. `%d' The day of the month as a decimal number (01-31). +`%D' + Equivalent to specifying `%m/%d/%y'. + +`%e' + The day of the month, padded with a space if it is only one digit. + +`%F' + Equivalent to specifying `%Y-%m-%d'. This is the ISO 8601 date + format. + +`%g' + The year modulo 100 of the ISO week number, as a decimal number + (00-99). For example, January 1, 1993, is in week 53 of 1992. + Thus, the year of its ISO week number is 1992, even though its + year is 1993. Similarly, December 31, 1973, is in week 1 of 1974. + Thus, the year of its ISO week number is 1974, even though its + year is 1973. + +`%G' + The full year of the ISO week number, as a decimal number. + +`%h' + Equivalent to `%b'. + `%H' The hour (24-hour clock) as a decimal number (00-23). @@ -8540,17 +9793,44 @@ following date format specifications: `%M' The minute as a decimal number (00-59). +`%n' + A newline character (ASCII LF). + `%p' The locale's equivalent of the AM/PM designations associated with a 12-hour clock. +`%r' + The locale's 12-hour clock time. (This is `%I:%M:%S %p' in the + `"C"' locale.) + +`%R' + Equivalent to specifying `%H:%M'. + `%S' - The second as a decimal number (00-60).(1) + The second as a decimal number (00-60). + +`%t' + A tab character. + +`%T' + Equivalent to specifying `%H:%M:%S'. + +`%u' + The weekday as a decimal number (1-7). Monday is day one. `%U' The week number of the year (the first Sunday as the first day of week one) as a decimal number (00-53). +`%V' + The week number of the year (the first Monday as the first day of + week one) as a decimal number (01-53). The method for determining + the week number is as specified by ISO 8601. (To wit: if the week + containing January 1 has four or more days in the new year, then + it is week one, otherwise it is week 53 of the previous year and + the next week is week one.) + `%w' The weekday as a decimal number (0-6). Sunday is day zero. @@ -8559,65 +9839,54 @@ following date format specifications: week one) as a decimal number (00-53). `%x' - The locale's "appropriate" date representation. + The locale's "appropriate" date representation. (This is `%A %B + %d %Y' in the `"C"' locale.) `%X' - The locale's "appropriate" time representation. + The locale's "appropriate" time representation. (This is `%T' in + the `"C"' locale.) `%y' - The year without century as a decimal number (00-99). + The year modulo 100 as a decimal number (00-99). `%Y' - The year with century as a decimal number (e.g., 1995). + The full year as a decimal number (e.g., 1995). + +`%z' + The timezone offset in a +HHMM format (e.g., the format necessary + to produce RFC 822/RFC 1036 date headers). `%Z' - The time zone name or abbreviation, or no characters if no time - zone is determinable. + The time zone name or abbreviation; no characters if no time zone + is determinable. + +`%Ec %EC %Ex %EX %Ey %EY %Od %Oe %OH' +`%OI %Om %OM %OS %Ou %OU %OV %Ow %OW %Oy' + These are "alternate representations" for the specifications that + use only the second letter (`%c', `%C', and so on).(5) (These + facilitate compliance with the POSIX `date' utility.) `%%' A literal `%'. If a conversion specifier is not one of the above, the behavior is -undefined.(2) +undefined.(6) Informally, a "locale" is the geographic place in which a program is meant to run. For example, a common way to abbreviate the date -September 4, 1991 in the United States would be "9/4/91". In many -countries in Europe, however, it would be abbreviated "4.9.91". Thus, -the `%x' specification in a `"US"' locale might produce `9/4/91', while -in a `"EUROPE"' locale, it might produce `4.9.91'. The ANSI C standard +September 4, 1991 in the United States is "9/4/91." In many countries +in Europe, however, it is abbreviated "4.9.91." Thus, the `%x' +specification in a `"US"' locale might produce `9/4/91', while in a +`"EUROPE"' locale, it might produce `4.9.91'. The ISO C standard defines a default `"C"' locale, which is an environment that is typical of what most C programmers are used to. A public-domain C version of `strftime' is supplied with `gawk' for -systems that are not yet fully ANSI-compliant. If that version is used -to compile `gawk' (*note Installing `gawk': Installation.), then the +systems that are not yet fully standards-compliant. It supports all of +the just listed format specifications. If that version is used to +compile `gawk' (*note Installing `gawk': Installation.), then the following additional format specifications are available: -`%D' - Equivalent to specifying `%m/%d/%y'. - -`%e' - The day of the month, padded with a space if it is only one digit. - -`%h' - Equivalent to `%b', above. - -`%n' - A newline character (ASCII LF). - -`%r' - Equivalent to specifying `%I:%M:%S %p'. - -`%R' - Equivalent to specifying `%H:%M'. - -`%T' - Equivalent to specifying `%H:%M:%S'. - -`%t' - A tab character. - `%k' The hour (24-hour clock) as a decimal number (0-23). Single digit numbers are padded with a space. @@ -8626,66 +9895,41 @@ following additional format specifications are available: The hour (12-hour clock) as a decimal number (1-12). Single digit numbers are padded with a space. -`%C' - The century, as a number between 00 and 99. - -`%u' - The weekday as a decimal number [1 (Monday)-7]. - -`%V' - The week number of the year (the first Monday as the first day of - week one) as a decimal number (01-53). The method for determining - the week number is as specified by ISO 8601 (to wit: if the week - containing January 1 has four or more days in the new year, then - it is week one, otherwise it is week 53 of the previous year and - the next week is week one). - -`%G' - The year with century of the ISO week number, as a decimal number. - - For example, January 1, 1993, is in week 53 of 1992. Thus, the year - of its ISO week number is 1992, even though its year is 1993. - Similarly, December 31, 1973, is in week 1 of 1974. Thus, the year - of its ISO week number is 1974, even though its year is 1973. +`%N' + The "Emperor/Era" name. Equivalent to `%C'. -`%g' - The year without century of the ISO week number, as a decimal - number (00-99). +`%o' + The "Emperor/Era" year. Equivalent to `%y'. -`%Ec %EC %Ex %Ey %EY %Od %Oe %OH %OI' -`%Om %OM %OS %Ou %OU %OV %Ow %OW %Oy' - These are "alternate representations" for the specifications that - use only the second letter (`%c', `%C', and so on). They are - recognized, but their normal representations are used.(3) (These - facilitate compliance with the POSIX `date' utility.) +`%s' + The time as a decimal timestamp in seconds since the epoch. `%v' - The date in VMS format (e.g., 20-JUN-1991). + The date in VMS format (e.g., `20-JUN-1991'). -`%z' - The timezone offset in a +HHMM format (e.g., the format necessary - to produce RFC-822/RFC-1036 date headers). + Additionally, the alternate representations are recognized but their +normal representations are used. This example is an `awk' implementation of the POSIX `date' utility. Normally, the `date' utility prints the current date and time of day -in a well known format. However, if you provide an argument to it that -begins with a `+', `date' will copy non-format specifier characters to -the standard output, and will interpret the current time according to -the format specifiers in the string. For example: +in a well-known format. However, if you provide an argument to it that +begins with a `+', `date' copies non-format specifier characters to the +standard output and interprets the current time according to the format +specifiers in the string. For example: $ date '+Today is %A, %B %d, %Y.' - -| Today is Thursday, July 11, 1991. + -| Today is Thursday, September 14, 2000. Here is the `gawk' version of the `date' utility. It has a shell -"wrapper", to handle the `-u' option, which requires that `date' run as -if the time zone was set to UTC. +"wrapper" to handle the `-u' option, which requires that `date' run as +if the time zone is set to UTC: #! /bin/sh # # date --- approximate the P1003.2 'date' command case $1 in - -u) TZ=GMT0 # use UTC + -u) TZ=UTC0 # use UTC export TZ shift ;; esac @@ -8707,27 +9951,184 @@ if the time zone was set to UTC. ---------- Footnotes ---------- - (1) Occasionally there are minutes in a year with a leap second, + (1) *Note Glossary::, especially the entries for "Epoch" and "UTC." + + (2) The GNU `date' utility can also do many of the things described +here. It's use may be preferable for simple time-related operations in +shell scripts. + + (3) Occasionally there are minutes in a year with a leap second, which is why the seconds can go up to 60. - (2) This is because ANSI C leaves the behavior of the C version of -`strftime' undefined, and `gawk' will use the system's version of -`strftime' if it's there. Typically, the conversion specifier will -either not appear in the returned string, or it will appear literally. + (4) As this is a recent standard, not every system's `strftime' +necessarily supports all of the conversions listed here. - (3) If you don't understand any of this, don't worry about it; these + (5) If you don't understand any of this, don't worry about it; these facilities are meant to make it easier to "internationalize" programs. +Other internationalization features are described in *Note +Internationalization with `gawk': Internationalization. + + (6) This is because ISO C leaves the behavior of the C version of +`strftime' undefined and `gawk' uses the system's version of `strftime' +if it's there. Typically, the conversion specifier either does not +appear in the returned string or it appears literally. + + +File: gawk.info, Node: Bitwise Functions, Next: I18N Functions, Prev: Time Functions, Up: Built-in + +Using `gawk''s Bit Manipulation Functions +----------------------------------------- + + I can explain it for you, but I can't understand it for you. + Anonymous + + Many languages provide the ability to perform "bitwise" operations +on two integer numbers. In other words, the operation is performed on +each successive pair of bits in the operands. Three common operations +are bitwise AND, OR, and XOR. The operations are described by the +following table: + + Bit Operator + | AND | OR | XOR + |---+---+---+---+---+--- + Operands | 0 | 1 | 0 | 1 | 0 | 1 + ----------+---+---+---+---+---+--- + 0 | 0 0 | 0 1 | 0 1 + 1 | 0 1 | 1 1 | 1 0 + + As you can see, the result of an AND operation is 1 only when _both_ +bits are 1. The result of an OR operation is 1 if _either_ bit is 1. +The result of an XOR operation is 1 if either bit is 1, but not both. +The next operation is the "complement"; the complement of 1 is 0 and +the complement of 0 is 1. Thus, this operation "flips" all the bits of +a given value. + + Finally, two other common operations are to shift the bits left or +right. For example, if you have a bit string `10111001' and you shift +it right by three bits, you end up with `00010111'.(1) If you start over +again with `10111001' and shift it left by three bits, you end up with +`11001000'. `gawk' provides built-in functions that implement the +bitwise operations just described. They are: + +`and(V1, V2)' Return the bitwise AND of the values provided by V1 + and V2. +`or(V1, V2)' Return the bitwise OR of the values provided by V1 and + V2. +`xor(V1, V2)' Return the bitwise XOR of the values provided by V1 + and V2. +`compl(VAL)' Return the bitwise complement of VAL. +`lshift(VAL, COUNT)' Return the value of VAL, shifted left by COUNT bits. +`rshift(VAL, COUNT)' Return the value of VAL, shifted right by COUNT bits. + + For all of these functions, first the double-precision +floating-point value is converted to a C `unsigned long', then the +bitwise operation is performed and then the result is converted back +into a C `double'. (If you don't understand this paragraph, don't worry +about it.) + + Here is a user-defined function (*note User-Defined Functions: +User-defined.) that illustrates the use of these functions: + + # bits2str --- turn a byte into readable 1's and 0's + + function bits2str(bits, data, mask) + { + if (bits == 0) + return "0" + + mask = 1 + for (; bits != 0; bits = rshift(bits, 1)) + data = (and(bits, mask) ? "1" : "0") data + + while ((length(data) % 8) != 0) + data = "0" data + + return data + } + + BEGIN { + printf "123 = %s\n", bits2str(123) + printf "0123 = %s\n", bits2str(0123) + printf "0x99 = %s\n", bits2str(0x99) + comp = compl(0x99) + printf "compl(0x99) = %#x = %s\n", comp, bits2str(comp) + shift = lshift(0x99, 2) + printf "lshift(0x99, 2) = %#x = %s\n", shift, bits2str(shift) + shift = rshift(0x99, 2) + printf "rshift(0x99, 2) = %#x = %s\n", shift, bits2str(shift) + } + +This program produces the following output when run: + + $ gawk -f testbits.awk + -| 123 = 01111011 + -| 0123 = 01010011 + -| 0x99 = 10011001 + -| compl(0x99) = 0xffffff66 = 11111111111111111111111101100110 + -| lshift(0x99, 2) = 0x264 = 0000001001100100 + -| rshift(0x99, 2) = 0x26 = 00100110 + + The `bits2str' function turns a binary number into a string. The +number `1' represents a binary value where the rightmost bit is set to +1. Using this mask, the function repeatedly checks the rightmost bit. +AND-ing the mask with the value indicates whether the rightmost bit is +1 or not. If so, a `"1"' is concatenated onto the front of the string. +Otherwise, a `"0"' is added. The value is then shifted right by one +bit and the loop continues until there are no more 1 bits. + + If the initial value is zero it returns a simple `"0"'. Otherwise, +at the end, it pads the value with zeros to represent multiples of +eight-bit quantities. This is typical in modern computers. + + The main code in the `BEGIN' rule shows the difference between the +decimal and octal values for the same numbers (*note Octal and +Hexadecimal Numbers: Non-decimal-numbers.), and then demonstrates the +results of the `compl', `lshift', and `rshift' functions. + + ---------- Footnotes ---------- + + (1) This example shows that 0's come in on the left side. For +`gawk', this is always true, but in some languages, it's possible to +have the left side fill with 1's. Caveat emptor. + + +File: gawk.info, Node: I18N Functions, Prev: Bitwise Functions, Up: Built-in + +Using `gawk''s String Translation Functions +------------------------------------------- + + `gawk' provides facilities for internationalizing `awk' programs. +These include the functions described in the following list. The +description here is purposely brief. *Note Internationalization with +`gawk': Internationalization, for the full story. Optional parameters +are enclosed in square brackets ([ and ]): + +`dcgettext(STRING [, DOMAIN [, CATEGORY]])' + This function returns the translation of STRING in text domain + DOMAIN for locale category CATEGORY. The default value for DOMAIN + is the current value of `TEXTDOMAIN'. The default value for + CATEGORY is `"LC_MESSAGES"'. + +`bindtextdomain(DIRECTORY [, DOMAIN])' + This function allows you to specify the directory where `gawk' + will look for message translation files, in case they will not or + cannot be placed in the "standard" locations (e.g., during + testing). It returns the directory where DOMAIN is "bound." + + The default DOMAIN is the value of `TEXTDOMAIN'. If DIRECTORY is + the null string (`""'), then `bindtextdomain' returns the current + binding for the given DOMAIN.  -File: gawk.info, Node: User-defined, Next: Invoking Gawk, Prev: Built-in, Up: Top +File: gawk.info, Node: User-defined, Prev: Built-in, Up: Functions -User-defined Functions -********************** +User-Defined Functions +====================== Complicated `awk' programs can often be simplified by defining your own functions. User-defined functions can be called just like built-in -ones (*note Function Calls::), but it is up to you to define them--to -tell `awk' what they should do. +ones (*note Function Calls::), but it is up to you to define them; +i.e., to tell `awk' what they should do. * Menu: @@ -8736,19 +10137,20 @@ tell `awk' what they should do. does. * Function Caveats:: Things to watch out for. * Return Statement:: Specifying the value a function returns. +* Dynamic Typing:: How variable types can change at runtime.  File: gawk.info, Node: Definition Syntax, Next: Function Example, Prev: User-defined, Up: User-defined Function Definition Syntax -========================== +-------------------------- Definitions of functions can appear anywhere between the rules of an `awk' program. Thus, the general form of an `awk' program is extended to include sequences of rules _and_ user-defined function definitions. -There is no need in `awk' to put the definition of a function before -all uses of the function. This is because `awk' reads the entire -program before starting to execute any of it. +There is no need to put the definition of a function before all uses of +the function. This is because `awk' reads the entire program before +starting to execute any of it. The definition of a function named NAME looks like this: @@ -8757,39 +10159,41 @@ program before starting to execute any of it. BODY-OF-FUNCTION } -NAME is the name of the function to be defined. A valid function name -is like a valid variable name: a sequence of letters, digits and -underscores, not starting with a digit. Within a single `awk' program, -any particular name can only be used as a variable, array or function. +NAME is the name of the function to define. A valid function name is +like a valid variable name: a sequence of letters, digits, and +underscores, that doesn't start with a digit. Within a single `awk' +program, any particular name can only be used as a variable, array, or +function. PARAMETER-LIST is a list of the function's arguments and local variable names, separated by commas. When the function is called, the argument names are used to hold the argument values given in the call. The local variables are initialized to the empty string. A function -cannot have two parameters with the same name. +cannot have two parameters with the same name, nor may it have a +parameter with the same name as the function itself. The BODY-OF-FUNCTION consists of `awk' statements. It is the most important part of the definition, because it says what the function should actually _do_. The argument names exist to give the body a way -to talk about the arguments; local variables, to give the body places -to keep temporary values. +to talk about the arguments; local variables exist to give the body +places to keep temporary values. Argument names are not distinguished syntactically from local -variable names; instead, the number of arguments supplied when the +variable names. Instead, the number of arguments supplied when the function is called determines how many argument variables there are. Thus, if three argument values are given, the first three names in -PARAMETER-LIST are arguments, and the rest are local variables. +PARAMETER-LIST are arguments and the rest are local variables. It follows that if the number of arguments is not the same in all calls to the function, some of the names in PARAMETER-LIST may be arguments on some occasions and local variables on others. Another way to think of this is that omitted arguments default to the null string. - Usually when you write a function you know how many names you intend -to use for arguments and how many you intend to use as local variables. -It is conventional to place some extra space between the arguments and -the local variables, to document how your function is supposed to be -used. + Usually when you write a function, you know how many names you +intend to use for arguments and how many you intend to use as local +variables. It is conventional to place some extra space between the +arguments and the local variables, in order to document how your +function is supposed to be used. During execution of the function body, the arguments and local variable values hide or "shadow" any variables of the same names used @@ -8803,25 +10207,26 @@ in the function's body. body is executing. Once the body finishes, you can once again access the variables that were shadowed while the function was running. - The function body can contain expressions which call functions. They + The function body can contain expressions that call functions. They can even call this function, either directly or by way of another -function. When this happens, we say the function is "recursive". +function. When this happens, we say the function is "recursive". The +act of a function calling itself is called "recursion". In many `awk' implementations, including `gawk', the keyword `function' may be abbreviated `func'. However, POSIX only specifies the use of the keyword `function'. This actually has some practical -implications. If `gawk' is in POSIX-compatibility mode (*note Command -Line Options: Options.), then the following statement will _not_ define -a function: +implications. If `gawk' is in POSIX-compatibility mode (*note +Command-Line Options: Options.), then the following statement does +_not_ define a function: func foo() { a = sqrt($1) ; print a } Instead it defines a rule that, for each record, concatenates the value of the variable `func' with the return value of the function `foo'. If the resulting string is non-null, the action is executed. This is -probably not what was desired. (`awk' accepts this input as -syntactically valid, since functions may be used before they are defined -in `awk' programs.) +probably not what is desired. (`awk' accepts this input as +syntactically valid, because functions may be used before they are +defined in `awk' programs.) To ensure that your `awk' programs are portable, always use the keyword `function' when defining a function. @@ -8830,22 +10235,23 @@ keyword `function' when defining a function. File: gawk.info, Node: Function Example, Next: Function Caveats, Prev: Definition Syntax, Up: User-defined Function Definition Examples -============================ +---------------------------- Here is an example of a user-defined function, called `myprint', that -takes a number and prints it in a specific format. +takes a number and prints it in a specific format: function myprint(num) { printf "%6.3g\n", num } -To illustrate, here is an `awk' rule which uses our `myprint' function: +To illustrate, here is an `awk' rule that uses our `myprint' function: $3 > 0 { myprint($3) } This program prints, in our special format, all the third fields that -contain a positive number in our input. Therefore, when given: +contain a positive number in our input. Therefore, when given the +following: 1.2 3.4 5.6 7.8 9.10 11.12 -13.14 15.16 @@ -8856,7 +10262,7 @@ this program, using our function to format the results, prints: 5.6 21.2 - This function deletes all the elements in an array. + This function deletes all the elements in an array: function delarray(a, i) { @@ -8867,13 +10273,16 @@ this program, using our function to format the results, prints: When working with arrays, it is often necessary to delete all the elements in an array and start over with a new list of elements (*note The `delete' Statement: Delete.). Instead of having to repeat this -loop everywhere in your program that you need to clear out an array, -your program can just call `delarray'. (This guarantees portability. -The usage `delete ARRAY' to delete the contents of an entire array is a +loop everywhere that you need to clear out an array, your program can +just call `delarray'. (This guarantees portability. The use of +`delete ARRAY' to delete the contents of an entire array is a non-standard extension.) - Here is an example of a recursive function. It takes a string as an -input parameter, and returns the string in backwards order. + The following is an example of a recursive function. It takes a +string as an input parameter and returns the string in backwards order. +Recursive functions must always have a test that stops the recursion. +In this case, the recursion terminates when the starting position is +zero; i.e., when there are no more characters left in the string. function rev(str, start) { @@ -8883,18 +10292,17 @@ input parameter, and returns the string in backwards order. return (substr(str, start, 1) rev(str, start - 1)) } - If this function is in a file named `rev.awk', we can test it this + If this function is in a file named `rev.awk', it can be tested this way: $ echo "Don't Panic!" | > gawk --source '{ print rev($0, length($0)) }' -f rev.awk -| !cinaP t'noD - Here is an example that uses the built-in function `strftime'. -(*Note Functions for Dealing with Time Stamps: Time Functions, for more -information on `strftime'.) The C `ctime' function takes a timestamp -and returns it in a string, formatted in a well known fashion. Here is -an `awk' version: + The C `ctime' function takes a timestamp and returns it in a string, +formatted in a well-known fashion. The following example uses the +built-in `strftime' function (*note Using `gawk''s Timestamp Functions: +Time Functions.) to create an `awk' version of `ctime': # ctime.awk # @@ -8911,23 +10319,23 @@ an `awk' version:  File: gawk.info, Node: Function Caveats, Next: Return Statement, Prev: Function Example, Up: User-defined -Calling User-defined Functions -============================== +Calling User-Defined Functions +------------------------------ "Calling a function" means causing the function to run and do its -job. A function call is an expression, and its value is the value +job. A function call is an expression and its value is the value returned by the function. A function call consists of the function name followed by the -arguments in parentheses. What you write in the call for the arguments -are `awk' expressions; each time the call is executed, these +arguments in parentheses. `awk' expressions are what you write in the +call for the arguments. Each time the call is executed, these expressions are evaluated, and the values are the actual arguments. For example, here is a call to `foo' with three arguments (the first being a string concatenation): foo(x y, "lose", 4 * z) - *Caution:* whitespace characters (spaces and tabs) are not allowed + *Caution:* Whitespace characters (spaces and tabs) are not allowed between the function name and the open-parenthesis of the argument list. If you write whitespace by mistake, `awk' might think that you mean to concatenate a variable with an expression in parentheses. However, it @@ -8937,18 +10345,17 @@ reports an error. When a function is called, it is given a _copy_ of the values of its arguments. This is known as "call by value". The caller may use a variable as the expression for the argument, but the called function -does not know this: it only knows what value the argument had. For -example, if you write this code: +does not know this--it only knows what value the argument had. For +example, if you write the following code: foo = "bar" z = myfunc(foo) then you should not think of the argument to `myfunc' as being "the -variable `foo'." Instead, think of the argument as the string value, -`"bar"'. - - If the function `myfunc' alters the values of its local variables, -this has no effect on any other variables. Thus, if `myfunc' does this: +variable `foo'." Instead, think of the argument as the string value +`"bar"'. If the function `myfunc' alters the values of its local +variables, this has no effect on any other variables. Thus, if `myfunc' +does this: function myfunc(str) { @@ -8957,9 +10364,9 @@ this has no effect on any other variables. Thus, if `myfunc' does this: print str } -to change its first argument variable `str', this _does not_ change the +to change its first argument variable `str', it _does not_ change the value of `foo' in the caller. The role of `foo' in calling `myfunc' -ended when its value, `"bar"', was computed. If `str' also exists +ended when its value (`"bar"') was computed. If `str' also exists outside of `myfunc', the function body cannot alter this outer value, because it is shadowed during the execution of `myfunc' and cannot be seen or changed from there. @@ -8968,7 +10375,9 @@ seen or changed from there. copied. Instead, the array itself is made available for direct manipulation by the function. This is usually called "call by reference". Changes made to an array parameter inside the body of a -function _are_ visible outside that function. This can be *very* +function _are_ visible outside that function. + + *Note:* Changing an array parameter inside a function can be very dangerous if you do not watch what you are doing. For example: function changeit(array, ind, nvalue) @@ -8987,7 +10396,7 @@ This program prints `a[1] = 1, a[2] = two, a[3] = 3', because `changeit' stores `"two"' in the second element of `a'. Some `awk' implementations allow you to call a function that has not -been defined, and only report a problem at run-time when the program +been defined. They only report a problem at runtime when the program actually tries to call the function. For example: BEGIN { @@ -8999,46 +10408,46 @@ actually tries to call the function. For example: function bar() { ... } # note that `foo' is not defined -Since the `if' statement will never be true, it is not really a problem -that `foo' has not been defined. Usually though, it is a problem if a -program calls an undefined function. +Because the `if' statement will never be true, it is not really a +problem that `foo' has not been defined. Usually though, it is a +problem if a program calls an undefined function. - If `--lint' has been specified (*note Command Line Options: -Options.), `gawk' will report about calls to undefined functions. + If `--lint' is specified (*note Command-Line Options: Options.), +`gawk' reports calls to undefined functions. - Some `awk' implementations generate a run-time error if you use the + Some `awk' implementations generate a runtime error if you use the `next' statement (*note The `next' Statement: Next Statement.) inside -a user-defined function. `gawk' does not have this problem. +a user-defined function. `gawk' does not have this limitation.  -File: gawk.info, Node: Return Statement, Prev: Function Caveats, Up: User-defined +File: gawk.info, Node: Return Statement, Next: Dynamic Typing, Prev: Function Caveats, Up: User-defined The `return' Statement -====================== +---------------------- The body of a user-defined function can contain a `return' statement. -This statement returns control to the rest of the `awk' program. It -can also be used to return a value for use in the rest of the `awk' -program. It looks like this: +This statement returns control to the calling part of the `awk' +program. It can also be used to return a value for use in the rest of +the `awk' program. It looks like this: return [EXPRESSION] The EXPRESSION part is optional. If it is omitted, then the returned -value is undefined and, therefore, unpredictable. +value is undefined, and therefore, unpredictable. A `return' statement with no value expression is assumed at the end of every function definition. So if control reaches the end of the function body, then the function returns an unpredictable value. `awk' -will _not_ warn you if you use the return value of such a function. +does _not_ warn you if you use the return value of such a function. Sometimes, you want to write a function for what it does, not for what it returns. Such a function corresponds to a `void' function in C or to a `procedure' in Pascal. Thus, it may be appropriate to not -return any value; you should simply bear in mind that if you use the -return value of such a function, you do so at your own risk. +return any value; simply bear in mind that if you use the return value +of such a function, you do so at your own risk. - Here is an example of a user-defined function that returns a value -for the largest number among the elements of an array: + The following is an example of a user-defined function that returns +a value for the largest number among the elements of an array: function maxelt(vec, i, ret) { @@ -9057,11 +10466,10 @@ function parameter list indicates that `i' and `ret' are not supposed to be arguments. This is a convention that you should follow when you define functions. - Here is a program that uses our `maxelt' function. It loads an + The following program uses the `maxelt' function. It loads an array, calls `maxelt', and then reports the maximum number in that array: - awk ' function maxelt(vec, i, ret) { for (i in vec) { @@ -9079,7 +10487,7 @@ array: END { print maxelt(nums) - }' + } Given the following input: @@ -9089,2198 +10497,1727 @@ array: -6 467 998 1101 99385 11 0 225 -our program tells us (predictably) that `99385' is the largest number -in our array. +the program reports (predictably) that `99385' is the largest number in +the array.  -File: gawk.info, Node: Invoking Gawk, Next: Library Functions, Prev: User-defined, Up: Top +File: gawk.info, Node: Dynamic Typing, Prev: Return Statement, Up: User-defined -Running `awk' -************* +Functions and Their Effect on Variable Typing +--------------------------------------------- - There are two ways to run `awk': with an explicit program, or with -one or more program files. Here are templates for both of them; items -enclosed in `[...]' in these templates are optional. + `awk' is a very fluid language. It is possible that `awk' can't +tell if an identifier represents a regular variable or an array until +runtime. Here is an annotated sample program: - Besides traditional one-letter POSIX-style options, `gawk' also -supports GNU long options. + function foo(a) + { + a[1] = 1 # parameter is an array + } + + BEGIN { + b = 1 + foo(b) # invalid: fatal type mismatch + + foo(x) # x uninitialized, becomes an array dynamically + x = 1 # now not allowed, runtime error + } - awk [OPTIONS] -f progfile [`--'] FILE ... - awk [OPTIONS] [`--'] 'PROGRAM' FILE ... + Usually, such things aren't a big issue, but it's worth being aware +of them. - It is possible to invoke `awk' with an empty program: + +File: gawk.info, Node: Internationalization, Next: Advanced Features, Prev: Functions, Up: Top + +Internationalization with `gawk' +******************************** + + Once upon a time, computer makers wrote software that only worked in +English. Eventually, hardware and software vendors noticed that if +their systems worked in the native languages of non-English-speaking +countries, they were able to sell more systems. As a result, +internationalization and localization of programs and software systems +became a common practice. + + Until recently, the ability to provide internationalization was +largely restricted to programs written in C and C++. This major node +describes the underlying library `gawk' uses for internationalization, +as well as how `gawk' makes internationalization features available at +the `awk' program level. Having internationalization available at the +`awk' level gives software developers additional flexibility--they are +no longer required to write in C when internationalization is a +requirement. - $ awk '' datafile1 datafile2 +* Menu: -Doing so makes little sense though; `awk' will simply exit silently -when given an empty program (d.c.). If `--lint' has been specified on -the command line, `gawk' will issue a warning that the program is empty. +* I18N and L10N:: Internationalization and Localization. +* Explaining gettext:: How GNU `gettext' works. +* Programmer i18n:: Features for the programmer. +* Translator i18n:: Features for the translator. +* I18N Example:: A simple i18n example. +* Gawk I18N:: `gawk' is also internationalized. -* Menu: + +File: gawk.info, Node: I18N and L10N, Next: Explaining gettext, Prev: Internationalization, Up: Internationalization -* Options:: Command line options and their meanings. -* Other Arguments:: Input file names and variable assignments. -* AWKPATH Variable:: Searching directories for `awk' programs. -* Obsolete:: Obsolete Options and/or features. -* Undocumented:: Undocumented Options and Features. -* Known Bugs:: Known Bugs in `gawk'. +Internationalization and Localization +===================================== + + "Internationalization" means writing (or modifying) a program once, +in such a way that it can use multiple languages without requiring +further source code changes. "Localization" means providing the data +necessary for an internationalized program to work in a particular +language. Most typically, these terms refer to features such as the +language used for printing error messages, the language used to read +responses, and information related to how numerical and monetary values +are printed and read.  -File: gawk.info, Node: Options, Next: Other Arguments, Prev: Invoking Gawk, Up: Invoking Gawk +File: gawk.info, Node: Explaining gettext, Next: Programmer i18n, Prev: I18N and L10N, Up: Internationalization -Command Line Options -==================== +GNU `gettext' +============= - Options begin with a dash, and consist of a single character. GNU -style long options consist of two dashes and a keyword. The keyword -can be abbreviated, as long the abbreviation allows the option to be -uniquely identified. If the option takes an argument, then the keyword -is either immediately followed by an equals sign (`=') and the -argument's value, or the keyword and the argument's value are separated -by whitespace. For brevity, the discussion below only refers to the -traditional short options; however the long and short options are -interchangeable in all contexts. + The facilities in GNU `gettext' focus on messages; strings printed +by a program, either directly or via formatting with `printf' or +`sprintf'.(1) - Each long option for `gawk' has a corresponding POSIX-style option. -The options and their meanings are as follows: + When using GNU `gettext', each application has its own "text +domain". This is a unique name such as `kpilot' or `gawk', that +identifies the application. A complete application may have multiple +components--programs written in C or C++, as well as scripts written in +`sh' or `awk'. All of the components use the same text domain. -`-F FS' -`--field-separator FS' - Sets the `FS' variable to FS (*note Specifying How Fields are - Separated: Field Separators.). + To make the discussion concrete, assume we're writing an application +named `guide'. Internationalization consists of the following steps, +in this order: -`-f SOURCE-FILE' -`--file SOURCE-FILE' - Indicates that the `awk' program is to be found in SOURCE-FILE - instead of in the first non-option argument. + 1. The programmer goes through the source for all of `guide''s + components and marks each string that is a candidate for + translation. For example, `"`-F': option required"' is a good + candidate for translation. A table with strings of option names + is not (e.g., `gawk''s `--profile' option should remain the same, + no matter what the local language). -`-v VAR=VAL' -`--assign VAR=VAL' - Sets the variable VAR to the value VAL *before* execution of the - program begins. Such variable values are available inside the - `BEGIN' rule (*note Other Command Line Arguments: Other - Arguments.). + 2. The programmer indicates the application's text domain (`"guide"') + to the `gettext' library, by calling the `textdomain' function. - The `-v' option can only set one variable, but you can use it more - than once, setting another variable each time, like this: `awk - -v foo=1 -v bar=2 ...'. + 3. Messages from the application are extracted from the source code + and collected into a Portable Object file (`guide.po'), which + lists the strings and their translations. The translations are + initially empty. The original (usually English) messages serve as + the key for lookup of the translations. - *Caution:* Using `-v' to set the values of the builtin variables - may lead to suprising results. `awk' will reset the values of - those variables as it needs to, possibly ignoring any predefined - value you may have given. + 4. For each language with a translator, `guide.po' is copied and + translations are created and shipped with the application. -`-mf NNN' -`-mr NNN' - Set various memory limits to the value NNN. The `f' flag sets the - maximum number of fields, and the `r' flag sets the maximum record - size. These two flags and the `-m' option are from the Bell Labs - research version of Unix `awk'. They are provided for - compatibility, but otherwise ignored by `gawk', since `gawk' has - no predefined limits. + 5. Each language's `.po' file is converted into a binary message + object (`.mo') file. A message object file contains the original + messages and their translations in a binary format that allows + fast lookup of translations at runtime. -`-W GAWK-OPT' - Following the POSIX standard, options that are implementation - specific are supplied as arguments to the `-W' option. These - options also have corresponding GNU style long options. See below. + 6. When `guide' is built and installed, the binary translation files + are installed in a standard place. -`--' - Signals the end of the command line options. The following - arguments are not treated as options even if they begin with `-'. - This interpretation of `--' follows the POSIX argument parsing - conventions. + 7. For testing and development, it is possible to tell `gettext' to + use `.mo' files in a different directory than the standard one by + using the `bindtextdomain' function. - This is useful if you have file names that start with `-', or in - shell scripts, if you have file names that will be specified by - the user which could start with `-'. + 8. At runtime, `guide' looks up each string via a call to `gettext'. + The returned string is the translated string if available, or the + original string if not. - The following `gawk'-specific options are available: + 9. If necessary, it is possible to access messages from a different + text domain than the one belonging to the application, without + having to switch the application's default text domain back and + forth. -`-W traditional' -`-W compat' -`--traditional' -`--compat' - Specifies "compatibility mode", in which the GNU extensions to the - `awk' language are disabled, so that `gawk' behaves just like the - Bell Labs research version of Unix `awk'. `--traditional' is the - preferred form of this option. *Note Extensions in `gawk' Not in - POSIX `awk': POSIX/GNU, which summarizes the extensions. Also see - *Note Downward Compatibility and Debugging: Compatibility Mode. + In C (or C++), the string marking and dynamic translation lookup are +accomplished by wrapping each string in a call to `gettext': -`-W copyleft' -`-W copyright' -`--copyleft' -`--copyright' - Print the short version of the General Public License, and then - exit. This option may disappear in a future version of `gawk'. + printf(gettext("Don't Panic!\n")); -`-W help' -`-W usage' -`--help' -`--usage' - Print a "usage" message summarizing the short and long style - options that `gawk' accepts, and then exit. + The tools that extract messages from source code pull out all +strings enclosed in calls to `gettext'. -`-W lint' -`--lint' - Warn about constructs that are dubious or non-portable to other - `awk' implementations. Some warnings are issued when `gawk' first - reads your program. Others are issued at run-time, as your - program executes. + The GNU `gettext' developers, recognizing that typing `gettext' over +and over again is both painful and ugly to look at, use the macro `_' +(an underscore) to make things easier: -`-W lint-old' -`--lint-old' - Warn about constructs that are not available in the original - Version 7 Unix version of `awk' (*note Major Changes between V7 - and SVR3.1: V7/SVR3.1.). + /* In the standard header file: */ + #define _(str) gettext(str) + + /* In the program text: */ + printf(_("Don't Panic!\n")); + +This reduces the typing overhead to just three extra characters per +string and is considerably easier to read as well. There are locale +"categories" for different types of locale-related information. The +defined locale categories that `gettext' knows about are: + +`LC_MESSAGES' + Text messages. This is the default category for `gettext' + operations, but it is possible to supply a different one + explicitly, if necessary. (It is almost never necessary to supply + a different category.) + +`LC_COLLATE' + Text collation information; i.e., how different characters and/or + groups of characters sort in a given language. + +`LC_CTYPE' + Character type information (alphabetic, digit, upper- or + lowercase, and so on). This information is accessed via the POSIX + character classes in regular expressions, such as `/[[:alnum:]]/' + (*note Regular Expression Operators: Regexp Operators.). + +`LC_MONETARY' + Monetary information, such as the currency symbol, and whether the + symbol goes before or after a number. + +`LC_NUMERIC' + Numeric information, such as which characters to use for the + decimal point and the thousands separator.(2) + +`LC_RESPONSE' + Response information, such as how "yes" and "no" appear in the + local language, and possibly other information as well. + +`LC_TIME' + Time and date related information, such as 12- or 24-hour clock, + month printed before or after day in a date, local month + abbreviations, and so on. + +`LC_ALL' + All of the above. (Not too useful in the context of `gettext'.) -`-W posix' -`--posix' - Operate in strict POSIX mode. This disables all `gawk' extensions - (just like `--traditional'), and adds the following additional - restrictions: + ---------- Footnotes ---------- - * `\x' escape sequences are not recognized (*note Escape - Sequences::). + (1) For some operating systems, the `gawk' port doesn't support GNU +`gettext'. This applies most notably to the PC operating systems. As +such, these features are not available if you are using one of those +operating systems. Sorry. - * Newlines do not act as whitespace to separate fields when - `FS' is equal to a single space. + (2) Americans use a comma every three decimal places and a period +for the decimal point, while many Europeans do exactly the opposite: +`1,234.56' vs. `1.234,56'. - * The synonym `func' for the keyword `function' is not - recognized (*note Function Definition Syntax: Definition - Syntax.). + +File: gawk.info, Node: Programmer i18n, Next: Translator i18n, Prev: Explaining gettext, Up: Internationalization - * The operators `**' and `**=' cannot be used in place of `^' - and `^=' (*note Arithmetic Operators: Arithmetic Ops., and - also *note Assignment Expressions: Assignment Ops.). +Internationalizing `awk' Programs +================================= - * Specifying `-Ft' on the command line does not set the value - of `FS' to be a single tab character (*note Specifying How - Fields are Separated: Field Separators.). + `gawk' provides the following variables and functions for +internationalization: + +`TEXTDOMAIN' + This variable indicates the application's text domain. For + compatibility with GNU `gettext', the default value is + `"messages"'. + +`_"your message here"' + String constants marked with a leading underscore are candidates + for translation at runtime. String constants without a leading + underscore are not translated. + +`dcgettext(STRING [, DOMAIN [, CATEGORY]])' + This built-in function returns the translation of STRING in text + domain DOMAIN for locale category CATEGORY. The default value for + DOMAIN is the current value of `TEXTDOMAIN'. The default value + for CATEGORY is `"LC_MESSAGES"'. + + If you supply a value for CATEGORY, it must be a string equal to + one of the known locale categories described in *Note GNU + `gettext': Explaining gettext. You must also supply a text + domain. Use `TEXTDOMAIN' if you want to use the current domain. + + *Caution:* The order of arguments to the `awk' version of the + `dcgettext' function is purposely different from the order for the + C version. The `awk' version's order was chosen to be simple and + to allow for reasonable `awk'-style default arguments. + +`bindtextdomain(DIRECTORY [, DOMAIN])' + This built-in function allows you to specify the directory where + `gettext' looks for `.mo' files, in case they will not or cannot + be placed in the standard locations (e.g., during testing). It + returns the directory where DOMAIN is "bound." + + The default DOMAIN is the value of `TEXTDOMAIN'. If DIRECTORY is + the null string (`""'), then `bindtextdomain' returns the current + binding for the given DOMAIN. + + To use these facilities in your `awk' program, follow the steps +outlined in *Note GNU `gettext': Explaining gettext, like so: + + 1. Set the variable `TEXTDOMAIN' to the text domain of your program. + This is best done in a `BEGIN' rule (*note The `BEGIN' and `END' + Special Patterns: BEGIN/END.), or it can also be done via the `-v' + command-line option (*note Command-Line Options: Options.): + + BEGIN { + TEXTDOMAIN = "guide" + ... + } - * The `fflush' built-in function is not supported (*note - Built-in Functions for Input/Output: I/O Functions.). + 2. Mark all translatable strings with a leading underscore (`_') + character. It _must_ be adjacent to the opening quote of the + string. For example: - If you supply both `--traditional' and `--posix' on the command - line, `--posix' will take precedence. `gawk' will also issue a - warning if both options are supplied. + print _"hello, world" + x = _"you goofed" + printf(_"Number of users is %d\n", nusers) -`-W re-interval' -`--re-interval' - Allow interval expressions (*note Regular Expression Operators: - Regexp Operators.), in regexps. Because interval expressions were - traditionally not available in `awk', `gawk' does not provide them - by default. This prevents old `awk' programs from breaking. + 3. If you are creating strings dynamically, you can still translate + them, using the `dcgettext' built-in function. -`-W source PROGRAM-TEXT' -`--source PROGRAM-TEXT' - Program source code is taken from the PROGRAM-TEXT. This option - allows you to mix source code in files with source code that you - enter on the command line. This is particularly useful when you - have library functions that you wish to use from your command line - programs (*note The `AWKPATH' Environment Variable: AWKPATH - Variable.). + message = nusers " users logged in" + message = dcgettext(message, "adminprog") + print message -`-W version' -`--version' - Prints version information for this particular copy of `gawk'. - This allows you to determine if your copy of `gawk' is up to date - with respect to whatever the Free Software Foundation is currently - distributing. It is also useful for bug reports (*note Reporting - Problems and Bugs: Bugs.). + Here, the call to `dcgettext' supplies a different text domain + (`"adminprog"') in which to find the message, but it uses the + default `"LC_MESSAGES"' category. - Any other options are flagged as invalid with a warning message, but -are otherwise ignored. + 4. During development, you might want to put the `.mo' file in a + private directory for testing. This is done with the + `bindtextdomain' built-in function: - In compatibility mode, as a special case, if the value of FS supplied -to the `-F' option is `t', then `FS' is set to the tab character -(`"\t"'). This is only true for `--traditional', and not for `--posix' -(*note Specifying How Fields are Separated: Field Separators.). + BEGIN { + TEXTDOMAIN = "guide" # our text domain + if (Testing) { + # where to find our files + bindtextdomain("testdir") + # joe is in charge of adminprog + bindtextdomain("../joe/testdir", "adminprog") + } + ... + } - The `-f' option may be used more than once on the command line. If -it is, `awk' reads its program source from all of the named files, as -if they had been concatenated together into one big file. This is -useful for creating libraries of `awk' functions. Useful functions can -be written once, and then retrieved from a standard place, instead of -having to be included into each individual program. - - You can type in a program at the terminal and still use library -functions, by specifying `-f /dev/tty'. `awk' will read a file from -the terminal to use as part of the `awk' program. After typing your -program, type `Control-d' (the end-of-file character) to terminate it. -(You may also use `-f -' to read program source from the standard -input, but then you will not be able to also use the standard input as a -source of data.) - Because it is clumsy using the standard `awk' mechanisms to mix -source file and command line `awk' programs, `gawk' provides the -`--source' option. This does not require you to pre-empt the standard -input for your source code, and allows you to easily mix command line -and library source code (*note The `AWKPATH' Environment Variable: -AWKPATH Variable.). + *Note A Simple Internationalization Example: I18N Example, for an +example program showing the steps necessary to create and use +translations from `awk'. - If no `-f' or `--source' option is specified, then `gawk' will use -the first non-option command line argument as the text of the program -source code. + +File: gawk.info, Node: Translator i18n, Next: I18N Example, Prev: Programmer i18n, Up: Internationalization - If the environment variable `POSIXLY_CORRECT' exists, then `gawk' -will behave in strict POSIX mode, exactly as if you had supplied the -`--posix' command line option. Many GNU programs look for this -environment variable to turn on strict POSIX mode. If you supply -`--lint' on the command line, and `gawk' turns on POSIX mode because of -`POSIXLY_CORRECT', then it will print a warning message indicating that -POSIX mode is in effect. +Translating `awk' Programs +========================== - You would typically set this variable in your shell's startup file. -For a Bourne compatible shell (such as Bash), you would add these lines -to the `.profile' file in your home directory. + Once a program's translatable strings have been marked, they must be +extracted to create the initial `.po' file. As part of translation, it +is often helpful to rearrange the order in which arguments to `printf' +are output. - POSIXLY_CORRECT=true - export POSIXLY_CORRECT + `gawk''s `--gen-po' command-line option extracts the messages and is +discussed next. After that, `printf''s ability to rearrange the order +for `printf' arguments at runtime is covered. - For a `csh' compatible shell,(1) you would add this line to the -`.login' file in your home directory. +* Menu: - setenv POSIXLY_CORRECT true +* String Extraction:: Extracting marked strings. +* Printf Ordering:: Rearranging `printf' arguments. +* I18N Portability:: `awk'-level portability issues. + + +File: gawk.info, Node: String Extraction, Next: Printf Ordering, Prev: Translator i18n, Up: Translator i18n + +Extracting Marked Strings +------------------------- + + Once your `awk' program is working, and all the strings have been +marked and you've set (and perhaps bound) the text domain, it is time +to produce translations. First, use the `--gen-po' command-line option +to create the initial `.po' file: + + $ gawk --gen-po -f guide.awk > guide.po + + When run with `--gen-po', `gawk' does not execute your program. +Instead, it parses it as usual and prints all marked strings to +standard output in the format of a GNU `gettext' Portable Object file. +Also included in the output are any constant strings that appear as the +first argument to `dcgettext'.(1) *Note A Simple Internationalization +Example: I18N Example, for the full list of steps to go through to +create and test translations for `guide'. ---------- Footnotes ---------- - (1) Not recommended. + (1) Eventually, the `xgettext' utility that comes with GNU `gettext' +will be taught to automatically run `gawk --gen-po' for `.awk' files, +freeing the translator from having to do it manually.  -File: gawk.info, Node: Other Arguments, Next: AWKPATH Variable, Prev: Options, Up: Invoking Gawk +File: gawk.info, Node: Printf Ordering, Next: I18N Portability, Prev: String Extraction, Up: Translator i18n -Other Command Line Arguments -============================ +Rearranging `printf' Arguments +------------------------------ - Any additional arguments on the command line are normally treated as -input files to be processed in the order specified. However, an -argument that has the form `VAR=VALUE', assigns the value VALUE to the -variable VAR--it does not specify a file at all. + Format strings for `printf' and `sprintf' (*note Using `printf' +Statements for Fancier Printing: Printf.) present a special problem +for translation. Consider the following:(1) - All these arguments are made available to your `awk' program in the -`ARGV' array (*note Built-in Variables::). Command line options and -the program text (if present) are omitted from `ARGV'. All other -arguments, including variable assignments, are included. As each -element of `ARGV' is processed, `gawk' sets the variable `ARGIND' to -the index in `ARGV' of the current element. + printf(_"String `%s' has %d characters\n", + string, length(string))) - The distinction between file name arguments and variable-assignment -arguments is made when `awk' is about to open the next input file. At -that point in execution, it checks the "file name" to see whether it is -really a variable assignment; if so, `awk' sets the variable instead of -reading a file. + A possible German translation for this might be: - Therefore, the variables actually receive the given values after all -previously specified files have been read. In particular, the values of -variables assigned in this fashion are _not_ available inside a `BEGIN' -rule (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.), since -such rules are run before `awk' begins scanning the argument list. + "%d Zeichen lang ist die Zeichenkette `%s'\n" - The variable values given on the command line are processed for -escape sequences (d.c.) (*note Escape Sequences::). + The problem should be obvious: the order of the format +specifications is different from the original! Even though `gettext' +can return the translated string at runtime, it cannot change the +argument order in the call to `printf'. - In some earlier implementations of `awk', when a variable assignment -occurred before any file names, the assignment would happen _before_ -the `BEGIN' rule was executed. `awk''s behavior was thus inconsistent; -some command line assignments were available inside the `BEGIN' rule, -while others were not. However, some applications came to depend upon -this "feature." When `awk' was changed to be more consistent, the `-v' -option was added to accommodate applications that depended upon the old -behavior. + To solve this problem, `printf' format specificiers may have an +additional optional element, which we call a "positional specifier". +For example: - The variable assignment feature is most useful for assigning to -variables such as `RS', `OFS', and `ORS', which control input and -output formats, before scanning the data files. It is also useful for -controlling state if multiple passes are needed over a data file. For -example: + "%2$d Zeichen lang ist die Zeichenkette `%1$s'\n" - awk 'pass == 1 { PASS 1 STUFF } - pass == 2 { PASS 2 STUFF }' pass=1 mydata pass=2 mydata + Here, the positional specifier consists of an integer count, which +indicates which argument to use, and a `$'. Counts are one-based, and +the format string itself is _not_ included. Thus, in the following +example, `string' is the first argument and `length(string)' is the +second. - Given the variable assignment feature, the `-F' option for setting -the value of `FS' is not strictly necessary. It remains for historical -compatibility. + $ gawk 'BEGIN { + > string = "Dont Panic" + > printf _"%2$d characters live in \"%1$s\"\n", + > string, length(string) + > }' + -| 10 characters live in "Dont Panic" + + If present, positional specifiers come first in the format +specification, before the flags, the field width, and/or the precision. + + Positional specifiers can be used with the dynamic field width and +precision capability: + + $ gawk 'BEGIN { + > printf("%*.*s\n", 10, 20, "hello") + > printf("%3$*2$.*1$s\n", 20, 10, "hello") + > }' + -| hello + -| hello + +*Note:* When using `*' with a positional specifier, the `*' comes +first, then the integer position, and then the `$'. This is somewhat +counter-intutive. + + `gawk' does not allow you to mix regular format specifiers and those +with positional specifiers in the same string: + + $ gawk 'BEGIN { printf _"%d %3$s\n", 1, 2, "hi" }' + error--> gawk: cmd. line:1: fatal: must use `count$' on all formats or none + + *Note:* There are some pathological cases that `gawk' may fail to +diagnose. In such cases, the output may not be what you expect. It's +still a bad idea to try mixing them, even if `gawk' doesn't detect it. + + Although positional specifiers can be used directly in `awk' +programs, their primary purpose is to help in producing correct +translations of format strings into languages different from the one in +which the program is first written. + + ---------- Footnotes ---------- + + (1) This example is borrowed from the GNU `gettext' manual.  -File: gawk.info, Node: AWKPATH Variable, Next: Obsolete, Prev: Other Arguments, Up: Invoking Gawk +File: gawk.info, Node: I18N Portability, Prev: Printf Ordering, Up: Translator i18n -The `AWKPATH' Environment Variable -================================== +`awk' Portability Issues +------------------------ - The previous section described how `awk' program files can be named -on the command line with the `-f' option. In most `awk' -implementations, you must supply a precise path name for each program -file, unless the file is in the current directory. + `gawk''s internationalization features were purposely chosen to have +as little impact as possible on the portability of `awk' programs that +use them to other versions of `awk'. Consider this program: - But in `gawk', if the file name supplied to the `-f' option does not -contain a `/', then `gawk' searches a list of directories (called the -"search path"), one by one, looking for a file with the specified name. + BEGIN { + TEXTDOMAIN = "guide" + if (Test_Guide) # set with -v + bindtextdomain("/test/guide/messages") + print _"don't panic!" + } - The search path is a string consisting of directory names separated -by colons. `gawk' gets its search path from the `AWKPATH' environment -variable. If that variable does not exist, `gawk' uses a default path, -which is `.:/usr/local/share/awk'.(1) (Programs written for use by -system administrators should use an `AWKPATH' variable that does not -include the current directory, `.'.) +As written, it won't work on other versions of `awk'. However, it is +actually almost portable, requiring very little change. - The search path feature is particularly useful for building up -libraries of useful `awk' functions. The library files can be placed -in a standard directory that is in the default path, and then specified -on the command line with a short file name. Otherwise, the full file -name would have to be typed for each file. + * Assignments to `TEXTDOMAIN' won't have any effect, since + `TEXTDOMAIN' is not special in other `awk' implementations. - By using both the `--source' and `-f' options, your command line -`awk' programs can use facilities in `awk' library files. *Note A -Library of `awk' Functions: Library Functions. + * Non-GNU versions of `awk' treat marked strings as the + concatenation of a variable named `_' with the string following + it.(1) Typically, the variable `_' has the null string (`""') as + its value, leaving the original string constant as the result. - Path searching is not done if `gawk' is in compatibility mode. This -is true for both `--traditional' and `--posix'. *Note Command Line -Options: Options. + * By defining "dummy" functions to replace `dcgettext' and + `bindtextdomain', the `awk' program can be made to run, but all + the messages are output in the original language. For example: - *Note:* if you want files in the current directory to be found, you -must include the current directory in the path, either by including `.' -explicitly in the path, or by writing a null entry in the path. (A -null entry is indicated by starting or ending the path with a colon, or -by placing two colons next to each other (`::').) If the current -directory is not included in the path, then files cannot be found in -the current directory. This path search mechanism is identical to the -shell's. + function bindtextdomain(dir, domain) + { + return dir + } + + function dcgettext(string, domain, category) + { + return string + } - Starting with version 3.0, if `AWKPATH' is not defined in the -environment, `gawk' will place its default search path into -`ENVIRON["AWKPATH"]'. This makes it easy to determine the actual search -path `gawk' will use. + * The use of positional specifications in `printf' or `sprintf' is + _not_ portable. To support `gettext' at the C level, many + systems' C versions of `sprintf' do support positional specifiers. + But it works only if enough arguments are supplied in the + function call. Many versions of `awk' pass `printf' formats and + arguments unchanged to the underlying C library version of + `sprintf', but only one format and argument at a time. What + happens if a positional specification is used is anybody's guess. + However, since the positional specifications are primarily for use + in _translated_ format strings, and since non-GNU `awk's never + retrieve the translated string, this should not be a problem in + practice. ---------- Footnotes ---------- - (1) Your version of `gawk' may use a different directory; it will -depend upon how `gawk' was built and installed. The actual directory -will be the value of `$(datadir)' generated when `gawk' was configured. -You probably don't need to worry about this though. + (1) This is good fodder for an "Obfuscated `awk'" contest.  -File: gawk.info, Node: Obsolete, Next: Undocumented, Prev: AWKPATH Variable, Up: Invoking Gawk +File: gawk.info, Node: I18N Example, Next: Gawk I18N, Prev: Translator i18n, Up: Internationalization -Obsolete Options and/or Features -================================ +A Simple Internationalization Example +===================================== - This section describes features and/or command line options from -previous releases of `gawk' that are either not available in the -current version, or that are still supported but deprecated (meaning -that they will _not_ be in the next release). + Now let's look at a step-by-step example of how to internationalize +and localize a simple `awk' program, using `guide.awk' as our original +source: - For version 3.0.6 of `gawk', there are no command line options or -other deprecated features from the previous version of `gawk'. This -node is thus essentially a place holder, in case some option becomes -obsolete in a future version of `gawk'. + BEGIN { + TEXTDOMAIN = "guide" + bindtextdomain(".") # for testing + print _"Don't Panic" + print _"The Answer Is", 42 + print "Pardon me, Zaphod who?" + } - -File: gawk.info, Node: Undocumented, Next: Known Bugs, Prev: Obsolete, Up: Invoking Gawk +Run `gawk --gen-po' to create the `.po' file: -Undocumented Options and Features -================================= + $ gawk --gen-po -f guide.awk > guide.po - Use the Source, Luke! - Obi-Wan +This produces: + + #: guide.awk:4 + msgid "Don't Panic" + msgstr "" + + #: guide.awk:5 + msgid "The Answer Is" + msgstr "" + + This original portable object file is saved and reused for each +language into which the application is translated. The `msgid' is the +original string and the `msgstr' is the translation. + + *Note:* Strings not marked with a leading underscore do not appear +in the `guide.po' file. + + Next, the messages must be translated. Here is a translation to a +hypothetical dialect of English, called "Mellow":(1) + $ cp guide.po guide-mellow.po + ADD TRANSLATIONS TO guide-mellow.po ... +Following are the translations: - This section intentionally left blank. + #: guide.awk:4 + msgid "Don't Panic" + msgstr "Hey man, relax!" + + #: guide.awk:5 + msgid "The Answer Is" + msgstr "Like, the scoop is" + + The next step is to make the directory to hold the binary message +object file and then to create the `guide.mo' file. The directory +layout shown here is standard for GNU `gettext' on GNU/Linux systems. +Other versions of `gettext' may use a different layout: + + $ mkdir en_US en_US/LC_MESSAGES + + The `msgfmt' utility does the conversion from human-readable `.po' +file to machine-readable `.mo' file. By default, `msgfmt' creates a +file named `messages'. This file must be renamed and placed in the +proper directory so that `gawk' can find it: + + $ msgfmt guide-mellow.po + $ mv messages en_US/LC_MESSAGES/guide.mo + + Finally, we run the program to test it: + + $ gawk -f guide.awk + -| Hey man, relax! + -| Like, the scoop is 42 + -| Pardon me, Zaphod who? + + If the two replacement functions for `dcgettext' and `bindtextdomain' +(*note `awk' Portability Issues: I18N Portability.) are in a file +named `libintl.awk', then we can run `guide.awk' unchanged as follows: + + $ gawk --posix -f guide.awk -f libintl.awk + -| Don't Panic + -| The Answer Is 42 + -| Pardon me, Zaphod who? + + ---------- Footnotes ---------- + + (1) Perhaps it would be better if it were called "Hippy." Ah, well.  -File: gawk.info, Node: Known Bugs, Prev: Undocumented, Up: Invoking Gawk +File: gawk.info, Node: Gawk I18N, Prev: I18N Example, Up: Internationalization -Known Bugs in `gawk' -==================== +`gawk' Can Speak Your Language +============================== - * The `-F' option for changing the value of `FS' (*note Command Line - Options: Options.) is not necessary given the command line - variable assignment feature; it remains only for backwards - compatibility. + As of version 3.1, `gawk' itself has been internationalized using +the GNU `gettext' package. (GNU `gettext' is described in complete +detail in *Note Top::.) As of this writing, the latest version of GNU +`gettext' is version 0.10.37 +(ftp://gnudist.gnu.org/gnu/gettext/gettext-0.10.37.tar.gz). - * If your system actually has support for `/dev/fd' and the - associated `/dev/stdin', `/dev/stdout', and `/dev/stderr' files, - you may get different output from `gawk' than you would get on a - system without those files. When `gawk' interprets these files - internally, it synchronizes output to the standard output with - output to `/dev/stdout', while on a system with those files, the - output is actually to different open files (*note Special File - Names in `gawk': Special Files.). + If a translation of `gawk''s messages exists, then `gawk' produces +usage messages, warnings, and fatal errors in the local language. - * Syntactically invalid single character programs tend to overflow - the parse stack, generating a rather unhelpful message. Such - programs are surprisingly difficult to diagnose in the completely - general case, and the effort to do so really is not worth it. + On systems that do not use version 2 (or later) of the GNU C +library, you should configure `gawk' with the `--with-included-gettext' +option before compiling and installing it. *Note Additional +Configuration Options::, for more information.  -File: gawk.info, Node: Library Functions, Next: Sample Programs, Prev: Invoking Gawk, Up: Top +File: gawk.info, Node: Advanced Features, Next: Invoking Gawk, Prev: Internationalization, Up: Top -A Library of `awk' Functions -**************************** +Advanced Features of `gawk' +*************************** - This chapter presents a library of useful `awk' functions. The -sample programs presented later (*note Practical `awk' Programs: Sample -Programs.) use these functions. The functions are presented here in a -progression from simple to complex. + Write documentation as if whoever reads it is a violent psychopath + who knows where you live. + Steve English, as quoted by Peter Langston - *Note Extracting Programs from Texinfo Source Files: Extract Program, -presents a program that you can use to extract the source code for -these example library functions and programs from the Texinfo source -for this Info file. (This has already been done as part of the `gawk' -distribution.) + This major node discusses advanced features in `gawk'. It's a bit +of a "grab bag" of items that are otherwise unrelated to each other. +First, a command-line option allows `gawk' to recognize non-decimal +numbers in input data, not just in `awk' programs. Next, two-way I/O, +discussed briefly in earlier parts of this Info file, is described in +full detail, along with the basics of TCP/IP networking and BSD portal +files. Finally, `gawk' can "profile" an `awk' program, making it +possible to tune it for performance. - If you have written one or more useful, general purpose `awk' -functions, and would like to contribute them for a subsequent edition -of this Info file, please contact the author. *Note Reporting Problems -and Bugs: Bugs, for information on doing this. Don't just send code, -as you will be required to either place your code in the public domain, -publish it under the GPL (*note GNU GENERAL PUBLIC LICENSE: Copying.), -or assign the copyright in it to the Free Software Foundation. + *Note Adding New Built-in Functions to `gawk': Dynamic Extensions, +discusses the ability to dynamically add new built-in functions to +`gawk'. As this feature is still immature and likely to change, its +description is relegated to an appendix. * Menu: -* Portability Notes:: What to do if you don't have `gawk'. -* Nextfile Function:: Two implementations of a `nextfile' - function. -* Assert Function:: A function for assertions in `awk' - programs. -* Round Function:: A function for rounding if `sprintf' does - not do it correctly. -* Ordinal Functions:: Functions for using characters as numbers and - vice versa. -* Join Function:: A function to join an array into a string. -* Mktime Function:: A function to turn a date into a timestamp. -* Gettimeofday Function:: A function to get formatted times. -* Filetrans Function:: A function for handling data file transitions. -* Getopt Function:: A function for processing command line - arguments. -* Passwd Functions:: Functions for getting user information. -* Group Functions:: Functions for getting group information. -* Library Names:: How to best name private global variables in - library functions. +* Non-decimal Data:: Allowing non-decimal input data. +* Two-way I/O:: Two-way communications with another process. +* TCP/IP Networking:: Using `gawk' for network programming. +* Portal Files:: Using `gawk' with BSD portals. +* Profiling:: Profiling your `awk' programs.  -File: gawk.info, Node: Portability Notes, Next: Nextfile Function, Prev: Library Functions, Up: Library Functions +File: gawk.info, Node: Non-decimal Data, Next: Two-way I/O, Prev: Advanced Features, Up: Advanced Features -Simulating `gawk'-specific Features -=================================== +Allowing Non-Decimal Input Data +=============================== - The programs in this chapter and in *Note Practical `awk' Programs: -Sample Programs, freely use features that are specific to `gawk'. This -section briefly discusses how you can rewrite these programs for -different implementations of `awk'. + If you run `gawk' with the `--non-decimal-data' option, you can have +non-decimal constants in your input data: - Diagnostic error messages are sent to `/dev/stderr'. Use `| "cat -1>&2"' instead of `> "/dev/stderr"', if your system does not have a -`/dev/stderr', or if you cannot use `gawk'. + $ echo 0123 123 0x123 | + > gawk --non-decimal-data '{ printf "%d, %d, %d\n", + > $1, $2, $3 }' + -| 83, 123, 291 - A number of programs use `nextfile' (*note The `nextfile' Statement: -Nextfile Statement.), to skip any remaining input in the input file. -*Note Implementing `nextfile' as a Function: Nextfile Function, shows -you how to write a function that will do the same thing. + For this feature to work, write your program so that `gawk' treats +your data as numeric: - Finally, some of the programs choose to ignore upper-case and -lower-case distinctions in their input. They do this by assigning one -to `IGNORECASE'. You can achieve the same effect by adding the -following rule to the beginning of the program: + $ echo 0123 123 0x123 | gawk '{ print $1, $2, $3 }' + -| 0123 123 0x123 - # ignore case - { $0 = tolower($0) } +The `print' statement treats its expressions as strings. Although the +fields can act as numbers when necessary, they are still strings, so +`print' does not try to treat them numerically. You may need to add +zero to a field to force it to be treated as a number. For example: -Also, verify that all regexp and string constants used in comparisons -only use lower-case letters. + $ echo 0123 123 0x123 | gawk --non-decimal-data ' + > { print $1, $2, $3 + > print $1 + 0, $2 + 0, $3 + 0 }' + -| 0123 123 0x123 + -| 83 123 291 - -File: gawk.info, Node: Nextfile Function, Next: Assert Function, Prev: Portability Notes, Up: Library Functions + Because it is common to have decimal data with leading zeros, and +because using it could lead to surprising results, the default is to +leave this facility disabled. If you want it, you must explicitly +request it. -Implementing `nextfile' as a Function -===================================== + *Caution:* _Use of this option is not recommended._ It can break old +programs very badly. Instead, use the `strtonum' function to convert +your data (*note Octal and Hexadecimal Numbers: Non-decimal-numbers.). +This makes your programs easier to write and easier to read, and leads +to less surprising results. - The `nextfile' statement presented in *Note The `nextfile' -Statement: Nextfile Statement, is a `gawk'-specific extension. It is -not available in other implementations of `awk'. This section shows -two versions of a `nextfile' function that you can use to simulate -`gawk''s `nextfile' statement if you cannot use `gawk'. + +File: gawk.info, Node: Two-way I/O, Next: TCP/IP Networking, Prev: Non-decimal Data, Up: Advanced Features - Here is a first attempt at writing a `nextfile' function. +Two-Way Communications with Another Process +=========================================== - # nextfile --- skip remaining records in current file + From: brennan@whidbey.com (Mike Brennan) + Newsgroups: comp.lang.awk + Subject: Re: Learn the SECRET to Attract Women Easily + Date: 4 Aug 1997 17:34:46 GMT + Message-ID: <5s53rm$eca@news.whidbey.com> - # this should be read in before the "main" awk program + On 3 Aug 1997 13:17:43 GMT, Want More Dates??? + wrote: + >Learn the SECRET to Attract Women Easily + > + >The SCENT(tm) Pheromone Sex Attractant For Men to Attract Women - function nextfile() { _abandon_ = FILENAME; next } + The scent of awk programmers is a lot more attractive to women than + the scent of perl programmers. + -- + Mike Brennan + + It is often useful to be able to send data to a separate program for +processing and then read the result. This can always be done with +temporary files: + + # write the data for processing + tempfile = ("/tmp/mydata." PROCINFO["pid"]) + while (NOT DONE WITH DATA) + print DATA | ("subprogram > " tempfile) + close("subprogram > " tempfile) - _abandon_ == FILENAME { next } + # read the results, remove tempfile when done + while ((getline newdata < tempfile) > 0) + PROCESS newdata APPROPRIATELY + close(tempfile) + system("rm " tempfile) + +This works, but not elegantly. + + Starting with version 3.1 of `gawk', it is possible to open a +_two-way_ pipe to another process. The second process is termed a +"coprocess", since it runs in parallel with `gawk'. The two-way +connection is created using the new `|&' operator (borrowed from the +Korn Shell, `ksh'):(1) + + do { + print DATA |& "subprogram" + "subprogram" |& getline results + } while (DATA LEFT TO PROCESS) + close("subprogram") + + The first time an I/O operation is executed using the `|&' operator, +`gawk' creates a two-way pipeline to a child process that runs the +other program. Output created with `print' or `printf' is written to +the program's standard input, and output from the program's standard +output can be read by the `gawk' program using `getline'. As is the +case with processes started by `|', the subprogram can be any program, +or pipeline of programs, that can be started by the shell. + + There are some cautionary items to be aware of: + + * As the code inside `gawk' currently stands, the coprocess's + standard error goes to the same place that the parent `gawk''s + standard error goes. It is not possible to read the child's + standard error separately. + + * I/O buffering may be a problem. `gawk' automatically flushes all + output down the pipe to the child process. However, if the + coprocess does not flush its output, `gawk' may hang when doing a + `getline' in order to read the coprocess's results. This could + lead to a situation known as "deadlock", where each process is + waiting for the other one to do something. + + It is possible to close just one end of the two-way pipe to a +coprocess, by supplying a second argument to the `close' function of +either `"to"' or `"from"' (*note Closing Input and Output Redirections: +Close Files And Pipes.). These strings tell `gawk' to close the end of +the pipe that sends data to the process or the end that reads from it, +respectively. - This file should be included before the main program, because it -supplies a rule that must be executed first. This rule compares the -current data file's name (which is always in the `FILENAME' variable) -to a private variable named `_abandon_'. If the file name matches, -then the action part of the rule executes a `next' statement, to go on -to the next record. (The use of `_' in the variable name is a -convention. It is discussed more fully in *Note Naming Library -Function Global Variables: Library Names.) + This is particularly necessary in order to use the system `sort' +utility as part of a coprocess; `sort' must read _all_ of its input +data before it can produce any output. The `sort' program does not +receive an end-of-file indication until `gawk' closes the write end of +the pipe. - The use of the `next' statement effectively creates a loop that reads -all the records from the current data file. Eventually, the end of the -file is reached, and a new data file is opened, changing the value of -`FILENAME'. Once this happens, the comparison of `_abandon_' to -`FILENAME' fails, and execution continues with the first rule of the -"real" program. - - The `nextfile' function itself simply sets the value of `_abandon_' -and then executes a `next' statement to start the loop going.(1) - - This initial version has a subtle problem. What happens if the same -data file is listed _twice_ on the command line, one right after the -other, or even with just a variable assignment between the two -occurrences of the file name? + When you have finished writing data to the `sort' utility, you can +close the `"to"' end of the pipe, and then start reading sorted data +via `getline'. For example: - In such a case, this code will skip right through the file, a second -time, even though it should stop when it gets to the end of the first -occurrence. Here is a second version of `nextfile' that remedies this -problem. - - # nextfile --- skip remaining records in current file - # correctly handle successive occurrences of the same file - # Arnold Robbins, arnold@gnu.org, Public Domain - # May, 1993 - - # this should be read in before the "main" awk program + BEGIN { + command = "LC_ALL=C sort" + n = split("abcdefghijklmnopqrstuvwxyz", a, "") - function nextfile() { _abandon_ = FILENAME; next } + for (i = n; i > 0; i--) + print a[i] |& command + close(command, "to") - _abandon_ == FILENAME { - if (FNR == 1) - _abandon_ = "" - else - next + while ((command |& getline line) > 0) + print "got", line + close(command) } - The `nextfile' function has not changed. It sets `_abandon_' equal -to the current file name and then executes a `next' satement. The -`next' statement reads the next record and increments `FNR', so `FNR' -is guaranteed to have a value of at least two. However, if `nextfile' -is called for the last record in the file, then `awk' will close the -current data file and move on to the next one. Upon doing so, -`FILENAME' will be set to the name of the new file, and `FNR' will be -reset to one. If this next file is the same as the previous one, -`_abandon_' will still be equal to `FILENAME'. However, `FNR' will be -equal to one, telling us that this is a new occurrence of the file, and -not the one we were reading when the `nextfile' function was executed. -In that case, `_abandon_' is reset to the empty string, so that further -executions of this rule will fail (until the next time that `nextfile' -is called). - - If `FNR' is not one, then we are still in the original data file, -and the program executes a `next' statement to skip through it. - - An important question to ask at this point is: "Given that the -functionality of `nextfile' can be provided with a library file, why is -it built into `gawk'?" This is an important question. Adding features -for little reason leads to larger, slower programs that are harder to -maintain. - - The answer is that building `nextfile' into `gawk' provides -significant gains in efficiency. If the `nextfile' function is executed -at the beginning of a large data file, `awk' still has to scan the -entire file, splitting it up into records, just to skip over it. The -built-in `nextfile' can simply close the file immediately and proceed -to the next one, saving a lot of time. This is particularly important -in `awk', since `awk' programs are generally I/O bound (i.e. they -spend most of their time doing input and output, instead of performing -computations). + This program writes the letters of the alphabet in reverse order, one +per line, down the two-way pipe to `sort'. It then closes the write +end of the pipe, so that `sort' receives an end-of-file indication. +This causes `sort' to sort the data and write the sorted data back to +the `gawk' program. Once all of the data has been read, `gawk' +terminates the coprocess and exits. + + As a side note, the assignment `LC_ALL=C' in the `sort' command +ensures traditional Unix (ASCII) sorting from `sort'. ---------- Footnotes ---------- - (1) Some implementations of `awk' do not allow you to execute `next' -from within a function body. Some other work-around will be necessary -if you use such a version. + (1) This is very different from the same operator in the C shell, +`csh'.  -File: gawk.info, Node: Assert Function, Next: Round Function, Prev: Nextfile Function, Up: Library Functions +File: gawk.info, Node: TCP/IP Networking, Next: Portal Files, Prev: Two-way I/O, Up: Advanced Features -Assertions -========== +Using `gawk' for Network Programming +==================================== - When writing large programs, it is often useful to be able to know -that a condition or set of conditions is true. Before proceeding with a -particular computation, you make a statement about what you believe to -be the case. Such a statement is known as an "assertion." The C -language provides an `' header file and corresponding -`assert' macro that the programmer can use to make assertions. If an -assertion fails, the `assert' macro arranges to print a diagnostic -message describing the condition that should have been true but was -not, and then it kills the program. In C, using `assert' looks this: + `EMISTERED': A host is a host from coast to coast, + and no-one can talk to host that's close, + unless the host that isn't close + is busy hung or dead. - #include - - int myfunc(int a, double b) - { - assert(a <= 5 && b >= 17); - ... - } + In addition to being able to open a two-way pipeline to a coprocess +on the same system (*note Two-Way Communications with Another Process: +Two-way I/O.), it is possible to make a two-way connection to another +process on another system across an IP networking connection. - If the assertion failed, the program would print a message similar to -this: + You can think of this as just a _very long_ two-way pipeline to a +coprocess. The way `gawk' decides that you want to use TCP/IP +networking is by recognizing special file names that begin with +`/inet/'. - prog.c:5: assertion failed: a <= 5 && b >= 17 + The full syntax of the special file name is +`/inet/PROTOCOL/LOCAL-PORT/REMOTE-HOST/REMOTE-PORT'. The meaning of +the components are: - The ANSI C language makes it possible to turn the condition into a -string for use in printing the diagnostic message. This is not -possible in `awk', so this `assert' function also requires a string -version of the condition that is being tested. +PROTOCOL + The protocol to use over IP. This must be either `tcp', `udp', or + `raw', for a TCP, UDP, or raw IP connection, respectively. The + use of TCP is recommended for most applications. - # assert --- assert that a condition is true. Otherwise exit. - # Arnold Robbins, arnold@gnu.org, Public Domain - # May, 1993 - - function assert(condition, string) - { - if (! condition) { - printf("%s:%d: assertion failed: %s\n", - FILENAME, FNR, string) > "/dev/stderr" - _assert_exit = 1 - exit 1 - } - } - - END { - if (_assert_exit) - exit 1 - } + *Caution:* The use of raw sockets is not currently supported in + version 3.1 of `gawk'. - The `assert' function tests the `condition' parameter. If it is -false, it prints a message to standard error, using the `string' -parameter to describe the failed condition. It then sets the variable -`_assert_exit' to one, and executes the `exit' statement. The `exit' -statement jumps to the `END' rule. If the `END' rules finds -`_assert_exit' to be true, then it exits immediately. +LOCAL-PORT + The local TCP or UDP port number to use. Use a port number of `0' + when you want the system to pick a port. This is what you should do + when writing a TCP or UDP client. You may also use a well-known + service name, such as `smtp' or `http', in which case `gawk' + attempts to determine the pre-defined port number using the C + `getservbyname' function. - The purpose of the `END' rule with its test is to keep any other -`END' rules from running. When an assertion fails, the program should -exit immediately. If no assertions fail, then `_assert_exit' will -still be false when the `END' rule is run normally, and the rest of the -program's `END' rules will execute. For all of this to work correctly, -`assert.awk' must be the first source file read by `awk'. +REMOTE-HOST + The IP address or fully-qualified domain name of the Internet host + to which you want to connect. - You would use this function in your programs this way: +REMOTE-PORT + The TCP or UDP port number to use on the given REMOTE-HOST. + Again, use `0' if you don't care, or else a well-known service + name. - function myfunc(a, b) - { - assert(a <= 5 && b >= 17, "a <= 5 && b >= 17") - ... - } + Consider the following very simple example: -If the assertion failed, you would see a message like this: + BEGIN { + Service = "/inet/tcp/0/localhost/daytime" + Service |& getline + print $0 + close(Service) + } - mydata:1357: assertion failed: a <= 5 && b >= 17 + This program reads the current date and time from the local system's +TCP `daytime' server. It then prints the results and closes the +connection. - There is a problem with this version of `assert', that it may not be -possible to work around with standard `awk'. An `END' rule is -automatically added to the program calling `assert'. Normally, if a -program consists of just a `BEGIN' rule, the input files and/or -standard input are not read. However, now that the program has an `END' -rule, `awk' will attempt to read the input data files, or standard input -(*note Startup and Cleanup Actions: Using BEGIN/END.), most likely -causing the program to hang, waiting for input. + Because this topic is extensive, the use of `gawk' for TCP/IP +programming is documented separately. *Note Top::, for a much more +complete introduction and discussion, as well as extensive examples.  -File: gawk.info, Node: Round Function, Next: Ordinal Functions, Prev: Assert Function, Up: Library Functions +File: gawk.info, Node: Portal Files, Next: Profiling, Prev: TCP/IP Networking, Up: Advanced Features -Rounding Numbers -================ +Using `gawk' with BSD Portals +============================= - The way `printf' and `sprintf' (*note Using `printf' Statements for -Fancier Printing: Printf.) do rounding will often depend upon the -system's C `sprintf' subroutine. On many machines, `sprintf' rounding -is "unbiased," which means it doesn't always round a trailing `.5' up, -contrary to naive expectations. In unbiased rounding, `.5' rounds to -even, rather than always up, so 1.5 rounds to 2 but 4.5 rounds to 4. -The result is that if you are using a format that does rounding (e.g., -`"%.0f"') you should check what your system does. The following -function does traditional rounding; it might be useful if your awk's -`printf' does unbiased rounding. + Similar to the `/inet' special files, if `gawk' is configured with +the `--enable-portals' option (*note Compiling `gawk' for Unix: Quick +Installation.), then `gawk' treats files whose pathnames begin with +`/p' as 4.4 BSD-style portals. - # round --- do normal rounding - # - # Arnold Robbins, arnold@gnu.org, August, 1996 - # Public Domain - - function round(x, ival, aval, fraction) - { - ival = int(x) # integer part, int() truncates - - # see if fractional part - if (ival == x) # no fraction - return x - - if (x < 0) { - aval = -x # absolute value - ival = int(aval) - fraction = aval - ival - if (fraction >= .5) - return int(x) - 1 # -2.5 --> -3 - else - return int(x) # -2.3 --> -2 - } else { - fraction = x - ival - if (fraction >= .5) - return ival + 1 - else - return ival - } - } - - # test harness - { print $0, round($0) } + When used with the `|&' operator, `gawk' opens the file for two-way +communications. The operating system's portal mechanism then manages +creating the process associated with the portal and the corresponding +communications with the portal's process.  -File: gawk.info, Node: Ordinal Functions, Next: Join Function, Prev: Round Function, Up: Library Functions +File: gawk.info, Node: Profiling, Prev: Portal Files, Up: Advanced Features -Translating Between Characters and Numbers -========================================== +Profiling Your `awk' Programs +============================= - One commercial implementation of `awk' supplies a built-in function, -`ord', which takes a character and returns the numeric value for that -character in the machine's character set. If the string passed to -`ord' has more than one character, only the first one is used. + Beginning with version 3.1 of `gawk', you may produce execution +traces of your `awk' programs. This is done with a specially compiled +version of `gawk', called `pgawk' ("profiling `gawk'"). - The inverse of this function is `chr' (from the function of the same -name in Pascal), which takes a number and returns the corresponding -character. + `pgawk' is identical in every way to `gawk', except that when it has +finished running, it creates a profile of your program in a file named +`awkprof.out'. Because it is profiling, it also executes up to 45 +percent slower than `gawk' normally does. - Both functions can be written very nicely in `awk'; there is no real -reason to build them into the `awk' interpreter. + As shown in the following example, the `--profile' option can be +used to change the name of the file where `pgawk' will write the +profile: - # ord.awk --- do ord and chr - # - # Global identifiers: - # _ord_: numerical values indexed by characters - # _ord_init: function to initialize _ord_ - # - # Arnold Robbins - # arnold@gnu.org - # Public Domain - # 16 January, 1992 - # 20 July, 1992, revised - - BEGIN { _ord_init() } - - function _ord_init( low, high, i, t) - { - low = sprintf("%c", 7) # BEL is ascii 7 - if (low == "\a") { # regular ascii - low = 0 - high = 127 - } else if (sprintf("%c", 128 + 7) == "\a") { - # ascii, mark parity - low = 128 - high = 255 - } else { # ebcdic(!) - low = 0 - high = 255 - } - - for (i = low; i <= high; i++) { - t = sprintf("%c", i) - _ord_[t] = i - } - } + $ pgawk --profile=myprog.prof -f myprog.awk data1 data2 - Some explanation of the numbers used by `chr' is worthwhile. The -most prominent character set in use today is ASCII. Although an -eight-bit byte can hold 256 distinct values (from zero to 255), ASCII -only defines characters that use the values from zero to 127.(1) At -least one computer manufacturer that we know of uses ASCII, but with -mark parity, meaning that the leftmost bit in the byte is always one. -What this means is that on those systems, characters have numeric -values from 128 to 255. Finally, large mainframe systems use the -EBCDIC character set, which uses all 256 values. While there are other -character sets in use on some older systems, they are not really worth -worrying about. +In the above example, `pgawk' places the profile in `myprog.prof' +instead of in `awkprof.out'. - function ord(str, c) - { - # only first character is of interest - c = substr(str, 1, 1) - return _ord_[c] + Regular `gawk' also accepts this option. When called with just +`--profile', `gawk' "pretty prints" the program into `awkprof.out', +without any execution counts. You may supply an option to `--profile' +to change the file name. Here is a sample session showing a simple +`awk' program, its input data, and the results from running `pgawk'. +First, the `awk' program: + + BEGIN { print "First BEGIN rule" } + + END { print "First END rule" } + + /foo/ { + print "matched /foo/, gosh" + for (i = 1; i <= 3; i++) + sing() } - function chr(c) { - # force c to be numeric by adding 0 - return sprintf("%c", c + 0) + if (/foo/) + print "if is true" + else + print "else is true" } - #### test code #### - # BEGIN \ - # { - # for (;;) { - # printf("enter a character: ") - # if (getline var <= 0) - # break - # printf("ord(%s) = %d\n", var, ord(var)) - # } - # } - - An obvious improvement to these functions would be to move the code -for the `_ord_init' function into the body of the `BEGIN' rule. It was -written this way initially for ease of development. - - There is a "test program" in a `BEGIN' rule, for testing the -function. It is commented out for production use. - - ---------- Footnotes ---------- - - (1) ASCII has been extended in many countries to use the values from -128 to 255 for country-specific characters. If your system uses these -extensions, you can simplify `_ord_init' to simply loop from zero to -255. - - -File: gawk.info, Node: Join Function, Next: Mktime Function, Prev: Ordinal Functions, Up: Library Functions - -Merging an Array Into a String -============================== - - When doing string processing, it is often useful to be able to join -all the strings in an array into one long string. The following -function, `join', accomplishes this task. It is used later in several -of the application programs (*note Practical `awk' Programs: Sample -Programs.). - - Good function design is important; this function needs to be -general, but it should also have a reasonable default behavior. It is -called with an array and the beginning and ending indices of the -elements in the array to be merged. This assumes that the array -indices are numeric--a reasonable assumption since the array was likely -created with `split' (*note Built-in Functions for String Manipulation: -String Functions.). - - # join.awk --- join an array into a string - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 + BEGIN { print "Second BEGIN rule" } - function join(array, start, end, sep, result, i) + END { print "Second END rule" } + + function sing( dummy) { - if (sep == "") - sep = " " - else if (sep == SUBSEP) # magic value - sep = "" - result = array[start] - for (i = start + 1; i <= end; i++) - result = result sep array[i] - return result + print "I gotta be me!" } - An optional additional argument is the separator to use when joining -the strings back together. If the caller supplies a non-empty value, -`join' uses it. If it is not supplied, it will have a null value. In -this case, `join' uses a single blank as a default separator for the -strings. If the value is equal to `SUBSEP', then `join' joins the -strings with no separator between them. `SUBSEP' serves as a "magic" -value to indicate that there should be no separation between the -component strings. - - It would be nice if `awk' had an assignment operator for -concatenation. The lack of an explicit operator for concatenation -makes string operations more difficult than they really need to be. + Following is the input data: - -File: gawk.info, Node: Mktime Function, Next: Gettimeofday Function, Prev: Join Function, Up: Library Functions + foo + bar + baz + foo + junk -Turning Dates Into Timestamps -============================= + Here is the `awkprof.out' that results from running `pgawk' on this +program and data. (This example also illustrates that `awk' +programmers sometimes have to work late.): - The `systime' function built in to `gawk' returns the current time -of day as a timestamp in "seconds since the Epoch." This timestamp can -be converted into a printable date of almost infinitely variable format -using the built-in `strftime' function. (For more information on -`systime' and `strftime', *note Functions for Dealing with Time Stamps: -Time Functions..) - - An interesting but difficult problem is to convert a readable -representation of a date back into a timestamp. The ANSI C library -provides a `mktime' function that does the basic job, converting a -canonical representation of a date into a timestamp. - - It would appear at first glance that `gawk' would have to supply a -`mktime' built-in function that was simply a "hook" to the C language -version. In fact though, `mktime' can be implemented entirely in -`awk'.(1) - - Here is a version of `mktime' for `awk'. It takes a simple -representation of the date and time, and converts it into a timestamp. - - The code is presented here intermixed with explanatory prose. In -*Note Extracting Programs from Texinfo Source Files: Extract Program, -you will see how the Texinfo source file for this Info file can be -processed to extract the code into a single source file. - - The program begins with a descriptive comment and a `BEGIN' rule -that initializes a table `_tm_months'. This table is a two-dimensional -array that has the lengths of the months. The first index is zero for -regular years, and one for leap years. The values are the same for all -the months in both kinds of years, except for February; thus the use of -multiple assignment. - - # mktime.awk --- convert a canonical date representation - # into a timestamp - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 + # gawk profile, created Sun Aug 13 00:00:15 2000 - BEGIN \ - { - # Initialize table of month lengths - _tm_months[0,1] = _tm_months[1,1] = 31 - _tm_months[0,2] = 28; _tm_months[1,2] = 29 - _tm_months[0,3] = _tm_months[1,3] = 31 - _tm_months[0,4] = _tm_months[1,4] = 30 - _tm_months[0,5] = _tm_months[1,5] = 31 - _tm_months[0,6] = _tm_months[1,6] = 30 - _tm_months[0,7] = _tm_months[1,7] = 31 - _tm_months[0,8] = _tm_months[1,8] = 31 - _tm_months[0,9] = _tm_months[1,9] = 30 - _tm_months[0,10] = _tm_months[1,10] = 31 - _tm_months[0,11] = _tm_months[1,11] = 30 - _tm_months[0,12] = _tm_months[1,12] = 31 - } - - The benefit of merging multiple `BEGIN' rules (*note The `BEGIN' and -`END' Special Patterns: BEGIN/END.) is particularly clear when writing -library files. Functions in library files can cleanly initialize their -own private data and also provide clean-up actions in private `END' -rules. - - The next function is a simple one that computes whether a given year -is or is not a leap year. If a year is evenly divisible by four, but -not evenly divisible by 100, or if it is evenly divisible by 400, then -it is a leap year. Thus, 1904 was a leap year, 1900 was not, but 2000 -will be. - - # decide if a year is a leap year - function _tm_isleap(year, ret) - { - ret = (year % 4 == 0 && year % 100 != 0) || - (year % 400 == 0) + # BEGIN block(s) - return ret - } - - This function is only used a few times in this file, and its -computation could have been written "in-line" (at the point where it's -used). Making it a separate function made the original development -easier, and also avoids the possibility of typing errors when -duplicating the code in multiple places. - - The next function is more interesting. It does most of the work of -generating a timestamp, which is converting a date and time into some -number of seconds since the Epoch. The caller passes an array (rather -imaginatively named `a') containing six values: the year including -century, the month as a number between one and 12, the day of the -month, the hour as a number between zero and 23, the minute in the -hour, and the seconds within the minute. - - The function uses several local variables to precompute the number of -seconds in an hour, seconds in a day, and seconds in a year. Often, -similar C code simply writes out the expression in-line, expecting the -compiler to do "constant folding". E.g., most C compilers would turn -`60 * 60' into `3600' at compile time, instead of recomputing it every -time at run time. Precomputing these values makes the function more -efficient. - - # convert a date into seconds - function _tm_addup(a, total, yearsecs, daysecs, - hoursecs, i, j) - { - hoursecs = 60 * 60 - daysecs = 24 * hoursecs - yearsecs = 365 * daysecs + BEGIN { + 1 print "First BEGIN rule" + 1 print "Second BEGIN rule" + } + + # Rule(s) + + 5 /foo/ { # 2 + 2 print "matched /foo/, gosh" + 6 for (i = 1; i <= 3; i++) { + 6 sing() + } + } - total = (a[1] - 1970) * yearsecs + 5 { + 5 if (/foo/) { # 2 + 2 print "if is true" + 3 } else { + 3 print "else is true" + } + } - # extra day for leap years - for (i = 1970; i < a[1]; i++) - if (_tm_isleap(i)) - total += daysecs + # END block(s) - j = _tm_isleap(a[1]) - for (i = 1; i < a[2]; i++) - total += _tm_months[j, i] * daysecs + END { + 1 print "First END rule" + 1 print "Second END rule" + } - total += (a[3] - 1) * daysecs - total += a[4] * hoursecs - total += a[5] * 60 - total += a[6] + # Functions, listed alphabetically - return total + 6 function sing(dummy) + { + 6 print "I gotta be me!" + } + + The previous example illustrates many of the basic rules for +profiling output. The rules are as follows: + + * The program is printed in the order `BEGIN' rule, pattern/action + rules, `END' rule and functions, listed alphabetically. Multiple + `BEGIN' and `END' rules are merged together. + + * Pattern-action rules have two counts. The first count, to the + left of the rule, shows how many times the rule's pattern was + _tested_. The second count, to the right of the rule's opening + left brace in a comment, shows how many times the rule's action + was _executed_. The difference between the two indicates how many + times the rule's pattern evaluated to false. + + * Similarly, the count for an `if'-`else' statement shows how many + times the condition was tested. To the right of the opening left + brace for the `if''s body is a count showing how many times the + condition was true. The count for the `else' indicates how many + times the test failed. + + * The count for a loop header (such as `for' or `while') shows how + many times the loop test was executed. (Because of this, you + can't just look at the count on the first statement in a rule to + determine how many times the rule was executed. If the first + statement is a loop, the count is misleading.) + + * For user-defined functions, the count next to the `function' + keyword indicates how many times the function was called. The + counts next to the statements in the body show how many times + those statements were executed. + + * The layout uses "K&R" style using tabs. Braces are used + everywhere, even when the body of an `if', `else', or loop is only + a single statement. + + * Parentheses are used only where needed, as indicated by the + structure of the program and the precedence rules. For example, + `(3 + 5) * 4' means add three plus five, then multiply the total + by four. However, `3 + 5 * 4' has no parentheses, and means `3 + + (5 * 4)'. + + * All string concatenations are parenthesized too. (This could be + made a bit smarter.) + + * Parentheses are used around the arguments to `print' and `printf' + only when the `print' or `printf' statement is followed by a + redirection. Similarly, if the target of a redirection isn't a + scalar, it gets parenthesized. + + * `pgawk' supplies leading comments in front of the `BEGIN' and + `END' rules, the pattern/action rules, and the functions. + + + The profiled version of your program may not look exactly like what +you typed when you wrote it. This is because `pgawk' creates the +profiled version by "pretty printing" its internal representation of +the program. The advantage to this is that `pgawk' can produce a +standard representation. The disadvantage is that all source code +comments are lost, as are the distinctions among multiple `BEGIN' and +`END' rules. Also, things such as: + + /foo/ + +come out as: + + /foo/ { + print $0 } - The function starts with a first approximation of all the seconds -between Midnight, January 1, 1970,(2) and the beginning of the current -year. It then goes through all those years, and for every leap year, -adds an additional day's worth of seconds. +which is correct, but possibly surprising. - The variable `j' holds either one or zero, if the current year is or -is not a leap year. For every month in the current year prior to the -current month, it adds the number of seconds in the month, using the -appropriate entry in the `_tm_months' array. + Besides creating profiles when a program has completed, `pgawk' can +produce a profile while it is running. This is useful if your `awk' +program goes into an infinite loop and you want to see what has been +executed. To use this feature, run `pgawk' in the background: - Finally, it adds in the seconds for the number of days prior to the -current day, and the number of hours, minutes, and seconds in the -current day. + $ pgawk -f myprog & + [1] 13992 - The result is a count of seconds since January 1, 1970. This value -is not yet what is needed though. The reason why is described shortly. +The shell prints a job number and process ID number, in this case, +13992. Use the `kill' command to send the `USR1' signal to `pgawk': - The main `mktime' function takes a single character string argument. -This string is a representation of a date and time in a "canonical" -(fixed) form. This string should be `"YEAR MONTH DAY HOUR MINUTE -SECOND"'. + $ kill -USR1 13992 - # mktime --- convert a date into seconds, - # compensate for time zone - - function mktime(str, res1, res2, a, b, i, j, t, diff) - { - i = split(str, a, " ") # don't rely on FS - - if (i != 6) - return -1 - - # force numeric - for (j in a) - a[j] += 0 - - # validate - if (a[1] < 1970 || - a[2] < 1 || a[2] > 12 || - a[3] < 1 || a[3] > 31 || - a[4] < 0 || a[4] > 23 || - a[5] < 0 || a[5] > 59 || - a[6] < 0 || a[6] > 60 ) - return -1 - - res1 = _tm_addup(a) - t = strftime("%Y %m %d %H %M %S", res1) - - if (_tm_debug) - printf("(%s) -> (%s)\n", str, t) > "/dev/stderr" - - split(t, b, " ") - res2 = _tm_addup(b) - - diff = res1 - res2 - - if (_tm_debug) - printf("diff = %d seconds\n", diff) > "/dev/stderr" - - res1 += diff - - return res1 - } +As usual, the profiled version of the program is written to +`awkprof.out', or to a different file if you use the `--profile' option. - The function first splits the string into an array, using spaces and -tabs as separators. If there are not six elements in the array, it -returns an error, signaled as the value -1. Next, it forces each -element of the array to be numeric, by adding zero to it. The -following `if' statement then makes sure that each element is within an -allowable range. (This checking could be extended further, e.g., to -make sure that the day of the month is within the correct range for the -particular month supplied.) All of this is essentially preliminary -set-up and error checking. - - Recall that `_tm_addup' generated a value in seconds since Midnight, -January 1, 1970. This value is not directly usable as the result we -want, _since the calculation does not account for the local timezone_. -In other words, the value represents the count in seconds since the -Epoch, but only for UTC (Universal Coordinated Time). If the local -timezone is east or west of UTC, then some number of hours should be -either added to, or subtracted from the resulting timestamp. - - For example, 6:23 p.m. in Atlanta, Georgia (USA), is normally five -hours west of (behind) UTC. It is only four hours behind UTC if -daylight savings time is in effect. If you are calling `mktime' in -Atlanta, with the argument `"1993 5 23 18 23 12"', the result from -`_tm_addup' will be for 6:23 p.m. UTC, which is only 2:23 p.m. in -Atlanta. It is necessary to add another four hours worth of seconds to -the result. - - How can `mktime' determine how far away it is from UTC? This is -surprisingly easy. The returned timestamp represents the time passed to -`mktime' _as UTC_. This timestamp can be fed back to `strftime', which -will format it as a _local_ time; i.e. as if it already had the UTC -difference added in to it. This is done by giving -`"%Y %m %d %H %M %S"' to `strftime' as the format argument. It returns -the computed timestamp in the original string format. The result -represents a time that accounts for the UTC difference. When the new -time is converted back to a timestamp, the difference between the two -timestamps is the difference (in seconds) between the local timezone -and UTC. This difference is then added back to the original result. -An example demonstrating this is presented below. - - Finally, there is a "main" program for testing the function. + Along with the regular profile, as shown earlier, the profile +includes a trace of any active functions: - BEGIN { - if (_tm_test) { - printf "Enter date as yyyy mm dd hh mm ss: " - getline _tm_test_date - t = mktime(_tm_test_date) - r = strftime("%Y %m %d %H %M %S", t) - printf "Got back (%s)\n", r - } - } + # Function Call Stack: + + # 3. baz + # 2. bar + # 1. foo + # -- main -- - The entire program uses two variables that can be set on the command -line to control debugging output and to enable the test in the final -`BEGIN' rule. Here is the result of a test run. (Note that debugging -output is to standard error, and test output is to standard output.) - - $ gawk -f mktime.awk -v _tm_test=1 -v _tm_debug=1 - -| Enter date as yyyy mm dd hh mm ss: 1993 5 23 15 35 10 - error--> (1993 5 23 15 35 10) -> (1993 05 23 11 35 10) - error--> diff = 14400 seconds - -| Got back (1993 05 23 15 35 10) - - The time entered was 3:35 p.m. (15:35 on a 24-hour clock), on May -23, 1993. The first line of debugging output shows the resulting time -as UTC--four hours ahead of the local time zone. The second line shows -that the difference is 14400 seconds, which is four hours. (The -difference is only four hours, since daylight savings time is in effect -during May.) The final line of test output shows that the timezone -compensation algorithm works; the returned time is the same as the -entered time. - - This program does not solve the general problem of turning an -arbitrary date representation into a timestamp. That problem is very -involved. However, the `mktime' function provides a foundation upon -which to build. Other software can convert month names into numeric -months, and AM/PM times into 24-hour clocks, to generate the -"canonical" format that `mktime' requires. + You may send `pgawk' the `USR1' signal as many times as you like. +Each time, the profile and function call trace are appended to the +output profile file. - ---------- Footnotes ---------- + If you use the `HUP' signal instead of the `USR1' signal, `pgawk' +produces the profile and the function call trace, and then exits. - (1) July, 2000: Actually, I was mistaken when I wrote this. The -version presented here doesn't always work correctly, and the next -major version of `gawk' will provide `mktime' as a built-in function. + +File: gawk.info, Node: Invoking Gawk, Next: Library Functions, Prev: Advanced Features, Up: Top - (2) This is the Epoch on POSIX systems. It may be different on -other systems. +Running `awk' and `gawk' +************************ - -File: gawk.info, Node: Gettimeofday Function, Next: Filetrans Function, Prev: Mktime Function, Up: Library Functions + This major node covers how to run awk, both POSIX-standard and +`gawk'-specific command-line options, and what `awk' and `gawk' do with +non-option arguments. It then proceeds to cover how `gawk' searches +for source files, obsolete options and/or features, and known bugs in +`gawk'. This major node rounds out the discussion of `awk' as a +program and as a language. -Managing the Time of Day -======================== + While a number of the options and features described here were +discussed in passing earlier in the book, this major node provides the +full details. - The `systime' and `strftime' functions described in *Note Functions -for Dealing with Time Stamps: Time Functions, provide the minimum -functionality necessary for dealing with the time of day in human -readable form. While `strftime' is extensive, the control formats are -not necessarily easy to remember or intuitively obvious when reading a -program. +* Menu: - The following function, `gettimeofday', populates a user-supplied -array with pre-formatted time information. It returns a string with -the current time formatted in the same way as the `date' utility. +* Command Line:: How to run `awk'. +* Options:: Command-line options and their meanings. +* Other Arguments:: Input file names and variable assignments. +* AWKPATH Variable:: Searching directories for `awk' + programs. +* Obsolete:: Obsolete Options and/or features. +* Undocumented:: Undocumented Options and Features. +* Known Bugs:: Known Bugs in `gawk'. - # gettimeofday --- get the time of day in a usable format - # Arnold Robbins, arnold@gnu.org, Public Domain, May 1993 - # - # Returns a string in the format of output of date(1) - # Populates the array argument time with individual values: - # time["second"] -- seconds (0 - 59) - # time["minute"] -- minutes (0 - 59) - # time["hour"] -- hours (0 - 23) - # time["althour"] -- hours (0 - 12) - # time["monthday"] -- day of month (1 - 31) - # time["month"] -- month of year (1 - 12) - # time["monthname"] -- name of the month - # time["shortmonth"] -- short name of the month - # time["year"] -- year within century (0 - 99) - # time["fullyear"] -- year with century (19xx or 20xx) - # time["weekday"] -- day of week (Sunday = 0) - # time["altweekday"] -- day of week (Monday = 0) - # time["weeknum"] -- week number, Sunday first day - # time["altweeknum"] -- week number, Monday first day - # time["dayname"] -- name of weekday - # time["shortdayname"] -- short name of weekday - # time["yearday"] -- day of year (0 - 365) - # time["timezone"] -- abbreviation of timezone name - # time["ampm"] -- AM or PM designation - - function gettimeofday(time, ret, now, i) - { - # get time once, avoids unnecessary system calls - now = systime() - - # return date(1)-style output - ret = strftime("%a %b %d %H:%M:%S %Z %Y", now) - - # clear out target array - for (i in time) - delete time[i] - - # fill in values, force numeric values to be - # numeric by adding 0 - time["second"] = strftime("%S", now) + 0 - time["minute"] = strftime("%M", now) + 0 - time["hour"] = strftime("%H", now) + 0 - time["althour"] = strftime("%I", now) + 0 - time["monthday"] = strftime("%d", now) + 0 - time["month"] = strftime("%m", now) + 0 - time["monthname"] = strftime("%B", now) - time["shortmonth"] = strftime("%b", now) - time["year"] = strftime("%y", now) + 0 - time["fullyear"] = strftime("%Y", now) + 0 - time["weekday"] = strftime("%w", now) + 0 - time["altweekday"] = strftime("%u", now) + 0 - time["dayname"] = strftime("%A", now) - time["shortdayname"] = strftime("%a", now) - time["yearday"] = strftime("%j", now) + 0 - time["timezone"] = strftime("%Z", now) - time["ampm"] = strftime("%p", now) - time["weeknum"] = strftime("%U", now) + 0 - time["altweeknum"] = strftime("%W", now) + 0 - - return ret - } + +File: gawk.info, Node: Command Line, Next: Options, Prev: Invoking Gawk, Up: Invoking Gawk - The string indices are easier to use and read than the various -formats required by `strftime'. The `alarm' program presented in *Note -An Alarm Clock Program: Alarm Program, uses this function. +Invoking `awk' +============== - The `gettimeofday' function is presented above as it was written. A -more general design for this function would have allowed the user to -supply an optional timestamp value that would have been used instead of -the current time. + There are two ways to run `awk'--with an explicit program or with +one or more program files. Here are templates for both of them; items +enclosed in [...] in these templates are optional: - -File: gawk.info, Node: Filetrans Function, Next: Getopt Function, Prev: Gettimeofday Function, Up: Library Functions + awk [OPTIONS] -f progfile [`--'] FILE ... + awk [OPTIONS] [`--'] 'PROGRAM' FILE ... -Noting Data File Boundaries -=========================== + Besides traditional one-letter POSIX-style options, `gawk' also +supports GNU long options. - The `BEGIN' and `END' rules are each executed exactly once, at the -beginning and end respectively of your `awk' program (*note The `BEGIN' -and `END' Special Patterns: BEGIN/END.). We (the `gawk' authors) once -had a user who mistakenly thought that the `BEGIN' rule was executed at -the beginning of each data file and the `END' rule was executed at the -end of each data file. When informed that this was not the case, the -user requested that we add new special patterns to `gawk', named -`BEGIN_FILE' and `END_FILE', that would have the desired behavior. He -even supplied us the code to do so. - - However, after a little thought, I came up with the following -library program. It arranges to call two user-supplied functions, -`beginfile' and `endfile', at the beginning and end of each data file. -Besides solving the problem in only nine(!) lines of code, it does so -_portably_; this will work with any implementation of `awk'. + It is possible to invoke `awk' with an empty program: - # transfile.awk - # - # Give the user a hook for filename transitions - # - # The user must supply functions beginfile() and endfile() - # that each take the name of the file being started or - # finished, respectively. - # - # Arnold Robbins, arnold@gnu.org, January 1992 - # Public Domain - - FILENAME != _oldfilename \ - { - if (_oldfilename != "") - endfile(_oldfilename) - _oldfilename = FILENAME - beginfile(FILENAME) - } - - END { endfile(FILENAME) } + awk '' datafile1 datafile2 - This file must be loaded before the user's "main" program, so that -the rule it supplies will be executed first. +Doing so makes little sense though; `awk' exits silently when given an +empty program. (d.c.) If `--lint' has been specified on the +command-line, `gawk' issues a warning that the program is empty. - This rule relies on `awk''s `FILENAME' variable that automatically -changes for each new data file. The current file name is saved in a -private variable, `_oldfilename'. If `FILENAME' does not equal -`_oldfilename', then a new data file is being processed, and it is -necessary to call `endfile' for the old file. Since `endfile' should -only be called if a file has been processed, the program first checks -to make sure that `_oldfilename' is not the null string. The program -then assigns the current file name to `_oldfilename', and calls -`beginfile' for the file. Since, like all `awk' variables, -`_oldfilename' will be initialized to the null string, this rule -executes correctly even for the first data file. + +File: gawk.info, Node: Options, Next: Other Arguments, Prev: Command Line, Up: Invoking Gawk - The program also supplies an `END' rule, to do the final processing -for the last file. Since this `END' rule comes before any `END' rules -supplied in the "main" program, `endfile' will be called first. Once -again the value of multiple `BEGIN' and `END' rules should be clear. +Command-Line Options +==================== - This version has same problem as the first version of `nextfile' -(*note Implementing `nextfile' as a Function: Nextfile Function.). If -the same data file occurs twice in a row on command line, then -`endfile' and `beginfile' will not be executed at the end of the first -pass and at the beginning of the second pass. This version solves the -problem. + Options begin with a dash and consist of a single character. +GNU-style long options consist of two dashes and a keyword. The +keyword can be abbreviated, as long as the abbreviation allows the +option to be uniquely identified. If the option takes an argument, +then the keyword is either immediately followed by an equals sign (`=') +and the argument's value, or the keyword and the argument's value are +separated by whitespace. If a particular option with a value is given +more than once, it is the last value that counts. - # ftrans.awk --- handle data file transitions - # - # user supplies beginfile() and endfile() functions - # - # Arnold Robbins, arnold@gnu.org, November 1992 - # Public Domain - - FNR == 1 { - if (_filename_ != "") - endfile(_filename_) - _filename_ = FILENAME - beginfile(FILENAME) - } - - END { endfile(_filename_) } + Each long option for `gawk' has a corresponding POSIX-style option. +The long and short options are interchangeable in all contexts. The +options and their meanings are as follows: - In *Note Counting Things: Wc Program, you will see how this library -function can be used, and how it simplifies writing the main program. +`-F FS' +`--field-separator FS' + Sets the `FS' variable to FS (*note Specifying How Fields Are + Separated: Field Separators.). - -File: gawk.info, Node: Getopt Function, Next: Passwd Functions, Prev: Filetrans Function, Up: Library Functions +`-f SOURCE-FILE' +`--file SOURCE-FILE' + Indicates that the `awk' program is to be found in SOURCE-FILE + instead of in the first non-option argument. -Processing Command Line Options -=============================== +`-v VAR=VAL' +`--assign VAR=VAL' + Sets the variable VAR to the value VAL _before_ execution of the + program begins. Such variable values are available inside the + `BEGIN' rule (*note Other Command-Line Arguments: Other + Arguments.). - Most utilities on POSIX compatible systems take options or -"switches" on the command line that can be used to change the way a -program behaves. `awk' is an example of such a program (*note Command -Line Options: Options.). Often, options take "arguments", data that -the program needs to correctly obey the command line option. For -example, `awk''s `-F' option requires a string to use as the field -separator. The first occurrence on the command line of either `--' or a -string that does not begin with `-' ends the options. - - Most Unix systems provide a C function named `getopt' for processing -command line arguments. The programmer provides a string describing -the one letter options. If an option requires an argument, it is -followed in the string with a colon. `getopt' is also passed the count -and values of the command line arguments, and is called in a loop. -`getopt' processes the command line arguments for option letters. Each -time around the loop, it returns a single character representing the -next option letter that it found, or `?' if it found an invalid option. -When it returns -1, there are no options left on the command line. + The `-v' option can only set one variable, but it can be used more + than once, setting another variable each time, like this: `awk + -v foo=1 -v bar=2 ...'. - When using `getopt', options that do not take arguments can be -grouped together. Furthermore, options that take arguments require -that the argument be present. The argument can immediately follow the -option letter, or it can be a separate command line argument. + *Caution:* Using `-v' to set the values of the built-in variables + may lead to surprising results. `awk' will reset the values of + those variables as it needs to, possibly ignoring any predefined + value you may have given. - Given a hypothetical program that takes three command line options, -`-a', `-b', and `-c', and `-b' requires an argument, all of the -following are valid ways of invoking the program: +`-mf N' +`-mr N' + Set various memory limits to the value N. The `f' flag sets the + maximum number of fields and the `r' flag sets the maximum record + size. These two flags and the `-m' option are from the Bell + Laboratories research version of Unix `awk'. They are provided + for compatibility but otherwise ignored by `gawk', since `gawk' + has no predefined limits. (The Bell Laboratories `awk' no longer + needs these options; it continues to accept them to avoid breaking + old programs.) - prog -a -b foo -c data1 data2 data3 - prog -ac -bfoo -- data1 data2 data3 - prog -acbfoo data1 data2 data3 +`-W GAWK-OPT' + Following the POSIX standard, implementation-specific options are + supplied as arguments to the `-W' option. These options also have + corresponding GNU-style long options. Note that the long options + may be abbreviated, as long as the abbreviations remain unique. + The full list of `gawk'-specific options is provided next. - Notice that when the argument is grouped with its option, the rest of -the command line argument is considered to be the option's argument. -In the above example, `-acbfoo' indicates that all of the `-a', `-b', -and `-c' options were supplied, and that `foo' is the argument to the -`-b' option. +`--' + Signals the end of the command-line options. The following + arguments are not treated as options even if they begin with `-'. + This interpretation of `--' follows the POSIX argument parsing + conventions. - `getopt' provides four external variables that the programmer can -use. + This is useful if you have file names that start with `-', or in + shell scripts, if you have file names that will be specified by + the user that could start with `-'. -`optind' - The index in the argument value array (`argv') where the first - non-option command line argument can be found. + The previous list described options mandated by the POSIX standard, +as well as options available in the Bell Laboratories version of `awk'. +The following list describes `gawk'-specific options: -`optarg' - The string value of the argument to an option. +`-W compat' +`-W traditional' +`--compat' +`--traditional' + Specifies "compatibility mode", in which the GNU extensions to the + `awk' language are disabled, so that `gawk' behaves just like the + Bell Laboratories research version of Unix `awk'. `--traditional' + is the preferred form of this option. *Note Extensions in `gawk' + Not in POSIX `awk': POSIX/GNU, which summarizes the extensions. + Also see *Note Downward Compatibility and Debugging: Compatibility + Mode. -`opterr' - Usually `getopt' prints an error message when it finds an invalid - option. Setting `opterr' to zero disables this feature. (An - application might wish to print its own error message.) +`-W copyright' +`--copyright' + Print the short version of the General Public License and then + exit. -`optopt' - The letter representing the command line option. While not - usually documented, most versions supply this variable. +`-W copyleft' +`--copyleft' + Just like `--copyright'. This option may disappear in a future + version of `gawk'. - The following C fragment shows how `getopt' might process command -line arguments for `awk'. +`-W dump-variables[=FILE]' +`--dump-variables[=FILE]' + Print a sorted list of global variables, their types, and final + values to FILE. If no FILE is provided, `gawk' prints this list + to a file named `awkvars.out' in the current directory. + + Having a list of all the global variables is a good way to look for + typographical errors in your programs. You would also use this + option if you have a large program with a lot of functions, and + you want to be sure that your functions don't inadvertently use + global variables that you meant to be local. (This is a + particularly easy mistake to make with simple variable names like + `i', `j', and so on.) + +`-W gen-po' +`--gen-po' + Analyze the source program and generate a GNU `gettext' Portable + Object file on standard output for all string constants that have + been marked for translation. *Note Internationalization with + `gawk': Internationalization, for information about this option. - int - main(int argc, char *argv[]) - { - ... - /* print our own message */ - opterr = 0; - while ((c = getopt(argc, argv, "v:f:F:W:")) != -1) { - switch (c) { - case 'f': /* file */ - ... - break; - case 'F': /* field separator */ - ... - break; - case 'v': /* variable assignment */ - ... - break; - case 'W': /* extension */ - ... - break; - case '?': - default: - usage(); - break; - } - } - ... - } +`-W help' +`-W usage' +`--help' +`--usage' + Print a "usage" message summarizing the short and long style + options that `gawk' accepts and then exit. - As a side point, `gawk' actually uses the GNU `getopt_long' function -to process both normal and GNU-style long options (*note Command Line -Options: Options.). +`-W lint[=fatal]' +`--lint[=fatal]' + Warn about constructs that are dubious or non-portable to other + `awk' implementations. Some warnings are issued when `gawk' first + reads your program. Others are issued at runtime, as your program + executes. With an optional argument of `fatal', lint warnings + become fatal errors. This may be drastic but its use will + certainly encourage the development of cleaner `awk' programs. - The abstraction provided by `getopt' is very useful, and would be -quite handy in `awk' programs as well. Here is an `awk' version of -`getopt'. This function highlights one of the greatest weaknesses in -`awk', which is that it is very poor at manipulating single characters. -Repeated calls to `substr' are necessary for accessing individual -characters (*note Built-in Functions for String Manipulation: String -Functions.). +`-W lint-old' +`--lint-old' + Warn about constructs that are not available in the original + version of `awk' from Version 7 Unix (*note Major Changes Between + V7 and SVR3.1: V7/SVR3.1.). - The discussion walks through the code a bit at a time. +`-W non-decimal-data' +`--non-decimal-data' + Enable automatic interpretation of octal and hexadecimal values in + input data (*note Allowing Non-Decimal Input Data: Non-decimal + Data.). - # getopt --- do C library getopt(3) function in awk - # - # arnold@gnu.org - # Public domain - # - # Initial version: March, 1991 - # Revised: May, 1993 - - # External variables: - # Optind -- index of ARGV for first non-option argument - # Optarg -- string value of argument to current option - # Opterr -- if non-zero, print our own diagnostic - # Optopt -- current option letter - - # Returns - # -1 at end of options - # ? for unrecognized option - # a character representing the current option - - # Private Data - # _opti index in multi-flag option, e.g., -abc + *Caution:* This option can severely break old programs. Use with + care. - The function starts out with some documentation: who wrote the code, -and when it was revised, followed by a list of the global variables it -uses, what the return values are and what they mean, and any global -variables that are "private" to this library function. Such -documentation is essential for any program, and particularly for -library functions. +`-W posix' +`--posix' + Operate in strict POSIX mode. This disables all `gawk' extensions + (just like `--traditional') and adds the following additional + restrictions: - function getopt(argc, argv, options, optl, thisopt, i) - { - optl = length(options) - if (optl == 0) # no options given - return -1 - - if (argv[Optind] == "--") { # all done - Optind++ - _opti = 0 - return -1 - } else if (argv[Optind] !~ /^-[^: \t\n\f\r\v\b]/) { - _opti = 0 - return -1 - } + * `\x' escape sequences are not recognized (*note Escape + Sequences::). - The function first checks that it was indeed called with a string of -options (the `options' parameter). If `options' has a zero length, -`getopt' immediately returns -1. + * Newlines do not act as whitespace to separate fields when + `FS' is equal to a single space (*note Examining Fields: + Fields.). - The next thing to check for is the end of the options. A `--' ends -the command line options, as does any command line argument that does -not begin with a `-'. `Optind' is used to step through the array of -command line arguments; it retains its value across calls to `getopt', -since it is a global variable. + * Newlines are not allowed after `?' or `:' (*note Conditional + Expressions: Conditional Exp.). - The regexp used, `/^-[^: \t\n\f\r\v\b]/', is perhaps a bit of -overkill; it checks for a `-' followed by anything that is not -whitespace and not a colon. If the current command line argument does -not match this pattern, it is not an option, and it ends option -processing. + * The synonym `func' for the keyword `function' is not + recognized (*note Function Definition Syntax: Definition + Syntax.). - if (_opti == 0) - _opti = 2 - thisopt = substr(argv[Optind], _opti, 1) - Optopt = thisopt - i = index(options, thisopt) - if (i == 0) { - if (Opterr) - printf("%c -- invalid option\n", - thisopt) > "/dev/stderr" - if (_opti >= length(argv[Optind])) { - Optind++ - _opti = 0 - } else - _opti++ - return "?" - } + * The `**' and `**=' operators cannot be used in place of `^' + and `^=' (*note Arithmetic Operators: Arithmetic Ops., and + also *note Assignment Expressions: Assignment Ops.). - The `_opti' variable tracks the position in the current command line -argument (`argv[Optind]'). In the case that multiple options were -grouped together with one `-' (e.g., `-abx'), it is necessary to return -them to the user one at a time. + * Specifying `-Ft' on the command-line does not set the value + of `FS' to be a single tab character (*note Specifying How + Fields Are Separated: Field Separators.). - If `_opti' is equal to zero, it is set to two, the index in the -string of the next character to look at (we skip the `-', which is at -position one). The variable `thisopt' holds the character, obtained -with `substr'. It is saved in `Optopt' for the main program to use. + * The `fflush' built-in function is not supported (*note + Input/Output Functions: I/O Functions.). - If `thisopt' is not in the `options' string, then it is an invalid -option. If `Opterr' is non-zero, `getopt' prints an error message on -the standard error that is similar to the message from the C version of -`getopt'. + If you supply both `--traditional' and `--posix' on the + command-line, `--posix' takes precedence. `gawk' also issues a + warning if both options are supplied. - Since the option is invalid, it is necessary to skip it and move on -to the next option character. If `_opti' is greater than or equal to -the length of the current command line argument, then it is necessary -to move on to the next one, so `Optind' is incremented and `_opti' is -reset to zero. Otherwise, `Optind' is left alone and `_opti' is merely -incremented. +`-W profile[=FILE]' +`--profile[=FILE]' + Enable profiling of `awk' programs (*note Profiling Your `awk' + Programs: Profiling.). By default, profiles are created in a file + named `awkprof.out'. The optional FILE argument allows you to + specify a different file name for the profile file. - In any case, since the option was invalid, `getopt' returns `?'. -The main program can examine `Optopt' if it needs to know what the -invalid option letter actually was. + When run with `gawk', the profile is just a "pretty printed" + version of the program. When run with `pgawk', the profile + contains execution counts for each statement in the program in the + left margin, and function call counts for each function. - if (substr(options, i + 1, 1) == ":") { - # get option argument - if (length(substr(argv[Optind], _opti + 1)) > 0) - Optarg = substr(argv[Optind], _opti + 1) - else - Optarg = argv[++Optind] - _opti = 0 - } else - Optarg = "" +`-W re-interval' +`--re-interval' + Allow interval expressions (*note Regular Expression Operators: + Regexp Operators.) in regexps. Because interval expressions were + traditionally not available in `awk', `gawk' does not provide them + by default. This prevents old `awk' programs from breaking. - If the option requires an argument, the option letter is followed by -a colon in the `options' string. If there are remaining characters in -the current command line argument (`argv[Optind]'), then the rest of -that string is assigned to `Optarg'. Otherwise, the next command line -argument is used (`-xFOO' vs. `-x FOO'). In either case, `_opti' is -reset to zero, since there are no more characters left to examine in -the current command line argument. +`-W source PROGRAM-TEXT' +`--source PROGRAM-TEXT' + Program source code is taken from the PROGRAM-TEXT. This option + allows you to mix source code in files with source code that you + enter on the command-line. This is particularly useful when you + have library functions that you want to use from your command-line + programs (*note The `AWKPATH' Environment Variable: AWKPATH + Variable.). - if (_opti == 0 || _opti >= length(argv[Optind])) { - Optind++ - _opti = 0 - } else - _opti++ - return thisopt - } +`-W version' +`--version' + Print version information for this particular copy of `gawk'. + This allows you to determine if your copy of `gawk' is up to date + with respect to whatever the Free Software Foundation is currently + distributing. It is also useful for bug reports (*note Reporting + Problems and Bugs: Bugs.). - Finally, if `_opti' is either zero or greater than the length of the -current command line argument, it means this element in `argv' is -through being processed, so `Optind' is incremented to point to the -next element in `argv'. If neither condition is true, then only -`_opti' is incremented, so that the next option letter can be processed -on the next call to `getopt'. + As long as program text has been supplied, any other options are +flagged as invalid with a warning message but are otherwise ignored. - BEGIN { - Opterr = 1 # default is to diagnose - Optind = 1 # skip ARGV[0] - - # test program - if (_getopt_test) { - while ((_go_c = getopt(ARGC, ARGV, "ab:cd")) != -1) - printf("c = <%c>, optarg = <%s>\n", - _go_c, Optarg) - printf("non-option arguments:\n") - for (; Optind < ARGC; Optind++) - printf("\tARGV[%d] = <%s>\n", - Optind, ARGV[Optind]) - } - } + In compatibility mode, as a special case, if the value of FS supplied +to the `-F' option is `t', then `FS' is set to the tab character +(`"\t"'). This is only true for `--traditional' and not for `--posix' +(*note Specifying How Fields Are Separated: Field Separators.). - The `BEGIN' rule initializes both `Opterr' and `Optind' to one. -`Opterr' is set to one, since the default behavior is for `getopt' to -print a diagnostic message upon seeing an invalid option. `Optind' is -set to one, since there's no reason to look at the program name, which -is in `ARGV[0]'. + The `-f' option may be used more than once on the command-line. If +it is, `awk' reads its program source from all of the named files, as +if they had been concatenated together into one big file. This is +useful for creating libraries of `awk' functions. These functions can +be written once and then retrieved from a standard place, instead of +having to be included into each individual program. (As mentioned in +*Note Function Definition Syntax: Definition Syntax, function names +must be unique.) + + Library functions can still be used, even if the program is entered +at the terminal, by specifying `-f /dev/tty'. After typing your +program, type `Ctrl-d' (the end-of-file character) to terminate it. +(You may also use `-f -' to read program source from the standard input +but then you will not be able to also use the standard input as a +source of data.) - The rest of the `BEGIN' rule is a simple test program. Here is the -result of two sample runs of the test program. + Because it is clumsy using the standard `awk' mechanisms to mix +source file and command-line `awk' programs, `gawk' provides the +`--source' option. This does not require you to pre-empt the standard +input for your source code; it allows you to easily mix command-line +and library source code (*note The `AWKPATH' Environment Variable: +AWKPATH Variable.). - $ awk -f getopt.awk -v _getopt_test=1 -- -a -cbARG bax -x - -| c = , optarg = <> - -| c = , optarg = <> - -| c = , optarg = - -| non-option arguments: - -| ARGV[3] = - -| ARGV[4] = <-x> - - $ awk -f getopt.awk -v _getopt_test=1 -- -a -x -- xyz abc - -| c = , optarg = <> - error--> x -- invalid option - -| c = , optarg = <> - -| non-option arguments: - -| ARGV[4] = - -| ARGV[5] = + If no `-f' or `--source' option is specified, then `gawk' uses the +first non-option command-line argument as the text of the program +source code. - The first `--' terminates the arguments to `awk', so that it does -not try to interpret the `-a' etc. as its own options. + If the environment variable `POSIXLY_CORRECT' exists, then `gawk' +behaves in strict POSIX mode, exactly as if you had supplied the +`--posix' command-line option. Many GNU programs look for this +environment variable to turn on strict POSIX mode. If `--lint' is +supplied on the command-line and `gawk' turns on POSIX mode because of +`POSIXLY_CORRECT', then it issues a warning message indicating that +POSIX mode is in effect. You would typically set this variable in your +shell's startup file. For a Bourne-compatible shell (such as `bash'), +you would add these lines to the `.profile' file in your home directory: - Several of the sample programs presented in *Note Practical `awk' -Programs: Sample Programs, use `getopt' to process their arguments. + POSIXLY_CORRECT=true + export POSIXLY_CORRECT - -File: gawk.info, Node: Passwd Functions, Next: Group Functions, Prev: Getopt Function, Up: Library Functions + For a `csh' compatible shell,(1) you would add this line to the +`.login' file in your home directory: -Reading the User Database -========================= + setenv POSIXLY_CORRECT true - The `/dev/user' special file (*note Special File Names in `gawk': -Special Files.) provides access to the current user's real and -effective user and group id numbers, and if available, the user's -supplementary group set. However, since these are numbers, they do not -provide very useful information to the average user. There needs to be -some way to find the user information associated with the user and -group numbers. This section presents a suite of functions for -retrieving information from the user database. *Note Reading the Group -Database: Group Functions, for a similar suite that retrieves -information from the group database. + Having `POSIXLY_CORRECT' set is not recommended for daily use, but +it is good for testing the portability of your programs to other +environments. - The POSIX standard does not define the file where user information is -kept. Instead, it provides the `' header file and several C -language subroutines for obtaining user information. The primary -function is `getpwent', for "get password entry." The "password" comes -from the original user database file, `/etc/passwd', which kept user -information, along with the encrypted passwords (hence the name). + ---------- Footnotes ---------- - While an `awk' program could simply read `/etc/passwd' directly (the -format is well known), because of the way password files are handled on -networked systems, this file may not contain complete information about -the system's set of users. + (1) Not recommended. - To be sure of being able to produce a readable, complete version of -the user database, it is necessary to write a small C program that -calls `getpwent'. `getpwent' is defined to return a pointer to a -`struct passwd'. Each time it is called, it returns the next entry in -the database. When there are no more entries, it returns `NULL', the -null pointer. When this happens, the C program should call `endpwent' -to close the database. Here is `pwcat', a C program that "cats" the -password database. + +File: gawk.info, Node: Other Arguments, Next: AWKPATH Variable, Prev: Options, Up: Invoking Gawk - /* - * pwcat.c - * - * Generate a printable version of the password database - * - * Arnold Robbins - * arnold@gnu.org - * May 1993 - * Public Domain - */ - - #include - #include - - int - main(argc, argv) - int argc; - char **argv; - { - struct passwd *p; - - while ((p = getpwent()) != NULL) - printf("%s:%s:%d:%d:%s:%s:%s\n", - p->pw_name, p->pw_passwd, p->pw_uid, - p->pw_gid, p->pw_gecos, p->pw_dir, p->pw_shell); - - endpwent(); - exit(0); - } +Other Command-Line Arguments +============================ - If you don't understand C, don't worry about it. The output from -`pwcat' is the user database, in the traditional `/etc/passwd' format -of colon-separated fields. The fields are: + Any additional arguments on the command-line are normally treated as +input files to be processed in the order specified. However, an +argument that has the form `VAR=VALUE', assigns the value VALUE to the +variable VAR--it does not specify a file at all. (This was discussed +earlier in *Note Assigning Variables on the Command Line: Assignment +Options.) -Login name - The user's login name. + All these arguments are made available to your `awk' program in the +`ARGV' array (*note Built-in Variables::). Command-line options and +the program text (if present) are omitted from `ARGV'. All other +arguments, including variable assignments, are included. As each +element of `ARGV' is processed, `gawk' sets the variable `ARGIND' to +the index in `ARGV' of the current element. -Encrypted password - The user's encrypted password. This may not be available on some - systems. + The distinction between file name arguments and variable-assignment +arguments is made when `awk' is about to open the next input file. At +that point in execution, it checks the file name to see whether it is +really a variable assignment; if so, `awk' sets the variable instead of +reading a file. -User-ID - The user's numeric user-id number. + Therefore, the variables actually receive the given values after all +previously specified files have been read. In particular, the values of +variables assigned in this fashion are _not_ available inside a `BEGIN' +rule (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.), +because such rules are run before `awk' begins scanning the argument +list. -Group-ID - The user's numeric group-id number. + The variable values given on the command-line are processed for +escape sequences (*note Escape Sequences::). (d.c.) -Full name - The user's full name, and perhaps other information associated - with the user. + In some earlier implementations of `awk', when a variable assignment +occurred before any file names, the assignment would happen _before_ +the `BEGIN' rule was executed. `awk''s behavior was thus inconsistent; +some command-line assignments were available inside the `BEGIN' rule, +while others were not. Unfortunately, some applications came to depend +upon this "feature." When `awk' was changed to be more consistent, the +`-v' option was added to accommodate applications that depended upon +the old behavior. -Home directory - The user's login, or "home" directory (familiar to shell - programmers as `$HOME'). + The variable assignment feature is most useful for assigning to +variables such as `RS', `OFS', and `ORS', which control input and +output formats before scanning the data files. It is also useful for +controlling state if multiple passes are needed over a data file. For +example: -Login shell - The program that will be run when the user logs in. This is - usually a shell, such as Bash (the Gnu Bourne-Again shell). + awk 'pass == 1 { PASS 1 STUFF } + pass == 2 { PASS 2 STUFF }' pass=1 mydata pass=2 mydata - Here are a few lines representative of `pwcat''s output. + Given the variable assignment feature, the `-F' option for setting +the value of `FS' is not strictly necessary. It remains for historical +compatibility. - $ pwcat - -| root:3Ov02d5VaUPB6:0:1:Operator:/:/bin/sh - -| nobody:*:65534:65534::/: - -| daemon:*:1:1::/: - -| sys:*:2:2::/:/bin/csh - -| bin:*:3:3::/bin: - -| arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/sh - -| miriam:yxaay:112:10:Miriam Robbins:/home/miriam:/bin/sh - -| andy:abcca2:113:10:Andy Jacobs:/home/andy:/bin/sh - ... + +File: gawk.info, Node: AWKPATH Variable, Next: Obsolete, Prev: Other Arguments, Up: Invoking Gawk - With that introduction, here is a group of functions for getting user -information. There are several functions here, corresponding to the C -functions of the same name. +The `AWKPATH' Environment Variable +================================== - # passwd.awk --- access password file information - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - - BEGIN { - # tailor this to suit your system - _pw_awklib = "/usr/local/libexec/awk/" - } - - function _pw_init( oldfs, oldrs, olddol0, pwcat) - { - if (_pw_inited) - return - oldfs = FS - oldrs = RS - olddol0 = $0 - FS = ":" - RS = "\n" - pwcat = _pw_awklib "pwcat" - while ((pwcat | getline) > 0) { - _pw_byname[$1] = $0 - _pw_byuid[$3] = $0 - _pw_bycount[++_pw_total] = $0 - } - close(pwcat) - _pw_count = 0 - _pw_inited = 1 - FS = oldfs - RS = oldrs - $0 = olddol0 - } + The previous minor node described how `awk' program files can be +named on the command-line with the `-f' option. In most `awk' +implementations, you must supply a precise path name for each program +file, unless the file is in the current directory. But in `gawk', if +the file name supplied to the `-f' option does not contain a `/', then +`gawk' searches a list of directories (called the "search path"), one +by one, looking for a file with the specified name. - The `BEGIN' rule sets a private variable to the directory where -`pwcat' is stored. Since it is used to help out an `awk' library -routine, we have chosen to put it in `/usr/local/libexec/awk'. You -might want it to be in a different directory on your system. + The search path is a string consisting of directory names separated +by colons. `gawk' gets its search path from the `AWKPATH' environment +variable. If that variable does not exist, `gawk' uses a default path, +which is `.:/usr/local/share/awk'.(1) (Programs written for use by +system administrators should use an `AWKPATH' variable that does not +include the current directory, `.'.) - The function `_pw_init' keeps three copies of the user information -in three associative arrays. The arrays are indexed by user name -(`_pw_byname'), by user-id number (`_pw_byuid'), and by order of -occurrence (`_pw_bycount'). + The search path feature is particularly useful for building libraries +of useful `awk' functions. The library files can be placed in a +standard directory in the default path and then specified on the +command-line with a short file name. Otherwise, the full file name +would have to be typed for each file. - The variable `_pw_inited' is used for efficiency; `_pw_init' only -needs to be called once. + By using both the `--source' and `-f' options, your command-line +`awk' programs can use facilities in `awk' library files. *Note A +Library of `awk' Functions: Library Functions. Path searching is not +done if `gawk' is in compatibility mode. This is true for both +`--traditional' and `--posix'. *Note Command-Line Options: Options. - Since this function uses `getline' to read information from `pwcat', -it first saves the values of `FS', `RS', and `$0'. Doing so is -necessary, since these functions could be called from anywhere within a -user's program, and the user may have his or her own values for `FS' -and `RS'. + *Note:* If you want files in the current directory to be found, you +must include the current directory in the path, either by including `.' +explicitly in the path or by writing a null entry in the path. (A null +entry is indicated by starting or ending the path with a colon or by +placing two colons next to each other (`::').) If the current +directory is not included in the path, then files cannot be found in +the current directory. This path search mechanism is identical to the +shell's. - The main part of the function uses a loop to read database lines, -split the line into fields, and then store the line into each array as -necessary. When the loop is done, `_pw_init' cleans up by closing the -pipeline, setting `_pw_inited' to one, and restoring `FS', `RS', and -`$0'. The use of `_pw_count' will be explained below. + Starting with version 3.0, if `AWKPATH' is not defined in the +environment, `gawk' places its default search path into +`ENVIRON["AWKPATH"]'. This makes it easy to determine the actual search +path that `gawk' will use from within an `awk' program. - function getpwnam(name) - { - _pw_init() - if (name in _pw_byname) - return _pw_byname[name] - return "" - } - - The `getpwnam' function takes a user name as a string argument. If -that user is in the database, it returns the appropriate line. -Otherwise it returns the null string. - - function getpwuid(uid) - { - _pw_init() - if (uid in _pw_byuid) - return _pw_byuid[uid] - return "" - } - - Similarly, the `getpwuid' function takes a user-id number argument. -If that user number is in the database, it returns the appropriate -line. Otherwise it returns the null string. - - function getpwent() - { - _pw_init() - if (_pw_count < _pw_total) - return _pw_bycount[++_pw_count] - return "" - } - - The `getpwent' function simply steps through the database, one entry -at a time. It uses `_pw_count' to track its current position in the -`_pw_bycount' array. - - function endpwent() - { - _pw_count = 0 - } + While you can change `ENVIRON["AWKPATH"]' within your `awk' program, +this has no effect on the running program's behavior. This makes +sense: the `AWKPATH' environment variable is used to find the program +source files. Once your program is running, all the files have been +found, and `gawk' no longer needs to use `AWKPATH'. - The `endpwent' function resets `_pw_count' to zero, so that -subsequent calls to `getpwent' will start over again. - - A conscious design decision in this suite is that each subroutine -calls `_pw_init' to initialize the database arrays. The overhead of -running a separate process to generate the user database, and the I/O -to scan it, will only be incurred if the user's main program actually -calls one of these functions. If this library file is loaded along -with a user's program, but none of the routines are ever called, then -there is no extra run-time overhead. (The alternative would be to move -the body of `_pw_init' into a `BEGIN' rule, which would always run -`pwcat'. This simplifies the code but runs an extra process that may -never be needed.) - - In turn, calling `_pw_init' is not too expensive, since the -`_pw_inited' variable keeps the program from reading the data more than -once. If you are worried about squeezing every last cycle out of your -`awk' program, the check of `_pw_inited' could be moved out of -`_pw_init' and duplicated in all the other functions. In practice, -this is not necessary, since most `awk' programs are I/O bound, and it -would clutter up the code. + ---------- Footnotes ---------- - The `id' program in *Note Printing Out User Information: Id Program, -uses these functions. + (1) Your version of `gawk' may use a different directory; it will +depend upon how `gawk' was built and installed. The actual directory is +the value of `$(datadir)' generated when `gawk' was configured. You +probably don't need to worry about this though.  -File: gawk.info, Node: Group Functions, Next: Library Names, Prev: Passwd Functions, Up: Library Functions - -Reading the Group Database -========================== - - Much of the discussion presented in *Note Reading the User Database: -Passwd Functions, applies to the group database as well. Although -there has traditionally been a well known file, `/etc/group', in a well -known format, the POSIX standard only provides a set of C library -routines (`' and `getgrent') for accessing the information. -Even though this file may exist, it likely does not have complete -information. Therefore, as with the user database, it is necessary to -have a small C program that generates the group database as its output. - - Here is `grcat', a C program that "cats" the group database. - - /* - * grcat.c - * - * Generate a printable version of the group database - * - * Arnold Robbins, arnold@gnu.org - * May 1993 - * Public Domain - */ - - #include - #include - - int - main(argc, argv) - int argc; - char **argv; - { - struct group *g; - int i; - - while ((g = getgrent()) != NULL) { - printf("%s:%s:%d:", g->gr_name, g->gr_passwd, - g->gr_gid); - for (i = 0; g->gr_mem[i] != NULL; i++) { - printf("%s", g->gr_mem[i]); - if (g->gr_mem[i+1] != NULL) - putchar(','); - } - putchar('\n'); - } - endgrent(); - exit(0); - } - - Each line in the group database represent one group. The fields are -separated with colons, and represent the following information. - -Group Name - The name of the group. +File: gawk.info, Node: Obsolete, Next: Undocumented, Prev: AWKPATH Variable, Up: Invoking Gawk -Group Password - The encrypted group password. In practice, this field is never - used. It is usually empty, or set to `*'. +Obsolete Options and/or Features +================================ -Group ID Number - The numeric group-id number. This number should be unique within - the file. + This minor node describes features and/or command-line options from +previous releases of `gawk' that are either not available in the +current version or that are still supported but deprecated (meaning that +they will _not_ be in the next release). + + For version 3.1 of `gawk', there are no deprecated command-line +options from the previous version of `gawk'. The use of `next file' +(two words) for `nextfile' was deprecated in `gawk' 3.0 but still +worked. Starting with version 3.1, the two word usage is no longer +accepted. + + The process-related special files described in *Note Special Files +for Process-Related Information: Special Process, work as described, but +are now considered deprecated. `gawk' prints a warning message every +time they are used. (Use `PROCINFO' instead; see *Note Built-in +Variables That Convey Information: Auto-set.) They will be removed +from the next release of `gawk'. -Group Member List - A comma-separated list of user names. These users are members of - the group. Most Unix systems allow users to be members of several - groups simultaneously. If your system does, then reading - `/dev/user' will return those group-id numbers in `$5' through - `$NF'. (Note that `/dev/user' is a `gawk' extension; *note - Special File Names in `gawk': Special Files..) + +File: gawk.info, Node: Undocumented, Next: Known Bugs, Prev: Obsolete, Up: Invoking Gawk - Here is what running `grcat' might produce: +Undocumented Options and Features +================================= - $ grcat - -| wheel:*:0:arnold - -| nogroup:*:65534: - -| daemon:*:1: - -| kmem:*:2: - -| staff:*:10:arnold,miriam,andy - -| other:*:20: - ... + Use the Source, Luke! + Obi-Wan - Here are the functions for obtaining information from the group -database. There are several, modeled after the C library functions of -the same names. + This minor node intentionally left blank. - # group.awk --- functions for dealing with the group file - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - - BEGIN \ - { - # Change to suit your system - _gr_awklib = "/usr/local/libexec/awk/" - } - - function _gr_init( oldfs, oldrs, olddol0, grcat, n, a, i) - { - if (_gr_inited) - return - - oldfs = FS - oldrs = RS - olddol0 = $0 - FS = ":" - RS = "\n" - - grcat = _gr_awklib "grcat" - while ((grcat | getline) > 0) { - if ($1 in _gr_byname) - _gr_byname[$1] = _gr_byname[$1] "," $4 - else - _gr_byname[$1] = $0 - if ($3 in _gr_bygid) - _gr_bygid[$3] = _gr_bygid[$3] "," $4 - else - _gr_bygid[$3] = $0 - - n = split($4, a, "[ \t]*,[ \t]*") - for (i = 1; i <= n; i++) - if (a[i] in _gr_groupsbyuser) - _gr_groupsbyuser[a[i]] = \ - _gr_groupsbyuser[a[i]] " " $1 - else - _gr_groupsbyuser[a[i]] = $1 - - _gr_bycount[++_gr_count] = $0 - } - close(grcat) - _gr_count = 0 - _gr_inited++ - FS = oldfs - RS = oldrs - $0 = olddol0 - } + +File: gawk.info, Node: Known Bugs, Prev: Undocumented, Up: Invoking Gawk - The `BEGIN' rule sets a private variable to the directory where -`grcat' is stored. Since it is used to help out an `awk' library -routine, we have chosen to put it in `/usr/local/libexec/awk'. You -might want it to be in a different directory on your system. +Known Bugs in `gawk' +==================== - These routines follow the same general outline as the user database -routines (*note Reading the User Database: Passwd Functions.). The -`_gr_inited' variable is used to ensure that the database is scanned no -more than once. The `_gr_init' function first saves `FS', `RS', and -`$0', and then sets `FS' and `RS' to the correct values for scanning -the group information. + * The `-F' option for changing the value of `FS' (*note Command-Line + Options: Options.) is not necessary given the command-line + variable assignment feature; it remains only for backwards + compatibility. - The group information is stored is several associative arrays. The -arrays are indexed by group name (`_gr_byname'), by group-id number -(`_gr_bygid'), and by position in the database (`_gr_bycount'). There -is an additional array indexed by user name (`_gr_groupsbyuser'), that -is a space separated list of groups that each user belongs to. + * Syntactically invalid single character programs tend to overflow + the parse stack, generating a rather unhelpful message. Such + programs are surprisingly difficult to diagnose in the completely + general case and the effort to do so really is not worth it. - Unlike the user database, it is possible to have multiple records in -the database for the same group. This is common when a group has a -large number of members. Such a pair of entries might look like: + +File: gawk.info, Node: Library Functions, Next: Sample Programs, Prev: Invoking Gawk, Up: Top - tvpeople:*:101:johny,jay,arsenio - tvpeople:*:101:david,conan,tom,joan +A Library of `awk' Functions +**************************** - For this reason, `_gr_init' looks to see if a group name or group-id -number has already been seen. If it has, then the user names are -simply concatenated onto the previous list of users. (There is -actually a subtle problem with the code presented above. Suppose that -the first time there were no names. This code adds the names with a -leading comma. It also doesn't check that there is a `$4'.) + *Note User-Defined Functions: User-defined, describes how to write +your own `awk' functions. Writing functions is important, because it +allows you to encapsulate algorithms and program tasks in a single +place. It simplifies programming, making program development more +manageable, and making programs more readable. - Finally, `_gr_init' closes the pipeline to `grcat', restores `FS', -`RS', and `$0', initializes `_gr_count' to zero (it is used later), and -makes `_gr_inited' non-zero. + One valuable way to learn a new programming language is to _read_ +programs in that language. To that end, this major node and *Note +Practical `awk' Programs: Sample Programs, provide a good-sized body of +code for you to read, and hopefully, to learn from. - function getgrnam(group) - { - _gr_init() - if (group in _gr_byname) - return _gr_byname[group] - return "" - } + This major node presents a library of useful `awk' functions. Many +of the sample programs presented later in this Info file use these +functions. The functions are presented here in a progression from +simple to complex. - The `getgrnam' function takes a group name as its argument, and if -that group exists, it is returned. Otherwise, `getgrnam' returns the -null string. + *Note Extracting Programs from Texinfo Source Files: Extract Program, +presents a program that you can use to extract the source code for +these example library functions and programs from the Texinfo source +for this Info file. (This has already been done as part of the `gawk' +distribution.) - function getgrgid(gid) - { - _gr_init() - if (gid in _gr_bygid) - return _gr_bygid[gid] - return "" - } + If you have written one or more useful, general purpose `awk' +functions and would like to contribute them to the author's collection +of `awk' programs, see *Note How to Contribute: How To Contribute, for +more information. - The `getgrgid' function is similar, it takes a numeric group-id, and -looks up the information associated with that group-id. + The programs in this major node and in *Note Practical `awk' +Programs: Sample Programs, freely use features that are `gawk'-specific. +It is straightforward to rewrite these programs for different +implementations of `awk'. - function getgruser(user) - { - _gr_init() - if (user in _gr_groupsbyuser) - return _gr_groupsbyuser[user] - return "" - } + Diagnostic error messages are sent to `/dev/stderr'. Use `| "cat +1>&2"' instead of `> "/dev/stderr"', if your system does not have a +`/dev/stderr' or if you cannot use `gawk'. - The `getgruser' function does not have a C counterpart. It takes a -user name, and returns the list of groups that have the user as a -member. + A number of programs use `nextfile' (*note Using `gawk''s `nextfile' +Statement: Nextfile Statement.) to skip any remaining input in the +input file. *Note Implementing `nextfile' as a Function: Nextfile +Function, shows you how to write a function that does the same thing. - function getgrent() - { - _gr_init() - if (++_gr_count in _gr_bycount) - return _gr_bycount[_gr_count] - return "" - } + Finally, some of the programs choose to ignore upper- and lowercase +distinctions in their input. They do so by assigning one to +`IGNORECASE'. You can achieve almost the same effect(1) by adding the +following rule to the beginning of the program: - The `getgrent' function steps through the database one entry at a -time. It uses `_gr_count' to track its position in the list. + # ignore case + { $0 = tolower($0) } - function endgrent() - { - _gr_count = 0 - } +Also, verify that all regexp and string constants used in comparisons +only use lowercase letters. - `endgrent' resets `_gr_count' to zero so that `getgrent' can start -over again. +* Menu: - As with the user database routines, each function calls `_gr_init' to -initialize the arrays. Doing so only incurs the extra overhead of -running `grcat' if these functions are used (as opposed to moving the -body of `_gr_init' into a `BEGIN' rule). +* Library Names:: How to best name private global variables in + library functions. +* General Functions:: Functions that are of general use. +* Data File Management:: Functions for managing command-line data + files. +* Getopt Function:: A function for processing command-line + arguments. +* Passwd Functions:: Functions for getting user information. +* Group Functions:: Functions for getting group information. - Most of the work is in scanning the database and building the various -associative arrays. The functions that the user calls are themselves -very simple, relying on `awk''s associative arrays to do work. + ---------- Footnotes ---------- - The `id' program in *Note Printing Out User Information: Id Program, -uses these functions. + (1) The effects are not identical. Output of the transformed record +will be in all lowercase, while `IGNORECASE' preserves the original +contents of the input record.  -File: gawk.info, Node: Library Names, Prev: Group Functions, Up: Library Functions +File: gawk.info, Node: Library Names, Next: General Functions, Prev: Library Functions, Up: Library Functions Naming Library Function Global Variables ======================================== Due to the way the `awk' language evolved, variables are either -"global" (usable by the entire program), or "local" (usable just by a +"global" (usable by the entire program) or "local" (usable just by a specific function). There is no intermediate state analogous to `static' variables in C. Library functions often need to have global variables that they can -use to preserve state information between calls to the function. For -example, `getopt''s variable `_opti' (*note Processing Command Line -Options: Getopt Function.), and the `_tm_months' array used by `mktime' -(*note Turning Dates Into Timestamps: Mktime Function.). Such -variables are called "private", since the only functions that need to -use them are the ones in the library. +use to preserve state information between calls to the function--for +example, `getopt''s variable `_opti' (*note Processing Command-Line +Options: Getopt Function.). Such variables are called "private", since +the only functions that need to use them are the ones in the library. When writing a library function, you should try to choose names for -your private variables so that they will not conflict with any -variables used by either another library function or a user's main -program. For example, a name like `i' or `j' is not a good choice, -since user programs often use variable names like these for their own -purposes. +your private variables that will not conflict with any variables used by +either another library function or a user's main program. For example, +a name like `i' or `j' is not a good choice, because user programs +often use variable names like these for their own purposes. - The example programs shown in this chapter all start the names of + The example programs shown in this major node all start the names of their private variables with an underscore (`_'). Users generally don't use leading underscores in their variable names, so this convention immediately decreases the chances that the variable name will be accidentally shared with the user's program. In addition, several of the library functions use a prefix that helps -indicate what function or set of functions uses the variables. For -example, `_tm_months' in `mktime' (*note Turning Dates Into Timestamps: -Mktime Function.), and `_pw_byname' in the user data base routines -(*note Reading the User Database: Passwd Functions.). This convention -is recommended, since it even further decreases the chance of -inadvertent conflict among variable names. Note that this convention -can be used equally well both for variable names and for private -function names too. - - While I could have re-written all the library routines to use this -convention, I did not do so, in order to show how my own `awk' -programming style has evolved, and to provide some basis for this -discussion. +indicate what function or set of functions use the variables--for +example, `_pw_byname' in the user database routines (*note Reading the +User Database: Passwd Functions.). This convention is recommended, +since it even further decreases the chance of inadvertent conflict +among variable names. Note that this convention is used equally well +for variable names and for private function names as well.(1) As a final note on variable naming, if a function makes global variables available for use by a main program, it is a good convention -to start that variable's name with a capital letter. For example, -`getopt''s `Opterr' and `Optind' variables (*note Processing Command -Line Options: Getopt Function.). The leading capital letter indicates -that it is global, while the fact that the variable name is not all -capital letters indicates that the variable is not one of `awk''s -built-in variables, like `FS'. +to start that variable's name with a capital letter--for example, +`getopt''s `Opterr' and `Optind' variables (*note Processing +Command-Line Options: Getopt Function.). The leading capital letter +indicates that it is global, while the fact that the variable name is +not all capital letters indicates that the variable is not one of +`awk''s built-in variables, such as `FS'. It is also important that _all_ variables in library functions that -do not need to save state are in fact declared local. If this is not -done, the variable could accidentally be used in the user's program, -leading to bugs that are very difficult to track down. +do not need to save state are, in fact, declared local.(2) If this is +not done, the variable could accidentally be used in the user's +program, leading to bugs that are very difficult to track down: function lib_func(x, y, l1, l2) { ... - USE VARIABLE some_var # some_var could be local + USE VARIABLE some_var # some_var should be local ... # but is not by oversight } @@ -11289,4039 +12226,4450 @@ single associative array to hold the values needed by the library function(s), or "package." This significantly decreases the number of actual global names in use. For example, the functions described in *Note Reading the User Database: Passwd Functions, might have used -`PW_data["inited"]', `PW_data["total"]', `PW_data["count"]' and -`PW_data["awklib"]', instead of `_pw_inited', `_pw_awklib', `_pw_total', -and `_pw_count'. +array elements `PW_data["inited"]', `PW_data["total"]', +`PW_data["count"]', and `PW_data["awklib"]', instead of `_pw_inited', +`_pw_awklib', `_pw_total', and `_pw_count'. - The conventions presented in this section are exactly that, -conventions. You are not required to write your programs this way, we + The conventions presented in this minor node are exactly that: +conventions. You are not required to write your programs this way--we merely recommend that you do so. - -File: gawk.info, Node: Sample Programs, Next: Language History, Prev: Library Functions, Up: Top + ---------- Footnotes ---------- -Practical `awk' Programs -************************ + (1) While all the library routines could have been rewritten to use +this convention, this was not done, in order to show how my own `awk' +programming style has evolved, and to provide some basis for this +discussion. - This chapter presents a potpourri of `awk' programs for your reading -enjoyment. - - Many of these programs use the library functions presented in *Note -A Library of `awk' Functions: Library Functions. - -* Menu: - -* Clones:: Clones of common utilities. -* Miscellaneous Programs:: Some interesting `awk' programs. + (2) `gawk''s `--dump-variables' command-line option is useful for +verifying this.  -File: gawk.info, Node: Clones, Next: Miscellaneous Programs, Prev: Sample Programs, Up: Sample Programs - -Re-inventing Wheels for Fun and Profit -====================================== - - This section presents a number of POSIX utilities that are -implemented in `awk'. Re-inventing these programs in `awk' is often -enjoyable, since the algorithms can be very clearly expressed, and -usually the code is very concise and simple. This is true because -`awk' does so much for you. +File: gawk.info, Node: General Functions, Next: Data File Management, Prev: Library Names, Up: Library Functions - It should be noted that these programs are not necessarily intended -to replace the installed versions on your system. Instead, their -purpose is to illustrate `awk' language programming for "real world" -tasks. +General Programming +=================== - The programs are presented in alphabetical order. + This minor node presents a number of functions that are of general +programming use. * Menu: -* Cut Program:: The `cut' utility. -* Egrep Program:: The `egrep' utility. -* Id Program:: The `id' utility. -* Split Program:: The `split' utility. -* Tee Program:: The `tee' utility. -* Uniq Program:: The `uniq' utility. -* Wc Program:: The `wc' utility. +* Nextfile Function:: Two implementations of a `nextfile' + function. +* Assert Function:: A function for assertions in `awk' + programs. +* Round Function:: A function for rounding if `sprintf' does + not do it correctly. +* Cliff Random Function:: The Cliff Random Number Generator. +* Ordinal Functions:: Functions for using characters as numbers and + vice versa. +* Join Function:: A function to join an array into a string. +* Gettimeofday Function:: A function to get formatted times.  -File: gawk.info, Node: Cut Program, Next: Egrep Program, Prev: Clones, Up: Clones - -Cutting Out Fields and Columns ------------------------------- - - The `cut' utility selects, or "cuts," either characters or fields -from its standard input and sends them to its standard output. `cut' -can cut out either a list of characters, or a list of fields. By -default, fields are separated by tabs, but you may supply a command -line option to change the field "delimiter", i.e. the field separator -character. `cut''s definition of fields is less general than `awk''s. +File: gawk.info, Node: Nextfile Function, Next: Assert Function, Prev: General Functions, Up: General Functions - A common use of `cut' might be to pull out just the login name of -logged-on users from the output of `who'. For example, the following -pipeline generates a sorted, unique list of the logged on users: - - who | cut -c1-8 | sort | uniq +Implementing `nextfile' as a Function +------------------------------------- - The options for `cut' are: + The `nextfile' statement presented in *Note Using `gawk''s +`nextfile' Statement: Nextfile Statement, is a `gawk'-specific +extension--it is not available in most other implementations of `awk'. +This minor node shows two versions of a `nextfile' function that you +can use to simulate `gawk''s `nextfile' statement if you cannot use +`gawk'. -`-c LIST' - Use LIST as the list of characters to cut out. Items within the - list may be separated by commas, and ranges of characters can be - separated with dashes. The list `1-8,15,22-35' specifies - characters one through eight, 15, and 22 through 35. + A first attempt at writing a `nextfile' function is as follows: -`-f LIST' - Use LIST as the list of fields to cut out. + # nextfile --- skip remaining records in current file + # this should be read in before the "main" awk program + + function nextfile() { _abandon_ = FILENAME; next } + _abandon_ == FILENAME { next } -`-d DELIM' - Use DELIM as the field separator character instead of the tab - character. + Because it supplies a rule that must be executed first, this file +should be included before the main program. This rule compares the +current data file's name (which is always in the `FILENAME' variable) to +a private variable named `_abandon_'. If the file name matches, then +the action part of the rule executes a `next' statement to go on to the +next record. (The use of `_' in the variable name is a convention. It +is discussed more fully in *Note Naming Library Function Global +Variables: Library Names.) -`-s' - Suppress printing of lines that do not contain the field delimiter. + The use of the `next' statement effectively creates a loop that reads +all the records from the current data file. The end of the file is +eventually reached and a new data file is opened, changing the value of +`FILENAME'. Once this happens, the comparison of `_abandon_' to +`FILENAME' fails and execution continues with the first rule of the +"real" program. - The `awk' implementation of `cut' uses the `getopt' library function -(*note Processing Command Line Options: Getopt Function.), and the -`join' library function (*note Merging an Array Into a String: Join -Function.). + The `nextfile' function itself simply sets the value of `_abandon_' +and then executes a `next' statement to start the loop. - The program begins with a comment describing the options and a -`usage' function which prints out a usage message and exits. `usage' -is called if invalid arguments are supplied. + This initial version has a subtle problem. If the same data file is +listed _twice_ on the commandline, one right after the other or even +with just a variable assignment between them, this code skips right +through the file, a second time, even though it should stop when it +gets to the end of the first occurrence. A second version of +`nextfile' that remedies this problem is shown here: - # cut.awk --- implement cut in awk - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 + # nextfile --- skip remaining records in current file + # correctly handle successive occurrences of the same file + # this should be read in before the "main" awk program - # Options: - # -f list Cut fields - # -d c Field delimiter character - # -c list Cut characters - # - # -s Suppress lines without the delimiter character + function nextfile() { _abandon_ = FILENAME; next } - function usage( e1, e2) - { - e1 = "usage: cut [-f list] [-d c] [-s] [files...]" - e2 = "usage: cut [-c list] [files...]" - print e1 > "/dev/stderr" - print e2 > "/dev/stderr" - exit 1 + _abandon_ == FILENAME { + if (FNR == 1) + _abandon_ = "" + else + next } -The variables `e1' and `e2' are used so that the function fits nicely -on the screen. - - Next comes a `BEGIN' rule that parses the command line options. It -sets `FS' to a single tab character, since that is `cut''s default -field separator. The output field separator is also set to be the same -as the input field separator. Then `getopt' is used to step through -the command line options. One or the other of the variables -`by_fields' or `by_chars' is set to true, to indicate that processing -should be done by fields or by characters respectively. When cutting -by characters, the output field separator is set to the null string. + The `nextfile' function has not changed. It makes `_abandon_' equal +to the current file name and then executes a `next' statement. The +`next' statement reads the next record and increments `FNR' so that +`FNR' is guaranteed to have a value of at least two. However, if +`nextfile' is called for the last record in the file, then `awk' closes +the current data file and moves on to the next one. Upon doing so, +`FILENAME' is set to the name of the new file and `FNR' is reset to +one. If this next file is the same as the previous one, `_abandon_' is +still equal to `FILENAME'. However, `FNR' is equal to one, telling us +that this is a new occurrence of the file and not the one we were +reading when the `nextfile' function was executed. In that case, +`_abandon_' is reset to the empty string, so that further executions of +this rule fail (until the next time that `nextfile' is called). + + If `FNR' is not one, then we are still in the original data file and +the program executes a `next' statement to skip through it. + + An important question to ask at this point is: given that the +functionality of `nextfile' can be provided with a library file, why is +it built into `gawk'? Adding features for little reason leads to +larger, slower programs that are harder to maintain. The answer is +that building `nextfile' into `gawk' provides significant gains in +efficiency. If the `nextfile' function is executed at the beginning of +a large data file, `awk' still has to scan the entire file, splitting +it up into records, just to skip over it. The built-in `nextfile' can +simply close the file immediately and proceed to the next one, which +saves a lot of time. This is particularly important in `awk', because +`awk' programs are generally I/O-bound (i.e., they spend most of their +time doing input and output, instead of performing computations). - BEGIN \ - { - FS = "\t" # default - OFS = FS - while ((c = getopt(ARGC, ARGV, "sf:c:d:")) != -1) { - if (c == "f") { - by_fields = 1 - fieldlist = Optarg - } else if (c == "c") { - by_chars = 1 - fieldlist = Optarg - OFS = "" - } else if (c == "d") { - if (length(Optarg) > 1) { - printf("Using first character of %s" \ - " for delimiter\n", Optarg) > "/dev/stderr" - Optarg = substr(Optarg, 1, 1) - } - FS = Optarg - OFS = FS - if (FS == " ") # defeat awk semantics - FS = "[ ]" - } else if (c == "s") - suppress++ - else - usage() - } - - for (i = 1; i < Optind; i++) - ARGV[i] = "" + +File: gawk.info, Node: Assert Function, Next: Round Function, Prev: Nextfile Function, Up: General Functions - Special care is taken when the field delimiter is a space. Using -`" "' (a single space) for the value of `FS' is incorrect--`awk' would -separate fields with runs of spaces, tabs and/or newlines, and we want -them to be separated with individual spaces. Also, note that after -`getopt' is through, we have to clear out all the elements of `ARGV' -from one to `Optind', so that `awk' will not try to process the command -line options as file names. +Assertions +---------- - After dealing with the command line options, the program verifies -that the options make sense. Only one or the other of `-c' and `-f' -should be used, and both require a field list. Then either -`set_fieldlist' or `set_charlist' is called to pull apart the list of -fields or characters. + When writing large programs, it is often useful to know that a +condition or set of conditions is true. Before proceeding with a +particular computation, you make a statement about what you believe to +be the case. Such a statement is known as an "assertion". The C +language provides an `' header file and corresponding +`assert' macro that the programmer can use to make assertions. If an +assertion fails, the `assert' macro arranges to print a diagnostic +message describing the condition that should have been true but was +not, and then it kills the program. In C, using `assert' looks this: - if (by_fields && by_chars) - usage() - - if (by_fields == 0 && by_chars == 0) - by_fields = 1 # default - - if (fieldlist == "") { - print "cut: needs list for -c or -f" > "/dev/stderr" - exit 1 - } + #include - if (by_fields) - set_fieldlist() - else - set_charlist() - } - - Here is `set_fieldlist'. It first splits the field list apart at -the commas, into an array. Then, for each element of the array, it -looks to see if it is actually a range, and if so splits it apart. The -range is verified to make sure the first number is smaller than the -second. Each number in the list is added to the `flist' array, which -simply lists the fields that will be printed. Normal field splitting -is used. The program lets `awk' handle the job of doing the field -splitting. - - function set_fieldlist( n, m, i, j, k, f, g) + int myfunc(int a, double b) { - n = split(fieldlist, f, ",") - j = 1 # index in flist - for (i = 1; i <= n; i++) { - if (index(f[i], "-") != 0) { # a range - m = split(f[i], g, "-") - if (m != 2 || g[1] >= g[2]) { - printf("bad field list: %s\n", - f[i]) > "/dev/stderr" - exit 1 - } - for (k = g[1]; k <= g[2]; k++) - flist[j++] = k - } else - flist[j++] = f[i] - } - nfields = j - 1 + assert(a <= 5 && b >= 17.1); + ... } - The `set_charlist' function is more complicated than `set_fieldlist'. -The idea here is to use `gawk''s `FIELDWIDTHS' variable (*note Reading -Fixed-width Data: Constant Size.), which describes constant width -input. When using a character list, that is exactly what we have. + If the assertion fails, the program prints a message similar to this: - Setting up `FIELDWIDTHS' is more complicated than simply listing the -fields that need to be printed. We have to keep track of the fields to -be printed, and also the intervening characters that have to be skipped. -For example, suppose you wanted characters one through eight, 15, and -22 through 35. You would use `-c 1-8,15,22-35'. The necessary value -for `FIELDWIDTHS' would be `"8 6 1 6 14"'. This gives us five fields, -and what should be printed are `$1', `$3', and `$5'. The intermediate -fields are "filler," stuff in between the desired data. + prog.c:5: assertion failed: a <= 5 && b >= 17.1 - `flist' lists the fields to be printed, and `t' tracks the complete -field list, including filler fields. + The C language makes it possible to turn the condition into a string +for use in printing the diagnostic message. This is not possible in +`awk', so this `assert' function also requires a string version of the +condition that is being tested. Following is the function: - function set_charlist( field, i, j, f, g, t, - filler, last, len) + # assert --- assert that a condition is true. Otherwise exit. + function assert(condition, string) { - field = 1 # count total fields - n = split(fieldlist, f, ",") - j = 1 # index in flist - for (i = 1; i <= n; i++) { - if (index(f[i], "-") != 0) { # range - m = split(f[i], g, "-") - if (m != 2 || g[1] >= g[2]) { - printf("bad character list: %s\n", - f[i]) > "/dev/stderr" - exit 1 - } - len = g[2] - g[1] + 1 - if (g[1] > 1) # compute length of filler - filler = g[1] - last - 1 - else - filler = 0 - if (filler) - t[field++] = filler - t[field++] = len # length of field - last = g[2] - flist[j++] = field - 1 - } else { - if (f[i] > 1) - filler = f[i] - last - 1 - else - filler = 0 - if (filler) - t[field++] = filler - t[field++] = 1 - last = f[i] - flist[j++] = field - 1 - } + if (! condition) { + printf("%s:%d: assertion failed: %s\n", + FILENAME, FNR, string) > "/dev/stderr" + _assert_exit = 1 + exit 1 } - FIELDWIDTHS = join(t, 1, field - 1) - nfields = j - 1 + } + + END { + if (_assert_exit) + exit 1 } - Here is the rule that actually processes the data. If the `-s' -option was given, then `suppress' will be true. The first `if' -statement makes sure that the input record does have the field -separator. If `cut' is processing fields, `suppress' is true, and the -field separator character is not in the record, then the record is -skipped. + The `assert' function tests the `condition' parameter. If it is +false, it prints a message to standard error, using the `string' +parameter to describe the failed condition. It then sets the variable +`_assert_exit' to one and executes the `exit' statement. The `exit' +statement jumps to the `END' rule. If the `END' rules finds +`_assert_exit' to be true, it then exits immediately. - If the record is valid, then at this point, `gawk' has split the data -into fields, either using the character in `FS' or using fixed-length -fields and `FIELDWIDTHS'. The loop goes through the list of fields -that should be printed. If the corresponding field has data in it, it -is printed. If the next field also has data, then the separator -character is written out in between the fields. + The purpose of the test in the `END' rule is to keep any other `END' +rules from running. When an assertion fails, the program should exit +immediately. If no assertions fail, then `_assert_exit' is still false +when the `END' rule is run normally, and the rest of the program's +`END' rules execute. For all of this to work correctly, `assert.awk' +must be the first source file read by `awk'. The function can be used +in a program in the following way: + function myfunc(a, b) { - if (by_fields && suppress && $0 !~ FS) - next - - for (i = 1; i <= nfields; i++) { - if ($flist[i] != "") { - printf "%s", $flist[i] - if (i < nfields && $flist[i+1] != "") - printf "%s", OFS - } - } - print "" + assert(a <= 5 && b >= 17.1, "a <= 5 && b >= 17.1") + ... } - This version of `cut' relies on `gawk''s `FIELDWIDTHS' variable to -do the character-based cutting. While it would be possible in other -`awk' implementations to use `substr' (*note Built-in Functions for -String Manipulation: String Functions.), it would also be extremely -painful to do so. The `FIELDWIDTHS' variable supplies an elegant -solution to the problem of picking the input line apart by characters. - - -File: gawk.info, Node: Egrep Program, Next: Id Program, Prev: Cut Program, Up: Clones +If the assertion fails, you see a message similar to the following: -Searching for Regular Expressions in Files ------------------------------------------- + mydata:1357: assertion failed: a <= 5 && b >= 17.1 - The `egrep' utility searches files for patterns. It uses regular -expressions that are almost identical to those available in `awk' -(*note Regular Expression Constants: Regexp Constants.). It is used -this way: + There is a small problem with this version of `assert'. An `END' +rule is automatically added to the program calling `assert'. Normally, +if a program consists of just a `BEGIN' rule, the input files and/or +standard input are not read. However, now that the program has an `END' +rule, `awk' attempts to read the input data files or standard input +(*note Startup and Cleanup Actions: Using BEGIN/END.), most likely +causing the program to hang as it waits for input. - egrep [ OPTIONS ] 'PATTERN' FILES ... + There is a simple workaround to this: make sure the `BEGIN' rule +always ends with an `exit' statement. - The PATTERN is a regexp. In typical usage, the regexp is quoted to -prevent the shell from expanding any of the special characters as file -name wildcards. Normally, `egrep' prints the lines that matched. If -multiple file names are provided on the command line, each output line -is preceded by the name of the file and a colon. + +File: gawk.info, Node: Round Function, Next: Cliff Random Function, Prev: Assert Function, Up: General Functions - The options are: +Rounding Numbers +---------------- -`-c' - Print out a count of the lines that matched the pattern, instead - of the lines themselves. + The way `printf' and `sprintf' (*note Using `printf' Statements for +Fancier Printing: Printf.) perform rounding often depends upon the +system's C `sprintf' subroutine. On many machines, `sprintf' rounding +is "unbiased," which means it doesn't always round a trailing `.5' up, +contrary to naive expectations. In unbiased rounding, `.5' rounds to +even, rather than always up, so 1.5 rounds to 2 but 4.5 rounds to 4. +This means that if you are using a format that does rounding (e.g., +`"%.0f"'), you should check what your system does. The following +function does traditional rounding; it might be useful if your awk's +`printf' does unbiased rounding: -`-s' - Be silent. No output is produced, and the exit value indicates - whether or not the pattern was matched. - -`-v' - Invert the sense of the test. `egrep' prints the lines that do - _not_ match the pattern, and exits successfully if the pattern was - not matched. - -`-i' - Ignore case distinctions in both the pattern and the input data. - -`-l' - Only print the names of the files that matched, not the lines that - matched. - -`-e PATTERN' - Use PATTERN as the regexp to match. The purpose of the `-e' - option is to allow patterns that start with a `-'. - - This version uses the `getopt' library function (*note Processing -Command Line Options: Getopt Function.), and the file transition -library program (*note Noting Data File Boundaries: Filetrans -Function.). - - The program begins with a descriptive comment, and then a `BEGIN' -rule that processes the command line arguments with `getopt'. The `-i' -(ignore case) option is particularly easy with `gawk'; we just use the -`IGNORECASE' built in variable (*note Built-in Variables::). - - # egrep.awk --- simulate egrep in awk - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - - # Options: - # -c count of lines - # -s silent - use exit value - # -v invert test, success if no match - # -i ignore case - # -l print filenames only - # -e argument is pattern - - BEGIN { - while ((c = getopt(ARGC, ARGV, "ce:svil")) != -1) { - if (c == "c") - count_only++ - else if (c == "s") - no_print++ - else if (c == "v") - invert++ - else if (c == "i") - IGNORECASE = 1 - else if (c == "l") - filenames_only++ - else if (c == "e") - pattern = Optarg - else - usage() - } - - Next comes the code that handles the `egrep' specific behavior. If no -pattern was supplied with `-e', the first non-option on the command -line is used. The `awk' command line arguments up to `ARGV[Optind]' -are cleared, so that `awk' won't try to process them as files. If no -files were specified, the standard input is used, and if multiple files -were specified, we make sure to note this so that the file names can -precede the matched lines in the output. - - The last two lines are commented out, since they are not needed in -`gawk'. They should be uncommented if you have to use another version -of `awk'. - - if (pattern == "") - pattern = ARGV[Optind++] + # round --- do normal rounding + function round(x, ival, aval, fraction) + { + ival = int(x) # integer part, int() truncates - for (i = 1; i < Optind; i++) - ARGV[i] = "" - if (Optind >= ARGC) { - ARGV[1] = "-" - ARGC = 2 - } else if (ARGC - Optind > 1) - do_filenames++ + # see if fractional part + if (ival == x) # no fraction + return x - # if (IGNORECASE) - # pattern = tolower(pattern) + if (x < 0) { + aval = -x # absolute value + ival = int(aval) + fraction = aval - ival + if (fraction >= .5) + return int(x) - 1 # -2.5 --> -3 + else + return int(x) # -2.3 --> -2 + } else { + fraction = x - ival + if (fraction >= .5) + return ival + 1 + else + return ival + } } + + # test harness + { print $0, round($0) } - The next set of lines should be uncommented if you are not using -`gawk'. This rule translates all the characters in the input line into -lower-case if the `-i' option was specified. The rule is commented out -since it is not necessary with `gawk'. + +File: gawk.info, Node: Cliff Random Function, Next: Ordinal Functions, Prev: Round Function, Up: General Functions - #{ - # if (IGNORECASE) - # $0 = tolower($0) - #} +The Cliff Random Number Generator +--------------------------------- - The `beginfile' function is called by the rule in `ftrans.awk' when -each new file is processed. In this case, it is very simple; all it -does is initialize a variable `fcount' to zero. `fcount' tracks how -many lines in the current file matched the pattern. + The Cliff random number generator(1) is a very simple random number +generator that "passes the noise sphere test for randomness by showing +no structure." It is easily programmed, in less than 10 lines of `awk' +code: - function beginfile(junk) + # cliff_rand.awk --- generate Cliff random numbers + BEGIN { _cliff_seed = 0.1 } + + function cliff_rand() { - fcount = 0 + _cliff_seed = (100 * log(_cliff_seed)) % 1 + if (_cliff_seed < 0) + _cliff_seed = - _cliff_seed + return _cliff_seed } - The `endfile' function is called after each file has been processed. -It is used only when the user wants a count of the number of lines that -matched. `no_print' will be true only if the exit status is desired. -`count_only' will be true if line counts are desired. `egrep' will -therefore only print line counts if printing and counting are enabled. -The output format must be adjusted depending upon the number of files -to be processed. Finally, `fcount' is added to `total', so that we -know how many lines altogether matched the pattern. + This algorithm requires an initial "seed" of 0.1. Each new value +uses the current seed as input for the calculation. If the built-in +`rand' function (*note Numeric Functions::) isn't random enough, you +might try using this function instead. - function endfile(file) - { - if (! no_print && count_only) - if (do_filenames) - print file ":" fcount - else - print fcount - - total += fcount - } + ---------- Footnotes ---------- - This rule does most of the work of matching lines. The variable -`matches' will be true if the line matched the pattern. If the user -wants lines that did not match, the sense of the `matches' is inverted -using the `!' operator. `fcount' is incremented with the value of -`matches', which will be either one or zero, depending upon a -successful or unsuccessful match. If the line did not match, the -`next' statement just moves on to the next record. + (1) `http://mathworld.wolfram.com/CliffRandomNumberGenerator.hmtl' - There are several optimizations for performance in the following few -lines of code. If the user only wants exit status (`no_print' is true), -and we don't have to count lines, then it is enough to know that one -line in this file matched, and we can skip on to the next file with -`nextfile'. Along similar lines, if we are only printing file names, -and we don't need to count lines, we can print the file name, and then -skip to the next file with `nextfile'. + +File: gawk.info, Node: Ordinal Functions, Next: Join Function, Prev: Cliff Random Function, Up: General Functions - Finally, each line is printed, with a leading filename and colon if -necessary. +Translating Between Characters and Numbers +------------------------------------------ - { - matches = ($0 ~ pattern) - if (invert) - matches = ! matches - - fcount += matches # 1 or 0 - - if (! matches) - next + One commercial implementation of `awk' supplies a built-in function, +`ord', which takes a character and returns the numeric value for that +character in the machine's character set. If the string passed to +`ord' has more than one character, only the first one is used. + + The inverse of this function is `chr' (from the function of the same +name in Pascal), which takes a number and returns the corresponding +character. Both functions are written very nicely in `awk'; there is +no real reason to build them into the `awk' interpreter: + + # ord.awk --- do ord and chr - if (no_print && ! count_only) - nextfile + # Global identifiers: + # _ord_: numerical values indexed by characters + # _ord_init: function to initialize _ord_ + BEGIN { _ord_init() } - if (filenames_only && ! count_only) { - print FILENAME - nextfile + function _ord_init( low, high, i, t) + { + low = sprintf("%c", 7) # BEL is ascii 7 + if (low == "\a") { # regular ascii + low = 0 + high = 127 + } else if (sprintf("%c", 128 + 7) == "\a") { + # ascii, mark parity + low = 128 + high = 255 + } else { # ebcdic(!) + low = 0 + high = 255 } - if (do_filenames && ! count_only) - print FILENAME ":" $0 - else if (! count_only) - print + for (i = low; i <= high; i++) { + t = sprintf("%c", i) + _ord_[t] = i + } } - The `END' rule takes care of producing the correct exit status. If -there were no matches, the exit status is one, otherwise it is zero. + Some explanation of the numbers used by `chr' is worthwhile. The +most prominent character set in use today is ASCII. Although an +eight-bit byte can hold 256 distinct values (from 0 to 255), ASCII only +defines characters that use the values from 0 to 127.(1) In the now +distant past, at least one minicomputer manufacturer used ASCII, but +with mark parity, meaning that the leftmost bit in the byte is always +1. This means that on those systems, characters have numeric values +from 128 to 255. Finally, large mainframe systems use the EBCDIC +character set, which uses all 256 values. While there are other +character sets in use on some older systems, they are not really worth +worrying about: - END \ + function ord(str, c) { - if (total == 0) - exit 1 - exit 0 + # only first character is of interest + c = substr(str, 1, 1) + return _ord_[c] } - - The `usage' function prints a usage message in case of invalid -options and then exits. - - function usage( e) + + function chr(c) { - e = "Usage: egrep [-csvil] [-e pat] [files ...]" - print e > "/dev/stderr" - exit 1 + # force c to be numeric by adding 0 + return sprintf("%c", c + 0) } + + #### test code #### + # BEGIN \ + # { + # for (;;) { + # printf("enter a character: ") + # if (getline var <= 0) + # break + # printf("ord(%s) = %d\n", var, ord(var)) + # } + # } - The variable `e' is used so that the function fits nicely on the -printed page. + An obvious improvement to these functions is to move the code for the +`_ord_init' function into the body of the `BEGIN' rule. It was written +this way initially for ease of development. There is a "test program" +in a `BEGIN' rule, to test the function. It is commented out for +production use. - Just a note on programming style. You may have noticed that the `END' -rule uses backslash continuation, with the open brace on a line by -itself. This is so that it more closely resembles the way functions -are written. Many of the examples use this style. You can decide for -yourself if you like writing your `BEGIN' and `END' rules this way, or -not. + ---------- Footnotes ---------- + + (1) ASCII has been extended in many countries to use the values from +128 to 255 for country-specific characters. If your system uses these +extensions, you can simplify `_ord_init' to simply loop from 0 to 255.  -File: gawk.info, Node: Id Program, Next: Split Program, Prev: Egrep Program, Up: Clones +File: gawk.info, Node: Join Function, Next: Gettimeofday Function, Prev: Ordinal Functions, Up: General Functions -Printing Out User Information ------------------------------ +Merging an Array into a String +------------------------------ - The `id' utility lists a user's real and effective user-id numbers, -real and effective group-id numbers, and the user's group set, if any. -`id' will only print the effective user-id and group-id if they are -different from the real ones. If possible, `id' will also supply the -corresponding user and group names. The output might look like this: + When doing string processing, it is often useful to be able to join +all the strings in an array into one long string. The following +function, `join', accomplishes this task. It is used later in several +of the application programs (*note Practical `awk' Programs: Sample +Programs.). - $ id - -| uid=2076(arnold) gid=10(staff) groups=10(staff),4(tty) + Good function design is important; this function needs to be general +but it should also have a reasonable default behavior. It is called +with an array as well as the beginning and ending indices of the +elements in the array to be merged. This assumes that the array +indices are numeric--a reasonable assumption since the array was likely +created with `split' (*note String Manipulation Functions: String +Functions.): + + # join.awk --- join an array into a string + function join(array, start, end, sep, result, i) + { + if (sep == "") + sep = " " + else if (sep == SUBSEP) # magic value + sep = "" + result = array[start] + for (i = start + 1; i <= end; i++) + result = result sep array[i] + return result + } - This information is exactly what is provided by `gawk''s `/dev/user' -special file (*note Special File Names in `gawk': Special Files.). -However, the `id' utility provides a more palatable output than just a -string of numbers. + An optional additional argument is the separator to use when joining +the strings back together. If the caller supplies a non-empty value, +`join' uses it; if it is not supplied, it has a null value. In this +case, `join' uses a single blank as a default separator for the +strings. If the value is equal to `SUBSEP', then `join' joins the +strings with no separator between them. `SUBSEP' serves as a "magic" +value to indicate that there should be no separation between the +component strings.(1) - Here is a simple version of `id' written in `awk'. It uses the user -database library functions (*note Reading the User Database: Passwd -Functions.), and the group database library functions (*note Reading -the Group Database: Group Functions.). + ---------- Footnotes ---------- - The program is fairly straightforward. All the work is done in the -`BEGIN' rule. The user and group id numbers are obtained from -`/dev/user'. If there is no support for `/dev/user', the program gives -up. + (1) It would be nice if `awk' had an assignment operator for +concatenation. The lack of an explicit operator for concatenation +makes string operations more difficult than they really need to be. - The code is repetitive. The entry in the user database for the real -user-id number is split into parts at the `:'. The name is the first -field. Similar code is used for the effective user-id number, and the -group numbers. + +File: gawk.info, Node: Gettimeofday Function, Prev: Join Function, Up: General Functions - # id.awk --- implement id in awk - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 +Managing the Time of Day +------------------------ + + The `systime' and `strftime' functions described in *Note Using +`gawk''s Timestamp Functions: Time Functions, provide the minimum +functionality necessary for dealing with the time of day in human +readable form. While `strftime' is extensive, the control formats are +not necessarily easy to remember or intuitively obvious when reading a +program. + + The following function, `gettimeofday', populates a user-supplied +array with preformatted time information. It returns a string with the +current time formatted in the same way as the `date' utility: + + # gettimeofday.awk --- get the time of day in a usable format - # output is: - # uid=12(foo) euid=34(bar) gid=3(baz) \ - # egid=5(blat) groups=9(nine),2(two),1(one) + # Returns a string in the format of output of date(1) + # Populates the array argument time with individual values: + # time["second"] -- seconds (0 - 59) + # time["minute"] -- minutes (0 - 59) + # time["hour"] -- hours (0 - 23) + # time["althour"] -- hours (0 - 12) + # time["monthday"] -- day of month (1 - 31) + # time["month"] -- month of year (1 - 12) + # time["monthname"] -- name of the month + # time["shortmonth"] -- short name of the month + # time["year"] -- year modulo 100 (0 - 99) + # time["fullyear"] -- full year + # time["weekday"] -- day of week (Sunday = 0) + # time["altweekday"] -- day of week (Monday = 0) + # time["dayname"] -- name of weekday + # time["shortdayname"] -- short name of weekday + # time["yearday"] -- day of year (0 - 365) + # time["timezone"] -- abbreviation of timezone name + # time["ampm"] -- AM or PM designation + # time["weeknum"] -- week number, Sunday first day + # time["altweeknum"] -- week number, Monday first day - BEGIN \ + function gettimeofday(time, ret, now, i) { - if ((getline < "/dev/user") < 0) { - err = "id: no /dev/user support - cannot run" - print err > "/dev/stderr" - exit 1 - } - close("/dev/user") - - uid = $1 - euid = $2 - gid = $3 - egid = $4 - - printf("uid=%d", uid) - pw = getpwuid(uid) - if (pw != "") { - split(pw, a, ":") - printf("(%s)", a[1]) - } + # get time once, avoids unnecessary system calls + now = systime() - if (euid != uid) { - printf(" euid=%d", euid) - pw = getpwuid(euid) - if (pw != "") { - split(pw, a, ":") - printf("(%s)", a[1]) - } - } + # return date(1)-style output + ret = strftime("%a %b %d %H:%M:%S %Z %Y", now) - printf(" gid=%d", gid) - pw = getgrgid(gid) - if (pw != "") { - split(pw, a, ":") - printf("(%s)", a[1]) - } + # clear out target array + delete time - if (egid != gid) { - printf(" egid=%d", egid) - pw = getgrgid(egid) - if (pw != "") { - split(pw, a, ":") - printf("(%s)", a[1]) - } - } + # fill in values, force numeric values to be + # numeric by adding 0 + time["second"] = strftime("%S", now) + 0 + time["minute"] = strftime("%M", now) + 0 + time["hour"] = strftime("%H", now) + 0 + time["althour"] = strftime("%I", now) + 0 + time["monthday"] = strftime("%d", now) + 0 + time["month"] = strftime("%m", now) + 0 + time["monthname"] = strftime("%B", now) + time["shortmonth"] = strftime("%b", now) + time["year"] = strftime("%y", now) + 0 + time["fullyear"] = strftime("%Y", now) + 0 + time["weekday"] = strftime("%w", now) + 0 + time["altweekday"] = strftime("%u", now) + 0 + time["dayname"] = strftime("%A", now) + time["shortdayname"] = strftime("%a", now) + time["yearday"] = strftime("%j", now) + 0 + time["timezone"] = strftime("%Z", now) + time["ampm"] = strftime("%p", now) + time["weeknum"] = strftime("%U", now) + 0 + time["altweeknum"] = strftime("%W", now) + 0 - if (NF > 4) { - printf(" groups="); - for (i = 5; i <= NF; i++) { - printf("%d", $i) - pw = getgrgid($i) - if (pw != "") { - split(pw, a, ":") - printf("(%s)", a[1]) - } - if (i < NF) - printf(",") - } - } - print "" + return ret } + The string indices are easier to use and read than the various +formats required by `strftime'. The `alarm' program presented in *Note +An Alarm Clock Program: Alarm Program, uses this function. A more +general design for the `gettimeofday' function would have allowed the +user to supply an optional timestamp value to use instead of the +current time. +  -File: gawk.info, Node: Split Program, Next: Tee Program, Prev: Id Program, Up: Clones +File: gawk.info, Node: Data File Management, Next: Getopt Function, Prev: General Functions, Up: Library Functions -Splitting a Large File Into Pieces ----------------------------------- +Data File Management +==================== - The `split' program splits large text files into smaller pieces. By -default, the output files are named `xaa', `xab', and so on. Each file -has 1000 lines in it, with the likely exception of the last file. To -change the number of lines in each file, you supply a number on the -command line preceded with a minus, e.g., `-500' for files with 500 -lines in them instead of 1000. To change the name of the output files -to something like `myfileaa', `myfileab', and so on, you supply an -additional argument that specifies the filename. + This minor node presents functions that are useful for managing +command-line datafiles. - Here is a version of `split' in `awk'. It uses the `ord' and `chr' -functions presented in *Note Translating Between Characters and -Numbers: Ordinal Functions. +* Menu: - The program first sets its defaults, and then tests to make sure -there are not too many arguments. It then looks at each argument in -turn. The first argument could be a minus followed by a number. If it -is, this happens to look like a negative number, so it is made -positive, and that is the count of lines. The data file name is -skipped over, and the final argument is used as the prefix for the -output file names. +* Filetrans Function:: A function for handling data file transitions. +* Rewind Function:: A function for rereading the current file. +* File Checking:: Checking that data files are readable. +* Ignoring Assigns:: Treating assignments as file names. - # split.awk --- do split in awk - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - - # usage: split [-num] [file] [outname] - - BEGIN { - outfile = "x" # default - count = 1000 - if (ARGC > 4) - usage() - - i = 1 - if (ARGV[i] ~ /^-[0-9]+$/) { - count = -ARGV[i] - ARGV[i] = "" - i++ - } - # test argv in case reading from stdin instead of file - if (i in ARGV) - i++ # skip data file name - if (i in ARGV) { - outfile = ARGV[i] - ARGV[i] = "" - } + +File: gawk.info, Node: Filetrans Function, Next: Rewind Function, Prev: Data File Management, Up: Data File Management + +Noting Data File Boundaries +--------------------------- + + The `BEGIN' and `END' rules are each executed exactly once, at the +beginning and end of your `awk' program, respectively (*note The +`BEGIN' and `END' Special Patterns: BEGIN/END.). We (the `gawk' +authors) once had a user who mistakenly thought that the `BEGIN' rule +is executed at the beginning of each data file and the `END' rule is +executed at the end of each data file. When informed that this was not +the case, the user requested that we add new special patterns to +`gawk', named `BEGIN_FILE' and `END_FILE', that would have the desired +behavior. He even supplied us the code to do so. + + Adding these special patterns to `gawk' wasn't necessary; the job +can be done cleanly in `awk' itself, as illustrated by the following +library program. It arranges to call two user-supplied functions, +`beginfile' and `endfile', at the beginning and end of each data file. +Besides solving the problem in only nine(!) lines of code, it does so +_portably_; this works with any implementation of `awk': + + # transfile.awk + # + # Give the user a hook for filename transitions + # + # The user must supply functions beginfile() and endfile() + # that each take the name of the file being started or + # finished, respectively. - s1 = s2 = "a" - out = (outfile s1 s2) + FILENAME != _oldfilename \ + { + if (_oldfilename != "") + endfile(_oldfilename) + _oldfilename = FILENAME + beginfile(FILENAME) } + + END { endfile(FILENAME) } - The next rule does most of the work. `tcount' (temporary count) -tracks how many lines have been printed to the output file so far. If -it is greater than `count', it is time to close the current file and -start a new one. `s1' and `s2' track the current suffixes for the file -name. If they are both `z', the file is just too big. Otherwise, `s1' -moves to the next letter in the alphabet and `s2' starts over again at -`a'. + This file must be loaded before the user's "main" program, so that +the rule it supplies is executed first. - { - if (++tcount > count) { - close(out) - if (s2 == "z") { - if (s1 == "z") { - printf("split: %s is too large to split\n", \ - FILENAME) > "/dev/stderr" - exit 1 - } - s1 = chr(ord(s1) + 1) - s2 = "a" - } else - s2 = chr(ord(s2) + 1) - out = (outfile s1 s2) - tcount = 1 - } - print > out + This rule relies on `awk''s `FILENAME' variable that automatically +changes for each new data file. The current file name is saved in a +private variable, `_oldfilename'. If `FILENAME' does not equal +`_oldfilename', then a new data file is being processed and it is +necessary to call `endfile' for the old file. Because `endfile' should +only be called if a file has been processed, the program first checks +to make sure that `_oldfilename' is not the null string. The program +then assigns the current file name to `_oldfilename' and calls +`beginfile' for the file. Because, like all `awk' variables, +`_oldfilename' is initialized to the null string, this rule executes +correctly even for the first data file. + + The program also supplies an `END' rule to do the final processing +for the last file. Because this `END' rule comes before any `END' rules +supplied in the "main" program, `endfile' is called first. Once again +the value of multiple `BEGIN' and `END' rules should be clear. + + This version has same problem as the first version of `nextfile' +(*note Implementing `nextfile' as a Function: Nextfile Function.). If +the same data file occurs twice in a row on the command line, then +`endfile' and `beginfile' are not executed at the end of the first pass +and at the beginning of the second pass. The following version solves +the problem: + + # ftrans.awk --- handle data file transitions + # + # user supplies beginfile() and endfile() functions + FNR == 1 { + if (_filename_ != "") + endfile(_filename_) + _filename_ = FILENAME + beginfile(FILENAME) } + + END { endfile(_filename_) } - The `usage' function simply prints an error message and exits. + *Note Counting Things: Wc Program, shows how this library function +can be used and how it simplifies writing the main program. - function usage( e) + +File: gawk.info, Node: Rewind Function, Next: File Checking, Prev: Filetrans Function, Up: Data File Management + +Rereading the Current File +-------------------------- + + Another request for a new built-in function was for a `rewind' +function that would make it possible to reread the current file. The +requesting user didn't want to have to use `getline' (*note Explicit +Input with `getline': Getline.) inside a loop. + + However, as long as you are not in the `END' rule, it is quite easy +to arrange to immediately close the current input file and then start +over with it from the top. For lack of a better name, we'll call it +`rewind': + + # rewind.awk --- rewind the current file and start over + function rewind( i) { - e = "usage: split [-num] [file] [outname]" - print e > "/dev/stderr" - exit 1 + # shift remaining arguments up + for (i = ARGC; i > ARGIND; i--) + ARGV[i] = ARGV[i-1] + + # make sure gawk knows to keep going + ARGC++ + + # make current file next to get done + ARGV[ARGIND+1] = FILENAME + + # do it + nextfile } -The variable `e' is used so that the function fits nicely on the screen. + This code relies on the `ARGIND' variable (*note Built-in Variables +That Convey Information: Auto-set.), which is specific to `gawk'. If +you are not using `gawk', you can use ideas presented in *Note Noting +Data File Boundaries: Filetrans Function, to either update `ARGIND' on +your own or modify this code as appropriate. - This program is a bit sloppy; it relies on `awk' to close the last -file for it automatically, instead of doing it in an `END' rule. + The `rewind' function also relies on the `nextfile' keyword (*note +Using `gawk''s `nextfile' Statement: Nextfile Statement.). *Note +Implementing `nextfile' as a Function: Nextfile Function, for a +function version of `nextfile'.  -File: gawk.info, Node: Tee Program, Next: Uniq Program, Prev: Split Program, Up: Clones +File: gawk.info, Node: File Checking, Next: Ignoring Assigns, Prev: Rewind Function, Up: Data File Management -Duplicating Output Into Multiple Files --------------------------------------- +Checking for Readable Data Files +-------------------------------- - The `tee' program is known as a "pipe fitting." `tee' copies its -standard input to its standard output, and also duplicates it to the -files named on the command line. Its usage is: + Normally, if you give `awk' a data file that isn't readable, it +stops with a fatal error. There are times when you might want to just +ignore such files and keep going. You can do this by prepending the +following program to your `awk' program: - tee [-a] file ... + # readable.awk --- library file to skip over unreadable files + BEGIN { + for (i = 1; i < ARGC; i++) { + if (ARGV[i] ~ /^[A-Za-z_][A-Za-z0-9_]*=.*/ \ + || ARGV[i] == "-") + continue # assignment or standard input + else if ((getline junk < ARGV[i]) < 0) # unreadable + delete ARGV[i] + else + close(ARGV[i]) + } + } - The `-a' option tells `tee' to append to the named files, instead of -truncating them and starting over. + In `gawk', the `getline' won't be fatal (unless `--posix' is in +force). Removing the element from `ARGV' with `delete' skips the file +(since it's no longer in the list). + + +File: gawk.info, Node: Ignoring Assigns, Prev: File Checking, Up: Data File Management - The `BEGIN' rule first makes a copy of all the command line -arguments, into an array named `copy'. `ARGV[0]' is not copied, since -it is not needed. `tee' cannot use `ARGV' directly, since `awk' will -attempt to process each file named in `ARGV' as input data. +Treating Assignments as File Names +---------------------------------- - If the first argument is `-a', then the flag variable `append' is -set to true, and both `ARGV[1]' and `copy[1]' are deleted. If `ARGC' is -less than two, then no file names were supplied, and `tee' prints a -usage message and exits. Finally, `awk' is forced to read the standard -input by setting `ARGV[1]' to `"-"', and `ARGC' to two. + Occasionally, you might not want `awk' to process command-line +variable assignments (*note Assigning Variables on the Command Line: +Assignment Options.). In particular, if you have file names that +contain an `=' character, `awk' treats the file name as an assignment, +and does not process it. - # tee.awk --- tee in awk - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - # Revised December 1995 - - BEGIN \ + Some users have suggested an additional command-line option for +`gawk' to disable command-line assignments. However, some simple +programming with a library file does the trick: + + # noassign.awk --- library file to avoid the need for a + # special option that disables command-line assignments + function disable_assigns(argc, argv, i) { - for (i = 1; i < ARGC; i++) - copy[i] = ARGV[i] + for (i = 1; i < argc; i++) + if (argv[i] ~ /^[A-Za-z_][A-Za-z_0-9]*=.*/) + argv[i] = ("./" argv[i]) + } - if (ARGV[1] == "-a") { - append = 1 - delete ARGV[1] - delete copy[1] - ARGC-- - } - if (ARGC < 2) { - print "usage: tee [-a] file ..." > "/dev/stderr" - exit 1 - } - ARGV[1] = "-" - ARGC = 2 + BEGIN { + if (No_command_assign) + disable_assigns(ARGC, ARGV) } - The single rule does all the work. Since there is no pattern, it is -executed for each line of input. The body of the rule simply prints the -line into each file on the command line, and then to the standard -output. + You then run your program this way: - { - # moving the if outside the loop makes it run faster - if (append) - for (i in copy) - print >> copy[i] - else - for (i in copy) - print > copy[i] - print - } - - It would have been possible to code the loop this way: - - for (i in copy) - if (append) - print >> copy[i] - else - print > copy[i] - -This is more concise, but it is also less efficient. The `if' is -tested for each record and for each output file. By duplicating the -loop body, the `if' is only tested once for each input record. If -there are N input records and M input files, the first method only -executes N `if' statements, while the second would execute N`*'M `if' -statements. + awk -v No_command_assign=1 -f noassign.awk -f yourprog.awk * - Finally, the `END' rule cleans up, by closing all the output files. + The function works by looping through the arguments. It prepends +`./' to any argument that matches the form of a variable assignment, +turning that argument into a file name. - END \ - { - for (i in copy) - close(copy[i]) - } + The use of `No_command_assign' allows you to disable command-line +assignments at invocation time, by giving the variable a true value. +When not set, it is initially zero (i.e., false), so the command-line +arguments are left alone.  -File: gawk.info, Node: Uniq Program, Next: Wc Program, Prev: Tee Program, Up: Clones - -Printing Non-duplicated Lines of Text -------------------------------------- - - The `uniq' utility reads sorted lines of data on its standard input, -and (by default) removes duplicate lines. In other words, only unique -lines are printed, hence the name. `uniq' has a number of options. The -usage is: +File: gawk.info, Node: Getopt Function, Next: Passwd Functions, Prev: Data File Management, Up: Library Functions - uniq [-udc [-N]] [+N] [ INPUT FILE [ OUTPUT FILE ]] +Processing Command-Line Options +=============================== - The option meanings are: + Most utilities on POSIX compatible systems take options, or +"switches," on the command line that can be used to change the way a +program behaves. `awk' is an example of such a program (*note +Command-Line Options: Options.). Often, options take "arguments"; +i.e., data that the program needs to correctly obey the command-line +option. For example, `awk''s `-F' option requires a string to use as +the field separator. The first occurrence on the command line of +either `--' or a string that does not begin with `-' ends the options. + + Modern Unix systems provide a C function named `getopt' for +processing command-line arguments. The programmer provides a string +describing the one-letter options. If an option requires an argument, +it is followed in the string with a colon. `getopt' is also passed the +count and values of the command-line arguments and is called in a loop. +`getopt' processes the command-line arguments for option letters. Each +time around the loop, it returns a single character representing the +next option letter that it finds, or `?' if it finds an invalid option. +When it returns -1, there are no options left on the command line. -`-d' - Only print repeated lines. + When using `getopt', options that do not take arguments can be +grouped together. Furthermore, options that take arguments require +that the argument is present. The argument can immediately follow the +option letter or it can be a separate command-line argument. -`-u' - Only print non-repeated lines. + Given a hypothetical program that takes three command-line options, +`-a', `-b', and `-c', where `-b' requires an argument, all of the +following are valid ways of invoking the program: -`-c' - Count lines. This option overrides `-d' and `-u'. Both repeated - and non-repeated lines are counted. + prog -a -b foo -c data1 data2 data3 + prog -ac -bfoo -- data1 data2 data3 + prog -acbfoo data1 data2 data3 -`-N' - Skip N fields before comparing lines. The definition of fields is - similar to `awk''s default: non-whitespace characters separated by - runs of spaces and/or tabs. + Notice that when the argument is grouped with its option, the rest of +the argument is considered to be the option's argument. In this +example, `-acbfoo' indicates that all of the `-a', `-b', and `-c' +options were supplied, and that `foo' is the argument to the `-b' +option. -`+N' - Skip N characters before comparing lines. Any fields specified - with `-N' are skipped first. + `getopt' provides four external variables that the programmer can +use: -`INPUT FILE' - Data is read from the input file named on the command line, - instead of from the standard input. +`optind' + The index in the argument value array (`argv') where the first + non-option command-line argument can be found. -`OUTPUT FILE' - The generated output is sent to the named output file, instead of - to the standard output. +`optarg' + The string value of the argument to an option. - Normally `uniq' behaves as if both the `-d' and `-u' options had -been provided. +`opterr' + Usually `getopt' prints an error message when it finds an invalid + option. Setting `opterr' to zero disables this feature. (An + application might want to print its own error message.) - Here is an `awk' implementation of `uniq'. It uses the `getopt' -library function (*note Processing Command Line Options: Getopt -Function.), and the `join' library function (*note Merging an Array -Into a String: Join Function.). +`optopt' + The letter representing the command-line option. - The program begins with a `usage' function and then a brief outline -of the options and their meanings in a comment. - - The `BEGIN' rule deals with the command line arguments and options. -It uses a trick to get `getopt' to handle options of the form `-25', -treating such an option as the option letter `2' with an argument of -`5'. If indeed two or more digits were supplied (`Optarg' looks like a -number), `Optarg' is concatenated with the option digit, and then -result is added to zero to make it into a number. If there is only one -digit in the option, then `Optarg' is not needed, and `Optind' must be -decremented so that `getopt' will process it next time. This code is -admittedly a bit tricky. - - If no options were supplied, then the default is taken, to print both -repeated and non-repeated lines. The output file, if provided, is -assigned to `outputfile'. Earlier, `outputfile' was initialized to the -standard output, `/dev/stdout'. + The following C fragment shows how `getopt' might process +command-line arguments for `awk': - # uniq.awk --- do uniq in awk - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - - function usage( e) - { - e = "Usage: uniq [-udc [-n]] [+n] [ in [ out ]]" - print e > "/dev/stderr" - exit 1 - } - - # -c count lines. overrides -d and -u - # -d only repeated lines - # -u only non-repeated lines - # -n skip n fields - # +n skip n characters, skip fields first - - BEGIN \ + int + main(int argc, char *argv[]) { - count = 1 - outputfile = "/dev/stdout" - opts = "udc0:1:2:3:4:5:6:7:8:9:" - while ((c = getopt(ARGC, ARGV, opts)) != -1) { - if (c == "u") - non_repeated_only++ - else if (c == "d") - repeated_only++ - else if (c == "c") - do_count++ - else if (index("0123456789", c) != 0) { - # getopt requires args to options - # this messes us up for things like -5 - if (Optarg ~ /^[0-9]+$/) - fcount = (c Optarg) + 0 - else { - fcount = c + 0 - Optind-- - } - } else - usage() - } - - if (ARGV[Optind] ~ /^\+[0-9]+$/) { - charcount = substr(ARGV[Optind], 2) + 0 - Optind++ - } - - for (i = 1; i < Optind; i++) - ARGV[i] = "" - - if (repeated_only == 0 && non_repeated_only == 0) - repeated_only = non_repeated_only = 1 - - if (ARGC - Optind == 2) { - outputfile = ARGV[ARGC - 1] - ARGV[ARGC - 1] = "" + ... + /* print our own message */ + opterr = 0; + while ((c = getopt(argc, argv, "v:f:F:W:")) != -1) { + switch (c) { + case 'f': /* file */ + ... + break; + case 'F': /* field separator */ + ... + break; + case 'v': /* variable assignment */ + ... + break; + case 'W': /* extension */ + ... + break; + case '?': + default: + usage(); + break; + } } + ... } - The following function, `are_equal', compares the current line, -`$0', to the previous line, `last'. It handles skipping fields and -characters. - - If no field count and no character count were specified, `are_equal' -simply returns one or zero depending upon the result of a simple string -comparison of `last' and `$0'. Otherwise, things get more complicated. + As a side point, `gawk' actually uses the GNU `getopt_long' function +to process both normal and GNU-style long options (*note Command-Line +Options: Options.). - If fields have to be skipped, each line is broken into an array using -`split' (*note Built-in Functions for String Manipulation: String -Functions.), and then the desired fields are joined back into a line -using `join'. The joined lines are stored in `clast' and `cline'. If -no fields are skipped, `clast' and `cline' are set to `last' and `$0' -respectively. + The abstraction provided by `getopt' is very useful and is quite +handy in `awk' programs as well. Following is an `awk' version of +`getopt'. This function highlights one of the greatest weaknesses in +`awk', which is that it is very poor at manipulating single characters. +Repeated calls to `substr' are necessary for accessing individual +characters (*note String Manipulation Functions: String Functions.).(1) - Finally, if characters are skipped, `substr' is used to strip off the -leading `charcount' characters in `clast' and `cline'. The two strings -are then compared, and `are_equal' returns the result. + The discussion that follows walks through the code a bit at a time: - function are_equal( n, m, clast, cline, alast, aline) - { - if (fcount == 0 && charcount == 0) - return (last == $0) + # getopt.awk --- do C library getopt(3) function in awk + # External variables: + # Optind -- index in ARGV of first non-option argument + # Optarg -- string value of argument to current option + # Opterr -- if nonzero, print our own diagnostic + # Optopt -- current option letter - if (fcount > 0) { - n = split(last, alast) - m = split($0, aline) - clast = join(alast, fcount+1, n) - cline = join(aline, fcount+1, m) - } else { - clast = last - cline = $0 - } - if (charcount) { - clast = substr(clast, charcount + 1) - cline = substr(cline, charcount + 1) - } + # Returns: + # -1 at end of options + # ? for unrecognized option + # a character representing the current option - return (clast == cline) - } - - The following two rules are the body of the program. The first one -is executed only for the very first line of data. It sets `last' equal -to `$0', so that subsequent lines of text have something to be compared -to. + # Private Data: + # _opti -- index in multi-flag option, e.g., -abc - The second rule does the work. The variable `equal' will be one or -zero depending upon the results of `are_equal''s comparison. If `uniq' -is counting repeated lines, then the `count' variable is incremented if -the lines are equal. Otherwise the line is printed and `count' is -reset, since the two lines are not equal. + The function starts out with a list of the global variables it uses, +what the return values are, what they mean, and any global variables +that are "private" to this library function. Such documentation is +essential for any program, and particularly for library functions. - If `uniq' is not counting, `count' is incremented if the lines are -equal. Otherwise, if `uniq' is counting repeated lines, and more than -one line has been seen, or if `uniq' is counting non-repeated lines, -and only one line has been seen, then the line is printed, and `count' -is reset. + The `getopt' function first checks that it was indeed called with a +string of options (the `options' parameter). If `options' has a zero +length, `getopt' immediately returns -1: - Finally, similar logic is used in the `END' rule to print the final -line of input data. - - NR == 1 { - last = $0 - next - } - + function getopt(argc, argv, options, thisopt, i) { - equal = are_equal() - - if (do_count) { # overrides -d and -u - if (equal) - count++ - else { - printf("%4d %s\n", count, last) > outputfile - last = $0 - count = 1 # reset - } - next - } + if (length(options) == 0) # no options given + return -1 - if (equal) - count++ - else { - if ((repeated_only && count > 1) || - (non_repeated_only && count == 1)) - print last > outputfile - last = $0 - count = 1 + if (argv[Optind] == "--") { # all done + Optind++ + _opti = 0 + return -1 + } else if (argv[Optind] !~ /^-[^: \t\n\f\r\v\b]/) { + _opti = 0 + return -1 } - } - - END { - if (do_count) - printf("%4d %s\n", count, last) > outputfile - else if ((repeated_only && count > 1) || - (non_repeated_only && count == 1)) - print last > outputfile - } - -File: gawk.info, Node: Wc Program, Prev: Uniq Program, Up: Clones + The next thing to check for is the end of the options. A `--' ends +the command-line options, as does any command-line argument that does +not begin with a `-'. `Optind' is used to step through the array of +command-line arguments; it retains its value across calls to `getopt', +because it is a global variable. -Counting Things ---------------- + The regular expression that is used, `/^-[^: \t\n\f\r\v\b]/', is +perhaps a bit of overkill; it checks for a `-' followed by anything +that is not whitespace and not a colon. If the current command-line +argument does not match this pattern, it is not an option, and it ends +option processing. - The `wc' (word count) utility counts lines, words, and characters in -one or more input files. Its usage is: + if (_opti == 0) + _opti = 2 + thisopt = substr(argv[Optind], _opti, 1) + Optopt = thisopt + i = index(options, thisopt) + if (i == 0) { + if (Opterr) + printf("%c -- invalid option\n", + thisopt) > "/dev/stderr" + if (_opti >= length(argv[Optind])) { + Optind++ + _opti = 0 + } else + _opti++ + return "?" + } - wc [-lwc] [ FILES ... ] + The `_opti' variable tracks the position in the current command-line +argument (`argv[Optind]'). If multiple options are grouped together +with one `-' (e.g., `-abx'), it is necessary to return them to the user +one at a time. - If no files are specified on the command line, `wc' reads its -standard input. If there are multiple files, it will also print total -counts for all the files. The options and their meanings are: + If `_opti' is equal to zero, it is set to two, which is the index in +the string of the next character to look at (we skip the `-', which is +at position one). The variable `thisopt' holds the character, obtained +with `substr'. It is saved in `Optopt' for the main program to use. -`-l' - Only count lines. - -`-w' - Only count words. A "word" is a contiguous sequence of - non-whitespace characters, separated by spaces and/or tabs. - Happily, this is the normal way `awk' separates fields in its - input data. - -`-c' - Only count characters. + If `thisopt' is not in the `options' string, then it is an invalid +option. If `Opterr' is nonzero, `getopt' prints an error message on +the standard error that is similar to the message from the C version of +`getopt'. - Implementing `wc' in `awk' is particularly elegant, since `awk' does -a lot of the work for us; it splits lines into words (i.e. fields) and -counts them, it counts lines (i.e. records) for us, and it can easily -tell us how long a line is. + Because the option is invalid, it is necessary to skip it and move +on to the next option character. If `_opti' is greater than or equal +to the length of the current command-line argument, it is necessary to +move on to the next argument, so `Optind' is incremented and `_opti' is +reset to zero. Otherwise, `Optind' is left alone and `_opti' is merely +incremented. - This version uses the `getopt' library function (*note Processing -Command Line Options: Getopt Function.), and the file transition -functions (*note Noting Data File Boundaries: Filetrans Function.). + In any case, because the option is invalid, `getopt' returns `?'. +The main program can examine `Optopt' if it needs to know what the +invalid option letter actually is. Continuing on: - This version has one major difference from traditional versions of -`wc'. Our version always prints the counts in the order lines, words, -and characters. Traditional versions note the order of the `-l', `-w', -and `-c' options on the command line, and print the counts in that -order. + if (substr(options, i + 1, 1) == ":") { + # get option argument + if (length(substr(argv[Optind], _opti + 1)) > 0) + Optarg = substr(argv[Optind], _opti + 1) + else + Optarg = argv[++Optind] + _opti = 0 + } else + Optarg = "" - The `BEGIN' rule does the argument processing. The variable -`print_total' will be true if more than one file was named on the -command line. + If the option requires an argument, the option letter is followed by +a colon in the `options' string. If there are remaining characters in +the current command-line argument (`argv[Optind]'), then the rest of +that string is assigned to `Optarg'. Otherwise, the next command-line +argument is used (`-xFOO' vs. `-x FOO'). In either case, `_opti' is +reset to zero, because there are no more characters left to examine in +the current command-line argument. Continuing: - # wc.awk --- count lines, words, characters - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - - # Options: - # -l only count lines - # -w only count words - # -c only count characters - # - # Default is to count lines, words, characters - - BEGIN { - # let getopt print a message about - # invalid options. we ignore them - while ((c = getopt(ARGC, ARGV, "lwc")) != -1) { - if (c == "l") - do_lines = 1 - else if (c == "w") - do_words = 1 - else if (c == "c") - do_chars = 1 - } - for (i = 1; i < Optind; i++) - ARGV[i] = "" - - # if no options, do all - if (! do_lines && ! do_words && ! do_chars) - do_lines = do_words = do_chars = 1 - - print_total = (ARGC - i > 2) + if (_opti == 0 || _opti >= length(argv[Optind])) { + Optind++ + _opti = 0 + } else + _opti++ + return thisopt } - The `beginfile' function is simple; it just resets the counts of -lines, words, and characters to zero, and saves the current file name in -`fname'. + Finally, if `_opti' is either zero or greater than the length of the +current command-line argument, it means this element in `argv' is +through being processed, so `Optind' is incremented to point to the +next element in `argv'. If neither condition is true, then only +`_opti' is incremented, so that the next option letter can be processed +on the next call to `getopt'. - The `endfile' function adds the current file's numbers to the running -totals of lines, words, and characters. It then prints out those -numbers for the file that was just read. It relies on `beginfile' to -reset the numbers for the following data file. + The `BEGIN' rule initializes both `Opterr' and `Optind' to one. +`Opterr' is set to one, since the default behavior is for `getopt' to +print a diagnostic message upon seeing an invalid option. `Optind' is +set to one, since there's no reason to look at the program name, which +is in `ARGV[0]': - function beginfile(file) { - chars = lines = words = 0 - fname = FILENAME - } + BEGIN { + Opterr = 1 # default is to diagnose + Optind = 1 # skip ARGV[0] - function endfile(file) - { - tchars += chars - tlines += lines - twords += words - if (do_lines) - printf "\t%d", lines - if (do_words) - printf "\t%d", words - if (do_chars) - printf "\t%d", chars - printf "\t%s\n", fname + # test program + if (_getopt_test) { + while ((_go_c = getopt(ARGC, ARGV, "ab:cd")) != -1) + printf("c = <%c>, optarg = <%s>\n", + _go_c, Optarg) + printf("non-option arguments:\n") + for (; Optind < ARGC; Optind++) + printf("\tARGV[%d] = <%s>\n", + Optind, ARGV[Optind]) + } } - There is one rule that is executed for each line. It adds the length -of the record to `chars'. It has to add one, since the newline -character separating records (the value of `RS') is not part of the -record itself. `lines' is incremented for each line read, and `words' -is incremented by the value of `NF', the number of "words" on this -line.(1) - - Finally, the `END' rule simply prints the totals for all the files. + The rest of the `BEGIN' rule is a simple test program. Here is the +result of two sample runs of the test program: - # do per line - { - chars += length($0) + 1 # get newline - lines++ - words += NF - } + $ awk -f getopt.awk -v _getopt_test=1 -- -a -cbARG bax -x + -| c = , optarg = <> + -| c = , optarg = <> + -| c = , optarg = + -| non-option arguments: + -| ARGV[3] = + -| ARGV[4] = <-x> - END { - if (print_total) { - if (do_lines) - printf "\t%d", tlines - if (do_words) - printf "\t%d", twords - if (do_chars) - printf "\t%d", tchars - print "\ttotal" - } - } + $ awk -f getopt.awk -v _getopt_test=1 -- -a -x -- xyz abc + -| c = , optarg = <> + error--> x -- invalid option + -| c = , optarg = <> + -| non-option arguments: + -| ARGV[4] = + -| ARGV[5] = + + In both runs, the first `--' terminates the arguments to `awk', so +that it does not try to interpret the `-a', etc., as its own options. +Several of the sample programs presented in *Note Practical `awk' +Programs: Sample Programs, use `getopt' to process their arguments. ---------- Footnotes ---------- - (1) Examine the code in *Note Noting Data File Boundaries: Filetrans -Function. Why must `wc' use a separate `lines' variable, instead of -using the value of `FNR' in `endfile'? + (1) This function was written before `gawk' acquired the ability to +split strings into single characters using `""' as the separator. We +have left it alone, since using `substr' is more portable.  -File: gawk.info, Node: Miscellaneous Programs, Prev: Clones, Up: Sample Programs +File: gawk.info, Node: Passwd Functions, Next: Group Functions, Prev: Getopt Function, Up: Library Functions -A Grab Bag of `awk' Programs -============================ +Reading the User Database +========================= - This section is a large "grab bag" of miscellaneous programs. We -hope you find them both interesting and enjoyable. + The `PROCINFO' array (*note Built-in Variables::) provides access to +the current user's real and effective user and group id numbers, and if +available, the user's supplementary group set. However, because these +are numbers, they do not provide very useful information to the average +user. There needs to be some way to find the user information +associated with the user and group numbers. This minor node presents a +suite of functions for retrieving information from the user database. +*Note Reading the Group Database: Group Functions, for a similar suite +that retrieves information from the group database. -* Menu: + The POSIX standard does not define the file where user information is +kept. Instead, it provides the `' header file and several C +language subroutines for obtaining user information. The primary +function is `getpwent', for "get password entry." The "password" comes +from the original user database file, `/etc/passwd', which stores user +information, along with the encrypted passwords (hence the name). -* Dupword Program:: Finding duplicated words in a document. -* Alarm Program:: An alarm clock. -* Translate Program:: A program similar to the `tr' utility. -* Labels Program:: Printing mailing labels. -* Word Sorting:: A program to produce a word usage count. -* History Sorting:: Eliminating duplicate entries from a history - file. -* Extract Program:: Pulling out programs from Texinfo source - files. -* Simple Sed:: A Simple Stream Editor. -* Igawk Program:: A wrapper for `awk' that includes files. + While an `awk' program could simply read `/etc/passwd' directly, +this file may not contain complete information about the system's set +of users.(1) To be sure you are able to produce a readable and complete +version of the user database, it is necessary to write a small C +program that calls `getpwent'. `getpwent' is defined as returning a +pointer to a `struct passwd'. Each time it is called, it returns the +next entry in the database. When there are no more entries, it returns +`NULL', the null pointer. When this happens, the C program should call +`endpwent' to close the database. Following is `pwcat', a C program +that "cats" the password database. - -File: gawk.info, Node: Dupword Program, Next: Alarm Program, Prev: Miscellaneous Programs, Up: Miscellaneous Programs + /* + * pwcat.c + * + * Generate a printable version of the password database + */ + #include + #include + + int + main(argc, argv) + int argc; + char **argv; + { + struct passwd *p; + + while ((p = getpwent()) != NULL) + printf("%s:%s:%d:%d:%s:%s:%s\n", + p->pw_name, p->pw_passwd, p->pw_uid, + p->pw_gid, p->pw_gecos, p->pw_dir, p->pw_shell); + + endpwent(); + exit(0); + } -Finding Duplicated Words in a Document --------------------------------------- + If you don't understand C, don't worry about it. The output from +`pwcat' is the user database, in the traditional `/etc/passwd' format +of colon-separated fields. The fields are: - A common error when writing large amounts of prose is to accidentally -duplicate words. Often you will see this in text as something like "the -the program does the following ...." When the text is on-line, often -the duplicated words occur at the end of one line and the beginning of -another, making them very difficult to spot. +Login name The user's login name. +Encrypted password The user's encrypted password. This may not be + available on some systems. +User-ID The user's numeric user-id number. +Group-ID The user's numeric group-id number. +Full name The user's full name, and perhaps other + information associated with the user. +Home directory The user's login (or "home") directory + (familiar to shell programmers as `$HOME'). +Login shell The program that is run when the user logs in. + This is usually a shell, such as `bash'. - This program, `dupword.awk', scans through a file one line at a time, -and looks for adjacent occurrences of the same word. It also saves the -last word on a line (in the variable `prev') for comparison with the -first word on the next line. + A few lines representative of `pwcat''s output are as follows: - The first two statements make sure that the line is all lower-case, -so that, for example, "The" and "the" compare equal to each other. The -second statement removes all non-alphanumeric and non-whitespace -characters from the line, so that punctuation does not affect the -comparison either. This sometimes leads to reports of duplicated words -that really are different, but this is unusual. - - # dupword --- find duplicate words in text - # Arnold Robbins, arnold@gnu.org, Public Domain - # December 1991 + $ pwcat + -| root:3Ov02d5VaUPB6:0:1:Operator:/:/bin/sh + -| nobody:*:65534:65534::/: + -| daemon:*:1:1::/: + -| sys:*:2:2::/:/bin/csh + -| bin:*:3:3::/bin: + -| arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/sh + -| miriam:yxaay:112:10:Miriam Robbins:/home/miriam:/bin/sh + -| andy:abcca2:113:10:Andy Jacobs:/home/andy:/bin/sh + ... + + With that introduction, following is a group of functions for +getting user information. There are several functions here, +corresponding to the C functions of the same names: + + # passwd.awk --- access password file information + BEGIN { + # tailor this to suit your system + _pw_awklib = "/usr/local/libexec/awk/" + } + function _pw_init( oldfs, oldrs, olddol0, pwcat, using_fw) { - $0 = tolower($0) - gsub(/[^A-Za-z0-9 \t]/, ""); - if ($1 == prev) - printf("%s:%d: duplicate %s\n", - FILENAME, FNR, $1) - for (i = 2; i <= NF; i++) - if ($i == $(i-1)) - printf("%s:%d: duplicate %s\n", - FILENAME, FNR, $i) - prev = $NF + if (_pw_inited) + return + + oldfs = FS + oldrs = RS + olddol0 = $0 + using_fw = (PROCINFO["FS"] == "FIELDWIDTHS") + FS = ":" + RS = "\n" + + pwcat = _pw_awklib "pwcat" + while ((pwcat | getline) > 0) { + _pw_byname[$1] = $0 + _pw_byuid[$3] = $0 + _pw_bycount[++_pw_total] = $0 + } + close(pwcat) + _pw_count = 0 + _pw_inited = 1 + FS = oldfs + if (using_fw) + FIELDWIDTHS = FIELDWIDTHS + RS = oldrs + $0 = olddol0 } - -File: gawk.info, Node: Alarm Program, Next: Translate Program, Prev: Dupword Program, Up: Miscellaneous Programs + The `BEGIN' rule sets a private variable to the directory where +`pwcat' is stored. Because it is used to help out an `awk' library +routine, we have chosen to put it in `/usr/local/libexec/awk'; however, +you might want it to be in a different directory on your system. -An Alarm Clock Program ----------------------- + The function `_pw_init' keeps three copies of the user information +in three associative arrays. The arrays are indexed by username +(`_pw_byname'), by user-id number (`_pw_byuid'), and by order of +occurrence (`_pw_bycount'). The variable `_pw_inited' is used for +efficiency; `_pw_init' needs only to be called once. + + Because this function uses `getline' to read information from +`pwcat', it first saves the values of `FS', `RS', and `$0'. It notes +in the variable `using_fw' whether field splitting with `FIELDWIDTHS' +is in effect or not. Doing so is necessary, since these functions +could be called from anywhere within a user's program, and the user may +have his or her own way of splitting records and fields. + + The `using_fw' variable checks `PROCINFO["FS"]', which is +`"FIELDWIDTHS"' if field splitting is being done with `FIELDWIDTHS'. +This makes it possible to restore the correct field-splitting mechanism +later. The test can only be true for `gawk'. It is false if using +`FS' or on some other `awk' implementation. - The following program is a simple "alarm clock" program. You give -it a time of day, and an optional message. At the given time, it -prints the message on the standard output. In addition, you can give it -the number of times to repeat the message, and also a delay between -repetitions. + The main part of the function uses a loop to read database lines, +split the line into fields, and then store the line into each array as +necessary. When the loop is done, `_pw_init' cleans up by closing the +pipeline, setting `_pw_inited' to one, and restoring `FS' (and +`FIELDWIDTHS' if necessary), `RS', and `$0'. The use of `_pw_count' is +explained shortly. - This program uses the `gettimeofday' function from *Note Managing -the Time of Day: Gettimeofday Function. + The `getpwnam' function takes a username as a string argument. If +that user is in the database, it returns the appropriate line. +Otherwise it returns the null string: - All the work is done in the `BEGIN' rule. The first part is argument -checking and setting of defaults; the delay, the count, and the message -to print. If the user supplied a message, but it does not contain the -ASCII BEL character (known as the "alert" character, `\a'), then it is -added to the message. (On many systems, printing the ASCII BEL -generates some sort of audible alert. Thus, when the alarm goes off, -the system calls attention to itself, in case the user is not looking -at their computer or terminal.) - - # alarm --- set an alarm - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - - # usage: alarm time [ "message" [ count [ delay ] ] ] - - BEGIN \ + function getpwnam(name) { - # Initial argument sanity checking - usage1 = "usage: alarm time ['message' [count [delay]]]" - usage2 = sprintf("\t(%s) time ::= hh:mm", ARGV[1]) - - if (ARGC < 2) { - print usage > "/dev/stderr" - exit 1 - } else if (ARGC == 5) { - delay = ARGV[4] + 0 - count = ARGV[3] + 0 - message = ARGV[2] - } else if (ARGC == 4) { - count = ARGV[3] + 0 - message = ARGV[2] - } else if (ARGC == 3) { - message = ARGV[2] - } else if (ARGV[1] !~ /[0-9]?[0-9]:[0-9][0-9]/) { - print usage1 > "/dev/stderr" - print usage2 > "/dev/stderr" - exit 1 - } - - # set defaults for once we reach the desired time - if (delay == 0) - delay = 180 # 3 minutes - if (count == 0) - count = 5 - if (message == "") - message = sprintf("\aIt is now %s!\a", ARGV[1]) - else if (index(message, "\a") == 0) - message = "\a" message "\a" - - The next section of code turns the alarm time into hours and minutes, -and converts it if necessary to a 24-hour clock. Then it turns that -time into a count of the seconds since midnight. Next it turns the -current time into a count of seconds since midnight. The difference -between the two is how long to wait before setting off the alarm. - - # split up dest time - split(ARGV[1], atime, ":") - hour = atime[1] + 0 # force numeric - minute = atime[2] + 0 # force numeric - - # get current broken down time - gettimeofday(now) - - # if time given is 12-hour hours and it's after that - # hour, e.g., `alarm 5:30' at 9 a.m. means 5:30 p.m., - # then add 12 to real hour - if (hour < 12 && now["hour"] > hour) - hour += 12 - - # set target time in seconds since midnight - target = (hour * 60 * 60) + (minute * 60) - - # get current time in seconds since midnight - current = (now["hour"] * 60 * 60) + \ - (now["minute"] * 60) + now["second"] - - # how long to sleep for - naptime = target - current - if (naptime <= 0) { - print "time is in the past!" > "/dev/stderr" - exit 1 - } + _pw_init() + if (name in _pw_byname) + return _pw_byname[name] + return "" + } - Finally, the program uses the `system' function (*note Built-in -Functions for Input/Output: I/O Functions.) to call the `sleep' -utility. The `sleep' utility simply pauses for the given number of -seconds. If the exit status is not zero, the program assumes that -`sleep' was interrupted, and exits. If `sleep' exited with an OK status -(zero), then the program prints the message in a loop, again using -`sleep' to delay for however many seconds are necessary. + Similarly, the `getpwuid' function takes a user-id number argument. +If that user number is in the database, it returns the appropriate +line. Otherwise it returns the null string: - # zzzzzz..... go away if interrupted - if (system(sprintf("sleep %d", naptime)) != 0) - exit 1 - - # time to notify! - command = sprintf("sleep %d", delay) - for (i = 1; i <= count; i++) { - print message - # if sleep command interrupted, go away - if (system(command) != 0) - break - } - - exit 0 + function getpwuid(uid) + { + _pw_init() + if (uid in _pw_byuid) + return _pw_byuid[uid] + return "" } - -File: gawk.info, Node: Translate Program, Next: Labels Program, Prev: Alarm Program, Up: Miscellaneous Programs + The `getpwent' function simply steps through the database, one entry +at a time. It uses `_pw_count' to track its current position in the +`_pw_bycount' array: -Transliterating Characters --------------------------- + function getpwent() + { + _pw_init() + if (_pw_count < _pw_total) + return _pw_bycount[++_pw_count] + return "" + } - The system `tr' utility transliterates characters. For example, it -is often used to map upper-case letters into lower-case, for further -processing. - - GENERATE DATA | tr '[A-Z]' '[a-z]' | PROCESS DATA ... - - You give `tr' two lists of characters enclosed in square brackets. -Usually, the lists are quoted to keep the shell from attempting to do a -filename expansion.(1) When processing the input, the first character -in the first list is replaced with the first character in the second -list, the second character in the first list is replaced with the -second character in the second list, and so on. If there are more -characters in the "from" list than in the "to" list, the last character -of the "to" list is used for the remaining characters in the "from" -list. + The `endpwent' function resets `_pw_count' to zero, so that +subsequent calls to `getpwent' start over again: - Some time ago, a user proposed to us that we add a transliteration -function to `gawk'. Being opposed to "creeping featurism," I wrote the -following program to prove that character transliteration could be done -with a user-level function. This program is not as complete as the -system `tr' utility, but it will do most of the job. + function endpwent() + { + _pw_count = 0 + } - The `translate' program demonstrates one of the few weaknesses of -standard `awk': dealing with individual characters is very painful, -requiring repeated use of the `substr', `index', and `gsub' built-in -functions (*note Built-in Functions for String Manipulation: String -Functions.).(2) + A conscious design decision in this suite is that each subroutine +calls `_pw_init' to initialize the database arrays. The overhead of +running a separate process to generate the user database, and the I/O +to scan it, are only incurred if the user's main program actually calls +one of these functions. If this library file is loaded along with a +user's program, but none of the routines are ever called, then there is +no extra runtime overhead. (The alternative is move the body of +`_pw_init' into a `BEGIN' rule, which always runs `pwcat'. This +simplifies the code but runs an extra process that may never be needed.) + + In turn, calling `_pw_init' is not too expensive, because the +`_pw_inited' variable keeps the program from reading the data more than +once. If you are worried about squeezing every last cycle out of your +`awk' program, the check of `_pw_inited' could be moved out of +`_pw_init' and duplicated in all the other functions. In practice, +this is not necessary, since most `awk' programs are I/O-bound, and it +clutters up the code. - There are two functions. The first, `stranslate', takes three -arguments. + The `id' program in *Note Printing out User Information: Id Program, +uses these functions. -`from' - A list of characters to translate from. + ---------- Footnotes ---------- -`to' - A list of characters to translate to. + (1) It is often the case that password information is stored in a +network database. -`target' - The string to do the translation on. + +File: gawk.info, Node: Group Functions, Prev: Passwd Functions, Up: Library Functions - Associative arrays make the translation part fairly easy. `t_ar' -holds the "to" characters, indexed by the "from" characters. Then a -simple loop goes through `from', one character at a time. For each -character in `from', if the character appears in `target', `gsub' is -used to change it to the corresponding `to' character. +Reading the Group Database +========================== - The `translate' function simply calls `stranslate' using `$0' as the -target. The main program sets two global variables, `FROM' and `TO', -from the command line, and then changes `ARGV' so that `awk' will read -from the standard input. + Much of the discussion presented in *Note Reading the User Database: +Passwd Functions, applies to the group database as well. Although +there has traditionally been a well-known file (`/etc/group') in a +well-known format, the POSIX standard only provides a set of C library +routines (`' and `getgrent') for accessing the information. +Even though this file may exist, it likely does not have complete +information. Therefore, as with the user database, it is necessary to +have a small C program that generates the group database as its output. - Finally, the processing rule simply calls `translate' for each -record. + `grcat', a C program that "cats" the group database, is as follows: - # translate --- do tr like stuff - # Arnold Robbins, arnold@gnu.org, Public Domain - # August 1989 - - # bugs: does not handle things like: tr A-Z a-z, it has - # to be spelled out. However, if `to' is shorter than `from', - # the last character in `to' is used for the rest of `from'. - - function stranslate(from, to, target, lf, lt, t_ar, i, c) - { - lf = length(from) - lt = length(to) - for (i = 1; i <= lt; i++) - t_ar[substr(from, i, 1)] = substr(to, i, 1) - if (lt < lf) - for (; i <= lf; i++) - t_ar[substr(from, i, 1)] = substr(to, lt, 1) - for (i = 1; i <= lf; i++) { - c = substr(from, i, 1) - if (index(target, c) > 0) - gsub(c, t_ar[c], target) - } - return target - } + /* + * grcat.c + * + * Generate a printable version of the group database + */ + #include + #include - function translate(from, to) + int + main(argc, argv) + int argc; + char **argv; { - return $0 = stranslate(from, to, $0) - } + struct group *g; + int i; - # main program - BEGIN { - if (ARGC < 3) { - print "usage: translate from to" > "/dev/stderr" - exit + while ((g = getgrent()) != NULL) { + printf("%s:%s:%d:", g->gr_name, g->gr_passwd, + g->gr_gid); + for (i = 0; g->gr_mem[i] != NULL; i++) { + printf("%s", g->gr_mem[i]); + if (g->gr_mem[i+1] != NULL) + putchar(','); + } + putchar('\n'); } - FROM = ARGV[1] - TO = ARGV[2] - ARGC = 2 - ARGV[1] = "-" - } - - { - translate(FROM, TO) - print + endgrent(); + exit(0); } - While it is possible to do character transliteration in a user-level -function, it is not necessarily efficient, and we started to consider -adding a built-in function. However, shortly after writing this -program, we learned that the System V Release 4 `awk' had added the -`toupper' and `tolower' functions. These functions handle the vast -majority of the cases where character transliteration is necessary, and -so we chose to simply add those functions to `gawk' as well, and then -leave well enough alone. - - An obvious improvement to this program would be to set up the `t_ar' -array only once, in a `BEGIN' rule. However, this assumes that the -"from" and "to" lists will never change throughout the lifetime of the -program. - - ---------- Footnotes ---------- - - (1) On older, non-POSIX systems, `tr' often does not require that -the lists be enclosed in square brackets and quoted. This is a feature. + Each line in the group database represents one group. The fields are +separated with colons and represent the following information: + +Group name The group's name. +Group password The group's encrypted password. In practice, + this field is never used; it is usually empty + or set to `*'. +Group-ID The group's numeric group-id number; this + number should be unique within the file. +Group member list A comma-separated list of usernames. These + users are members of the group. Modern Unix + systems allow users to be members of several + groups simultaneously. If your system does, + then there are elements `"group1"' through + `"groupN"' in `PROCINFO' for those group-id + numbers. (Note that `PROCINFO' is a `gawk' + extension; *note Built-in Variables::.) - (2) This program was written before `gawk' acquired the ability to -split each character in a string into separate array elements. How -might you use this new feature to simplify the program? - - -File: gawk.info, Node: Labels Program, Next: Word Sorting, Prev: Translate Program, Up: Miscellaneous Programs - -Printing Mailing Labels ------------------------ - - Here is a "real world"(1) program. This script reads lists of names -and addresses, and generates mailing labels. Each page of labels has -20 labels on it, two across and ten down. The addresses are guaranteed -to be no more than five lines of data. Each address is separated from -the next by a blank line. - - The basic idea is to read 20 labels worth of data. Each line of -each label is stored in the `line' array. The single rule takes care -of filling the `line' array and printing the page when 20 labels have -been read. - - The `BEGIN' rule simply sets `RS' to the empty string, so that `awk' -will split records at blank lines (*note How Input is Split into -Records: Records.). It sets `MAXLINES' to 100, since `MAXLINE' is the -maximum number of lines on the page (20 * 5 = 100). - - Most of the work is done in the `printpage' function. The label -lines are stored sequentially in the `line' array. But they have to be -printed horizontally; `line[1]' next to `line[6]', `line[2]' next to -`line[7]', and so on. Two loops are used to accomplish this. The -outer loop, controlled by `i', steps through every 10 lines of data; -this is each row of labels. The inner loop, controlled by `j', goes -through the lines within the row. As `j' goes from zero to four, `i+j' -is the `j''th line in the row, and `i+j+5' is the entry next to it. -The output ends up looking something like this: - - line 1 line 6 - line 2 line 7 - line 3 line 8 - line 4 line 9 - line 5 line 10 + Here is what running `grcat' might produce: - As a final note, at lines 21 and 61, an extra blank line is printed, -to keep the output lined up on the labels. This is dependent on the -particular brand of labels in use when the program was written. You -will also note that there are two blank lines at the top and two blank -lines at the bottom. + $ grcat + -| wheel:*:0:arnold + -| nogroup:*:65534: + -| daemon:*:1: + -| kmem:*:2: + -| staff:*:10:arnold,miriam,andy + -| other:*:20: + ... - The `END' rule arranges to flush the final page of labels; there may -not have been an even multiple of 20 labels in the data. + Here are the functions for obtaining information from the group +database. There are several, modeled after the C library functions of +the same names: - # labels.awk - # Arnold Robbins, arnold@gnu.org, Public Domain - # June 1992 - - # Program to print labels. Each label is 5 lines of data - # that may have blank lines. The label sheets have 2 - # blank lines at the top and 2 at the bottom. - - BEGIN { RS = "" ; MAXLINES = 100 } + # group.awk --- functions for dealing with the group file + BEGIN \ + { + # Change to suit your system + _gr_awklib = "/usr/local/libexec/awk/" + } - function printpage( i, j) + function _gr_init( oldfs, oldrs, olddol0, grcat, + using_fw, n, a, i) { - if (Nlines <= 0) + if (_gr_inited) return - printf "\n\n" # header - - for (i = 1; i <= Nlines; i += 10) { - if (i == 21 || i == 61) - print "" - for (j = 0; j < 5; j++) { - if (i + j > MAXLINES) - break - printf " %-41s %s\n", line[i+j], line[i+j+5] - } - print "" - } + oldfs = FS + oldrs = RS + olddol0 = $0 + using_fw = (PROCINFO["FS"] == "FIELDWIDTHS") + FS = ":" + RS = "\n" - printf "\n\n" # footer + grcat = _gr_awklib "grcat" + while ((grcat | getline) > 0) { + if ($1 in _gr_byname) + _gr_byname[$1] = _gr_byname[$1] "," $4 + else + _gr_byname[$1] = $0 + if ($3 in _gr_bygid) + _gr_bygid[$3] = _gr_bygid[$3] "," $4 + else + _gr_bygid[$3] = $0 - for (i in line) - line[i] = "" - } + n = split($4, a, "[ \t]*,[ \t]*") + for (i = 1; i <= n; i++) + if (a[i] in _gr_groupsbyuser) + _gr_groupsbyuser[a[i]] = \ + _gr_groupsbyuser[a[i]] " " $1 + else + _gr_groupsbyuser[a[i]] = $1 - # main rule - { - if (Count >= 20) { - printpage() - Count = 0 - Nlines = 0 + _gr_bycount[++_gr_count] = $0 } - n = split($0, a, "\n") - for (i = 1; i <= n; i++) - line[++Nlines] = a[i] - for (; i <= 5; i++) - line[++Nlines] = "" - Count++ + close(grcat) + _gr_count = 0 + _gr_inited++ + FS = oldfs + if (using_fw) + FIELDWIDTHS = FIELDWIDTHS + RS = oldrs + $0 = olddol0 } - - END \ + + The `BEGIN' rule sets a private variable to the directory where +`grcat' is stored. Because it is used to help out an `awk' library +routine, we have chosen to put it in `/usr/local/libexec/awk'. You +might want it to be in a different directory on your system. + + These routines follow the same general outline as the user database +routines (*note Reading the User Database: Passwd Functions.). The +`_gr_inited' variable is used to ensure that the database is scanned no +more than once. The `_gr_init' function first saves `FS', +`FIELDWIDTHS', `RS', and `$0', and then sets `FS' and `RS' to the +correct values for scanning the group information. + + The group information is stored is several associative arrays. The +arrays are indexed by group name (`_gr_byname'), by group-id number +(`_gr_bygid'), and by position in the database (`_gr_bycount'). There +is an additional array indexed by username (`_gr_groupsbyuser'), which +is a space-separated list of groups that each user belongs to. + + Unlike the user database, it is possible to have multiple records in +the database for the same group. This is common when a group has a +large number of members. A pair of such entries might look like the +following: + + tvpeople:*:101:johnny,jay,arsenio + tvpeople:*:101:david,conan,tom,joan + + For this reason, `_gr_init' looks to see if a group name or group-id +number is already seen. If it is, then the usernames are simply +concatenated onto the previous list of users. (There is actually a +subtle problem with the code just presented. Suppose that the first +time there were no names. This code adds the names with a leading +comma. It also doesn't check that there is a `$4'.) + + Finally, `_gr_init' closes the pipeline to `grcat', restores `FS' +(and `FIELDWIDTHS' if necessary), `RS', and `$0', initializes +`_gr_count' to zero (it is used later), and makes `_gr_inited' nonzero. + + The `getgrnam' function takes a group name as its argument, and if +that group exists, it is returned. Otherwise, `getgrnam' returns the +null string: + + function getgrnam(group) { - printpage() + _gr_init() + if (group in _gr_byname) + return _gr_byname[group] + return "" } - ---------- Footnotes ---------- + The `getgrgid' function is similar, it takes a numeric group-id and +looks up the information associated with that group-id: - (1) "Real world" is defined as "a program actually used to get -something done." + function getgrgid(gid) + { + _gr_init() + if (gid in _gr_bygid) + return _gr_bygid[gid] + return "" + } - -File: gawk.info, Node: Word Sorting, Next: History Sorting, Prev: Labels Program, Up: Miscellaneous Programs + The `getgruser' function does not have a C counterpart. It takes a +username and returns the list of groups that have the user as a member: -Generating Word Usage Counts ----------------------------- + function getgruser(user) + { + _gr_init() + if (user in _gr_groupsbyuser) + return _gr_groupsbyuser[user] + return "" + } - The following `awk' program prints the number of occurrences of each -word in its input. It illustrates the associative nature of `awk' -arrays by using strings as subscripts. It also demonstrates the `for X -in ARRAY' construction. Finally, it shows how `awk' can be used in -conjunction with other utility programs to do a useful task of some -complexity with a minimum of effort. Some explanations follow the -program listing. + The `getgrent' function steps through the database one entry at a +time. It uses `_gr_count' to track its position in the list: - awk ' - # Print list of word frequencies + function getgrent() { - for (i = 1; i <= NF; i++) - freq[$i]++ + _gr_init() + if (++_gr_count in _gr_bycount) + return _gr_bycount[_gr_count] + return "" + } + + The `endgrent' function resets `_gr_count' to zero so that +`getgrent' can start over again: + + function endgrent() + { + _gr_count = 0 } - - END { - for (word in freq) - printf "%s\t%d\n", word, freq[word] - }' - The first thing to notice about this program is that it has two -rules. The first rule, because it has an empty pattern, is executed on -every line of the input. It uses `awk''s field-accessing mechanism -(*note Examining Fields: Fields.) to pick out the individual words from -the line, and the built-in variable `NF' (*note Built-in Variables::) -to know how many fields are available. + As with the user database routines, each function calls `_gr_init' to +initialize the arrays. Doing so only incurs the extra overhead of +running `grcat' if these functions are used (as opposed to moving the +body of `_gr_init' into a `BEGIN' rule). - For each input word, an element of the array `freq' is incremented to -reflect that the word has been seen an additional time. + Most of the work is in scanning the database and building the various +associative arrays. The functions that the user calls are themselves +very simple, relying on `awk''s associative arrays to do work. - The second rule, because it has the pattern `END', is not executed -until the input has been exhausted. It prints out the contents of the -`freq' table that has been built up inside the first action. + The `id' program in *Note Printing out User Information: Id Program, +uses these functions. - This program has several problems that would prevent it from being -useful by itself on real text files: + +File: gawk.info, Node: Sample Programs, Next: Language History, Prev: Library Functions, Up: Top - * Words are detected using the `awk' convention that fields are - separated by whitespace and that other characters in the input - (except newlines) don't have any special meaning to `awk'. This - means that punctuation characters count as part of words. +Practical `awk' Programs +************************ - * The `awk' language considers upper- and lower-case characters to be - distinct. Therefore, `bartender' and `Bartender' are not treated - as the same word. This is undesirable since, in normal text, words - are capitalized if they begin sentences, and a frequency analyzer - should not be sensitive to capitalization. + *Note A Library of `awk' Functions: Library Functions, presents the +idea that reading programs in a language contributes to learning that +language. This major node continues that theme, presenting a potpourri +of `awk' programs for your reading enjoyment. - * The output does not come out in any useful order. You're more - likely to be interested in which words occur most frequently, or - having an alphabetized table of how frequently each word occurs. + Many of these programs use the library functions presented in *Note +A Library of `awk' Functions: Library Functions. - The way to solve these problems is to use some of the more advanced -features of the `awk' language. First, we use `tolower' to remove case -distinctions. Next, we use `gsub' to remove punctuation characters. -Finally, we use the system `sort' utility to process the output of the -`awk' script. Here is the new version of the program: +* Menu: - # Print list of word frequencies - { - $0 = tolower($0) # remove case distinctions - gsub(/[^a-z0-9_ \t]/, "", $0) # remove punctuation - for (i = 1; i <= NF; i++) - freq[$i]++ - } - - END { - for (word in freq) - printf "%s\t%d\n", word, freq[word] - } +* Running Examples:: How to run these examples. +* Clones:: Clones of common utilities. +* Miscellaneous Programs:: Some interesting `awk' programs. - Assuming we have saved this program in a file named `wordfreq.awk', -and that the data is in `file1', the following pipeline + +File: gawk.info, Node: Running Examples, Next: Clones, Prev: Sample Programs, Up: Sample Programs - awk -f wordfreq.awk file1 | sort +1 -nr +Running the Example Programs +============================ -produces a table of the words appearing in `file1' in order of -decreasing frequency. + To run a given program, you would typically do something like this: - The `awk' program suitably massages the data and produces a word -frequency table, which is not ordered. + awk -f PROGRAM -- OPTIONS FILES - The `awk' script's output is then sorted by the `sort' utility and -printed on the terminal. The options given to `sort' in this example -specify to sort using the second field of each input line (skipping one -field), that the sort keys should be treated as numeric quantities -(otherwise `15' would come before `5'), and that the sorting should be -done in descending (reverse) order. +Here, PROGRAM is the name of the `awk' program (such as `cut.awk'), +OPTIONS are any command-line options for the program that start with a +`-', and FILES are the actual data files. - We could have even done the `sort' from within the program, by -changing the `END' action to: + If your system supports the `#!' executable interpreter mechanism +(*note Executable `awk' Programs: Executable Scripts.), you can instead +run your program directly: - END { - sort = "sort +1 -nr" - for (word in freq) - printf "%s\t%d\n", word, freq[word] | sort - close(sort) - } + cut.awk -c1-8 myfiles > results - You would have to use this way of sorting on systems that do not -have true pipes. + If your `awk' is not `gawk', you may instead need to use this: - See the general operating system documentation for more information -on how to use the `sort' program. + cut.awk -- -c1-8 myfiles > results  -File: gawk.info, Node: History Sorting, Next: Extract Program, Prev: Word Sorting, Up: Miscellaneous Programs +File: gawk.info, Node: Clones, Next: Miscellaneous Programs, Prev: Running Examples, Up: Sample Programs -Removing Duplicates from Unsorted Text --------------------------------------- +Reinventing Wheels for Fun and Profit +===================================== - The `uniq' program (*note Printing Non-duplicated Lines of Text: -Uniq Program.), removes duplicate lines from _sorted_ data. + This minor node presents a number of POSIX utilities that are +implemented in `awk'. Reinventing these programs in `awk' is often +enjoyable, because the algorithms can be very clearly expressed, and +the code is usually very concise and simple. This is true because +`awk' does so much for you. - Suppose, however, you need to remove duplicate lines from a data -file, but that you wish to preserve the order the lines are in? A good -example of this might be a shell history file. The history file keeps -a copy of all the commands you have entered, and it is not unusual to -repeat a command several times in a row. Occasionally you might wish -to compact the history by removing duplicate entries. Yet it is -desirable to maintain the order of the original commands. + It should be noted that these programs are not necessarily intended +to replace the installed versions on your system. Instead, their +purpose is to illustrate `awk' language programming for "real world" +tasks. - This simple program does the job. It uses two arrays. The `data' -array is indexed by the text of each line. For each line, `data[$0]' -is incremented. + The programs are presented in alphabetical order. - If a particular line has not been seen before, then `data[$0]' will -be zero. In that case, the text of the line is stored in -`lines[count]'. Each element of `lines' is a unique command, and the -indices of `lines' indicate the order in which those lines were -encountered. The `END' rule simply prints out the lines, in order. +* Menu: - # histsort.awk --- compact a shell history file - # Arnold Robbins, arnold@gnu.org, Public Domain - # May 1993 - - # Thanks to Byron Rakitzis for the general idea - { - if (data[$0]++ == 0) - lines[++count] = $0 - } - - END { - for (i = 1; i <= count; i++) - print lines[i] - } +* Cut Program:: The `cut' utility. +* Egrep Program:: The `egrep' utility. +* Id Program:: The `id' utility. +* Split Program:: The `split' utility. +* Tee Program:: The `tee' utility. +* Uniq Program:: The `uniq' utility. +* Wc Program:: The `wc' utility. - This program also provides a foundation for generating other useful -information. For example, using the following `print' satement in the -`END' rule would indicate how often a particular command was used. + +File: gawk.info, Node: Cut Program, Next: Egrep Program, Prev: Clones, Up: Clones - print data[lines[i]], lines[i] +Cutting out Fields and Columns +------------------------------ - This works because `data[$0]' was incremented each time a line was -seen. + The `cut' utility selects, or "cuts," characters or fields from its +standard input and sends them to its standard output. Fields are +separated by tabs by default, but you may supply a command-line option +to change the field "delimiter" (i.e., the field separator character). +`cut''s definition of fields is less general than `awk''s. - -File: gawk.info, Node: Extract Program, Next: Simple Sed, Prev: History Sorting, Up: Miscellaneous Programs + A common use of `cut' might be to pull out just the login name of +logged-on users from the output of `who'. For example, the following +pipeline generates a sorted, unique list of the logged-on users: -Extracting Programs from Texinfo Source Files ---------------------------------------------- + who | cut -c1-8 | sort | uniq - The nodes *Note A Library of `awk' Functions: Library Functions, and -*Note Practical `awk' Programs: Sample Programs, are the top level -nodes for a large number of `awk' programs. If you wish to experiment -with these programs, it is tedious to have to type them in by hand. -Here we present a program that can extract parts of a Texinfo input -file into separate files. + The options for `cut' are: - This Info file is written in Texinfo, the GNU project's document -formatting language. A single Texinfo source file can be used to -produce both printed and on-line documentation. The Texinfo language -is described fully, starting with *Note Introduction: (texi)Top. +`-c LIST' + Use LIST as the list of characters to cut out. Items within the + list may be separated by commas, and ranges of characters can be + separated with dashes. The list `1-8,15,22-35' specifies + characters 1 through 8, 15, and 22 through 35. - For our purposes, it is enough to know three things about Texinfo -input files. +`-f LIST' + Use LIST as the list of fields to cut out. - * The "at" symbol, `@', is special in Texinfo, much like `\' in C or - `awk'. Literal `@' symbols are represented in Texinfo source - files as `@@'. +`-d DELIM' + Use DELIM as the field separator character instead of the tab + character. - * Comments start with either `@c' or `@comment'. The file - extraction program will work by using special comments that start - at the beginning of a line. +`-s' + Suppress printing of lines that do not contain the field delimiter. - * Example text that should not be split across a page boundary is - bracketed between lines containing `@group' and `@end group' - commands. + The `awk' implementation of `cut' uses the `getopt' library function +(*note Processing Command-Line Options: Getopt Function.) and the +`join' library function (*note Merging an Array into a String: Join +Function.). - The following program, `extract.awk', reads through a Texinfo source -file, and does two things, based on the special comments. Upon seeing -`@c system ...', it runs a command, by extracting the command text from -the control line and passing it on to the `system' function (*note -Built-in Functions for Input/Output: I/O Functions.). Upon seeing `@c -file FILENAME', each subsequent line is sent to the file FILENAME, -until `@c endfile' is encountered. The rules in `extract.awk' will -match either `@c' or `@comment' by letting the `omment' part be -optional. Lines containing `@group' and `@end group' are simply -removed. `extract.awk' uses the `join' library function (*note Merging -an Array Into a String: Join Function.). - - The example programs in the on-line Texinfo source for `Effective -AWK Programming' (`gawk.texi') have all been bracketed inside `file', -and `endfile' lines. The `gawk' distribution uses a copy of -`extract.awk' to extract the sample programs and install many of them -in a standard directory, where `gawk' can find them. The Texinfo file -looks something like this: + The program begins with a comment describing the options, the library +functions needed, and a `usage' function that prints out a usage +message and exits. `usage' is called if invalid arguments are supplied: - ... - This program has a @code{BEGIN} block, - which prints a nice message: - - @example - @c file examples/messages.awk - BEGIN @{ print "Don't panic!" @} - @c end file - @end example + # cut.awk --- implement cut in awk + # Options: + # -f list Cut fields + # -d c Field delimiter character + # -c list Cut characters + # + # -s Suppress lines without the delimiter + # + # Requires getopt and join library functions - It also prints some final advice: + function usage( e1, e2) + { + e1 = "usage: cut [-f list] [-d c] [-s] [files...]" + e2 = "usage: cut [-c list] [files...]" + print e1 > "/dev/stderr" + print e2 > "/dev/stderr" + exit 1 + } + +The variables `e1' and `e2' are used so that the function fits nicely +on the screen. + + Next comes a `BEGIN' rule that parses the command-line options. It +sets `FS' to a single tab character, because that is `cut''s default +field separator. The output field separator is also set to be the same +as the input field separator. Then `getopt' is used to step through +the command-line options. One or the other of the variables +`by_fields' or `by_chars' is set to true, to indicate that processing +should be done by fields or by characters, respectively. When cutting +by characters, the output field separator is set to the null string. + + BEGIN \ + { + FS = "\t" # default + OFS = FS + while ((c = getopt(ARGC, ARGV, "sf:c:d:")) != -1) { + if (c == "f") { + by_fields = 1 + fieldlist = Optarg + } else if (c == "c") { + by_chars = 1 + fieldlist = Optarg + OFS = "" + } else if (c == "d") { + if (length(Optarg) > 1) { + printf("Using first character of %s" \ + " for delimiter\n", Optarg) > "/dev/stderr" + Optarg = substr(Optarg, 1, 1) + } + FS = Optarg + OFS = FS + if (FS == " ") # defeat awk semantics + FS = "[ ]" + } else if (c == "s") + suppress++ + else + usage() + } - @example - @c file examples/messages.awk - END @{ print "Always avoid bored archeologists!" @} - @c end file - @end example - ... + for (i = 1; i < Optind; i++) + ARGV[i] = "" - `extract.awk' begins by setting `IGNORECASE' to one, so that mixed -upper-case and lower-case letters in the directives won't matter. + Special care is taken when the field delimiter is a space. Using a +single space (`" "') for the value of `FS' is incorrect--`awk' would +separate fields with runs of spaces, tabs, and/or newlines, and we want +them to be separated with individual spaces. Also, note that after +`getopt' is through, we have to clear out all the elements of `ARGV' +from 1 to `Optind', so that `awk' does not try to process the +command-line options as file names. - The first rule handles calling `system', checking that a command was -given (`NF' is at least three), and also checking that the command -exited with a zero exit status, signifying OK. + After dealing with the command-line options, the program verifies +that the options make sense. Only one or the other of `-c' and `-f' +should be used, and both require a field list. Then the program calls +either `set_fieldlist' or `set_charlist' to pull apart the list of +fields or characters: - # extract.awk --- extract files and run programs - # from texinfo files - # Arnold Robbins, arnold@gnu.org, Public Domain, May 1993 + if (by_fields && by_chars) + usage() - BEGIN { IGNORECASE = 1 } + if (by_fields == 0 && by_chars == 0) + by_fields = 1 # default - /^@c(omment)?[ \t]+system/ \ - { - if (NF < 3) { - e = (FILENAME ":" FNR) - e = (e ": badly formed `system' line") - print e > "/dev/stderr" - next - } - $1 = "" - $2 = "" - stat = system($0) - if (stat != 0) { - e = (FILENAME ":" FNR) - e = (e ": warning: system returned " stat) - print e > "/dev/stderr" + if (fieldlist == "") { + print "cut: needs list for -c or -f" > "/dev/stderr" + exit 1 } + + if (by_fields) + set_fieldlist() + else + set_charlist() } -The variable `e' is used so that the function fits nicely on the screen. - - The second rule handles moving data into files. It verifies that a -file name was given in the directive. If the file named is not the -current file, then the current file is closed. This means that an `@c -endfile' was not given for that file. (We should probably print a -diagnostic in this case, although at the moment we do not.) - - The `for' loop does the work. It reads lines using `getline' (*note -Explicit Input with `getline': Getline.). For an unexpected end of -file, it calls the `unexpected_eof' function. If the line is an -"endfile" line, then it breaks out of the loop. If the line is an -`@group' or `@end group' line, then it ignores it, and goes on to the -next line. (These Texinfo control lines keep blocks of code together -on one page; unfortunately, TeX isn't always smart enough to do things -exactly right, and we have to give it some advice.) + `set_fieldlist' is used to split the field list apart at the commas, +and into an array. Then, for each element of the array, it looks to +see if it is actually a range, and if so, splits it apart. The range is +verified to make sure the first number is smaller than the second. +Each number in the list is added to the `flist' array, which simply +lists the fields that will be printed. Normal field splitting is used. +The program lets `awk' handle the job of doing the field splitting: - Most of the work is in the following few lines. If the line has no -`@' symbols, it can be printed directly. Otherwise, each leading `@' -must be stripped off. + function set_fieldlist( n, m, i, j, k, f, g) + { + n = split(fieldlist, f, ",") + j = 1 # index in flist + for (i = 1; i <= n; i++) { + if (index(f[i], "-") != 0) { # a range + m = split(f[i], g, "-") + if (m != 2 || g[1] >= g[2]) { + printf("bad field list: %s\n", + f[i]) > "/dev/stderr" + exit 1 + } + for (k = g[1]; k <= g[2]; k++) + flist[j++] = k + } else + flist[j++] = f[i] + } + nfields = j - 1 + } - To remove the `@' symbols, the line is split into separate elements -of the array `a', using the `split' function (*note Built-in Functions -for String Manipulation: String Functions.). Each element of `a' that -is empty indicates two successive `@' symbols in the original line. -For each two empty elements (`@@' in the original file), we have to add -back in a single `@' symbol. + The `set_charlist' function is more complicated than `set_fieldlist'. +The idea here is to use `gawk''s `FIELDWIDTHS' variable (*note Reading +Fixed-Width Data: Constant Size.), which describes constant width +input. When using a character list, that is exactly what we have. - When the processing of the array is finished, `join' is called with -the value of `SUBSEP', to rejoin the pieces back into a single line. -That line is then printed to the output file. + Setting up `FIELDWIDTHS' is more complicated than simply listing the +fields that need to be printed. We have to keep track of the fields to +print and also the intervening characters that have to be skipped. For +example, suppose you wanted characters 1 through 8, 15, and 22 through +35. You would use `-c 1-8,15,22-35'. The necessary value for +`FIELDWIDTHS' is `"8 6 1 6 14"'. This yields five fields, and the +fields to print are `$1', `$3', and `$5'. The intermediate fields are +"filler", which is stuff in between the desired data. `flist' lists +the fields to print, and `t' tracks the complete field list, including +filler fields: - /^@c(omment)?[ \t]+file/ \ + function set_charlist( field, i, j, f, g, t, + filler, last, len) { - if (NF != 3) { - e = (FILENAME ":" FNR ": badly formed `file' line") - print e > "/dev/stderr" - next - } - if ($3 != curfile) { - if (curfile != "") - close(curfile) - curfile = $3 - } - - for (;;) { - if ((getline line) <= 0) - unexpected_eof() - if (line ~ /^@c(omment)?[ \t]+endfile/) - break - else if (line ~ /^@(end[ \t]+)?group/) - continue - if (index(line, "@") == 0) { - print line > curfile - continue - } - n = split(line, a, "@") - # if a[1] == "", means leading @, - # don't add one back in. - for (i = 2; i <= n; i++) { - if (a[i] == "") { # was an @@ - a[i] = "@" - if (a[i+1] == "") - i++ + field = 1 # count total fields + n = split(fieldlist, f, ",") + j = 1 # index in flist + for (i = 1; i <= n; i++) { + if (index(f[i], "-") != 0) { # range + m = split(f[i], g, "-") + if (m != 2 || g[1] >= g[2]) { + printf("bad character list: %s\n", + f[i]) > "/dev/stderr" + exit 1 } + len = g[2] - g[1] + 1 + if (g[1] > 1) # compute length of filler + filler = g[1] - last - 1 + else + filler = 0 + if (filler) + t[field++] = filler + t[field++] = len # length of field + last = g[2] + flist[j++] = field - 1 + } else { + if (f[i] > 1) + filler = f[i] - last - 1 + else + filler = 0 + if (filler) + t[field++] = filler + t[field++] = 1 + last = f[i] + flist[j++] = field - 1 } - print join(a, 1, n, SUBSEP) > curfile } + FIELDWIDTHS = join(t, 1, field - 1) + nfields = j - 1 } - An important thing to note is the use of the `>' redirection. -Output done with `>' only opens the file once; it stays open and -subsequent output is appended to the file (*note Redirecting Output of -`print' and `printf': Redirection.). This allows us to easily mix -program text and explanatory prose for the same sample source file (as -has been done here!) without any hassle. The file is only closed when -a new data file name is encountered, or at the end of the input file. - - Finally, the function `unexpected_eof' prints an appropriate error -message and then exits. + Next is the rule that actually processes the data. If the `-s' +option is given, then `suppress' is true. The first `if' statement +makes sure that the input record does have the field separator. If +`cut' is processing fields, `suppress' is true, and the field separator +character is not in the record, then the record is skipped. - The `END' rule handles the final cleanup, closing the open file. + If the record is valid, then `gawk' has split the data into fields, +either using the character in `FS' or using fixed-length fields and +`FIELDWIDTHS'. The loop goes through the list of fields that should be +printed. The corresponding field is printed if it contains data. If +the next field also has data, then the separator character is written +out between the fields: - function unexpected_eof() { - printf("%s:%d: unexpected EOF or error\n", \ - FILENAME, FNR) > "/dev/stderr" - exit 1 - } + if (by_fields && suppress && index($0, FS) != 0) + next - END { - if (curfile) - close(curfile) + for (i = 1; i <= nfields; i++) { + if ($flist[i] != "") { + printf "%s", $flist[i] + if (i < nfields && $flist[i+1] != "") + printf "%s", OFS + } + } + print "" } + This version of `cut' relies on `gawk''s `FIELDWIDTHS' variable to +do the character-based cutting. While it is possible in other `awk' +implementations to use `substr' (*note String Manipulation Functions: +String Functions.), it is also extremely painful. The `FIELDWIDTHS' +variable supplies an elegant solution to the problem of picking the +input line apart by characters. +  -File: gawk.info, Node: Simple Sed, Next: Igawk Program, Prev: Extract Program, Up: Miscellaneous Programs +File: gawk.info, Node: Egrep Program, Next: Id Program, Prev: Cut Program, Up: Clones -A Simple Stream Editor ----------------------- +Searching for Regular Expressions in Files +------------------------------------------ - The `sed' utility is a "stream editor," a program that reads a -stream of data, makes changes to it, and passes the modified data on. -It is often used to make global changes to a large file, or to a stream -of data generated by a pipeline of commands. + The `egrep' utility searches files for patterns. It uses regular +expressions that are almost identical to those available in `awk' +(*note Regular Expressions: Regexp.). It is used in the following +manner: - While `sed' is a complicated program in its own right, its most -common use is to perform global substitutions in the middle of a -pipeline: + egrep [ OPTIONS ] 'PATTERN' FILES ... - command1 < orig.data | sed 's/old/new/g' | command2 > result + The PATTERN is a regular expression. In typical usage, the regular +expression is quoted to prevent the shell from expanding any of the +special characters as file name wildcards. Normally, `egrep' prints +the lines that matched. If multiple file names are provided on the +command line, each output line is preceded by the name of the file and +a colon. - Here, the `s/old/new/g' tells `sed' to look for the regexp `old' on -each input line, and replace it with the text `new', globally (i.e. all -the occurrences on a line). This is similar to `awk''s `gsub' function -(*note Built-in Functions for String Manipulation: String Functions.). + The options to `egrep' are as follows: - The following program, `awksed.awk', accepts at least two command -line arguments; the pattern to look for and the text to replace it -with. Any additional arguments are treated as data file names to -process. If none are provided, the standard input is used. +`-c' + Print out a count of the lines that matched the pattern, instead + of the lines themselves. - # awksed.awk --- do s/foo/bar/g using just print - # Thanks to Michael Brennan for the idea - - # Arnold Robbins, arnold@gnu.org, Public Domain - # August 1995 - - function usage() - { - print "usage: awksed pat repl [files...]" > "/dev/stderr" - exit 1 - } - - BEGIN { - # validate arguments - if (ARGC < 3) - usage() - - RS = ARGV[1] - ORS = ARGV[2] - - # don't use arguments as files - ARGV[1] = ARGV[2] = "" - } - - # look ma, no hands! - { - if (RT == "") - printf "%s", $0 - else - print - } +`-s' + Be silent. No output is produced and the exit value indicates + whether the pattern was matched. - The program relies on `gawk''s ability to have `RS' be a regexp and -on the setting of `RT' to the actual text that terminated the record -(*note How Input is Split into Records: Records.). +`-v' + Invert the sense of the test. `egrep' prints the lines that do + _not_ match the pattern and exits successfully if the pattern is + not matched. - The idea is to have `RS' be the pattern to look for. `gawk' will -automatically set `$0' to the text between matches of the pattern. -This is text that we wish to keep, unmodified. Then, by setting `ORS' -to the replacement text, a simple `print' statement will output the -text we wish to keep, followed by the replacement text. +`-i' + Ignore case distinctions in both the pattern and the input data. - There is one wrinkle to this scheme, which is what to do if the last -record doesn't end with text that matches `RS'? Using a `print' -statement unconditionally prints the replacement text, which is not -correct. +`-l' + Only print (list) the names of the files that matched, not the + lines that matched. - However, if the file did not end in text that matches `RS', `RT' -will be set to the null string. In this case, we can print `$0' using -`printf' (*note Using `printf' Statements for Fancier Printing: -Printf.). +`-e PATTERN' + Use PATTERN as the regexp to match. The purpose of the `-e' + option is to allow patterns that start with a `-'. - The `BEGIN' rule handles the setup, checking for the right number of -arguments, and calling `usage' if there is a problem. Then it sets `RS' -and `ORS' from the command line arguments, and sets `ARGV[1]' and -`ARGV[2]' to the null string, so that they will not be treated as file -names (*note Using `ARGC' and `ARGV': ARGC and ARGV.). + This version uses the `getopt' library function (*note Processing +Command-Line Options: Getopt Function.) and the file transition +library program (*note Noting Data File Boundaries: Filetrans +Function.). - The `usage' function prints an error message and exits. + The program begins with a descriptive comment and then a `BEGIN' rule +that processes the command-line arguments with `getopt'. The `-i' +(ignore case) option is particularly easy with `gawk'; we just use the +`IGNORECASE' built-in variable (*note Built-in Variables::): - Finally, the single rule handles the printing scheme outlined above, -using `print' or `printf' as appropriate, depending upon the value of -`RT'. + # egrep.awk --- simulate egrep in awk + # Options: + # -c count of lines + # -s silent - use exit value + # -v invert test, success if no match + # -i ignore case + # -l print filenames only + # -e argument is pattern + # + # Requires getopt and file transition library functions + + BEGIN { + while ((c = getopt(ARGC, ARGV, "ce:svil")) != -1) { + if (c == "c") + count_only++ + else if (c == "s") + no_print++ + else if (c == "v") + invert++ + else if (c == "i") + IGNORECASE = 1 + else if (c == "l") + filenames_only++ + else if (c == "e") + pattern = Optarg + else + usage() + } - -File: gawk.info, Node: Igawk Program, Prev: Simple Sed, Up: Miscellaneous Programs + Next comes the code that handles the `egrep'-specific behavior. If no +pattern is supplied with `-e', the first non-option on the command line +is used. The `awk' command-line arguments up to `ARGV[Optind]' are +cleared, so that `awk' won't try to process them as files. If no files +are specified, the standard input is used, and if multiple files are +specified, we make sure to note this so that the file names can precede +the matched lines in the output: -An Easy Way to Use Library Functions ------------------------------------- + if (pattern == "") + pattern = ARGV[Optind++] + + for (i = 1; i < Optind; i++) + ARGV[i] = "" + if (Optind >= ARGC) { + ARGV[1] = "-" + ARGC = 2 + } else if (ARGC - Optind > 1) + do_filenames++ + + # if (IGNORECASE) + # pattern = tolower(pattern) + } - Using library functions in `awk' can be very beneficial. It -encourages code re-use and the writing of general functions. Programs -are smaller, and therefore clearer. However, using library functions -is only easy when writing `awk' programs; it is painful when running -them, requiring multiple `-f' options. If `gawk' is unavailable, then -so too is the `AWKPATH' environment variable and the ability to put -`awk' functions into a library directory (*note Command Line Options: -Options.). + The last two lines are commented out, since they are not needed in +`gawk'. They should be uncommented if you have to use another version +of `awk'. - It would be nice to be able to write programs like so: + The next set of lines should be uncommented if you are not using +`gawk'. This rule translates all the characters in the input line into +lowercase if the `-i' option is specified.(1) The rule is commented out +since it is not necessary with `gawk': - # library functions - @include getopt.awk - @include join.awk - ... - - # main program - BEGIN { - while ((c = getopt(ARGC, ARGV, "a:b:cde")) != -1) - ... - ... - } + #{ + # if (IGNORECASE) + # $0 = tolower($0) + #} - The following program, `igawk.sh', provides this service. It -simulates `gawk''s searching of the `AWKPATH' variable, and also allows -"nested" includes; i.e. a file that has been included with `@include' -can contain further `@include' statements. `igawk' will make an effort -to only include files once, so that nested includes don't accidentally -include a library function twice. - - `igawk' should behave externally just like `gawk'. This means it -should accept all of `gawk''s command line arguments, including the -ability to have multiple source files specified via `-f', and the -ability to mix command line and library source files. + The `beginfile' function is called by the rule in `ftrans.awk' when +each new file is processed. In this case, it is very simple; all it +does is initialize a variable `fcount' to zero. `fcount' tracks how +many lines in the current file matched the pattern. (Naming the +parameter `junk' shows we know that `beginfile' is called with a +parameter, but that we're not interested in its value.): - The program is written using the POSIX Shell (`sh') command language. -The way the program works is as follows: + function beginfile(junk) + { + fcount = 0 + } - 1. Loop through the arguments, saving anything that doesn't represent - `awk' source code for later, when the expanded program is run. + The `endfile' function is called after each file has been processed. +It affects the output only when the user wants a count of the number of +lines that matched. `no_print' is true only if the exit status is +desired. `count_only' is true if line counts are desired. `egrep' +therefore only prints line counts if printing and counting are enabled. +The output format must be adjusted depending upon the number of files to +process. Finally, `fcount' is added to `total', so that we know how +many lines altogether matched the pattern: - 2. For any arguments that do represent `awk' text, put the arguments - into a temporary file that will be expanded. There are two cases. + function endfile(file) + { + if (! no_print && count_only) + if (do_filenames) + print file ":" fcount + else + print fcount + + total += fcount + } + + The following rule does most of the work of matching lines. The +variable `matches' is true if the line matched the pattern. If the user +wants lines that did not match, the sense of `matches' is inverted +using the `!' operator. `fcount' is incremented with the value of +`matches', which is either one or zero, depending upon a successful or +unsuccessful match. If the line does not match, the `next' statement +just moves on to the next record. + + A number of additional tests are made, but they are only done if we +are not counting lines. First, if the user only wants exit status +(`no_print' is true), then it is enough to know that _one_ line in this +file matched, and we can skip on to the next file with `nextfile'. +Similarly, if we are only printing file names, we can print the file +name, and then skip to the next file with `nextfile'. Finally, each +line is printed, with a leading file name and colon if necessary: - a. Literal text, provided with `--source' or `--source='. This - text is just echoed directly. The `echo' program will - automatically supply a trailing newline. + { + matches = ($0 ~ pattern) + if (invert) + matches = ! matches + + fcount += matches # 1 or 0 + + if (! matches) + next + + if (! count_only) { + if (no_print) + nextfile + + if (filenames_only) { + print FILENAME + nextfile + } + + if (do_filenames) + print FILENAME ":" $0 + else + print + } + } - b. File names provided with `-f'. We use a neat trick, and echo - `@include FILENAME' into the temporary file. Since the file - inclusion program will work the way `gawk' does, this will - get the text of the file included into the program at the - correct point. + The `END' rule takes care of producing the correct exit status. If +there are no matches, the exit status is one, otherwise it is zero: - 3. Run an `awk' program (naturally) over the temporary file to expand - `@include' statements. The expanded program is placed in a second - temporary file. + END \ + { + if (total == 0) + exit 1 + exit 0 + } - 4. Run the expanded program with `gawk' and any other original - command line arguments that the user supplied (such as the data - file names). + The `usage' function prints a usage message in case of invalid +options, and then exits: - The initial part of the program turns on shell tracing if the first -argument was `debug'. Otherwise, a shell `trap' statement arranges to -clean up any temporary files on program exit or upon an interrupt. + function usage( e) + { + e = "Usage: egrep [-csvil] [-e pat] [files ...]" + e = e "\n\tegrep [-csvil] pat [files ...]" + print e > "/dev/stderr" + exit 1 + } - The next part loops through all the command line arguments. There -are several cases of interest. + The variable `e' is used so that the function fits nicely on the +printed page. -`--' - This ends the arguments to `igawk'. Anything else should be - passed on to the user's `awk' program without being evaluated. + Just a note on programming style: you may have noticed that the `END' +rule uses backslash continuation, with the open brace on a line by +itself. This is so that it more closely resembles the way functions +are written. Many of the examples in this major node use this style. +You can decide for yourself if you like writing your `BEGIN' and `END' +rules this way or not. -`-W' - This indicates that the next option is specific to `gawk'. To make - argument processing easier, the `-W' is appended to the front of - the remaining arguments and the loop continues. (This is an `sh' - programming trick. Don't worry about it if you are not familiar - with `sh'.) + ---------- Footnotes ---------- -`-v' -`-F' - These are saved and passed on to `gawk'. + (1) It also introduces a subtle bug; if a match happens, we output +the translated line, not the original. -`-f' -`--file' -`--file=' -`-Wfile=' - The file name is saved to the temporary file `/tmp/ig.s.$$' with an - `@include' statement. The `sed' utility is used to remove the - leading option part of the argument (e.g., `--file='). + +File: gawk.info, Node: Id Program, Next: Split Program, Prev: Egrep Program, Up: Clones -`--source' -`--source=' -`-Wsource=' - The source text is echoed into `/tmp/ig.s.$$'. +Printing out User Information +----------------------------- -`--version' -`-Wversion' - `igawk' prints its version number, and runs `gawk --version' to - get the `gawk' version information, and then exits. + The `id' utility lists a user's real and effective user-id numbers, +real and effective group-id numbers, and the user's group set, if any. +`id' only prints the effective user-id and group-id if they are +different from the real ones. If possible, `id' also supplies the +corresponding user and group names. The output might look like this: - If none of `-f', `--file', `-Wfile', `--source', or `-Wsource', were -supplied, then the first non-option argument should be the `awk' -program. If there are no command line arguments left, `igawk' prints -an error message and exits. Otherwise, the first argument is echoed -into `/tmp/ig.s.$$'. + $ id + -| uid=2076(arnold) gid=10(staff) groups=10(staff),4(tty) - In any case, after the arguments have been processed, `/tmp/ig.s.$$' -contains the complete text of the original `awk' program. + This information is part of what is provided by `gawk''s `PROCINFO' +array (*note Built-in Variables::). However, the `id' utility provides +a more palatable output than just individual numbers. - The `$$' in `sh' represents the current process ID number. It is -often used in shell programs to generate unique temporary file names. -This allows multiple users to run `igawk' without worrying that the -temporary file names will clash. + Here is a simple version of `id' written in `awk'. It uses the user +database library functions (*note Reading the User Database: Passwd +Functions.) and the group database library functions (*note Reading +the Group Database: Group Functions.): - Here's the program: + The program is fairly straightforward. All the work is done in the +`BEGIN' rule. The user and group ID numbers are obtained from +`PROCINFO'. The code is repetitive. The entry in the user database +for the real user-id number is split into parts at the `:'. The name is +the first field. Similar code is used for the effective user-id number +and the group numbers. - #! /bin/sh - - # igawk --- like gawk but do @include processing - # Arnold Robbins, arnold@gnu.org, Public Domain - # July 1993 - - if [ "$1" = debug ] - then - set -x - shift - else - # cleanup on exit, hangup, interrupt, quit, termination - trap 'rm -f /tmp/ig.[se].$$' 0 1 2 3 15 - fi - - while [ $# -ne 0 ] # loop over arguments - do - case $1 in - --) shift; break;; - - -W) shift - set -- -W"$@" - continue;; - - -[vF]) opts="$opts $1 '$2'" - shift;; - - -[vF]*) opts="$opts '$1'" ;; - - -f) echo @include "$2" >> /tmp/ig.s.$$ - shift;; - - -f*) f=`echo "$1" | sed 's/-f//'` - echo @include "$f" >> /tmp/ig.s.$$ ;; - - -?file=*) # -Wfile or --file - f=`echo "$1" | sed 's/-.file=//'` - echo @include "$f" >> /tmp/ig.s.$$ ;; - - -?file) # get arg, $2 - echo @include "$2" >> /tmp/ig.s.$$ - shift;; + # id.awk --- implement id in awk + # + # Requires user and group library functions + # output is: + # uid=12(foo) euid=34(bar) gid=3(baz) \ + # egid=5(blat) groups=9(nine),2(two),1(one) - -?source=*) # -Wsource or --source - t=`echo "$1" | sed 's/-.source=//'` - echo "$t" >> /tmp/ig.s.$$ ;; + BEGIN \ + { + uid = PROCINFO["uid"] + euid = PROCINFO["euid"] + gid = PROCINFO["gid"] + egid = PROCINFO["egid"] - -?source) # get arg, $2 - echo "$2" >> /tmp/ig.s.$$ - shift;; + printf("uid=%d", uid) + pw = getpwuid(uid) + if (pw != "") { + split(pw, a, ":") + printf("(%s)", a[1]) + } - -?version) - echo igawk: version 1.0 1>&2 - gawk --version - exit 0 ;; + if (euid != uid) { + printf(" euid=%d", euid) + pw = getpwuid(euid) + if (pw != "") { + split(pw, a, ":") + printf("(%s)", a[1]) + } + } - -[W-]*) opts="$opts '$1'" ;; + printf(" gid=%d", gid) + pw = getgrgid(gid) + if (pw != "") { + split(pw, a, ":") + printf("(%s)", a[1]) + } - *) break;; - esac - shift - done + if (egid != gid) { + printf(" egid=%d", egid) + pw = getgrgid(egid) + if (pw != "") { + split(pw, a, ":") + printf("(%s)", a[1]) + } + } - if [ ! -s /tmp/ig.s.$$ ] - then - if [ -z "$1" ] - then - echo igawk: no program! 1>&2 - exit 1 - else - echo "$1" > /tmp/ig.s.$$ - shift - fi - fi + for (i = 1; ("group" i) in PROCINFO; i++) { + if (i == 1) + printf(" groups=") + group = PROCINFO["group" i] + printf("%d", group) + pw = getgrgid(group) + if (pw != "") { + split(pw, a, ":") + printf("(%s)", a[1]) + } + if (("group" (i+1)) in PROCINFO) + printf(",") + } - # at this point, /tmp/ig.s.$$ has the program + print "" + } - The `awk' program to process `@include' directives reads through the -program, one line at a time using `getline' (*note Explicit Input with -`getline': Getline.). The input file names and `@include' statements -are managed using a stack. As each `@include' is encountered, the -current file name is "pushed" onto the stack, and the file named in the -`@include' directive becomes the current file name. As each file is -finished, the stack is "popped," and the previous input file becomes -the current input file again. The process is started by making the -original file the first one on the stack. + The test in the `for' loop is worth noting. Any supplementary +groups in the `PROCINFO' array have the indices `"group1"' through +`"groupN"' for some N; i.e., the total number of supplementary groups. +The problem is, we don't know in advance how many of these groups there +are. - The `pathto' function does the work of finding the full path to a -file. It simulates `gawk''s behavior when searching the `AWKPATH' -environment variable (*note The `AWKPATH' Environment Variable: AWKPATH -Variable.). If a file name has a `/' in it, no path search is done. -Otherwise, the file name is concatenated with the name of each -directory in the path, and an attempt is made to open the generated file -name. The only way in `awk' to test if a file can be read is to go -ahead and try to read it with `getline'; that is what `pathto' does.(1) -If the file can be read, it is closed, and the file name is returned. + This loop works by starting at one, concatenating the value with +`"group"', and then using `in' to see if that value is in the array. +Eventually, `i' is incremented past the last group in the array and the +loop exits. - gawk -- ' - # process @include directives - - function pathto(file, i, t, junk) - { - if (index(file, "/") != 0) - return file - - for (i = 1; i <= ndirs; i++) { - t = (pathlist[i] "/" file) - if ((getline junk < t) > 0) { - # found it - close(t) - return t - } - } - return "" - } + The loop is also correct if there are _no_ supplementary groups; +then the condition is false the first time it's tested, and the loop +body never executes. - The main program is contained inside one `BEGIN' rule. The first -thing it does is set up the `pathlist' array that `pathto' uses. After -splitting the path on `:', null elements are replaced with `"."', which -represents the current directory. + +File: gawk.info, Node: Split Program, Next: Tee Program, Prev: Id Program, Up: Clones + +Splitting a Large File into Pieces +---------------------------------- + + The `split' program splits large text files into smaller pieces. +The usage is as follows: + + split [-COUNT] file [ PREFIX ] + + By default, the output files are named `xaa', `xab', and so on. Each +file has 1000 lines in it, with the likely exception of the last file. +To change the number of lines in each file, supply a number on the +command line preceded with a minus; e.g., `-500' for files with 500 +lines in them instead of 1000. To change the name of the output files +to something like `myfileaa', `myfileab', and so on, supply an +additional argument that specifies the file name prefix. + + Here is a version of `split' in `awk'. It uses the `ord' and `chr' +functions presented in *Note Translating Between Characters and +Numbers: Ordinal Functions. + + The program first sets its defaults, and then tests to make sure +there are not too many arguments. It then looks at each argument in +turn. The first argument could be a minus followed by a number. If it +is, this happens to look like a negative number, so it is made +positive, and that is the count of lines. The data file name is +skipped over and the final argument is used as the prefix for the +output file names: + # split.awk --- do split in awk + # + # Requires ord and chr library functions + # usage: split [-num] [file] [outname] + BEGIN { - path = ENVIRON["AWKPATH"] - ndirs = split(path, pathlist, ":") - for (i = 1; i <= ndirs; i++) { - if (pathlist[i] == "") - pathlist[i] = "." + outfile = "x" # default + count = 1000 + if (ARGC > 4) + usage() + + i = 1 + if (ARGV[i] ~ /^-[0-9]+$/) { + count = -ARGV[i] + ARGV[i] = "" + i++ + } + # test argv in case reading from stdin instead of file + if (i in ARGV) + i++ # skip data file name + if (i in ARGV) { + outfile = ARGV[i] + ARGV[i] = "" } + + s1 = s2 = "a" + out = (outfile s1 s2) + } - The stack is initialized with `ARGV[1]', which will be -`/tmp/ig.s.$$'. The main loop comes next. Input lines are read in -succession. Lines that do not start with `@include' are printed -verbatim. - - If the line does start with `@include', the file name is in `$2'. -`pathto' is called to generate the full path. If it could not, then we -print an error message and continue. - - The next thing to check is if the file has been included already. -The `processed' array is indexed by the full file name of each included -file, and it tracks this information for us. If the file has been -seen, a warning message is printed. Otherwise, the new file name is -pushed onto the stack and processing continues. - - Finally, when `getline' encounters the end of the input file, the -file is closed and the stack is popped. When `stackptr' is less than -zero, the program is done. + The next rule does most of the work. `tcount' (temporary count) +tracks how many lines have been printed to the output file so far. If +it is greater than `count', it is time to close the current file and +start a new one. `s1' and `s2' track the current suffixes for the file +name. If they are both `z', the file is just too big. Otherwise, `s1' +moves to the next letter in the alphabet and `s2' starts over again at +`a': - stackptr = 0 - input[stackptr] = ARGV[1] # ARGV[1] is first file - - for (; stackptr >= 0; stackptr--) { - while ((getline < input[stackptr]) > 0) { - if (tolower($1) != "@include") { - print - continue - } - fpath = pathto($2) - if (fpath == "") { - printf("igawk:%s:%d: cannot find %s\n", \ - input[stackptr], FNR, $2) > "/dev/stderr" - continue + { + if (++tcount > count) { + close(out) + if (s2 == "z") { + if (s1 == "z") { + printf("split: %s is too large to split\n", + FILENAME) > "/dev/stderr" + exit 1 } - if (! (fpath in processed)) { - processed[fpath] = input[stackptr] - input[++stackptr] = fpath - } else - print $2, "included in", input[stackptr], \ - "already included in", \ - processed[fpath] > "/dev/stderr" + s1 = chr(ord(s1) + 1) + s2 = "a" } - close(input[stackptr]) + else + s2 = chr(ord(s2) + 1) + out = (outfile s1 s2) + tcount = 1 } - }' /tmp/ig.s.$$ > /tmp/ig.e.$$ + print > out + } - The last step is to call `gawk' with the expanded program and the -original options and command line arguments that the user supplied. -`gawk''s exit status is passed back on to `igawk''s calling program. +The `usage' function simply prints an error message and exits: - eval gawk -f /tmp/ig.e.$$ $opts -- "$@" - - exit $? + function usage( e) + { + e = "usage: split [-num] [file] [outname]" + print e > "/dev/stderr" + exit 1 + } - This version of `igawk' represents my third attempt at this program. -There are three key simplifications that made the program work better. +The variable `e' is used so that the function fits nicely on the screen. - 1. Using `@include' even for the files named with `-f' makes building - the initial collected `awk' program much simpler; all the - `@include' processing can be done once. + This program is a bit sloppy; it relies on `awk' to close the last +file for it automatically, instead of doing it in an `END' rule. It +also assumes that letters are contiguous in the character set, which +isn't true for EBCDIC systems. - 2. The `pathto' function doesn't try to save the line read with - `getline' when testing for the file's accessibility. Trying to - save this line for use with the main program complicates things - considerably. + +File: gawk.info, Node: Tee Program, Next: Uniq Program, Prev: Split Program, Up: Clones - 3. Using a `getline' loop in the `BEGIN' rule does it all in one - place. It is not necessary to call out to a separate loop for - processing nested `@include' statements. +Duplicating Output into Multiple Files +-------------------------------------- - Also, this program illustrates that it is often worthwhile to combine -`sh' and `awk' programming together. You can usually accomplish quite -a lot, without having to resort to low-level programming in C or C++, -and it is frequently easier to do certain kinds of string and argument -manipulation using the shell than it is in `awk'. + The `tee' program is known as a "pipe fitting." `tee' copies its +standard input to its standard output and also duplicates it to the +files named on the command line. Its usage is as follows: - Finally, `igawk' shows that it is not always necessary to add new -features to a program; they can often be layered on top. With `igawk', -there is no real reason to build `@include' processing into `gawk' -itself. + tee [-a] file ... - As an additional example of this, consider the idea of having two -files in a directory in the search path. + The `-a' option tells `tee' to append to the named files, instead of +truncating them and starting over. -`default.awk' - This file would contain a set of default library functions, such - as `getopt' and `assert'. + The `BEGIN' rule first makes a copy of all the command-line arguments +into an array named `copy'. `ARGV[0]' is not copied, since it is not +needed. `tee' cannot use `ARGV' directly, since `awk' attempts to +process each file name in `ARGV' as input data. -`site.awk' - This file would contain library functions that are specific to a - site or installation, i.e. locally developed functions. Having a - separate file allows `default.awk' to change with new `gawk' - releases, without requiring the system administrator to update it - each time by adding the local functions. + If the first argument is `-a', then the flag variable `append' is +set to true, and both `ARGV[1]' and `copy[1]' are deleted. If `ARGC' is +less than two, then no file names were supplied and `tee' prints a +usage message and exits. Finally, `awk' is forced to read the standard +input by setting `ARGV[1]' to `"-"' and `ARGC' to two: - One user suggested that `gawk' be modified to automatically read -these files upon startup. Instead, it would be very simple to modify -`igawk' to do this. Since `igawk' can process nested `@include' -directives, `default.awk' could simply contain `@include' statements -for the desired library functions. + # tee.awk --- tee in awk + BEGIN \ + { + for (i = 1; i < ARGC; i++) + copy[i] = ARGV[i] + + if (ARGV[1] == "-a") { + append = 1 + delete ARGV[1] + delete copy[1] + ARGC-- + } + if (ARGC < 2) { + print "usage: tee [-a] file ..." > "/dev/stderr" + exit 1 + } + ARGV[1] = "-" + ARGC = 2 + } - ---------- Footnotes ---------- + The single rule does all the work. Since there is no pattern, it is +executed for each line of input. The body of the rule simply prints the +line into each file on the command line, and then to the standard +output: - (1) On some very old versions of `awk', the test `getline junk < t' -can loop forever if the file exists but is empty. Caveat Emptor. + { + # moving the if outside the loop makes it run faster + if (append) + for (i in copy) + print >> copy[i] + else + for (i in copy) + print > copy[i] + print + } - -File: gawk.info, Node: Language History, Next: Gawk Summary, Prev: Sample Programs, Up: Top +It is also possible to write the loop this way: -The Evolution of the `awk' Language -*********************************** + for (i in copy) + if (append) + print >> copy[i] + else + print > copy[i] - This Info file describes the GNU implementation of `awk', which -follows the POSIX specification. Many `awk' users are only familiar -with the original `awk' implementation in Version 7 Unix. (This -implementation was the basis for `awk' in Berkeley Unix, through -4.3-Reno. The 4.4 release of Berkeley Unix uses `gawk' 2.15.2 for its -version of `awk'.) This chapter briefly describes the evolution of the -`awk' language, with cross references to other parts of the Info file -where you can find more information. +This is more concise but it is also less efficient. The `if' is tested +for each record and for each output file. By duplicating the loop +body, the `if' is only tested once for each input record. If there are +N input records and M output files, the first method only executes N +`if' statements, while the second executes N`*'M `if' statements. -* Menu: + Finally, the `END' rule cleans up by closing all the output files: -* V7/SVR3.1:: The major changes between V7 and System V - Release 3.1. -* SVR4:: Minor changes between System V Releases 3.1 - and 4. -* POSIX:: New features from the POSIX standard. -* BTL:: New features from the Bell Laboratories - version of `awk'. -* POSIX/GNU:: The extensions in `gawk' not in POSIX - `awk'. + END \ + { + for (i in copy) + close(copy[i]) + }  -File: gawk.info, Node: V7/SVR3.1, Next: SVR4, Prev: Language History, Up: Language History +File: gawk.info, Node: Uniq Program, Next: Wc Program, Prev: Tee Program, Up: Clones -Major Changes between V7 and SVR3.1 -=================================== +Printing Non-Duplicated Lines of Text +------------------------------------- - The `awk' language evolved considerably between the release of -Version 7 Unix (1978) and the new version first made generally -available in System V Release 3.1 (1987). This section summarizes the -changes, with cross-references to further details. + The `uniq' utility reads sorted lines of data on its standard input, +and by default removes duplicate lines. In other words, it only prints +unique lines--hence the name. `uniq' has a number of options. The +usage is as follows: - * The requirement for `;' to separate rules on a line (*note `awk' - Statements Versus Lines: Statements/Lines.). + uniq [-udc [-N]] [+N] [ INPUT FILE [ OUTPUT FILE ]] - * User-defined functions, and the `return' statement (*note - User-defined Functions: User-defined.). + The option meanings are: - * The `delete' statement (*note The `delete' Statement: Delete.). +`-d' + Only print repeated lines. - * The `do'-`while' statement (*note The `do'-`while' Statement: Do - Statement.). +`-u' + Only print non-repeated lines. - * The built-in functions `atan2', `cos', `sin', `rand' and `srand' - (*note Numeric Built-in Functions: Numeric Functions.). +`-c' + Count lines. This option overrides `-d' and `-u'. Both repeated + and non-repeated lines are counted. - * The built-in functions `gsub', `sub', and `match' (*note Built-in - Functions for String Manipulation: String Functions.). +`-N' + Skip N fields before comparing lines. The definition of fields is + similar to `awk''s default: non-whitespace characters separated by + runs of spaces and/or tabs. - * The built-in functions `close', and `system' (*note Built-in - Functions for Input/Output: I/O Functions.). +`+N' + Skip N characters before comparing lines. Any fields specified + with `-N' are skipped first. - * The `ARGC', `ARGV', `FNR', `RLENGTH', `RSTART', and `SUBSEP' - built-in variables (*note Built-in Variables::). +`INPUT FILE' + Data is read from the input file named on the command line, + instead of from the standard input. - * The conditional expression using the ternary operator `?:' (*note - Conditional Expressions: Conditional Exp.). +`OUTPUT FILE' + The generated output is sent to the named output file, instead of + to the standard output. - * The exponentiation operator `^' (*note Arithmetic Operators: - Arithmetic Ops.) and its assignment operator form `^=' (*note - Assignment Expressions: Assignment Ops.). + Normally `uniq' behaves as if both the `-d' and `-u' options are +provided. + + `uniq' uses the `getopt' library function (*note Processing +Command-Line Options: Getopt Function.) and the `join' library function +(*note Merging an Array into a String: Join Function.). + + The program begins with a `usage' function and then a brief outline +of the options and their meanings in a comment. The `BEGIN' rule deals +with the command-line arguments and options. It uses a trick to get +`getopt' to handle options of the form `-25', treating such an option +as the option letter `2' with an argument of `5'. If indeed two or more +digits are supplied (`Optarg' looks like a number), `Optarg' is +concatenated with the option digit and then the result is added to zero +to make it into a number. If there is only one digit in the option, +then `Optarg' is not needed. `Optind' must be decremented so that +`getopt' processes it next time. This code is admittedly a bit tricky. + + If no options are supplied, then the default is taken, to print both +repeated and non-repeated lines. The output file, if provided, is +assigned to `outputfile'. Early on, `outputfile' is initialized to the +standard output, `/dev/stdout': + + # uniq.awk --- do uniq in awk + # + # Requires getopt and join library functions + function usage( e) + { + e = "Usage: uniq [-udc [-n]] [+n] [ in [ out ]]" + print e > "/dev/stderr" + exit 1 + } + + # -c count lines. overrides -d and -u + # -d only repeated lines + # -u only non-repeated lines + # -n skip n fields + # +n skip n characters, skip fields first + + BEGIN \ + { + count = 1 + outputfile = "/dev/stdout" + opts = "udc0:1:2:3:4:5:6:7:8:9:" + while ((c = getopt(ARGC, ARGV, opts)) != -1) { + if (c == "u") + non_repeated_only++ + else if (c == "d") + repeated_only++ + else if (c == "c") + do_count++ + else if (index("0123456789", c) != 0) { + # getopt requires args to options + # this messes us up for things like -5 + if (Optarg ~ /^[0-9]+$/) + fcount = (c Optarg) + 0 + else { + fcount = c + 0 + Optind-- + } + } else + usage() + } + + if (ARGV[Optind] ~ /^\+[0-9]+$/) { + charcount = substr(ARGV[Optind], 2) + 0 + Optind++ + } + + for (i = 1; i < Optind; i++) + ARGV[i] = "" + + if (repeated_only == 0 && non_repeated_only == 0) + repeated_only = non_repeated_only = 1 + + if (ARGC - Optind == 2) { + outputfile = ARGV[ARGC - 1] + ARGV[ARGC - 1] = "" + } + } - * C-compatible operator precedence, which breaks some old `awk' - programs (*note Operator Precedence (How Operators Nest): - Precedence.). + The following function, `are_equal', compares the current line, +`$0', to the previous line, `last'. It handles skipping fields and +characters. If no field count and no character count are specified, +`are_equal' simply returns one or zero depending upon the result of a +simple string comparison of `last' and `$0'. Otherwise, things get more +complicated. If fields have to be skipped, each line is broken into an +array using `split' (*note String Manipulation Functions: String +Functions.); the desired fields are then joined back into a line using +`join'. The joined lines are stored in `clast' and `cline'. If no +fields are skipped, `clast' and `cline' are set to `last' and `$0', +respectively. Finally, if characters are skipped, `substr' is used to +strip off the leading `charcount' characters in `clast' and `cline'. +The two strings are then compared and `are_equal' returns the result: - * Regexps as the value of `FS' (*note Specifying How Fields are - Separated: Field Separators.), and as the third argument to the - `split' function (*note Built-in Functions for String - Manipulation: String Functions.). + function are_equal( n, m, clast, cline, alast, aline) + { + if (fcount == 0 && charcount == 0) + return (last == $0) + + if (fcount > 0) { + n = split(last, alast) + m = split($0, aline) + clast = join(alast, fcount+1, n) + cline = join(aline, fcount+1, m) + } else { + clast = last + cline = $0 + } + if (charcount) { + clast = substr(clast, charcount + 1) + cline = substr(cline, charcount + 1) + } + + return (clast == cline) + } - * Dynamic regexps as operands of the `~' and `!~' operators (*note - How to Use Regular Expressions: Regexp Usage.). + The following two rules are the body of the program. The first one +is executed only for the very first line of data. It sets `last' equal +to `$0', so that subsequent lines of text have something to be compared +to. - * The escape sequences `\b', `\f', and `\r' (*note Escape - Sequences::). (Some vendors have updated their old versions of - `awk' to recognize `\r', `\b', and `\f', but this is not something - you can rely on.) + The second rule does the work. The variable `equal' is one or zero, +depending upon the results of `are_equal''s comparison. If `uniq' is +counting repeated lines, and the lines are equal, then it increments +the `count' variable. Otherwise it prints the line and resets `count', +since the two lines are not equal. - * Redirection of input for the `getline' function (*note Explicit - Input with `getline': Getline.). + If `uniq' is not counting, and if the lines are equal, `count' is +incremented. Nothing is printed, since the point is to remove +duplicates. Otherwise, if `uniq' is counting repeated lines and more +than one line is seen, or if `uniq' is counting non-repeated lines and +only one line is seen, then the line is printed, and `count' is reset. - * Multiple `BEGIN' and `END' rules (*note The `BEGIN' and `END' - Special Patterns: BEGIN/END.). + Finally, similar logic is used in the `END' rule to print the final +line of input data: - * Multi-dimensional arrays (*note Multi-dimensional Arrays: - Multi-dimensional.). + NR == 1 { + last = $0 + next + } + + { + equal = are_equal() + + if (do_count) { # overrides -d and -u + if (equal) + count++ + else { + printf("%4d %s\n", count, last) > outputfile + last = $0 + count = 1 # reset + } + next + } + + if (equal) + count++ + else { + if ((repeated_only && count > 1) || + (non_repeated_only && count == 1)) + print last > outputfile + last = $0 + count = 1 + } + } + + END { + if (do_count) + printf("%4d %s\n", count, last) > outputfile + else if ((repeated_only && count > 1) || + (non_repeated_only && count == 1)) + print last > outputfile + }  -File: gawk.info, Node: SVR4, Next: POSIX, Prev: V7/SVR3.1, Up: Language History +File: gawk.info, Node: Wc Program, Prev: Uniq Program, Up: Clones -Changes between SVR3.1 and SVR4 -=============================== +Counting Things +--------------- - The System V Release 4 version of Unix `awk' added these features -(some of which originated in `gawk'): + The `wc' (word count) utility counts lines, words, and characters in +one or more input files. Its usage is as follows: - * The `ENVIRON' variable (*note Built-in Variables::). + wc [-lwc] [ FILES ... ] - * Multiple `-f' options on the command line (*note Command Line - Options: Options.). + If no files are specified on the command line, `wc' reads its +standard input. If there are multiple files, it also prints total +counts for all the files. The options and their meanings are shown in +the following list: - * The `-v' option for assigning variables before program execution - begins (*note Command Line Options: Options.). +`-l' + Only count lines. - * The `--' option for terminating command line options. +`-w' + Only count words. A "word" is a contiguous sequence of + non-whitespace characters, separated by spaces and/or tabs. + Happily, this is the normal way `awk' separates fields in its + input data. - * The `\a', `\v', and `\x' escape sequences (*note Escape - Sequences::). +`-c' + Only count characters. - * A defined return value for the `srand' built-in function (*note - Numeric Built-in Functions: Numeric Functions.). + Implementing `wc' in `awk' is particularly elegant, since `awk' does +a lot of the work for us; it splits lines into words (i.e., fields) and +counts them, it counts lines (i.e., records), and it can easily tell us +how long a line is. - * The `toupper' and `tolower' built-in string functions for case - translation (*note Built-in Functions for String Manipulation: - String Functions.). + This uses the `getopt' library function (*note Processing +Command-Line Options: Getopt Function.) and the file transition +functions (*note Noting Data File Boundaries: Filetrans Function.). - * A cleaner specification for the `%c' format-control letter in the - `printf' function (*note Format-Control Letters: Control Letters.). + This version has one notable difference from traditional versions of +`wc': it always prints the counts in the order lines, words, and +characters. Traditional versions note the order of the `-l', `-w', and +`-c' options on the command line, and print the counts in that order. - * The ability to dynamically pass the field width and precision - (`"%*.*d"') in the argument list of the `printf' function (*note - Format-Control Letters: Control Letters.). + The `BEGIN' rule does the argument processing. The variable +`print_total' is true if more than one file is named on the command +line: - * The use of regexp constants such as `/foo/' as expressions, where - they are equivalent to using the matching operator, as in `$0 ~ - /foo/' (*note Using Regular Expression Constants: Using Constant - Regexps.). + # wc.awk --- count lines, words, characters + + # Options: + # -l only count lines + # -w only count words + # -c only count characters + # + # Default is to count lines, words, characters + # + # Requires getopt and file transition library functions + + BEGIN { + # let getopt print a message about + # invalid options. we ignore them + while ((c = getopt(ARGC, ARGV, "lwc")) != -1) { + if (c == "l") + do_lines = 1 + else if (c == "w") + do_words = 1 + else if (c == "c") + do_chars = 1 + } + for (i = 1; i < Optind; i++) + ARGV[i] = "" + + # if no options, do all + if (! do_lines && ! do_words && ! do_chars) + do_lines = do_words = do_chars = 1 + + print_total = (ARGC - i > 2) + } - -File: gawk.info, Node: POSIX, Next: BTL, Prev: SVR4, Up: Language History + The `beginfile' function is simple; it just resets the counts of +lines, words, and characters to zero, and saves the current file name in +`fname': -Changes between SVR4 and POSIX `awk' -==================================== + function beginfile(file) + { + chars = lines = words = 0 + fname = FILENAME + } - The POSIX Command Language and Utilities standard for `awk' -introduced the following changes into the language: + The `endfile' function adds the current file's numbers to the running +totals of lines, words, and characters. It then prints out those +numbers for the file that was just read. It relies on `beginfile' to +reset the numbers for the following data file: - * The use of `-W' for implementation-specific options. + function endfile(file) + { + tchars += chars + tlines += lines + twords += words + if (do_lines) + printf "\t%d", lines + if (do_words) + printf "\t%d", words + if (do_chars) + printf "\t%d", chars + printf "\t%s\n", fname + } - * The use of `CONVFMT' for controlling the conversion of numbers to - strings (*note Conversion of Strings and Numbers: Conversion.). + There is one rule that is executed for each line. It adds the length +of the record, plus one, to `chars'. Adding one plus the record length +is needed because the newline character separating records (the value +of `RS') is not part of the record itself, and thus not included in its +length. Next, `lines' is incremented for each line read, and `words' +is incremented by the value of `NF', which is the number of "words" on +this line:(1) - * The concept of a numeric string, and tighter comparison rules to go - with it (*note Variable Typing and Comparison Expressions: Typing - and Comparison.). + # do per line + { + chars += length($0) + 1 # get newline + lines++ + words += NF + } - * More complete documentation of many of the previously undocumented - features of the language. + Finally, the `END' rule simply prints the totals for all the files. - The following common extensions are not permitted by the POSIX -standard: + END { + if (print_total) { + if (do_lines) + printf "\t%d", tlines + if (do_words) + printf "\t%d", twords + if (do_chars) + printf "\t%d", tchars + print "\ttotal" + } + } - * `\x' escape sequences are not recognized (*note Escape - Sequences::). + ---------- Footnotes ---------- - * Newlines do not act as whitespace to separate fields when `FS' is - equal to a single space. + (1) `wc' can't just use the value of `FNR' in `endfile'. If you +examine the code in *Note Noting Data File Boundaries: Filetrans +Function, you will see that `FNR' has already been reset by the time +`endfile' is called. - * The synonym `func' for the keyword `function' is not recognized - (*note Function Definition Syntax: Definition Syntax.). + +File: gawk.info, Node: Miscellaneous Programs, Prev: Clones, Up: Sample Programs - * The operators `**' and `**=' cannot be used in place of `^' and - `^=' (*note Arithmetic Operators: Arithmetic Ops., and also *note - Assignment Expressions: Assignment Ops.). +A Grab Bag of `awk' Programs +============================ - * Specifying `-Ft' on the command line does not set the value of - `FS' to be a single tab character (*note Specifying How Fields are - Separated: Field Separators.). + This minor node is a large "grab bag" of miscellaneous programs. We +hope you find them both interesting and enjoyable. - * The `fflush' built-in function is not supported (*note Built-in - Functions for Input/Output: I/O Functions.). +* Menu: - -File: gawk.info, Node: BTL, Next: POSIX/GNU, Prev: POSIX, Up: Language History +* Dupword Program:: Finding duplicated words in a document. +* Alarm Program:: An alarm clock. +* Translate Program:: A program similar to the `tr' utility. +* Labels Program:: Printing mailing labels. +* Word Sorting:: A program to produce a word usage count. +* History Sorting:: Eliminating duplicate entries from a history + file. +* Extract Program:: Pulling out programs from Texinfo source + files. +* Simple Sed:: A Simple Stream Editor. +* Igawk Program:: A wrapper for `awk' that includes + files. -Extensions in the Bell Laboratories `awk' -========================================= + +File: gawk.info, Node: Dupword Program, Next: Alarm Program, Prev: Miscellaneous Programs, Up: Miscellaneous Programs - Brian Kernighan, one of the original designers of Unix `awk', has -made his version available via anonymous `ftp' (*note Other Freely -Available `awk' Implementations: Other Versions.). This section -describes extensions in his version of `awk' that are not in POSIX -`awk'. +Finding Duplicated Words in a Document +-------------------------------------- - * The `-mf NNN' and `-mr NNN' command line options to set the - maximum number of fields, and the maximum record size, respectively - (*note Command Line Options: Options.). + A common error when writing large amounts of prose is to accidentally +duplicate words. Typically you will see this in text as something like +"the the program does the following ...." When the text is online, +often the duplicated words occur at the end of one line and the +beginning of another, making them very difficult to spot. - * The `fflush' built-in function for flushing buffered output (*note - Built-in Functions for Input/Output: I/O Functions.). + This program, `dupword.awk', scans through a file one line at a time +and looks for adjacent occurrences of the same word. It also saves the +last word on a line (in the variable `prev') for comparison with the +first word on the next line. + The first two statements make sure that the line is all lowercase, +so that, for example, "The" and "the" compare equal to each other. The +next statement replaces non-alphanumeric and non-whitespace characters +with spaces, so that punctuation does not affect the comparison either. +The characters are replaced with spaces so that formatting controls +don't create nonsense words (e.g., the Texinfo `@code{NF}' becomes +`codeNF' if punctuation is simply deleted). The record is then +re-split into fields, yielding just the actual words on the line, and +insuring that there are no empty fields. + + If there are no fields left after removing all the punctuation, the +current record is skipped. Otherwise, the program loops through each +word, comparing it to the previous one: + + # dupword.awk --- find duplicate words in text + { + $0 = tolower($0) + gsub(/[^[:alnum:][:blank:]]/, " "); + $0 = $0 # re-split + if (NF == 0) + next + if ($1 == prev) + printf("%s:%d: duplicate %s\n", + FILENAME, FNR, $1) + for (i = 2; i <= NF; i++) + if ($i == $(i-1)) + printf("%s:%d: duplicate %s\n", + FILENAME, FNR, $i) + prev = $NF + }  -File: gawk.info, Node: POSIX/GNU, Prev: BTL, Up: Language History +File: gawk.info, Node: Alarm Program, Next: Translate Program, Prev: Dupword Program, Up: Miscellaneous Programs -Extensions in `gawk' Not in POSIX `awk' -======================================= +An Alarm Clock Program +---------------------- - The GNU implementation, `gawk', adds a number of features. This -sections lists them in the order they were added to `gawk'. They can -all be disabled with either the `--traditional' or `--posix' options -(*note Command Line Options: Options.). + Nothing cures insomnia like a ringing alarm clock. + Arnold Robbins - Version 2.10 of `gawk' introduced these features: + The following program is a simple "alarm clock" program. You give +it a time of day and an optional message. At the specified time, it +prints the message on the standard output. In addition, you can give it +the number of times to repeat the message as well as a delay between +repetitions. - * The `AWKPATH' environment variable for specifying a path search for - the `-f' command line option (*note Command Line Options: - Options.). + This program uses the `gettimeofday' function from *Note Managing +the Time of Day: Gettimeofday Function. - * The `IGNORECASE' variable and its effects (*note Case-sensitivity - in Matching: Case-sensitivity.). + All the work is done in the `BEGIN' rule. The first part is argument +checking and setting of defaults: the delay, the count, and the message +to print. If the user supplied a message without the ASCII BEL +character (known as the "alert" character, `"\a"'), then it is added to +the message. (On many systems, printing the ASCII BEL generates some +sort of audible alert. Thus when the alarm goes off, the system calls +attention to itself in case the user is not looking at their computer +or terminal.): + + # alarm.awk --- set an alarm + # + # Requires gettimeofday library function + # usage: alarm time [ "message" [ count [ delay ] ] ] + + BEGIN \ + { + # Initial argument sanity checking + usage1 = "usage: alarm time ['message' [count [delay]]]" + usage2 = sprintf("\t(%s) time ::= hh:mm", ARGV[1]) + + if (ARGC < 2) { + print usage1 > "/dev/stderr" + print usage2 > "/dev/stderr" + exit 1 + } else if (ARGC == 5) { + delay = ARGV[4] + 0 + count = ARGV[3] + 0 + message = ARGV[2] + } else if (ARGC == 4) { + count = ARGV[3] + 0 + message = ARGV[2] + } else if (ARGC == 3) { + message = ARGV[2] + } else if (ARGV[1] !~ /[0-9]?[0-9]:[0-9][0-9]/) { + print usage1 > "/dev/stderr" + print usage2 > "/dev/stderr" + exit 1 + } + + # set defaults for once we reach the desired time + if (delay == 0) + delay = 180 # 3 minutes + if (count == 0) + count = 5 + if (message == "") + message = sprintf("\aIt is now %s!\a", ARGV[1]) + else if (index(message, "\a") == 0) + message = "\a" message "\a" - * The `/dev/stdin', `/dev/stdout', `/dev/stderr', and `/dev/fd/N' - file name interpretation (*note Special File Names in `gawk': - Special Files.). + The next minor node of code turns the alarm time into hours and +minutes, converts it (if necessary) to a 24-hour clock, and then turns +that time into a count of the seconds since midnight. Next it turns +the current time into a count of seconds since midnight. The +difference between the two is how long to wait before setting off the +alarm: - Version 2.13 of `gawk' introduced these features: + # split up alarm time + split(ARGV[1], atime, ":") + hour = atime[1] + 0 # force numeric + minute = atime[2] + 0 # force numeric + + # get current broken down time + gettimeofday(now) + + # if time given is 12-hour hours and it's after that + # hour, e.g., `alarm 5:30' at 9 a.m. means 5:30 p.m., + # then add 12 to real hour + if (hour < 12 && now["hour"] > hour) + hour += 12 + + # set target time in seconds since midnight + target = (hour * 60 * 60) + (minute * 60) + + # get current time in seconds since midnight + current = (now["hour"] * 60 * 60) + \ + (now["minute"] * 60) + now["second"] + + # how long to sleep for + naptime = target - current + if (naptime <= 0) { + print "time is in the past!" > "/dev/stderr" + exit 1 + } - * The `FIELDWIDTHS' variable and its effects (*note Reading - Fixed-width Data: Constant Size.). + Finally, the program uses the `system' function (*note Input/Output +Functions: I/O Functions.) to call the `sleep' utility. The `sleep' +utility simply pauses for the given number of seconds. If the exit +status is not zero, the program assumes that `sleep' was interrupted +and exits. If `sleep' exited with an OK status (zero), then the program +prints the message in a loop, again using `sleep' to delay for however +many seconds are necessary: - * The `systime' and `strftime' built-in functions for obtaining and - printing time stamps (*note Functions for Dealing with Time - Stamps: Time Functions.). + # zzzzzz..... go away if interrupted + if (system(sprintf("sleep %d", naptime)) != 0) + exit 1 + + # time to notify! + command = sprintf("sleep %d", delay) + for (i = 1; i <= count; i++) { + print message + # if sleep command interrupted, go away + if (system(command) != 0) + break + } + + exit 0 + } - * The `-W lint' option to provide source code and run time error and - portability checking (*note Command Line Options: Options.). + +File: gawk.info, Node: Translate Program, Next: Labels Program, Prev: Alarm Program, Up: Miscellaneous Programs - * The `-W compat' option to turn off these extensions (*note Command - Line Options: Options.). +Transliterating Characters +-------------------------- - * The `-W posix' option for full POSIX compliance (*note Command - Line Options: Options.). + The system `tr' utility transliterates characters. For example, it +is often used to map uppercase letters into lowercase for further +processing: - Version 2.14 of `gawk' introduced these features: + GENERATE DATA | tr 'A-Z' 'a-z' | PROCESS DATA ... - * The `next file' statement for skipping to the next data file - (*note The `nextfile' Statement: Nextfile Statement.). + `tr' requires two lists of characters.(1) When processing the +input, the first character in the first list is replaced with the first +character in the second list, the second character in the first list is +replaced with the second character in the second list, and so on. If +there are more characters in the "from" list than in the "to" list, the +last character of the "to" list is used for the remaining characters in +the "from" list. - Version 2.15 of `gawk' introduced these features: + Some time ago, a user proposed that a transliteration function should +be added to `gawk'. The following program was written to prove that +character transliteration could be done with a user-level function. +This program is not as complete as the system `tr' utility but it does +most of the job. - * The `ARGIND' variable, that tracks the movement of `FILENAME' - through `ARGV' (*note Built-in Variables::). + The `translate' program demonstrates one of the few weaknesses of +standard `awk': dealing with individual characters is very painful, +requiring repeated use of the `substr', `index', and `gsub' built-in +functions (*note String Manipulation Functions: String Functions.).(2) - * The `ERRNO' variable, that contains the system error message when - `getline' returns -1, or when `close' fails (*note Built-in - Variables::). + There are two functions. The first, `stranslate', takes three +arguments: - * The ability to use GNU-style long named options that start with - `--' (*note Command Line Options: Options.). +`from' + A list of characters to translate from. - * The `--source' option for mixing command line and library file - source code (*note Command Line Options: Options.). +`to' + A list of characters to translate to. - * The `/dev/pid', `/dev/ppid', `/dev/pgrpid', and `/dev/user' file - name interpretation (*note Special File Names in `gawk': Special - Files.). +`target' + The string to do the translation on. - Version 3.0 of `gawk' introduced these features: + Associative arrays make the translation part fairly easy. `t_ar' +holds the "to" characters, indexed by the "from" characters. Then a +simple loop goes through `from', one character at a time. For each +character in `from', if the character appears in `target', `gsub' is +used to change it to the corresponding `to' character. - * The `next file' statement became `nextfile' (*note The `nextfile' - Statement: Nextfile Statement.). + The `translate' function simply calls `stranslate' using `$0' as the +target. The main program sets two global variables, `FROM' and `TO', +from the command line, and then changes `ARGV' so that `awk' reads from +the standard input. - * The `--lint-old' option to warn about constructs that are not - available in the original Version 7 Unix version of `awk' (*note - Major Changes between V7 and SVR3.1: V7/SVR3.1.). + Finally, the processing rule simply calls `translate' for each +record: - * The `--traditional' option was added as a better name for - `--compat' (*note Command Line Options: Options.). + # translate.awk --- do tr-like stuff + # Bugs: does not handle things like: tr A-Z a-z, it has + # to be spelled out. However, if `to' is shorter than `from', + # the last character in `to' is used for the rest of `from'. + + function stranslate(from, to, target, lf, lt, t_ar, i, c) + { + lf = length(from) + lt = length(to) + for (i = 1; i <= lt; i++) + t_ar[substr(from, i, 1)] = substr(to, i, 1) + if (lt < lf) + for (; i <= lf; i++) + t_ar[substr(from, i, 1)] = substr(to, lt, 1) + for (i = 1; i <= lf; i++) { + c = substr(from, i, 1) + if (index(target, c) > 0) + gsub(c, t_ar[c], target) + } + return target + } + + function translate(from, to) + { + return $0 = stranslate(from, to, $0) + } + + # main program + BEGIN { + if (ARGC < 3) { + print "usage: translate from to" > "/dev/stderr" + exit + } + FROM = ARGV[1] + TO = ARGV[2] + ARGC = 2 + ARGV[1] = "-" + } + + { + translate(FROM, TO) + print + } - * The ability for `FS' to be a null string, and for the third - argument to `split' to be the null string (*note Making Each - Character a Separate Field: Single Character Fields.). + While it is possible to do character transliteration in a user-level +function, it is not necessarily efficient, and we (the `gawk' authors) +started to consider adding a built-in function. However, shortly after +writing this program, we learned that the System V Release 4 `awk' had +added the `toupper' and `tolower' functions (*note String Manipulation +Functions: String Functions.). These functions handle the vast +majority of the cases where character transliteration is necessary, and +so we chose to simply add those functions to `gawk' as well and then +leave well enough alone. - * The ability for `RS' to be a regexp (*note How Input is Split into - Records: Records.). + An obvious improvement to this program would be to set up the `t_ar' +array only once, in a `BEGIN' rule. However, this assumes that the +"from" and "to" lists will never change throughout the lifetime of the +program. - * The `RT' variable (*note How Input is Split into Records: - Records.). + ---------- Footnotes ---------- - * The `gensub' function for more powerful text manipulation (*note - Built-in Functions for String Manipulation: String Functions.). + (1) On some older System V systems, `tr' may require that the lists +be written as range expressions enclosed in square brackets (`[a-z]') +and quoted, to prevent the shell from attempting a file name expansion. +This is not a feature. - * The `strftime' function acquired a default time format, allowing - it to be called with no arguments (*note Functions for Dealing - with Time Stamps: Time Functions.). + (2) This program was written before `gawk' acquired the ability to +split each character in a string into separate array elements. - * Full support for both POSIX and GNU regexps (*note Regular - Expressions: Regexp.). + +File: gawk.info, Node: Labels Program, Next: Word Sorting, Prev: Translate Program, Up: Miscellaneous Programs - * The `--re-interval' option to provide interval expressions in - regexps (*note Regular Expression Operators: Regexp Operators.). +Printing Mailing Labels +----------------------- - * `IGNORECASE' changed, now applying to string comparison as well as - regexp operations (*note Case-sensitivity in Matching: - Case-sensitivity.). + Here is a "real world"(1) program. This script reads lists of names +and addresses and generates mailing labels. Each page of labels has 20 +labels on it, two across and ten down. The addresses are guaranteed to +be no more than five lines of data. Each address is separated from the +next by a blank line. - * The `-m' option and the `fflush' function from the Bell Labs - research version of `awk' (*note Command Line Options: Options.; - also *note Built-in Functions for Input/Output: I/O Functions.). + The basic idea is to read 20 labels worth of data. Each line of +each label is stored in the `line' array. The single rule takes care +of filling the `line' array and printing the page when 20 labels have +been read. - * The use of GNU Autoconf to control the configuration process - (*note Compiling `gawk' for Unix: Quick Installation.). + The `BEGIN' rule simply sets `RS' to the empty string, so that `awk' +splits records at blank lines (*note How Input Is Split into Records: +Records.). It sets `MAXLINES' to 100, since 100 is the maximum number +of lines on the page (20 * 5 = 100). - * Amiga support (*note Installing `gawk' on an Amiga: Amiga - Installation.). + Most of the work is done in the `printpage' function. The label +lines are stored sequentially in the `line' array. But they have to +print horizontally; `line[1]' next to `line[6]', `line[2]' next to +`line[7]', and so on. Two loops are used to accomplish this. The +outer loop, controlled by `i', steps through every 10 lines of data; +this is each row of labels. The inner loop, controlled by `j', goes +through the lines within the row. As `j' goes from 0 to 4, `i+j' is +the `j''th line in the row, and `i+j+5' is the entry next to it. The +output ends up looking something like this: + line 1 line 6 + line 2 line 7 + line 3 line 8 + line 4 line 9 + line 5 line 10 + ... - -File: gawk.info, Node: Gawk Summary, Next: Installation, Prev: Language History, Up: Top + As a final note, an extra blank line is printed at lines 21 and 61, +to keep the output lined up on the labels. This is dependent on the +particular brand of labels in use when the program was written. You +will also note that there are two blank lines at the top and two blank +lines at the bottom. -`gawk' Summary -************** + The `END' rule arranges to flush the final page of labels; there may +not have been an even multiple of 20 labels in the data: - This appendix provides a brief summary of the `gawk' command line -and the `awk' language. It is designed to serve as "quick reference." -It is therefore terse, but complete. + # labels.awk --- print mailing labels + + # Each label is 5 lines of data that may have blank lines. + # The label sheets have 2 blank lines at the top and 2 at + # the bottom. + + BEGIN { RS = "" ; MAXLINES = 100 } + + function printpage( i, j) + { + if (Nlines <= 0) + return + + printf "\n\n" # header + + for (i = 1; i <= Nlines; i += 10) { + if (i == 21 || i == 61) + print "" + for (j = 0; j < 5; j++) { + if (i + j > MAXLINES) + break + printf " %-41s %s\n", line[i+j], line[i+j+5] + } + print "" + } + + printf "\n\n" # footer + + for (i in line) + line[i] = "" + } + + # main rule + { + if (Count >= 20) { + printpage() + Count = 0 + Nlines = 0 + } + n = split($0, a, "\n") + for (i = 1; i <= n; i++) + line[++Nlines] = a[i] + for (; i <= 5; i++) + line[++Nlines] = "" + Count++ + } + + END \ + { + printpage() + } -* Menu: + ---------- Footnotes ---------- -* Command Line Summary:: Recapitulation of the command line. -* Language Summary:: A terse review of the language. -* Variables/Fields:: Variables, fields, and arrays. -* Rules Summary:: Patterns and Actions, and their component - parts. -* Actions Summary:: Quick overview of actions. -* Functions Summary:: Defining and calling functions. -* Historical Features:: Some undocumented but supported ``features''. + (1) "Real world" is defined as "a program actually used to get +something done."  -File: gawk.info, Node: Command Line Summary, Next: Language Summary, Prev: Gawk Summary, Up: Gawk Summary - -Command Line Options Summary -============================ - - The command line consists of options to `gawk' itself, the `awk' -program text (if not supplied via the `-f' option), and values to be -made available in the `ARGC' and `ARGV' predefined `awk' variables: - - gawk [POSIX OR GNU STYLE OPTIONS] -f SOURCE-FILE [`--'] FILE ... - gawk [POSIX OR GNU STYLE OPTIONS] [`--'] 'PROGRAM' FILE ... - - The options that `gawk' accepts are: - -`-F FS' -`--field-separator FS' - Use FS for the input field separator (the value of the `FS' - predefined variable). - -`-f PROGRAM-FILE' -`--file PROGRAM-FILE' - Read the `awk' program source from the file PROGRAM-FILE, instead - of from the first command line argument. - -`-mf NNN' -`-mr NNN' - The `f' flag sets the maximum number of fields, and the `r' flag - sets the maximum record size. These options are ignored by - `gawk', since `gawk' has no predefined limits; they are only for - compatibility with the Bell Labs research version of Unix `awk'. - -`-v VAR=VAL' -`--assign VAR=VAL' - Assign the variable VAR the value VAL before program execution - begins. - -`-W traditional' -`-W compat' -`--traditional' -`--compat' - Use compatibility mode, in which `gawk' extensions are turned off. - -`-W copyleft' -`-W copyright' -`--copyleft' -`--copyright' - Print the short version of the General Public License on the - standard output, and exit. This option may disappear in a future - version of `gawk'. - -`-W help' -`-W usage' -`--help' -`--usage' - Print a relatively short summary of the available options on the - standard output, and exit. - -`-W lint' -`--lint' - Give warnings about dubious or non-portable `awk' constructs. - -`-W lint-old' -`--lint-old' - Warn about constructs that are not available in the original - Version 7 Unix version of `awk'. +File: gawk.info, Node: Word Sorting, Next: History Sorting, Prev: Labels Program, Up: Miscellaneous Programs -`-W posix' -`--posix' - Use POSIX compatibility mode, in which `gawk' extensions are - turned off and additional restrictions apply. +Generating Word Usage Counts +---------------------------- -`-W re-interval' -`--re-interval' - Allow interval expressions (*note Regular Expression Operators: - Regexp Operators.), in regexps. + The following `awk' program prints the number of occurrences of each +word in its input. It illustrates the associative nature of `awk' +arrays by using strings as subscripts. It also demonstrates the `for +INDEX in ARRAY' mechanism. Finally, it shows how `awk' is used in +conjunction with other utility programs to do a useful task of some +complexity with a minimum of effort. Some explanations follow the +program listing: -`-W source=PROGRAM-TEXT' -`--source PROGRAM-TEXT' - Use PROGRAM-TEXT as `awk' program source code. This option allows - mixing command line source code with source code from files, and is - particularly useful for mixing command line programs with library - functions. + # Print list of word frequencies + { + for (i = 1; i <= NF; i++) + freq[$i]++ + } + + END { + for (word in freq) + printf "%s\t%d\n", word, freq[word] + } -`-W version' -`--version' - Print version information for this particular copy of `gawk' on - the error output. + This program has two rules. The first rule, because it has an empty +pattern, is executed for every input line. It uses `awk''s +field-accessing mechanism (*note Examining Fields: Fields.) to pick out +the individual words from the line, and the built-in variable `NF' +(*note Built-in Variables::) to know how many fields are available. +For each input word, it increments an element of the array `freq' to +reflect that the word has been seen an additional time. -`--' - Signal the end of options. This is useful to allow further - arguments to the `awk' program itself to start with a `-'. This - is mainly for consistency with POSIX argument parsing conventions. + The second rule, because it has the pattern `END', is not executed +until the input has been exhausted. It prints out the contents of the +`freq' table that has been built up inside the first action. This +program has several problems that would prevent it from being useful by +itself on real text files: - Any other options are flagged as invalid, but are otherwise ignored. -*Note Command Line Options: Options, for more details. + * Words are detected using the `awk' convention that fields are + separated just by whitespace. Other characters in the input + (except newlines) don't have any special meaning to `awk'. This + means that punctuation characters count as part of words. - -File: gawk.info, Node: Language Summary, Next: Variables/Fields, Prev: Command Line Summary, Up: Gawk Summary + * The `awk' language considers upper- and lowercase characters to be + distinct. Therefore, "bartender" and "Bartender" are not treated + as the same word. This is undesirable, since in normal text, words + are capitalized if they begin sentences, and a frequency analyzer + should not be sensitive to capitalization. -Language Summary -================ + * The output does not come out in any useful order. You're more + likely to be interested in which words occur most frequently or in + having an alphabetized table of how frequently each word occurs. - An `awk' program consists of a sequence of zero or more -pattern-action statements and optional function definitions. One or -the other of the pattern and action may be omitted. + The way to solve these problems is to use some of `awk''s more +advanced features. First, we use `tolower' to remove case +distinctions. Next, we use `gsub' to remove punctuation characters. +Finally, we use the system `sort' utility to process the output of the +`awk' script. Here is the new version of the program: - PATTERN { ACTION STATEMENTS } - PATTERN - { ACTION STATEMENTS } + # wordfreq.awk --- print list of word frequencies + + { + $0 = tolower($0) # remove case distinctions + # remove punctuation + gsub(/[^[:alnum:]_[:blank:]]/, "", $0) + for (i = 1; i <= NF; i++) + freq[$i]++ + } - function NAME(PARAMETER LIST) { ACTION STATEMENTS } - - `gawk' first reads the program source from the PROGRAM-FILE(s), if -specified, or from the first non-option argument on the command line. -The `-f' option may be used multiple times on the command line. `gawk' -reads the program text from all the PROGRAM-FILE files, effectively -concatenating them in the order they are specified. This is useful for -building libraries of `awk' functions, without having to include them -in each new `awk' program that uses them. To use a library function in -a file from a program typed in on the command line, specify `--source -'PROGRAM'', and type your program in between the single quotes. *Note -Command Line Options: Options. - - The environment variable `AWKPATH' specifies a search path to use -when finding source files named with the `-f' option. The default -path, which is `.:/usr/local/share/awk'(1) is used if `AWKPATH' is not -set. If a file name given to the `-f' option contains a `/' character, -no path search is performed. *Note The `AWKPATH' Environment Variable: -AWKPATH Variable. - - `gawk' compiles the program into an internal form, and then proceeds -to read each file named in the `ARGV' array. The initial values of -`ARGV' come from the command line arguments. If there are no files -named on the command line, `gawk' reads the standard input. - - If a "file" named on the command line has the form `VAR=VAL', it is -treated as a variable assignment: the variable VAR is assigned the -value VAL. If any of the files have a value that is the null string, -that element in the list is skipped. - - For each record in the input, `gawk' tests to see if it matches any -PATTERN in the `awk' program. For each pattern that the record -matches, the associated ACTION is executed. + END { + for (word in freq) + printf "%s\t%d\n", word, freq[word] + } - ---------- Footnotes ---------- + Assuming we have saved this program in a file named `wordfreq.awk', +and that the data is in `file1', the following pipeline: - (1) The path may use a directory other than `/usr/local/share/awk', -depending upon how `gawk' was built and installed. + awk -f wordfreq.awk file1 | sort +1 -nr - -File: gawk.info, Node: Variables/Fields, Next: Rules Summary, Prev: Language Summary, Up: Gawk Summary +produces a table of the words appearing in `file1' in order of +decreasing frequency. The `awk' program suitably massages the data and +produces a word frequency table, which is not ordered. -Variables and Fields -==================== + The `awk' script's output is then sorted by the `sort' utility and +printed on the terminal. The options given to `sort' specify a sort +that uses the second field of each input line (skipping one field), +that the sort keys should be treated as numeric quantities (otherwise +`15' would come before `5'), and that the sorting should be done in +descending (reverse) order. - `awk' variables are not declared; they come into existence when they -are first used. Their values are either floating-point numbers or -strings. `awk' also has one-dimensional arrays; multiple-dimensional -arrays may be simulated. There are several predefined variables that -`awk' sets as a program runs; these are summarized below. + The `sort' could even be done from within the program, by changing +the `END' action to: -* Menu: + END { + sort = "sort +1 -nr" + for (word in freq) + printf "%s\t%d\n", word, freq[word] | sort + close(sort) + } -* Fields Summary:: Input field splitting. -* Built-in Summary:: `awk''s built-in variables. -* Arrays Summary:: Using arrays. -* Data Type Summary:: Values in `awk' are numbers or strings. + This way of sorting must be used on systems that do not have true +pipes at the command-line (or batch-file) level. See the general +operating system documentation for more information on how to use the +`sort' program.  -File: gawk.info, Node: Fields Summary, Next: Built-in Summary, Prev: Variables/Fields, Up: Variables/Fields +File: gawk.info, Node: History Sorting, Next: Extract Program, Prev: Word Sorting, Up: Miscellaneous Programs -Fields ------- +Removing Duplicates from Unsorted Text +-------------------------------------- - As each input line is read, `gawk' splits the line into FIELDS, -using the value of the `FS' variable as the field separator. If `FS' -is a single character, fields are separated by that character. -Otherwise, `FS' is expected to be a full regular expression. In the -special case that `FS' is a single space, fields are separated by runs -of spaces, tabs and/or newlines.(1) If `FS' is the null string (`""'), -then each individual character in the record becomes a separate field. -Note that the value of `IGNORECASE' (*note Case-sensitivity in -Matching: Case-sensitivity.) also affects how fields are split when -`FS' is a regular expression. + The `uniq' program (*note Printing Non-Duplicated Lines of Text: +Uniq Program.), removes duplicate lines from _sorted_ data. - Each field in the input line may be referenced by its position, `$1', -`$2', and so on. `$0' is the whole line. The value of a field may be -assigned to as well. Field numbers need not be constants: + Suppose, however, you need to remove duplicate lines from a data +file but that you want to preserve the order the lines are in. A good +example of this might be a shell history file. The history file keeps +a copy of all the commands you have entered, and it is not unusual to +repeat a command several times in a row. Occasionally you might want +to compact the history by removing duplicate entries. Yet it is +desirable to maintain the order of the original commands. - n = 5 - print $n + This simple program does the job. It uses two arrays. The `data' +array is indexed by the text of each line. For each line, `data[$0]' +is incremented. If a particular line has not been seen before, then +`data[$0]' is zero. In this case, the text of the line is stored in +`lines[count]'. Each element of `lines' is a unique command, and the +indices of `lines' indicate the order in which those lines are +encountered. The `END' rule simply prints out the lines, in order: -prints the fifth field in the input line. The variable `NF' is set to -the total number of fields in the input line. + # histsort.awk --- compact a shell history file + # Thanks to Byron Rakitzis for the general idea + { + if (data[$0]++ == 0) + lines[++count] = $0 + } + + END { + for (i = 1; i <= count; i++) + print lines[i] + } - References to non-existent fields (i.e. fields after `$NF') return -the null string. However, assigning to a non-existent field (e.g., -`$(NF+2) = 5') increases the value of `NF', creates any intervening -fields with the null string as their value, and causes the value of -`$0' to be recomputed, with the fields being separated by the value of -`OFS'. Decrementing `NF' causes the values of fields past the new -value to be lost, and the value of `$0' to be recomputed, with the -fields being separated by the value of `OFS'. *Note Reading Input -Files: Reading Files. + This program also provides a foundation for generating other useful +information. For example, using the following `print' statement in the +`END' rule indicates how often a particular command is used: - ---------- Footnotes ---------- + print data[lines[i]], lines[i] - (1) In POSIX `awk', newline does not separate fields. + This works because `data[$0]' is incremented each time a line is +seen.  -File: gawk.info, Node: Built-in Summary, Next: Arrays Summary, Prev: Fields Summary, Up: Variables/Fields - -Built-in Variables ------------------- - - `gawk''s built-in variables are: - -`ARGC' - The number of elements in `ARGV'. See below for what is actually - included in `ARGV'. - -`ARGIND' - The index in `ARGV' of the current file being processed. When - `gawk' is processing the input data files, it is always true that - `FILENAME == ARGV[ARGIND]'. +File: gawk.info, Node: Extract Program, Next: Simple Sed, Prev: History Sorting, Up: Miscellaneous Programs -`ARGV' - The array of command line arguments. The array is indexed from - zero to `ARGC' - 1. Dynamically changing `ARGC' and the contents - of `ARGV' can control the files used for data. A null-valued - element in `ARGV' is ignored. `ARGV' does not include the options - to `awk' or the text of the `awk' program itself. +Extracting Programs from Texinfo Source Files +--------------------------------------------- -`CONVFMT' - The conversion format to use when converting numbers to strings. + The nodes *Note A Library of `awk' Functions: Library Functions, and +*Note Practical `awk' Programs: Sample Programs, are the top level +nodes for a large number of `awk' programs. If you want to experiment +with these programs, it is tedious to have to type them in by hand. +Here we present a program that can extract parts of a Texinfo input +file into separate files. -`FIELDWIDTHS' - A space separated list of numbers describing the fixed-width input - data. + This Info file is written in Texinfo, the GNU project's document +formatting language. A single Texinfo source file can be used to +produce both printed and online documentation. The Texinfo language is +described fully, starting with *Note Top::. -`ENVIRON' - An array of environment variable values. The array is indexed by - variable name, each element being the value of that variable. - Thus, the environment variable `HOME' is `ENVIRON["HOME"]'. One - possible value might be `/home/arnold'. + For our purposes, it is enough to know three things about Texinfo +input files: - Changing this array does not affect the environment seen by - programs which `gawk' spawns via redirection or the `system' - function. (This may change in a future version of `gawk'.) + * The "at" symbol (`@') is special in Texinfo, much as the backslash + (`\') is in C or `awk'. Literal `@' symbols are represented in + Texinfo source files as `@@'. - Some operating systems do not have environment variables. The - `ENVIRON' array is empty when running on these systems. + * Comments start with either `@c' or `@comment'. The file + extraction program works by using special comments that start at + the beginning of a line. -`ERRNO' - The system error message when an error occurs using `getline' or - `close'. + * Lines containing `@group' and `@end group' commands bracket + example text that should not be split across a page boundary. + (Unfortunately, TeX isn't always smart enough to do things exactly + right and we have to give it some help.) -`FILENAME' - The name of the current input file. If no files are specified on - the command line, the value of `FILENAME' is the null string. + The following program, `extract.awk', reads through a Texinfo source +file and does two things, based on the special comments. Upon seeing +`@c system ...', it runs a command, by extracting the command text from +the control line and passing it on to the `system' function (*note +Input/Output Functions: I/O Functions.). Upon seeing `@c file +FILENAME', each subsequent line is sent to the file FILENAME, until `@c +endfile' is encountered. The rules in `extract.awk' match either `@c' +or `@comment' by letting the `omment' part be optional. Lines +containing `@group' and `@end group' are simply removed. `extract.awk' +uses the `join' library function (*note Merging an Array into a String: +Join Function.). + + The example programs in the online Texinfo source for `GAWK: +Effective AWK Programming' (`gawk.texi') have all been bracketed inside +`file' and `endfile' lines. The `gawk' distribution uses a copy of +`extract.awk' to extract the sample programs and install many of them +in a standard directory where `gawk' can find them. The Texinfo file +looks something like this: -`FNR' - The input record number in the current input file. + ... + This program has a @code{BEGIN} rule, + that prints a nice message: + + @example + @c file examples/messages.awk + BEGIN @{ print "Don't panic!" @} + @c end file + @end example + + It also prints some final advice: + + @example + @c file examples/messages.awk + END @{ print "Always avoid bored archeologists!" @} + @c end file + @end example + ... -`FS' - The input field separator, a space by default. - -`IGNORECASE' - The case-sensitivity flag for string comparisons and regular - expression operations. If `IGNORECASE' has a non-zero value, then - pattern matching in rules, record separating with `RS', field - splitting with `FS', regular expression matching with `~' and - `!~', and the `gensub', `gsub', `index', `match', `split' and - `sub' built-in functions all ignore case when doing regular - expression operations, and all string comparisons are done - ignoring case. The value of `IGNORECASE' does _not_ affect array - subscripting. + `extract.awk' begins by setting `IGNORECASE' to one, so that mixed +upper- and lowercase letters in the directives won't matter. -`NF' - The number of fields in the current input record. + The first rule handles calling `system', checking that a command is +given (`NF' is at least three) and also checking that the command exits +with a zero exit status, signifying OK: -`NR' - The total number of input records seen so far. + # extract.awk --- extract files and run programs + # from texinfo files + BEGIN { IGNORECASE = 1 } + + /^@c(omment)?[ \t]+system/ \ + { + if (NF < 3) { + e = (FILENAME ":" FNR) + e = (e ": badly formed `system' line") + print e > "/dev/stderr" + next + } + $1 = "" + $2 = "" + stat = system($0) + if (stat != 0) { + e = (FILENAME ":" FNR) + e = (e ": warning: system returned " stat) + print e > "/dev/stderr" + } + } -`OFMT' - The output format for numbers for the `print' statement, `"%.6g"' - by default. +The variable `e' is used so that the function fits nicely on the screen. -`OFS' - The output field separator, a space by default. + The second rule handles moving data into files. It verifies that a +file name is given in the directive. If the file named is not the +current file, then the current file is closed. Keeping the current file +open until a new file is encountered allows the use of the `>' +redirection for printing the contents, keeping open file management +simple. -`ORS' - The output record separator, by default a newline. + The `for' loop does the work. It reads lines using `getline' (*note +Explicit Input with `getline': Getline.). For an unexpected end of +file, it calls the `unexpected_eof' function. If the line is an +"endfile" line, then it breaks out of the loop. If the line is an +`@group' or `@end group' line, then it ignores it and goes on to the +next line. Similarly, comments within examples are also ignored. -`RS' - The input record separator, by default a newline. If `RS' is set - to the null string, then records are separated by blank lines. - When `RS' is set to the null string, then the newline character - always acts as a field separator, in addition to whatever value - `FS' may have. If `RS' is set to a multi-character string, it - denotes a regexp; input text matching the regexp separates records. + Most of the work is in the following few lines. If the line has no +`@' symbols, the program can print it directly. Otherwise, each +leading `@' must be stripped off. To remove the `@' symbols, the line +is split into separate elements of the array `a', using the `split' +function (*note String Manipulation Functions: String Functions.). The +`@' symbol is used as the separator character. Each element of `a' +that is empty indicates two successive `@' symbols in the original +line. For each two empty elements (`@@' in the original file), we have +to add a single `@' symbol back in. -`RT' - The input text that matched the text denoted by `RS', the record - separator. + When the processing of the array is finished, `join' is called with +the value of `SUBSEP', to rejoin the pieces back into a single line. +That line is then printed to the output file: -`RSTART' - The index of the first character last matched by `match'; zero if - no match. + /^@c(omment)?[ \t]+file/ \ + { + if (NF != 3) { + e = (FILENAME ":" FNR ": badly formed `file' line") + print e > "/dev/stderr" + next + } + if ($3 != curfile) { + if (curfile != "") + close(curfile) + curfile = $3 + } + + for (;;) { + if ((getline line) <= 0) + unexpected_eof() + if (line ~ /^@c(omment)?[ \t]+endfile/) + break + else if (line ~ /^@(end[ \t]+)?group/) + continue + else if (line ~ /^@c(omment+)?[ \t]+/) + continue + if (index(line, "@") == 0) { + print line > curfile + continue + } + n = split(line, a, "@") + # if a[1] == "", means leading @, + # don't add one back in. + for (i = 2; i <= n; i++) { + if (a[i] == "") { # was an @@ + a[i] = "@" + if (a[i+1] == "") + i++ + } + } + print join(a, 1, n, SUBSEP) > curfile + } + } -`RLENGTH' - The length of the string last matched by `match'; -1 if no match. + An important thing to note is the use of the `>' redirection. +Output done with `>' only opens the file once; it stays open and +subsequent output is appended to the file (*note Redirecting Output of +`print' and `printf': Redirection.). This makes it easy to mix program +text and explanatory prose for the same sample source file (as has been +done here!) without any hassle. The file is only closed when a new +data file name is encountered or at the end of the input file. -`SUBSEP' - The string used to separate multiple subscripts in array elements, - by default `"\034"'. + Finally, the function `unexpected_eof' prints an appropriate error +message and then exits. The `END' rule handles the final cleanup, +closing the open file: - *Note Built-in Variables::, for more information. + function unexpected_eof() { + printf("%s:%d: unexpected EOF or error\n", + FILENAME, FNR) > "/dev/stderr" + exit 1 + } + + END { + if (curfile) + close(curfile) + }  -File: gawk.info, Node: Arrays Summary, Next: Data Type Summary, Prev: Built-in Summary, Up: Variables/Fields +File: gawk.info, Node: Simple Sed, Next: Igawk Program, Prev: Extract Program, Up: Miscellaneous Programs + +A Simple Stream Editor +---------------------- -Arrays ------- + The `sed' utility is a "stream editor," a program that reads a +stream of data, makes changes to it, and passes it on. It is often +used to make global changes to a large file or to a stream of data +generated by a pipeline of commands. While `sed' is a complicated +program in its own right, its most common use is to perform global +substitutions in the middle of a pipeline: - Arrays are subscripted with an expression between square brackets -(`[' and `]'). Array subscripts are _always_ strings; numbers are -converted to strings as necessary, following the standard conversion -rules (*note Conversion of Strings and Numbers: Conversion.). + command1 < orig.data | sed 's/old/new/g' | command2 > result - If you use multiple expressions separated by commas inside the square -brackets, then the array subscript is a string consisting of the -concatenation of the individual subscript values, converted to strings, -separated by the subscript separator (the value of `SUBSEP'). + Here, `s/old/new/g' tells `sed' to look for the regexp `old' on each +input line and globally replace it with the text `new', (i.e., all the +occurrences on a line). This is similar to `awk''s `gsub' function +(*note String Manipulation Functions: String Functions.). - The special operator `in' may be used in a conditional context to -see if an array has an index consisting of a particular value. + The following program, `awksed.awk', accepts at least two +command-line arguments: the pattern to look for and the text to replace +it with. Any additional arguments are treated as data file names to +process. If none are provided, the standard input is used: - if (val in array) - print array[val] + # awksed.awk --- do s/foo/bar/g using just print + # Thanks to Michael Brennan for the idea + function usage() + { + print "usage: awksed pat repl [files...]" > "/dev/stderr" + exit 1 + } + + BEGIN { + # validate arguments + if (ARGC < 3) + usage() + + RS = ARGV[1] + ORS = ARGV[2] + + # don't use arguments as files + ARGV[1] = ARGV[2] = "" + } + + # look ma, no hands! + { + if (RT == "") + printf "%s", $0 + else + print + } - If the array has multiple subscripts, use `(i, j, ...) in ARRAY' to -test for existence of an element. + The program relies on `gawk''s ability to have `RS' be a regexp, as +well as on the setting of `RT' to the actual text that terminates the +record (*note How Input Is Split into Records: Records.). - The `in' construct may also be used in a `for' loop to iterate over -all the elements of an array. *Note Scanning All Elements of an Array: -Scanning an Array. + The idea is to have `RS' be the pattern to look for. `gawk' +automatically sets `$0' to the text between matches of the pattern. +This is text that we want to keep, unmodified. Then, by setting `ORS' +to the replacement text, a simple `print' statement outputs the text we +want to keep, followed by the replacement text. - You can remove an element from an array using the `delete' statement. + There is one wrinkle to this scheme, which is what to do if the last +record doesn't end with text that matches `RS'. Using a `print' +statement unconditionally prints the replacement text, which is not +correct. However, if the file did not end in text that matches `RS', +`RT' is set to the null string. In this case, we can print `$0' using +`printf' (*note Using `printf' Statements for Fancier Printing: +Printf.). - You can clear an entire array using `delete ARRAY'. + The `BEGIN' rule handles the setup, checking for the right number of +arguments and calling `usage' if there is a problem. Then it sets `RS' +and `ORS' from the command-line arguments and sets `ARGV[1]' and +`ARGV[2]' to the null string, so that they are not treated as file names +(*note Using `ARGC' and `ARGV': ARGC and ARGV.). - *Note Arrays in `awk': Arrays. + The `usage' function prints an error message and exits. Finally, +the single rule handles the printing scheme outlined above, using +`print' or `printf' as appropriate, depending upon the value of `RT'.  -File: gawk.info, Node: Data Type Summary, Prev: Arrays Summary, Up: Variables/Fields +File: gawk.info, Node: Igawk Program, Prev: Simple Sed, Up: Miscellaneous Programs -Data Types ----------- +An Easy Way to Use Library Functions +------------------------------------ - The value of an `awk' expression is always either a number or a -string. + Using library functions in `awk' can be very beneficial. It +encourages code reuse and the writing of general functions. Programs are +smaller and therefore clearer. However, using library functions is +only easy when writing `awk' programs; it is painful when running them, +requiring multiple `-f' options. If `gawk' is unavailable, then so too +is the `AWKPATH' environment variable and the ability to put `awk' +functions into a library directory (*note Command-Line Options: +Options.). It would be nice to be able to write programs in the +following manner: - Some contexts (such as arithmetic operators) require numeric values. -They convert strings to numbers by interpreting the text of the string -as a number. If the string does not look like a number, it converts to -zero. + # library functions + @include getopt.awk + @include join.awk + ... + + # main program + BEGIN { + while ((c = getopt(ARGC, ARGV, "a:b:cde")) != -1) + ... + ... + } - Other contexts (such as concatenation) require string values. They -convert numbers to strings by effectively printing them with `sprintf'. -*Note Conversion of Strings and Numbers: Conversion, for the details. + The following program, `igawk.sh', provides this service. It +simulates `gawk''s searching of the `AWKPATH' variable and also allows +"nested" includes; i.e., a file that is included with `@include' can +contain further `@include' statements. `igawk' makes an effort to only +include files once, so that nested includes don't accidentally include +a library function twice. + + `igawk' should behave just like `gawk' externally. This means it +should accept all of `gawk''s command-line arguments, including the +ability to have multiple source files specified via `-f', and the +ability to mix command-line and library source files. - To force conversion of a string value to a number, simply add zero -to it. If the value you start with is already a number, this does not -change it. + The program is written using the POSIX Shell (`sh') command language. +The way the program works is as follows: - To force conversion of a numeric value to a string, concatenate it -with the null string. + 1. Loop through the arguments, saving anything that doesn't represent + `awk' source code for later, when the expanded program is run. - Comparisons are done numerically if both operands are numeric, or if -one is numeric and the other is a numeric string. Otherwise one or -both operands are converted to strings and a string comparison is -performed. Fields, `getline' input, `FILENAME', `ARGV' elements, -`ENVIRON' elements and the elements of an array created by `split' are -the only items that can be numeric strings. String constants, such as -`"3.1415927"' are not numeric strings, they are string constants. The -full rules for comparisons are described in *Note Variable Typing and -Comparison Expressions: Typing and Comparison. + 2. For any arguments that do represent `awk' text, put the arguments + into a temporary file that will be expanded. There are two cases: - Uninitialized variables have the string value `""' (the null, or -empty, string). In contexts where a number is required, this is -equivalent to zero. + a. Literal text, provided with `--source' or `--source='. This + text is just echoed directly. The `echo' program + automatically supplies a trailing newline. - *Note Variables::, for more information on variable naming and -initialization; *note Conversion of Strings and Numbers: Conversion., -for more information on how variable values are interpreted. + b. Source file names provided with `-f'. We use a neat trick + and echo `@include FILENAME' into the temporary file. Since + the file inclusion program works the way `gawk' does, this + gets the text of the file included into the program at the + correct point. - -File: gawk.info, Node: Rules Summary, Next: Actions Summary, Prev: Variables/Fields, Up: Gawk Summary + 3. Run an `awk' program (naturally) over the temporary file to expand + `@include' statements. The expanded program is placed in a second + temporary file. -Patterns -======== + 4. Run the expanded program with `gawk' and any other original + command-line arguments that the user supplied (such as the data + file names). -* Menu: + The initial part of the program turns on shell tracing if the first +argument is `debug'. Otherwise, a shell `trap' statement arranges to +clean up any temporary files on program exit or upon an interrupt. -* Pattern Summary:: Quick overview of patterns. -* Regexp Summary:: Quick overview of regular expressions. + The next part loops through all the command-line arguments. There +are several cases of interest: - An `awk' program is mostly composed of rules, each consisting of a -pattern followed by an action. The action is enclosed in `{' and `}'. -Either the pattern may be missing, or the action may be missing, but -not both. If the pattern is missing, the action is executed for every -input record. A missing action is equivalent to `{ print }', which -prints the entire line. +`--' + This ends the arguments to `igawk'. Anything else should be + passed on to the user's `awk' program without being evaluated. - Comments begin with the `#' character, and continue until the end of -the line. Blank lines may be used to separate statements. Statements -normally end with a newline; however, this is not the case for lines -ending in a `,', `{', `?', `:', `&&', or `||'. Lines ending in `do' or -`else' also have their statements automatically continued on the -following line. In other cases, a line can be continued by ending it -with a `\', in which case the newline is ignored. +`-W' + This indicates that the next option is specific to `gawk'. To make + argument processing easier, the `-W' is appended to the front of + the remaining arguments and the loop continues. (This is an `sh' + programming trick. Don't worry about it if you are not familiar + with `sh'.) - Multiple statements may be put on one line by separating each one -with a `;'. This applies to both the statements within the action part -of a rule (the usual case), and to the rule statements. +`-v, -F' + These are saved and passed on to `gawk'. - *Note Comments in `awk' Programs: Comments, for information on -`awk''s commenting convention; *note `awk' Statements Versus Lines: -Statements/Lines., for a description of the line continuation mechanism -in `awk'. +`-f, --file, --file=, -Wfile=' + The file name is saved to the temporary file `/tmp/ig.s.$$' with an + `@include' statement. The `sed' utility is used to remove the + leading option part of the argument (e.g., `--file='). - -File: gawk.info, Node: Pattern Summary, Next: Regexp Summary, Prev: Rules Summary, Up: Rules Summary +`--source, --source=, -Wsource=' + The source text is echoed into `/tmp/ig.s.$$'. -Pattern Summary ---------------- +`--version, -Wversion' + `igawk' prints its version number, runs `gawk --version' to get + the `gawk' version information, and then exits. - `awk' patterns may be one of the following: - - /REGULAR EXPRESSION/ - RELATIONAL EXPRESSION - PATTERN && PATTERN - PATTERN || PATTERN - PATTERN ? PATTERN : PATTERN - (PATTERN) - ! PATTERN - PATTERN1, PATTERN2 - BEGIN - END - - `BEGIN' and `END' are two special kinds of patterns that are not -tested against the input. The action parts of all `BEGIN' rules are -concatenated as if all the statements had been written in a single -`BEGIN' rule. They are executed before any of the input is read. -Similarly, all the `END' rules are concatenated, and executed when all -the input is exhausted (or when an `exit' statement is executed). -`BEGIN' and `END' patterns cannot be combined with other patterns in -pattern expressions. `BEGIN' and `END' rules cannot have missing -action parts. - - For `/REGULAR-EXPRESSION/' patterns, the associated statement is -executed for each input record that matches the regular expression. -Regular expressions are summarized below. - - A RELATIONAL EXPRESSION may use any of the operators defined below in -the section on actions. These generally test whether certain fields -match certain regular expressions. - - The `&&', `||', and `!' operators are logical "and," logical "or," -and logical "not," respectively, as in C. They do short-circuit -evaluation, also as in C, and are used for combining more primitive -pattern expressions. As in most languages, parentheses may be used to -change the order of evaluation. - - The `?:' operator is like the same operator in C. If the first -pattern matches, then the second pattern is matched against the input -record; otherwise, the third is matched. Only one of the second and -third patterns is matched. - - The `PATTERN1, PATTERN2' form of a pattern is called a range -pattern. It matches all input lines starting with a line that matches -PATTERN1, and continuing until a line that matches PATTERN2, inclusive. -A range pattern cannot be used as an operand of any of the pattern -operators. + If none of the `-f', `--file', `-Wfile', `--source', or `-Wsource' +arguments are supplied, then the first non-option argument should be +the `awk' program. If there are no command-line arguments left, +`igawk' prints an error message and exits. Otherwise, the first +argument is echoed into `/tmp/ig.s.$$'. In any case, after the +arguments have been processed, `/tmp/ig.s.$$' contains the complete +text of the original `awk' program. - *Note Pattern Elements: Pattern Overview. + The `$$' in `sh' represents the current process ID number. It is +often used in shell programs to generate unique temporary file names. +This allows multiple users to run `igawk' without worrying that the +temporary file names will clash. The program is as follows: - -File: gawk.info, Node: Regexp Summary, Prev: Pattern Summary, Up: Rules Summary + #! /bin/sh + # igawk --- like gawk but do @include processing + if [ "$1" = debug ] + then + set -x + shift + else + # cleanup on exit, hangup, interrupt, quit, termination + trap 'rm -f /tmp/ig.[se].$$' 0 1 2 3 15 + fi + + while [ $# -ne 0 ] # loop over arguments + do + case $1 in + --) shift; break;; + + -W) shift + set -- -W"$@" + continue;; + + -[vF]) opts="$opts $1 '$2'" + shift;; + + -[vF]*) opts="$opts '$1'" ;; + + -f) echo @include "$2" >> /tmp/ig.s.$$ + shift;; + + -f*) f=`echo "$1" | sed 's/-f//'` + echo @include "$f" >> /tmp/ig.s.$$ ;; + + -?file=*) # -Wfile or --file + f=`echo "$1" | sed 's/-.file=//'` + echo @include "$f" >> /tmp/ig.s.$$ ;; + + -?file) # get arg, $2 + echo @include "$2" >> /tmp/ig.s.$$ + shift;; + + -?source=*) # -Wsource or --source + t=`echo "$1" | sed 's/-.source=//'` + echo "$t" >> /tmp/ig.s.$$ ;; + + -?source) # get arg, $2 + echo "$2" >> /tmp/ig.s.$$ + shift;; + + -?version) + echo igawk: version 1.0 1>&2 + gawk --version + exit 0 ;; + + -[W-]*) opts="$opts '$1'" ;; + + *) break;; + esac + shift + done + + if [ ! -s /tmp/ig.s.$$ ] + then + if [ -z "$1" ] + then + echo igawk: no program! 1>&2 + exit 1 + else + echo "$1" > /tmp/ig.s.$$ + shift + fi + fi + + # at this point, /tmp/ig.s.$$ has the program -Regular Expressions -------------------- + The `awk' program to process `@include' directives reads through the +program, one line at a time, using `getline' (*note Explicit Input with +`getline': Getline.). The input file names and `@include' statements +are managed using a stack. As each `@include' is encountered, the +current file name is "pushed" onto the stack and the file named in the +`@include' directive becomes the current file name. As each file is +finished, the stack is "popped," and the previous input file becomes +the current input file again. The process is started by making the +original file the first one on the stack. + + The `pathto' function does the work of finding the full path to a +file. It simulates `gawk''s behavior when searching the `AWKPATH' +environment variable (*note The `AWKPATH' Environment Variable: AWKPATH +Variable.). If a file name has a `/' in it, no path search is done. +Otherwise, the file name is concatenated with the name of each +directory in the path, and an attempt is made to open the generated +file name. The only way to test if a file can be read in `awk' is to go +ahead and try to read it with `getline'; this is what `pathto' does.(1) +If the file can be read, it is closed and the file name is returned: - Regular expressions are based on POSIX EREs (extended regular -expressions). The escape sequences allowed in string constants are -also valid in regular expressions (*note Escape Sequences::). Regexps -are composed of characters as follows: + gawk -- ' + # process @include directives + + function pathto(file, i, t, junk) + { + if (index(file, "/") != 0) + return file + + for (i = 1; i <= ndirs; i++) { + t = (pathlist[i] "/" file) + if ((getline junk < t) > 0) { + # found it + close(t) + return t + } + } + return "" + } -`C' - matches the character C (assuming C is none of the characters - listed below). + The main program is contained inside one `BEGIN' rule. The first +thing it does is set up the `pathlist' array that `pathto' uses. After +splitting the path on `:', null elements are replaced with `"."', which +represents the current directory: -`\C' - matches the literal character C. + BEGIN { + path = ENVIRON["AWKPATH"] + ndirs = split(path, pathlist, ":") + for (i = 1; i <= ndirs; i++) { + if (pathlist[i] == "") + pathlist[i] = "." + } -`.' - matches any character, _including_ newline. In strict POSIX mode, - `.' does not match the NUL character, which is a character with - all bits equal to zero. + The stack is initialized with `ARGV[1]', which will be +`/tmp/ig.s.$$'. The main loop comes next. Input lines are read in +succession. Lines that do not start with `@include' are printed +verbatim. If the line does start with `@include', the file name is in +`$2'. `pathto' is called to generate the full path. If it cannot, +then we print an error message and continue. -`^' - matches the beginning of a string. + The next thing to check is if the file is included already. The +`processed' array is indexed by the full file name of each included +file and it tracks this information for us. If the file is seen again, +a warning message is printed. Otherwise, the new file name is pushed +onto the stack and processing continues. -`$' - matches the end of a string. + Finally, when `getline' encounters the end of the input file, the +file is closed and the stack is popped. When `stackptr' is less than +zero, the program is done: -`[ABC...]' - matches any of the characters ABC... (character list). + stackptr = 0 + input[stackptr] = ARGV[1] # ARGV[1] is first file + + for (; stackptr >= 0; stackptr--) { + while ((getline < input[stackptr]) > 0) { + if (tolower($1) != "@include") { + print + continue + } + fpath = pathto($2) + if (fpath == "") { + printf("igawk:%s:%d: cannot find %s\n", + input[stackptr], FNR, $2) > "/dev/stderr" + continue + } + if (! (fpath in processed)) { + processed[fpath] = input[stackptr] + input[++stackptr] = fpath # push onto stack + } else + print $2, "included in", input[stackptr], + "already included in", + processed[fpath] > "/dev/stderr" + } + close(input[stackptr]) + } + }' /tmp/ig.s.$$ > /tmp/ig.e.$$ -`[[:CLASS:]]' - matches any character in the character class CLASS. Allowable - classes are `alnum', `alpha', `blank', `cntrl', `digit', `graph', - `lower', `print', `punct', `space', `upper', and `xdigit'. + The last step is to call `gawk' with the expanded program, along +with the original options and command-line arguments that the user +supplied. `gawk''s exit status is passed back on to `igawk''s calling +program: -`[[.SYMBOL.]]' - matches the multi-character collating symbol SYMBOL. `gawk' does - not currently support collating symbols. + eval gawk -f /tmp/ig.e.$$ $opts -- "$@" + + exit $? -`[[=CLASSNAME=]]' - matches any of the equivalent characters in the current locale - named by the equivalence class CLASSNAME. `gawk' does not - currently support equivalence classes. + This version of `igawk' represents my third attempt at this program. +There are three key simplifications that make the program work better: -`[^ABC...]' - matches any character except ABC... (negated character list). + * Using `@include' even for the files named with `-f' makes building + the initial collected `awk' program much simpler; all the + `@include' processing can be done once. -`R1|R2' - matches either R1 or R2 (alternation). + * The `pathto' function doesn't try to save the line read with + `getline' when testing for the file's accessibility. Trying to + save this line for use with the main program complicates things + considerably. -`R1R2' - matches R1, and then R2 (concatenation). + * Using a `getline' loop in the `BEGIN' rule does it all in one + place. It is not necessary to call out to a separate loop for + processing nested `@include' statements. -`R+' - matches one or more R's. + Also, this program illustrates that it is often worthwhile to combine +`sh' and `awk' programming together. You can usually accomplish quite +a lot, without having to resort to low-level programming in C or C++, +and it is frequently easier to do certain kinds of string and argument +manipulation using the shell than it is in `awk'. -`R*' - matches zero or more R's. + Finally, `igawk' shows that it is not always necessary to add new +features to a program; they can often be layered on top. With `igawk', +there is no real reason to build `@include' processing into `gawk' +itself. -`R?' - matches zero or one R's. + As an additional example of this, consider the idea of having two +files in a directory in the search path: -`(R)' - matches R (grouping). +`default.awk' + This file contains a set of default library functions, such as + `getopt' and `assert'. -`R{N}' -`R{N,}' -`R{N,M}' - matches at least N, N to any number, or N to M occurrences of R - (interval expressions). +`site.awk' + This file contains library functions that are specific to a site or + installation; i.e., locally developed functions. Having a + separate file allows `default.awk' to change with new `gawk' + releases, without requiring the system administrator to update it + each time by adding the local functions. -`\y' - matches the empty string at either the beginning or the end of a - word. + One user suggested that `gawk' be modified to automatically read +these files upon startup. Instead, it would be very simple to modify +`igawk' to do this. Since `igawk' can process nested `@include' +directives, `default.awk' could simply contain `@include' statements +for the desired library functions. -`\B' - matches the empty string within a word. + ---------- Footnotes ---------- -`\<' - matches the empty string at the beginning of a word. + (1) On some very old versions of `awk', the test `getline junk < t' +can loop forever if the file exists but is empty. Caveat emptor. -`\>' - matches the empty string at the end of a word. + +File: gawk.info, Node: Language History, Next: Installation, Prev: Sample Programs, Up: Top -`\w' - matches any word-constituent character (alphanumeric characters and - the underscore). +The Evolution of the `awk' Language +*********************************** -`\W' - matches any character that is not word-constituent. + This Info file describes the GNU implementation of `awk', which +follows the POSIX specification. Many long-time `awk' users learned +`awk' programming with the original `awk' implementation in Version 7 +Unix. (This implementation was the basis for `awk' in Berkeley Unix, +through 4.3-Reno. Subsequent versions of Berkeley Unix, and systems +derived from 4.4BSD-Lite, use various versions of `gawk' for their +`awk'.) This major node briefly describes the evolution of the `awk' +language, with cross references to other parts of the Info file where +you can find more information. -`\`' - matches the empty string at the beginning of a buffer (same as a - string in `gawk'). +* Menu: -`\'' - matches the empty string at the end of a buffer. +* V7/SVR3.1:: The major changes between V7 and System V + Release 3.1. +* SVR4:: Minor changes between System V Releases 3.1 + and 4. +* POSIX:: New features from the POSIX standard. +* BTL:: New features from the Bell Laboratories + version of `awk'. +* POSIX/GNU:: The extensions in `gawk' not in POSIX + `awk'. +* Contributors:: The major contributors to `gawk'. - The various command line options control how `gawk' interprets -characters in regexps. + +File: gawk.info, Node: V7/SVR3.1, Next: SVR4, Prev: Language History, Up: Language History -No options - In the default case, `gawk' provide all the facilities of POSIX - regexps and the GNU regexp operators described above. However, - interval expressions are not supported. +Major Changes Between V7 and SVR3.1 +=================================== -`--posix' - Only POSIX regexps are supported, the GNU operators are not special - (e.g., `\w' matches a literal `w'). Interval expressions are - allowed. + The `awk' language evolved considerably between the release of +Version 7 Unix (1978) and the new version that was first made generally +available in System V Release 3.1 (1987). This minor node summarizes +the changes, with cross-references to further details: -`--traditional' - Traditional Unix `awk' regexps are matched. The GNU operators are - not special, interval expressions are not available, and neither - are the POSIX character classes (`[[:alnum:]]' and so on). - Characters described by octal and hexadecimal escape sequences are - treated literally, even if they represent regexp metacharacters. + * The requirement for `;' to separate rules on a line (*note `awk' + Statements Versus Lines: Statements/Lines.). -`--re-interval' - Allow interval expressions in regexps, even if `--traditional' has - been provided. + * User-defined functions and the `return' statement (*note + User-Defined Functions: User-defined.). - *Note Regular Expressions: Regexp. + * The `delete' statement (*note The `delete' Statement: Delete.). - -File: gawk.info, Node: Actions Summary, Next: Functions Summary, Prev: Rules Summary, Up: Gawk Summary + * The `do'-`while' statement (*note The `do'-`while' Statement: Do + Statement.). -Actions -======= + * The built-in functions `atan2', `cos', `sin', `rand', and `srand' + (*note Numeric Functions::). - Action statements are enclosed in braces, `{' and `}'. A missing -action statement is equivalent to `{ print }'. + * The built-in functions `gsub', `sub', and `match' (*note String + Manipulation Functions: String Functions.). - Action statements consist of the usual assignment, conditional, and -looping statements found in most languages. The operators, control -statements, and Input/Output statements available are similar to those -in C. + * The built-in functions `close' and `system' (*note Input/Output + Functions: I/O Functions.). - Comments begin with the `#' character, and continue until the end of -the line. Blank lines may be used to separate statements. Statements -normally end with a newline; however, this is not the case for lines -ending in a `,', `{', `?', `:', `&&', or `||'. Lines ending in `do' or -`else' also have their statements automatically continued on the -following line. In other cases, a line can be continued by ending it -with a `\', in which case the newline is ignored. + * The `ARGC', `ARGV', `FNR', `RLENGTH', `RSTART', and `SUBSEP' + built-in variables (*note Built-in Variables::). - Multiple statements may be put on one line by separating each one -with a `;'. This applies to both the statements within the action part -of a rule (the usual case), and to the rule statements. + * The conditional expression using the ternary operator `?:' (*note + Conditional Expressions: Conditional Exp.). - *Note Comments in `awk' Programs: Comments, for information on -`awk''s commenting convention; *note `awk' Statements Versus Lines: -Statements/Lines., for a description of the line continuation mechanism -in `awk'. + * The exponentiation operator `^' (*note Arithmetic Operators: + Arithmetic Ops.) and its assignment operator form `^=' (*note + Assignment Expressions: Assignment Ops.). -* Menu: + * C-compatible operator precedence, which breaks some old `awk' + programs (*note Operator Precedence (How Operators Nest): + Precedence.). -* Operator Summary:: `awk' operators. -* Control Flow Summary:: The control statements. -* I/O Summary:: The I/O statements. -* Printf Summary:: A summary of `printf'. -* Special File Summary:: Special file names interpreted internally. -* Built-in Functions Summary:: Built-in numeric and string functions. -* Time Functions Summary:: Built-in time functions. -* String Constants Summary:: Escape sequences in strings. + * Regexps as the value of `FS' (*note Specifying How Fields Are + Separated: Field Separators.) and as the third argument to the + `split' function (*note String Manipulation Functions: String + Functions.). - -File: gawk.info, Node: Operator Summary, Next: Control Flow Summary, Prev: Actions Summary, Up: Actions Summary + * Dynamic regexps as operands of the `~' and `!~' operators (*note + How to Use Regular Expressions: Regexp Usage.). -Operators ---------- + * The escape sequences `\b', `\f', and `\r' (*note Escape + Sequences::). (Some vendors have updated their old versions of + `awk' to recognize `\b', `\f', and `\r', but this is not something + you can rely on.) - The operators in `awk', in order of decreasing precedence, are: + * Redirection of input for the `getline' function (*note Explicit + Input with `getline': Getline.). -`(...)' - Grouping. + * Multiple `BEGIN' and `END' rules (*note The `BEGIN' and `END' + Special Patterns: BEGIN/END.). -`$' - Field reference. + * Multidimensional arrays (*note Multidimensional Arrays: + Multi-dimensional.). -`++ --' - Increment and decrement, both prefix and postfix. + +File: gawk.info, Node: SVR4, Next: POSIX, Prev: V7/SVR3.1, Up: Language History -`^' - Exponentiation (`**' may also be used, and `**=' for the assignment - operator, but they are not specified in the POSIX standard). +Changes Between SVR3.1 and SVR4 +=============================== -`+ - !' - Unary plus, unary minus, and logical negation. + The System V Release 4 (1989) version of Unix `awk' added these +features (some of which originated in `gawk'): -`* / %' - Multiplication, division, and modulus. + * The `ENVIRON' variable (*note Built-in Variables::). -`+ -' - Addition and subtraction. + * Multiple `-f' options on the command line (*note Command-Line + Options: Options.). -`SPACE' - String concatenation. + * The `-v' option for assigning variables before program execution + begins (*note Command-Line Options: Options.). -`< <= > >= != ==' - The usual relational operators. + * The `--' option for terminating command-line options. -`~ !~' - Regular expression match, negated match. + * The `\a', `\v', and `\x' escape sequences (*note Escape + Sequences::). -`in' - Array membership. + * A defined return value for the `srand' built-in function (*note + Numeric Functions::). -`&&' - Logical "and". + * The `toupper' and `tolower' built-in string functions for case + translation (*note String Manipulation Functions: String + Functions.). -`||' - Logical "or". + * A cleaner specification for the `%c' format-control letter in the + `printf' function (*note Format-Control Letters: Control Letters.). -`?:' - A conditional expression. This has the form `EXPR1 ? EXPR2 : - EXPR3'. If EXPR1 is true, the value of the expression is EXPR2; - otherwise it is EXPR3. Only one of EXPR2 and EXPR3 is evaluated. + * The ability to dynamically pass the field width and precision + (`"%*.*d"') in the argument list of the `printf' function (*note + Format-Control Letters: Control Letters.). -`= += -= *= /= %= ^=' - Assignment. Both absolute assignment (`VAR=VALUE') and operator - assignment (the other forms) are supported. + * The use of regexp constants, such as `/foo/', as expressions, where + they are equivalent to using the matching operator, as in `$0 ~ + /foo/' (*note Using Regular Expression Constants: Using Constant + Regexps.). - *Note Expressions::. + * Processing of escape sequences inside command-line variable + assignments (*note Assigning Variables on the Command Line: + Assignment Options.).  -File: gawk.info, Node: Control Flow Summary, Next: I/O Summary, Prev: Operator Summary, Up: Actions Summary - -Control Statements ------------------- - - The control statements are as follows: - - if (CONDITION) STATEMENT [ else STATEMENT ] - while (CONDITION) STATEMENT - do STATEMENT while (CONDITION) - for (EXPR1; EXPR2; EXPR3) STATEMENT - for (VAR in ARRAY) STATEMENT - break - continue - delete ARRAY[INDEX] - delete ARRAY - exit [ EXPRESSION ] - { STATEMENTS } +File: gawk.info, Node: POSIX, Next: BTL, Prev: SVR4, Up: Language History - *Note Control Statements in Actions: Statements. +Changes Between SVR4 and POSIX `awk' +==================================== - -File: gawk.info, Node: I/O Summary, Next: Printf Summary, Prev: Control Flow Summary, Up: Actions Summary + The POSIX Command Language and Utilities standard for `awk' (1992) +introduced the following changes into the language: -I/O Statements --------------- + * The use of `-W' for implementation-specific options (*note + Command-Line Options: Options.). - The Input/Output statements are as follows: + * The use of `CONVFMT' for controlling the conversion of numbers to + strings (*note Conversion of Strings and Numbers: Conversion.). -`getline' - Set `$0' from next input record; set `NF', `NR', `FNR'. *Note - Explicit Input with `getline': Getline. + * The concept of a numeric string and tighter comparison rules to go + with it (*note Variable Typing and Comparison Expressions: Typing + and Comparison.). -`getline FILE' - Prints expressions to FILE. If FILE does not exist, it is created. - If it does exist, its contents are deleted the first time the - `print' is executed. + +File: gawk.info, Node: BTL, Next: POSIX/GNU, Prev: POSIX, Up: Language History -`print EXPR-LIST >> FILE' - Prints expressions to FILE. The previous contents of FILE are - retained, and the output of `print' is appended to the file. +Extensions in the Bell Laboratories `awk' +========================================= -`print EXPR-LIST | COMMAND' - Prints expressions, sending the output down a pipe to COMMAND. - The pipeline to the command stays open until the `close' function - is called. + Brian Kernighan, one of the original designers of Unix `awk', has +made his version available via his home page (*note Other Freely +Available `awk' Implementations: Other Versions.). This minor node +describes extensions in his version of `awk' that are not in POSIX +`awk'. -`printf FMT, EXPR-LIST' - Format and print. + * The `-mf N' and `-mr N' command-line options to set the maximum + number of fields and the maximum record size, respectively (*note + Command-Line Options: Options.). As a side note, his `awk' no + longer needs these options; it continues to accept them to avoid + breaking old programs. -`printf FMT, EXPR-LIST > FILE' - Format and print to FILE. If FILE does not exist, it is created. - If it does exist, its contents are deleted the first time the - `printf' is executed. + * The `fflush' built-in function for flushing buffered output (*note + Input/Output Functions: I/O Functions.). -`printf FMT, EXPR-LIST >> FILE' - Format and print to FILE. The previous contents of FILE are - retained, and the output of `printf' is appended to the file. + * The `**' and `**=' operators (*note Arithmetic Operators: + Arithmetic Ops. and *Note Assignment Expressions: Assignment Ops). -`printf FMT, EXPR-LIST | COMMAND' - Format and print, sending the output down a pipe to COMMAND. The - pipeline to the command stays open until the `close' function is - called. + * The use of `func' as an abbreviation for `function' (*note + Function Definition Syntax: Definition Syntax.). - `getline' returns zero on end of file, and -1 on an error. In the -event of an error, `getline' will set `ERRNO' to the value of a -system-dependent string that describes the error. - -File: gawk.info, Node: Printf Summary, Next: Special File Summary, Prev: I/O Summary, Up: Actions Summary + The Bell Laboratories `awk' also incorporates the following +extensions, originally developed for `gawk': -`printf' Summary ----------------- + * The `\x' escape sequence (*note Escape Sequences::). - Conversion specification have the form -`%'[FLAG][WIDTH][`.'PREC]FORMAT. Items in brackets are optional. + * The `/dev/stdin', `/dev/stdout', and `/dev/stderr' special files + (*note Special File Names in `gawk': Special Files.). - The `awk' `printf' statement and `sprintf' function accept the -following conversion specification formats: + * The ability for `FS' and for the third argument to `split' to be + null strings (*note Making Each Character a Separate Field: Single + Character Fields.). -`%c' - An ASCII character. If the argument used for `%c' is numeric, it - is treated as a character and printed. Otherwise, the argument is - assumed to be a string, and the only first character of that - string is printed. + * The `nextfile' statement (*note Using `gawk''s `nextfile' + Statement: Nextfile Statement.). -`%d' -`%i' - A decimal number (the integer part). + * The ability to delete all of an array at once with `delete ARRAY' + (*note The `delete' Statement: Delete.). -`%e' -`%E' - A floating point number of the form `[-]d.dddddde[+-]dd'. The - `%E' format uses `E' instead of `e'. + +File: gawk.info, Node: POSIX/GNU, Next: Contributors, Prev: BTL, Up: Language History -`%f' - A floating point number of the form [`-']`ddd.dddddd'. +Extensions in `gawk' Not in POSIX `awk' +======================================= -`%g' -`%G' - Use either the `%e' or `%f' formats, whichever produces a shorter - string, with non-significant zeros suppressed. `%G' will use `%E' - instead of `%e'. + The GNU implementation, `gawk', adds a large number of features. +This minor node lists them in the order they were added to `gawk'. +They can all be disabled with either the `--traditional' or `--posix' +options (*note Command-Line Options: Options.). -`%o' - An unsigned octal number (also an integer). + Version 2.10 of `gawk' introduced the following features: -`%u' - An unsigned decimal number (again, an integer). + * The `AWKPATH' environment variable for specifying a path search for + the `-f' command-line option (*note Command-Line Options: + Options.). -`%s' - A character string. + * The `IGNORECASE' variable and its effects (*note Case Sensitivity + in Matching: Case-sensitivity.). -`%x' -`%X' - An unsigned hexadecimal number (an integer). The `%X' format uses - `A' through `F' instead of `a' through `f' for decimal 10 through - 15. + * The `/dev/stdin', `/dev/stdout', `/dev/stderr' and `/dev/fd/N' + special file names (*note Special File Names in `gawk': Special + Files.). -`%%' - A single `%' character; no argument is converted. + Version 2.13 of `gawk' introduced the following features: - There are optional, additional parameters that may lie between the -`%' and the control letter: + * The `FIELDWIDTHS' variable and its effects (*note Reading + Fixed-Width Data: Constant Size.). -`-' - The expression should be left-justified within its field. + * The `systime' and `strftime' built-in functions for obtaining and + printing timestamps (*note Using `gawk''s Timestamp Functions: + Time Functions.). -`SPACE' - For numeric conversions, prefix positive values with a space, and - negative values with a minus sign. + * The `-W lint' option to provide error and portability checking for + both the source code and at runtime (*note Command-Line Options: + Options.). -`+' - The plus sign, used before the width modifier (see below), says to - always supply a sign for numeric conversions, even if the data to - be formatted is positive. The `+' overrides the space modifier. + * The `-W compat' option to turn off the GNU extensions (*note + Command-Line Options: Options.). -`#' - Use an "alternate form" for certain control letters. For `o', - supply a leading zero. For `x', and `X', supply a leading `0x' or - `0X' for a non-zero result. For `e', `E', and `f', the result - will always contain a decimal point. For `g', and `G', trailing - zeros are not removed from the result. + * The `-W posix' option for full POSIX compliance (*note + Command-Line Options: Options.). -`0' - A leading `0' (zero) acts as a flag, that indicates output should - be padded with zeros instead of spaces. This applies even to - non-numeric output formats. This flag only has an effect when the - field width is wider than the value to be printed. + Version 2.14 of `gawk' introduced the following feature: -`WIDTH' - The field should be padded to this width. The field is normally - padded with spaces. If the `0' flag has been used, it is padded - with zeros. + * The `next file' statement for skipping to the next data file + (*note Using `gawk''s `nextfile' Statement: Nextfile Statement.). -`.PREC' - A number that specifies the precision to use when printing. For - the `e', `E', and `f' formats, this specifies the number of digits - you want printed to the right of the decimal point. For the `g', - and `G' formats, it specifies the maximum number of significant - digits. For the `d', `o', `i', `u', `x', and `X' formats, it - specifies the minimum number of digits to print. For the `s' - format, it specifies the maximum number of characters from the - string that should be printed. + Version 2.15 of `gawk' introduced the following features: - Either or both of the WIDTH and PREC values may be specified as `*'. -In that case, the particular value is taken from the argument list. + * The `ARGIND' variable, which tracks the movement of `FILENAME' + through `ARGV' (*note Built-in Variables::). - *Note Using `printf' Statements for Fancier Printing: Printf. + * The `ERRNO' variable, which contains the system error message when + `getline' returns -1 or when `close' fails (*note Built-in + Variables::). - -File: gawk.info, Node: Special File Summary, Next: Built-in Functions Summary, Prev: Printf Summary, Up: Actions Summary + * The `/dev/pid', `/dev/ppid', `/dev/pgrpid', and `/dev/user' file + name interpretation (*note Special File Names in `gawk': Special + Files.). -Special File Names ------------------- + * The ability to delete all of an array at once with `delete ARRAY' + (*note The `delete' Statement: Delete.). - When doing I/O redirection from either `print' or `printf' into a -file, or via `getline' from a file, `gawk' recognizes certain special -file names internally. These file names allow access to open file -descriptors inherited from `gawk''s parent process (usually the shell). -The file names are: + * The ability to use GNU-style long-named options that start with + `--' (*note Command-Line Options: Options.). -`/dev/stdin' - The standard input. + * The `--source' option for mixing command-line and library file + source code (*note Command-Line Options: Options.). -`/dev/stdout' - The standard output. + Version 3.0 of `gawk' introduced the following features: -`/dev/stderr' - The standard error output. + * `IGNORECASE' changed, now applying to string comparison as well as + regexp operations (*note Case Sensitivity in Matching: + Case-sensitivity.). -`/dev/fd/N' - The file denoted by the open file descriptor N. + * The `RT' variable that contains the input text that matched `RS' + (*note How Input Is Split into Records: Records.). - In addition, reading the following files provides process related -information about the running `gawk' program. All returned records are -terminated with a newline. + * Full support for both POSIX and GNU regexps (*note Regular + Expressions: Regexp.). -`/dev/pid' - Returns the process ID of the current process. + * The `gensub' function for more powerful text manipulation (*note + String Manipulation Functions: String Functions.). -`/dev/ppid' - Returns the parent process ID of the current process. + * The `strftime' function acquired a default time format, allowing + it to be called with no arguments (*note Using `gawk''s Timestamp + Functions: Time Functions.). -`/dev/pgrpid' - Returns the process group ID of the current process. + * The ability for `FS' and for the third argument to `split' to be + null strings (*note Making Each Character a Separate Field: Single + Character Fields.). -`/dev/user' - At least four space-separated fields, containing the return values - of the `getuid', `geteuid', `getgid', and `getegid' system calls. - If there are any additional fields, they are the group IDs - returned by `getgroups' system call. (Multiple groups may not be - supported on all systems.) + * The ability for `RS' to be a regexp (*note How Input Is Split into + Records: Records.). -These file names may also be used on the command line to name data -files. These file names are only recognized internally if you do not -actually have files with these names on your system. + * The `next file' statement became `nextfile' (*note Using `gawk''s + `nextfile' Statement: Nextfile Statement.). - *Note Special File Names in `gawk': Special Files, for a longer -description that provides the motivation for this feature. + * The `--lint-old' option to warn about constructs that are not + available in the original Version 7 Unix version of `awk' (*note + Major Changes Between V7 and SVR3.1: V7/SVR3.1.). - -File: gawk.info, Node: Built-in Functions Summary, Next: Time Functions Summary, Prev: Special File Summary, Up: Actions Summary + * The `-m' option and the `fflush' function from the Bell + Laboratories research version of `awk' (*note Command-Line + Options: Options.; also *note Input/Output Functions: I/O + Functions.). -Built-in Functions ------------------- + * The `--re-interval' option to provide interval expressions in + regexps (*note Regular Expression Operators: Regexp Operators.). - `awk' provides a number of built-in functions for performing numeric -operations, string related operations, and I/O related operations. + * The `--traditional' option was added as a better name for + `--compat' (*note Command-Line Options: Options.). - The built-in arithmetic functions are: + * The use of GNU Autoconf to control the configuration process + (*note Compiling `gawk' for Unix: Quick Installation.). -`atan2(Y, X)' - the arctangent of Y/X in radians. + * Amiga support (*note Installing `gawk' on an Amiga: Amiga + Installation.). -`cos(EXPR)' - the cosine of EXPR, which is in radians. -`exp(EXPR)' - the exponential function (`e ^ EXPR'). + Version 3.1 of `gawk' introduced the following features: -`int(EXPR)' - truncates to integer. + * The `BINMODE' special variable for non-POSIX systems, which allows + binary I/O for input and/or output files (*note Using `gawk' on PC + Operating Systems: PC Using.). -`log(EXPR)' - the natural logarithm of `expr'. + * The `LINT' special variable, which dynamically controls lint + warnings (*note Built-in Variables::). -`rand()' - a random number between zero and one. - -`sin(EXPR)' - the sine of EXPR, which is in radians. - -`sqrt(EXPR)' - the square root function. - -`srand([EXPR])' - use EXPR as a new seed for the random number generator. If no EXPR - is provided, the time of day is used. The return value is the - previous seed for the random number generator. - - `awk' has the following built-in string functions: - -`gensub(REGEX, SUBST, HOW [, TARGET])' - If HOW is a string beginning with `g' or `G', then replace each - match of REGEX in TARGET with SUBST. Otherwise, replace the - HOW'th occurrence. If TARGET is not supplied, use `$0'. The - return value is the changed string; the original TARGET is not - modified. Within SUBST, `\N', where N is a digit from one to nine, - can be used to indicate the text that matched the N'th - parenthesized subexpression. This function is `gawk'-specific. - -`gsub(REGEX, SUBST [, TARGET])' - for each substring matching the regular expression REGEX in the - string TARGET, substitute the string SUBST, and return the number - of substitutions. If TARGET is not supplied, use `$0'. - -`index(STR, SEARCH)' - returns the index of the string SEARCH in the string STR, or zero - if SEARCH is not present. - -`length([STR])' - returns the length of the string STR. The length of `$0' is - returned if no argument is supplied. - -`match(STR, REGEX)' - returns the position in STR where the regular expression REGEX - occurs, or zero if REGEX is not present, and sets the values of - `RSTART' and `RLENGTH'. - -`split(STR, ARR [, REGEX])' - splits the string STR into the array ARR on the regular expression - REGEX, and returns the number of elements. If REGEX is omitted, - `FS' is used instead. REGEX can be the null string, causing each - character to be placed into its own array element. The array ARR - is cleared first. - -`sprintf(FMT, EXPR-LIST)' - prints EXPR-LIST according to FMT, and returns the resulting - string. + * The `PROCINFO' array for providing process-related information + (*note Built-in Variables::). -`sub(REGEX, SUBST [, TARGET])' - just like `gsub', but only the first matching substring is - replaced. + * The `TEXTDOMAIN' special variable for setting an application's + internationalization text domain (*note Built-in Variables::, and + *Note Internationalization with `gawk': Internationalization). -`substr(STR, INDEX [, LEN])' - returns the LEN-character substring of STR starting at INDEX. If - LEN is omitted, the rest of STR is used. + * The ability to use octal and hexadecimal constants in `awk' + program source code (*note Octal and Hexadecimal Numbers: + Non-decimal-numbers.). -`tolower(STR)' - returns a copy of the string STR, with all the upper-case - characters in STR translated to their corresponding lower-case - counterparts. Non-alphabetic characters are left unchanged. + * The `|&' operator for two-way I/O to a coprocess (*note Two-Way + Communications with Another Process: Two-way I/O.). -`toupper(STR)' - returns a copy of the string STR, with all the lower-case - characters in STR translated to their corresponding upper-case - counterparts. Non-alphabetic characters are left unchanged. + * The `/inet' special files for TCP/IP networking using `|&' (*note + Using `gawk' for Network Programming: TCP/IP Networking.). - The I/O related functions are: + * The optional second argument to `close' that allows closing one end + of a two-way pipe to a coprocess (*note Two-Way Communications + with Another Process: Two-way I/O.). -`close(EXPR)' - Close the open file or pipe denoted by EXPR. + * The optional third argument to the `match' function for capturing + text-matching subexpressions within a regexp (*note String + Manipulation Functions: String Functions.). -`fflush([EXPR])' - Flush any buffered output for the output file or pipe denoted by - EXPR. If EXPR is omitted, standard output is flushed. If EXPR is - the null string (`""'), all output buffers are flushed. + * Positional specifiers in `printf' formats for making translations + easier (*note Rearranging `printf' Arguments: Printf Ordering.). -`system(CMD-LINE)' - Execute the command CMD-LINE, and return the exit status. If your - operating system does not support `system', calling it will - generate a fatal error. + * The `asort' function for sorting arrays (*note Sorting Array + Values and Indices with `gawk': Array Sorting.). - `system("")' can be used to force `awk' to flush any pending - output. This is more portable, but less obvious, than calling - `fflush'. + * The `bindtextdomain' and `dcgettext' functions for + internationalization (*note Internationalizing `awk' Programs: + Programmer i18n.). - -File: gawk.info, Node: Time Functions Summary, Next: String Constants Summary, Prev: Built-in Functions Summary, Up: Actions Summary + * The `extension' built-in function and the ability to add new + built-in functions dynamically (*note Adding New Built-in + Functions to `gawk': Dynamic Extensions.). -Time Functions --------------- + * The `mktime' built-in function for creating timestamps (*note + Using `gawk''s Timestamp Functions: Time Functions.). - The following two functions are available for getting the current -time of day, and for formatting time stamps. They are specific to -`gawk'. + * The `and', `or', `xor', `compl', `lshift', `rshift', and + `strtonum' built-in functions (*note Using `gawk''s Bit + Manipulation Functions: Bitwise Functions.). -`systime()' - returns the current time of day as the number of seconds since a - particular epoch (Midnight, January 1, 1970 UTC, on POSIX systems). + * The support for `next file' as two words was removed completely + (*note Using `gawk''s `nextfile' Statement: Nextfile Statement.). -`strftime([FORMAT[, TIMESTAMP]])' - formats TIMESTAMP according to the specification in FORMAT. The - current time of day is used if no TIMESTAMP is supplied. A - default format equivalent to the output of the `date' utility is - used if no FORMAT is supplied. *Note Functions for Dealing with - Time Stamps: Time Functions, for the details on the conversion - specifiers that `strftime' accepts. + * The `--dump-variables' option to print a list of all global + variables (*note Command-Line Options: Options.). - -File: gawk.info, Node: String Constants Summary, Prev: Time Functions Summary, Up: Actions Summary + * The `--gen-po' command-line option and the use of a leading + underscore to mark strings that should be translated (*note + Extracting Marked Strings: String Extraction.). -String Constants ----------------- + * The `--non-decimal-data' option to allow non-decimal input data + (*note Allowing Non-Decimal Input Data: Non-decimal Data.). - String constants in `awk' are sequences of characters enclosed in -double quotes (`"'). Within strings, certain "escape sequences" are -recognized, as in C. These are: + * The `--profile' option and `pgawk', the profiling version of + `gawk', for producing execution profiles of `awk' programs (*note + Profiling Your `awk' Programs: Profiling.). -`\\' - A literal backslash. + * The `--enable-portals' configuration option to enable special + treatment of pathnames that begin with `/p' as BSD portals (*note + Using `gawk' with BSD Portals: Portal Files.). -`\a' - The "alert" character; usually the ASCII BEL character. + * The use of GNU Automake to help in standardizing the configuration + process (*note Compiling `gawk' for Unix: Quick Installation.). -`\b' - Backspace. + * The use of GNU `gettext' for `gawk''s own message output (*note + `gawk' Can Speak Your Language: Gawk I18N.). -`\f' - Formfeed. + * BeOS support (*note Installing `gawk' on BeOS: BeOS Installation.). -`\n' - Newline. + * Tandem support (*note Installing `gawk' on a Tandem: Tandem + Installation.). -`\r' - Carriage return. + * The Atari port became officially unsupported (*note Installing + `gawk' on the Atari ST: Atari Installation.). -`\t' - Horizontal tab. + * The source code now uses new-style function definitions, with + `ansi2knr' to convert the code on systems with old compilers. -`\v' - Vertical tab. -`\xHEX DIGITS' - The character represented by the string of hexadecimal digits - following the `\x'. As in ANSI C, all following hexadecimal - digits are considered part of the escape sequence. E.g., `"\x1B"' - is a string containing the ASCII ESC (escape) character. (The `\x' - escape sequence is not in POSIX `awk'.) + +File: gawk.info, Node: Contributors, Prev: POSIX/GNU, Up: Language History -`\DDD' - The character represented by the one, two, or three digit sequence - of octal digits. Thus, `"\033"' is also a string containing the - ASCII ESC (escape) character. +Major Contributors to `gawk' +============================ -`\C' - The literal character C, if C is not one of the above. + Always give credit where credit is due. + Anonymous - The escape sequences may also be used inside constant regular -expressions (e.g., the regexp `/[ \t\f\n\r\v]/' matches whitespace -characters). + This minor node names the major contributors to `gawk' and/or this +Info file, in approximate chronological order: - *Note Escape Sequences::. + * Dr. Alfred V. Aho, Dr. Peter J. Weinberger, and Dr. Brian W. + Kernighan, all of Bell Laboratories, designed and implemented Unix + `awk', from which `gawk' gets the majority of its feature set. - -File: gawk.info, Node: Functions Summary, Next: Historical Features, Prev: Actions Summary, Up: Gawk Summary + * Paul Rubin did the initial design and implementation in 1986, and + wrote the first draft (around 40 pages) of this Info file. -User-defined Functions -====================== + * Jay Fenlason finished the initial implementation. - Functions in `awk' are defined as follows: + * Diane Close revised the first draft of this Info file, bringing it + to around 90 pages. - function NAME(PARAMETER LIST) { STATEMENTS } + * Richard Stallman helped finish the implementation and the initial + draft of this Info file. He is also the founder of the FSF and + the GNU project. - Actual parameters supplied in the function call are used to -instantiate the formal parameters declared in the function. Arrays are -passed by reference, other variables are passed by value. + * John Woods contributed parts of the code (mostly fixes) in the + initial version of `gawk'. - If there are fewer arguments passed than there are names in -PARAMETER-LIST, the extra names are given the null string as their -value. Extra names have the effect of local variables. + * In 1988, David Trueman took over primary maintenance of `gawk', + making it compatible with "new" `awk', and greatly improving its + performance. - The open-parenthesis in a function call of a user-defined function -must immediately follow the function name, without any intervening -white space. This is to avoid a syntactic ambiguity with the -concatenation operator. + * Pat Rankin provided the VMS port and its documentation. - The word `func' may be used in place of `function' (but not in POSIX -`awk'). + * Conrad Kwok, Scott Garfinkle, and Kent Williams did the initial + ports to MS-DOS with various versions of MSC. - Use the `return' statement to return a value from a function. + * Hal Peterson provided help in porting `gawk' to Cray systems. - *Note User-defined Functions: User-defined. + * Kai Uwe Rommel provided the port to OS/2 and its documentation. - -File: gawk.info, Node: Historical Features, Prev: Functions Summary, Up: Gawk Summary + * Michal Jaegermann provided the port to Atari systems and its + documentation. He continues to provide portability checking with + DEC Alpha systems, and has done a lot of work to make sure `gawk' + works on non-32-bit systems. -Historical Features -=================== + * Fred Fish provided the port to Amiga systems and its documentation. - There are two features of historical `awk' implementations that -`gawk' supports. + * Scott Deifik currently maintains the MS-DOS port. - First, it is possible to call the `length' built-in function not only -with no arguments, but even without parentheses! + * Juan Grigera maintains the port to Win32 systems. - a = length + * Dr. Darrel Hankerson acts as coordinator for the various ports to + different PC platforms and creates binary distributions for + various PC operating systems. He is also instrumental in keeping + the documentation up to date for the various PC platforms. -is the same as either of + * Christos Zoulas provided the `extension' built-in function for + dynamically adding new modules. - a = length() - a = length($0) + * Ju"rgen Kahrs contributed the initial version of the TCP/IP + networking code and documentation, and motivated the inclusion of + the `|&' operator. -For example: + * Stephen Davies provided the port to Tandem systems and its + documentation. - $ echo abcdef | awk '{ print length }' - -| 6 + * Martin Brown provided the port to BeOS and its documentation. -This feature is marked as "deprecated" in the POSIX standard, and -`gawk' will issue a warning about its use if `--lint' is specified on -the command line. (The ability to use `length' this way was actually -an accident of the original Unix `awk' implementation. If any built-in -function used `$0' as its default argument, it was possible to call -that function without the parentheses. In particular, it was common -practice to use the `length' function in this fashion, and this usage -was documented in the `awk' manual page.) + * Arno Peters did the initial work to convert `gawk' to use GNU + Automake and `gettext'. - The other historical feature is the use of either the `break' -statement, or the `continue' statement outside the body of a `while', -`for', or `do' loop. Traditional `awk' implementations have treated -such usage as equivalent to the `next' statement. More recent versions -of Unix `awk' do not allow it. `gawk' supports this usage if -`--traditional' has been specified. + * Alan J. Broder provided the initial version of the `asort' function + as well as the code for the new optional third argument to the + `match' function. - *Note Command Line Options: Options, for more information about the -`--posix' and `--lint' options. + * Arnold Robbins has been working on `gawk' since 1988, at first + helping David Trueman, and as the primary maintainer since around + 1994.  -File: gawk.info, Node: Installation, Next: Notes, Prev: Gawk Summary, Up: Top +File: gawk.info, Node: Installation, Next: Notes, Prev: Language History, Up: Top Installing `gawk' ***************** This appendix provides instructions for installing `gawk' on the various platforms that are supported by the developers. The primary -developers support Unix (and one day, GNU), while the other ports were -contributed. The file `ACKNOWLEDGMENT' in the `gawk' distribution -lists the electronic mail addresses of the people who did the -respective ports, and they are also provided in *Note Reporting -Problems and Bugs: Bugs. +developer supports GNU/Linux (and Unix), whereas the other ports are +contributed. *Note Reporting Problems and Bugs: Bugs, for the +electronic mail addresses of the people who did the respective ports. * Menu: * Gawk Distribution:: What is in the `gawk' distribution. -* Unix Installation:: Installing `gawk' under various versions - of Unix. -* VMS Installation:: Installing `gawk' on VMS. -* PC Installation:: Installing and Compiling `gawk' on MS-DOS - and OS/2 -* Atari Installation:: Installing `gawk' on the Atari ST. -* Amiga Installation:: Installing `gawk' on an Amiga. +* Unix Installation:: Installing `gawk' under various + versions of Unix. +* Non-Unix Installation:: Installation on Other Operating Systems. +* Unsupported:: Systems whose ports are no longer supported. * Bugs:: Reporting Problems and Bugs. * Other Versions:: Other freely available `awk' implementations. @@ -15332,8 +16680,8 @@ File: gawk.info, Node: Gawk Distribution, Next: Unix Installation, Prev: Inst The `gawk' Distribution ======================= - This section first describes how to get the `gawk' distribution, how -to extract it, and then what is in the various files and subdirectories. + This minor node describes how to get the `gawk' distribution, how to +extract it, and then what is in the various files and subdirectories. * Menu: @@ -15347,101 +16695,33 @@ File: gawk.info, Node: Getting, Next: Extracting, Prev: Gawk Distribution, U Getting the `gawk' Distribution ------------------------------- - There are three ways you can get GNU software. + There are three ways to get GNU software: - 1. You can copy it from someone else who already has it. + * Copy it from someone else who already has it. - 2. You can order `gawk' directly from the Free Software Foundation. - Software distributions are available for Unix, MS-DOS, and VMS, on - tape and CD-ROM. The address is: + * Order `gawk' directly from the Free Software Foundation. Software + distributions are available for Unix, MS-DOS, and VMS, on tape and + CD-ROM. Their address is: Free Software Foundation - 59 Temple Place--Suite 330 + 59 Temple Place, Suite 330 Boston, MA 02111-1307 USA Phone: +1-617-542-5942 Fax (including Japan): +1-617-542-2652 - Email: `gnu@gnu.org' + Email: URL: `http://www.gnu.org/' Ordering from the FSF directly contributes to the support of the foundation and to the production of more free software. - 3. You can get `gawk' by using anonymous `ftp' to the Internet host + * Retrieve `gawk' by using anonymous `ftp' to the Internet host `gnudist.gnu.org', in the directory `/gnu/gawk'. - Here is a list of alternate `ftp' sites from which you can obtain - GNU software. When a site is listed as "SITE`:'DIRECTORY" the - DIRECTORY indicates the directory where GNU software is kept. You - should use a site that is geographically close to you. - - Asia: - - `cair-archive.kaist.ac.kr:/pub/gnu' - `ftp.cs.titech.ac.jp' - `ftp.nectec.or.th:/pub/mirrors/gnu' - `utsun.s.u-tokyo.ac.jp:/ftpsync/prep' - - Australia: - - `archie.au:/gnu' - (`archie.oz' or `archie.oz.au' for ACSnet) - - Africa: - - `ftp.sun.ac.za:/pub/gnu' - - Middle East: - - `ftp.technion.ac.il:/pub/unsupported/gnu' - - Europe: - - `archive.eu.net' - `ftp.denet.dk' - `ftp.eunet.ch' - `ftp.funet.fi:/pub/gnu' - `ftp.ieunet.ie:pub/gnu' - `ftp.informatik.rwth-aachen.de:/pub/gnu' - `ftp.informatik.tu-muenchen.de' - `ftp.luth.se:/pub/unix/gnu' - `ftp.mcc.ac.uk' - `ftp.stacken.kth.se' - `ftp.sunet.se:/pub/gnu' - `ftp.univ-lyon1.fr:pub/gnu' - `ftp.win.tue.nl:/pub/gnu' - `irisa.irisa.fr:/pub/gnu' - `isy.liu.se' - `nic.switch.ch:/mirror/gnu' - `src.doc.ic.ac.uk:/gnu' - `unix.hensa.ac.uk:/pub/uunet/systems/gnu' - - South America: - - `ftp.inf.utfsm.cl:/pub/gnu' - `ftp.unicamp.br:/pub/gnu' - - Western Canada: - - `ftp.cs.ubc.ca:/mirror2/gnu' - - USA: - - `col.hp.com:/mirrors/gnu' - `f.ms.uky.edu:/pub3/gnu' - `ftp.cc.gatech.edu:/pub/gnu' - `ftp.cs.columbia.edu:/archives/gnu/prep' - `ftp.digex.net:/pub/gnu' - `ftp.hawaii.edu:/mirrors/gnu' - `ftp.kpc.com:/pub/mirror/gnu' - - USA (continued): - `ftp.uu.net:/systems/gnu' - `gatekeeper.dec.com:/pub/GNU' - `jaguar.utah.edu:/gnustuff' - `labrea.stanford.edu' - `mrcnext.cso.uiuc.edu:/pub/gnu' - `vixen.cso.uiuc.edu:/gnu' - `wuarchive.wustl.edu:/systems/gnu' + The GNU software archive is mirrored around the world. The +up-to-date list of mirror sites is available from the main FSF web site +(http://www.gnu.org/order/ftp.html). Try to use one of the mirrors; +they will be less busy, and you can usually find one closer to your +site.  File: gawk.info, Node: Extracting, Next: Distribution contents, Prev: Getting, Up: Gawk Distribution @@ -15452,29 +16732,26 @@ Extracting the Distribution `gawk' is distributed as a `tar' file compressed with the GNU Zip program, `gzip'. - Once you have the distribution (for example, `gawk-3.0.6.tar.gz'), -first use `gzip' to expand the file, and then use `tar' to extract it. -You can use the following pipeline to produce the `gawk' distribution: + Once you have the distribution (for example, `gawk-3.1.0.tar.gz'), +use `gzip' to expand the file and then use `tar' to extract it. You +can use the following pipeline to produce the `gawk' distribution: - # Under System V, add 'o' to the tar flags - gzip -d -c gawk-3.0.6.tar.gz | tar -xvpf - + # Under System V, add 'o' to the tar options + gzip -d -c gawk-3.1.0.tar.gz | tar -xvpf - -This will create a directory named `gawk-3.0.6' in the current -directory. +This creates a directory named `gawk-3.1.0' in the current directory. - The distribution file name is of the form `gawk-V.R.N.tar.gz'. The + The distribution file name is of the form `gawk-V.R.P.tar.gz'. The V represents the major version of `gawk', the R represents the current -release of version V, and the N represents a "patch level", meaning +release of version V, and the P represents a "patch level", meaning that minor bugs have been fixed in the release. The current patch -level is 6, but when retrieving distributions, you should get the -version with the highest version, release, and patch level. (Note that -release levels greater than or equal to 90 denote "beta," or -non-production software; you may not wish to retrieve such a version -unless you don't mind experimenting.) - - If you are not on a Unix system, you will need to make other -arrangements for getting and extracting the `gawk' distribution. You -should consult a local expert. +level is 0, but when retrieving distributions, you should get the +version with the highest version, release, and patch level. (Note, +however, that patch levels greater than or equal to 80 denote "beta" or +non-production software; you might not want to retrieve such a version +unless you don't mind experimenting.) If you are not on a Unix system, +you need to make other arrangements for getting and extracting the +`gawk' distribution. You should consult a local expert.  File: gawk.info, Node: Distribution contents, Prev: Extracting, Up: Gawk Distribution @@ -15483,31 +16760,23 @@ Contents of the `gawk' Distribution ----------------------------------- The `gawk' distribution has a number of C source files, -documentation files, subdirectories and files related to the +documentation files, subdirectories, and files related to the configuration process (*note Compiling and Installing `gawk' on Unix: -Unix Installation.), and several subdirectories related to different, -non-Unix, operating systems. +Unix Installation.), as well as several subdirectories related to +different non-Unix operating systems: -various `.c', `.y', and `.h' files +Various `.c', `.y', and `.h' files: These files are the actual `gawk' source code. `README' `README_d/README.*' - Descriptive files: `README' for `gawk' under Unix, and the rest - for the various hardware and software combinations. + Descriptive files: `README' for `gawk' under Unix and the rest for + the various hardware and software combinations. `INSTALL' A file providing an overview of the configuration and installation process. -`PORTS' - A list of systems to which `gawk' has been ported, and which have - successfully run the test suite. - -`ACKNOWLEDGMENT' - A list of the people who contributed major parts of the code or - documentation. - `ChangeLog' A detailed list of source code changes as bugs are fixed or improvements made. @@ -15519,9 +16788,9 @@ various `.c', `.y', and `.h' files The GNU General Public License. `FUTURES' - A brief list of features and/or changes being contemplated for - future releases, with some indication of the time frame for the - feature, based on its difficulty. + A brief list of features and changes being contemplated for future + releases, with some indication of the time frame for the feature, + based on its difficulty. `LIMITATIONS' A list of those factors that limit `gawk''s performance. Most of @@ -15530,10 +16799,7 @@ various `.c', `.y', and `.h' files `POSIX.STD' A description of one area where the POSIX standard for `awk' is - incorrect, and how `gawk' handles the problem. - -`PROBLEMS' - A file describing known problems with the current release. + incorrect as well as how `gawk' handles the problem. `doc/awkforai.txt' A short article describing why `gawk' is a good language for AI @@ -15548,7 +16814,7 @@ various `.c', `.y', and `.h' files `doc/no.colors' `doc/setter.outline' The `troff' source for a five-color `awk' reference card. A - modern version of `troff', such as GNU Troff (`groff') is needed + modern version of `troff' such as GNU `troff' (`groff') is needed to produce the color version. See the file `README.card' for instructions if you have an older `troff'. @@ -15559,11 +16825,19 @@ various `.c', `.y', and `.h' files `doc/gawk.texi' The Texinfo source file for this Info file. It should be processed with TeX to produce a printed document, and with - `makeinfo' to produce an Info file. + `makeinfo' to produce an Info or HTML file. `doc/gawk.info' The generated Info file for this Info file. +`doc/gawkinet.texi' + The Texinfo source file for *Note Top::. It should be processed + with TeX to produce a printed document and with `makeinfo' to + produce an Info or HTML file. + +`doc/gawkinet.info' + The generated Info file for `TCP/IP Internetworking with `gawk''. + `doc/igawk.1' The `troff' source for a manual page describing the `igawk' program presented in *Note An Easy Way to Use Library Functions: @@ -15573,159 +16847,458 @@ various `.c', `.y', and `.h' files The input file used during the configuration process to generate the actual `Makefile' for creating the documentation. +`Makefile.am' +`*/Makefile.am' + Files used by the GNU `automake' software for generating the + `Makefile.in' files used by `autoconf' and `configure'. + `Makefile.in' `acconfig.h' +`acinclude.m4' `aclocal.m4' `configh.in' `configure.in' `configure' `custom.h' -`missing/*' - These files and subdirectory are used when configuring `gawk' for - various Unix systems. They are explained in detail in *Note - Compiling and Installing `gawk' on Unix: Unix Installation. +`missing_d/*' +`m4/*' + These files and subdirectories are used when configuring `gawk' + for various Unix systems. They are explained in *Note Compiling + and Installing `gawk' on Unix: Unix Installation. + +`intl/*' +`po/*' + The `intl' directory provides the GNU `gettext' library, which + implements `gawk''s internationalization features, while the `po' + library contains message translations. `awklib/extract.awk' +`awklib/Makefile.am' `awklib/Makefile.in' +`awklib/eg/*' The `awklib' directory contains a copy of `extract.awk' (*note Extracting Programs from Texinfo Source Files: Extract Program.), which can be used to extract the sample programs from the Texinfo - source file for this Info file, and a `Makefile.in' file, which - `configure' uses to generate a `Makefile'. As part of the process - of building `gawk', the library functions from *Note A Library of - `awk' Functions: Library Functions, and the `igawk' program from - *Note An Easy Way to Use Library Functions: Igawk Program, are - extracted into ready to use files. They are installed as part of - the installation process. - -`atari/*' - Files needed for building `gawk' on an Atari ST. *Note Installing - `gawk' on the Atari ST: Atari Installation, for details. + source file for this Info file. It also contains a `Makefile.in' + file, which `configure' uses to generate a `Makefile'. + `Makefile.am' is used by GNU Automake to create `Makefile.in'. + The library functions from *Note A Library of `awk' Functions: + Library Functions, and the `igawk' program from *Note An Easy Way + to Use Library Functions: Igawk Program, are included as + ready-to-use files in the `gawk' distribution. They are installed + as part of the installation process. The rest of the programs in + this Info file are available in appropriate subdirectories of + `awklib/eg'. + +`unsupported/atari/*' + Files needed for building `gawk' on an Atari ST (*note Installing + `gawk' on the Atari ST: Atari Installation., for details). + +`unsupported/tandem/*' + Files needed for building `gawk' on a Tandem (*note Installing + `gawk' on a Tandem: Tandem Installation., for details). + +`posix/*' + Files needed for building `gawk' on POSIX-compliant systems. `pc/*' - Files needed for building `gawk' under MS-DOS and OS/2. *Note - MS-DOS and OS/2 Installation and Compilation: PC Installation, for - details. + Files needed for building `gawk' under MS-DOS, MS Windows and OS/2 + (*note Installation on PC Operating Systems: PC Installation., for + details). `vms/*' - Files needed for building `gawk' under VMS. *Note How to Compile - and Install `gawk' on VMS: VMS Installation, for details. + Files needed for building `gawk' under VMS (*note How to Compile + and Install `gawk' on VMS: VMS Installation., for details). `test/*' - A test suite for `gawk'. You can use `make check' from the top - level `gawk' directory to run your version of `gawk' against the - test suite. If `gawk' successfully passes `make check' then you - can be confident of a successful port. + A test suite for `gawk'. You can use `make check' from the + top-level `gawk' directory to run your version of `gawk' against + the test suite. If `gawk' successfully passes `make check', then + you can be confident of a successful port.  -File: gawk.info, Node: Unix Installation, Next: VMS Installation, Prev: Gawk Distribution, Up: Installation +File: gawk.info, Node: Unix Installation, Next: Non-Unix Installation, Prev: Gawk Distribution, Up: Installation Compiling and Installing `gawk' on Unix ======================================= Usually, you can compile and install `gawk' by typing only two -commands. However, if you do use an unusual system, you may need to +commands. However, if you use an unusual system, you may need to configure `gawk' for your system yourself. * Menu: -* Quick Installation:: Compiling `gawk' under Unix. -* Configuration Philosophy:: How it's all supposed to work. +* Quick Installation:: Compiling `gawk' under Unix. +* Additional Configuration Options:: Other compile-time options. +* Configuration Philosophy:: How it's all supposed to work.  -File: gawk.info, Node: Quick Installation, Next: Configuration Philosophy, Prev: Unix Installation, Up: Unix Installation +File: gawk.info, Node: Quick Installation, Next: Additional Configuration Options, Prev: Unix Installation, Up: Unix Installation Compiling `gawk' for Unix ------------------------- After you have extracted the `gawk' distribution, `cd' to -`gawk-3.0.6'. Like most GNU software, `gawk' is configured +`gawk-3.1.0'. Like most GNU software, `gawk' is configured automatically for your Unix system by running the `configure' program. -This program is a Bourne shell script that was generated automatically +This program is a Bourne shell script that is generated automatically using GNU `autoconf'. (The `autoconf' software is described fully -starting with *Note Introduction: (autoconf)Top.) +starting with *Note Top::.) To configure `gawk', simply run `configure': sh ./configure This produces a `Makefile' and `config.h' tailored to your system. -The `config.h' file describes various facts about your system. You may -wish to edit the `Makefile' to change the `CFLAGS' variable, which -controls the command line options that are passed to the C compiler -(such as optimization levels, or compiling for debugging). +The `config.h' file describes various facts about your system. You +might want to edit the `Makefile' to change the `CFLAGS' variable, +which controls the command-line options that are passed to the C +compiler (such as optimization levels or compiling for debugging). - Alternatively, you can add your own values for most `make' -variables, such as `CC' and `CFLAGS', on the command line when running + Alternatively, you can add your own values for most `make' variables +on the command line, such as `CC' and `CFLAGS', when running `configure': CC=cc CFLAGS=-g sh ./configure See the file `INSTALL' in the `gawk' distribution for all the details. - After you have run `configure', and possibly edited the `Makefile', + After you have run `configure' and possibly edited the `Makefile', type: make -and shortly thereafter, you should have an executable version of `gawk'. -That's all there is to it! (If these steps do not work, please send in -a bug report; *note Reporting Problems and Bugs: Bugs..) +Shortly thereafter, you should have an executable version of `gawk'. +That's all there is to it! To verify that `gawk' is working properly, +run `make check'. All of the tests should succeed. If these steps do +not work, or if any of the tests fail, check the files in the +`README_d' directory to see if you've found a known problem. If the +failure is not described there, please send in a bug report (*note +Reporting Problems and Bugs: Bugs..) + + +File: gawk.info, Node: Additional Configuration Options, Next: Configuration Philosophy, Prev: Quick Installation, Up: Unix Installation + +Additional Configuration Options +-------------------------------- + + There are several additional options you may use on the `configure' +command line when compiling `gawk' from scratch. + +`--enable-portals' + This option causes `gawk' to treat pathnames that begin with `/p' + as BSD portal files when doing two-way I/O with the `|&' operator + (*note Using `gawk' with BSD Portals: Portal Files.). + +`--with-included-gettext' + Use the version of the `gettext' library that comes with `gawk'. + This option should be used on systems that do _not_ use version 2 + (or later) of the GNU C library. All known modern GNU/Linux + systems use Glibc 2. Use this option on any other system. + +`--disable-nls' + Disable all message translation facilities. This is usually not + desirable, but it may bring you some slight performance + improvement. You should also use this option if + `--with-included-gettext' doesn't work on your system.  -File: gawk.info, Node: Configuration Philosophy, Prev: Quick Installation, Up: Unix Installation +File: gawk.info, Node: Configuration Philosophy, Prev: Additional Configuration Options, Up: Unix Installation The Configuration Process ------------------------- - (This section is of interest only if you know something about using -the C language and the Unix operating system.) + This minor node is of interest only if you know something about +using the C language and the Unix operating system. The source code for `gawk' generally attempts to adhere to formal standards wherever possible. This means that `gawk' uses library -routines that are specified by the ANSI C standard and by the POSIX -operating system interface standard. When using an ANSI C compiler, +routines that are specified by the ISO C standard and by the POSIX +operating system interface standard. When using an ISO C compiler, function prototypes are used to help improve the compile-time checking. - Many Unix systems do not support all of either the ANSI or the POSIX -standards. The `missing' subdirectory in the `gawk' distribution -contains replacement versions of those subroutines that are most likely + Many Unix systems do not support all of either the ISO or the POSIX +standards. The `missing_d' subdirectory in the `gawk' distribution +contains replacement versions of those functions that are most likely to be missing. - The `config.h' file that is created by the `configure' program -contains definitions that describe features of the particular operating -system where you are attempting to compile `gawk'. The three things -described by this file are what header files are available, so that -they can be correctly included, what (supposedly) standard functions -are actually available in your C libraries, and other miscellaneous -facts about your variant of Unix. For example, there may not be an -`st_blksize' element in the `stat' structure. In this case -`HAVE_ST_BLKSIZE' would be undefined. + The `config.h' file that `configure' creates contains definitions +that describe features of the particular operating system where you are +attempting to compile `gawk'. The three things described by this file +are: what header files are available, so that they can be correctly +included, what (supposedly) standard functions are actually available +in your C libraries, and various miscellaneous facts about your variant +of Unix. For example, there may not be an `st_blksize' element in the +`stat' structure. In this case, `HAVE_ST_BLKSIZE' is undefined. It is possible for your C compiler to lie to `configure'. It may do so by not exiting with an error when a library function is not -available. To get around this, you can edit the file `custom.h'. Use -an `#ifdef' that is appropriate for your system, and either `#define' -any constants that `configure' should have defined but didn't, or -`#undef' any constants that `configure' defined and should not have. -`custom.h' is automatically included by `config.h'. +available. To get around this, edit the file `custom.h'. Use an +`#ifdef' that is appropriate for your system, and either `#define' any +constants that `configure' should have defined but didn't, or `#undef' +any constants that `configure' defined and should not have. `custom.h' +is automatically included by `config.h'. It is also possible that the `configure' program generated by `autoconf' will not work on your system in some other fashion. If you do have a problem, the file `configure.in' is the input for `autoconf'. -You may be able to change this file, and generate a new version of -`configure' that will work on your system. *Note Reporting Problems -and Bugs: Bugs, for information on how to report problems in -configuring `gawk'. The same mechanism may be used to send in updates -to `configure.in' and/or `custom.h'. +You may be able to change this file and generate a new version of +`configure' that works on your system (*note Reporting Problems and +Bugs: Bugs., for information on how to report problems in configuring +`gawk'). The same mechanism may be used to send in updates to +`configure.in' and/or `custom.h'. + + +File: gawk.info, Node: Non-Unix Installation, Next: Unsupported, Prev: Unix Installation, Up: Installation + +Installation on Other Operating Systems +======================================= + + This minor node describes how to install `gawk' on various non-Unix +systems. + +* Menu: + +* Amiga Installation:: Installing `gawk' on an Amiga. +* BeOS Installation:: Installing `gawk' on BeOS. +* PC Installation:: Installing and Compiling `gawk' on + MS-DOS and OS/2. +* VMS Installation:: Installing `gawk' on VMS. + + +File: gawk.info, Node: Amiga Installation, Next: BeOS Installation, Prev: Non-Unix Installation, Up: Non-Unix Installation + +Installing `gawk' on an Amiga +----------------------------- + + You can install `gawk' on an Amiga system using a Unix emulation +environment, available via anonymous `ftp' from `ftp.ninemoons.com' in +the directory `pub/ade/current'. This includes a shell based on +`pdksh'. The primary component of this environment is a Unix emulation +library, `ixemul.lib'. + + A more complete distribution for the Amiga is available on the Geek +Gadgets CD-ROM, available from: + + CRONUS + 1840 E. Warner Road #105-265 + Tempe, AZ 85284 USA + US Toll Free: (800) 804-0833 + Phone: +1-602-491-0442 + FAX: +1-602-491-0048 + Email: + WWW: `http://www.ninemoons.com' + Anonymous `ftp' site: `ftp.ninemoons.com' + + Once you have the distribution, you can configure `gawk' simply by +running `configure': + + configure -v m68k-amigaos + + Then run `make' and you should be all set! If these steps do not +work, please send in a bug report (*note Reporting Problems and Bugs: +Bugs.). + + +File: gawk.info, Node: BeOS Installation, Next: PC Installation, Prev: Amiga Installation, Up: Non-Unix Installation + +Installing `gawk' on BeOS +------------------------- + + Since BeOS DR9, all the tools that you should need to build `gawk' +are included with BeOS. The process is basically identical to the Unix +process of running `configure' and then `make'. Full instructions are +given below. + + You can compile `gawk' under BeOS by extracting the standard sources +and running `configure'. You _must_ specify the location prefix for the +installation directory. For BeOS DR9 and beyond, the best directory to +use is `/boot/home/config', so the `configure' command is: + + configure --prefix=/boot/home/config + + This installs the compiled application into `/boot/home/config/bin', +which is already specified in the standard `PATH'. + + Once the configuration process is completed, you can run `make', and +then `make install': + + $ make + ... + $ make install + + BeOS uses `bash' as its shell; thus, you use `gawk' the same way you +would under Unix. If these steps do not work, please send in a bug +report (*note Reporting Problems and Bugs: Bugs.). + + +File: gawk.info, Node: PC Installation, Next: VMS Installation, Prev: BeOS Installation, Up: Non-Unix Installation + +Installation on PC Operating Systems +------------------------------------ + + This minor node covers installation and usage of `gawk' on x86 +machines running DOS, any version of Windows, or OS/2. In this minor +node, the term "Win32" refers to any of Windows-95/98/ME/NT/2000. + + The limitations of DOS (and DOS shells under Windows or OS/2) has +meant that various "DOS extenders" are often used with programs such as +`gawk'. The varying capabilities of Microsoft Windows 3.1 and Win32 +can add to the confusion. For an overview of the considerations, +please refer to `README_d/README.pc' in the distribution. + +* Menu: + +* PC Binary Installation:: Installing a prepared distribution. +* PC Compiling:: Compiling `gawk' for MS-DOS, Win32, + and OS/2. +* PC Using:: Running `gawk' on MS-DOS, Win32 and + OS/2. + + +File: gawk.info, Node: PC Binary Installation, Next: PC Compiling, Prev: PC Installation, Up: PC Installation + +Installing a Prepared Distribution for PC Systems +................................................. + + If you have received a binary distribution prepared by the DOS +maintainers, then `gawk' and the necessary support files appear under +the `gnu' directory, with executables in `gnu/bin', libraries in +`gnu/lib/awk', and manual pages under `gnu/man'. This is designed for +easy installation to a `/gnu' directory on your drive--however, the +files can be installed anywhere provided `AWKPATH' is set properly. +Regardless of the installation directory, the first line of `igawk.cmd' +and `igawk.bat' (in `gnu/bin') may need to be edited. + + The binary distribution contains a separate file describing the +contents. In particular, it may include more than one version of the +`gawk' executable. OS/2 binary distributions may have a different +arrangement, but installation is similar. + + +File: gawk.info, Node: PC Compiling, Next: PC Using, Prev: PC Binary Installation, Up: PC Installation + +Compiling `gawk' for PC Operating Systems +......................................... + + `gawk' can be compiled for MS-DOS, Win32, and OS/2 using the GNU +development tools from DJ Delorie (DJGPP; MS-DOS only) or Eberhard +Mattes (EMX; MS-DOS, Win32 and OS/2). Microsoft Visual C/C++ can be +used to build a Win32 version, and Microsoft C/C++ can be used to build +16-bit versions for MS-DOS and OS/2. The file `README_d/README.pc' in +the `gawk' distribution contains additional notes, and `pc/Makefile' +contains important information on compilation options. + + To build `gawk', copy the files in the `pc' directory (_except_ for +`ChangeLog') to the directory with the rest of the `gawk' sources. The +`Makefile' contains a configuration section with comments and may need +to be edited in order to work with your `make' utility. + + The `Makefile' contains a number of targets for building various +MS-DOS, Win32, and OS/2 versions. A list of targets is printed if the +`make' command is given without a target. As an example, to build `gawk' +using the DJGPP tools, enter `make djgpp'. + + Using `make' to run the standard tests and to install `gawk' +requires additional Unix-like tools, including `sh', `sed', and `cp'. +In order to run the tests, the `test/*.ok' files may need to be +converted so that they have the usual DOS-style end-of-line markers. +Most of the tests work properly with Stewartson's shell along with the +companion utilities or appropriate GNU utilities. However, some +editing of `test/Makefile' is required. It is recommended that you copy +the file `pc/Makefile.tst' over the file `test/Makefile' as a +replacement. Details can be found in `README_d/README.pc' and in the +file `pc/Makefile.tst'. + + +File: gawk.info, Node: PC Using, Prev: PC Compiling, Up: PC Installation + +Using `gawk' on PC Operating Systems +.................................... + + The OS/2 and MS-DOS versions of `gawk' search for program files as +described in *Note The `AWKPATH' Environment Variable: AWKPATH Variable. +However, semicolons (rather than colons) separate elements in the +`AWKPATH' variable. If `AWKPATH' is not set or is empty, then the +default search path is `".;c:/lib/awk;c:/gnu/lib/awk"'. + + An `sh'-like shell (as opposed to `command.com' under MS-DOS or +`cmd.exe' under OS/2) may be useful for `awk' programming. Ian +Stewartson has written an excellent shell for MS-DOS and OS/2, Daisuke +Aoyama has ported GNU `bash' to MS-DOS using the DJGPP tools, and +several shells are available for OS/2, including `ksh'. The file +`README_d/README.pc' in the `gawk' distribution contains information on +these shells. Users of Stewartson's shell on DOS should examine its +documentation for handling command lines; in particular, the setting +for `gawk' in the shell configuration may need to be changed and the +`ignoretype' option may also be of interest. + + Under OS/2 and DOS, `gawk' (and many other text programs) silently +translate end-of-line `"\r\n"' to `"\n"' on input and `"\n"' to +`"\r\n"' on output. A special `BINMODE' variable allows control over +these translations and is interpreted as follows. + + * If `BINMODE' is `"r"', or `(BINMODE & 1)' is nonzero, then binary + mode is set on read (i.e., no translations on reads). + + * If `BINMODE' is `"w"', or `(BINMODE & 2)' is nonzero, then binary + mode is set on write (i.e., no translations on writes). + + * If `BINMODE' is `"rw"' or `"wr"', binary mode is set for both read + and write (same as `(BINMODE & 3)'). + + * `BINMODE=NON-NULL-STRING' is the same as `BINMODE=3' (i.e., no + translations on reads or writes). However, `gawk' issues a warning + message if the string is not one of `"rw"' or `"wr"'. + +The modes for standard input and standard output are set one time only +(after the command line is read, but before processing any of the `awk' +program). Setting `BINMODE' for standard input or standard output is +accomplished by using an appropriate `-v BINMODE=N' option on the +command line. `BINMODE' is set at the time a file or pipe is opened +and cannot be changed mid-stream. + + The name `BINMODE' was chosen to match `mawk' (*note Other Freely +Available `awk' Implementations: Other Versions.). Both `mawk' and +`gawk' handle `BINMODE' similarly; however, `mawk' adds a `-W +BINMODE=N' option and an environment variable that can set `BINMODE', +`RS', and `ORS'. The files `binmode[1-3].awk' (under `gnu/lib/awk' in +some of the prepared distributions) have been chosen to match `mawk''s +`-W BINMODE=N' option. These can be changed or discarded; in +particular, the setting of `RS' giving the fewest "surprises" is open +to debate. `mawk' uses `RS = "\r\n"' if binary mode is set on read, +which is appropriate for files with the DOS-style end-of-line. + + To Illustrate, the following examples set binary mode on writes for +standard output and other files, and set `ORS' as the "usual" DOS-style +end-of-line: + + gawk -v BINMODE=2 -v ORS="\r\n" ... + +or: + + gawk -v BINMODE=w -f binmode2.awk ... + +These give the same result as the `-W BINMODE=2' option in `mawk'. The +following changes the record separator to `"\r\n"' and sets binary mode +on reads, but does not affect the mode on standard input: + + gawk -v RS="\r\n" --source "BEGIN { BINMODE = 1 }" ... + +or: + + gawk -f binmode1.awk ... + +With proper quoting, in the first example the setting of `RS' can be +moved into the `BEGIN' rule.  -File: gawk.info, Node: VMS Installation, Next: PC Installation, Prev: Unix Installation, Up: Installation +File: gawk.info, Node: VMS Installation, Prev: PC Installation, Up: Non-Unix Installation How to Compile and Install `gawk' on VMS -======================================== +---------------------------------------- - This section describes how to compile and install `gawk' under VMS. + This node describes how to compile and install `gawk' under VMS. * Menu: @@ -15738,16 +17311,16 @@ How to Compile and Install `gawk' on VMS File: gawk.info, Node: VMS Compilation, Next: VMS Installation Details, Prev: VMS Installation, Up: VMS Installation Compiling `gawk' on VMS ------------------------ +....................... To compile `gawk' under VMS, there is a `DCL' command procedure that -will issue all the necessary `CC' and `LINK' commands, and there is -also a `Makefile' for use with the `MMS' utility. From the source -directory, use either +issues all the necessary `CC' and `LINK' commands. There is also a +`Makefile' for use with the `MMS' utility. From the source directory, +use either: $ @[.VMS]VMSBUILD.COM -or +or: $ MMS/DESCRIPTION=[.VMS]DESCRIP.MMS GAWK @@ -15768,62 +17341,64 @@ VAX C V2.x GNU C Edit `vmsbuild.com' or `descrip.mms'; the changes are different - from those for VAX C V2.x, but equally straightforward. No - changes to `config.h' should be needed. + from those for VAX C V2.x but equally straightforward. No changes + to `config.h' are needed. DEC C Edit `vmsbuild.com' or `descrip.mms' according to their comments. - No changes to `config.h' should be needed. + No changes to `config.h' are needed. - `gawk' has been tested under VAX/VMS 5.5-1 using VAX C V3.2, GNU C -1.40 and 2.3. It should work without modifications for VMS V4.6 and up. + `gawk' has been tested under VAX/VMS 5.5-1 using VAX C V3.2, and GNU +C 1.40 and 2.3. It should work without modifications for VMS V4.6 and +up.  File: gawk.info, Node: VMS Installation Details, Next: VMS Running, Prev: VMS Compilation, Up: VMS Installation Installing `gawk' on VMS ------------------------- +........................ To install `gawk', all you need is a "foreign" command, which is a `DCL' symbol whose value begins with a dollar sign. For example: $ GAWK :== $disk1:[gnubin]GAWK -(Substitute the actual location of `gawk.exe' for `$disk1:[gnubin]'.) -The symbol should be placed in the `login.com' of any user who wishes -to run `gawk', so that it will be defined every time the user logs on. +Substitute the actual location of `gawk.exe' for `$disk1:[gnubin]'. The +symbol should be placed in the `login.com' of any user who wants to run +`gawk', so that it is defined every time the user logs on. Alternatively, the symbol may be placed in the system-wide -`sylogin.com' procedure, which will allow all users to run `gawk'. +`sylogin.com' procedure, which allows all users to run `gawk'. Optionally, the help entry can be loaded into a VMS help library: $ LIBRARY/HELP SYS$HELP:HELPLIB [.VMS]GAWK.HLP (You may want to substitute a site-specific help library rather than -the standard VMS library `HELPLIB'.) After loading the help text, +the standard VMS library `HELPLIB'.) After loading the help text, the +command: $ HELP GAWK -will provide information about both the `gawk' implementation and the -`awk' programming language. +provides information about both the `gawk' implementation and the `awk' +programming language. The logical name `AWK_LIBRARY' can designate a default location for -`awk' program files. For the `-f' option, if the specified filename -has no device or directory path information in it, `gawk' will look in -the current directory first, then in the directory specified by the -translation of `AWK_LIBRARY' if the file was not found. If after -searching in both directories, the file still is not found, then `gawk' -appends the suffix `.awk' to the filename and the file search will be -re-tried. If `AWK_LIBRARY' is not defined, that portion of the file -search will fail benignly. +`awk' program files. For the `-f' option, if the specified file name +has no device or directory path information in it, `gawk' looks in the +current directory first, then in the directory specified by the +translation of `AWK_LIBRARY' if the file is not found. If, after +searching in both directories, the file still is not found, `gawk' +appends the suffix `.awk' to the filename and retries the file search. +If `AWK_LIBRARY' is not defined, that portion of the file search fails +benignly.  File: gawk.info, Node: VMS Running, Next: VMS POSIX, Prev: VMS Installation Details, Up: VMS Installation Running `gawk' on VMS ---------------------- +..................... - Command line parsing and quoting conventions are significantly + Command-line parsing and quoting conventions are significantly different on VMS, so examples in this Info file or from other sources often need minor changes. They _are_ minor though, and all `awk' programs should run correctly. @@ -15834,168 +17409,122 @@ programs should run correctly. $ gawk -"W" version ! could also be -"W version" or "-W version" -Note that upper-case and mixed-case text must be quoted. +Note that uppercase and mixed-case text must be quoted. The VMS port of `gawk' includes a `DCL'-style interface in addition to the original shell-style interface (see the help entry for details). -One side-effect of dual command line parsing is that if there is only a +One side effect of dual command-line parsing is that if there is only a single parameter (as in the quoted string program above), the command becomes ambiguous. To work around this, the normally optional `--' flag is required to force Unix style rather than `DCL' parsing. If any -other dash-type options (or multiple parameters such as data files to be -processed) are present, there is no ambiguity and `--' can be omitted. +other dash-type options (or multiple parameters such as data files to +process) are present, there is no ambiguity and `--' can be omitted. - The default search path when looking for `awk' program files -specified by the `-f' option is `"SYS$DISK:[],AWK_LIBRARY:"'. The + The default search path, when looking for `awk' program files +specified by the `-f' option, is `"SYS$DISK:[],AWK_LIBRARY:"'. The logical name `AWKPATH' can be used to override this default. The format of `AWKPATH' is a comma-separated list of directory specifications. When defining it, the value should be quoted so that it retains a single -translation, and not a multi-translation `RMS' searchlist. +translation and not a multitranslation `RMS' searchlist.  File: gawk.info, Node: VMS POSIX, Prev: VMS Running, Up: VMS Installation Building and Using `gawk' on VMS POSIX --------------------------------------- +...................................... Ignore the instructions above, although `vms/gawk.hlp' should still be made available in a help library. The source tree should be unpacked -into a container file subsystem rather than into the ordinary VMS file -system. Make sure that the two scripts, `configure' and +into a container file subsystem rather than into the ordinary VMS +filesystem. Make sure that the two scripts, `configure' and `vms/posix-cc.sh', are executable; use `chmod +x' on them if necessary. Then execute the following two commands: psx> CC=vms/posix-cc.sh configure psx> make CC=c89 gawk -The first command will construct files `config.h' and `Makefile' out of +The first command constructs files `config.h' and `Makefile' out of templates, using a script to make the C compiler fit `configure''s -expectations. The second command will compile and link `gawk' using -the C compiler directly; ignore any warnings from `make' about being -unable to redefine `CC'. `configure' will take a very long time to -execute, but at least it provides incremental feedback as it runs. +expectations. The second command compiles and links `gawk' using the C +compiler directly; ignore any warnings from `make' about being unable +to redefine `CC'. `configure' takes a very long time to execute, but +at least it provides incremental feedback as it runs. This has been tested with VAX/VMS V6.2, VMS POSIX V2.0, and DEC C V5.2. - Once built, `gawk' will work like any other shell utility. Unlike -the normal VMS port of `gawk', no special command line manipulation is + Once built, `gawk' works like any other shell utility. Unlike the +normal VMS port of `gawk', no special command-line manipulation is needed in the VMS POSIX environment.  -File: gawk.info, Node: PC Installation, Next: Atari Installation, Prev: VMS Installation, Up: Installation - -MS-DOS and OS/2 Installation and Compilation -============================================ - - If you have received a binary distribution prepared by the DOS -maintainers, then `gawk' and the necessary support files will appear -under the `gnu' directory, with executables in `gnu/bin', libraries in -`gnu/lib/awk', and manual pages under `gnu/man'. This is designed for -easy installation to a `/gnu' directory on your drive, but the files -can be installed anywhere provided `AWKPATH' is set properly. -Regardless of the installation directory, the first line of `igawk.cmd' -and `igawk.bat' (in `gnu/bin') may need to be edited. - - The binary distribution will contain a separate file describing the -contents. In particular, it may include more than one version of the -`gawk' executable. OS/2 binary distributions may have a different -arrangement, but installation is similar. - - The OS/2 and MS-DOS versions of `gawk' search for program files as -described in *Note The `AWKPATH' Environment Variable: AWKPATH Variable. -However, semicolons (rather than colons) separate elements in the -`AWKPATH' variable. If `AWKPATH' is not set or is empty, then the -default search path is `".;c:/lib/awk;c:/gnu/lib/awk"'. - - An `sh'-like shell (as opposed to `command.com' under MS-DOS or -`cmd.exe' under OS/2) may be useful for `awk' programming. Ian -Stewartson has written an excellent shell for MS-DOS and OS/2, and a -`ksh' clone and GNU Bash are available for OS/2. The file -`README_d/README.pc' in the `gawk' distribution contains information on -these shells. Users of Stewartson's shell on DOS should examine its -documentation on handling of command-lines. In particular, the setting -for `gawk' in the shell configuration may need to be changed, and the -`ignoretype' option may also be of interest. +File: gawk.info, Node: Unsupported, Next: Bugs, Prev: Non-Unix Installation, Up: Installation - `gawk' can be compiled for MS-DOS and OS/2 using the GNU development -tools from DJ Delorie (DJGPP, MS-DOS-only) or Eberhard Mattes (EMX, -MS-DOS and OS/2). Microsoft C can be used to build 16-bit versions for -MS-DOS and OS/2. The file `README_d/README.pc' in the `gawk' -distribution contains additional notes, and `pc/Makefile' contains -important notes on compilation options. +Unsupported Operating System Ports +================================== - To build `gawk', copy the files in the `pc' directory (_except_ for -`ChangeLog') to the directory with the rest of the `gawk' sources. The -`Makefile' contains a configuration section with comments, and may need -to be edited in order to work with your `make' utility. + This sections describes systems for which the `gawk' port is no +longer supported. - The `Makefile' contains a number of targets for building various -MS-DOS and OS/2 versions. A list of targets will be printed if the -`make' command is given without a target. As an example, to build `gawk' -using the DJGPP tools, enter `make djgpp'. +* Menu: - Using `make' to run the standard tests and to install `gawk' -requires additional Unix-like tools, including `sh', `sed', and `cp'. -In order to run the tests, the `test/*.ok' files may need to be -converted so that they have the usual DOS-style end-of-line markers. -Most of the tests will work properly with Stewartson's shell along with -the companion utilities or appropriate GNU utilities. However, some -editing of `test/Makefile' is required. It is recommended that the file -`pc/Makefile.tst' be copied to `test/Makefile' as a replacement. -Details can be found in `README_d/README.pc'. +* Atari Installation:: Installing `gawk' on the Atari ST. +* Tandem Installation:: Installing `gawk' on a Tandem.  -File: gawk.info, Node: Atari Installation, Next: Amiga Installation, Prev: PC Installation, Up: Installation +File: gawk.info, Node: Atari Installation, Next: Tandem Installation, Prev: Unsupported, Up: Unsupported Installing `gawk' on the Atari ST -================================= +--------------------------------- + + The Atari port is no longer supported. It is included for those who +might want to use it but it is no longer being actively maintained. There are no substantial differences when installing `gawk' on various Atari models. Compiled `gawk' executables do not require a -large amount of memory with most `awk' programs and should run on all -Motorola processor based models (called further ST, even if that is not +large amount of memory with most `awk' programs, and should run on all +Motorola processor-based models (called further ST, even if that is not exactly right). In order to use `gawk', you need to have a shell, either text or graphics, that does not map all the characters of a command line to -upper-case. Maintaining case distinction in option flags is very -important (*note Command Line Options: Options.). These days this is -the default, and it may only be a problem for some very old machines. -If your system does not preserve the case of option flags, you will -need to upgrade your tools. Support for I/O redirection is necessary -to make it easy to import `awk' programs from other environments. -Pipes are nice to have, but not vital. +uppercase. Maintaining case distinction in option flags is very +important (*note Command-Line Options: Options.). These days this is +the default and it may only be a problem for some very old machines. +If your system does not preserve the case of option flags, you need to +upgrade your tools. Support for I/O redirection is necessary to make +it easy to import `awk' programs from other environments. Pipes are +nice to have but not vital. * Menu: -* Atari Compiling:: Compiling `gawk' on Atari -* Atari Using:: Running `gawk' on Atari +* Atari Compiling:: Compiling `gawk' on Atari. +* Atari Using:: Running `gawk' on Atari.  File: gawk.info, Node: Atari Compiling, Next: Atari Using, Prev: Atari Installation, Up: Atari Installation Compiling `gawk' on the Atari ST --------------------------------- +................................ A proper compilation of `gawk' sources when `sizeof(int)' differs -from `sizeof(void *)' requires an ANSI C compiler. An initial port was +from `sizeof(void *)' requires an ISO C compiler. An initial port was done with `gcc'. You may actually prefer executables where `int's are -four bytes wide, but the other variant works as well. +four bytes wide but the other variant works as well. You may need quite a bit of memory when trying to recompile the `gawk' sources, as some source files (`regex.c' in particular) are quite big. If you run out of memory compiling such a file, try reducing the -optimization level for this particular file; this may help. +optimization level for this particular file, which may help. - With a reasonable shell (Bash will do), and in particular if you run -Linux, MiNT or a similar operating system, you have a pretty good -chance that the `configure' utility will succeed. Otherwise sample -versions of `config.h' and `Makefile.st' are given in the `atari' -subdirectory and can be edited and copied to the corresponding files in -the main source directory. Even if `configure' produced something, it -might be advisable to compare its results with the sample versions and -possibly make adjustments. + With a reasonable shell (`bash' will do), you have a pretty good +chance that the `configure' utility will succeed, and in particular if +you run GNU/Linux, MiNT or a similar operating system. Otherwise +sample versions of `config.h' and `Makefile.st' are given in the +`atari' subdirectory and can be edited and copied to the corresponding +files in the main source directory. Even if `configure' produces +something, it might be advisable to compare its results with the sample +versions and possibly make adjustments. Some `gawk' source code fragments depend on a preprocessor define `atarist'. This basically assumes the TOS environment with `gcc'. @@ -16005,100 +17534,104 @@ environment. Also see the remarks about `AWKPATH' and `envsep' in As shipped, the sample `config.h' claims that the `system' function is missing from the libraries, which is not true, and an alternative -implementation of this function is provided in `atari/system.c'. -Depending upon your particular combination of shell and operating -system, you may wish to change the file to indicate that `system' is -available. +implementation of this function is provided in +`unsupported/atari/system.c'. Depending upon your particular +combination of shell and operating system, you might want to change the +file to indicate that `system' is available.  File: gawk.info, Node: Atari Using, Prev: Atari Compiling, Up: Atari Installation Running `gawk' on the Atari ST ------------------------------- +.............................. An executable version of `gawk' should be placed, as usual, anywhere in your `PATH' where your shell can find it. - While executing, `gawk' creates a number of temporary files. When -using `gcc' libraries for TOS, `gawk' looks for either of the -environment variables `TEMP' or `TMPDIR', in that order. If either one -is found, its value is assumed to be a directory for temporary files. -This directory must exist, and if you can spare the memory, it is a -good idea to put it on a RAM drive. If neither `TEMP' nor `TMPDIR' are -found, then `gawk' uses the current directory for its temporary files. - - The ST version of `gawk' searches for its program files as described -in *Note The `AWKPATH' Environment Variable: AWKPATH Variable. The -default value for the `AWKPATH' variable is taken from `DEFPATH' + While executing, the Atari version of `gawk' creates a number of +temporary files. When using `gcc' libraries for TOS, `gawk' looks for +either of the environment variables, `TEMP' or `TMPDIR', in that order. +If either one is found, its value is assumed to be a directory for +temporary files. This directory must exist, and if you can spare the +memory, it is a good idea to put it on a RAM drive. If neither `TEMP' +nor `TMPDIR' are found, then `gawk' uses the current directory for its +temporary files. + + The ST version of `gawk' searches for its program files, as +described in *Note The `AWKPATH' Environment Variable: AWKPATH Variable. +The default value for the `AWKPATH' variable is taken from `DEFPATH' defined in `Makefile'. The sample `gcc'/TOS `Makefile' for the ST in the distribution sets `DEFPATH' to `".,c:\lib\awk,c:\gnu\lib\awk"'. The search path can be modified by explicitly setting `AWKPATH' to -whatever you wish. Note that colons cannot be used on the ST to -separate elements in the `AWKPATH' variable, since they have another, -reserved, meaning. Instead, you must use a comma to separate elements +whatever you want. Note that colons cannot be used on the ST to +separate elements in the `AWKPATH' variable, since they have another +reserved meaning. Instead, you must use a comma to separate elements in the path. When recompiling, the separating character can be -modified by initializing the `envsep' variable in `atari/gawkmisc.atr' -to another value. +modified by initializing the `envsep' variable in +`unsupported/atari/gawkmisc.atr' to another value. Although `awk' allows great flexibility in doing I/O redirections from within a program, this facility should be used with care on the ST -running under TOS. In some circumstances the OS routines for file -handle pool processing lose track of certain events, causing the -computer to crash, and requiring a reboot. Often a warm reboot is -sufficient. Fortunately, this happens infrequently, and in rather +running under TOS. In some circumstances, the OS routines for +file-handle pool processing lose track of certain events, causing the +computer to crash and requiring a reboot. Often a warm reboot is +sufficient. Fortunately, this happens infrequently and in rather esoteric situations. In particular, avoid having one part of an `awk' program using `print' statements explicitly redirected to -`"/dev/stdout"', while other `print' statements use the default -standard output, and a calling shell has redirected standard output to -a file. +`/dev/stdout', while other `print' statements use the default standard +output, and a calling shell has redirected standard output to a file. When `gawk' is compiled with the ST version of `gcc' and its usual -libraries, it will accept both `/' and `\' as path separators. While -this is convenient, it should be remembered that this removes one, -technically valid, character (`/') from your file names, and that it -may create problems for external programs, called via the `system' -function, which may not support this convention. Whenever it is -possible that a file created by `gawk' will be used by some other -program, use only backslashes. Also remember that in `awk', -backslashes in strings have to be doubled in order to get literal -backslashes (*note Escape Sequences::). +libraries, it accepts both `/' and `\' as path separators. While this +is convenient, it should be remembered that this removes one +technically valid character (`/') from your file name. It may also +create problems for external programs called via the `system' function, +which may not support this convention. Whenever it is possible that a +file created by `gawk' will be used by some other program, use only +backslashes. Also remember that in `awk', backslashes in strings have +to be doubled in order to get literal backslashes (*note Escape +Sequences::).  -File: gawk.info, Node: Amiga Installation, Next: Bugs, Prev: Atari Installation, Up: Installation - -Installing `gawk' on an Amiga -============================= - - You can install `gawk' on an Amiga system using a Unix emulation -environment available via anonymous `ftp' from `ftp.ninemoons.com' in -the directory `pub/ade/current'. This includes a shell based on -`pdksh'. The primary component of this environment is a Unix emulation -library, `ixemul.lib'. - - A more complete distribution for the Amiga is available on the Geek -Gadgets CD-ROM from: - - CRONUS - 1840 E. Warner Road #105-265 - Tempe, AZ 85284 USA - US Toll Free: (800) 804-0833 - Phone: +1-602-491-0442 - FAX: +1-602-491-0048 - Email: `info@ninemoons.com' - WWW: `http://www.ninemoons.com' - Anonymous `ftp' site: `ftp.ninemoons.com' - - Once you have the distribution, you can configure `gawk' simply by -running `configure': +File: gawk.info, Node: Tandem Installation, Prev: Atari Installation, Up: Unsupported - configure -v m68k-amigaos +Installing `gawk' on a Tandem +----------------------------- - Then run `make', and you should be all set! (If these steps do not -work, please send in a bug report; *note Reporting Problems and Bugs: -Bugs..) + The Tandem port is only minimally supported. The port's contributor +no longer has access to a Tandem system. + + The Tandem port was done on a Cyclone machine running D20. The port +is pretty clean and all facilities seem to work except for the I/O +piping facilities (*note Using `getline' from a Pipe: Getline/Pipe., +*Note Using `getline' into a Variable from a Pipe: +Getline/Variable/Pipe, and *Note Redirecting Output of `print' and +`printf': Redirection), which is just too foreign a concept for Tandem. + + To build a Tandem executable from source, download all of the files +so that the file names on the Tandem box conform to the restrictions of +D20. For example, `array.c' becomes `ARRAYC', and `awk.h' becomes +`AWKH'. The totally Tandem-specific files are in the `tandem' +"subvolume" (`unsupported/tandem' in the `gawk' distribution) and +should be copied to the main source directory before building `gawk'. + + The file `compit' can then be used to compile and bind an executable. +Alas, there is no `configure' or `make'. + + Usage is the same as for Unix, except that D20 requires all `{' and +`}' characters to be escaped with `~' on the command line (but _not_ in +script files). Also, the standard Tandem syntax for `/in filename,out +filename/' must be used instead of the usual Unix `<' and `>' for file +redirection. (Redirection options on `getline', `print' etc., are +supported.) + + The `-mr VAL' option (*note Command-Line Options: Options.) has +been "stolen" to enable Tandem users to process fixed-length records +with no "end-of-line" character. That is, `-mr 74' tells `gawk' to read +the input file as fixed 74-byte records.  -File: gawk.info, Node: Bugs, Next: Other Versions, Prev: Amiga Installation, Up: Installation +File: gawk.info, Node: Bugs, Next: Other Versions, Prev: Unsupported, Up: Installation Reporting Problems and Bugs =========================== @@ -16106,8 +17639,6 @@ Reporting Problems and Bugs There is nothing more dangerous than a bored archeologist. The Hitchhiker's Guide to the Galaxy - - If you have problems with `gawk' or think that you have found a bug, please report it to the developers; we cannot promise to do anything but we might well want to fix it. @@ -16121,56 +17652,52 @@ documentation! Before reporting a bug or trying to fix it yourself, try to isolate it to the smallest possible `awk' program and input data file that reproduces the problem. Then send us the program and data file, some -idea of what kind of Unix system you're using, and the exact results -`gawk' gave you. Also say what you expected to occur; this will help -us decide whether the problem was really in the documentation. +idea of what kind of Unix system you're using, the compiler you used to +compile `gawk', and the exact results `gawk' gave you. Also say what +you expected to occur; this helps us decide whether the problem is +really in the documentation. Once you have a precise problem, send email to . Please include the version number of `gawk' you are using. You can get this information with the command `gawk --version'. Using this -address will automatically send a carbon copy of your mail to Arnold -Robbins. If necessary, he can be reached directly at . +address automatically sends a carbon copy of your mail to me. If +necessary, I can be reached directly at . The bug +reporting address is preferred since the email list is archived at the +GNU Project. _All email should be in English, since that is my native +language._ - *Important!* Do _not_ try to report bugs in `gawk' by posting to the + *Caution:* Do _not_ try to report bugs in `gawk' by posting to the Usenet/Internet newsgroup `comp.lang.awk'. While the `gawk' developers do occasionally read this newsgroup, there is no guarantee that we will -see your posting. The steps described above are the official, +see your posting. The steps described above are the official recognized ways for reporting bugs. Non-bug suggestions are always welcome as well. If you have questions about things that are unclear in the documentation or are -just obscure features, ask Arnold Robbins; he will try to help you out, -although he may not have the time to fix the problem. You can send him -electronic mail at the Internet address above. +just obscure features, ask me; I will try to help you out, although I +may not have the time to fix the problem. You can send me electronic +mail at the Internet address noted previously. If you find bugs in one of the non-Unix ports of `gawk', please send an electronic mail message to the person who maintains that port. They -are listed below, and also in the `README' file in the `gawk' -distribution. Information in the `README' file should be considered -authoritative if it conflicts with this Info file. - - The people maintaining the non-Unix ports of `gawk' are: - -MS-DOS - Scott Deifik, `scottd@amgen.com', and Darrel Hankerson, - `hankedr@mail.auburn.edu'. +are named in the following list, as well as in the `README' file in the +`gawk' distribution. Information in the `README' file should be +considered authoritative if it conflicts with this Info file. -OS/2 - Kai Uwe Rommel, `rommel@ars.de'. + The people maintaining the non-Unix ports of `gawk' are as follows: -VMS - Pat Rankin, `rankin@eql.caltech.edu'. +Amiga Fred Fish, . +BeOS Martin Brown, . +MS-DOS Scott Deifik, and Darrel + Hankerson, . +MS-Windows Juan Grigera, . +OS/2 Kai Uwe Rommel, . +Tandem Stephen Davies, . +VMS Pat Rankin, . -Atari ST - Michal Jaegermann, `michal@gortel.phys.ualberta.ca'. - -Amiga - Fred Fish, `fnf@ninemoons.com'. - - If your bug is also reproducible under Unix, please send copies of -your report to the general GNU bug list, as well as to Arnold Robbins, -at the addresses listed above. + If your bug is also reproducible under Unix, please send a copy of +your report to the email list as well.  File: gawk.info, Node: Other Versions, Prev: Bugs, Up: Installation @@ -16179,59 +17706,113 @@ Other Freely Available `awk' Implementations ============================================ It's kind of fun to put comments like this in your awk code. - `// Do C++ comments work? answer: yes! of course' + `// Do C++ comments work? answer: yes! of course' Michael Brennan + There are three other freely available `awk' implementations. This +minor node briefly describes where to get them: +Unix `awk' + Brian Kernighan has made his implementation of `awk' freely + available. You can retrieve this version via the World Wide Web + from his home page.(1) It is available in several archive formats: - There are two other freely available `awk' implementations. This -section briefly describes where to get them. + Shell archive + `http://cm.bell-labs.com/who/bwk/awk.shar' -Unix `awk' - Brian Kernighan has been able to make his implementation of `awk' - freely available. You can get it via anonymous `ftp' to the host - `netlib.bell-labs.com'. Change directory to `/netlib/research'. - Use "binary" or "image" mode, and retrieve `awk.bundle.gz'. + Compressed `tar' file + `http://cm.bell-labs.com/who/bwk/awk.tar.gz' - This is a shell archive that has been compressed with the GNU - `gzip' utility. It can be uncompressed with the `gunzip' utility. + Zip file + `http://cm.bell-labs.com/who/bwk/awk.zip' - You can also retrieve this version via the World Wide Web from his - home page (http://cm.bell-labs.com/who/bwk). + This version requires an ISO C (1990 standard) compiler; the C + compiler from GCC (the GNU Compiler Collection) works quite nicely. - This version requires an ANSI C compiler; GCC (the GNU C compiler) - works quite nicely. + *Note Extensions in the Bell Laboratories `awk': BTL, for a list + of extensions in this `awk' that are not in POSIX `awk'. `mawk' Michael Brennan has written an independent implementation of `awk', - called `mawk'. It is available under the GPL (*note GNU GENERAL - PUBLIC LICENSE: Copying.), just as `gawk' is. + called `mawk'. It is available under the GPL (*note GNU General + Public License: Copying.), just as `gawk' is. You can get it via anonymous `ftp' to the host `ftp.whidbey.net'. Change directory to `/pub/brennan'. Use "binary" or "image" mode, and retrieve `mawk1.3.3.tar.gz' (or the latest version that is there). - `gunzip' may be used to decompress this file. Installation is - similar to `gawk''s (*note Compiling and Installing `gawk' on - Unix: Unix Installation.). + `gunzip' may be used to decompress this file. Installation is + similar to `gawk''s (*note Compiling and Installing `gawk' on + Unix: Unix Installation.). + + `mawk' has the following extensions that are not in POSIX `awk': + + * The `fflush' built-in function for flushing buffered output + (*note Input/Output Functions: I/O Functions.). + + * The `**' and `**=' operators (*note Arithmetic Operators: + Arithmetic Ops. and also see *Note Assignment Expressions: + Assignment Ops). + + * The use of `func' as an abbreviation for `function' (*note + Function Definition Syntax: Definition Syntax.). + + * The `\x' escape sequence (*note Escape Sequences::). + + * The `/dev/stdout', and `/dev/stderr' special files (*note + Special File Names in `gawk': Special Files.). Use `"-"' + instead of `"/dev/stdin"' with `mawk'. + + * The ability for `FS' and for the third argument to `split' to + be null strings (*note Making Each Character a Separate + Field: Single Character Fields.). + + * The ability to delete all of an array at once with `delete + ARRAY' (*note The `delete' Statement: Delete.). + + * The ability for `RS' to be a regexp (*note How Input Is Split + into Records: Records.). + + * The `BINMODE' special variable for non-Unix operating systems + (*note Using `gawk' on PC Operating Systems: PC Using.). + + The next version of `mawk' will support `nextfile'. + +`awka' + Written by Andrew Sumner, `awka' translates `awk' programs into C, + compiles them, and links them with a library of functions that + provides the core `awk' functionality. It also has a number of + extensions. + + The `awk' translator is released under the GPL, and the library is + under the LGPL. + + To get `awka', go to `http://awka.sourceforge.net'. You can reach + Andrew Sumner at . + + ---------- Footnotes ---------- + + (1) `http://cm.bell-labs.com/who/bwk'  -File: gawk.info, Node: Notes, Next: Glossary, Prev: Installation, Up: Top +File: gawk.info, Node: Notes, Next: Basic Concepts, Prev: Installation, Up: Top Implementation Notes ******************** This appendix contains information mainly of interest to implementors and maintainers of `gawk'. Everything in it applies -specifically to `gawk', and not to other implementations. +specifically to `gawk' and not to other implementations. * Menu: -* Compatibility Mode:: How to disable certain `gawk' extensions. +* Compatibility Mode:: How to disable certain `gawk' + extensions. * Additions:: Making Additions To `gawk'. +* Dynamic Extensions:: Adding new built-in functions to + `gawk'. * Future Extensions:: New features that may be implemented one day. -* Improvements:: Suggestions for improvements by volunteers.  File: gawk.info, Node: Compatibility Mode, Next: Additions, Prev: Notes, Up: Notes @@ -16242,7 +17823,7 @@ Downward Compatibility and Debugging *Note Extensions in `gawk' Not in POSIX `awk': POSIX/GNU, for a summary of the GNU extensions to the `awk' language and program. All of these features can be turned off by invoking `gawk' with the -`--traditional' option, or with the `--posix' option. +`--traditional' option or with the `--posix' option. If `gawk' is compiled for debugging with `-DDEBUG', then there is one more option available on the command line: @@ -16252,28 +17833,30 @@ one more option available on the command line: Print out the parse stack information as the program is being parsed. - This option is intended only for serious `gawk' developers, and not + This option is intended only for serious `gawk' developers and not for the casual user. It probably has not even been compiled into your version of `gawk', since it slows down execution.  -File: gawk.info, Node: Additions, Next: Future Extensions, Prev: Compatibility Mode, Up: Notes +File: gawk.info, Node: Additions, Next: Dynamic Extensions, Prev: Compatibility Mode, Up: Notes Making Additions to `gawk' ========================== - If you should find that you wish to enhance `gawk' in a significant + If you find that you want to enhance `gawk' in a significant fashion, you are perfectly free to do so. That is the point of having -free software; the source code is available, and you are free to change -it as you wish (*note GNU GENERAL PUBLIC LICENSE: Copying.). +free software; the source code is available and you are free to change +it as you want (*note GNU General Public License: Copying.). - This section discusses the ways you might wish to change `gawk', and -any considerations you should bear in mind. + This minor node discusses the ways you might want to change `gawk' +as well as any considerations you should bear in mind. * Menu: -* Adding Code:: Adding code to the main body of `gawk'. -* New Ports:: Porting `gawk' to a new operating system. +* Adding Code:: Adding code to the main body of + `gawk'. +* New Ports:: Porting `gawk' to a new operating + system.  File: gawk.info, Node: Adding Code, Next: New Ports, Prev: Additions, Up: Additions @@ -16284,28 +17867,35 @@ Adding New Features You are free to add any new features you like to `gawk'. However, if you want your changes to be incorporated into the `gawk' distribution, there are several steps that you need to take in order to -make it possible for me to include your changes. +make it possible for me to include your changes: + + 1. Before building the new feature into `gawk' itself, consider + writing it as an extension module (*note Adding New Built-in + Functions to `gawk': Dynamic Extensions.). If that's not + possible, continue with the rest of the steps in this list. - 1. Get the latest version. It is much easier for me to integrate + 2. Get the latest version. It is much easier for me to integrate changes if they are relative to the most recent distributed version of `gawk'. If your version of `gawk' is very old, I may - not be able to integrate them at all. *Note Getting the `gawk' + not be able to integrate them at all. (*Note Getting the `gawk' Distribution: Getting, for information on getting the latest - version of `gawk'. + version of `gawk'.) - 2. See *note (Version)Top:: standards, GNU Coding Standards. This + 3. See *note (Version)Top:: standards, GNU Coding Standards. This document describes how GNU software should be written. If you haven't read it, please do so, preferably _before_ starting to - modify `gawk'. (The `GNU Coding Standards' are available as part - of the Autoconf distribution, from the FSF.) + modify `gawk'. (The `GNU Coding Standards' are available from the + GNU Project's `ftp' site, at + `ftp://gnudist.gnu.org/gnu/GNUInfo/standards.text'. Texinfo, + Info, and DVI versions are also available.) - 3. Use the `gawk' coding style. The C code for `gawk' follows the + 4. Use the `gawk' coding style. The C code for `gawk' follows the instructions in the `GNU Coding Standards', with minor exceptions. The code is formatted using the traditional "K&R" style, - particularly as regards the placement of braces and the use of - tabs. In brief, the coding rules for `gawk' are: + particularly as regards to the placement of braces and the use of + tabs. In brief, the coding rules for `gawk' are as follows: - * Use old style (non-prototype) function headers when defining + * Use ANSI/ISO style (prototype) function headers when defining functions. * Put the name of the function at the beginning of its own line. @@ -16314,34 +17904,35 @@ make it possible for me to include your changes. the line above the line with the name and arguments of the function. - * The declarations for the function arguments should not be - indented. - * Put spaces around parentheses used in control structures - (`if', `while', `for', `do', `switch' and `return'). + (`if', `while', `for', `do', `switch', and `return'). * Do not put spaces in front of parentheses used in function calls. - * Put spaces around all C operators, and after commas in + * Put spaces around all C operators and after commas in function calls. - * Do not use the comma operator to produce multiple - side-effects, except in `for' loop initialization and - increment parts, and in macro bodies. + * Do not use the comma operator to produce multiple side + effects, except in `for' loop initialization and increment + parts, and in macro bodies. * Use real tabs for indenting, not spaces. * Use the "K&R" brace layout style. * Use comparisons against `NULL' and `'\0'' in the conditions of - `if', `while' and `for' statements, and in the `case's of - `switch' statements, instead of just the plain pointer or + `if', `while', and `for' statements, as well as in the `case's + of `switch' statements, instead of just the plain pointer or character value. - * Use the `TRUE', `FALSE', and `NULL' symbolic constants, and - the character constant `'\0'' where appropriate, instead of - `1' and `0'. + * Use the `TRUE', `FALSE' and `NULL' symbolic constants and the + character constant `'\0'' where appropriate, instead of `1' + and `0'. + + * Use the `ISALPHA', `ISDIGIT', etc. macros, instead of the + traditional lowercase versions; these macros are better + behaved for non-ASCII character sets. * Provide one-line descriptive comments for each function. @@ -16349,54 +17940,54 @@ make it possible for me to include your changes. it. * Do not use the `alloca' function for allocating memory off - the stack. Its use causes more portability trouble than the - minor benefit of not having to free the storage. Instead, use - `malloc' and `free'. + the stack. Its use causes more portability trouble than is + worth the minor benefit of not having to free the storage. + Instead, use `malloc' and `free'. - If I have to reformat your code to follow the coding style used in - `gawk', I may not bother. + *Note:* If I have to reformat your code to follow the coding style + used in `gawk', I may not bother to integrate your changes at all. - 4. Be prepared to sign the appropriate paperwork. In order for the + 5. Be prepared to sign the appropriate paperwork. In order for the FSF to distribute your changes, you must either place those - changes in the public domain, and submit a signed statement to that + changes in the public domain and submit a signed statement to that effect, or assign the copyright in your changes to the FSF. Both - of these actions are easy to do, and _many_ people have done so + of these actions are easy to do and _many_ people have done so already. If you have questions, please contact me (*note Reporting - Problems and Bugs: Bugs.), or `gnu@gnu.org'. + Problems and Bugs: Bugs.), or . - 5. Update the documentation. Along with your new code, please supply - new sections and or chapters for this Info file. If at all + 6. Update the documentation. Along with your new code, please supply + new sections and/or chapters for this Info file. If at all possible, please use real Texinfo, instead of just supplying unformatted ASCII text (although even that is better than no - documentation at all). Conventions to be followed in `Effective - AWK Programming' are provided after the `@bye' at the end of the - Texinfo source file. If possible, please update the man page as - well. + documentation at all). Conventions to be followed in `GAWK: + Effective AWK Programming' are provided after the `@bye' at the + end of the Texinfo source file. If possible, please update the + `man' page as well. You will also have to sign paperwork for your documentation changes. - 6. Submit changes as context diffs or unified diffs. Use `diff -c -r + 7. Submit changes as context diffs or unified diffs. Use `diff -c -r -N' or `diff -u -r -N' to compare the original `gawk' source tree - with your version. (I find context diffs to be more readable, but + with your version. (I find context diffs to be more readable but unified diffs are more compact.) I recommend using the GNU version of `diff'. Send the output produced by either run of - `diff' to me when you submit your changes. *Note Reporting - Problems and Bugs: Bugs, for the electronic mail information. + `diff' to me when you submit your changes. (*Note Reporting + Problems and Bugs: Bugs, for the electronic mail information.) Using this format makes it easy for me to apply your changes to the master version of the `gawk' source code (using `patch'). If I have to apply the changes manually, using a text editor, I may not do so, particularly if there are lots of changes. - 7. Include an entry for the `ChangeLog' file with your submission. - This further helps minimize the amount of work I have to do, + 8. Include an entry for the `ChangeLog' file with your submission. + This helps further minimize the amount of work I have to do, making it easier for me to accept patches. Although this sounds like a lot of work, please remember that while -you may write the new code, I have to maintain it and support it, and -if it isn't possible for me to do that with a minimum of extra work, -then I probably will not. +you may write the new code, I have to maintain it and support it. If it +isn't possible for me to do that with a minimum of extra work, then I +probably will not.  File: gawk.info, Node: New Ports, Prev: Adding Code, Up: Additions @@ -16404,37 +17995,37 @@ File: gawk.info, Node: New Ports, Prev: Adding Code, Up: Additions Porting `gawk' to a New Operating System ---------------------------------------- - If you wish to port `gawk' to a new operating system, there are -several steps to follow. + If you want to port `gawk' to a new operating system, there are +several steps to follow: 1. Follow the guidelines in *Note Adding New Features: Adding Code, concerning coding style, submission of diffs, and so on. 2. When doing a port, bear in mind that your code must co-exist - peacefully with the rest of `gawk', and the other ports. Avoid + peacefully with the rest of `gawk' and the other ports. Avoid gratuitous changes to the system-independent parts of the code. If at all possible, avoid sprinkling `#ifdef's just for your port throughout the code. If the changes needed for a particular system affect too much of the code, I probably will not accept them. In such a case, you - will, of course, be able to distribute your changes on your own, - as long as you comply with the GPL (*note GNU GENERAL PUBLIC - LICENSE: Copying.). + can, of course, distribute your changes on your own, as long as + you comply with the GPL (*note GNU General Public License: + Copying.). 3. A number of the files that come with `gawk' are maintained by other people at the Free Software Foundation. Thus, you should not - change them unless it is for a very good reason. I.e. changes are - not out of the question, but changes to these files will be - scrutinized extra carefully. The files are `alloca.c', - `getopt.h', `getopt.c', `getopt1.c', `regex.h', `regex.c', `dfa.h', - `dfa.c', `install-sh', and `mkinstalldirs'. + change them unless it is for a very good reason; i.e., changes are + not out of the question, but changes to these files are + scrutinized extra carefully. The files are `getopt.h', `getopt.c', + `getopt1.c', `regex.h', `regex.c', `dfa.h', `dfa.c', `install-sh', + and `mkinstalldirs'. 4. Be willing to continue to maintain the port. Non-Unix operating systems are supported by volunteers who maintain the code needed - to compile and run `gawk' on their systems. If no-one volunteers - to maintain a port, that port becomes unsupported, and it may be - necessary to remove it from the distribution. + to compile and run `gawk' on their systems. If noone volunteers to + maintain a port, it becomes unsupported and it may be necessary to + remove it from the distribution. 5. Supply an appropriate `gawkmisc.???' file. Each port has its own `gawkmisc.???' that implements certain operating system specific @@ -16444,120 +18035,690 @@ several steps to follow. subdirectory. Be sure to update it as well. Each port's `gawkmisc.???' file has a suffix reminiscent of the - machine or operating system for the port. For example, + machine or operating system for the port--for example, `pc/gawkmisc.pc' and `vms/gawkmisc.vms'. The use of separate suffixes, instead of plain `gawkmisc.c', makes it possible to move files from a port's subdirectory into the main subdirectory, without accidentally destroying the real `gawkmisc.c' file. - (Currently, this is only an issue for the MS-DOS and OS/2 ports.) - - 6. Supply a `Makefile' and any other C source and header files that - are necessary for your operating system. All your code should be - in a separate subdirectory, with a name that is the same as, or - reminiscent of, either your operating system or the computer - system. If possible, try to structure things so that it is not - necessary to move files out of the subdirectory into the main - source directory. If that is not possible, then be sure to avoid - using names for your files that duplicate the names of files in - the main source directory. + (Currently, this is only an issue for the PC operating system + ports.) + + 6. Supply a `Makefile' as well as any other C source and header files + that are necessary for your operating system. All your code + should be in a separate subdirectory, with a name that is the same + as, or reminiscent of, either your operating system or the + computer system. If possible, try to structure things so that it + is not necessary to move files out of the subdirectory into the + main source directory. If that is not possible, then be sure to + avoid using names for your files that duplicate the names of files + in the main source directory. 7. Update the documentation. Please write a section (or sections) for this Info file describing the installation and compilation - steps needed to install and/or compile `gawk' for your system. + steps needed to compile and/or install `gawk' for your system. 8. Be prepared to sign the appropriate paperwork. In order for the FSF to distribute your code, you must either place your code in - the public domain, and submit a signed statement to that effect, - or assign the copyright in your code to the FSF. Both of these - actions are easy to do, and _many_ people have done so already. If - you have questions, please contact me, or `gnu@gnu.org'. + the public domain and submit a signed statement to that effect, or + assign the copyright in your code to the FSF. Both of these + actions are easy to do and _many_ people have done so already. If + you have questions, please contact me, or . + + Following these steps makes it much easier to integrate your changes +into `gawk' and have them co-exist happily with other operating +systems' code that is already there. + + In the code that you supply and maintain, feel free to use a coding +style and brace layout that suits your taste. + + +File: gawk.info, Node: Dynamic Extensions, Next: Future Extensions, Prev: Additions, Up: Notes + +Adding New Built-in Functions to `gawk' +======================================= + + Danger Will Robinson! Danger!! + Warning! Warning! + The Robot + + Beginning with `gawk' 3.1, it is possible to add new built-in +functions to `gawk' using dynamically loaded libraries. This facility +is available on systems (such as GNU/Linux) that support the `dlopen' +and `dlsym' functions. This minor node describes how to write and use +dynamically loaded extentions for `gawk'. Experience with programming +in C or C++ is necessary when reading this minor node. + + *Caution:* The facilities described in this minor node are very much +subject to change in the next `gawk' release. Be aware that you may +have to re-do everything, perhaps from scratch, upon the next release. + +* Menu: + +* Internals:: A brief look at some `gawk' internals. +* Sample Library:: A example of new functions. + + +File: gawk.info, Node: Internals, Next: Sample Library, Prev: Dynamic Extensions, Up: Dynamic Extensions + +A Minimal Introduction to `gawk' Internals +------------------------------------------ + + The truth is that `gawk' was not designed for simple extensibility. +The facilities for adding functions using shared libraries work, but +are something of a "bag on the side." Thus, this tour is brief and +simplistic; would-be `gawk' hackers are encouraged to spend some time +reading the source code before trying to write extensions based on the +material presented here. Of particular note are the files `awk.h', +`builtin.c', and `eval.c'. Reading `awk.y' in order to see how the +parse tree is built would also be of use. + + With the disclaimers out of the way, the following types, structure +members, functions, and macros are declared in `awk.h' and are of use +when writing extensions. The next minor node shows how they are used: + +`AWKNUM' + An `AWKNUM' is the internal type of `awk' floating-point numbers. + Typically, it is a C `double'. + +`NODE' + Just about everything is done using objects of type `NODE'. These + contain both strings and numbers, as well as variables and arrays. + +`AWKNUM force_number(NODE *n)' + This macro forces a value to be numeric. It returns the actual + numeric value contained in the node. It may end up calling an + internal `gawk' function. + +`void force_string(NODE *n)' + This macro guarantees that a `NODE''s string value is current. It + may end up calling an internal `gawk' function. It also + guarantees that the string is zero-terminated. + +`n->param_cnt' + The number of parameters actually passed in a function call at + runtime. + +`n->stptr' +`n->stlen' + The data and length of a `NODE''s string value, respectively. The + string is _not_ guaranteed to be zero-terminated. If you need to + pass the string value to a C library function, save the value in + `n->stptr[n->stlen]', assign `'\0'' to it, call the routine, and + then restore the value. + +`n->type' + The type of the `NODE'. This is a C `enum'. Values should be + either `Node_var' or `Node_var_array' for function parameters. + +`n->vname' + The "variable name" of a node. This is not of much use inside + externally written extensions. + +`void assoc_clear(NODE *n)' + Clears the associative array pointed to by `n'. Make sure that + `n->type == Node_var_array' first. + +`NODE **assoc_lookup(NODE *symbol, NODE *subs, int reference)' + Finds, and installs if necessary, array elements. `symbol' is the + array, `subs' is the subscript. This is usually a value created + with `tmp_string' (see below). `reference' should be `TRUE' if it + is an error to use the value before it is created. Typically, + `FALSE' is the correct value to use from extension functions. + +`NODE *make_string(char *s, size_t len)' + Take a C string and turn it into a pointer to a `NODE' that can be + stored appropriately. This is permanent storage; understanding of + `gawk' memory management is helpful. + +`NODE *make_number(AWKNUM val)' + Take an `AWKNUM' and turn it into a pointer to a `NODE' that can + be stored appropriately. This is permanent storage; understanding + of `gawk' memory management is helpful. + +`NODE *tmp_string(char *s, size_t len);' + Take a C string and turn it into a pointer to a `NODE' that can be + stored appropriately. This is temporary storage; understanding of + `gawk' memory management is helpful. + +`NODE *tmp_number(AWKNUM val)' + Take an `AWKNUM' and turn it into a pointer to a `NODE' that can + be stored appropriately. This is temporary storage; understanding + of `gawk' memory management is helpful. + +`NODE *dupnode(NODE *n)' + Duplicate a node. In most cases, this increments an internal + reference count instead of actually duplicating the entire `NODE'; + understanding of `gawk' memory management is helpful. + +`void free_temp(NODE *n)' + This macro releases the memory associated with a `NODE' allocated + with `tmp_string' or `tmp_number'. Understanding of `gawk' memory + management is helpful. + +`void make_builtin(char *name, NODE *(*func)(NODE *), int count)' + Register a C function pointed to by `func' as new built-in + function `name'. `name' is a regular C string. `count' is the + maximum number of arguments that the function takes. The function + should be written in the following manner: + + /* do_xxx --- do xxx function for gawk */ + + NODE * + do_xxx(NODE *tree) + { + ... + } + +`NODE *get_argument(NODE *tree, int i)' + This function is called from within a C extension function to get + the `i''th argument from the function call. The first argument is + argument zero. + +`void set_value(NODE *tree)' + This function is called from within a C extension function to set + the return value from the extension function. This value is what + the `awk' program sees as the return value from the new `awk' + function. + +`void update_ERRNO(void)' + This function is called from within a C extension function to set + the value of `gawk''s `ERRNO' variable, based on the current value + of the C `errno' variable. It is provided as a convenience. + + An argument that is supposed to be an array needs to be handled with +some extra code, in case the array being passed in is actually from a +function parameter. The following "boiler plate" code shows how to do +this: + + NODE *the_arg; + + the_arg = get_argument(tree, 2); /* assume need 3rd arg, 0-based */ + + /* if a parameter, get it off the stack */ + if (the_arg->type == Node_param_list) + the_arg = stack_ptr[the_arg->param_cnt]; + + /* parameter referenced an array, get it */ + if (the_arg->type == Node_array_ref) + the_arg = the_arg->orig_array; + + /* check type */ + if (the_arg->type != Node_var && the_arg->type != Node_var_array) + fatal("newfunc: third argument is not an array"); + + /* force it to be an array, if necessary, clear it */ + the_arg->type = Node_var_array; + assoc_clear(the_arg); + + Again, you should spend time studying the `gawk' internals; don't +just blindly copy this code. + + +File: gawk.info, Node: Sample Library, Prev: Internals, Up: Dynamic Extensions + +Directory and File Operation Built-ins +-------------------------------------- + + Two useful functions that are not in `awk' are `chdir' (so that an +`awk' program can change its directory) and `stat' (so that an `awk' +program can gather information about a file). This minor node +implements these functions for `gawk' in an external extension library. + +* Menu: + +* Internal File Description:: What the new functions will do. +* Internal File Ops:: The code for internal file operations. +* Using Internal File Ops:: How to use an external extension. + + +File: gawk.info, Node: Internal File Description, Next: Internal File Ops, Prev: Sample Library, Up: Sample Library + +Using `chdir' and `stat' +........................ + + This minor node shows how to use the new functions at the `awk' +level once they've been integrated into the running `gawk' interpreter. +Using `chdir' is very straightforward. It takes one argument, the new +directory to change to: + + ... + newdir = "/home/arnold/funstuff" + ret = chdir(newdir) + if (ret < 0) { + printf("could not change to %s: %s\n", + newdir, ERRNO) > "/dev/stderr" + exit 1 + } + ... + + The return value is negative if the `chdir' failed, and `ERRNO' +(*note Built-in Variables::) is set to a string indicating the error. + + Using `stat' is a bit more complicated. The C `stat' function fills +in a structure that has a fair amount of information. The right way to +model this in `awk' is to fill in an associative array with the +appropriate information: + + file = "/home/arnold/.profile" + fdata[1] = "x" # force `fdata' to be an array + ret = stat(file, fdata) + if (ret < 0) { + printf("could not stat %s: %s\n", + file, ERRNO) > "/dev/stderr" + exit 1 + } + printf("size of %s is %d bytes\n", file, fdata["size"]) + + The `stat' function always clears the data array, even if the `stat' +fails. It fills in the following elements: + +`"name"' + The name of the file that was `stat''ed. + +`"dev"' +`"ino"' + The file's device and inode numbers, respectively. + +`"mode"' + The file's mode, as a numeric value. This includes both the file's + type and its permissions. + +`"nlink"' + The number of hard links (directory entries) the file has. + +`"uid"' +`"gid"' + The numeric user and group ID numbers of the file's owner. + +`"size"' + The size in bytes of the file. + +`"blocks"' + The number of disk blocks the file actually occupies. This may not + be a function of the file's size if the file has holes. + +`"atime"' +`"mtime"' +`"ctime"' + The file's last access, modification, and inode update times, + respectively. These are numeric timestamps, suitable for + formatting with `strftime' (*note Built-in Functions: Built-in.). + +`"pmode"' + The file's "printable mode." This is a string representation of + the file's type and permissions, such as what is produced by `ls + -l'--for example, `"drwxr-xr-x"'. + +`"type"' + A printable string representation of the file's type. The value + is one of the following: + + `"blockdev"' + `"chardev"' + The file is a block or character device ("special file"). + + `"directory"' + The file is a directory. + + `"fifo"' + The file is a named-pipe (also known as a FIFO). + + `"file"' + The file is just a regular file. + + `"socket"' + The file is an `AF_UNIX' ("Unix domain") socket in the + filesystem. + + `"symlink"' + The file is a symbolic link. + + Several additional elements may be present depending upon the +operating system and the type of the file. You can test for them in +your `awk' program by using the `in' operator (*note Referring to an +Array Element: Reference to Elements.): + +`"blksize"' + The preferred block size for I/O to the file. This field is not + present on all POSIX-like systems in the C `stat' structure. + +`"linkval"' + If the file is a symbolic link, this element is the name of the + file the link points to (i.e., the value of the link). + +`"rdev"' +`"major"' +`"minor"' + If the file is a block or character device file, then these values + represent the numeric device number and the major and minor + components of that number, respectively. + + +File: gawk.info, Node: Internal File Ops, Next: Using Internal File Ops, Prev: Internal File Description, Up: Sample Library + +C Code for `chdir' and `stat' +............................. + + Here is the C code for these extensions. They were written for +GNU/Linux. The code needs some more work for complete portability to +other POSIX-compliant systems:(1) + + #include "awk.h" + + #include + + /* do_chdir --- provide dynamically loaded + chdir() builtin for gawk */ + + static NODE * + do_chdir(tree) + NODE *tree; + { + NODE *newdir; + int ret = -1; + + newdir = get_argument(tree, 0); + + The file includes the `"awk.h"' header file for definitions for the +`gawk' internals. It includes `' for access to the +`major' and `minor' macros. + + By convention, for an `awk' function `foo', the function that +implements it is called `do_foo'. The function should take a `NODE *' +argument, usually called `tree', that represents the argument list to +the function. The `newdir' variable represents the new directory to +change to, retrieved with `get_argument'. Note that the first argument +is numbered zero. + + This code actually accomplishes the `chdir'. It first forces the +argument to be a string and passes the string value to the `chdir' +system call. If the `chdir' fails, `ERRNO' is updated. The result of +`force_string' has to be freed with `free_temp': + + if (newdir != NULL) { + (void) force_string(newdir); + ret = chdir(newdir->stptr); + if (ret < 0) + update_ERRNO(); + + free_temp(newdir); + } + + Finally, the function returns the return value to the `awk' level, +using `set_value'. Then it must return a value from the call to the new +built-in (this value ignored by the interpreter): + + /* Set the return value */ + set_value(tmp_number((AWKNUM) ret)); + + /* Just to make the interpreter happy */ + return tmp_number((AWKNUM) 0); + } + + The `stat' built-in is more involved. First comes a function that +turns a numeric mode into a printable representation (e.g., 644 becomes +`-rw-r--r--'). This is omitted here for brevity: + + /* format_mode --- turn a stat mode field + into something readable */ + + static char * + format_mode(fmode) + unsigned long fmode; + { + ... + } + + Next comes the actual `do_stat' function itself. First come the +variable declarations and argument checking: + + /* do_stat --- provide a stat() function for gawk */ + + static NODE * + do_stat(tree) + NODE *tree; + { + NODE *file, *array; + struct stat sbuf; + int ret; + char *msg; + NODE **aptr; + char *pmode; /* printable mode */ + char *type = "unknown"; + + /* check arg count */ + if (tree->param_cnt != 2) + fatal( + "stat: called with %d arguments, should be 2", + tree->param_cnt); + + Then comes the actual work. First, we get the arguments. Then, we +always clear the array. To get the file information, we use `lstat', +in case the file is a symbolic link. If there's an error, we set +`ERRNO' and return: + + /* + * directory is first arg, + * array to hold results is second + */ + file = get_argument(tree, 0); + array = get_argument(tree, 1); + + /* empty out the array */ + assoc_clear(array); + + /* lstat the file, if error, set ERRNO and return */ + (void) force_string(file); + ret = lstat(file->stptr, & sbuf); + if (ret < 0) { + update_ERRNO(); + + set_value(tmp_number((AWKNUM) ret)); + + free_temp(file); + return tmp_number((AWKNUM) 0); + } + + Now comes the tedious part: filling in the array. Only a few of the +calls are shown here, since they all follow the same pattern: + + /* fill in the array */ + aptr = assoc_lookup(array, tmp_string("name", 4), FALSE); + *aptr = dupnode(file); + + aptr = assoc_lookup(array, tmp_string("mode", 4), FALSE); + *aptr = make_number((AWKNUM) sbuf.st_mode); + + aptr = assoc_lookup(array, tmp_string("pmode", 5), FALSE); + pmode = format_mode(sbuf.st_mode); + *aptr = make_string(pmode, strlen(pmode)); + + When done, we free the temporary value containing the file name, set +the return value, and return: + + free_temp(file); + + /* Set the return value */ + set_value(tmp_number((AWKNUM) ret)); + + /* Just to make the interpreter happy */ + return tmp_number((AWKNUM) 0); + } + + Finally, it's necessary to provide the "glue" that loads the new +function(s) into `gawk'. By convention, each library has a routine +named `dlload' that does the job: + + /* dlload --- load new builtins in this library */ + + NODE * + dlload(tree, dl) + NODE *tree; + void *dl; + { + make_builtin("chdir", do_chdir, 1); + make_builtin("stat", do_stat, 2); + return tmp_number((AWKNUM) 0); + } + + And that's it! As an exercise, consider adding functions to +implement system calls such as `chown', `chmod', and `umask'. - Following these steps will make it much easier to integrate your -changes into `gawk', and have them co-exist happily with the code for -other operating systems that is already there. + ---------- Footnotes ---------- + + (1) This version is edited slightly for presentation. The complete +version can be found in `extension/filefuncs.c' in the `gawk' +distribution. + + +File: gawk.info, Node: Using Internal File Ops, Prev: Internal File Ops, Up: Sample Library + +Integrating the Extensions +.......................... + + Now that the code is written, it must be possible to add it at +runtime to the running `gawk' interpreter. First, the code must be +compiled. Assuming that the functions are in a file named +`filefuncs.c', and IDIR is the location of the `gawk' include files, +the following steps create a GNU/Linux shared library: + + $ gcc -shared -DHAVE_CONFIG_H -c -O -g -IIDIR filefuncs.c + $ ld -o filefuncs.so -shared filefuncs.o + + Once the library exists, it is loaded by calling the `extension' +built-in function. This function takes two arguments: the name of the +library to load and the name of a function to call when the library is +first loaded. This function adds the new functions to `gawk'. It +returns the value returned by the initialization function within the +shared library: - In the code that you supply, and that you maintain, feel free to use -a coding style and brace layout that suits your taste. + # file testff.awk + BEGIN { + extension("./filefuncs.so", "dlload") + + chdir(".") # no-op + + data[1] = 1 # force `data' to be an array + print "Info for testff.awk" + ret = stat("testff.awk", data) + print "ret =", ret + for (i in data) + printf "data[\"%s\"] = %s\n", i, data[i] + print "testff.awk modified:", + strftime("%m %d %y %H:%M:%S", data["mtime"]) + } + + Here are the results of running the program: + + $ gawk -f testff.awk + -| Info for testff.awk + -| ret = 0 + -| data["blksize"] = 4096 + -| data["mtime"] = 932361936 + -| data["mode"] = 33188 + -| data["type"] = file + -| data["dev"] = 2065 + -| data["gid"] = 10 + -| data["ino"] = 878597 + -| data["ctime"] = 971431797 + -| data["blocks"] = 2 + -| data["nlink"] = 1 + -| data["name"] = testff.awk + -| data["atime"] = 971608519 + -| data["pmode"] = -rw-r--r-- + -| data["size"] = 607 + -| data["uid"] = 2076 + -| testff.awk modified: 07 19 99 08:25:36  -File: gawk.info, Node: Future Extensions, Next: Improvements, Prev: Additions, Up: Notes +File: gawk.info, Node: Future Extensions, Prev: Dynamic Extensions, Up: Notes Probable Future Extensions ========================== AWK is a language similar to PERL, only considerably more elegant. Arnold Robbins - + Hey! Larry Wall + This minor node briefly lists extensions and possible improvements +that indicate the directions we are currently considering for `gawk'. +The file `FUTURES' in the `gawk' distribution lists these extensions as +well. + Following is a list of probable future changes visible at the `awk' +language level: - This section briefly lists extensions and possible improvements that -indicate the directions we are currently considering for `gawk'. The -file `FUTURES' in the `gawk' distributions lists these extensions as -well. +Loadable Module Interface + It is not clear that the `awk'-level interface to the modules + facility is as good as it should be. The interface needs to be + redesigned, particularly taking namespace issues into account, as + well as possibly including issues such as library search path order + and versioning. - This is a list of probable future changes that will be usable by the -`awk' language programmer. +`RECLEN' variable for fixed length records + Along with `FIELDWIDTHS', this would speed up the processing of + fixed-length records. `PROCINFO["RS"]' would be `"RS"' or + `"RECLEN"', depending upon which kind of record processing is in + effect. -Localization - The GNU project is starting to support multiple languages. It - will at least be possible to make `gawk' print its warnings and - error messages in languages other than English. It may be - possible for `awk' programs to also use the multiple language - facilities, separate from `gawk' itself. +Additional `printf' specifiers + The 1999 ISO C standard added a number of additional `printf' + format specifiers. These should be evaluated for possible + inclusion in `gawk'. Databases It may be possible to map a GDBM/NDBM/SDBM file into an `awk' array. -A `PROCINFO' Array - The special files that provide process-related information (*note - Special File Names in `gawk': Special Files.) will be superseded - by a `PROCINFO' array that would provide the same information, in - an easier to access fashion. +Large Character Sets + It would be nice if `gawk' could handle UTF-8 and other character + sets that are larger than eight bits. More `lint' warnings There are more things that could be checked for portability. -Control of subprocess environment - Changes made in `gawk' to the array `ENVIRON' may be propagated to - subprocesses run by `gawk'. + Following is a list of probable improvements that will make `gawk''s +source code easier to work with: + +Loadable Module Mechanics + The current extension mechanism works (*note Adding New Built-in + Functions to `gawk': Dynamic Extensions.), but is rather + primitive. It requires a fair amount of manual work to create and + integrate a loadable module. Nor is the current mechanism as + portable as might be desired. The GNU `libtool' package provides + a number of features that would make using loadable modules much + easier. `gawk' should be changed to use `libtool'. + +Loadable Module Internals + The API to its internals that `gawk' "exports" should be revised. + Too many things are needlessly exposed. A new API should be + designed and implemented to make module writing easier. - This is a list of probable improvements that will make `gawk' -perform better. +Better Array Subscript Management + `gawk''s management of array subscript storage could use revamping, + so that using the same value to index multiple arrays only stores + one copy of the index value. + +Integrating the DBUG Library + Integrating Fred Fish's DBUG library would be helpful during + development, but it's a lot of work to do. + + Following is a list of probable improvements that will make `gawk' +perform better: An Improved Version of `dfa' The `dfa' pattern matcher from GNU `grep' has some problems. Either a new version or a fixed one will deal with some important regexp matching issues. -Use of GNU `malloc' - The GNU version of `malloc' could potentially speed up `gawk', - since it relies heavily on the use of dynamic memory allocation. - - -File: gawk.info, Node: Improvements, Prev: Future Extensions, Up: Notes - -Suggestions for Improvements -============================ - - Here are some projects that would-be `gawk' hackers might like to -take on. They vary in size from a few days to a few weeks of -programming, depending on which one you choose and how fast a -programmer you are. Please send any improvements you write to the -maintainers at the GNU project. *Note Adding New Features: Adding Code, -for guidelines to follow when adding new features to `gawk'. *Note -Reporting Problems and Bugs: Bugs, for information on contacting the -maintainers. - - 1. Compilation of `awk' programs: `gawk' uses a Bison (YACC-like) - parser to convert the script given it into a syntax tree; the - syntax tree is then executed by a simple recursive evaluator. - This method incurs a lot of overhead, since the recursive - evaluator performs many procedure calls to do even the simplest - things. +Compilation of `awk' programs + `gawk' uses a Bison (YACC-like) parser to convert the script given + it into a syntax tree; the syntax tree is then executed by a + simple recursive evaluator. This method incurs a lot of overhead, + since the recursive evaluator performs many procedure calls to do + even the simplest things. It should be possible for `gawk' to convert the script's parse tree into a C program which the user would then compile, using the @@ -16565,21 +18726,330 @@ maintainers. needed functions (regexps, fields, associative arrays, type coercion, and so on). - An easier possibility might be for an intermediate phase of `awk' + An easier possibility might be for an intermediate phase of `gawk' to convert the parse tree into a linear byte code form like the one used in GNU Emacs Lisp. The recursive evaluator would then be replaced by a straight line byte code interpreter that would be intermediate in speed between running a compiled program and doing what `gawk' does now. - 2. The programs in the test suite could use documenting in this - Info file. + Finally, the programs in the test suite could use documenting in +this Info file. + + *Note Making Additions to `gawk': Additions, if you are interested +in tackling any of these projects. + + +File: gawk.info, Node: Basic Concepts, Next: Glossary, Prev: Notes, Up: Top + +Basic Programming Concepts +************************** + + This major node attempts to define some of the basic concepts and +terms that are used throughout the rest of this Info file. As this +Info file is specifically about `awk', and not about computer +programming in general, the coverage here is by necessity fairly +cursory and simplistic. (If you need more background, there are many +other introductory texts that you should refer to instead.) + +* Menu: + +* Basic High Level:: The high level view. +* Basic Data Typing:: A very quick intro to data types. +* Floating Point Issues:: Stuff to know about floating-point numbers. + + +File: gawk.info, Node: Basic High Level, Next: Basic Data Typing, Prev: Basic Concepts, Up: Basic Concepts + +What a Program Does +=================== + + At the most basic level, the job of a program is to process some +input data and produce results. + + _______ + +------+ / \ +---------+ + | Data | -----> < Program > -----> | Results | + +------+ \_______/ +---------+ + + The "program" in the figure can be either a compiled program(1) +(such as `ls'), or it may be "interpreted". In the latter case, a +machine-executable program such as `awk' reads your program, and then +uses the instructions in your program to process the data. + + When you write a program, it usually consists of the following, very +basic set of steps: + + ______ + +----------------+ / More \ No +----------+ + | Initialization | -------> < Data > -------> | Clean Up | + +----------------+ ^ \ ? / +----------+ + | +--+-+ + | | Yes + | | + | V + | +---------+ + +-----+ Process | + +---------+ + +Initialization + These are the things you do before actually starting to process + data, such as checking arguments, initializing any data you need + to work with, and so on. This step corresponds to `awk''s `BEGIN' + rule (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.). + + If you were baking a cake, this might consist of laying out all the + mixing bowls and the baking pan, and making sure you have all the + ingredients that you need. + +Processing + This is where the actual work is done. Your program reads data, + one logical chunk at a time, and processes it as appropriate. + + In most programming languages, you have to manually manage the + reading of data, checking to see if there is more each time you + read a chunk. `awk''s pattern-action paradigm (*note Getting + Started with `awk': Getting Started.) handles the mechanics of + this for you. + + In baking a cake, the processing corresponds to the actual labor: + breaking eggs, mixing the flour, water, and other ingredients, and + then putting the cake into the oven. + +Clean Up + Once you've processed all the data, you may have things you need to + do before exiting. This step corresponds to `awk''s `END' rule + (*note The `BEGIN' and `END' Special Patterns: BEGIN/END.). + + After the cake comes out of the oven, you still have to wrap it in + plastic wrap to keep anyone from tasting it, as well as wash the + mixing bowls and other utensils. + + An "algorithm" is a detailed set of instructions necessary to +accomplish a task, or process data. It is much the same as a recipe +for baking a cake. Programs implement algorithms. Often, it is up to +you to design the algorithm and implement it, simultaneously. + + The "logical chunks" we talked about previously are called "records", +similar to the records a company keeps on employees, a school keeps for +students, or a doctor keeps for patients. Each record has many +component parts, such as first and last names, date of birth, address, +and so on. The component parts are referred to as the "fields" of the +record. + + The act of reading data is termed "input", and that of generating +results, not too surprisingly, is termed "output". They are often +referred to together as "Input/Output," and even more often, as "I/O" +for short. (You will also see "input" and "output" used as verbs.) + + `awk' manages the reading of data for you, as well as the breaking +it up into records and fields. Your program's job is to tell `awk' +what to with the data. You do this by describing "patterns" in the +data to look for, and "actions" to execute when those patterns are +seen. This "data-driven" nature of `awk' programs usually makes them +both easier to write and easier to read. + + ---------- Footnotes ---------- + + (1) Compiled programs are typically written in lower-level languages +such as C, C++, Fortran, or Ada, and then translated, or "compiled", +into a form that the computer can execute directly. + + +File: gawk.info, Node: Basic Data Typing, Next: Floating Point Issues, Prev: Basic High Level, Up: Basic Concepts + +Data Values in a Computer +========================= + + In a program, you keep track of information and values in things +called "variables". A variable is just a name for a given value, such +as `first_name', `last_name', `address', and so on. `awk' has several +pre-defined variables, and it has special names to refer to the current +input record and the fields of the record. You may also group multiple +associated values under one name, as an array. + + Data, particularly in `awk', consists of either numeric values, such +as 42 or 3.1415927, or string values. String values are essentially +anything that's not a number, such as a name. Strings are sometimes +referred to as "character data", since they store the individual +characters that comprise them. Individual variables, as well as +numeric and string variables, are referred to as "scalar" values. +Groups of values, such as arrays, are not scalars. + + Within computers, there are two kinds of numeric values: "integers", +and "floating-point". In school, integer values were referred to as +"whole" numbers--that is, numbers without any fractional part, such as +1, 42, or -17. The advantage to integer numbers is that they represent +values exactly. The disadvantage is that their range is limited. On +most modern systems, this range is -2,147,483,648 to 2,147,483,647. + + Integer values come in two flavors: "signed" and "unsigned". Signed +values may be negative or positive, with the range of values just +described. Unsigned values are always positive. On most modern +systems, the range is from 0 to 4,294,967,295. + + Floating-point numbers represent what are called "real" numbers; +i.e., those that do have a fractional part, such as 3.1415927. The +advantage to floating-point numbers is that they can represent a much +larger range of values. The disadvantage is that there are numbers +that they cannot represent exactly. `awk' uses "double-precision" +floating-point numbers, which can hold more digits than +"single-precision" floating-point numbers. Floating-point issues are +discussed more fully in *Note Floating-Point Number Caveats: Floating +Point Issues. + + At the very lowest level, computers store values as groups of binary +digits, or "bits". Modern computers group bits into groups of eight, +called "bytes". Advanced applications sometimes have to manipulate +bits directly, and `gawk' provides functions for doing so. + + While you are probably used to the idea of a number without a value +(i.e., zero), it takes a bit more getting used to the idea of +zero-length character data. Nevertheless, such a thing exists. It is +called the "null string". The null string is character data that has +no value. In other words, it is empty. It is written in `awk' programs +like this: `""'. + + Humans are used to working in decimal; i.e., base 10. In base 10, +numbers go from 0 to 9, and then "roll over" into the next column. +(Remember grade school? 42 is 4 times 10 plus 2.) + + There are other number bases though. Computers commonly use base 2 +or "binary", base 8 or "octal", and base 16 or "hexadecimal". In +binary, each column represents two times the value in the column to its +right. Each column may contain either a 0 or a 1. Thus, binary 1010 +represents 1 times 8, plus 0 times 4, plus 1 times 2, plus 0 times 1, +or decimal 10. Octal and hexadecimal are discussed more in *Note Octal +and Hexadecimal Numbers: Non-decimal-numbers. + + Programs are written in programming languages. Hundreds, if not +thousands, of programming languages exist. One of the most popular is +the C programming language. The C language had a very strong influence +on the design of the `awk' language. + + There have been several versions of C. The first is often referred +to as "K&R" C, after the initials of Brian Kernighan and Dennis Ritchie, +the authors of the first book on C. (Dennis Ritchie created the +language, and Brian Kernighan was one of the creators of `awk'.) + + In the mid-1980's, an effort began to produce an international +standard for C. This work culminated in 1989, with the production of +the ANSI standard for C. This standard became an ISO standard in 1990. +Where it makes sense, POSIX `awk' is compatible with 1990 ISO C. + + In 1999, a revised ISO C standard was approved and released. Future +versions of `gawk' will be as compatible as possible with this standard. + + +File: gawk.info, Node: Floating Point Issues, Prev: Basic Data Typing, Up: Basic Concepts + +Floating-Point Number Caveats +============================= + + As mentioned earlier, floating-point numbers represent what are +called "real" numbers; i.e., those that have a fractional part. `awk' +uses double-precision floating-point numbers to represent all numeric +values. This minor node describes some of the issues involved in using +floating-point numbers. + + There is a very nice paper on floating-point arithmetic by David +Goldberg, `What Every Computer Scientist Should Know About +Floating-point Arithmetic', `ACM Computing Surveys' *23*, 1 (1991-03), +5-48.(1) This is worth reading if you are interested in the details, +but it does require a background in Computer Science. + + Internally, `awk' keeps both the numeric value (double-precision +floating-point) and the string value for a variable. Separately, `awk' +keeps track of what type the variable has (*note Variable Typing and +Comparison Expressions: Typing and Comparison.), which plays a role in +how variables are used in comparisons. + + It is important to note that the string value for a number may not +reflect the full value (all the digits) that the numeric value actually +contains. The following program (`values.awk') illustrates this: + + { + $1 = $2 + $3 + # see it for what it is + printf("$1 = %.12g\n", $1) + # use CONVFMT + a = "<" $1 ">" + print "a =", a + # use OFMT + print "$1 =", $1 + } + +This program shows the full value of the sum of `$2' and `$3' using +`printf', and then prints the string values obtained from both +automatic conversion (via `CONVFMT') and from printing (via `OFMT'). + + Here is what happens when the program is run: + + $ echo 2 3.654321 1.2345678 | awk -f values.awk + -| $1 = 4.8888888 + -| a = <4.88889> + -| $1 = 4.88889 + + This makes it clear that the full numeric value is different from +what the default string representations show. + + `CONVFMT''s default value is `"%.6g"', which yields a value with at +least six significant digits. For some applications, you might want to +change it to specify more precision. On most modern machines, most of +the time, 17 digits is enough to capture a floating-point number's +value exactly.(2) + + Unlike numbers in the abstract sense (such as what you studied in +high school or college math), numbers stored in computers are limited +in certain ways. They cannot represent an infinite number of digits, +nor can they always represent things exactly. In particular, +floating-point numbers cannot always represent values exactly. Here is +an example: + + $ awk '{ printf("%010d\n", $1 * 100) }' + 515.79 + -| 0000051579 + 515.80 + -| 0000051579 + 515.81 + -| 0000051580 + 515.82 + -| 0000051582 + Ctrl-d + +This shows that some values can be represented exactly, whereas others +are only approximated. This is not a "bug" in `awk', but simply an +artifact of how computers represent numbers. + + Another peculiarity of floating-point numbers on modern systems is +that they often have more than one representation for the number zero! +In particular, it is possible to represent "minus zero" as well as +regular, or "positive" zero. + + This example shows that negative and positive zero are distinct +values when stored internally, but that they are in fact equal to each +other, as well as to "regular" zero: + + $ gawk 'BEGIN { mz = -0 ; pz = 0 + > printf "-0 = %g, +0 = %g, (-0 == +0) -> %d\n", mz, pz, mz == pz + > printf "mz == 0 -> %d, pz == 0 -> %d\n", mz == 0, pz == 0 + > }' + -| -0 = -0, +0 = 0, (-0 == +0) -> 1 + -| mz == 0 -> 1, pz == 0 -> 1 + + It helps to keep this in mind should you process numeric data that +contains negative zero values; the fact that the zero is negative is +noted and can affect comparisons. + + ---------- Footnotes ---------- - 3. See the `FUTURES' file for more ideas. Contact us if you would - seriously like to tackle any of the items listed there. + (1) `http://www.validgh.com/goldberg/paper.ps' + + (2) Pathological cases can require up to 752 digits (!), but we +doubt that you need to worry about this.  -File: gawk.info, Node: Glossary, Next: Copying, Prev: Notes, Up: Top +File: gawk.info, Node: Glossary, Next: Copying, Prev: Basic Concepts, Up: Top Glossary ******** @@ -16587,25 +19057,42 @@ Glossary Action A series of `awk' statements attached to a rule. If the rule's pattern matches an input record, `awk' executes the rule's action. - Actions are always enclosed in curly braces. *Note Overview of - Actions: Action Overview. + Actions are always enclosed in curly braces. (*Note Actions: + Action Overview.) Amazing `awk' Assembler Henry Spencer at the University of Toronto wrote a retargetable - assembler completely as `awk' scripts. It is thousands of lines - long, including machine descriptions for several eight-bit + assembler completely as `sed' and `awk' scripts. It is thousands + of lines long, including machine descriptions for several eight-bit microcomputers. It is a good example of a program that would have - been better written in another language. + been better written in another language. You can get it from + `ftp://ftp.freefriends.org/arnold/Awkstuff/aaa.tgz'. Amazingly Workable Formatter (`awf') Henry Spencer at the University of Toronto wrote a formatter that accepts a large subset of the `nroff -ms' and `nroff -man' - formatting commands, using `awk' and `sh'. + formatting commands, using `awk' and `sh'. It is available over + the Internet from + `ftp://ftp.freefriends.org/arnold/Awkstuff/awf.tgz'. + +Anchor + The regexp metacharacters `^' and `$', which force the match to + the beginning or end of the string, respectively. ANSI The American National Standards Institute. This organization produces many standards, among them the standards for the C and - C++ programming languages. + C++ programming languages. These standards often become + international standards as well. See also "ISO." + +Array + A grouping of multiple values under the same name. Most languages + just provide sequential arrays. `awk' provides associative arrays. + +Assertion + A statement in a program that a condition is true at this point in + the program. Useful for reasoning about how a program is supposed + to behave. Assignment An `awk' expression that changes the value of some `awk' variable @@ -16613,6 +19100,10 @@ Assignment "lvalue". The assigned values are called "rvalues". *Note Assignment Expressions: Assignment Ops. +Associative Array + Arrays in which the indices may be numbers or strings, not just + sequential integers in a fixed range. + `awk' Language The language in which `awk' programs are written. @@ -16626,36 +19117,54 @@ Assignment Another name for an `awk' program. Bash - The GNU version of the standard shell (the Bourne-Again shell). - See "Bourne Shell." + The GNU version of the standard shell (the Bourne-Again SHell). + See also "Bourne Shell." BBS See "Bulletin Board System." +Bit + Short for "Binary Digit." All values in computer memory + ultimately reduce to binary digits: values that are either zero or + one. Groups of bits may be interpreted differently--as integers, + floating-point numbers, character data, addresses of other memory + objects, or other data. `awk' lets you work with floating-point + numbers and strings. `gawk' lets you manipulate bit values with + the built-in functions described in *Note Using `gawk''s Bit + Manipulation Functions: Bitwise Functions. + + Computers are often defined by how many bits they use to represent + integer values. Typical systems are 32-bit systems, but 64-bit + systems are becoming increasingly popular, and 16-bit systems are + waning in popularity. + Boolean Expression - Named after the English mathematician Boole. See "Logical + Named after the English mathematician Boole. See also "Logical Expression." Bourne Shell The standard shell (`/bin/sh') on Unix and Unix-like systems, - originally written by Steven R. Bourne. Many shells (Bash, `ksh', - `pdksh', `zsh') are generally upwardly compatible with the Bourne - shell. + originally written by Steven R. Bourne. Many shells (`bash', + `ksh', `pdksh', `zsh') are generally upwardly compatible with the + Bourne shell. Built-in Function The `awk' language provides built-in functions that perform various - numerical, time stamp related, and string computations. Examples - are `sqrt' (for the square root of a number) and `substr' (for a - substring of a string). *Note Built-in Functions: Built-in. + numerical, I/O-related, and string computations. Examples are + `sqrt' (for the square root of a number) and `substr' (for a + substring of a string). `gawk' provides functions for timestamp + management, bit manipulation, and runtime string translation. + (*Note Built-in Functions: Built-in.) Built-in Variable - `ARGC', `ARGIND', `ARGV', `CONVFMT', `ENVIRON', `ERRNO', - `FIELDWIDTHS', `FILENAME', `FNR', `FS', `IGNORECASE', `NF', `NR', - `OFMT', `OFS', `ORS', `RLENGTH', `RSTART', `RS', `RT', and - `SUBSEP', are the variables that have special meaning to `awk'. - Changing some of them affects `awk''s running environment. - Several of these variables are specific to `gawk'. *Note Built-in - Variables::. + `ARGC', `ARGV', `CONVFMT', `ENVIRON', `FILENAME', `FNR', `FS', + `NF', `NR', `OFMT', `OFS', `ORS', `RLENGTH', `RSTART', `RS', and + `SUBSEP' are the variables that have special meaning to `awk'. In + addition, `ARGIND', `BINMODE', `ERRNO', `FIELDWIDTHS', + `IGNORECASE', `LINT', `PROCINFO', `RT', and `TEXTDOMAIN' are the + variables that have special meaning to `gawk'. Changing some of + them affects `awk''s running environment. (*Note Built-in + Variables::.) Braces See "Curly Braces." @@ -16671,6 +19180,13 @@ C Info file points out similarities between `awk' and C when appropriate. + In general, `gawk' attempts to be as similar to the 1990 version + of ISO C as makes sense. Future versions of `gawk' may adopt + features from the newer 1999 standard, as appropriate. + +C++ + A popular object-oriented programming language derived from C. + Character Set The set of numeric codes used by a computer system to represent the characters (letters, numbers, punctuation, etc.) of a particular @@ -16683,33 +19199,42 @@ CHEM A preprocessor for `pic' that reads descriptions of molecules and produces `pic' input for drawing them. It was written in `awk' by Brian Kernighan and Jon Bentley, and is available from - . + `http://cm.bell-labs.com/netlib/typesetting/chem.gz'. + +Coprocess + A subordinate program with which two-way communications is + possible. + +Compiler + A program that translates human-readable source code into + machine-executable object code. The object code is then executed + directly by the computer. See also "Interpreter." Compound Statement A series of `awk' statements, enclosed in curly braces. Compound - statements may be nested. *Note Control Statements in Actions: - Statements. + statements may be nested. (*Note Control Statements in Actions: + Statements.) Concatenation Concatenating two strings means sticking them together, one after - another, giving a new string. For example, the string `foo' + another, producing a new string. For example, the string `foo' concatenated with the string `bar' gives the string `foobar'. - *Note String Concatenation: Concatenation. + (*Note String Concatenation: Concatenation.) Conditional Expression An expression using the `?:' ternary operator, such as `EXPR1 ? EXPR2 : EXPR3'. The expression EXPR1 is evaluated; if the result - is true, the value of the whole expression is the value of EXPR2, + is true, the value of the whole expression is the value of EXPR2; otherwise the value is EXPR3. In either case, only one of EXPR2 - and EXPR3 is evaluated. *Note Conditional Expressions: - Conditional Exp. + and EXPR3 is evaluated. (*Note Conditional Expressions: + Conditional Exp.) Comparison Expression A relation that is either true or false, such as `(a < b)'. Comparison expressions are used in `if', `while', `do', and `for' statements, and in patterns to select which input records to - process. *Note Variable Typing and Comparison Expressions: Typing - and Comparison. + process. (*Note Variable Typing and Comparison Expressions: + Typing and Comparison.) Curly Braces The characters `{' and `}'. Curly braces are used in `awk' for @@ -16718,26 +19243,35 @@ Curly Braces Dark Corner An area in the language where specifications often were (or still are) not clear, leading to unexpected or undesirable behavior. - Such areas are marked in this Info file with "(d.c.)" in the text, + Such areas are marked in this Info file with "(d.c.)" in the text and are indexed under the heading "dark corner." +Data Driven + A description of `awk' programs, where you specify the data you + are interested in processing, and what to do when that data is + seen. + Data Objects These are numbers and strings of characters. Numbers are - converted into strings and vice versa, as needed. *Note - Conversion of Strings and Numbers: Conversion. + converted into strings and vice versa, as needed. (*Note + Conversion of Strings and Numbers: Conversion.) + +Deadlock + The situation in which two communicating processes are each waiting + for the other to perform an action. -Double Precision +Double-Precision An internal representation of numbers that can have fractional - parts. Double precision numbers keep track of more digits than do - single precision numbers, but operations on them are more - expensive. This is the way `awk' stores numeric values. It is - the C type `double'. + parts. Double-precision numbers keep track of more digits than do + single-precision numbers, but operations on them are sometimes + more expensive. This is the way `awk' stores numeric values. It + is the C type `double'. Dynamic Regular Expression A dynamic regular expression is a regular expression written as an ordinary expression. It could be a string constant, such as `"foo"', but it may also be an expression whose value can vary. - *Note Using Dynamic Regexps: Computed Regexps. + (*Note Using Dynamic Regexps: Computed Regexps.) Environment A collection of strings, of the form NAME`='VAL, that each program @@ -16748,36 +19282,58 @@ Environment Empty String See "Null String." +Epoch + The date used as the "beginning of time" for timestamps. Time + values in Unix systems are represented as seconds since the epoch, + with library functions available for converting these values into + standard date and time formats. + + The epoch on Unix and POSIX systems is 1970-01-01 00:00:00 UTC. + See also "GMT" and "UTC." + Escape Sequences A special sequence of characters used for describing non-printing - characters, such as `\n' for newline, or `\033' for the ASCII ESC - (escape) character. *Note Escape Sequences::. + characters, such as `\n' for newline or `\033' for the ASCII ESC + (Escape) character. (*Note Escape Sequences::.) + +FDL + See "Free Documentation License." Field When `awk' reads an input record, it splits the record into pieces - separated by whitespace (or by a separator regexp which you can + separated by whitespace (or by a separator regexp that you can change by setting the built-in variable `FS'). Such pieces are called fields. If the pieces are of fixed length, you can use the - built-in variable `FIELDWIDTHS' to describe their lengths. *Note - Specifying How Fields are Separated: Field Separators, and also see - *Note Reading Fixed-width Data: Constant Size. + built-in variable `FIELDWIDTHS' to describe their lengths. (*Note + Specifying How Fields Are Separated: Field Separators, and *Note + Reading Fixed-Width Data: Constant Size.) + +Flag + A variable whose truth value indicates the existence or + non-existence of some condition. -Floating Point Number - Often referred to in mathematical terms as a "rational" number, - this is just a number that can have a fractional part. See - "Double Precision" and "Single Precision." +Floating-Point Number + Often referred to in mathematical terms as a "rational" or real + number, this is just a number that can have a fractional part. + See also "Double-Precision" and "Single-Precision." Format Format strings are used to control the appearance of output in the - `printf' statement. Also, data conversions from numbers to strings + `strftime' and `sprintf' functions, and are used in the `printf' + statement as well. Also, data conversions from numbers to strings are controlled by the format string contained in the built-in - variable `CONVFMT'. *Note Format-Control Letters: Control Letters. + variable `CONVFMT'. (*Note Format-Control Letters: Control + Letters.) + +Free Documentation License + This document describes the terms under which this Info file is + published and may be copied. (*Note GNU Free Documentation + License::.) Function A specialized group of statements used to encapsulate general or program-specific tasks. `awk' has a number of built-in functions, - and also allows you to define your own. *Note Built-in Functions: - Built-in, and *Note User-defined Functions: User-defined. + and also allows you to define your own. (*Note Functions::.) FSF See "Free Software Foundation." @@ -16793,34 +19349,72 @@ Free Software Foundation General Public License This document describes the terms under which `gawk' and its source - code may be distributed. (*note GNU GENERAL PUBLIC LICENSE: + code may be distributed. (*Note GNU General Public License: Copying.) +GMT + "Greenwich Mean Time." This is the old term for UTC. It is the + time of day used as the epoch for Unix and POSIX systems. See + also "Epoch" and "UTC." + GNU "GNU's not Unix". An on-going project of the Free Software Foundation to create a complete, freely distributable, POSIX-compliant computing environment. +GNU/Linux + A variant of the GNU system using the Linux kernel, instead of the + Free Software Foundation's Hurd kernel. Linux is a stable, + efficient, full-featured clone of Unix that has been ported to a + variety of architectures. It is most popular on PC-class systems, + but runs well on a variety of other systems too. The Linux kernel + source code is available under the terms of the GNU General Public + License, which is perhaps its most important aspect. + GPL See "General Public License." Hexadecimal Base 16 notation, where the digits are `0'-`9' and `A'-`F', with - `A' representing 10, `B' representing 11, and so on up to `F' for + `A' representing 10, `B' representing 11, and so on, up to `F' for 15. Hexadecimal numbers are written in C using a leading `0x', to - indicate their base. Thus, `0x12' is 18 (one times 16 plus 2). + indicate their base. Thus, `0x12' is 18 (1 times 16 plus 2). I/O Abbreviation for "Input/Output," the act of moving data into and/or out of a running program. Input Record - A single chunk of data read in by `awk'. Usually, an `awk' input - record consists of one line of text. *Note How Input is Split - into Records: Records. + A single chunk of data that is read in by `awk'. Usually, an + `awk' input record consists of one line of text. (*Note How Input + Is Split into Records: Records.) Integer - A whole number, i.e. a number that does not have a fractional part. + A whole number, i.e., a number that does not have a fractional + part. + +Internationalization + The process of writing or modifying a program so that it can use + multiple languages without requiring further source code changes. + +Interpreter + A program that reads human-readable source code directly, and uses + the instructions in it to process data and produce results. `awk' + is typically (but not always) implemented as an interpreter. See + also "Compiler." + +Interval Expression + A component of a regular expression that lets you specify repeated + matches of some part of the regexp. Interval expressions were not + traditionally available in `awk' programs. + +ISO + The International Standards Organization. This organization + produces international standards for many things, including + programming languages, such as C and C++. In the computer arena, + important standards like those for C, C++, and POSIX become both + American national and ISO international standards simultaneously. + This Info file refers to Standard C as "ISO C" throughout. Keyword In the `awk' language, a keyword is a word that has special @@ -16831,6 +19425,21 @@ Keyword `do...while', `for', `for...in', `break', `continue', `delete', `next', `nextfile', `function', `func', and `exit'. +Lesser General Public License + This document describes the terms under which binary library + archives or shared objects, and their source code may be + distributed. + +Linux + See "GNU/Linux." + +LGPL + See "Lesser General Public License." + +Localization + The process of providing the data necessary for an + internationalized program to work in a particular language. + Logical Expression An expression using the operators for logic, AND, OR, and NOT, written `&&', `||', and `!' in `awk'. Often called Boolean @@ -16843,22 +19452,35 @@ Lvalue elements. In `awk', a field designator can also be used as an lvalue. +Matching + The act of testing a string against a regular expression. If the + regexp describes the contents of the string, it is said to "match" + it. + +Metacharacters + Characters used within a regexp that do not stand for themselves. + Instead, they denote regular expression operations, such as + repetition, grouping, or alternation. + Null String A string with no characters in it. It is represented explicitly in - `awk' programs by placing two double-quote characters next to each + `awk' programs by placing two double quote characters next to each other (`""'). It can appear in input data by having two successive occurrences of the field separator appear next to each other. Number - A numeric valued data object. The `gawk' implementation uses - double precision floating point to represent numbers. Very old - `awk' implementations use single precision floating point. + A numeric-valued data object. Modern `awk' implementations use + double-precision floating-point to represent numbers. Very old + `awk' implementations use single-precision floating-point. Octal Base-eight notation, where the digits are `0'-`7'. Octal numbers are written in C using a leading `0', to indicate their base. Thus, `013' is 11 (one times 8 plus 3). +P1003.2 + See "POSIX." + Pattern Patterns tell `awk' which input records are interesting to which rules. @@ -16866,43 +19488,48 @@ Pattern A pattern is an arbitrary conditional expression against which input is tested. If the condition is satisfied, the pattern is said to "match" the input record. A typical pattern might compare - the input record against a regular expression. *Note Pattern - Elements: Pattern Overview. + the input record against a regular expression. (*Note Pattern + Elements: Pattern Overview.) POSIX - The name for a series of standards being developed by the IEEE - that specify a Portable Operating System interface. The "IX" - denotes the Unix heritage of these standards. The main standard - of interest for `awk' users is `IEEE Standard for Information - Technology, Standard 1003.2-1992, Portable Operating System - Interface (POSIX) Part 2: Shell and Utilities'. Informally, this - standard is often referred to as simply "P1003.2." + The name for a series of standards that specify a Portable + Operating System interface. The "IX" denotes the Unix heritage of + these standards. The main standard of interest for `awk' users is + `IEEE Standard for Information Technology, Standard 1003.2-1992, + Portable Operating System Interface (POSIX) Part 2: Shell and + Utilities'. Informally, this standard is often referred to as + simply "P1003.2." + +Precedence + The order in which operations are performed when operators are used + without explicit parentheses. Private Variables and/or functions that are meant for use exclusively by - library functions, and not for the main `awk' program. Special - care must be taken when naming such variables and functions. - *Note Naming Library Function Global Variables: Library Names. + library functions and not for the main `awk' program. Special care + must be taken when naming such variables and functions. (*Note + Naming Library Function Global Variables: Library Names.) Range (of input lines) - A sequence of consecutive lines from the input file. A pattern - can specify ranges of input lines for `awk' to process, or it can - specify single lines. *Note Pattern Elements: Pattern Overview. + A sequence of consecutive lines from the input file(s). A pattern + can specify ranges of input lines for `awk' to process or it can + specify single lines. (*Note Pattern Elements: Pattern Overview.) Recursion When a function calls itself, either directly or indirectly. If this isn't clear, refer to the entry for "recursion." Redirection - Redirection means performing input from other than the standard - input stream, or output to other than the standard output stream. + Redirection means performing input from something other than the + standard input stream, or performing output to something other + than the standard output stream. You can redirect the output of the `print' and `printf' statements - to a file or a system command, using the `>', `>>', and `|' + to a file or a system command, using the `>', `>>', `|', and `|&' operators. You can redirect input to the `getline' statement using - the `<' and `|' operators. *Note Redirecting Output of `print' - and `printf': Redirection, and *Note Explicit Input with - `getline': Getline. + the `<', `|', and `|&' operators. (*Note Redirecting Output of + `print' and `printf': Redirection, and *Note Explicit Input with + `getline': Getline.) Regexp Short for "regular expression". A regexp is a pattern that @@ -16910,7 +19537,7 @@ Regexp the regexp `R.*xp' matches any string starting with the letter `R' and ending with the letters `xp'. In `awk', regexps are used in patterns and in conditional expressions. Regexps may contain - escape sequences. *Note Regular Expressions: Regexp. + escape sequences. (*Note Regular Expressions: Regexp.) Regular Expression See "regexp." @@ -16918,8 +19545,8 @@ Regular Expression Regular Expression Constant A regular expression constant is a regular expression written within slashes, such as `/foo/'. This regular expression is chosen - when you write the `awk' program, and cannot be changed doing its - execution. *Note How to Use Regular Expressions: Regexp Usage. + when you write the `awk' program and cannot be changed during its + execution. (*Note How to Use Regular Expressions: Regexp Usage.) Rule A segment of an `awk' program that specifies how to process single @@ -16933,77 +19560,111 @@ Rvalue operator. In `awk', essentially every expression has a value. These values are rvalues. +Scalar + A single value, be it a number or a string. Regular variables are + scalars; arrays and functions are not. + +Search Path + In `gawk', a list of directories to search for `awk' program + source files. In the shell, a list of directories to search for + executable programs. + +Seed + The initial value, or starting point, for a sequence of random + numbers. + `sed' See "Stream Editor." +Shell + The command interpreter for Unix and POSIX-compliant systems. The + shell works both interactively, and as a programming language for + batch files, or shell scripts. + Short-Circuit The nature of the `awk' logical operators `&&' and `||'. If the - value of the entire expression can be deduced from evaluating just - the left-hand side of these operators, the right-hand side will not - be evaluated (*note Boolean Expressions: Boolean Ops.). + value of the entire expression is determinable from evaluating just + the lefthand side of these operators, the righthand side is not + evaluated. (*Note Boolean Expressions: Boolean Ops.) Side Effect A side effect occurs when an expression has an effect aside from merely producing a value. Assignment expressions, increment and - decrement expressions and function calls have side effects. *Note - Assignment Expressions: Assignment Ops. + decrement expressions, and function calls have side effects. + (*Note Assignment Expressions: Assignment Ops.) -Single Precision +Single-Precision An internal representation of numbers that can have fractional - parts. Single precision numbers keep track of fewer digits than - do double precision numbers, but operations on them are less - expensive in terms of CPU time. This is the type used by some - very old versions of `awk' to store numeric values. It is the C - type `float'. + parts. Single-precision numbers keep track of fewer digits than + do double-precision numbers, but operations on them are sometimes + less expensive in terms of CPU time. This is the type used by + some very old versions of `awk' to store numeric values. It is + the C type `float'. Space The character generated by hitting the space bar on the keyboard. Special File A file name interpreted internally by `gawk', instead of being - handed directly to the underlying operating system. For example, - `/dev/stderr'. *Note Special File Names in `gawk': Special Files. + handed directly to the underlying operating system--for example, + `/dev/stderr'. (*Note Special File Names in `gawk': Special + Files.) Stream Editor A program that reads records from an input stream and processes them one or more at a time. This is in contrast with batch programs, which may expect to read their input files in entirety - before starting to do anything, and with interactive programs, - which require input from the user. + before starting to do anything, as well as with interactive + programs which require input from the user. String A datum consisting of a sequence of characters, such as `I am a - string'. Constant strings are written with double-quotes in the - `awk' language, and may contain escape sequences. *Note Escape - Sequences::. + string'. Constant strings are written with double quotes in the + `awk' language and may contain escape sequences. (*Note Escape + Sequences::.) Tab The character generated by hitting the `TAB' key on the keyboard. It usually expands to up to eight spaces upon output. +Text Domain + A unique name that identifies an application. Used for grouping + messages that are translated at runtime into the local language. + +Timestamp + A value in the "seconds since the epoch" format used by Unix and + POSIX systems. Used for the `gawk' functions `mktime', + `strftime', and `systime'. See also "Epoch" and "UTC." + Unix A computer operating system originally developed in the early 1970's at AT&T Bell Laboratories. It initially became popular in - universities around the world, and later moved into commercial - evnironments as a software development system and network server + universities around the world and later moved into commercial + environments as a software development system and network server system. There are many commercial versions of Unix, as well as several work-alike systems whose source code is freely available - (such as Linux, NetBSD, and FreeBSD). + (such as GNU/Linux, NetBSD, FreeBSD, and OpenBSD). + +UTC + The accepted abbreviation for "Universal Coordinated Time." This + is standard time in Greenwich, England, which is used as a + reference time for day and date calculations. See also "Epoch" + and "GMT." Whitespace A sequence of space, tab, or newline characters occurring inside an input record or a string.  -File: gawk.info, Node: Copying, Next: Index, Prev: Glossary, Up: Top +File: gawk.info, Node: Copying, Next: GNU Free Documentation License, Prev: Glossary, Up: Top -GNU GENERAL PUBLIC LICENSE +GNU General Public License ************************** Version 2, June 1991 Copyright (C) 1989, 1991 Free Software Foundation, Inc. - 59 Temple Place --- Suite 330, Boston, MA 02111-1307, USA + 59 Temple Place, Suite 330, Boston, MA 02111, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. @@ -17156,7 +19817,7 @@ modification follow. c. Accompany it with the information you received as to the offer to distribute corresponding source code. (This alternative is - allowed only for non-commercial distribution and only if you + allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.) @@ -17320,7 +19981,7 @@ the "copyright" line and a pointer to where the full notice is found. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software - Foundation, Inc., 59 Temple Place --- Suite 330, Boston, MA 02111-1307, USA. + Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA. Also add information on how to contact you by electronic and paper mail. @@ -17356,73 +20017,541 @@ if necessary. Here is a sample; alter the names: program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the -GNU Library General Public License instead of this License. +GNU Lesser General Public License instead of this License. + + +File: gawk.info, Node: GNU Free Documentation License, Next: Index, Prev: Copying, Up: Top + +GNU Free Documentation License +****************************** + + Version 1.1, March 2000 + + Copyright (C) 2000 Free Software Foundation, Inc. + 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + + + 0. PREAMBLE + + The purpose of this License is to make a manual, textbook, or other + written document "free" in the sense of freedom: to assure everyone + the effective freedom to copy and redistribute it, with or without + modifying it, either commercially or noncommercially. Secondarily, + this License preserves for the author and publisher a way to get + credit for their work, while not being considered responsible for + modifications made by others. + + This License is a kind of "copyleft", which means that derivative + works of the document must themselves be free in the same sense. + It complements the GNU General Public License, which is a copyleft + license designed for free software. + + We have designed this License in order to use it for manuals for + free software, because free software needs free documentation: a + free program should come with manuals providing the same freedoms + that the software does. But this License is not limited to + software manuals; it can be used for any textual work, regardless + of subject matter or whether it is published as a printed book. + We recommend this License principally for works whose purpose is + instruction or reference. + + + 1. APPLICABILITY AND DEFINITIONS + + This License applies to any manual or other work that contains a + notice placed by the copyright holder saying it can be distributed + under the terms of this License. The "Document", below, refers to + any such manual or work. 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COPYING IN QUANTITY + + If you publish printed copies of the Document numbering more than + 100, and the Document's license notice requires Cover Texts, you + must enclose the copies in covers that carry, clearly and legibly, + all these Cover Texts: Front-Cover Texts on the front cover, and + Back-Cover Texts on the back cover. Both covers must also clearly + and legibly identify you as the publisher of these copies. The + front cover must present the full title with all words of the + title equally prominent and visible. You may add other material + on the covers in addition. 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In addition, you must do these + things in the Modified Version: + + A. Use in the Title Page (and on the covers, if any) a title + distinct from that of the Document, and from those of + previous versions (which should, if there were any, be listed + in the History section of the Document). You may use the + same title as a previous version if the original publisher of + that version gives permission. + + B. List on the Title Page, as authors, one or more persons or + entities responsible for authorship of the modifications in + the Modified Version, together with at least five of the + principal authors of the Document (all of its principal + authors, if it has less than five). + + C. State on the Title page the name of the publisher of the + Modified Version, as the publisher. + + D. Preserve all the copyright notices of the Document. + + E. Add an appropriate copyright notice for your modifications + adjacent to the other copyright notices. + + F. 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Preserve the network location, if any, given in the Document + for public access to a Transparent copy of the Document, and + likewise the network locations given in the Document for + previous versions it was based on. These may be placed in + the "History" section. You may omit a network location for a + work that was published at least four years before the + Document itself, or if the original publisher of the version + it refers to gives permission. + + K. In any section entitled "Acknowledgements" or "Dedications", + preserve the section's title, and preserve in the section all + the substance and tone of each of the contributor + acknowledgements and/or dedications given therein. + + L. Preserve all the Invariant Sections of the Document, + unaltered in their text and in their titles. Section numbers + or the equivalent are not considered part of the section + titles. + + M. Delete any section entitled "Endorsements". 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These titles must be distinct from any + other section titles. + + You may add a section entitled "Endorsements", provided it contains + nothing but endorsements of your Modified Version by various + parties-for example, statements of peer review or that the text has + been approved by an organization as the authoritative definition + of a standard. + + You may add a passage of up to five words as a Front-Cover Text, + and a passage of up to 25 words as a Back-Cover Text, to the end + of the list of Cover Texts in the Modified Version. Only one + passage of Front-Cover Text and one of Back-Cover Text may be + added by (or through arrangements made by) any one entity. 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COMBINING DOCUMENTS + + You may combine the Document with other documents released under + this License, under the terms defined in section 4 above for + modified versions, provided that you include in the combination + all of the Invariant Sections of all of the original documents, + unmodified, and list them all as Invariant Sections of your + combined work in its license notice. + + The combined work need only contain one copy of this License, and + multiple identical Invariant Sections may be replaced with a single + copy. If there are multiple Invariant Sections with the same name + but different contents, make the title of each such section unique + by adding at the end of it, in parentheses, the name of the + original author or publisher of that section if known, or else a + unique number. 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COLLECTIONS OF DOCUMENTS + + You may make a collection consisting of the Document and other + documents released under this License, and replace the individual + copies of this License in the various documents with a single copy + that is included in the collection, provided that you follow the + rules of this License for verbatim copying of each of the + documents in all other respects. + + You may extract a single document from such a collection, and + distribute it individually under this License, provided you insert + a copy of this License into the extracted document, and follow + this License in all other respects regarding verbatim copying of + that document. + + + 7. AGGREGATION WITH INDEPENDENT WORKS + + A compilation of the Document or its derivatives with other + separate and independent documents or works, in or on a volume of + a storage or distribution medium, does not as a whole count as a + Modified Version of the Document, provided no compilation + copyright is claimed for the compilation. Such a compilation is + called an "aggregate", and this License does not apply to the + other self-contained works thus compiled with the Document, on + account of their being thus compiled, if they are not themselves + derivative works of the Document. + + If the Cover Text requirement of section 3 is applicable to these + copies of the Document, then if the Document is less than one + quarter of the entire aggregate, the Document's Cover Texts may be + placed on covers that surround only the Document within the + aggregate. Otherwise they must appear on covers around the whole + aggregate. + + + 8. TRANSLATION + + Translation is considered a kind of modification, so you may + distribute translations of the Document under the terms of section + 4. Replacing Invariant Sections with translations requires special + permission from their copyright holders, but you may include + translations of some or all Invariant Sections in addition to the + original versions of these Invariant Sections. You may include a + translation of this License provided that you also include the + original English version of this License. In case of a + disagreement between the translation and the original English + version of this License, the original English version will prevail. + + + 9. TERMINATION + + You may not copy, modify, sublicense, or distribute the Document + except as expressly provided for under this License. Any other + attempt to copy, modify, sublicense or distribute the Document is + void, and will automatically terminate your rights under this + License. However, parties who have received copies, or rights, + from you under this License will not have their licenses + terminated so long as such parties remain in full compliance. + + + 10. FUTURE REVISIONS OF THIS LICENSE + + The Free Software Foundation may publish new, revised versions of + the GNU Free Documentation License from time to time. Such new + versions will be similar in spirit to the present version, but may + differ in detail to address new problems or concerns. See + `http://www.gnu.org/copyleft/'. + + Each version of the License is given a distinguishing version + number. If the Document specifies that a particular numbered + version of this License "or any later version" applies to it, you + have the option of following the terms and conditions either of + that specified version or of any later version that has been + published (not as a draft) by the Free Software Foundation. If + the Document does not specify a version number of this License, + you may choose any version ever published (not as a draft) by the + Free Software Foundation. + + +ADDENDUM: How to use this License for your documents +==================================================== + + To use this License in a document you have written, include a copy of +the License in the document and put the following copyright and license +notices just after the title page: + + + Copyright (C) YEAR YOUR NAME. + Permission is granted to copy, distribute and/or modify this document + under the terms of the GNU Free Documentation License, Version 1.1 + or any later version published by the Free Software Foundation; + with the Invariant Sections being LIST THEIR TITLES, with the + Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST. + A copy of the license is included in the section entitled ``GNU + Free Documentation License''. +If you have no Invariant Sections, write "with no Invariant +Sections" instead of saying which ones are invariant. If you have no +Front-Cover Texts, write "no Front-Cover Texts" instead of "Front-Cover +Texts being LIST"; likewise for Back-Cover Texts. + + If your document contains nontrivial examples of program code, we +recommend releasing these examples in parallel under your choice of +free software license, such as the GNU General Public License, to +permit their use in free software.  -File: gawk.info, Node: Index, Prev: Copying, Up: Top +File: gawk.info, Node: Index, Prev: GNU Free Documentation License, Up: Top Index ***** * Menu: +* ! operator <1>: Egrep Program. +* ! operator <2>: Ranges. +* ! operator <3>: Precedence. * ! operator: Boolean Ops. +* != operator <1>: Precedence. * != operator: Typing and Comparison. -* !~ operator <1>: Typing and Comparison. -* !~ operator <2>: Regexp Constants. -* !~ operator <3>: Computed Regexps. -* !~ operator <4>: Case-sensitivity. +* !~ operator <1>: Precedence. +* !~ operator <2>: Typing and Comparison. +* !~ operator <3>: Regexp Constants. +* !~ operator <4>: Computed Regexps. +* !~ operator <5>: Case-sensitivity. * !~ operator: Regexp Usage. * # (comment): Comments. * #! (executable scripts): Executable Scripts. -* $ (field operator): Fields. +* $ field operator <1>: Precedence. +* $ field operator: Fields. +* % operator: Precedence. +* %= operator <1>: Precedence. +* %= operator: Assignment Ops. +* && operator <1>: Precedence. * && operator: Boolean Ops. +* * operator: Precedence. +* ** operator: Precedence. +* **= operator <1>: Precedence. +* **= operator: Assignment Ops. +* *= operator <1>: Precedence. +* *= operator: Assignment Ops. +* + operator: Precedence. +* ++ operator <1>: Precedence. +* ++ operator: Increment Ops. +* += operator <1>: Precedence. +* += operator: Assignment Ops. +* - operator: Precedence. +* -- operator <1>: Precedence. +* -- operator: Increment Ops. * --assign option: Options. * --compat option: Options. * --copyleft option: Options. * --copyright option: Options. +* --disable-nls configuration option: Additional Configuration Options. +* --dump-variables option: Options. +* --enable-portals configuration option <1>: Additional Configuration Options. +* --enable-portals configuration option: Portal Files. * --field-separator option: Options. * --file option: Options. +* --gen-po option <1>: Options. +* --gen-po option: String Extraction. * --help option: Options. * --lint option: Options. * --lint-old option: Options. +* --non-decimal-data option <1>: Options. +* --non-decimal-data option: Non-decimal Data. * --posix option: Options. +* --profile option: Options. +* --re-interval option: Options. * --source option: Options. * --traditional option: Options. * --usage option: Options. * --version option: Options. +* --with-included-gettext configuration option <1>: Additional Configuration Options. +* --with-included-gettext configuration option: Gawk I18N. +* -= operator <1>: Precedence. +* -= operator: Assignment Ops. * -f option: Options. * -F option <1>: Options. * -F option: Command Line Field Separator. * -f option: Long. +* -mf option: Options. +* -mr option: Options. * -v option: Options. * -W option: Options. -* /dev/fd: Special Files. -* /dev/pgrpid: Special Files. -* /dev/pid: Special Files. -* /dev/ppid: Special Files. -* /dev/stderr: Special Files. -* /dev/stdin: Special Files. -* /dev/stdout: Special Files. -* /dev/user <1>: Passwd Functions. -* /dev/user: Special Files. +* / operator: Precedence. +* /= operator <1>: Precedence. +* /= operator: Assignment Ops. +* /= operator vs. /=.../ regexp constant: Assignment Ops. +* /dev/fd special files: Special FD. +* /dev/pgrpid special file: Special Process. +* /dev/pid special file: Special Process. +* /dev/ppid special file: Special Process. +* /dev/stderr special file: Special FD. +* /dev/stdin special file: Special FD. +* /dev/stdout special file: Special FD. +* /dev/user special file: Special Process. +* /inet special files: TCP/IP Networking. +* /p special files: Portal Files. +* < I/O operator: Getline/File. +* < operator <1>: Precedence. * < operator: Typing and Comparison. +* <= operator <1>: Precedence. * <= operator: Typing and Comparison. +* = operator: Assignment Ops. +* == operator <1>: Precedence. * == operator: Typing and Comparison. +* > I/O operator: Redirection. +* > operator <1>: Precedence. * > operator: Typing and Comparison. +* >= operator <1>: Precedence. * >= operator: Typing and Comparison. +* >> I/O operator <1>: Precedence. +* >> I/O operator: Redirection. +* ?: operator: Precedence. +* \" escape sequence: Escape Sequences. * \' regexp operator: GNU Regexp Operators. +* \/ escape sequence: Escape Sequences. * \< regexp operator: GNU Regexp Operators. * \> regexp operator: GNU Regexp Operators. * \` regexp operator: GNU Regexp Operators. +* \a escape sequence: Escape Sequences. +* \b escape sequence: Escape Sequences. * \B regexp operator: GNU Regexp Operators. +* \f escape sequence: Escape Sequences. +* \n escape sequence: Escape Sequences. +* \NNN escape sequence (octal): Escape Sequences. +* \r escape sequence: Escape Sequences. +* \t escape sequence: Escape Sequences. +* \v escape sequence: Escape Sequences. * \W regexp operator: GNU Regexp Operators. * \w regexp operator: GNU Regexp Operators. +* \x escape sequence: Escape Sequences. * \y regexp operator: GNU Regexp Operators. -* _gr_init: Group Functions. -* _pw_init: Passwd Functions. -* _tm_addup: Mktime Function. -* _tm_isleap: Mktime Function. +* ^ operator: Precedence. +* ^= operator <1>: Precedence. +* ^= operator: Assignment Ops. +* _ C macro (gettext): Explaining gettext. +* _gr_init user-defined function: Group Functions. +* _pw_init user-defined function: Passwd Functions. * accessing fields: Fields. * account information <1>: Group Functions. * account information: Passwd Functions. @@ -17434,91 +20563,165 @@ Index * action, separating statements: Action Overview. * adding new features: Adding Code. * addition: Arithmetic Ops. +* advanced features: Advanced Features. +* advanced notes <1>: I/O Functions. +* advanced notes <2>: Gory Details. +* advanced notes <3>: Auto-set. +* advanced notes <4>: Increment Ops. +* advanced notes <5>: Assignment Ops. +* advanced notes <6>: Non-decimal-numbers. +* advanced notes <7>: Close Files And Pipes. +* advanced notes <8>: Redirection. +* advanced notes <9>: Records. +* advanced notes <10>: Computed Regexps. +* advanced notes <11>: Escape Sequences. +* advanced notes: Executable Scripts. +* Aho, Alfred <1>: Contributors. * Aho, Alfred: History. * AI programming, using gawk: Distribution contents. -* alarm.awk: Alarm Program. +* alarm.awk program: Alarm Program. +* algorithm, definition of: Basic High Level. +* amazing awk assembler (aaa): Glossary. +* amazingly workable formatter (awf): Glossary. +* ambiguity, syntactic: /= operator vs. /=.../ regexp constant: Assignment Ops. * amiga: Amiga Installation. * anchors in regexps: Regexp Operators. -* and operator: Boolean Ops. -* anonymous ftp <1>: Other Versions. +* AND bitwise operation: Bitwise Functions. +* and built-in function: Bitwise Functions. +* AND logical operator: Boolean Ops. * anonymous ftp: Getting. -* applications of awk: When. -* ARGC: Auto-set. -* ARGIND <1>: Other Arguments. -* ARGIND: Auto-set. +* ANSI: Glossary. +* applications of awk <1>: When. +* applications of awk: Preface. +* archeologists: Bugs. +* ARGC variable: Auto-set. +* ARGIND variable <1>: Other Arguments. +* ARGIND variable: Auto-set. * argument processing: Getopt Function. * arguments in function call: Function Calls. -* arguments, command line: Invoking Gawk. -* ARGV <1>: Other Arguments. -* ARGV: Auto-set. +* arguments, command-line: Command Line. +* ARGV variable <1>: Other Arguments. +* ARGV variable: Auto-set. * arithmetic operators: Arithmetic Ops. * array assignment: Assigning Elements. * array reference: Reference to Elements. -* Array subscripts and IGNORECASE: Array Intro. -* array subscripts, uninitialized variables: Uninitialized Subscripts. * arrays: Array Intro. * arrays, associative: Array Intro. * arrays, definition of: Array Intro. * arrays, deleting an element: Delete. * arrays, deleting entire contents: Delete. -* arrays, multi-dimensional subscripts: Multi-dimensional. +* arrays, multidimensional subscripts: Multi-dimensional. * arrays, presence of elements: Reference to Elements. +* arrays, sorting: Array Sorting. +* arrays, sorting and IGNORECASE: Array Sorting. * arrays, sparse: Array Intro. * arrays, special for statement: Scanning an Array. +* arrays, subscripts, and IGNORECASE: Array Intro. +* arrays, subscripts, uninitialized variables: Uninitialized Subscripts. * arrays, the in operator: Reference to Elements. * artificial intelligence, using gawk: Distribution contents. * ASCII: Ordinal Functions. -* assert: Assert Function. -* assert, C version: Assert Function. +* asort built-in function <1>: String Functions. +* asort built-in function: Array Sorting. +* assert C library function: Assert Function. +* assert user-defined function: Assert Function. * assertions: Assert Function. * assignment operators: Assignment Ops. * assignment to fields: Changing Fields. +* assoc_clear internal function: Internals. +* assoc_lookup internal function: Internals. * associative arrays: Array Intro. -* atan2: Numeric Functions. +* atan2 built-in function: Numeric Functions. * atari: Atari Installation. * automatic initialization: More Complex. +* automatic warnings <1>: Options. +* automatic warnings <2>: I/O Functions. +* automatic warnings <3>: String Functions. +* automatic warnings <4>: Using Constant Regexps. +* automatic warnings <5>: Special Caveats. +* automatic warnings <6>: Special Process. +* automatic warnings: Escape Sequences. +* awf (amazingly workable formatter) program: Glossary. * awk language, POSIX version <1>: Definition Syntax. -* awk language, POSIX version <2>: String Functions. -* awk language, POSIX version <3>: User-modified. -* awk language, POSIX version <4>: Next Statement. -* awk language, POSIX version <5>: Continue Statement. -* awk language, POSIX version <6>: Break Statement. -* awk language, POSIX version <7>: Precedence. -* awk language, POSIX version <8>: Assignment Ops. -* awk language, POSIX version <9>: Arithmetic Ops. -* awk language, POSIX version <10>: Conversion. -* awk language, POSIX version <11>: Format Modifiers. -* awk language, POSIX version <12>: OFMT. -* awk language, POSIX version <13>: Field Splitting Summary. -* awk language, POSIX version <14>: Regexp Operators. +* awk language, POSIX version <2>: Gory Details. +* awk language, POSIX version <3>: String Functions. +* awk language, POSIX version <4>: User-modified. +* awk language, POSIX version <5>: Next Statement. +* awk language, POSIX version <6>: Continue Statement. +* awk language, POSIX version <7>: Break Statement. +* awk language, POSIX version <8>: Precedence. +* awk language, POSIX version <9>: Assignment Ops. +* awk language, POSIX version <10>: Arithmetic Ops. +* awk language, POSIX version <11>: Conversion. +* awk language, POSIX version <12>: Format Modifiers. +* awk language, POSIX version <13>: OFMT. +* awk language, POSIX version <14>: Field Splitting Summary. +* awk language, POSIX version <15>: Character Lists. +* awk language, POSIX version <16>: Regexp Operators. * awk language, POSIX version: Escape Sequences. * awk language, V.4 version <1>: SVR4. * awk language, V.4 version: Escape Sequences. +* awka compiler for awk programs: Other Versions. +* awka, source code: Other Versions. +* AWKNUM internal type: Internals. * AWKPATH environment variable: AWKPATH Variable. -* awksed: Simple Sed. +* awkprof.out profiling output file: Profiling. +* awksed.awk program: Simple Sed. +* awkvars.out global variable list output file: Options. * backslash continuation <1>: Egrep Program. * backslash continuation: Statements/Lines. -* backslash continuation and comments: Statements/Lines. -* backslash continuation in csh <1>: Statements/Lines. -* backslash continuation in csh: More Complex. +* backslash continuation, and comments: Statements/Lines. +* backslash continuation, in csh <1>: Statements/Lines. +* backslash continuation, in csh: More Complex. * basic function of awk: Getting Started. +* basic programming concepts: Basic Concepts. * BBS-list file: Sample Data Files. +* Beebe, Nelson: Acknowledgments. * BEGIN special pattern: BEGIN/END. -* beginfile: Filetrans Function. +* beginfile user-defined function: Filetrans Function. +* BeOS: BeOS Installation. +* Berry, Karl: Acknowledgments. +* binary I/O: User-modified. +* bindtextdomain built-in function <1>: Programmer i18n. +* bindtextdomain built-in function: I18N Functions. +* bindtextdomain C library function: Explaining gettext. +* bindtextdomain user-defined function: I18N Portability. +* BINMODE variable <1>: PC Using. +* BINMODE variable: User-modified. +* bits2str user-defined function: Bitwise Functions. +* bitwise complement: Bitwise Functions. +* bitwise operations: Bitwise Functions. +* bitwise shift: Bitwise Functions. +* blocks, BEGIN and END <1>: Profiling. +* blocks, BEGIN and END: BEGIN/END. * body of a loop: While Statement. * book, using this: This Manual. * boolean expressions: Boolean Ops. * boolean operators: Boolean Ops. +* bracket expression: Regexp Operators. +* Brandon, Dick: This Manual. * break statement: Break Statement. * break, outside of loops: Break Statement. * Brennan, Michael <1>: Other Versions. * Brennan, Michael <2>: Simple Sed. +* Brennan, Michael <3>: Two-way I/O. * Brennan, Michael: Delete. +* Broder, Alan J.: Contributors. +* Brown, Martin <1>: Bugs. +* Brown, Martin <2>: Contributors. +* Brown, Martin: Acknowledgments. +* BSD portal files: Portal Files. +* BSD-based operating systems <1>: Glossary. +* BSD-based operating systems <2>: Portal Files. +* BSD-based operating systems: Manual History. * buffer matching operators: GNU Regexp Operators. * buffering output: I/O Functions. * buffering, interactive vs. non-interactive: I/O Functions. * buffering, non-interactive vs. interactive: I/O Functions. * buffers, flushing: I/O Functions. +* bug reports: Bugs. +* bug reports, email address, bug-gawk@gnu.org: Bugs. +* bug-gawk@gnu.org bug reporting address: Bugs. * bugs, known in gawk: Known Bugs. * built-in functions: Built-in. * built-in variables: Built-in Variables. @@ -17532,91 +20735,180 @@ Index * case sensitivity: Case-sensitivity. * changing contents of a field: Changing Fields. * changing the record separator: Records. -* character classes: Regexp Operators. +* character class <1>: Character Lists. +* character class: Regexp Operators. * character encodings: Ordinal Functions. * character list: Regexp Operators. * character list, complemented: Regexp Operators. -* character sets: Ordinal Functions. -* chr: Ordinal Functions. -* close <1>: I/O Functions. -* close: Close Files And Pipes. +* character set (regexp component): Regexp Operators. +* character sets (machine character encodings) <1>: Glossary. +* character sets (machine character encodings): Ordinal Functions. +* Chassell, Robert J.: Acknowledgments. +* chem utility: Glossary. +* chr user-defined function: Ordinal Functions. +* Cliff random numbers: Cliff Random Function. +* cliff_rand user-defined function: Cliff Random Function. +* close built-in function <1>: I/O Functions. +* close built-in function: Close Files And Pipes. +* Close, Diane <1>: Contributors. +* Close, Diane: Manual History. +* close, return value: Close Files And Pipes. +* closing coprocesses: Close Files And Pipes. * closing input files and pipes: Close Files And Pipes. * closing output files and pipes: Close Files And Pipes. * coding style used in gawk: Adding Code. -* collating elements: Regexp Operators. -* collating symbols: Regexp Operators. -* command line: Invoking Gawk. -* command line formats: Running gawk. +* collating elements: Character Lists. +* collating symbols: Character Lists. +* comma operator, not supported: For Statement. +* command line: Command Line. * command line, setting FS on: Command Line Field Separator. +* command-line formats: Running gawk. +* command-line option, --assign: Options. +* command-line option, --compat: Options. +* command-line option, --copyleft: Options. +* command-line option, --copyright: Options. +* command-line option, --dump-variables: Options. +* command-line option, --field-separator: Options. +* command-line option, --file: Options. +* command-line option, --gen-po <1>: Options. +* command-line option, --gen-po: String Extraction. +* command-line option, --help: Options. +* command-line option, --lint: Options. +* command-line option, --lint-old: Options. +* command-line option, --non-decimal-data <1>: Options. +* command-line option, --non-decimal-data: Non-decimal Data. +* command-line option, --posix: Options. +* command-line option, --profile: Options. +* command-line option, --re-interval: Options. +* command-line option, --source: Options. +* command-line option, --traditional: Options. +* command-line option, --usage: Options. +* command-line option, --version: Options. +* command-line option, -f: Options. +* command-line option, -F <1>: Options. +* command-line option, -F: Command Line Field Separator. +* command-line option, -f: Long. +* command-line option, -mf: Options. +* command-line option, -mr: Options. +* command-line option, -v: Options. +* command-line option, -W: Options. * comments: Comments. * comments and backslash continuation: Statements/Lines. -* common mistakes <1>: Typing and Comparison. -* common mistakes <2>: Print Examples. -* common mistakes <3>: Basic Field Splitting. -* common mistakes: Computed Regexps. -* comp.lang.awk: Bugs. +* common mistakes <1>: Options. +* common mistakes <2>: String Functions. +* common mistakes <3>: Typing and Comparison. +* common mistakes <4>: Concatenation. +* common mistakes <5>: Arithmetic Ops. +* common mistakes <6>: Special FD. +* common mistakes <7>: Redirection. +* common mistakes <8>: Print Examples. +* common mistakes <9>: Field Separators. +* common mistakes <10>: Computed Regexps. +* common mistakes: Escape Sequences. +* comp.lang.awk Usenet news group: Bugs. * comparison expressions: Typing and Comparison. * comparisons, string vs. regexp: Typing and Comparison. * compatibility mode <1>: POSIX/GNU. * compatibility mode: Options. +* compiled programs <1>: Glossary. +* compiled programs: Basic High Level. +* compl built-in function: Bitwise Functions. +* complement, bitwise: Bitwise Functions. * complemented character list: Regexp Operators. * compound statement: Statements. * computed regular expressions: Computed Regexps. * concatenation: Concatenation. +* concatenation evaluation order: Concatenation. * conditional expression: Conditional Exp. +* configuration option, --disable-nls: Additional Configuration Options. +* configuration option, --enable-portals <1>: Additional Configuration Options. +* configuration option, --enable-portals: Portal Files. +* configuration option, --with-included-gettext <1>: Additional Configuration Options. +* configuration option, --with-included-gettext: Gawk I18N. * configuring gawk: Configuration Philosophy. * constants, types of: Constants. * continuation of lines: Statements/Lines. * continue statement: Continue Statement. * continue, outside of loops: Continue Statement. +* contributors to gawk: Contributors. * control statement: Statements. +* conventions, programming <1>: Internal File Ops. +* conventions, programming <2>: Nextfile Function. +* conventions, programming <3>: Library Names. +* conventions, programming <4>: Non-decimal Data. +* conventions, programming <5>: Return Statement. +* conventions, programming <6>: Definition Syntax. +* conventions, programming <7>: Calling Built-in. +* conventions, programming <8>: Auto-set. +* conventions, programming: Exit Statement. * conversion of case: String Functions. * conversion of strings and numbers: Conversion. * conversions, during subscripting: Numeric Array Subscripts. -* converting dates to timestamps: Mktime Function. -* CONVFMT <1>: Numeric Array Subscripts. -* CONVFMT <2>: User-modified. -* CONVFMT: Conversion. -* cos: Numeric Functions. +* converting dates to timestamps: Time Functions. +* CONVFMT variable <1>: Numeric Array Subscripts. +* CONVFMT variable <2>: User-modified. +* CONVFMT variable: Conversion. +* coprocess <1>: Two-way I/O. +* coprocess <2>: Close Files And Pipes. +* coprocess <3>: Redirection. +* coprocess: Getline/Coprocess. +* cos built-in function: Numeric Functions. +* csh utility <1>: Options. +* csh utility <2>: Two-way I/O. +* csh utility <3>: Statements/Lines. +* csh utility <4>: More Complex. +* csh utility: Quoting. * csh, backslash continuation <1>: Statements/Lines. * csh, backslash continuation: More Complex. * curly braces: Action Overview. * custom.h configuration file: Configuration Philosophy. * cut utility: Cut Program. -* cut.awk: Cut Program. -* d.c., see "dark corner": This Manual. -* dark corner <1>: Other Arguments. -* dark corner <2>: Invoking Gawk. -* dark corner <3>: String Functions. -* dark corner <4>: Uninitialized Subscripts. -* dark corner <5>: Auto-set. -* dark corner <6>: Exit Statement. -* dark corner <7>: Continue Statement. -* dark corner <8>: Break Statement. -* dark corner <9>: Using BEGIN/END. +* cut.awk program: Cut Program. +* d.c., see "dark corner": Conventions. +* dark corner <1>: Glossary. +* dark corner <2>: Other Arguments. +* dark corner <3>: Command Line. +* dark corner <4>: String Functions. +* dark corner <5>: Uninitialized Subscripts. +* dark corner <6>: Auto-set. +* dark corner <7>: Exit Statement. +* dark corner <8>: Continue Statement. +* dark corner <9>: Break Statement. * dark corner <10>: Truth Values. -* dark corner <11>: Conversion. -* dark corner <12>: Assignment Options. -* dark corner <13>: Using Constant Regexps. -* dark corner <14>: Format Modifiers. -* dark corner <15>: Control Letters. -* dark corner <16>: OFMT. -* dark corner <17>: Getline Summary. -* dark corner <18>: Plain Getline. -* dark corner <19>: Multiple Line. -* dark corner <20>: Field Splitting Summary. -* dark corner <21>: Single Character Fields. -* dark corner <22>: Records. -* dark corner <23>: Escape Sequences. -* dark corner: This Manual. +* dark corner <11>: Assignment Ops. +* dark corner <12>: Conversion. +* dark corner <13>: Assignment Options. +* dark corner <14>: Using Constant Regexps. +* dark corner <15>: Close Files And Pipes. +* dark corner <16>: Format Modifiers. +* dark corner <17>: Control Letters. +* dark corner <18>: OFMT. +* dark corner <19>: Getline Notes. +* dark corner <20>: Multiple Line. +* dark corner <21>: Field Splitting Summary. +* dark corner <22>: Single Character Fields. +* dark corner <23>: Changing Fields. +* dark corner <24>: Records. +* dark corner <25>: Escape Sequences. +* dark corner: Conventions. +* data files, non-readable, skipping: File Checking. +* data files, readable, checking: File Checking. +* data-driven languages <1>: Basic High Level. * data-driven languages: Getting Started. -* dates, converting to timestamps: Mktime Function. +* dates, converting to timestamps: Time Functions. +* Davies, Stephen <1>: Bugs. +* Davies, Stephen: Contributors. +* dcgettext built-in function <1>: Programmer i18n. +* dcgettext built-in function: I18N Functions. +* dcgettext user-defined function: I18N Portability. +* deadlock: Two-way I/O. * decrement operators: Increment Ops. * default action: Very Simple. * default pattern: Very Simple. * defining functions: Definition Syntax. * Deifik, Scott <1>: Bugs. -* Deifik, Scott: Acknowledgements. +* Deifik, Scott <2>: Contributors. +* Deifik, Scott: Acknowledgments. * delete statement: Delete. * deleting elements of arrays: Delete. * deleting entire arrays: Delete. @@ -17627,62 +20919,88 @@ Index * differences between gawk and awk <3>: Calling Built-in. * differences between gawk and awk <4>: Delete. * differences between gawk and awk <5>: ARGC and ARGV. -* differences between gawk and awk <6>: Nextfile Statement. -* differences between gawk and awk <7>: I/O And BEGIN/END. -* differences between gawk and awk <8>: Conditional Exp. -* differences between gawk and awk <9>: Arithmetic Ops. -* differences between gawk and awk <10>: Using Constant Regexps. -* differences between gawk and awk <11>: Scalar Constants. -* differences between gawk and awk <12>: Close Files And Pipes. -* differences between gawk and awk <13>: Special Files. -* differences between gawk and awk <14>: Redirection. -* differences between gawk and awk <15>: Getline Summary. -* differences between gawk and awk <16>: Getline Intro. -* differences between gawk and awk <17>: Single Character Fields. -* differences between gawk and awk <18>: Records. +* differences between gawk and awk <6>: User-modified. +* differences between gawk and awk <7>: Nextfile Statement. +* differences between gawk and awk <8>: I/O And BEGIN/END. +* differences between gawk and awk <9>: Conditional Exp. +* differences between gawk and awk <10>: Arithmetic Ops. +* differences between gawk and awk <11>: Using Constant Regexps. +* differences between gawk and awk <12>: Scalar Constants. +* differences between gawk and awk <13>: Close Files And Pipes. +* differences between gawk and awk <14>: Special FD. +* differences between gawk and awk <15>: Redirection. +* differences between gawk and awk <16>: Format Modifiers. +* differences between gawk and awk <17>: Getline Notes. +* differences between gawk and awk <18>: Getline/Coprocess. +* differences between gawk and awk <19>: Getline. +* differences between gawk and awk <20>: Single Character Fields. +* differences between gawk and awk <21>: Records. * differences between gawk and awk: Case-sensitivity. +* directory search <1>: VMS Running. +* directory search <2>: PC Using. +* directory search <3>: Igawk Program. * directory search: AWKPATH Variable. * division: Arithmetic Ops. +* do-while statement: Do Statement. +* documentation, online: Manual History. * documenting awk programs <1>: Library Names. * documenting awk programs: Comments. -* dupword.awk: Dupword Program. +* double-precision floating-point, definition of: Basic Data Typing. +* Drepper, Ulrich: Acknowledgments. +* dupnode internal function: Internals. +* dupword.awk program: Dupword Program. +* dynamic profiling: Profiling. * dynamic regular expressions: Computed Regexps. +* dynamic regular expressions with embedded newlines: Computed Regexps. * EBCDIC: Ordinal Functions. -* egrep <1>: Regexp Operators. -* egrep: One-shot. -* egrep utility: Egrep Program. -* egrep.awk: Egrep Program. +* egrep utility <1>: Egrep Program. +* egrep utility: Character Lists. +* egrep.awk program: Egrep Program. * element assignment: Assigning Elements. * element of array: Reference to Elements. +* emaill address for bug reports, bug-gawk@gnu.org: Bugs. +* embedded newlines, in dynamic regexps: Computed Regexps. +* EMISTERED: TCP/IP Networking. * empty action: Very Simple. * empty pattern: Empty. -* empty program: Invoking Gawk. +* empty program: Command Line. * empty string <1>: Truth Values. * empty string <2>: Conversion. * empty string <3>: Regexp Field Splitting. * empty string: Records. +* empty string, definition of: Basic Data Typing. * END special pattern: BEGIN/END. -* endfile: Filetrans Function. -* endgrent: Group Functions. -* endpwent: Passwd Functions. -* ENVIRON: Auto-set. +* endfile user-defined function: Filetrans Function. +* endgrent user-defined function: Group Functions. +* endpwent user-defined function: Passwd Functions. +* ENVIRON variable: Auto-set. * environment variable, AWKPATH: AWKPATH Variable. * environment variable, POSIXLY_CORRECT: Options. -* equivalence classes: Regexp Operators. -* ERRNO <1>: Auto-set. -* ERRNO <2>: Close Files And Pipes. -* ERRNO: Getline Intro. -* errors, common <1>: Typing and Comparison. -* errors, common <2>: Print Examples. -* errors, common <3>: Basic Field Splitting. -* errors, common: Computed Regexps. -* escape processing, sub et. al.: String Functions. +* epoch, definition of: Glossary. +* equivalence classes: Character Lists. +* ERRNO variable <1>: Auto-set. +* ERRNO variable: Getline. +* errors, common <1>: Options. +* errors, common <2>: String Functions. +* errors, common <3>: Typing and Comparison. +* errors, common <4>: Concatenation. +* errors, common <5>: Arithmetic Ops. +* errors, common <6>: Special FD. +* errors, common <7>: Redirection. +* errors, common <8>: Print Examples. +* errors, common <9>: Field Separators. +* errors, common <10>: Computed Regexps. +* errors, common: Escape Sequences. +* escape processing, sub et. al.: Gory Details. * escape sequence notation: Escape Sequences. -* evaluation, order of: Calling Built-in. +* evaluation, order of <1>: Calling Built-in. +* evaluation, order of <2>: Increment Ops. +* evaluation, order of: Concatenation. * examining fields: Fields. * executable scripts: Executable Scripts. * exit statement: Exit Statement. -* exp: Numeric Functions. +* exp built-in function: Numeric Functions. +* expand utility: Very Simple. * explicit input: Getline. * exponentiation: Arithmetic Ops. * expression: Expressions. @@ -17691,99 +21009,180 @@ Index * expression, comparison: Typing and Comparison. * expression, conditional: Conditional Exp. * expression, matching: Typing and Comparison. -* extract.awk: Extract Program. -* features, adding: Adding Code. -* fflush: I/O Functions. +* extension built-in function: Using Internal File Ops. +* extensions, Bell Laboratories awk: BTL. +* extensions, mawk: Other Versions. +* extract.awk program: Extract Program. +* extraction, of marked strings (internationalization): String Extraction. +* fatal errors <1>: File Checking. +* fatal errors <2>: Options. +* fatal errors <3>: I/O Functions. +* fatal errors <4>: String Functions. +* fatal errors <5>: Calling Built-in. +* fatal errors <6>: Format Modifiers. +* fatal errors: Constant Size. +* FDL: GNU Free Documentation License. +* features, adding to gawk: Adding Code. +* features, advanced: Advanced Features. +* features, undocumented: Undocumented. +* Fenlason, Jay <1>: Contributors. +* Fenlason, Jay: History. +* fflush built-in function: I/O Functions. * field operator $: Fields. -* field separator, choice of: Basic Field Splitting. -* field separator, FS: Basic Field Splitting. +* field separator, choice of: Field Separators. +* field separator, FS: Field Separators. * field separator, on command line: Command Line Field Separator. -* field, changing contents of: Changing Fields. * fields: Fields. -* fields, separating: Basic Field Splitting. -* FIELDWIDTHS: User-modified. -* file descriptors: Special Files. +* fields, changing contents of: Changing Fields. +* fields, definition of: Basic High Level. +* fields, separating: Field Separators. +* FIELDWIDTHS variable: User-modified. +* file descriptors: Special FD. * file, awk program: Long. -* FILENAME <1>: Auto-set. -* FILENAME <2>: Getline Summary. -* FILENAME: Reading Files. -* FILENAME, being set by getline: Getline Summary. -* Fish, Fred: Bugs. +* FILENAME variable <1>: Auto-set. +* FILENAME variable <2>: Getline Notes. +* FILENAME variable: Reading Files. +* FILENAME, being set by getline: Getline Notes. +* Fish, Fred <1>: Bugs. +* Fish, Fred: Contributors. +* flag variables <1>: Tee Program. +* flag variables <2>: Ranges. +* flag variables: Boolean Ops. +* floating-point, definition of: Basic Data Typing. +* floating-point, positive and negative values for zero: Floating Point Issues. +* floating-point, precision issues: Floating Point Issues. * flushing buffers: I/O Functions. -* FNR <1>: Auto-set. -* FNR: Records. -* for (x in ...): Scanning an Array. +* FNR variable <1>: Auto-set. +* FNR variable: Records. +* for (x in ...) statement: Scanning an Array. * for statement: For Statement. -* format specifier: Control Letters. +* force_number internal function: Internals. +* force_string internal function: Internals. +* format specifier, printf: Control Letters. +* format specifier, strftime: Time Functions. +* format specifiers, mixing regular with positional specifiers (printf): Printf Ordering. * format string: Basic Printf. * format, numeric output: OFMT. * formatted output: Printf. * formatted timestamps: Gettimeofday Function. -* Free Software Foundation <1>: Getting. +* Free Documentation License: GNU Free Documentation License. +* Free Software Foundation <1>: Glossary. +* Free Software Foundation <2>: Getting. * Free Software Foundation: Manual History. +* free_temp internal macro: Internals. +* FreeBSD <1>: Glossary. * FreeBSD: Manual History. -* Friedl, Jeffrey: Acknowledgements. -* FS <1>: User-modified. -* FS: Basic Field Splitting. -* ftp, anonymous <1>: Other Versions. +* FS variable <1>: User-modified. +* FS variable: Field Separators. +* FSF <1>: Glossary. +* FSF <2>: Getting. +* FSF: Manual History. * ftp, anonymous: Getting. * function call <1>: Function Caveats. * function call: Function Calls. * function definition: Definition Syntax. * function, recursive: Definition Syntax. +* function, user-defined: User-defined. * functions, undefined: Function Caveats. -* functions, user-defined: User-defined. -* gawk coding style: Adding Code. -* gensub: String Functions. -* getgrent: Group Functions. -* getgrent, C version: Group Functions. -* getgrgid: Group Functions. -* getgrnam: Group Functions. -* getgruser: Group Functions. -* getline: Getline. -* getline, return values: Getline Intro. -* getline, setting FILENAME: Getline Summary. -* getopt: Getopt Function. -* getopt, C version: Getopt Function. -* getpwent: Passwd Functions. -* getpwent, C version: Passwd Functions. -* getpwnam: Passwd Functions. -* getpwuid: Passwd Functions. -* gettimeofday: Gettimeofday Function. +* G-d: Acknowledgments. +* Garfinkle, Scott: Contributors. +* gawk, coding style: Adding Code. +* gawk, source code: Getting. +* General Public License <1>: Glossary. +* General Public License <2>: New Ports. +* General Public License <3>: Other Versions. +* General Public License: Manual History. +* gensub built-in function: String Functions. +* gensub, escape processing: Gory Details. +* get_argument internal function: Internals. +* getgrent C library function: Group Functions. +* getgrent user-defined function: Group Functions. +* getgrgid user-defined function: Group Functions. +* getgrnam user-defined function: Group Functions. +* getgruser user-defined function: Group Functions. +* getline built-in function: Getline. +* getline, return values: Getline. +* getline, setting FILENAME: Getline Notes. +* getopt C library function: Getopt Function. +* getopt user-defined function: Getopt Function. +* getpwent C library function: Passwd Functions. +* getpwent user-defined function: Passwd Functions. +* getpwnam user-defined function: Passwd Functions. +* getpwuid user-defined function: Passwd Functions. +* getservbyname C library function: TCP/IP Networking. +* gettext C library function: Explaining gettext. +* gettext, how it works: Explaining gettext. +* gettimeofday user-defined function: Gettimeofday Function. * getting gawk: Getting. +* GNITS mailing list: Acknowledgments. +* GNU Free Documentation License: GNU Free Documentation License. +* GNU General Public License <1>: Glossary. +* GNU General Public License <2>: New Ports. +* GNU General Public License <3>: Other Versions. +* GNU General Public License: Manual History. +* GNU Lesser General Public License <1>: Glossary. +* GNU Lesser General Public License: Other Versions. +* GNU Project <1>: Glossary. * GNU Project: Manual History. +* GNU/Linux <1>: Glossary. +* GNU/Linux <2>: Using Internal File Ops. +* GNU/Linux <3>: Internal File Ops. +* GNU/Linux <4>: Dynamic Extensions. +* GNU/Linux <5>: Atari Compiling. +* GNU/Linux <6>: Additional Configuration Options. +* GNU/Linux <7>: Installation. +* GNU/Linux <8>: I18N Example. +* GNU/Linux: Manual History. +* GPL <1>: Glossary. +* GPL <2>: New Ports. +* GPL <3>: Other Versions. +* GPL: Manual History. * grcat program: Group Functions. -* grcat.c: Group Functions. +* Grigera, Juan <1>: Bugs. +* Grigera, Juan: Contributors. * group file: Group Functions. * group information: Group Functions. -* gsub: String Functions. +* gsub built-in function: String Functions. +* gsub, escape processing: Gory Details. * gsub, third argument of: String Functions. * Hankerson, Darrel <1>: Bugs. -* Hankerson, Darrel: Acknowledgements. -* historical features <1>: Historical Features. -* historical features <2>: String Functions. -* historical features <3>: Continue Statement. -* historical features <4>: Break Statement. +* Hankerson, Darrel <2>: Contributors. +* Hankerson, Darrel: Acknowledgments. +* Hartholz, Elaine: Acknowledgments. +* Hartholz, Marshall: Acknowledgments. +* hexadecimal numbers: Non-decimal-numbers. +* historical features <1>: String Functions. +* historical features <2>: Continue Statement. +* historical features <3>: Break Statement. * historical features: Command Line Field Separator. * history of awk: History. -* histsort.awk: History Sorting. +* histsort.awk program: History Sorting. * how awk works: Two Rules. -* Hughes, Phil: Acknowledgements. -* I/O from BEGIN and END: I/O And BEGIN/END. +* Hughes, Phil: Acknowledgments. +* HUP signal: Profiling. +* I/O, binary: User-modified. +* I/O, from BEGIN and END: I/O And BEGIN/END. +* I/O, two-way: Two-way I/O. * id utility: Id Program. -* id.awk: Id Program. +* id.awk program: Id Program. * if-else statement: If Statement. -* igawk.sh: Igawk Program. -* IGNORECASE <1>: Array Intro. -* IGNORECASE <2>: User-modified. -* IGNORECASE: Case-sensitivity. -* IGNORECASE and array subscripts: Array Intro. +* igawk.sh program: Igawk Program. +* IGNORECASE variable <1>: Array Sorting. +* IGNORECASE variable <2>: Array Intro. +* IGNORECASE variable <3>: User-modified. +* IGNORECASE variable: Case-sensitivity. +* IGNORECASE, and array sorting: Array Sorting. +* IGNORECASE, and array subscripts: Array Intro. * ignoring case: Case-sensitivity. * implementation limits <1>: Redirection. -* implementation limits: Getline Summary. +* implementation limits: Getline Notes. +* in operator <1>: Id Program. +* in operator <2>: Scanning an Array. +* in operator <3>: For Statement. +* in operator <4>: Precedence. * in operator: Typing and Comparison. * increment operators: Increment Ops. -* index: String Functions. +* index built-in function: String Functions. * initialization, automatic: More Complex. * input: Reading Files. * input file, sample: Sample Data Files. @@ -17794,100 +21193,212 @@ Index * input, getline command: Getline. * input, multiple line records: Multiple Line. * input, standard: Read Terminal. +* insomnia, cure for: Alarm Program. * installation, amiga: Amiga Installation. * installation, atari: Atari Installation. -* installation, MS-DOS and OS/2: PC Installation. +* installation, beos: BeOS Installation. +* installation, pc operating systems: PC Installation. +* installation, tandem: Tandem Installation. * installation, unix: Quick Installation. * installation, vms: VMS Installation. -* int: Numeric Functions. +* int built-in function: Numeric Functions. +* integer, definition of: Basic Data Typing. +* integer, unsigned: Basic Data Typing. * interaction, awk and other programs: I/O Functions. * interactive buffering vs. non-interactive: I/O Functions. +* internal function, assoc_clear: Internals. +* internal function, assoc_lookup: Internals. +* internal function, dupnode: Internals. +* internal function, force_number: Internals. +* internal function, force_string: Internals. +* internal function, get_argument: Internals. +* internal function, make_builtin: Internals. +* internal function, make_number: Internals. +* internal function, make_string: Internals. +* internal function, set_value: Internals. +* internal function, tmp_number: Internals. +* internal function, tmp_string: Internals. +* internal function, update_ERRNO: Internals. +* internal macro, free_temp: Internals. +* internal type, AWKNUM: Internals. +* internal type, NODE: Internals. +* internal variable, param_cnt: Internals. +* internal variable, stlen: Internals. +* internal variable, stptr: Internals. +* internal variable, type: Internals. +* internal variable, vname: Internals. +* internationalization <1>: I18N and L10N. +* internationalization: User-modified. +* internationalization features in gawk: Internationalization. +* internationalization of awk programs, portability issues: I18N Portability. +* internationalization, marked strings: Programmer i18n. +* internationalizing a program: Explaining gettext. +* interpreted programs <1>: Glossary. +* interpreted programs: Basic High Level. * interval expressions: Regexp Operators. * inventory-shipped file: Sample Data Files. -* invocation of gawk: Invoking Gawk. +* invocation of gawk: Command Line. +* ISO: Glossary. * ISO 8601: Time Functions. * ISO 8859-1 <1>: Glossary. * ISO 8859-1: Case-sensitivity. * ISO Latin-1 <1>: Glossary. * ISO Latin-1: Case-sensitivity. -* Jaegermann, Michal <1>: Bugs. -* Jaegermann, Michal: Acknowledgements. -* join: Join Function. -* Kernighan, Brian <1>: Other Versions. -* Kernighan, Brian <2>: BTL. -* Kernighan, Brian <3>: Concatenation. -* Kernighan, Brian <4>: Acknowledgements. +* Jacobs, Andrew: Passwd Functions. +* Jaegermann, Michal <1>: Contributors. +* Jaegermann, Michal: Acknowledgments. +* Jedi knights: Undocumented. +* join user-defined function: Join Function. +* Kahrs, Ju"rgen <1>: Contributors. +* Kahrs, Ju"rgen: Acknowledgments. +* Kenobi, Obi-Wan: Undocumented. +* Kernighan, Brian <1>: Basic Data Typing. +* Kernighan, Brian <2>: Other Versions. +* Kernighan, Brian <3>: Contributors. +* Kernighan, Brian <4>: BTL. +* Kernighan, Brian <5>: Concatenation. +* Kernighan, Brian <6>: Acknowledgments. +* Kernighan, Brian <7>: Conventions. * Kernighan, Brian: History. +* kill command: Profiling. +* Knights, jedi: Undocumented. * known bugs: Known Bugs. -* labels.awk: Labels Program. +* Kwok, Conrad: Contributors. +* labels.awk program: Labels Program. * language, awk: This Manual. +* language, data-driven <1>: Basic High Level. * language, data-driven: Getting Started. * language, procedural: Getting Started. +* LC_ALL locale category: Explaining gettext. +* LC_COLLATE locale category: Explaining gettext. +* LC_CTYPE locale category: Explaining gettext. +* LC_MESSAGES locale category: Explaining gettext. +* LC_MONETARY locale category: Explaining gettext. +* LC_NUMERIC locale category: Explaining gettext. +* LC_RESPONSE locale category: Explaining gettext. +* LC_TIME locale category: Explaining gettext. +* left shift, bitwise: Bitwise Functions. * leftmost longest match <1>: Multiple Line. * leftmost longest match: Leftmost Longest. -* length: String Functions. +* length built-in function: String Functions. +* Lesser General Public License <1>: Glossary. +* Lesser General Public License: Other Versions. +* LGPL <1>: Glossary. +* LGPL: Other Versions. * limitations <1>: Redirection. -* limitations: Getline Summary. +* limitations: Getline Notes. * line break: Statements/Lines. * line continuation <1>: Conditional Exp. * line continuation <2>: Boolean Ops. * line continuation <3>: Print Examples. * line continuation: Statements/Lines. -* Linux <1>: Atari Compiling. +* lint checks <1>: Options. +* lint checks <2>: Command Line. +* lint checks <3>: Function Caveats. +* lint checks <4>: Uninitialized Subscripts. +* lint checks <5>: Delete. +* lint checks <6>: User-modified. +* lint checks: Format Modifiers. +* LINT variable: User-modified. +* Linux <1>: Glossary. +* Linux <2>: Using Internal File Ops. +* Linux <3>: Internal File Ops. +* Linux <4>: Dynamic Extensions. +* Linux <5>: Atari Compiling. +* Linux <6>: Additional Configuration Options. +* Linux <7>: Installation. +* Linux <8>: I18N Example. * Linux: Manual History. +* locale categories: Explaining gettext. * locale, definition of: Time Functions. -* log: Numeric Functions. +* localization: I18N and L10N. +* log built-in function: Numeric Functions. * logical false: Truth Values. -* logical operations: Boolean Ops. +* logical operators: Boolean Ops. * logical true: Truth Values. * login information: Passwd Functions. -* long options: Invoking Gawk. +* long options: Command Line. * loop: While Statement. * loops, exiting: Break Statement. +* Lost In Space: Dynamic Extensions. +* ls utility: More Complex. +* lshift built-in function: Bitwise Functions. * lvalue: Assignment Ops. +* make_builtin internal function: Internals. +* make_number internal function: Internals. +* make_string internal function: Internals. * mark parity: Ordinal Functions. -* match: String Functions. +* marked string extraction (internationalization): String Extraction. +* marked strings for internationalization: Programmer i18n. +* Marx, Groucho: Increment Ops. +* match built-in function: String Functions. * matching ranges of lines: Ranges. * matching, leftmost longest <1>: Multiple Line. * matching, leftmost longest: Leftmost Longest. -* mawk: Other Versions. +* matching, the null string: Gory Details. +* mawk, source code: Other Versions. * merging strings: Join Function. +* message object files (gettext): Explaining gettext. * metacharacters: Regexp Operators. -* mistakes, common <1>: Typing and Comparison. -* mistakes, common <2>: Print Examples. -* mistakes, common <3>: Basic Field Splitting. -* mistakes, common: Computed Regexps. -* mktime: Mktime Function. +* mistakes, common <1>: Options. +* mistakes, common <2>: String Functions. +* mistakes, common <3>: Typing and Comparison. +* mistakes, common <4>: Concatenation. +* mistakes, common <5>: Arithmetic Ops. +* mistakes, common <6>: Special FD. +* mistakes, common <7>: Redirection. +* mistakes, common <8>: Print Examples. +* mistakes, common <9>: Field Separators. +* mistakes, common <10>: Computed Regexps. +* mistakes, common: Escape Sequences. +* mktime built-in function: Time Functions. * modifiers (in format specifiers): Format Modifiers. -* multi-dimensional subscripts: Multi-dimensional. +* msgfmt utility: I18N Example. +* multidimensional subscripts: Multi-dimensional. * multiple line records: Multiple Line. * multiple passes over data: Other Arguments. * multiple statements on one line: Statements/Lines. * multiplication: Arithmetic Ops. -* names, use of: Definition Syntax. -* namespace issues in awk: Library Names. -* namespaces: Definition Syntax. +* mv utility: Redirection. +* names, use of <1>: Library Names. +* names, use of <2>: Definition Syntax. +* names, use of: Arrays. +* namespace issues in awk <1>: Library Names. +* namespace issues in awk <2>: Definition Syntax. +* namespace issues in awk: Arrays. +* negative zero: Floating Point Issues. +* NetBSD <1>: Glossary. * NetBSD: Manual History. +* networking, TCP/IP: TCP/IP Networking. * new awk: History. * new awk vs. old awk: Names. * newline: Statements/Lines. +* newlines, embedded in dynamic regexps: Computed Regexps. +* next file statement <1>: POSIX/GNU. * next file statement: Nextfile Statement. * next statement: Next Statement. * next, inside a user-defined function: Next Statement. -* nextfile function: Nextfile Function. * nextfile statement: Nextfile Statement. -* NF <1>: Auto-set. -* NF: Fields. +* nextfile user-defined function: Nextfile Function. +* nextfile, inside a user-defined function: Nextfile Statement. +* NF variable <1>: Auto-set. +* NF variable: Fields. +* noassign.awk program: Ignoring Assigns. +* NODE internal type: Internals. * non-interactive buffering vs. interactive: I/O Functions. -* not operator: Boolean Ops. -* NR <1>: Auto-set. -* NR: Records. +* non-readable data files, skipping: File Checking. +* NOT logical operator: Boolean Ops. +* NR variable <1>: Auto-set. +* NR variable: Records. * null string <1>: Truth Values. * null string <2>: Conversion. * null string: Regexp Field Splitting. * null string, as array subscript: Uninitialized Subscripts. +* null string, definition of: Basic Data Typing. * number of fields, NF: Fields. * number of records, NR, FNR: Records. +* numbers, hexadecimal: Non-decimal-numbers. +* numbers, octal: Non-decimal-numbers. * numbers, used as subscripts: Numeric Array Subscripts. * numeric character values: Ordinal Functions. * numeric constant: Scalar Constants. @@ -17896,33 +21407,42 @@ Index * numeric value: Scalar Constants. * obsolete features: Obsolete. * obsolete options: Obsolete. -* OFMT <1>: User-modified. -* OFMT <2>: Conversion. -* OFMT: OFMT. -* OFS <1>: User-modified. -* OFS: Output Separators. +* octal numbers: Non-decimal-numbers. +* OFMT variable <1>: User-modified. +* OFMT variable <2>: Conversion. +* OFMT variable: OFMT. +* OFS variable <1>: User-modified. +* OFS variable: Output Separators. * old awk: History. * old awk vs. new awk: Names. -* one-liners: One-liners. -* operations, logical: Boolean Ops. -* operator precedence: Precedence. +* one-liners: Very Simple. +* online documentation: Manual History. +* OpenBSD <1>: Glossary. +* OpenBSD: Manual History. +* operator precedence <1>: Precedence. +* operator precedence: Increment Ops. * operators, arithmetic: Arithmetic Ops. * operators, assignment: Assignment Ops. * operators, boolean: Boolean Ops. * operators, decrement: Increment Ops. * operators, increment: Increment Ops. +* operators, logical: Boolean Ops. * operators, regexp matching: Regexp Usage. * operators, relational: Typing and Comparison. * operators, short-circuit: Boolean Ops. * operators, string: Concatenation. * operators, string-matching: Regexp Usage. -* options, command line: Invoking Gawk. -* options, long: Invoking Gawk. -* or operator: Boolean Ops. -* ord: Ordinal Functions. +* options, command-line: Command Line. +* options, long: Command Line. +* OR bitwise operation: Bitwise Functions. +* or built-in function: Bitwise Functions. +* OR logical operator: Boolean Ops. +* ord user-defined function: Ordinal Functions. * order of evaluation: Calling Built-in. -* ORS <1>: User-modified. -* ORS: Output Separators. +* order of evaluation, concatenation: Concatenation. +* ORS variable <1>: User-modified. +* ORS variable: Output Separators. +* other awk implementations: Other Versions. * output: Printing. * output field separator, OFS: Output Separators. * output format specifier, OFMT: OFMT. @@ -17931,8 +21451,13 @@ Index * output, buffering: I/O Functions. * output, formatted: Printf. * output, piping: Redirection. +* P1003.2 POSIX standard: Glossary. +* param_cnt internal variable: Internals. * passes, multiple: Other Arguments. * password file: Passwd Functions. +* path, search <1>: VMS Running. +* path, search <2>: PC Using. +* path, search <3>: Igawk Program. * path, search: AWKPATH Variable. * pattern, BEGIN: BEGIN/END. * pattern, default: Very Simple. @@ -17941,485 +21466,747 @@ Index * pattern, END: BEGIN/END. * pattern, range: Ranges. * pattern, regular expressions: Regexp. -* patterns, types of: Kinds of Patterns. -* per file initialization and clean-up: Filetrans Function. +* patterns, types of: Pattern Overview. +* per file initialization and cleanup: Filetrans Function. * PERL: Future Extensions. +* Peters, Arno: Contributors. +* Peterson, Hal: Contributors. +* pgawk program: Profiling. * pipeline, input: Getline/Pipe. * pipes for output: Redirection. -* portability issues <1>: Portability Notes. -* portability issues <2>: Definition Syntax. -* portability issues <3>: I/O Functions. -* portability issues <4>: String Functions. -* portability issues <5>: Delete. -* portability issues <6>: Close Files And Pipes. -* portability issues <7>: Escape Sequences. -* portability issues: Statements/Lines. +* piping commands into the shell: Redirection. +* portability issues <1>: Library Functions. +* portability issues <2>: I18N Portability. +* portability issues <3>: Function Caveats. +* portability issues <4>: Definition Syntax. +* portability issues <5>: I/O Functions. +* portability issues <6>: String Functions. +* portability issues <7>: Delete. +* portability issues <8>: Precedence. +* portability issues <9>: Increment Ops. +* portability issues <10>: Assignment Ops. +* portability issues <11>: Arithmetic Ops. +* portability issues <12>: Close Files And Pipes. +* portability issues <13>: Changing Fields. +* portability issues <14>: Records. +* portability issues <15>: Escape Sequences. +* portability issues <16>: Statements/Lines. +* portability issues: Executable Scripts. +* portability issues, internationalization of awk programs: I18N Portability. +* portable object files (gettext): Explaining gettext. +* portal files: Portal Files. * porting gawk: New Ports. +* positional specifier, printf <1>: Printf Ordering. +* positional specifier, printf: Format Modifiers. +* positional specifiers, mixing with regular formats (printf): Printf Ordering. +* positive zero: Floating Point Issues. * POSIX awk <1>: Definition Syntax. -* POSIX awk <2>: String Functions. -* POSIX awk <3>: User-modified. -* POSIX awk <4>: Next Statement. -* POSIX awk <5>: Continue Statement. -* POSIX awk <6>: Break Statement. -* POSIX awk <7>: Precedence. -* POSIX awk <8>: Assignment Ops. -* POSIX awk <9>: Arithmetic Ops. -* POSIX awk <10>: Conversion. -* POSIX awk <11>: Format Modifiers. -* POSIX awk <12>: OFMT. -* POSIX awk <13>: Field Splitting Summary. -* POSIX awk <14>: Regexp Operators. +* POSIX awk <2>: Gory Details. +* POSIX awk <3>: String Functions. +* POSIX awk <4>: User-modified. +* POSIX awk <5>: Next Statement. +* POSIX awk <6>: Continue Statement. +* POSIX awk <7>: Break Statement. +* POSIX awk <8>: Precedence. +* POSIX awk <9>: Assignment Ops. +* POSIX awk <10>: Arithmetic Ops. +* POSIX awk <11>: Conversion. +* POSIX awk <12>: Format Modifiers. +* POSIX awk <13>: OFMT. +* POSIX awk <14>: Field Splitting Summary. +* POSIX awk <15>: Character Lists. +* POSIX awk <16>: Regexp Operators. * POSIX awk: Escape Sequences. * POSIX mode: Options. * POSIXLY_CORRECT environment variable: Options. -* precedence: Precedence. +* precedence <1>: Precedence. +* precedence: Increment Ops. * precedence, regexp operators: Regexp Operators. * print statement: Print. +* printf statement: Printf. * printf statement, syntax of: Basic Printf. * printf, format-control characters: Control Letters. +* printf, mixing positional specifiers with regular formats: Printf Ordering. * printf, modifiers: Format Modifiers. +* printf, positional specifier <1>: Printf Ordering. +* printf, positional specifier: Format Modifiers. * printing: Printing. +* problem reports: Bugs. * procedural languages: Getting Started. -* process information: Special Files. +* process information: Special Process. * processing arguments: Getopt Function. +* processing data: Basic High Level. +* PROCINFO variable: Auto-set. +* profiling awk programs: Profiling. +* profiling output file (awkprof.out): Profiling. +* profiling, dynamic: Profiling. * program file: Long. * program, awk: This Manual. * program, definition of: Getting Started. -* program, self contained: Executable Scripts. +* program, self-contained: Executable Scripts. +* programming concepts, basic: Basic Concepts. +* programming conventions <1>: Internal File Ops. +* programming conventions <2>: Nextfile Function. +* programming conventions <3>: Library Names. +* programming conventions <4>: Non-decimal Data. +* programming conventions <5>: Return Statement. +* programming conventions <6>: Definition Syntax. +* programming conventions <7>: Calling Built-in. +* programming conventions <8>: Auto-set. +* programming conventions: Exit Statement. +* programming language, recipe for: History. +* programming, basic steps: Basic High Level. +* programs, compiled: Basic High Level. * programs, documenting <1>: Library Names. * programs, documenting: Comments. +* programs, interpreted: Basic High Level. * pwcat program: Passwd Functions. -* pwcat.c: Passwd Functions. * quotient: Arithmetic Ops. -* quoting, shell <1>: Long. +* quoting rules, shell: Quoting. +* quoting, shell <1>: Comments. +* quoting, shell <2>: Long. * quoting, shell: Read Terminal. * Rakitzis, Byron: History Sorting. -* rand: Numeric Functions. +* rand built-in function: Numeric Functions. +* random numbers, Cliff: Cliff Random Function. * random numbers, seed of: Numeric Functions. * range pattern: Ranges. * Rankin, Pat <1>: Bugs. -* Rankin, Pat <2>: Assignment Ops. -* Rankin, Pat: Acknowledgements. +* Rankin, Pat <2>: Contributors. +* Rankin, Pat <3>: Assignment Ops. +* Rankin, Pat: Acknowledgments. +* readable data files, checking: File Checking. +* readable.awk program: File Checking. * reading files: Reading Files. * reading files, getline command: Getline. * reading files, multiple line records: Multiple Line. +* recipe for a programming language: History. * record separator, RS: Records. * record terminator, RT: Records. +* record, definition of <1>: Basic High Level. * record, definition of: Records. * records, multiple line: Multiple Line. * recursive function: Definition Syntax. * redirection of input: Getline/File. * redirection of output: Redirection. +* reference counting: Array Sorting. * reference to array: Reference to Elements. * regexp: Regexp. * regexp as expression: Typing and Comparison. * regexp comparison vs. string comparison: Typing and Comparison. * regexp constant: Regexp Usage. * regexp constants, difference between slashes and quotes: Computed Regexps. -* regexp match/non-match operators <1>: Typing and Comparison. -* regexp match/non-match operators: Regexp Usage. -* regexp matching operators: Regexp Usage. -* regexp operators: Regexp Operators. +* regexp operators <1>: Typing and Comparison. +* regexp operators <2>: Regexp Operators. +* regexp operators: Regexp Usage. * regexp operators, GNU specific: GNU Regexp Operators. * regexp operators, precedence of: Regexp Operators. * regexp, anchors: Regexp Operators. * regexp, dynamic: Computed Regexps. -* regexp, effect of command line options: GNU Regexp Operators. +* regexp, dynamic, with embedded newlines: Computed Regexps. +* regexp, effect of command-line options: GNU Regexp Operators. * regular expression: Regexp. * regular expression metacharacters: Regexp Operators. -* regular expressions as field separators: Basic Field Splitting. +* regular expressions as field separators: Field Separators. * regular expressions as patterns: Regexp. * regular expressions as record separators: Records. * regular expressions, computed: Computed Regexps. * relational operators: Typing and Comparison. * remainder: Arithmetic Ops. * removing elements of arrays: Delete. +* reporting bugs: Bugs. +* reporting problems: Bugs. * return statement: Return Statement. -* RFC-1036: Time Functions. -* RFC-822: Time Functions. -* RLENGTH <1>: String Functions. -* RLENGTH: Auto-set. -* Robbins, Miriam: Acknowledgements. +* return value from close: Close Files And Pipes. +* rewind user-defined function: Rewind Function. +* RFC 1036: Time Functions. +* RFC 822: Time Functions. +* right shift, bitwise: Bitwise Functions. +* Ritchie, Dennis: Basic Data Typing. +* RLENGTH variable <1>: String Functions. +* RLENGTH variable: Auto-set. +* Robbins, Arnold <1>: Future Extensions. +* Robbins, Arnold <2>: Bugs. +* Robbins, Arnold <3>: Contributors. +* Robbins, Arnold <4>: Alarm Program. +* Robbins, Arnold <5>: Passwd Functions. +* Robbins, Arnold <6>: Getline/Pipe. +* Robbins, Arnold: Command Line Field Separator. +* Robbins, Bill: Getline/Pipe. +* Robbins, Harry: Acknowledgments. +* Robbins, Jean: Acknowledgments. +* Robbins, Miriam <1>: Passwd Functions. +* Robbins, Miriam <2>: Getline/Pipe. +* Robbins, Miriam: Acknowledgments. +* Robinson, Will: Dynamic Extensions. +* robot, the: Dynamic Extensions. * Rommel, Kai Uwe <1>: Bugs. -* Rommel, Kai Uwe: Acknowledgements. -* round: Round Function. +* Rommel, Kai Uwe <2>: Contributors. +* Rommel, Kai Uwe: Acknowledgments. +* round user-defined function: Round Function. * rounding: Round Function. -* RS <1>: User-modified. -* RS: Records. -* RSTART <1>: String Functions. -* RSTART: Auto-set. -* RT <1>: Auto-set. -* RT <2>: Multiple Line. -* RT: Records. +* RS variable <1>: User-modified. +* RS variable: Records. +* rshift built-in function: Bitwise Functions. +* RSTART variable <1>: String Functions. +* RSTART variable: Auto-set. +* RT variable <1>: Auto-set. +* RT variable <2>: Multiple Line. +* RT variable: Records. +* Rubin, Paul <1>: Contributors. +* Rubin, Paul: History. * rule, definition of: Getting Started. * running awk programs: Running gawk. * running long programs: Long. * rvalue: Assignment Ops. -* sample input file: Sample Data Files. +* sample input files: Sample Data Files. +* scalar, definition of: Basic Data Typing. * scanning an array: Scanning an Array. +* Schreiber, Bert: Acknowledgments. +* Schreiber, Rita: Acknowledgments. * script, definition of: Getting Started. * scripts, executable: Executable Scripts. -* scripts, shell: Executable Scripts. +* search path <1>: VMS Running. +* search path <2>: PC Using. +* search path <3>: Igawk Program. * search path: AWKPATH Variable. +* search path, for source files <1>: VMS Running. +* search path, for source files <2>: PC Using. +* search path, for source files <3>: Igawk Program. * search path, for source files: AWKPATH Variable. -* sed utility <1>: Igawk Program. -* sed utility <2>: Simple Sed. +* sed utility <1>: Glossary. +* sed utility <2>: Igawk Program. +* sed utility <3>: Simple Sed. * sed utility: Field Splitting Summary. * seed for random numbers: Numeric Functions. -* self contained programs: Executable Scripts. -* shell quoting <1>: Long. +* self-contained programs: Executable Scripts. +* set_value internal function: Internals. +* sex, comparisons with <1>: Manual History. +* sex, comparisons with: This Manual. +* sex, programmer attractiveness: Two-way I/O. +* shell and awk interaction: Using Shell Variables. +* shell quoting <1>: Comments. +* shell quoting <2>: Long. * shell quoting: Read Terminal. -* shell scripts: Executable Scripts. +* shell quoting rules: Quoting. +* shell quoting, tricks: Quoting. +* shell varibles, using in awk programs: Using Shell Variables. +* shell, piping commands into: Redirection. +* shift, bitwise: Bitwise Functions. * short-circuit operators: Boolean Ops. -* side effect: Assignment Ops. +* side effects <1>: Array Sorting. +* side effects <2>: Reference to Elements. +* side effects <3>: Action Overview. +* side effects <4>: Function Calls. +* side effects <5>: Conditional Exp. +* side effects <6>: Boolean Ops. +* side effects <7>: Increment Ops. +* side effects <8>: Assignment Ops. +* side effects <9>: Concatenation. +* side effects: Getline Notes. +* SIGHUP signal: Profiling. +* signals, SIGHUP: Profiling. +* signals, SIGUSR1: Profiling. +* SIGUSR1 signal: Profiling. * simple stream editor: Simple Sed. -* sin: Numeric Functions. -* single character fields: Single Character Fields. +* sin built-in function: Numeric Functions. * single quotes, why needed: One-shot. +* single-character fields: Single Character Fields. +* single-precision floating-point, definition of: Basic Data Typing. * skipping input files: Nextfile Function. * skipping lines between markers: Ranges. +* Skywalker, Luke: Undocumented. +* sleep utility: Alarm Program. +* sort utility: Word Sorting. +* source code, awka: Other Versions. +* source code, gawk: Getting. +* source code, mawk: Other Versions. +* source code, Unix awk: Other Versions. * sparse arrays: Array Intro. -* split: String Functions. +* Spencer, Henry: Glossary. +* split built-in function: String Functions. * split utility: Split Program. -* split.awk: Split Program. -* sprintf: String Functions. -* sqrt: Numeric Functions. -* srand: Numeric Functions. -* Stallman, Richard <1>: Acknowledgements. +* split.awk program: Split Program. +* sprintf built-in function: String Functions. +* sqrt built-in function: Numeric Functions. +* srand built-in function: Numeric Functions. +* Stallman, Richard <1>: Glossary. +* Stallman, Richard <2>: Contributors. +* Stallman, Richard <3>: Acknowledgments. * Stallman, Richard: Manual History. -* standard error output: Special Files. -* standard input <1>: Special Files. +* standard error output: Special FD. +* standard input <1>: Special FD. * standard input <2>: Reading Files. * standard input: Read Terminal. -* standard output: Special Files. +* standard output: Special FD. * statement, compound: Statements. +* stlen internal variable: Internals. +* stptr internal variable: Internals. +* stream editor <1>: Igawk Program. +* stream editor <2>: Simple Sed. * stream editor: Field Splitting Summary. * stream editor, simple: Simple Sed. -* strftime: Time Functions. +* strftime built-in function: Time Functions. * string comparison vs. regexp comparison: Typing and Comparison. -* string constants: Constants. +* string constants: Scalar Constants. +* string extraction (internationalization): String Extraction. * string operators: Concatenation. * string-matching operators: Regexp Usage. -* sub: String Functions. +* strtonum built-in function: String Functions. +* sub built-in function: String Functions. +* sub, escape processing: Gory Details. * sub, third argument of: String Functions. * subscripts in arrays: Multi-dimensional. -* SUBSEP <1>: Multi-dimensional. -* SUBSEP: User-modified. -* substr: String Functions. +* SUBSEP variable <1>: Multi-dimensional. +* SUBSEP variable: User-modified. +* substr built-in function: String Functions. * subtraction: Arithmetic Ops. -* system: I/O Functions. -* systime: Time Functions. +* Sumner, Andrew: Other Versions. +* syntactic ambiguity: /= operator vs. /=.../ regexp constant: Assignment Ops. +* system built-in function: I/O Functions. +* systime built-in function: Time Functions. +* tandem: Tandem Installation. * Tcl: Library Names. +* TCP/IP networking <1>: Portal Files. +* TCP/IP networking: TCP/IP Networking. * tee utility: Tee Program. -* tee.awk: Tee Program. +* tee.awk program: Tee Program. * terminator, record: Records. +* testbits.awk program: Bitwise Functions. +* Texinfo <1>: Adding Code. +* Texinfo <2>: Distribution contents. +* Texinfo <3>: Extract Program. +* Texinfo <4>: Dupword Program. +* Texinfo <5>: Library Functions. +* Texinfo <6>: Regexp Operators. +* Texinfo <7>: Sample Data Files. +* Texinfo <8>: Acknowledgments. +* Texinfo: Conventions. +* textdomain C library function: Explaining gettext. +* TEXTDOMAIN variable <1>: Programmer i18n. +* TEXTDOMAIN variable: User-modified. * time of day: Time Functions. * timestamps: Time Functions. -* timestamps, converting from dates: Mktime Function. +* timestamps, converting from dates: Time Functions. * timestamps, formatted: Gettimeofday Function. -* tolower: String Functions. -* toupper: String Functions. -* translate.awk: Translate Program. -* Trueman, David: Acknowledgements. +* tmp_number internal function: Internals. +* tmp_string internal function: Internals. +* tolower built-in function: String Functions. +* Torvalds, Linus: Manual History. +* toupper built-in function: String Functions. +* tr utility: Translate Program. +* translate.awk program: Translate Program. +* Trueman, David <1>: Contributors. +* Trueman, David <2>: Acknowledgments. +* Trueman, David: History. * truth values: Truth Values. +* two-way I/O: Two-way I/O. * type conversion: Conversion. +* type internal variable: Internals. * types of variables <1>: Typing and Comparison. * types of variables: Assignment Ops. * undefined functions: Function Caveats. * undocumented features: Undocumented. * uninitialized variables, as array subscripts: Uninitialized Subscripts. * uniq utility: Uniq Program. -* uniq.awk: Uniq Program. +* uniq.awk program: Uniq Program. +* Unix: Glossary. +* Unix awk, source code: Other Versions. +* unsigned integers: Basic Data Typing. +* update_ERRNO internal function: Internals. * use of comments: Comments. * user information: Passwd Functions. * user-defined functions: User-defined. * user-defined variables: Using Variables. -* uses of awk: What Is Awk. +* uses of awk <1>: When. +* uses of awk: Preface. +* uses of gawk: Preface. +* using shell variables in awk programs: Using Shell Variables. * using this book: This Manual. +* USR1 signal: Profiling. * values of characters as numbers: Ordinal Functions. +* values, numeric: Basic Data Typing. +* values, string: Basic Data Typing. * variable shadowing: Definition Syntax. * variable typing: Typing and Comparison. +* variable, definition of: Basic Data Typing. * variables, user-defined: Using Variables. +* vname internal variable: Internals. +* w utility: Constant Size. * Wall, Larry: Future Extensions. +* warnings, automatic <1>: Options. +* warnings, automatic <2>: I/O Functions. +* warnings, automatic <3>: String Functions. +* warnings, automatic <4>: Using Constant Regexps. +* warnings, automatic <5>: Special Caveats. +* warnings, automatic <6>: Special Process. +* warnings, automatic: Escape Sequences. * wc utility: Wc Program. -* wc.awk: Wc Program. +* wc.awk program: Wc Program. +* Weinberger, Peter <1>: Contributors. * Weinberger, Peter: History. -* when to use awk: When. * while statement: While Statement. +* Williams, Kent: Contributors. +* Woods, John: Contributors. * word boundaries, matching: GNU Regexp Operators. * word, regexp definition of: GNU Regexp Operators. -* wordfreq.sh: Word Sorting. +* wordfreq.awk program: Word Sorting. +* xgettext utility: String Extraction. +* XOR bitwise operation: Bitwise Functions. +* xor built-in function: Bitwise Functions. +* Zaretskii, Eli: Acknowledgments. +* zero, negative vs. positive: Floating Point Issues. +* Zoulas, Christos: Contributors. +* | I/O operator <1>: Precedence. +* | I/O operator <2>: Redirection. +* | I/O operator: Getline/Pipe. +* |& I/O operator <1>: Two-way I/O. +* |& I/O operator <2>: Precedence. +* |& I/O operator <3>: Redirection. +* |& I/O operator: Getline/Coprocess. +* || operator <1>: Precedence. * || operator: Boolean Ops. -* ~ operator <1>: Typing and Comparison. -* ~ operator <2>: Regexp Constants. -* ~ operator <3>: Computed Regexps. -* ~ operator <4>: Case-sensitivity. +* ~ operator <1>: Precedence. +* ~ operator <2>: Typing and Comparison. +* ~ operator <3>: Regexp Constants. +* ~ operator <4>: Computed Regexps. +* ~ operator <5>: Case-sensitivity. * ~ operator: Regexp Usage.  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+Ref: Options-Footnote-1494190 +Node: Other Arguments494215 +Node: AWKPATH Variable496967 +Ref: AWKPATH Variable-Footnote-1499758 +Node: Obsolete500017 +Node: Undocumented501098 +Node: Known Bugs501350 +Node: Library Functions501969 +Ref: Library Functions-Footnote-1505152 +Node: Library Names505323 +Ref: Library Names-Footnote-1508932 +Ref: Library Names-Footnote-2509152 +Node: General Functions509238 +Node: Nextfile Function510174 +Node: Assert Function514638 +Node: Round Function517974 +Node: Cliff Random Function519529 +Ref: Cliff Random Function-Footnote-1520512 +Node: Ordinal Functions520583 +Ref: Ordinal Functions-Footnote-1523661 +Node: Join Function523877 +Ref: Join Function-Footnote-1525682 +Node: Gettimeofday Function525882 +Node: Data File Management529660 +Node: Filetrans Function530220 +Node: Rewind Function533772 +Node: File Checking535396 +Node: Ignoring Assigns536442 +Node: Getopt Function538026 +Ref: Getopt Function-Footnote-1549173 +Node: Passwd Functions549374 +Ref: Passwd Functions-Footnote-1558085 +Node: Group Functions558173 +Node: Sample Programs566271 +Node: Running Examples567001 +Node: Clones567772 +Node: Cut Program568897 +Node: Egrep Program578768 +Ref: Egrep Program-Footnote-1586632 +Node: Id Program586742 +Node: Split Program590434 +Node: Tee Program593950 +Node: Uniq Program596621 +Node: Wc Program604115 +Ref: Wc Program-Footnote-1608430 +Node: Miscellaneous Programs608654 +Node: Dupword Program609643 +Node: Alarm Program611699 +Node: Translate Program616315 +Ref: Translate Program-Footnote-1620617 +Ref: Translate Program-Footnote-2620854 +Node: Labels Program620988 +Ref: Labels Program-Footnote-1624355 +Node: Word Sorting624439 +Node: History Sorting628742 +Node: Extract Program630612 +Node: Simple Sed638193 +Node: Igawk Program641394 +Ref: Igawk Program-Footnote-1654472 +Node: Language History654610 +Node: V7/SVR3.1655977 +Node: SVR4658572 +Node: POSIX660219 +Node: BTL662007 +Node: POSIX/GNU663824 +Node: Contributors672461 +Node: Installation675554 +Node: Gawk Distribution676533 +Node: Getting677033 +Node: Extracting678270 +Node: Distribution contents679650 +Node: Unix Installation685262 +Node: Quick Installation685848 +Node: Additional Configuration Options687595 +Node: Configuration Philosophy688708 +Node: Non-Unix Installation691091 +Node: Amiga Installation691673 +Node: BeOS Installation692818 +Node: PC Installation693990 +Node: PC Binary Installation695019 +Node: PC Compiling696017 +Node: PC Using697840 +Node: VMS Installation701526 +Node: VMS Compilation702045 +Node: VMS Installation Details703634 +Node: VMS Running705251 +Node: VMS POSIX706835 +Node: Unsupported708099 +Node: Atari Installation708497 +Node: Atari Compiling709818 +Node: Atari Using711747 +Node: Tandem Installation714611 +Node: Bugs716417 +Node: Other Versions719667 +Ref: Other Versions-Footnote-1723253 +Node: Notes723295 +Node: Compatibility Mode723968 +Node: Additions724809 +Node: Adding Code725581 +Node: New Ports731627 +Node: Dynamic Extensions735742 +Node: Internals736758 +Node: Sample Library743097 +Node: Internal File Description743747 +Node: Internal File Ops747499 +Ref: Internal File Ops-Footnote-1752915 +Node: Using Internal File Ops753063 +Node: Future Extensions755084 +Node: Basic Concepts759427 +Node: Basic High Level760165 +Ref: Basic High Level-Footnote-1764332 +Node: Basic Data Typing764526 +Node: Floating Point Issues769020 +Ref: Floating Point Issues-Footnote-1772943 +Ref: Floating Point Issues-Footnote-2772994 +Node: Glossary773103 +Node: Copying797415 +Node: GNU Free Documentation License816614 +Node: Index836506  End Tag Table diff --git a/doc/gawk.texi b/doc/gawk.texi index 2657b146..808ef6e8 100644 --- a/doc/gawk.texi +++ b/doc/gawk.texi @@ -4,38 +4,74 @@ @settitle The GNU Awk User's Guide @c %**end of header (This is for running Texinfo on a region.) -@c inside ifinfo for older versions of texinfo.tex -@ifinfo -@c I hope this is the right category -@dircategory Programming Languages +@dircategory GNU Packages @direntry -* Gawk: (gawk). A Text Scanning and Processing Language. +* Gawk: (gawk). A text scanning and processing language. +@end direntry +@dircategory Individual utilities +@direntry +* awk: (gawk)Invoking gawk. Text scanning and processing. @end direntry -@end ifinfo @c @set xref-automatic-section-title -@c @set DRAFT @c The following information should be updated here only! @c This sets the edition of the document, the version of gawk it -@c applies to, and when the document was updated. -@set TITLE Effective AWK Programming +@c applies to and all the info about who's publishing this edition + +@c These apply across the board. +@set UPDATE-MONTH March, 2001 +@set VERSION 3.1 +@set PATCHLEVEL 0 + +@set FSF + +@set TITLE GAWK: Effective AWK Programming @set SUBTITLE A User's Guide for GNU Awk -@set PATCHLEVEL 6 -@set EDITION 1.0.@value{PATCHLEVEL} -@set VERSION 3.0 -@set UPDATE-MONTH July, 2000 +@set EDITION 3 + @iftex @set DOCUMENT book +@set CHAPTER chapter +@set APPENDIX appendix +@set SECTION section +@set SUBSECTION subsection +@set DARKCORNER @inmargin{@image{lflashlight,1cm}, @image{rflashlight,1cm}} @end iftex @ifinfo @set DOCUMENT Info file +@set CHAPTER major node +@set APPENDIX major node +@set SECTION minor node +@set SUBSECTION node +@set DARKCORNER (d.c.) @end ifinfo +@ifhtml +@set DOCUMENT Web page +@set CHAPTER chapter +@set APPENDIX appendix +@set SECTION section +@set SUBSECTION subsection +@set DARKCORNER (d.c.) +@end ifhtml + +@c some special symbols +@iftex +@set LEQ @math{@leq} +@end iftex +@ifnottex +@set LEQ <= +@end ifnottex + +@set FN file name +@set FFN File Name +@set DF data file +@set DDF Data File +@set PVERSION version @ignore Some comments on the layout for TeX. -1. Use at least texinfo.tex 2.159. It contains fixes that - are needed to get the footings for draft mode to not appear. +1. Use at least texinfo.tex 2000-09-06.09 2. I have done A LOT of work to make this look good. There are `@page' commands and use of `@group ... @end group' in a number of places. If you muck with anything, it's your responsibility not to break the layout. @@ -56,48 +92,45 @@ Some comments on the layout for TeX. @c unwise to comment it out when running a master in case there are @c overfulls which are deemed okay. -@ifclear DRAFT @iftex @finalout @end iftex -@end ifclear +@c Comment out the "smallbook" for technical review. Saves +@c considerable paper. Remember to turn it back on *before* +@c starting the page-breaking work. @smallbook -@iftex -@c @cropmarks -@end iftex @ifinfo -This file documents @code{awk}, a program that you can use to select +This file documents @command{awk}, a program that you can use to select particular records in a file and perform operations upon them. -This is Edition @value{EDITION} of @cite{@value{TITLE}}, +This is Edition @value{EDITION} of @cite{@value{TITLE}: @value{SUBTITLE}}, for the @value{VERSION}.@value{PATCHLEVEL} version of the GNU implementation of AWK. -Copyright (C) 1989, 1991, 1992, 1993, 1996-2000 Free Software Foundation, Inc. +Copyright (C) 1989, 1991, 1992, 1993, 1996-2001 Free Software Foundation, Inc. -Permission is granted to make and distribute verbatim copies of -this manual provided the copyright notice and this permission notice -are preserved on all copies. +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'', the Front-Cover +texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +``GNU Free Documentation License''. -@ignore -Permission is granted to process this file through TeX and print the -results, provided the printed document carries copying permission -notice identical to this one except for the removal of this paragraph -(this paragraph not being relevant to the printed manual). +@enumerate a +@item +``A GNU Manual'' -@end ignore -Permission is granted to copy and distribute modified versions of this -manual under the conditions for verbatim copying, provided that the entire -resulting derived work is distributed under the terms of a permission -notice identical to this one. - -Permission is granted to copy and distribute translations of this manual -into another language, under the above conditions for modified versions, -except that this permission notice may be stated in a translation approved -by the Foundation. +@item +``You have freedom to copy and modify this GNU Manual, like GNU +software. Copies published by the Free Software Foundation raise +funds for GNU development.'' +@end enumerate @end ifinfo +@c Uncomment this for the release. Leaving it off saves paper +@c during editing and review. @setchapternewpage odd @titlepage @@ -106,73 +139,72 @@ by the Foundation. @subtitle Edition @value{EDITION} @subtitle @value{UPDATE-MONTH} @author Arnold D. Robbins -@ignore -@sp 1 -@author Based on @cite{The GAWK Manual}, -@author by Robbins, Close, Rubin, and Stallman -@end ignore @c Include the Distribution inside the titlepage environment so @c that headings are turned off. Headings on and off do not work. @page @vskip 0pt plus 1filll -@ifset LEGALJUNK +@ignore The programs and applications presented in this book have been -included for their instructional value. They have been tested with care, +included for their instructional value. They have been tested with care but are not guaranteed for any particular purpose. The publisher does not offer any warranties or representations, nor does it accept any liabilities with respect to the programs or applications. So there. @sp 2 -UNIX is a registered trademark of X/Open, Ltd. @* -Microsoft, MS, and MS-DOS are registered trademarks, and Windows is a +UNIX is a registered trademark of The Open Group in the United States and other countries. @* +Microsoft, MS and MS-DOS are registered trademarks, and Windows is a trademark of Microsoft Corporation in the United States and other countries. @* -Atari, 520ST, 1040ST, TT, STE, Mega, and Falcon are registered trademarks +Atari, 520ST, 1040ST, TT, STE, Mega and Falcon are registered trademarks or trademarks of Atari Corporation. @* -DEC, Digital, OpenVMS, ULTRIX, and VMS, are trademarks of Digital Equipment +DEC, Digital, OpenVMS, ULTRIX and VMS are trademarks of Digital Equipment Corporation. @* -@end ifset +@end ignore ``To boldly go where no man has gone before'' is a Registered Trademark of Paramount Pictures Corporation. @* @c sorry, i couldn't resist @sp 3 -Copyright @copyright{} 1989, 1991, 1992, 1993, 1996-2000 Free Software Foundation, Inc. +Copyright @copyright{} 1989, 1991, 1992, 1993, 1996-2001 Free Software Foundation, Inc. @sp 2 - -This is Edition @value{EDITION} of @cite{@value{TITLE}}, @* -for the @value{VERSION}.@value{PATCHLEVEL} (or later) version of the GNU implementation of AWK. + +This is Edition @value{EDITION} of @cite{@value{TITLE}: @value{SUBTITLE}}, +for the @value{VERSION}.@value{PATCHLEVEL} (or later) version of the GNU +implementation of AWK. @sp 2 Published by: +@sp 1 Free Software Foundation @* 59 Temple Place --- Suite 330 @* Boston, MA 02111-1307 USA @* Phone: +1-617-542-5942 @* Fax: +1-617-542-2652 @* -Email: @code{gnu@@gnu.org} @* -URL: @code{http://www.gnu.org/} @* +Email: @email{gnu@@gnu.org} @* +URL: @uref{http://www.gnu.org/} @* -@sp 1 -@c this ISBN can change! -@c This one is correct for gawk 3.0 and edition 1.0 from the FSF -ISBN 1-882114-26-4 @* - -Permission is granted to make and distribute verbatim copies of -this manual provided the copyright notice and this permission notice -are preserved on all copies. - -Permission is granted to copy and distribute modified versions of this -manual under the conditions for verbatim copying, provided that the entire -resulting derived work is distributed under the terms of a permission -notice identical to this one. - -Permission is granted to copy and distribute translations of this manual -into another language, under the above conditions for modified versions, -except that this permission notice may be stated in a translation approved -by the Foundation. +@c This one is correct for gawk 3.1.0 from the FSF +ISBN 1-882114-28-0 @* + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'', the Front-Cover +texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +``GNU Free Documentation License''. + +@enumerate a +@item +``A GNU Manual'' + +@item +``You have freedom to copy and modify this GNU Manual, like GNU +software. Copies published by the Free Software Foundation raise +funds for GNU development.'' +@end enumerate @sp 2 Cover art by Etienne Suvasa. @end titlepage @@ -192,6 +224,7 @@ Cover art by Etienne Suvasa. @center @i{To Nachum, for the added dimension.} @sp 1 @center @i{To Malka, for the new beginning.} +@w{ } @page @w{ } @page @@ -202,330 +235,401 @@ Cover art by Etienne Suvasa. @headings off @evenheading @thispage@ @ @ @strong{@value{TITLE}} @| @| @oddheading @| @| @strong{@thischapter}@ @ @ @thispage -@ifset DRAFT -@evenfooting @today{} @| @emph{DRAFT!} @| Please Do Not Redistribute -@oddfooting Please Do Not Redistribute @| @emph{DRAFT!} @| @today{} -@end ifset @end iftex @ifinfo -@node Top, Preface, (dir), (dir) +@node Top, Foreword, (dir), (dir) @top General Introduction -@c Preface or Licensing nodes should come right after the Top +@c Preface node should come right after the Top @c node, in `unnumbered' sections, then the chapter, `What is gawk'. +@c Licensing nodes are appendices, they're not central to AWK. -This file documents @code{awk}, a program that you can use to select +This file documents @command{awk}, a program that you can use to select particular records in a file and perform operations upon them. -This is Edition @value{EDITION} of @cite{@value{TITLE}}, @* -for the @value{VERSION}.@value{PATCHLEVEL} version of the GNU implementation @* +This is Edition @value{EDITION} of @cite{@value{TITLE}: @value{SUBTITLE}}, +for the @value{VERSION}.@value{PATCHLEVEL} version of the GNU implementation of AWK. @end ifinfo @menu -* Preface:: What this @value{DOCUMENT} is about; brief - history and acknowledgements. -* What Is Awk:: What is the @code{awk} language; using this - @value{DOCUMENT}. -* Getting Started:: A basic introduction to using @code{awk}. How - to run an @code{awk} program. Command line - syntax. -* One-liners:: Short, sample @code{awk} programs. -* Regexp:: All about matching things using regular - expressions. -* Reading Files:: How to read files and manipulate fields. -* Printing:: How to print using @code{awk}. Describes the - @code{print} and @code{printf} statements. - Also describes redirection of output. -* Expressions:: Expressions are the basic building blocks of - statements. -* Patterns and Actions:: Overviews of patterns and actions. -* Statements:: The various control statements are described - in detail. -* Built-in Variables:: Built-in Variables -* Arrays:: The description and use of arrays. Also - includes array-oriented control statements. -* Built-in:: The built-in functions are summarized here. -* User-defined:: User-defined functions are described in - detail. -* Invoking Gawk:: How to run @code{gawk}. -* Library Functions:: A Library of @code{awk} Functions. -* Sample Programs:: Many @code{awk} programs with complete - explanations. -* Language History:: The evolution of the @code{awk} language. -* Gawk Summary:: @code{gawk} Options and Language Summary. -* Installation:: Installing @code{gawk} under various operating - systems. -* Notes:: Something about the implementation of - @code{gawk}. -* Glossary:: An explanation of some unfamiliar terms. -* Copying:: Your right to copy and distribute @code{gawk}. -* Index:: Concept and Variable Index. - -* History:: The history of @code{gawk} and @code{awk}. -* Manual History:: Brief history of the GNU project and this - @value{DOCUMENT}. -* Acknowledgements:: Acknowledgements. -* This Manual:: Using this @value{DOCUMENT}. Includes sample - input files that you can use. -* Conventions:: Typographical Conventions. -* Sample Data Files:: Sample data files for use in the @code{awk} - programs illustrated in this @value{DOCUMENT}. -* Names:: What name to use to find @code{awk}. -* Running gawk:: How to run @code{gawk} programs; includes - command line syntax. -* One-shot:: Running a short throw-away @code{awk} program. -* Read Terminal:: Using no input files (input from terminal - instead). -* Long:: Putting permanent @code{awk} programs in - files. -* Executable Scripts:: Making self-contained @code{awk} programs. -* Comments:: Adding documentation to @code{gawk} programs. -* Very Simple:: A very simple example. -* Two Rules:: A less simple one-line example with two rules. -* More Complex:: A more complex example. -* Statements/Lines:: Subdividing or combining statements into - lines. -* Other Features:: Other Features of @code{awk}. -* When:: When to use @code{gawk} and when to use other - things. -* Regexp Usage:: How to Use Regular Expressions. -* Escape Sequences:: How to write non-printing characters. -* Regexp Operators:: Regular Expression Operators. -* GNU Regexp Operators:: Operators specific to GNU software. -* Case-sensitivity:: How to do case-insensitive matching. -* Leftmost Longest:: How much text matches. -* Computed Regexps:: Using Dynamic Regexps. -* Records:: Controlling how data is split into records. -* Fields:: An introduction to fields. -* Non-Constant Fields:: Non-constant Field Numbers. -* Changing Fields:: Changing the Contents of a Field. -* Field Separators:: The field separator and how to change it. -* Basic Field Splitting:: How fields are split with single characters or - simple strings. -* Regexp Field Splitting:: Using regexps as the field separator. -* Single Character Fields:: Making each character a separate field. -* Command Line Field Separator:: Setting @code{FS} from the command line. -* Field Splitting Summary:: Some final points and a summary table. -* Constant Size:: Reading constant width data. -* Multiple Line:: Reading multi-line records. -* Getline:: Reading files under explicit program control - using the @code{getline} function. -* Getline Intro:: Introduction to the @code{getline} function. -* Plain Getline:: Using @code{getline} with no arguments. -* Getline/Variable:: Using @code{getline} into a variable. -* Getline/File:: Using @code{getline} from a file. -* Getline/Variable/File:: Using @code{getline} into a variable from a - file. -* Getline/Pipe:: Using @code{getline} from a pipe. -* Getline/Variable/Pipe:: Using @code{getline} into a variable from a - pipe. -* Getline Summary:: Summary Of @code{getline} Variants. -* Print:: The @code{print} statement. -* Print Examples:: Simple examples of @code{print} statements. -* Output Separators:: The output separators and how to change them. -* OFMT:: Controlling Numeric Output With @code{print}. -* Printf:: The @code{printf} statement. -* Basic Printf:: Syntax of the @code{printf} statement. -* Control Letters:: Format-control letters. -* Format Modifiers:: Format-specification modifiers. -* Printf Examples:: Several examples. -* Redirection:: How to redirect output to multiple files and - pipes. -* Special Files:: File name interpretation in @code{gawk}. - @code{gawk} allows access to inherited file - descriptors. -* Close Files And Pipes:: Closing Input and Output Files and Pipes. -* Constants:: String, numeric, and regexp constants. -* Scalar Constants:: Numeric and string constants. -* Regexp Constants:: Regular Expression constants. -* Using Constant Regexps:: When and how to use a regexp constant. -* Variables:: Variables give names to values for later use. -* Using Variables:: Using variables in your programs. -* Assignment Options:: Setting variables on the command line and a - summary of command line syntax. This is an - advanced method of input. -* Conversion:: The conversion of strings to numbers and vice - versa. -* Arithmetic Ops:: Arithmetic operations (@samp{+}, @samp{-}, - etc.) -* Concatenation:: Concatenating strings. -* Assignment Ops:: Changing the value of a variable or a field. -* Increment Ops:: Incrementing the numeric value of a variable. -* Truth Values:: What is ``true'' and what is ``false''. -* Typing and Comparison:: How variables acquire types, and how this - affects comparison of numbers and strings with - @samp{<}, etc. -* Boolean Ops:: Combining comparison expressions using boolean - operators @samp{||} (``or''), @samp{&&} - (``and'') and @samp{!} (``not''). -* Conditional Exp:: Conditional expressions select between two - subexpressions under control of a third - subexpression. -* Function Calls:: A function call is an expression. -* Precedence:: How various operators nest. -* Pattern Overview:: What goes into a pattern. -* Kinds of Patterns:: A list of all kinds of patterns. -* Regexp Patterns:: Using regexps as patterns. -* Expression Patterns:: Any expression can be used as a pattern. -* Ranges:: Pairs of patterns specify record ranges. -* BEGIN/END:: Specifying initialization and cleanup rules. -* Using BEGIN/END:: How and why to use BEGIN/END rules. -* I/O And BEGIN/END:: I/O issues in BEGIN/END rules. -* Empty:: The empty pattern, which matches every record. -* Action Overview:: What goes into an action. -* If Statement:: Conditionally execute some @code{awk} - statements. -* While Statement:: Loop until some condition is satisfied. -* Do Statement:: Do specified action while looping until some - condition is satisfied. -* For Statement:: Another looping statement, that provides - initialization and increment clauses. -* Break Statement:: Immediately exit the innermost enclosing loop. -* Continue Statement:: Skip to the end of the innermost enclosing - loop. -* Next Statement:: Stop processing the current input record. -* Nextfile Statement:: Stop processing the current file. -* Exit Statement:: Stop execution of @code{awk}. -* User-modified:: Built-in variables that you change to control - @code{awk}. -* Auto-set:: Built-in variables where @code{awk} gives you - information. -* ARGC and ARGV:: Ways to use @code{ARGC} and @code{ARGV}. -* Array Intro:: Introduction to Arrays -* Reference to Elements:: How to examine one element of an array. -* Assigning Elements:: How to change an element of an array. -* Array Example:: Basic Example of an Array -* Scanning an Array:: A variation of the @code{for} statement. It - loops through the indices of an array's - existing elements. -* Delete:: The @code{delete} statement removes an element - from an array. -* Numeric Array Subscripts:: How to use numbers as subscripts in - @code{awk}. -* Uninitialized Subscripts:: Using Uninitialized variables as subscripts. -* Multi-dimensional:: Emulating multi-dimensional arrays in - @code{awk}. -* Multi-scanning:: Scanning multi-dimensional arrays. -* Calling Built-in:: How to call built-in functions. -* Numeric Functions:: Functions that work with numbers, including - @code{int}, @code{sin} and @code{rand}. -* String Functions:: Functions for string manipulation, such as - @code{split}, @code{match}, and - @code{sprintf}. -* I/O Functions:: Functions for files and shell commands. -* Time Functions:: Functions for dealing with time stamps. -* Definition Syntax:: How to write definitions and what they mean. -* Function Example:: An example function definition and what it - does. -* Function Caveats:: Things to watch out for. -* Return Statement:: Specifying the value a function returns. -* Options:: Command line options and their meanings. -* Other Arguments:: Input file names and variable assignments. -* AWKPATH Variable:: Searching directories for @code{awk} programs. -* Obsolete:: Obsolete Options and/or features. -* Undocumented:: Undocumented Options and Features. -* Known Bugs:: Known Bugs in @code{gawk}. -* Portability Notes:: What to do if you don't have @code{gawk}. -* Nextfile Function:: Two implementations of a @code{nextfile} - function. -* Assert Function:: A function for assertions in @code{awk} - programs. -* Round Function:: A function for rounding if @code{sprintf} does - not do it correctly. -* Ordinal Functions:: Functions for using characters as numbers and - vice versa. -* Join Function:: A function to join an array into a string. -* Mktime Function:: A function to turn a date into a timestamp. -* Gettimeofday Function:: A function to get formatted times. -* Filetrans Function:: A function for handling data file transitions. -* Getopt Function:: A function for processing command line - arguments. -* Passwd Functions:: Functions for getting user information. -* Group Functions:: Functions for getting group information. -* Library Names:: How to best name private global variables in - library functions. -* Clones:: Clones of common utilities. -* Cut Program:: The @code{cut} utility. -* Egrep Program:: The @code{egrep} utility. -* Id Program:: The @code{id} utility. -* Split Program:: The @code{split} utility. -* Tee Program:: The @code{tee} utility. -* Uniq Program:: The @code{uniq} utility. -* Wc Program:: The @code{wc} utility. -* Miscellaneous Programs:: Some interesting @code{awk} programs. -* Dupword Program:: Finding duplicated words in a document. -* Alarm Program:: An alarm clock. -* Translate Program:: A program similar to the @code{tr} utility. -* Labels Program:: Printing mailing labels. -* Word Sorting:: A program to produce a word usage count. -* History Sorting:: Eliminating duplicate entries from a history - file. -* Extract Program:: Pulling out programs from Texinfo source - files. -* Simple Sed:: A Simple Stream Editor. -* Igawk Program:: A wrapper for @code{awk} that includes files. -* V7/SVR3.1:: The major changes between V7 and System V - Release 3.1. -* SVR4:: Minor changes between System V Releases 3.1 - and 4. -* POSIX:: New features from the POSIX standard. -* BTL:: New features from the Bell Laboratories - version of @code{awk}. -* POSIX/GNU:: The extensions in @code{gawk} not in POSIX - @code{awk}. -* Command Line Summary:: Recapitulation of the command line. -* Language Summary:: A terse review of the language. -* Variables/Fields:: Variables, fields, and arrays. -* Fields Summary:: Input field splitting. -* Built-in Summary:: @code{awk}'s built-in variables. -* Arrays Summary:: Using arrays. -* Data Type Summary:: Values in @code{awk} are numbers or strings. -* Rules Summary:: Patterns and Actions, and their component - parts. -* Pattern Summary:: Quick overview of patterns. -* Regexp Summary:: Quick overview of regular expressions. -* Actions Summary:: Quick overview of actions. -* Operator Summary:: @code{awk} operators. -* Control Flow Summary:: The control statements. -* I/O Summary:: The I/O statements. -* Printf Summary:: A summary of @code{printf}. -* Special File Summary:: Special file names interpreted internally. -* Built-in Functions Summary:: Built-in numeric and string functions. -* Time Functions Summary:: Built-in time functions. -* String Constants Summary:: Escape sequences in strings. -* Functions Summary:: Defining and calling functions. -* Historical Features:: Some undocumented but supported ``features''. -* Gawk Distribution:: What is in the @code{gawk} distribution. -* Getting:: How to get the distribution. -* Extracting:: How to extract the distribution. -* Distribution contents:: What is in the distribution. -* Unix Installation:: Installing @code{gawk} under various versions - of Unix. -* Quick Installation:: Compiling @code{gawk} under Unix. -* Configuration Philosophy:: How it's all supposed to work. -* VMS Installation:: Installing @code{gawk} on VMS. -* VMS Compilation:: How to compile @code{gawk} under VMS. -* VMS Installation Details:: How to install @code{gawk} under VMS. -* VMS Running:: How to run @code{gawk} under VMS. -* VMS POSIX:: Alternate instructions for VMS POSIX. -* PC Installation:: Installing and Compiling @code{gawk} on MS-DOS - and OS/2 -* Atari Installation:: Installing @code{gawk} on the Atari ST. -* Atari Compiling:: Compiling @code{gawk} on Atari -* Atari Using:: Running @code{gawk} on Atari -* Amiga Installation:: Installing @code{gawk} on an Amiga. -* Bugs:: Reporting Problems and Bugs. -* Other Versions:: Other freely available @code{awk} - implementations. -* Compatibility Mode:: How to disable certain @code{gawk} extensions. -* Additions:: Making Additions To @code{gawk}. -* Adding Code:: Adding code to the main body of @code{gawk}. -* New Ports:: Porting @code{gawk} to a new operating system. -* Future Extensions:: New features that may be implemented one day. -* Improvements:: Suggestions for improvements by volunteers. - +* Foreword:: Some nice words about this + @value{DOCUMENT}. +* Preface:: What this @value{DOCUMENT} is about; brief + history and acknowledgments. +* Getting Started:: A basic introduction to using + @command{awk}. How to run an @command{awk} + program. Command-line syntax. +* Regexp:: All about matching things using regular + expressions. +* Reading Files:: How to read files and manipulate fields. +* Printing:: How to print using @command{awk}. Describes + the @code{print} and @code{printf} + statements. Also describes redirection of + output. +* Expressions:: Expressions are the basic building blocks + of statements. +* Patterns and Actions:: Overviews of patterns and actions. +* Arrays:: The description and use of arrays. Also + includes array-oriented control statements. +* Functions:: Built-in and user-defined functions. +* Internationalization:: Getting @command{gawk} to speak your + language. +* Advanced Features:: Stuff for advanced users, specific to + @command{gawk}. +* Invoking Gawk:: How to run @command{gawk}. +* Library Functions:: A Library of @command{awk} Functions. +* Sample Programs:: Many @command{awk} programs with complete + explanations. +* Language History:: The evolution of the @command{awk} + language. +* Installation:: Installing @command{gawk} under various + operating systems. +* Notes:: Notes about @command{gawk} extensions and + possible future work. +* Basic Concepts:: A very quick intoduction to programming + concepts. +* Glossary:: An explanation of some unfamiliar terms. +* Copying:: Your right to copy and distribute + @command{gawk}. +* GNU Free Documentation License:: The license for this @value{DOCUMENT}. +* Index:: Concept and Variable Index. + +@detailmenu +* History:: The history of @command{gawk} and + @command{awk}. +* Names:: What name to use to find @command{awk}. +* This Manual:: Using this @value{DOCUMENT}. Includes + sample input files that you can use. +* Conventions:: Typographical Conventions. +* Manual History:: Brief history of the GNU project and this + @value{DOCUMENT}. +* How To Contribute:: Helping to save the world. +* Acknowledgments:: Acknowledgments. +* Running gawk:: How to run @command{gawk} programs; + includes command-line syntax. +* One-shot:: Running a short throw-away @command{awk} + program. +* Read Terminal:: Using no input files (input from terminal + instead). +* Long:: Putting permanent @command{awk} programs in + files. +* Executable Scripts:: Making self-contained @command{awk} + programs. +* Comments:: Adding documentation to @command{gawk} + programs. +* Quoting:: More discussion of shell quoting issues. +* Sample Data Files:: Sample data files for use in the + @command{awk} programs illustrated in this + @value{DOCUMENT}. +* Very Simple:: A very simple example. +* Two Rules:: A less simple one-line example using two + rules. +* More Complex:: A more complex example. +* Statements/Lines:: Subdividing or combining statements into + lines. +* Other Features:: Other Features of @command{awk}. +* When:: When to use @command{gawk} and when to use + other things. +* Regexp Usage:: How to Use Regular Expressions. +* Escape Sequences:: How to write non-printing characters. +* Regexp Operators:: Regular Expression Operators. +* Character Lists:: What can go between @samp{[...]}. +* GNU Regexp Operators:: Operators specific to GNU software. +* Case-sensitivity:: How to do case-insensitive matching. +* Leftmost Longest:: How much text matches. +* Computed Regexps:: Using Dynamic Regexps. +* Records:: Controlling how data is split into records. +* Fields:: An introduction to fields. +* Non-Constant Fields:: Non-constant Field Numbers. +* Changing Fields:: Changing the Contents of a Field. +* Field Separators:: The field separator and how to change it. +* Regexp Field Splitting:: Using regexps as the field separator. +* Single Character Fields:: Making each character a separate field. +* Command Line Field Separator:: Setting @code{FS} from the command-line. +* Field Splitting Summary:: Some final points and a summary table. +* Constant Size:: Reading constant width data. +* Multiple Line:: Reading multi-line records. +* Getline:: Reading files under explicit program + control using the @code{getline} function. +* Plain Getline:: Using @code{getline} with no arguments. +* Getline/Variable:: Using @code{getline} into a variable. +* Getline/File:: Using @code{getline} from a file. +* Getline/Variable/File:: Using @code{getline} into a variable from a + file. +* Getline/Pipe:: Using @code{getline} from a pipe. +* Getline/Variable/Pipe:: Using @code{getline} into a variable from a + pipe. +* Getline/Coprocess:: Using @code{getline} from a coprocess. +* Getline/Variable/Coprocess:: Using @code{getline} into a variable from a + coprocess. +* Getline Notes:: Important things to know about + @code{getline}. +* Getline Summary:: Summary of @code{getline} Variants. +* Print:: The @code{print} statement. +* Print Examples:: Simple examples of @code{print} statements. +* Output Separators:: The output separators and how to change + them. +* OFMT:: Controlling Numeric Output With + @code{print}. +* Printf:: The @code{printf} statement. +* Basic Printf:: Syntax of the @code{printf} statement. +* Control Letters:: Format-control letters. +* Format Modifiers:: Format-specification modifiers. +* Printf Examples:: Several examples. +* Redirection:: How to redirect output to multiple files + and pipes. +* Special Files:: File name interpretation in @command{gawk}. + @command{gawk} allows access to inherited + file descriptors. +* Special FD:: Special files for I/O. +* Special Process:: Special files for process information. +* Special Network:: Special files for network communications. +* Special Caveats:: Things to watch out for. +* Close Files And Pipes:: Closing Input and Output Files and Pipes. +* Constants:: String, numeric and regexp constants. +* Scalar Constants:: Numeric and string constants. +* Non-decimal-numbers:: What are octal and hex numbers. +* Regexp Constants:: Regular Expression constants. +* Using Constant Regexps:: When and how to use a regexp constant. +* Variables:: Variables give names to values for later + use. +* Using Variables:: Using variables in your programs. +* Assignment Options:: Setting variables on the command-line and a + summary of command-line syntax. This is an + advanced method of input. +* Conversion:: The conversion of strings to numbers and + vice versa. +* Arithmetic Ops:: Arithmetic operations (@samp{+}, @samp{-}, + etc.) +* Concatenation:: Concatenating strings. +* Assignment Ops:: Changing the value of a variable or a + field. +* Increment Ops:: Incrementing the numeric value of a + variable. +* Truth Values:: What is ``true'' and what is ``false''. +* Typing and Comparison:: How variables acquire types and how this + affects comparison of numbers and strings + with @samp{<}, etc. +* Boolean Ops:: Combining comparison expressions using + boolean operators @samp{||} (``or''), + @samp{&&} (``and'') and @samp{!} (``not''). +* Conditional Exp:: Conditional expressions select between two + subexpressions under control of a third + subexpression. +* Function Calls:: A function call is an expression. +* Precedence:: How various operators nest. +* Pattern Overview:: What goes into a pattern. +* Regexp Patterns:: Using regexps as patterns. +* Expression Patterns:: Any expression can be used as a pattern. +* Ranges:: Pairs of patterns specify record ranges. +* BEGIN/END:: Specifying initialization and cleanup + rules. +* Using BEGIN/END:: How and why to use BEGIN/END rules. +* I/O And BEGIN/END:: I/O issues in BEGIN/END rules. +* Empty:: The empty pattern, which matches every + record. +* Using Shell Variables:: How to use shell variables with + @command{awk}. +* Action Overview:: What goes into an action. +* Statements:: Describes the various control statements in + detail. +* If Statement:: Conditionally execute some @command{awk} + statements. +* While Statement:: Loop until some condition is satisfied. +* Do Statement:: Do specified action while looping until + some condition is satisfied. +* For Statement:: Another looping statement, that provides + initialization and increment clauses. +* Break Statement:: Immediately exit the innermost enclosing + loop. +* Continue Statement:: Skip to the end of the innermost enclosing + loop. +* Next Statement:: Stop processing the current input record. +* Nextfile Statement:: Stop processing the current file. +* Exit Statement:: Stop execution of @command{awk}. +* Built-in Variables:: Summarizes the built-in variables. +* User-modified:: Built-in variables that you change to + control @command{awk}. +* Auto-set:: Built-in variables where @command{awk} + gives you information. +* ARGC and ARGV:: Ways to use @code{ARGC} and @code{ARGV}. +* Array Intro:: Introduction to Arrays +* Reference to Elements:: How to examine one element of an array. +* Assigning Elements:: How to change an element of an array. +* Array Example:: Basic Example of an Array +* Scanning an Array:: A variation of the @code{for} statement. It + loops through the indices of an array's + existing elements. +* Delete:: The @code{delete} statement removes an + element from an array. +* Numeric Array Subscripts:: How to use numbers as subscripts in + @command{awk}. +* Uninitialized Subscripts:: Using Uninitialized variables as + subscripts. +* Multi-dimensional:: Emulating multidimensional arrays in + @command{awk}. +* Multi-scanning:: Scanning multidimensional arrays. +* Array Sorting:: Sorting array values and indices. +* Built-in:: Summarizes the built-in functions. +* Calling Built-in:: How to call built-in functions. +* Numeric Functions:: Functions that work with numbers, including + @code{int}, @code{sin} and @code{rand}. +* String Functions:: Functions for string manipulation, such as + @code{split}, @code{match} and + @code{sprintf}. +* Gory Details:: More than you want to know about @samp{\} + and @samp{&} with @code{sub}, @code{gsub}, + and @code{gensub}. +* I/O Functions:: Functions for files and shell commands. +* Time Functions:: Functions for dealing with timestamps. +* Bitwise Functions:: Functions for bitwise operations. +* I18N Functions:: Functions for string translation. +* User-defined:: Describes User-defined functions in detail. +* Definition Syntax:: How to write definitions and what they + mean. +* Function Example:: An example function definition and what it + does. +* Function Caveats:: Things to watch out for. +* Return Statement:: Specifying the value a function returns. +* Dynamic Typing:: How variable types can change at runtime. +* I18N and L10N:: Internationalization and Localization. +* Explaining gettext:: How GNU @code{gettext} works. +* Programmer i18n:: Features for the programmer. +* Translator i18n:: Features for the translator. +* String Extraction:: Extracting marked strings. +* Printf Ordering:: Rearranging @code{printf} arguments. +* I18N Portability:: @command{awk}-level portability issues. +* I18N Example:: A simple i18n example. +* Gawk I18N:: @command{gawk} is also internationalized. +* Non-decimal Data:: Allowing non-decimal input data. +* Two-way I/O:: Two-way communications with another + process. +* TCP/IP Networking:: Using @command{gawk} for network + programming. +* Portal Files:: Using @command{gawk} with BSD portals. +* Profiling:: Profiling your @command{awk} programs. +* Command Line:: How to run @command{awk}. +* Options:: Command-line options and their meanings. +* Other Arguments:: Input file names and variable assignments. +* AWKPATH Variable:: Searching directories for @command{awk} + programs. +* Obsolete:: Obsolete Options and/or features. +* Undocumented:: Undocumented Options and Features. +* Known Bugs:: Known Bugs in @command{gawk}. +* Library Names:: How to best name private global variables + in library functions. +* General Functions:: Functions that are of general use. +* Nextfile Function:: Two implementations of a @code{nextfile} + function. +* Assert Function:: A function for assertions in @command{awk} + programs. +* Round Function:: A function for rounding if @code{sprintf} + does not do it correctly. +* Cliff Random Function:: The Cliff Random Number Generator. +* Ordinal Functions:: Functions for using characters as numbers + and vice versa. +* Join Function:: A function to join an array into a string. +* Gettimeofday Function:: A function to get formatted times. +* Data File Management:: Functions for managing command-line data + files. +* Filetrans Function:: A function for handling data file + transitions. +* Rewind Function:: A function for rereading the current file. +* File Checking:: Checking that data files are readable. +* Ignoring Assigns:: Treating assignments as file names. +* Getopt Function:: A function for processing command-line + arguments. +* Passwd Functions:: Functions for getting user information. +* Group Functions:: Functions for getting group information. +* Running Examples:: How to run these examples. +* Clones:: Clones of common utilities. +* Cut Program:: The @command{cut} utility. +* Egrep Program:: The @command{egrep} utility. +* Id Program:: The @command{id} utility. +* Split Program:: The @command{split} utility. +* Tee Program:: The @command{tee} utility. +* Uniq Program:: The @command{uniq} utility. +* Wc Program:: The @command{wc} utility. +* Miscellaneous Programs:: Some interesting @command{awk} programs. +* Dupword Program:: Finding duplicated words in a document. +* Alarm Program:: An alarm clock. +* Translate Program:: A program similar to the @command{tr} + utility. +* Labels Program:: Printing mailing labels. +* Word Sorting:: A program to produce a word usage count. +* History Sorting:: Eliminating duplicate entries from a + history file. +* Extract Program:: Pulling out programs from Texinfo source + files. +* Simple Sed:: A Simple Stream Editor. +* Igawk Program:: A wrapper for @command{awk} that includes + files. +* V7/SVR3.1:: The major changes between V7 and System V + Release 3.1. +* SVR4:: Minor changes between System V Releases 3.1 + and 4. +* POSIX:: New features from the POSIX standard. +* BTL:: New features from the Bell Laboratories + version of @command{awk}. +* POSIX/GNU:: The extensions in @command{gawk} not in + POSIX @command{awk}. +* Contributors:: The major contributors to @command{gawk}. +* Gawk Distribution:: What is in the @command{gawk} distribution. +* Getting:: How to get the distribution. +* Extracting:: How to extract the distribution. +* Distribution contents:: What is in the distribution. +* Unix Installation:: Installing @command{gawk} under various + versions of Unix. +* Quick Installation:: Compiling @command{gawk} under Unix. +* Additional Configuration Options:: Other compile-time options. +* Configuration Philosophy:: How it's all supposed to work. +* Non-Unix Installation:: Installation on Other Operating Systems. +* Amiga Installation:: Installing @command{gawk} on an Amiga. +* BeOS Installation:: Installing @command{gawk} on BeOS. +* PC Installation:: Installing and Compiling @command{gawk} on + MS-DOS and OS/2. +* PC Binary Installation:: Installing a prepared distribution. +* PC Compiling:: Compiling @command{gawk} for MS-DOS, Win32, + and OS/2. +* PC Using:: Running @command{gawk} on MS-DOS, Win32 and + OS/2. +* VMS Installation:: Installing @command{gawk} on VMS. +* VMS Compilation:: How to compile @command{gawk} under VMS. +* VMS Installation Details:: How to install @command{gawk} under VMS. +* VMS Running:: How to run @command{gawk} under VMS. +* VMS POSIX:: Alternate instructions for VMS POSIX. +* Unsupported:: Systems whose ports are no longer + supported. +* Atari Installation:: Installing @command{gawk} on the Atari ST. +* Atari Compiling:: Compiling @command{gawk} on Atari. +* Atari Using:: Running @command{gawk} on Atari. +* Tandem Installation:: Installing @command{gawk} on a Tandem. +* Bugs:: Reporting Problems and Bugs. +* Other Versions:: Other freely available @command{awk} + implementations. +* Compatibility Mode:: How to disable certain @command{gawk} + extensions. +* Additions:: Making Additions To @command{gawk}. +* Adding Code:: Adding code to the main body of + @command{gawk}. +* New Ports:: Porting @command{gawk} to a new operating + system. +* Dynamic Extensions:: Adding new built-in functions to + @command{gawk}. +* Internals:: A brief look at some @command{gawk} + internals. +* Sample Library:: A example of new functions. +* Internal File Description:: What the new functions will do. +* Internal File Ops:: The code for internal file operations. +* Using Internal File Ops:: How to use an external extension. +* Future Extensions:: New features that may be implemented one + day. +* Basic High Level:: The high level view. +* Basic Data Typing:: A very quick intro to data types. +* Floating Point Issues:: Stuff to know about floating-point numbers. +@end detailmenu @end menu @c dedication for Info file @@ -541,687 +645,1052 @@ of AWK. @center To Malka, for the new beginning. @end ifinfo -@node Preface, What Is Awk, Top, Top -@unnumbered Preface +@summarycontents +@contents + +@node Foreword, Preface, Top, Top +@unnumbered Foreword + +Arnold Robbins and I are good friends. We were introduced 11 years ago +by circumstances---and our favorite programming language, AWK. +The circumstances started a couple of years +earlier. I was working at a new job and noticed an unplugged +Unix computer sitting in the corner. No one knew how to use it, +and neither did I. However, +a couple of days later it was running, and +I was @code{root} and the one-and-only user. +That day, I began the transition from statistician to Unix programmer. + +On one of many trips to the library or bookstore in search of +books on Unix, I found the gray AWK book, a.k.a. Aho, Kernighan and +Weinberger, @cite{The AWK Programming Language}, Addison-Wesley, +1988. AWK's simple programming paradigm---find a pattern in the +input and then perform an action---often reduced complex or tedious +data manipulations to few lines of code. I was excited to try my +hand at programming in AWK. + +Alas, the @command{awk} on my computer was a limited version of the +language described in the AWK book. I discovered that my computer +had ``old @command{awk}'' and the AWK book described ``new @command{awk}.'' +I learned that this was typical; the old version refused to step +aside or relinquish its name. If a system had a new @command{awk}, it was +invariably called @command{nawk}, and few systems had it. +The best way to get a new @command{awk} was to @command{ftp} the source code for +@command{gawk} from @code{prep.ai.mit.edu}. @command{gawk} was a version of +new @command{awk} written by David Trueman and Arnold, and available under +the GNU General Public License. + +(Incidentally, +it's no longer difficult to find a new @command{awk}. @command{gawk} ships with +Linux, and you can download binaries or source code for almost +any system; my wife uses @command{gawk} on her VMS box.) + +My Unix system started out unplugged from the wall; it certainly was not +plugged into a network. So, oblivious to the existence of @command{gawk} +and the Unix community in general, and desiring a new @command{awk}, I wrote +my own, called @command{mawk}. +Before I was finished I knew about @command{gawk}, +but it was too late to stop, so I eventually posted +to a @code{comp.sources} newsgroup. + +A few days after my posting, I got a friendly email +from Arnold introducing +himself. He suggested we share design and algorithms and +attached a draft of the POSIX standard so +that I could update @command{mawk} to support language extensions added +after publication of the AWK book. + +Frankly, if our roles had +been reversed, I would not have been so open and we probably would +have never met. I'm glad we did meet. +He is an AWK expert's AWK expert and a genuinely nice person. +Arnold contributes significant amounts of his +expertise and time to the Free Software Foundation. + +This book is the @command{gawk} reference manual, but at its core it +is a book about AWK programming that +will appeal to a wide audience. +It is a definitive reference to the AWK language as defined by the +1987 Bell Labs release and codified in the 1992 POSIX Utilities +standard. + +On the other hand, the novice AWK programmer can study +a wealth of practical programs that emphasize +the power of AWK's basic idioms: +data driven control-flow, pattern matching with regular expressions, +and associative arrays. +Those looking for something new can try out @command{gawk}'s +interface to network protocols via special @file{/inet} files. + +The programs in this book make clear that an AWK program is +typically much smaller and faster to develop than +a counterpart written in C. +Consequently, there is often a payoff to prototype an +algorithm or design in AWK to get it running quickly and expose +problems early. Often, the interpreted performance is adequate +and the AWK prototype becomes the product. + +The new @command{pgawk} (profiling @command{gawk}), produces +program execution counts. +I recently experimented with an algorithm that for +@math{n} lines of input, exhibited +@tex +$\sim\! Cn^2$ +@end tex +@ifnottex +~ C n^2 +@end ifnottex +performance, while +theory predicted +@tex +$\sim\! Cn\log n$ +@end tex +@ifnottex +~ C n log n +@end ifnottex +behavior. A few minutes poring +over the @file{awkprof.out} profile pinpointed the problem to +a single line of code. @command{pgawk} is a welcome addition to +my programmer's toolbox. + +Arnold has distilled over a decade of experience writing and +using AWK programs, and developing @command{gawk}, into this book. If you use +AWK or want to learn how, then read this book. + +@display +Michael Brennan +Author of @command{mawk} +@end display +@node Preface, Getting Started, Foreword, Top +@unnumbered Preface @c I saw a comment somewhere that the preface should describe the book itself, @c and the introduction should describe what the book covers. +@c +@c 12/2000: Chuck wants the preface & intro combined. + +Several kinds of tasks occur repeatedly +when working with text files. +You might want to extract certain lines and discard the rest. +Or you may need to make changes wherever certain patterns appear, +but leave the rest of the file alone. +Writing single-use programs for these tasks in languages such as C, C++ or Pascal +is time-consuming and inconvenient. +Such jobs are often easier with @command{awk}. +The @command{awk} utility interprets a special-purpose programming language +that makes it easy to handle simple data-reformatting jobs. + +The GNU implementation of @command{awk} is called @command{gawk}; it is fully +compatible with the System V Release 4 version of +@command{awk}. @command{gawk} is also compatible with the POSIX +specification of the @command{awk} language. This means that all +properly written @command{awk} programs should work with @command{gawk}. +Thus, we usually don't distinguish between @command{gawk} and other +@command{awk} implementations. + +@cindex uses of @command{awk} +@cindex applications of @command{awk} +Using @command{awk} allows you to: + +@itemize @bullet +@item +Manage small, personal databases + +@item +Generate reports + +@item +Validate data + +@item +Produce indexes and perform other document preparation tasks + +@item +Experiment with algorithms that you can adapt later to other computer +languages. +@end itemize + +@cindex uses of @command{gawk} +In addition, +@command{gawk} +provides facilities that make it easy to: -This @value{DOCUMENT} teaches you about the @code{awk} language and +@itemize @bullet +@item +Extract bits and pieces of data for processing + +@item +Sort data + +@item +Perform simple network communications. +@end itemize + +This @value{DOCUMENT} teaches you about the @command{awk} language and how you can use it effectively. You should already be familiar with basic -system commands, such as @code{cat} and @code{ls},@footnote{These commands -are available on POSIX compliant systems, as well as on traditional Unix +system commands, such as @command{cat} and @command{ls},@footnote{These commands +are available on POSIX-compliant systems, as well as on traditional Unix based systems. If you are using some other operating system, you still need to -be familiar with the ideas of I/O redirection and pipes.} and basic shell +be familiar with the ideas of I/O redirection and pipes.} as well as basic shell facilities, such as Input/Output (I/O) redirection and pipes. -Implementations of the @code{awk} language are available for many different -computing environments. This @value{DOCUMENT}, while describing the @code{awk} language -in general, also describes a particular implementation of @code{awk} called -@code{gawk} (which stands for ``GNU Awk''). @code{gawk} runs on a broad range -of Unix systems, ranging from 80386 PC-based computers, up through large scale -systems, such as Crays. @code{gawk} has also been ported to MS-DOS and -OS/2 PC's, Atari and Amiga micro-computers, and VMS. +Implementations of the @command{awk} language are available for many +different computing environments. This @value{DOCUMENT}, while describing +the @command{awk} language in general, also describes the particular +implementation of @command{awk} called @command{gawk} (which stands for +``GNU awk''). @command{gawk} runs on a broad range of Unix systems, +ranging from 80386 PC-based computers, up through large-scale systems, +such as Crays. @command{gawk} has also been ported to Mac OS X, +MS-DOS, Microsoft Windows (all versions) and OS/2 PC's, Atari and Amiga +micro-computers, BeOS, Tandem D20, and VMS. @menu -* History:: The history of @code{gawk} and @code{awk}. +* History:: The history of @command{gawk} and + @command{awk}. +* Names:: What name to use to find @command{awk}. +* This Manual:: Using this @value{DOCUMENT}. Includes sample + input files that you can use. +* Conventions:: Typographical Conventions. * Manual History:: Brief history of the GNU project and this @value{DOCUMENT}. -* Acknowledgements:: Acknowledgements. +* How To Contribute:: Helping to save the world. +* Acknowledgments:: Acknowledgments. @end menu -@node History, Manual History, Preface, Preface -@unnumberedsec History of @code{awk} and @code{gawk} +@node History, Names, Preface, Preface +@unnumberedsec History of @command{awk} and @command{gawk} +@cindex recipe for a programming language +@cindex programming language, recipe for +@center Recipe For A Programming Language + +@multitable {2 parts} {1 part @code{egrep}} {1 part @code{snobol}} +@item @tab 1 part @code{egrep} @tab 1 part @code{snobol} +@item @tab 2 parts @code{ed} @tab 3 parts C +@end multitable + +@quotation +Blend all parts well using @code{lex} and @code{yacc}. +Document minimally and release. + +After eight years, add another part @code{egrep} and two +more parts C. Document very well and release. +@end quotation @cindex acronym -@cindex history of @code{awk} +@cindex history of @command{awk} @cindex Aho, Alfred @cindex Weinberger, Peter @cindex Kernighan, Brian -@cindex old @code{awk} -@cindex new @code{awk} -The name @code{awk} comes from the initials of its designers: Alfred V.@: -Aho, Peter J.@: Weinberger, and Brian W.@: Kernighan. The original version of -@code{awk} was written in 1977 at AT&T Bell Laboratories. -In 1985 a new version made the programming +@cindex old @command{awk} +@cindex new @command{awk} +The name @command{awk} comes from the initials of its designers: Alfred V.@: +Aho, Peter J.@: Weinberger and Brian W.@: Kernighan. The original version of +@command{awk} was written in 1977 at AT&T Bell Laboratories. +In 1985, a new version made the programming language more powerful, introducing user-defined functions, multiple input streams, and computed regular expressions. -This new version became generally available with Unix System V Release 3.1. -The version in System V Release 4 added some new features and also cleaned +This new version became widely available with Unix System V +Release 3.1 (SVR3.1). +The version in SVR4 added some new features and cleaned up the behavior in some of the ``dark corners'' of the language. -The specification for @code{awk} in the POSIX Command Language -and Utilities standard further clarified the language based on feedback -from both the @code{gawk} designers, and the original Bell Labs @code{awk} -designers. +The specification for @command{awk} in the POSIX Command Language +and Utilities standard further clarified the language. +Both the @command{gawk} designers and the original Bell Laboratories @command{awk} +designers provided feedback for the POSIX specification. -The GNU implementation, @code{gawk}, was written in 1986 by Paul Rubin -and Jay Fenlason, with advice from Richard Stallman. John Woods +@cindex Rubin, Paul +@cindex Fenlason, Jay +@cindex Trueman, David +Paul Rubin wrote the GNU implementation, @command{gawk}, in 1986. +Jay Fenlason completed it, with advice from Richard Stallman. John Woods contributed parts of the code as well. In 1988 and 1989, David Trueman, with -help from Arnold Robbins, thoroughly reworked @code{gawk} for compatibility -with the newer @code{awk}. Current development focuses on bug fixes, +help from me, thoroughly reworked @command{gawk} for compatibility +with the newer @command{awk}. +Circa 1995, I became the primary maintainer. +Current development focuses on bug fixes, performance improvements, standards compliance, and occasionally, new features. -@node Manual History, Acknowledgements, History, Preface -@unnumberedsec The GNU Project and This Book +In May of 1997, J@"urgen Kahrs felt the need for network access +from @command{awk}, and with a little help from me, set about adding +features to do this for @command{gawk}. At that time, he also +wrote the bulk of +@cite{TCP/IP Internetworking with @command{gawk}} +(a separate document, available as part of the @command{gawk} distribution). +His code finally became part of the main @command{gawk} distribution +with @command{gawk} @value{PVERSION} 3.1. + +@xref{Contributors, ,Major Contributors to @command{gawk}}, +for a complete list of those who made important contributions to @command{gawk}. + +@node Names, This Manual, History, Preface +@section A Rose by Any Other Name + +@cindex old @command{awk} vs. new @command{awk} +@cindex new @command{awk} vs. old @command{awk} +The @command{awk} language has evolved over the years. Full details are +provided in @ref{Language History, ,The Evolution of the @command{awk} Language}. +The language described in this @value{DOCUMENT} +is often referred to as ``new @command{awk}'' (@command{nawk}). -@cindex Free Software Foundation -@cindex Stallman, Richard -The Free Software Foundation (FSF) is a non-profit organization dedicated -to the production and distribution of freely distributable software. -It was founded by Richard M.@: Stallman, the author of the original -Emacs editor. GNU Emacs is the most widely used version of Emacs today. +Because of this, many systems have multiple +versions of @command{awk}. +Some systems have an @command{awk} utility that implements the +original version of the @command{awk} language and a @command{nawk} utility +for the new +version. +Others have an @command{oawk} for the ``old @command{awk}'' +language and plain @command{awk} for the new one. Still others only +have one version, which is usually the new one.@footnote{Often, these systems +use @command{gawk} for their @command{awk} implementation!} -@cindex GNU Project -The GNU project is an on-going effort on the part of the Free Software -Foundation to create a complete, freely distributable, POSIX compliant -computing environment. (GNU stands for ``GNU's not Unix''.) -The FSF uses the ``GNU General Public License'' (or GPL) to ensure that -source code for their software is always available to the end user. A -copy of the GPL is included for your reference -(@pxref{Copying, ,GNU GENERAL PUBLIC LICENSE}). -The GPL applies to the C language source code for @code{gawk}. +All in all, this makes it difficult for you to know which version of +@command{awk} you should run when writing your programs. The best advice +I can give here is to check your local documentation. Look for @command{awk}, +@command{oawk}, and @command{nawk}, as well as for @command{gawk}. +It is likely that you already +have some version of new @command{awk} on your system, which is what +you should use when running your programs. (Of course, if you're reading +this @value{DOCUMENT}, chances are good that you have @command{gawk}!) -A shell, an editor (Emacs), highly portable optimizing C, C++, and -Objective-C compilers, a symbolic debugger, and dozens of large and -small utilities (such as @code{gawk}), have all been completed and are -freely available. As of this writing (early 1997), the GNU operating -system kernel (the HURD), has been released, but is still in an early -stage of development. +Throughout this @value{DOCUMENT}, whenever we refer to a language feature +that should be available in any complete implementation of POSIX @command{awk}, +we simply use the term @command{awk}. When referring to a feature that is +specific to the GNU implementation, we use the term @command{gawk}. + +@node This Manual, Conventions, Names, Preface +@section Using This Book +@cindex book, using this +@cindex using this book +@cindex language, @command{awk} +@cindex program, @command{awk} +@ignore +@cindex @command{awk} language +@cindex @command{awk} program +@end ignore +@cindex Brandon, Dick +@cindex sex, comparisons with +@quotation +@i{Documentation is like sex: when it is good, it is very, very good; and +when it is bad, it is better than nothing.}@* +Dick Brandon +@end quotation + +The term @command{awk} refers to a particular program as well as to the language you +use to tell this program what to do. When we need to be careful, we call +the program ``the @command{awk} utility'' and the language ``the @command{awk} +language.'' +This @value{DOCUMENT} explains +both the @command{awk} language and how to run the @command{awk} utility. +The term @dfn{@command{awk} program} refers to a program written by you in +the @command{awk} programming language. + +Primarily, this @value{DOCUMENT} explains the features of @command{awk}, +as defined in the POSIX standard. It does so in the context of the +@command{gawk} implementation. While doing so, it also +attempts to describe important differences between @command{gawk} +and other @command{awk} implementations.@footnote{All such differences +appear in the index under the heading ``differences between @command{gawk} and +@command{awk}.''} Finally, any @command{gawk} features that are not in +the POSIX standard for @command{awk} are noted. + +@ifnotinfo +This @value{DOCUMENT} has the difficult task of being both a tutorial and a reference. +If you are a novice, feel free to skip over details that seem too complex. +You should also ignore the many cross references; they are for the +expert user and for the online Info version of the document. +@end ifnotinfo + +There are +subsections labelled +as @strong{Advanced Notes} +scattered throughout the @value{DOCUMENT}. +They add a more complete explanation of points that are relevant, but not likely +to be of interest on first reading. +All appear in the index, under the heading ``advanced notes.'' + +Most of the time, the examples use complete @command{awk} programs. +In some of the more advanced sections, only the part of the @command{awk} +program that illustrates the concept currently being described is shown. + +While this @value{DOCUMENT} is aimed principally at people who have not been +exposed +to @command{awk}, there is a lot of information here that even the @command{awk} +expert should find useful. In particular, the description of POSIX +@command{awk} and the example programs in +@ref{Library Functions, ,A Library of @command{awk} Functions}, and in +@ref{Sample Programs, ,Practical @command{awk} Programs}, +should be of interest. + +@ref{Getting Started, ,Getting Started with @command{awk}}, +provides the essentials you need to know to begin using @command{awk}. + +@ref{Regexp, ,Regular Expressions}, +introduces regular expressions in general, and in particular the flavors +supported by POSIX @command{awk} and @command{gawk}. + +@ref{Reading Files, , Reading Input Files}, +describes how @command{awk} reads your data. +It introduces the concepts of records and fields, as well +as the @code{getline} command. +I/O redirection is first described here. + +@ref{Printing, , Printing Output}, +describes how @command{awk} programs can produce output with +@code{print} and @code{printf}. + +@ref{Expressions}, +describes expressions, which are the basic building blocks +for getting most things done in a program. + +@ref{Patterns and Actions, ,Patterns Actions and Variables}, +describes how to write patterns for matching records, actions for +doing something when a record is matched, and the built-in variables +@command{awk} and @command{gawk} use. + +@ref{Arrays, ,Arrays in @command{awk}}, +covers @command{awk}'s one-and-only data structure: associative arrays. +Deleting array elements and whole arrays is also described, as well as +sorting arrays in @command{gawk}. + +@ref{Functions}, +describes the built-in functions @command{awk} and +@command{gawk} provide for you, as well as how to define +your own functions. + +@ref{Internationalization, ,Internationalization with @command{gawk}}, +describes special features in @command{gawk} for translating program +messages into different languages at runtime. + +@ref{Advanced Features, ,Advanced Features of @command{gawk}}, +describes a number of @command{gawk}-specific advanced features. +Of particular note +are the abilities to have two-way communications with another process, +perform TCP/IP networking, and +profile your @command{awk} programs. + +@ref{Invoking Gawk, ,Running @command{awk} and @command{gawk}}, +describes how to run @command{gawk}, the meaning of its +command-line options, and how it finds @command{awk} +program source files. + +@ref{Library Functions, ,A Library of @command{awk} Functions}, and +@ref{Sample Programs, ,Practical @command{awk} Programs}, +provide many sample @command{awk} programs. +Reading them allows you to see @command{awk} being used +for solving real problems. + +@ref{Language History, ,The Evolution of the @command{awk} Language}, +describes how the @command{awk} language has evolved since it was +first released to present. It also describes how @command{gawk} +has acquired features over time. + +@ref{Installation, ,Installing @command{gawk}}, +describes how to get @command{gawk}, how to compile it +under Unix, and how to compile and use it on different +non-Unix systems. It also describes how to report bugs +in @command{gawk} and where to get three other freely +available implementations of @command{awk}. + +@ref{Notes, ,Implementation Notes}, +describes how to disable @command{gawk}'s extensions, as +well as how to contribute new code to @command{gawk}, +how to write extension libraries, and some possible +future directions for @command{gawk} development. + +@ref{Basic Concepts, ,Basic Programming Concepts}, +provides some very cursory background material for those who +are completely unfamiliar with computer programming. +Also centralized there is a discussion of some of the issues +involved in using floating-point numbers. + +The +@ref{Glossary}, +defines most, if not all, the significant terms used +throughout the book. +If you find terms that you aren't familiar with, try looking them up. + +@ref{Copying, ,GNU General Public License}, and +@ref{GNU Free Documentation License}, +present the licenses that cover the @command{gawk} source code, +and this @value{DOCUMENT}, respectively. + +@node Conventions, Manual History, This Manual, Preface +@section Typographical Conventions + +@cindex Texinfo +This @value{DOCUMENT} is written using Texinfo, the GNU documentation +formatting language. +A single Texinfo source file is used to produce both the printed and online +versions of the documentation. +@iftex +Because of this, the typographical conventions +are slightly different than in other books you may have read. +@end iftex +@ifnottex +This @value{SECTION} briefly documents the typographical conventions used in Texinfo. +@end ifnottex + +Examples you would type at the command-line are preceded by the common +shell primary and secondary prompts, @samp{$} and @samp{>}. +Output from the command is preceded by the glyph ``@print{}''. +This typically represents the command's standard output. +Error messages, and other output on the command's standard error, are preceded +by the glyph ``@error{}''. For example: + +@example +$ echo hi on stdout +@print{} hi on stdout +$ echo hello on stderr 1>&2 +@error{} hello on stderr +@end example + +@iftex +In the text, command names appear in @code{this font}, while code segments +appear in the same font and quoted, @samp{like this}. Some things are +emphasized @emph{like this}, and if a point needs to be made +strongly, it is done @strong{like this}. The first occurrence of +a new term is usually its @dfn{definition} and appears in the same +font as the previous occurrence of ``definition'' in this sentence. +@value{FN}s are indicated like this: @file{/path/to/ourfile}. +@end iftex + +Characters that you type at the keyboard look @kbd{like this}. In particular, +there are special characters called ``control characters.'' These are +characters that you type by holding down both the @kbd{CONTROL} key and +another key, at the same time. For example, a @kbd{Ctrl-d} is typed +by first pressing and holding the @kbd{CONTROL} key, next +pressing the @kbd{d} key and finally releasing both keys. + +@c fakenode --- for prepinfo +@subsubheading Dark Corners +@cindex Kernighan, Brian +@quotation +@i{Dark corners are basically fractal --- no matter how much +you illuminate, there's always a smaller but darker one.}@* +Brian Kernighan +@end quotation + +@cindex d.c., see ``dark corner'' +@cindex dark corner +Until the POSIX standard (and @cite{The Gawk Manual}), +many features of @command{awk} were either poorly documented or not +documented at all. Descriptions of such features +(often called ``dark corners'') are noted in this @value{DOCUMENT} with +@iftex +the picture of a flashlight in the margin, as shown here. +@value{DARKCORNER} +@end iftex +@ifnottex +``(d.c.)''. +@end ifnottex +They also appear in the index under the heading ``dark corner.'' + +As noted by the opening quote, though, any +coverage of dark corners +is, by definition, something that is incomplete. + +@node Manual History, How To Contribute, Conventions, Preface +@unnumberedsec The GNU Project and This Book +@cindex Torvalds, Linus +@cindex sex, comparisons with +@quotation +@i{Software is like sex: it's better when it's free.}@* +Linus Torvalds +@end quotation + +@cindex FSF +@cindex Free Software Foundation +@cindex Stallman, Richard +The Free Software Foundation (FSF) is a non-profit organization dedicated +to the production and distribution of freely distributable software. +It was founded by Richard M.@: Stallman, the author of the original +Emacs editor. GNU Emacs is the most widely used version of Emacs today. + +@cindex GNU Project +@cindex GPL +@cindex General Public License +@cindex GNU General Public License +@cindex online documentation +@cindex documentation, online +The GNU@footnote{GNU stands for ``GNU's not Unix.''} +Project is an ongoing effort on the part of the Free Software +Foundation to create a complete, freely distributable, POSIX-compliant +computing environment. +The FSF uses the ``GNU General Public License'' (GPL) to ensure that +their software's +source code is always available to the end user. A +copy of the GPL is included +@ifnotinfo +in this @value{DOCUMENT} +@end ifnotinfo +for your reference +(@pxref{Copying, ,GNU General Public License}). +The GPL applies to the C language source code for @command{gawk}. +To find out more about the FSF and the GNU Project online, +see @uref{http://www.gnu.org, the GNU Project's home page}. +This @value{DOCUMENT} may also be read from +@uref{http://www.gnu.org/manual/gawk/, their web site}. + +A shell, an editor (Emacs), highly portable optimizing C, C++, and +Objective-C compilers, a symbolic debugger and dozens of large and +small utilities (such as @command{gawk}), have all been completed and are +freely available. The GNU operating +system kernel (the HURD), has been released but is still in an early +stage of development. @cindex Linux +@cindex GNU/Linux +@cindex BSD-based operating systems @cindex NetBSD @cindex FreeBSD +@cindex OpenBSD Until the GNU operating system is more fully developed, you should -consider using Linux, a freely distributable, Unix-like operating -system for 80386, DEC Alpha, Sun SPARC and other systems. There are -many books on Linux. One freely available one is @cite{Linux +consider using GNU/Linux, a freely distributable, Unix-like operating +system for Intel 80386, DEC Alpha, Sun SPARC, IBM S/390, and other +systems.@footnote{The terminology ``GNU/Linux'' is explained +in the @ref{Glossary}.} +There are +many books on GNU/Linux. One that is freely available is @cite{Linux Installation and Getting Started}, by Matt Welsh. -Many Linux distributions are available, often in computer stores or -bundled on CD-ROM with books about Linux. +Many GNU/Linux distributions are often available in computer stores or +bundled on CD-ROMs with books about Linux. (There are three other freely available, Unix-like operating systems for -80386 and other systems, NetBSD, FreeBSD,and OpenBSD. All are based on the +80386 and other systems: NetBSD, FreeBSD, and OpenBSD. All are based on the 4.4-Lite Berkeley Software Distribution, and they use recent versions -of @code{gawk} for their versions of @code{awk}.) +of @command{gawk} for their versions of @command{awk}.) -@iftex -This @value{DOCUMENT} you are reading now is actually free. The -information in it is freely available to anyone, the machine readable -source code for the @value{DOCUMENT} comes with @code{gawk}, and anyone +@ifnotinfo +The @value{DOCUMENT} you are reading now is actually free---at least, the +information in it is free to anyone. The machine readable +source code for the @value{DOCUMENT} comes with @command{gawk}; anyone may take this @value{DOCUMENT} to a copying machine and make as many -copies of it as they like. (Take a moment to check the copying -permissions on the Copyright page.) - -If you paid money for this @value{DOCUMENT}, what you actually paid for -was the @value{DOCUMENT}'s nice printing and binding, and the -publisher's associated costs to produce it. We have made an effort to -keep these costs reasonable; most people would prefer a bound book to -over 330 pages of photo-copied text that would then have to be held in -a loose-leaf binder (not to mention the time and labor involved in -doing the copying). The same is true of producing this -@value{DOCUMENT} from the machine readable source; the retail price is -only slightly more than the cost per page of printing it -on a laser printer. -@end iftex +copies of it as they like. (Take a moment to check the Free Documentation +License; see @ref{GNU Free Documentation License}.) + +Although you could just print it out yourself, bound books are much +easier to read and use. Furthermore, +the proceeds from sales of this book go back to the FSF +to help fund development of more free software. +@end ifnotinfo -This @value{DOCUMENT} itself has gone through several previous, -preliminary editions. I started working on a preliminary draft of -@cite{The GAWK Manual}, by Diane Close, Paul Rubin, and Richard -Stallman in the fall of 1988. -It was around 90 pages long, and barely described the original, ``old'' -version of @code{awk}. After substantial revision, the first version of +@ignore +@cindex Close, Diane +The @value{DOCUMENT} itself has gone through several previous, +preliminary editions. +Paul Rubin wrote the very first draft of @cite{The GAWK Manual}; +it was around 40 pages in size. +Diane Close and Richard Stallman improved it, yielding the +version which I started working with in the fall of 1988. +It was around 90 pages long and barely described the original, ``old'' +version of @command{awk}. After substantial revision, the first version of the @cite{The GAWK Manual} to be released was Edition 0.11 Beta in October of 1989. The manual then underwent more substantial revision for Edition 0.13 of December 1991. -David Trueman, Pat Rankin, and Michal Jaegermann contributed sections +David Trueman, Pat Rankin and Michal Jaegermann contributed sections of the manual for Edition 0.13. That edition was published by the -FSF as a bound book early in 1992. Since then there have been several +FSF as a bound book early in 1992. Since then there were several minor revisions, notably Edition 0.14 of November 1992 that was published -by the FSF in January of 1993, and Edition 0.16 of August 1993. +by the FSF in January of 1993 and Edition 0.16 of August 1993. -Edition 1.0 of @cite{@value{TITLE}} represents a significant re-working +Edition 1.0 of @cite{GAWK: The GNU Awk User's Guide} represented a significant re-working of @cite{The GAWK Manual}, with much additional material. -The FSF and I agree that I am now the primary author. -I also felt that it needed a more descriptive title. +The FSF and I agreed that I was now the primary author. +@c I also felt that the manual needed a more descriptive title. + +In January 1996, SSC published Edition 1.0 under the title @cite{Effective AWK Programming}. +In February 1997, they published Edition 1.0.3 which had minor changes +as a ``second edition.'' +In 1999, the FSF published this same version as Edition 2 +of @cite{GAWK: The GNU Awk User's Guide}. + +Edition @value{EDITION} maintains the basic structure of Edition 1.0, +but with significant additional material, reflecting the host of new features +in @command{gawk} @value{PVERSION} @value{VERSION}. +Of particular note is +@ref{Array Sorting, ,Sorting Array Values and Indices with @command{gawk}}, +@ref{Bitwise Functions, ,Using @command{gawk}'s Bit Manipulation Functions}, +@ref{Internationalization, ,Internationalization with @command{gawk}}, +@ref{Advanced Features, ,Advanced Features of @command{gawk}}, +and +@ref{Dynamic Extensions, ,Adding New Built-in Functions to @command{gawk}}. +@end ignore + +@cindex Close, Diane +The @value{DOCUMENT} itself has gone through a number of previous editions. +Paul Rubin wrote the very first draft of @cite{The GAWK Manual}; +it was around 40 pages in size. +Diane Close and Richard Stallman improved it, yielding a +version that was +around 90 pages long and barely described the original, ``old'' +version of @command{awk}. + +I started working with that version in the fall of 1988. +As work on it progressed, +the FSF published several preliminary versions (numbered 0.@var{x}). +In 1996, Edition 1.0 was released with @command{gawk} 3.0.0. +The FSF published the first two editions under +the title @cite{The GNU Awk User's Guide}. + +This edition maintains the basic structure of Edition 1.0, +but with significant additional material, reflecting the host of new features +in @command{gawk} @value{PVERSION} @value{VERSION}. +Of particular note is +@ref{Array Sorting, ,Sorting Array Values and Indices with @command{gawk}}, +as well as +@ref{Bitwise Functions, ,Using @command{gawk}'s Bit Manipulation Functions}, +@ref{Internationalization, ,Internationalization with @command{gawk}}, +and also +@ref{Advanced Features, ,Advanced Features of @command{gawk}}, +and +@ref{Dynamic Extensions, ,Adding New Built-in Functions to @command{gawk}}. @cite{@value{TITLE}} will undoubtedly continue to evolve. An electronic version -comes with the @code{gawk} distribution from the FSF. +comes with the @command{gawk} distribution from the FSF. If you find an error in this @value{DOCUMENT}, please report it! @xref{Bugs, ,Reporting Problems and Bugs}, for information on submitting -problem reports electronically, or write to me in care of the FSF. +problem reports electronically, or write to me in care of the publisher. -@node Acknowledgements, , Manual History, Preface -@unnumberedsec Acknowledgements +@node How To Contribute, Acknowledgments, Manual History, Preface +@unnumberedsec How to Contribute -@cindex Stallman, Richard -I would like to acknowledge Richard M.@: Stallman, for his vision of a -better world, and for his courage in founding the FSF and starting the -GNU project. +As the maintainer of GNU @command{awk}, +I am starting a collection of publicly available @command{awk} +programs. +For more information, +see @uref{ftp://ftp.freefriends.org/arnold/Awkstuff}. +If you have written an interesting @command{awk} program, or have written a +@command{gawk} extension that you would like to +share with the rest of the world, please contact me (@email{arnold@@gnu.org}). +Making things available on the Internet helps keep the +@command{gawk} distribution down to manageable size. + +@node Acknowledgments, , How To Contribute, Preface +@unnumberedsec Acknowledgments -The initial draft of @cite{The GAWK Manual} had the following acknowledgements: +The initial draft of @cite{The GAWK Manual} had the following acknowledgments: @quotation Many people need to be thanked for their assistance in producing this manual. Jay Fenlason contributed many ideas and sample programs. Richard Mlynarik and Robert Chassell gave helpful comments on drafts of this -manual. The paper @cite{A Supplemental Document for @code{awk}} by John W.@: +manual. The paper @cite{A Supplemental Document for @command{awk}} by John W.@: Pierce of the Chemistry Department at UC San Diego, pinpointed several -issues relevant both to @code{awk} implementation and to this manual, that +issues relevant both to @command{awk} implementation and to this manual, that would otherwise have escaped us. @end quotation -The following people provided many helpful comments on Edition 0.13 of -@cite{The GAWK Manual}: Rick Adams, Michael Brennan, Rich Burridge, Diane Close, -Christopher (``Topher'') Eliot, Michael Lijewski, Pat Rankin, Miriam Robbins, -and Michal Jaegermann. +@cindex Stallman, Richard +I would like to acknowledge Richard M.@: Stallman, for his vision of a +better world and for his courage in founding the FSF and starting the +GNU project. -The following people provided many helpful comments for Edition 1.0 of -@cite{@value{TITLE}}: Karl Berry, Michael Brennan, Darrel -Hankerson, Michal Jaegermann, Michael Lijewski, and Miriam Robbins. -Pat Rankin, Michal Jaegermann, Darrel Hankerson and Scott Deifik -updated their respective sections for Edition 1.0. +The following people (in alphabetical order) +provided helpful comments on various +versions of this book, up to and including this edition. +Rick Adams, +Nelson H.F. Beebe, +Karl Berry, +Dr.@: Michael Brennan, +Rich Burridge, +Claire Coutier, +Diane Close, +Scott Deifik, +Christopher (``Topher'') Eliot, +Jeffrey Friedl, +Dr.@: Darrel Hankerson, +Michal Jaegermann, +Dr.@: Richard J.@: LeBlanc, +Michael Lijewski, +Pat Rankin, +Miriam Robbins, +Mary Sheehan, +and +Chuck Toporek. +@cindex Berry, Karl +@cindex Chassell, Robert J.@: +@cindex Texinfo Robert J.@: Chassell provided much valuable advice on -the use of Texinfo. He also deserves special thanks for +the use of Texinfo. +He also deserves special thanks for convincing me @emph{not} to title this @value{DOCUMENT} @cite{How To Gawk Politely}. Karl Berry helped significantly with the @TeX{} part of Texinfo. +@cindex Hartholz, Marshall +@cindex Hartholz, Elaine +@cindex Schreiber, Bert +@cindex Schreiber, Rita +I would like to thank Marshall and Elaine Hartholz of Seattle and +Dr.@: Bert and Rita Schreiber of Detroit for large amounts of quiet vacation +time in their homes, which allowed me to make significant progress on +this @value{DOCUMENT} and on @command{gawk} itself. + +@cindex Hughes, Phil +Phil Hughes of SSC +contributed in a very important way by loaning me his laptop GNU/Linux +system, not once, but twice, which allowed me to do a lot of work while +away from home. + @cindex Trueman, David David Trueman deserves special credit; he has done a yeoman job -of evolving @code{gawk} so that it performs well, and without bugs. -Although he is no longer involved with @code{gawk}, +of evolving @command{gawk} so that it performs well and without bugs. +Although he is no longer involved with @command{gawk}, working with him on this project was a significant pleasure. +@cindex Drepper, Ulrich +@cindex GNITS mailing list +The intrepid members of the GNITS mailing list, and most notably Ulrich +Drepper, provided invaluable help and feedback for the design of the +internationalization features. + +@cindex Beebe, Nelson +@cindex Brown, Martin @cindex Deifik, Scott @cindex Hankerson, Darrel -@cindex Rommel, Kai Uwe -@cindex Rankin, Pat @cindex Jaegermann, Michal -Scott Deifik, Darrel Hankerson, Kai Uwe Rommel, Pat Rankin, and Michal -Jaegermann (in no particular order) are long time members of the -@code{gawk} ``crack portability team.'' Without their hard work and -help, @code{gawk} would not be nearly the fine program it is today. It +@cindex Kahrs, J@"urgen +@cindex Rankin, Pat +@cindex Rommel, Kai Uwe +@cindex Zaretskii, Eli +Nelson Beebe, +Martin Brown, +Scott Deifik, +Darrel Hankerson, +Michal Jaegermann, +J@"urgen Kahrs, +Pat Rankin, +Kai Uwe Rommel, +and Eli Zaretskii +(in alphabetical order) +are long-time members of the +@command{gawk} ``crack portability team.'' Without their hard work and +help, @command{gawk} would not be nearly the fine program it is today. It has been and continues to be a pleasure working with this team of fine people. -@cindex Friedl, Jeffrey -Jeffrey Friedl provided invaluable help in tracking down a number -of last minute problems with regular expressions in @code{gawk} 3.0. - @cindex Kernighan, Brian -David and I would like to thank Brian Kernighan of Bell Labs for -invaluable assistance during the testing and debugging of @code{gawk}, and for +David and I would like to thank Brian Kernighan of Bell Laboratories for +invaluable assistance during the testing and debugging of @command{gawk}, and for help in clarifying numerous points about the language. We could not have -done nearly as good a job on either @code{gawk} or its documentation without +done nearly as good a job on either @command{gawk} or its documentation without his help. -@cindex Hughes, Phil -I would like to thank Marshall and Elaine Hartholz of Seattle, and Dr.@: -Bert and Rita Schreiber of Detroit for large amounts of quiet vacation -time in their homes, which allowed me to make significant progress on -this @value{DOCUMENT} and on @code{gawk} itself. Phil Hughes of SSC -contributed in a very important way by loaning me his laptop Linux -system, not once, but twice, allowing me to do a lot of work while -away from home. +Chuck Toporek, Mary Sheehan, and Claire Coutier of O'Reilly & Associates contributed +significant editorial help for this @value{DOCUMENT} for the +3.1 release of @command{gawk}. @cindex Robbins, Miriam -Finally, I must thank my wonderful wife, Miriam, for her patience through +@cindex Robbins, Jean +@cindex Robbins, Harry +@cindex G-d +I must thank my wonderful wife, Miriam, for her patience through the many versions of this project, for her proof-reading, and for sharing me with the computer. I would like to thank my parents for their love, and for the grace with which they raised and educated me. -I also must acknowledge my gratitude to G-d, for the many opportunities +Finally, I also must acknowledge my gratitude to G-d, for the many opportunities He has sent my way, as well as for the gifts He has given me with which to take advantage of those opportunities. @sp 2 @noindent Arnold Robbins @* -Atlanta, Georgia @* -February, 1997 +Nof Ayalon @* +ISRAEL @* +March, 2001 @ignore -Stuff still not covered anywhere: -BASICS: - Integer vs. floating point - Hex vs. octal vs. decimal - Interpreter vs compiler - input/output -@end ignore +@c Try this +@iftex +@page +@headings off +@majorheading I@ @ @ @ The @command{awk} Language and @command{gawk} +Part I describes the @command{awk} language and @command{gawk} program in detail. +It starts with the basics, and continues through all of the features of @command{awk} +and @command{gawk}. It contains the following chapters: -@node What Is Awk, Getting Started, Preface, Top -@chapter Introduction +@itemize @bullet +@item +@ref{Getting Started, ,Getting Started with @command{awk}}. -If you are like many computer users, you would frequently like to make -changes in various text files wherever certain patterns appear, or -extract data from parts of certain lines while discarding the rest. To -write a program to do this in a language such as C or Pascal is a -time-consuming inconvenience that may take many lines of code. The job -may be easier with @code{awk}. +@item +@ref{Regexp, ,Regular Expressions}. -The @code{awk} utility interprets a special-purpose programming language -that makes it possible to handle simple data-reformatting jobs -with just a few lines of code. +@item +@ref{Reading Files, , Reading Input Files}. -The GNU implementation of @code{awk} is called @code{gawk}; it is fully -upward compatible with the System V Release 4 version of -@code{awk}. @code{gawk} is also upward compatible with the POSIX -specification of the @code{awk} language. This means that all -properly written @code{awk} programs should work with @code{gawk}. -Thus, we usually don't distinguish between @code{gawk} and other @code{awk} -implementations. +@item +@ref{Printing, , Printing Output}. -@cindex uses of @code{awk} -Using @code{awk} you can: +@item +@ref{Expressions}. -@itemize @bullet @item -manage small, personal databases +@ref{Patterns and Actions, ,Patterns Actions and Variables}. @item -generate reports +@ref{Arrays, ,Arrays in @command{awk}}. @item -validate data +@ref{Functions}. @item -produce indexes, and perform other document preparation tasks +@ref{Internationalization, ,Internationalization with @command{gawk}}. @item -even experiment with algorithms that can be adapted later to other computer -languages -@end itemize +@ref{Advanced Features, ,Advanced Features of @command{gawk}}. -@menu -* This Manual:: Using this @value{DOCUMENT}. Includes sample - input files that you can use. -* Conventions:: Typographical Conventions. -* Sample Data Files:: Sample data files for use in the @code{awk} - programs illustrated in this @value{DOCUMENT}. -@end menu +@item +@ref{Invoking Gawk, ,Running @command{awk} and @command{gawk}}. +@end itemize -@node This Manual, Conventions, What Is Awk, What Is Awk -@section Using This Book -@cindex book, using this -@cindex using this book -@cindex language, @code{awk} -@cindex program, @code{awk} -@ignore -@cindex @code{awk} language -@cindex @code{awk} program +@page +@evenheading @thispage@ @ @ @strong{@value{TITLE}} @| @| +@oddheading @| @| @strong{@thischapter}@ @ @ @thispage +@end iftex @end ignore -The term @code{awk} refers to a particular program, and to the language you -use to tell this program what to do. When we need to be careful, we call -the program ``the @code{awk} utility'' and the language ``the @code{awk} -language.'' The term @code{gawk} refers to a version of @code{awk} developed -as part the GNU project. The purpose of this @value{DOCUMENT} is to explain -both the @code{awk} language and how to run the @code{awk} utility. - -The main purpose of the @value{DOCUMENT} is to explain the features -of @code{awk}, as defined in the POSIX standard. It does so in the context -of one particular implementation, @code{gawk}. While doing so, it will also -attempt to describe important differences between @code{gawk} and other -@code{awk} implementations. Finally, any @code{gawk} features that -are not in the POSIX standard for @code{awk} will be noted. +@node Getting Started, Regexp, Preface, Top +@chapter Getting Started with @command{awk} +@cindex script, definition of +@cindex rule, definition of +@cindex program, definition of +@cindex basic function of @command{awk} -@iftex -This @value{DOCUMENT} has the difficult task of being both tutorial and reference. -If you are a novice, feel free to skip over details that seem too complex. -You should also ignore the many cross references; they are for the -expert user, and for the on-line Info version of the document. -@end iftex +The basic function of @command{awk} is to search files for lines (or other +units of text) that contain certain patterns. When a line matches one +of the patterns, @command{awk} performs specified actions on that line. +@command{awk} keeps processing input lines in this way until it reaches +the end of the input files. -The term @dfn{@code{awk} program} refers to a program written by you in -the @code{awk} programming language. +@cindex data-driven languages +@cindex procedural languages +@cindex language, data-driven +@cindex language, procedural +Programs in @command{awk} are different from programs in most other languages, +because @command{awk} programs are @dfn{data-driven}; that is, you describe +the data you want to work with and then what to do when you find it. +Most other languages are @dfn{procedural}; you have to describe, in great +detail, every step the program is to take. When working with procedural +languages, it is usually much +harder to clearly describe the data your program will process. +For this reason, @command{awk} programs are often refreshingly easy to +write and read. -@xref{Getting Started, ,Getting Started with @code{awk}}, for the bare -essentials you need to know to start using @code{awk}. +@cindex program, definition of +@cindex rule, definition of +When you run @command{awk}, you specify an @command{awk} @dfn{program} that +tells @command{awk} what to do. The program consists of a series of +@dfn{rules}. (It may also contain @dfn{function definitions}, +an advanced feature that we will ignore for now. +@xref{User-defined, ,User-Defined Functions}.) Each rule specifies one +pattern to search for and one action to perform +upon finding the pattern. -Some useful ``one-liners'' are included to give you a feel for the -@code{awk} language (@pxref{One-liners, ,Useful One Line Programs}). +Syntactically, a rule consists of a pattern followed by an action. The +action is enclosed in curly braces to separate it from the pattern. +Newlines usually separate rules. Therefore, an @command{awk} +program looks like this: -Many sample @code{awk} programs have been provided for you -(@pxref{Library Functions, ,A Library of @code{awk} Functions}; also -@pxref{Sample Programs, ,Practical @code{awk} Programs}). +@example +@var{pattern} @{ @var{action} @} +@var{pattern} @{ @var{action} @} +@dots{} +@end example -The entire @code{awk} language is summarized for quick reference in -@ref{Gawk Summary, ,@code{gawk} Summary}. Look there if you just need -to refresh your memory about a particular feature. +@menu +* Running gawk:: How to run @command{gawk} programs; includes + command-line syntax. +* Sample Data Files:: Sample data files for use in the @command{awk} + programs illustrated in this @value{DOCUMENT}. +* Very Simple:: A very simple example. +* Two Rules:: A less simple one-line example using two + rules. +* More Complex:: A more complex example. +* Statements/Lines:: Subdividing or combining statements into + lines. +* Other Features:: Other Features of @command{awk}. +* When:: When to use @command{gawk} and when to use + other things. +@end menu -If you find terms that you aren't familiar with, try looking them -up in the glossary (@pxref{Glossary}). +@node Running gawk, Sample Data Files, Getting Started, Getting Started +@section How to Run @command{awk} Programs -Most of the time complete @code{awk} programs are used as examples, but in -some of the more advanced sections, only the part of the @code{awk} program -that illustrates the concept being described is shown. +@cindex command-line formats +@cindex running @command{awk} programs +There are several ways to run an @command{awk} program. If the program is +short, it is easiest to include it in the command that runs @command{awk}, +like this: -While this @value{DOCUMENT} is aimed principally at people who have not been -exposed -to @code{awk}, there is a lot of information here that even the @code{awk} -expert should find useful. In particular, the description of POSIX -@code{awk}, and the example programs in -@ref{Library Functions, ,A Library of @code{awk} Functions}, and -@ref{Sample Programs, ,Practical @code{awk} Programs}, -should be of interest. +@example +awk '@var{program}' @var{input-file1} @var{input-file2} @dots{} +@end example -@c fakenode --- for prepinfo -@unnumberedsubsec Dark Corners -@display -@i{Who opened that window shade?!?} -Count Dracula -@end display -@sp 1 +When the program is long, it is usually more convenient to put it in a file +and run it with a command like this: -@cindex d.c., see ``dark corner'' -@cindex dark corner -Until the POSIX standard (and @cite{The Gawk Manual}), -many features of @code{awk} were either poorly documented, or not -documented at all. Descriptions of such features -(often called ``dark corners'') are noted in this @value{DOCUMENT} with -``(d.c.)''. -They also appear in the index under the heading ``dark corner.'' +@example +awk -f @var{program-file} @var{input-file1} @var{input-file2} @dots{} +@end example -@node Conventions, Sample Data Files, This Manual, What Is Awk -@section Typographical Conventions +This @value{SECTION} discusses both mechanisms, along with several +variations of each. -This @value{DOCUMENT} is written using Texinfo, the GNU documentation formatting language. -A single Texinfo source file is used to produce both the printed and on-line -versions of the documentation. -@iftex -Because of this, the typographical conventions -are slightly different than in other books you may have read. -@end iftex -@ifinfo -This section briefly documents the typographical conventions used in Texinfo. -@end ifinfo +@menu +* One-shot:: Running a short throw-away @command{awk} + program. +* Read Terminal:: Using no input files (input from terminal + instead). +* Long:: Putting permanent @command{awk} programs in + files. +* Executable Scripts:: Making self-contained @command{awk} programs. +* Comments:: Adding documentation to @command{gawk} + programs. +* Quoting:: More discussion of shell quoting issues. +@end menu -Examples you would type at the command line are preceded by the common -shell primary and secondary prompts, @samp{$} and @samp{>}. -Output from the command is preceded by the glyph ``@print{}''. -This typically represents the command's standard output. -Error messages, and other output on the command's standard error, are preceded -by the glyph ``@error{}''. For example: +@node One-shot, Read Terminal, Running gawk, Running gawk +@subsection One-Shot Throw-Away @command{awk} Programs + +Once you are familiar with @command{awk}, you will often type in simple +programs the moment you want to use them. Then you can write the +program as the first argument of the @command{awk} command, like this: @example -@group -$ echo hi on stdout -@print{} hi on stdout -$ echo hello on stderr 1>&2 -@error{} hello on stderr -@end group +awk '@var{program}' @var{input-file1} @var{input-file2} @dots{} @end example -@iftex -In the text, command names appear in @code{this font}, while code segments -appear in the same font and quoted, @samp{like this}. Some things will -be emphasized @emph{like this}, and if a point needs to be made -strongly, it will be done @strong{like this}. The first occurrence of -a new term is usually its @dfn{definition}, and appears in the same -font as the previous occurrence of ``definition'' in this sentence. -File names are indicated like this: @file{/path/to/ourfile}. -@end iftex +@noindent +where @var{program} consists of a series of @var{patterns} and +@var{actions}, as described earlier. -Characters that you type at the keyboard look @kbd{like this}. In particular, -there are special characters called ``control characters.'' These are -characters that you type by holding down both the @kbd{CONTROL} key and -another key, at the same time. For example, a @kbd{Control-d} is typed -by first pressing and holding the @kbd{CONTROL} key, next -pressing the @kbd{d} key, and finally releasing both keys. +@cindex single quotes, why needed +This command format instructs the @dfn{shell}, or command interpreter, +to start @command{awk} and use the @var{program} to process records in the +input file(s). There are single quotes around @var{program} so +the shell won't interpret any @command{awk} characters as special shell +characters. The quotes also cause the shell to treat all of @var{program} as +a single argument for @command{awk}, and allow @var{program} to be more +than one line long. -@node Sample Data Files, , Conventions, What Is Awk -@section Data Files for the Examples +This format is also useful for running short or medium-sized @command{awk} +programs from shell scripts, because it avoids the need for a separate +file for the @command{awk} program. A self-contained shell script is more +reliable because there are no other files to misplace. + +@ref{Very Simple, ,Some Simple Examples}, +@ifnotinfo +later in this @value{CHAPTER}, +@end ifnotinfo +presents several short, +self-contained programs. -@cindex input file, sample -@cindex sample input file -@cindex @file{BBS-list} file -Many of the examples in this @value{DOCUMENT} take their input from two sample -data files. The first, called @file{BBS-list}, represents a list of -computer bulletin board systems together with information about those systems. -The second data file, called @file{inventory-shipped}, contains -information about shipments on a monthly basis. In both files, -each line is considered to be one @dfn{record}. - -In the file @file{BBS-list}, each record contains the name of a computer -bulletin board, its phone number, the board's baud rate(s), and a code for -the number of hours it is operational. An @samp{A} in the last column -means the board operates 24 hours a day. A @samp{B} in the last -column means the board operates evening and weekend hours, only. A -@samp{C} means the board operates only on weekends. - -@c 2e: Update the baud rates to reflect today's faster modems -@example -@c system mkdir eg -@c system mkdir eg/lib -@c system mkdir eg/data -@c system mkdir eg/prog -@c system mkdir eg/misc -@c file eg/data/BBS-list -aardvark 555-5553 1200/300 B -alpo-net 555-3412 2400/1200/300 A -barfly 555-7685 1200/300 A -bites 555-1675 2400/1200/300 A -camelot 555-0542 300 C -core 555-2912 1200/300 C -fooey 555-1234 2400/1200/300 B -foot 555-6699 1200/300 B -macfoo 555-6480 1200/300 A -sdace 555-3430 2400/1200/300 A -sabafoo 555-2127 1200/300 C -@c endfile -@end example - -@cindex @file{inventory-shipped} file -The second data file, called @file{inventory-shipped}, represents -information about shipments during the year. -Each record contains the month of the year, the number -of green crates shipped, the number of red boxes shipped, the number of -orange bags shipped, and the number of blue packages shipped, -respectively. There are 16 entries, covering the 12 months of one year -and four months of the next year. - -@example -@c file eg/data/inventory-shipped -Jan 13 25 15 115 -Feb 15 32 24 226 -Mar 15 24 34 228 -Apr 31 52 63 420 -May 16 34 29 208 -Jun 31 42 75 492 -Jul 24 34 67 436 -Aug 15 34 47 316 -Sep 13 55 37 277 -Oct 29 54 68 525 -Nov 20 87 82 577 -Dec 17 35 61 401 - -Jan 21 36 64 620 -Feb 26 58 80 652 -Mar 24 75 70 495 -Apr 21 70 74 514 -@c endfile -@end example - -@ifinfo -If you are reading this in GNU Emacs using Info, you can copy the regions -of text showing these sample files into your own test files. This way you -can try out the examples shown in the remainder of this document. You do -this by using the command @kbd{M-x write-region} to copy text from the Info -file into a file for use with @code{awk} -(@xref{Misc File Ops, , Miscellaneous File Operations, emacs, GNU Emacs Manual}, -for more information). Using this information, create your own -@file{BBS-list} and @file{inventory-shipped} files, and practice what you -learn in this @value{DOCUMENT}. - -If you are using the stand-alone version of Info, -see @ref{Extract Program, ,Extracting Programs from Texinfo Source Files}, -for an @code{awk} program that will extract these data files from -@file{gawk.texi}, the Texinfo source file for this Info file. -@end ifinfo - -@node Getting Started, One-liners, What Is Awk, Top -@chapter Getting Started with @code{awk} -@cindex script, definition of -@cindex rule, definition of -@cindex program, definition of -@cindex basic function of @code{awk} - -The basic function of @code{awk} is to search files for lines (or other -units of text) that contain certain patterns. When a line matches one -of the patterns, @code{awk} performs specified actions on that line. -@code{awk} keeps processing input lines in this way until the end of the -input files are reached. - -@cindex data-driven languages -@cindex procedural languages -@cindex language, data-driven -@cindex language, procedural -Programs in @code{awk} are different from programs in most other languages, -because @code{awk} programs are @dfn{data-driven}; that is, you describe -the data you wish to work with, and then what to do when you find it. -Most other languages are @dfn{procedural}; you have to describe, in great -detail, every step the program is to take. When working with procedural -languages, it is usually much -harder to clearly describe the data your program will process. -For this reason, @code{awk} programs are often refreshingly easy to both -write and read. - -@cindex program, definition of -@cindex rule, definition of -When you run @code{awk}, you specify an @code{awk} @dfn{program} that -tells @code{awk} what to do. The program consists of a series of -@dfn{rules}. (It may also contain @dfn{function definitions}, -an advanced feature which we will ignore for now. -@xref{User-defined, ,User-defined Functions}.) Each rule specifies one -pattern to search for, and one action to perform when that pattern is found. - -Syntactically, a rule consists of a pattern followed by an action. The -action is enclosed in curly braces to separate it from the pattern. -Rules are usually separated by newlines. Therefore, an @code{awk} -program looks like this: - -@example -@var{pattern} @{ @var{action} @} -@var{pattern} @{ @var{action} @} -@dots{} -@end example - -@menu -* Names:: What name to use to find @code{awk}. -* Running gawk:: How to run @code{gawk} programs; includes - command line syntax. -* Very Simple:: A very simple example. -* Two Rules:: A less simple one-line example with two rules. -* More Complex:: A more complex example. -* Statements/Lines:: Subdividing or combining statements into - lines. -* Other Features:: Other Features of @code{awk}. -* When:: When to use @code{gawk} and when to use other - things. -@end menu - -@node Names, Running gawk , Getting Started, Getting Started -@section A Rose By Any Other Name - -@cindex old @code{awk} vs. new @code{awk} -@cindex new @code{awk} vs. old @code{awk} -The @code{awk} language has evolved over the years. Full details are -provided in @ref{Language History, ,The Evolution of the @code{awk} Language}. -The language described in this @value{DOCUMENT} -is often referred to as ``new @code{awk}.'' - -Because of this, many systems have multiple -versions of @code{awk}. -Some systems have an @code{awk} utility that implements the -original version of the @code{awk} language, and a @code{nawk} utility -for the new version. Others have an @code{oawk} for the ``old @code{awk}'' -language, and plain @code{awk} for the new one. Still others only -have one version, usually the new one.@footnote{Often, these systems -use @code{gawk} for their @code{awk} implementation!} - -All in all, this makes it difficult for you to know which version of -@code{awk} you should run when writing your programs. The best advice -we can give here is to check your local documentation. Look for @code{awk}, -@code{oawk}, and @code{nawk}, as well as for @code{gawk}. Chances are, you -will have some version of new @code{awk} on your system, and that is what -you should use when running your programs. (Of course, if you're reading -this @value{DOCUMENT}, chances are good that you have @code{gawk}!) - -Throughout this @value{DOCUMENT}, whenever we refer to a language feature -that should be available in any complete implementation of POSIX @code{awk}, -we simply use the term @code{awk}. When referring to a feature that is -specific to the GNU implementation, we use the term @code{gawk}. - -@node Running gawk, Very Simple, Names, Getting Started -@section How to Run @code{awk} Programs - -@cindex command line formats -@cindex running @code{awk} programs -There are several ways to run an @code{awk} program. If the program is -short, it is easiest to include it in the command that runs @code{awk}, -like this: - -@example -awk '@var{program}' @var{input-file1} @var{input-file2} @dots{} -@end example - -@noindent -where @var{program} consists of a series of patterns and actions, as -described earlier. -(The reason for the single quotes is described below, in -@ref{One-shot, ,One-shot Throw-away @code{awk} Programs}.) - -When the program is long, it is usually more convenient to put it in a file -and run it with a command like this: - -@example -awk -f @var{program-file} @var{input-file1} @var{input-file2} @dots{} -@end example - -@menu -* One-shot:: Running a short throw-away @code{awk} program. -* Read Terminal:: Using no input files (input from terminal - instead). -* Long:: Putting permanent @code{awk} programs in - files. -* Executable Scripts:: Making self-contained @code{awk} programs. -* Comments:: Adding documentation to @code{gawk} programs. -@end menu - -@node One-shot, Read Terminal, Running gawk, Running gawk -@subsection One-shot Throw-away @code{awk} Programs - -Once you are familiar with @code{awk}, you will often type in simple -programs the moment you want to use them. Then you can write the -program as the first argument of the @code{awk} command, like this: - -@example -awk '@var{program}' @var{input-file1} @var{input-file2} @dots{} -@end example - -@noindent -where @var{program} consists of a series of @var{patterns} and -@var{actions}, as described earlier. - -@cindex single quotes, why needed -This command format instructs the @dfn{shell}, or command interpreter, -to start @code{awk} and use the @var{program} to process records in the -input file(s). There are single quotes around @var{program} so that -the shell doesn't interpret any @code{awk} characters as special shell -characters. They also cause the shell to treat all of @var{program} as -a single argument for @code{awk} and allow @var{program} to be more -than one line long. - -This format is also useful for running short or medium-sized @code{awk} -programs from shell scripts, because it avoids the need for a separate -file for the @code{awk} program. A self-contained shell script is more -reliable since there are no other files to misplace. - -@ref{One-liners, , Useful One Line Programs}, presents several short, -self-contained programs. - -As an interesting side point, the command +@c Removed for gawk 3.1, doesn't really add anything here. +@ignore +As an interesting side point, the command @example awk '/foo/' @var{files} @dots{} @@ -1230,34 +1699,35 @@ awk '/foo/' @var{files} @dots{} @noindent is essentially the same as -@cindex @code{egrep} +@cindex @command{egrep} utility @example egrep foo @var{files} @dots{} @end example +@end ignore @node Read Terminal, Long, One-shot, Running gawk -@subsection Running @code{awk} without Input Files +@subsection Running @command{awk} Without Input Files @cindex standard input @cindex input, standard -You can also run @code{awk} without any input files. If you type the -command line: +You can also run @command{awk} without any input files. If you type the +following command line: @example awk '@var{program}' @end example @noindent -then @code{awk} applies the @var{program} to the @dfn{standard input}, +@command{awk} applies the @var{program} to the @dfn{standard input}, which usually means whatever you type on the terminal. This continues -until you indicate end-of-file by typing @kbd{Control-d}. +until you indicate end-of-file by typing @kbd{Ctrl-d}. (On other operating systems, the end-of-file character may be different. -For example, on OS/2 and MS-DOS, it is @kbd{Control-z}.) +For example, on OS/2 and MS-DOS, it is @kbd{Ctrl-z}.) -For example, the following program prints a friendly piece of advice -(from Douglas Adams' @cite{The Hitchhiker's Guide to the Galaxy}), -to keep you from worrying about the complexities of computer programming -(@samp{BEGIN} is a feature we haven't discussed yet). +As an example, the following program prints a friendly piece of advice +(from Douglas Adams's @cite{The Hitchhiker's Guide to the Galaxy}), +to keep you from worrying about the complexities of computer programming. +(@code{BEGIN} is a feature we haven't discussed yet.): @example $ awk "BEGIN @{ print \"Don't Panic!\" @}" @@ -1267,11 +1737,14 @@ $ awk "BEGIN @{ print \"Don't Panic!\" @}" @cindex quoting, shell @cindex shell quoting This program does not read any input. The @samp{\} before each of the -inner double quotes is necessary because of the shell's quoting rules, -in particular because it mixes both single quotes and double quotes. - -This next simple @code{awk} program -emulates the @code{cat} utility; it copies whatever you type at the +inner double quotes is necessary because of the shell's quoting +rules---in particular because it mixes both single quotes and +double quotes.@footnote{Although we generally recommend the use of single +quotes around the program text, double quotes are needed here in order to +put the single quote into the message.} + +This next simple @command{awk} program +emulates the @command{cat} utility; it copies whatever you type at the keyboard to its standard output. (Why this works is explained shortly.) @example @@ -1284,7 +1757,7 @@ Four score and seven years ago, ... @print{} Four score and seven years ago, ... What, me worry? @print{} What, me worry? -@kbd{Control-d} +@kbd{Ctrl-d} @end example @node Long, Executable Scripts, Read Terminal, Running gawk @@ -1292,18 +1765,19 @@ What, me worry? @cindex running long programs @cindex @code{-f} option +@cindex command-line option, @code{-f} @cindex program file -@cindex file, @code{awk} program -Sometimes your @code{awk} programs can be very long. In this case it is -more convenient to put the program into a separate file. To tell -@code{awk} to use that file for its program, you type: +@cindex file, @command{awk} program +Sometimes your @command{awk} programs can be very long. In this case, it is +more convenient to put the program into a separate file. In order to tell +@command{awk} to use that file for its program, you type: @example awk -f @var{source-file} @var{input-file1} @var{input-file2} @dots{} @end example -The @samp{-f} instructs the @code{awk} utility to get the @code{awk} program -from the file @var{source-file}. Any file name can be used for +The @option{-f} instructs the @command{awk} utility to get the @command{awk} program +from the file @var{source-file}. Any @value{FN} can be used for @var{source-file}. For example, you could put the program: @example @@ -1327,112 +1801,106 @@ awk "BEGIN @{ print \"Don't Panic!\" @}" @cindex quoting, shell @cindex shell quoting @noindent -which was explained earlier (@pxref{Read Terminal, ,Running @code{awk} without Input Files}). -Note that you don't usually need single quotes around the file name that you -specify with @samp{-f}, because most file names don't contain any of the shell's -special characters. Notice that in @file{advice}, the @code{awk} +This was explained earlier +(@pxref{Read Terminal, ,Running @command{awk} Without Input Files}). +Note that you don't usually need single quotes around the @value{FN} that you +specify with @option{-f}, because most @value{FN}s don't contain any of the shell's +special characters. Notice that in @file{advice}, the @command{awk} program did not have single quotes around it. The quotes are only needed -for programs that are provided on the @code{awk} command line. +for programs that are provided on the @command{awk} command line. -If you want to identify your @code{awk} program files clearly as such, -you can add the extension @file{.awk} to the file name. This doesn't -affect the execution of the @code{awk} program, but it does make +If you want to identify your @command{awk} program files clearly as such, +you can add the extension @file{.awk} to the @value{FN}. This doesn't +affect the execution of the @command{awk} program but it does make ``housekeeping'' easier. @node Executable Scripts, Comments, Long, Running gawk -@subsection Executable @code{awk} Programs +@subsection Executable @command{awk} Programs @cindex executable scripts @cindex scripts, executable -@cindex self contained programs -@cindex program, self contained +@cindex self-contained programs +@cindex program, self-contained @cindex @code{#!} (executable scripts) -Once you have learned @code{awk}, you may want to write self-contained -@code{awk} scripts, using the @samp{#!} script mechanism. You can do +Once you have learned @command{awk}, you may want to write self-contained +@command{awk} scripts, using the @samp{#!} script mechanism. You can do this on many Unix systems@footnote{The @samp{#!} mechanism works on Linux systems, -Unix systems derived from Berkeley Unix, System V Release 4, and some System -V Release 3 systems.} (and someday on the GNU system). - +systems derived from the 4.4-Lite Berkeley Software Distribution, +and most commercial Unix systems.} as well as on the GNU system. For example, you could update the file @file{advice} to look like this: @example #! /bin/awk -f -BEGIN @{ print "Don't Panic!" @} +BEGIN @{ print "Don't Panic!" @} @end example @noindent -After making this file executable (with the @code{chmod} utility), you -can simply type @samp{advice} -at the shell, and the system will arrange to run @code{awk}@footnote{The -line beginning with @samp{#!} lists the full file name of an interpreter -to be run, and an optional initial command line argument to pass to that +After making this file executable (with the @command{chmod} utility), +simply type @samp{advice} +at the shell and the system arranges to run @command{awk}@footnote{The +line beginning with @samp{#!} lists the full @value{FN} of an interpreter +to run and an optional initial command-line argument to pass to that interpreter. The operating system then runs the interpreter with the given argument and the full argument list of the executed program. The first argument -in the list is the full file name of the @code{awk} program. The rest of the -argument list will either be options to @code{awk}, or data files, -or both.} as if you had typed @samp{awk -f advice}. +in the list is the full @value{FN} of the @command{awk} program. The rest of the +argument list is either options to @command{awk}, or @value{DF}s, +or both.} as if you had +typed @samp{awk -f advice}: @example -@group +$ chmod +x advice $ advice @print{} Don't Panic! -@end group @end example @noindent -Self-contained @code{awk} scripts are useful when you want to write a -program which users can invoke without their having to know that the program is -written in @code{awk}. - -@strong{Caution:} You should not put more than one argument on the @samp{#!} -line after the path to @code{awk}. This will not work. The operating system -treats the rest of the line as a single agument, and passes it to @code{awk}. -Doing this will lead to confusing behavior: most likely a usage diagnostic -of some sort from @code{awk}. - -@cindex shell scripts -@cindex scripts, shell -Some older systems do not support the @samp{#!} mechanism. You can get a -similar effect using a regular shell script. It would look something -like this: +Self-contained @command{awk} scripts are useful when you want to write a +program that users can invoke without their having to know that the program is +written in @command{awk}. -@example -: The colon ensures execution by the standard shell. -awk '@var{program}' "$@@" -@end example +@c fakenode --- for prepinfo +@subheading Advanced Notes: Portability Issues with @samp{#!} +@cindex advanced notes -Using this technique, it is @emph{vital} to enclose the @var{program} in -single quotes to protect it from interpretation by the shell. If you -omit the quotes, only a shell wizard can predict the results. +Some systems limit the length of the interpreter name to 32 characters. +Often, this can be dealt with by using a symbolic link. -The @code{"$@@"} causes the shell to forward all the command line -arguments to the @code{awk} program, without interpretation. The first -line, which starts with a colon, is used so that this shell script will -work even if invoked by a user who uses the C shell. (Not all older systems -obey this convention, but many do.) -@c 2e: -@c Someday: (See @cite{The Bourne Again Shell}, by ??.) +You should not put more than one argument on the @samp{#!} +line after the path to @command{awk}. It does not work. The operating system +treats the rest of the line as a single argument and passes it to @command{awk}. +Doing this leads to confusing behavior---most likely a usage diagnostic +of some sort from @command{awk}. -@node Comments, , Executable Scripts, Running gawk -@subsection Comments in @code{awk} Programs +@cindex portability issues +Finally, +the value of @code{ARGV[0]} +(@pxref{Built-in Variables}) +varies depending upon your operating system. +Some systems put @samp{awk} there, some put the full pathname +of @command{awk} (such as @file{/bin/awk}), and some put the name +of your script (@samp{advice}). Don't rely on the value of @code{ARGV[0]} +to provide your script name. + +@node Comments, Quoting, Executable Scripts, Running gawk +@subsection Comments in @command{awk} Programs @cindex @code{#} (comment) @cindex comments @cindex use of comments -@cindex documenting @code{awk} programs +@cindex documenting @command{awk} programs @cindex programs, documenting A @dfn{comment} is some text that is included in a program for the sake -of human readers; it is not really part of the program. Comments -can explain what the program does, and how it works. Nearly all -programming languages have provisions for comments, because programs are -typically hard to understand without their extra help. +of human readers; it is not really an executable part of the program. Comments +can explain what the program does and how it works. Nearly all +programming languages have provisions for comments, as programs are +typically hard to understand without them. -In the @code{awk} language, a comment starts with the sharp sign -character, @samp{#}, and continues to the end of the line. +In the @command{awk} language, a comment starts with the sharp sign +character (@samp{#}) and continues to the end of the line. The @samp{#} does not have to be the first character on the line. The -@code{awk} language ignores the rest of a line following a sharp sign. +@command{awk} language ignores the rest of a line following a sharp sign. For example, we could have put the following into @file{advice}: @example @@ -1441,226 +1909,568 @@ For example, we could have put the following into @file{advice}: BEGIN @{ print "Don't Panic!" @} @end example -You can put comment lines into keyboard-composed throw-away @code{awk} -programs also, but this usually isn't very useful; the purpose of a -comment is to help you or another person understand the program at -a later time. +You can put comment lines into keyboard-composed throw-away @command{awk} +programs, but this usually isn't very useful; the purpose of a +comment is to help you or another person understand the program +when reading it at a later time. +@cindex quoting, shell +@cindex shell quoting @strong{Caution:} As mentioned in -@ref{One-shot, ,One-shot Throw-away @code{awk} Programs}, +@ref{One-shot, ,One-Shot Throw-Away @command{awk} Programs}, you can enclose small to medium programs in single quotes, in order to keep your shell scripts self-contained. When doing so, @emph{don't} put an apostrophe (i.e., a single quote) into a comment (or anywhere else -in your program). The shell will interpret the quote as the closing -quote for the entire program. As a result, usually the shell will -print a message about mismatched quotes, and if @code{awk} actually +in your program). The shell interprets the quote as the closing +quote for the entire program. As a result, usually the shell +prints a message about mismatched quotes, and if @command{awk} actually runs, it will probably print strange messages about syntax errors. -For example: +For example, look at the following: @example -awk 'BEGIN @{ print "hello" @} # let's be cute' +$ awk '@{ print "hello" @} # let's be cute' +> @end example -@node Very Simple, Two Rules, Running gawk, Getting Started -@section A Very Simple Example - -The following command runs a simple @code{awk} program that searches the -input file @file{BBS-list} for the string of characters: @samp{foo}. (A -string of characters is usually called a @dfn{string}. -The term @dfn{string} is perhaps based on similar usage in English, such -as ``a string of pearls,'' or, ``a string of cars in a train.'') +The shell sees that the first two quotes match, and that +a new quoted object begins at the end of the command-line. +It therefore prompts with the secondary prompt, waiting for more input. +With Unix @command{awk}, closing the quoted string produces this result: @example -awk '/foo/ @{ print $0 @}' BBS-list +$ awk '@{ print "hello" @} # let's be cute' +> ' +@error{} awk: can't open file be +@error{} source line number 1 @end example -@noindent -When lines containing @samp{foo} are found, they are printed, because -@w{@samp{print $0}} means print the current line. (Just @samp{print} by -itself means the same thing, so we could have written that -instead.) +Putting a backslash before the single quote in @samp{let's} wouldn't help, +since backslashes are not special inside single quotes. +The next @value{SUBSECTION} describes the shell's quoting rules. -You will notice that slashes, @samp{/}, surround the string @samp{foo} -in the @code{awk} program. The slashes indicate that @samp{foo} -is a pattern to search for. This type of pattern is called a -@dfn{regular expression}, and is covered in more detail later -(@pxref{Regexp, ,Regular Expressions}). -The pattern is allowed to match parts of words. -There are -single-quotes around the @code{awk} program so that the shell won't -interpret any of it as special shell characters. +@node Quoting, , Comments, Running gawk +@subsection Shell Quoting Issues +@c the indexing here is purposely different, until we +@c get a way to mark the defining instance for an index entry +@cindex quoting rules, shell +@cindex shell quoting rules -Here is what this program prints: +For short to medium length @command{awk} programs, it is most convenient +to enter the program on the @command{awk} command line. +This is best done by enclosing the entire program in single quotes. +This is true whether you are entering the program interactively at +the shell prompt, or writing it as part of a larger shell script: @example -@group -$ awk '/foo/ @{ print $0 @}' BBS-list -@print{} fooey 555-1234 2400/1200/300 B -@print{} foot 555-6699 1200/300 B -@print{} macfoo 555-6480 1200/300 A -@print{} sabafoo 555-2127 1200/300 C -@end group +awk '@var{program text}' @var{input-file1} @var{input-file2} @dots{} @end example -@cindex action, default -@cindex pattern, default -@cindex default action -@cindex default pattern -In an @code{awk} rule, either the pattern or the action can be omitted, -but not both. If the pattern is omitted, then the action is performed -for @emph{every} input line. If the action is omitted, the default -action is to print all lines that match the pattern. - -@cindex empty action -@cindex action, empty -Thus, we could leave out the action (the @code{print} statement and the curly -braces) in the above example, and the result would be the same: all -lines matching the pattern @samp{foo} would be printed. By comparison, -omitting the @code{print} statement but retaining the curly braces makes an -empty action that does nothing; then no lines would be printed. +@cindex @command{csh} utility +Once you are working with the shell, it is helpful to have a basic +knowledge of shell quoting rules. The following rules apply only to +POSIX-compliant, Bourne-style shells (such as @command{bash}, the GNU Bourne-Again +Shell). If you use @command{csh}, you're on your own. -@node Two Rules, More Complex, Very Simple, Getting Started -@section An Example with Two Rules -@cindex how @code{awk} works +@itemize @bullet +@item +Quoted items can be concatenated with nonquoted items as well as with other +quoted items. The shell turns everything into one argument for +the command. -The @code{awk} utility reads the input files one line at a -time. For each line, @code{awk} tries the patterns of each of the rules. -If several patterns match then several actions are run, in the order in -which they appear in the @code{awk} program. If no patterns match, then -no actions are run. +@item +Preceding any single character with a backslash (@samp{\}) quotes +that character. The shell removes the backslash and passes the quoted +character on to the command. -After processing all the rules (perhaps none) that match the line, -@code{awk} reads the next line (however, -@pxref{Next Statement, ,The @code{next} Statement}, -and also @pxref{Nextfile Statement, ,The @code{nextfile} Statement}). -This continues until the end of the file is reached. +@item +Single quotes protect everything between the opening and closing quotes. +The shell does no interpretation of the quoted text, passing it on verbatim +to the command. +It is @emph{impossible} to embed a single quote inside single-quoted text. +Refer back to +@ref{Comments, ,Comments in @command{awk} Programs}, +for an example showing what happens if you try. -For example, the @code{awk} program: +@item +Double quotes protect most things between the opening and closing quotes. +The shell does at least variable and command substitution on the quoted text. +Different shells may do additional kinds of processing on double-quoted text. + +Since certain characters within double-quoted text are processed by the shell, +they must be @dfn{escaped} within the text. Of note are the characters +@samp{$}, @samp{`}, @samp{\} and @samp{"}, all of which must be preceded by +a backslash within double-quoted text if they are to be passed on literally +to the program. (The leading backslash is stripped first.) +Thus, the example seen +@ifnotinfo +previously +@end ifnotinfo +in @ref{Read Terminal, ,Running @command{awk} Without Input Files}, +is applicable: @example -/12/ @{ print $0 @} -/21/ @{ print $0 @} +$ awk "BEGIN @{ print \"Don't Panic!\" @}" +@print{} Don't Panic! @end example -@noindent -contains two rules. The first rule has the string @samp{12} as the -pattern and @samp{print $0} as the action. The second rule has the -string @samp{21} as the pattern and also has @samp{print $0} as the -action. Each rule's action is enclosed in its own pair of braces. - -This @code{awk} program prints every line that contains the string -@samp{12} @emph{or} the string @samp{21}. If a line contains both -strings, it is printed twice, once by each rule. +Note that the single quote is not special within double quotes. -This is what happens if we run this program on our two sample data files, -@file{BBS-list} and @file{inventory-shipped}, as shown here: +@item +Null strings are removed when they occur as part of a non-null +command-line argument, while explicit non-null objects are kept. +For example, to specify that the field separator @code{FS} should +be set to the null string, use: @example -$ awk '/12/ @{ print $0 @} -> /21/ @{ print $0 @}' BBS-list inventory-shipped -@print{} aardvark 555-5553 1200/300 B -@print{} alpo-net 555-3412 2400/1200/300 A -@print{} barfly 555-7685 1200/300 A -@print{} bites 555-1675 2400/1200/300 A -@print{} core 555-2912 1200/300 C -@print{} fooey 555-1234 2400/1200/300 B -@print{} foot 555-6699 1200/300 B -@print{} macfoo 555-6480 1200/300 A -@print{} sdace 555-3430 2400/1200/300 A -@print{} sabafoo 555-2127 1200/300 C -@print{} sabafoo 555-2127 1200/300 C -@print{} Jan 21 36 64 620 -@print{} Apr 21 70 74 514 +awk -F "" '@var{program}' @var{files} # correct @end example @noindent -Note how the line in @file{BBS-list} beginning with @samp{sabafoo} -was printed twice, once for each rule. - -@node More Complex, Statements/Lines, Two Rules, Getting Started -@section A More Complex Example - -@ignore -We have to use ls -lg here to get portable output across Unix systems. -The POSIX ls matches this behavior too. Sigh. -@end ignore -Here is an example to give you an idea of what typical @code{awk} -programs do. This example shows how @code{awk} can be used to -summarize, select, and rearrange the output of another utility. It uses -features that haven't been covered yet, so don't worry if you don't -understand all the details. +Don't use this: @example -ls -lg | awk '$6 == "Nov" @{ sum += $5 @} - END @{ print sum @}' +awk -F"" '@var{program}' @var{files} # wrong! @end example -@cindex @code{csh}, backslash continuation -@cindex backslash continuation in @code{csh} -This command prints the total number of bytes in all the files in the -current directory that were last modified in November (of any year). -(In the C shell you would need to type a semicolon and then a backslash -at the end of the first line; in a POSIX-compliant shell, such as the -Bourne shell or Bash, the GNU Bourne-Again shell, you can type the example -as shown.) -@ignore -FIXME: how can users tell what shell they are running? Need a footnote -or something, but getting into this is a distraction. -@end ignore +@noindent +In the second case, @command{awk} will attempt to use the text of the program +as the value of @code{FS}, and the first @value{FN} as the text of the program! +This results in syntax errors at best, and confusing behavior at worst. +@end itemize -The @w{@samp{ls -lg}} part of this example is a system command that gives -you a listing of the files in a directory, including file size and the date -the file was last modified. Its output looks like this: +@cindex shell quoting, tricks +Mixing single and double quotes is difficult. You have to resort +to shell quoting tricks, like this: @example --rw-r--r-- 1 arnold user 1933 Nov 7 13:05 Makefile --rw-r--r-- 1 arnold user 10809 Nov 7 13:03 gawk.h --rw-r--r-- 1 arnold user 983 Apr 13 12:14 gawk.tab.h --rw-r--r-- 1 arnold user 31869 Jun 15 12:20 gawk.y --rw-r--r-- 1 arnold user 22414 Nov 7 13:03 gawk1.c --rw-r--r-- 1 arnold user 37455 Nov 7 13:03 gawk2.c --rw-r--r-- 1 arnold user 27511 Dec 9 13:07 gawk3.c --rw-r--r-- 1 arnold user 7989 Nov 7 13:03 gawk4.c +$ awk 'BEGIN @{ print "Here is a single quote <'"'"'>" @}' +@print{} Here is a single quote <'> @end example @noindent -The first field contains read-write permissions, the second field contains +This program consists of three concatenated quoted strings. The first and the +third are single-quoted, the second is double-quoted. + +This can be ``simplified'' to: + +@example +$ awk 'BEGIN @{ print "Here is a single quote <'\''>" @}' +@print{} Here is a single quote <'> +@end example + +@noindent +Judge for yourself which of these two is the more readable. + +Another option is to use double quotes, escaping the embedded, @command{awk}-level +double quotes: + +@example +$ awk "BEGIN @{ print \"Here is a single quote <'>\" @}" +@print{} Here is a single quote <'> +@end example + +@noindent +This option is also painful, because double quotes, backslashes, and dollar signs +are very common in @command{awk} programs. + +If you really need both single and double quotes in your @command{awk} +program, it is probably best to move it into a separate file, where +the shell won't be part of the picture, and you can say what you mean. + +@node Sample Data Files, Very Simple, Running gawk, Getting Started +@section @value{DDF}s for the Examples +@c For gawk >= 3.2, update these data files. No-one has such slow modems! + +@cindex input file, sample +@cindex sample input files +@cindex @file{BBS-list} file +Many of the examples in this @value{DOCUMENT} take their input from two sample +@value{DF}s. The first, called @file{BBS-list}, represents a list of +computer bulletin board systems together with information about those systems. +The second @value{DF}, called @file{inventory-shipped}, contains +information about monthly shipments. In both files, +each line is considered to be one @dfn{record}. + +In the file @file{BBS-list}, each record contains the name of a computer +bulletin board, its phone number, the board's baud rate(s), and a code for +the number of hours it is operational. An @samp{A} in the last column +means the board operates 24 hours a day. A @samp{B} in the last +column means the board only operates on evening and weekend hours. +A @samp{C} means the board operates only on weekends: + +@c 2e: Update the baud rates to reflect today's faster modems +@example +@c system if test ! -d eg ; then mkdir eg ; fi +@c system if test ! -d eg/lib ; then mkdir eg/lib ; fi +@c system if test ! -d eg/data ; then mkdir eg/data ; fi +@c system if test ! -d eg/prog ; then mkdir eg/prog ; fi +@c system if test ! -d eg/misc ; then mkdir eg/misc ; fi +@c file eg/data/BBS-list +aardvark 555-5553 1200/300 B +alpo-net 555-3412 2400/1200/300 A +barfly 555-7685 1200/300 A +bites 555-1675 2400/1200/300 A +camelot 555-0542 300 C +core 555-2912 1200/300 C +fooey 555-1234 2400/1200/300 B +foot 555-6699 1200/300 B +macfoo 555-6480 1200/300 A +sdace 555-3430 2400/1200/300 A +sabafoo 555-2127 1200/300 C +@c endfile +@end example + +@cindex @file{inventory-shipped} file +The second @value{DF}, called @file{inventory-shipped}, represents +information about shipments during the year. +Each record contains the month, the number +of green crates shipped, the number of red boxes shipped, the number of +orange bags shipped, and the number of blue packages shipped, +respectively. There are 16 entries, covering the 12 months of last year +and the first four months of the current year. + +@example +@c file eg/data/inventory-shipped +Jan 13 25 15 115 +Feb 15 32 24 226 +Mar 15 24 34 228 +Apr 31 52 63 420 +May 16 34 29 208 +Jun 31 42 75 492 +Jul 24 34 67 436 +Aug 15 34 47 316 +Sep 13 55 37 277 +Oct 29 54 68 525 +Nov 20 87 82 577 +Dec 17 35 61 401 + +Jan 21 36 64 620 +Feb 26 58 80 652 +Mar 24 75 70 495 +Apr 21 70 74 514 +@c endfile +@end example + +@ifinfo +If you are reading this in GNU Emacs using Info, you can copy the regions +of text showing these sample files into your own test files. This way you +can try out the examples shown in the remainder of this document. You do +this by using the command @kbd{M-x write-region} to copy text from the Info +file into a file for use with @command{awk} +(@xref{Misc File Ops, , Miscellaneous File Operations, emacs, GNU Emacs Manual}, +for more information). Using this information, create your own +@file{BBS-list} and @file{inventory-shipped} files and practice what you +learn in this @value{DOCUMENT}. + +@cindex Texinfo +If you are using the stand-alone version of Info, +see @ref{Extract Program, ,Extracting Programs from Texinfo Source Files}, +for an @command{awk} program that extracts these @value{DF}s from +@file{gawk.texi}, the Texinfo source file for this Info file. +@end ifinfo + +@node Very Simple, Two Rules, Sample Data Files, Getting Started +@section Some Simple Examples + +The following command runs a simple @command{awk} program that searches the +input file @file{BBS-list} for the character string @samp{foo}. (A +string of characters is usually called a @dfn{string}. +The term @dfn{string} is based on similar usage in English, such +as ``a string of pearls,'' or, ``a string of cars in a train.''): + +@example +awk '/foo/ @{ print $0 @}' BBS-list +@end example + +@noindent +When lines containing @samp{foo} are found, they are printed because +@w{@samp{print $0}} means print the current line. (Just @samp{print} by +itself means the same thing, so we could have written that +instead.) + +You will notice that slashes (@samp{/}) surround the string @samp{foo} +in the @command{awk} program. The slashes indicate that @samp{foo} +is the pattern to search for. This type of pattern is called a +@dfn{regular expression}, which is covered in more detail later +(@pxref{Regexp, ,Regular Expressions}). +The pattern is allowed to match parts of words. +There are +single quotes around the @command{awk} program so that the shell won't +interpret any of it as special shell characters. + +Here is what this program prints: + +@example +$ awk '/foo/ @{ print $0 @}' BBS-list +@print{} fooey 555-1234 2400/1200/300 B +@print{} foot 555-6699 1200/300 B +@print{} macfoo 555-6480 1200/300 A +@print{} sabafoo 555-2127 1200/300 C +@end example + +@cindex action, default +@cindex pattern, default +@cindex default action +@cindex default pattern +In an @command{awk} rule, either the pattern or the action can be omitted, +but not both. If the pattern is omitted, then the action is performed +for @emph{every} input line. If the action is omitted, the default +action is to print all lines that match the pattern. + +@cindex empty action +@cindex action, empty +Thus, we could leave out the action (the @code{print} statement and the curly +braces) in the above example and the result would be the same: all +lines matching the pattern @samp{foo} are printed. By comparison, +omitting the @code{print} statement but retaining the curly braces makes an +empty action that does nothing (i.e., no lines are printed). + +@cindex one-liners +Many practical @command{awk} programs are just a line or two. Following is a +collection of useful, short programs to get you started. Some of these +programs contain constructs that haven't been covered yet. (The description +of the program will give you a good idea of what is going on, but please +read the rest of the @value{DOCUMENT} to become an @command{awk} expert!) +Most of the examples use a @value{DF} named @file{data}. This is just a +placeholder; if you use these programs yourself, substitute +your own @value{FN}s for @file{data}. +For future reference, note that there is often more than +one way to do things in @command{awk}. At some point, you may want +to look back at these examples and see if +you can come up with different ways to do the same things shown here: + +@itemize @bullet +@item +Print the length of the longest input line: + +@example +awk '@{ if (length($0) > max) max = length($0) @} + END @{ print max @}' data +@end example + +@item +Print every line that is longer than 80 characters: + +@example +awk 'length($0) > 80' data +@end example + +The sole rule has a relational expression as its pattern and it has no +action---so the default action, printing the record, is used. + +@cindex @command{expand} utility +@item +Print the length of the longest line in @file{data}: + +@example +expand data | awk '@{ if (x < length()) x = length() @} + END @{ print "maximum line length is " x @}' +@end example + +The input is processed by the @command{expand} utility to change tabs +into spaces, so the widths compared are actually the right-margin columns. + +@item +Print every line that has at least one field: + +@example +awk 'NF > 0' data +@end example + +This is an easy way to delete blank lines from a file (or rather, to +create a new file similar to the old file but from which the blank lines +have been removed). + +@item +Print seven random numbers from 0 to 100, inclusive: + +@example +awk 'BEGIN @{ for (i = 1; i <= 7; i++) + print int(101 * rand()) @}' +@end example + +@item +Print the total number of bytes used by @var{files}: + +@example +ls -l @var{files} | awk '@{ x += $5 @} + END @{ print "total bytes: " x @}' +@end example + +@item +Print the total number of kilobytes used by @var{files}: + +@c Don't use \ continuation, not discussed yet +@example +ls -l @var{files} | awk '@{ x += $5 @} + END @{ print "total K-bytes: " (x + 1023)/1024 @}' +@end example + +@item +Print a sorted list of the login names of all users: + +@example +awk -F: '@{ print $1 @}' /etc/passwd | sort +@end example + +@item +Count lines in a file: + +@example +awk 'END @{ print NR @}' data +@end example + +@item +Print the even-numbered lines in the @value{DF}: + +@example +awk 'NR % 2 == 0' data +@end example + +If you use the expression @samp{NR % 2 == 1} instead, +it would print the odd-numbered lines. +@end itemize + +@node Two Rules, More Complex, Very Simple, Getting Started +@section An Example with Two Rules +@cindex how @command{awk} works + +The @command{awk} utility reads the input files one line at a +time. For each line, @command{awk} tries the patterns of each of the rules. +If several patterns match, then several actions are run in the order in +which they appear in the @command{awk} program. If no patterns match, then +no actions are run. + +After processing all the rules that match the line (and perhaps there are none), +@command{awk} reads the next line. (However, +@pxref{Next Statement, ,The @code{next} Statement}, +and also @pxref{Nextfile Statement, ,Using @command{gawk}'s @code{nextfile} Statement}). +This continues until the end of the file is reached. +For example, the following @command{awk} program contains two rules: + +@example +/12/ @{ print $0 @} +/21/ @{ print $0 @} +@end example + +@noindent +The first rule has the string @samp{12} as the +pattern and @samp{print $0} as the action. The second rule has the +string @samp{21} as the pattern and also has @samp{print $0} as the +action. Each rule's action is enclosed in its own pair of braces. + +This program prints every line that contains the string +@samp{12} @emph{or} the string @samp{21}. If a line contains both +strings, it is printed twice, once by each rule. + +This is what happens if we run this program on our two sample @value{DF}s, +@file{BBS-list} and @file{inventory-shipped}, as shown here: + +@example +$ awk '/12/ @{ print $0 @} +> /21/ @{ print $0 @}' BBS-list inventory-shipped +@print{} aardvark 555-5553 1200/300 B +@print{} alpo-net 555-3412 2400/1200/300 A +@print{} barfly 555-7685 1200/300 A +@print{} bites 555-1675 2400/1200/300 A +@print{} core 555-2912 1200/300 C +@print{} fooey 555-1234 2400/1200/300 B +@print{} foot 555-6699 1200/300 B +@print{} macfoo 555-6480 1200/300 A +@print{} sdace 555-3430 2400/1200/300 A +@print{} sabafoo 555-2127 1200/300 C +@print{} sabafoo 555-2127 1200/300 C +@print{} Jan 21 36 64 620 +@print{} Apr 21 70 74 514 +@end example + +@noindent +Note how the line beginning with @samp{sabafoo} +in @file{BBS-list} was printed twice, once for each rule. + +@node More Complex, Statements/Lines, Two Rules, Getting Started +@section A More Complex Example + +Now that we've mastered some simple tasks, let's look at +what typical @command{awk} +programs do. This example shows how @command{awk} can be used to +summarize, select, and rearrange the output of another utility. It uses +features that haven't been covered yet, so don't worry if you don't +understand all the details: + +@example +ls -l | awk '$6 == "Nov" @{ sum += $5 @} + END @{ print sum @}' +@end example + +@cindex @command{csh} utility +@cindex @command{csh}, backslash continuation +@cindex backslash continuation, in @command{csh} +@cindex @command{ls} utility +This command prints the total number of bytes in all the files in the +current directory that were last modified in November (of any year). +@footnote{In the C shell (@command{csh}), you need to type +a semicolon and then a backslash at the end of the first line; see +@ref{Statements/Lines, ,@command{awk} Statements Versus Lines}, for an +explanation as to why. In a POSIX-compliant shell, such as the Bourne +shell or @command{bash}, you can type the example as shown. If the command +@samp{echo $path} produces an empty output line, you are most likely +using a POSIX-compliant shell. Otherwise, you are probably using the +C shell or a shell derived from it.} +The @w{@samp{ls -l}} part of this example is a system command that gives +you a listing of the files in a directory, including each file's size and the date +the file was last modified. Its output looks like this: + +@example +-rw-r--r-- 1 arnold user 1933 Nov 7 13:05 Makefile +-rw-r--r-- 1 arnold user 10809 Nov 7 13:03 awk.h +-rw-r--r-- 1 arnold user 983 Apr 13 12:14 awk.tab.h +-rw-r--r-- 1 arnold user 31869 Jun 15 12:20 awk.y +-rw-r--r-- 1 arnold user 22414 Nov 7 13:03 awk1.c +-rw-r--r-- 1 arnold user 37455 Nov 7 13:03 awk2.c +-rw-r--r-- 1 arnold user 27511 Dec 9 13:07 awk3.c +-rw-r--r-- 1 arnold user 7989 Nov 7 13:03 awk4.c +@end example + +@noindent +The first field contains read-write permissions, the second field contains the number of links to the file, and the third field identifies the owner of the file. The fourth field identifies the group of the file. The fifth field contains the size of the file in bytes. The sixth, seventh and eighth fields contain the month, day, and time, respectively, that the file was last modified. Finally, the ninth field -contains the name of the file. +contains the name of the file.@footnote{On some +very old systems, you may need to use @samp{ls -lg} to get this output.} @cindex automatic initialization @cindex initialization, automatic -The @samp{$6 == "Nov"} in our @code{awk} program is an expression that -tests whether the sixth field of the output from @w{@samp{ls -lg}} +The @samp{$6 == "Nov"} in our @command{awk} program is an expression that +tests whether the sixth field of the output from @w{@samp{ls -l}} matches the string @samp{Nov}. Each time a line has the string @samp{Nov} for its sixth field, the action @samp{sum += $5} is -performed. This adds the fifth field (the file size) to the variable -@code{sum}. As a result, when @code{awk} has finished reading all the -input lines, @code{sum} is the sum of the sizes of files whose -lines matched the pattern. (This works because @code{awk} variables +performed. This adds the fifth field (the file's size) to the variable +@code{sum}. As a result, when @command{awk} has finished reading all the +input lines, @code{sum} is the total of the sizes of the files whose +lines matched the pattern. (This works because @command{awk} variables are automatically initialized to zero.) -After the last line of output from @code{ls} has been processed, the -@code{END} rule is executed, and the value of @code{sum} is -printed. In this example, the value of @code{sum} would be 80600. +After the last line of output from @command{ls} has been processed, the +@code{END} rule executes and prints the value of @code{sum}. +In this example, the value of @code{sum} is 140963. -These more advanced @code{awk} techniques are covered in later sections -(@pxref{Action Overview, ,Overview of Actions}). Before you can move on to more -advanced @code{awk} programming, you have to know how @code{awk} interprets +These more advanced @command{awk} techniques are covered in later sections +(@pxref{Action Overview, ,Actions}). Before you can move on to more +advanced @command{awk} programming, you have to know how @command{awk} interprets your input and displays your output. By manipulating fields and using @code{print} statements, you can produce some very useful and impressive looking reports. @node Statements/Lines, Other Features, More Complex, Getting Started -@section @code{awk} Statements Versus Lines +@section @command{awk} Statements Versus Lines @cindex line break @cindex newline -Most often, each line in an @code{awk} program is a separate statement or +Most often, each line in an @command{awk} program is a separate statement or separate rule, like this: @example @@ -1668,27 +2478,30 @@ awk '/12/ @{ print $0 @} /21/ @{ print $0 @}' BBS-list inventory-shipped @end example -However, @code{gawk} will ignore newlines after any of the following: +However, @command{gawk} ignores newlines after any of the following +symbols and keywords: @example , @{ ? : || && do else @end example @noindent -A newline at any other point is considered the end of the statement. -(Splitting lines after @samp{?} and @samp{:} is a minor @code{gawk} -extension. The @samp{?} and @samp{:} referred to here is the -three operand conditional expression described in -@ref{Conditional Exp, ,Conditional Expressions}.) +A newline at any other point is considered the end of the +statement.@footnote{The @samp{?} and @samp{:} referred to here is the +three-operand conditional expression described in +@ref{Conditional Exp, ,Conditional Expressions}. +Splitting lines after @samp{?} and @samp{:} is a minor @command{gawk} +extension; if @option{--posix} is specified +(@pxref{Options, , Command-Line Options}), then this extension is disabled.} @cindex backslash continuation @cindex continuation of lines @cindex line continuation If you would like to split a single statement into two lines at a point where a newline would terminate it, you can @dfn{continue} it by ending the -first line with a backslash character, @samp{\}. The backslash must be -the final character on the line to be recognized as a continuation -character. This is allowed absolutely anywhere in the statement, even +first line with a backslash character (@samp{\}). The backslash must be +the final character on the line in order to be recognized as a continuation +character. A backslash is allowed anywhere in the statement, even in the middle of a string or regular expression. For example: @example @@ -1699,26 +2512,28 @@ awk '/This regular expression is too long, so continue it\ @noindent @cindex portability issues We have generally not used backslash continuation in the sample programs -in this @value{DOCUMENT}. Since in @code{gawk} there is no limit on the -length of a line, it is never strictly necessary; it just makes programs -more readable. For this same reason, as well as for clarity, we have -kept most statements short in the sample programs presented throughout -the @value{DOCUMENT}. Backslash continuation is most useful when your -@code{awk} program is in a separate source file, instead of typed in on -the command line. You should also note that many @code{awk} -implementations are more particular about where you may use backslash -continuation. For example, they may not allow you to split a string -constant using backslash continuation. Thus, for maximal portability of -your @code{awk} programs, it is best not to split your lines in the -middle of a regular expression or a string. - -@cindex @code{csh}, backslash continuation -@cindex backslash continuation in @code{csh} -@strong{Caution: backslash continuation does not work as described above -with the C shell.} Continuation with backslash works for @code{awk} -programs in files, and also for one-shot programs @emph{provided} you -are using a POSIX-compliant shell, such as the Bourne shell or Bash, the -GNU Bourne-Again shell. But the C shell (@code{csh}) behaves +in this @value{DOCUMENT}. In @command{gawk}, there is no limit on the +length of a line, so backslash continuation is never strictly necessary; +it just makes programs more readable. For this same reason, as well as +for clarity, we have kept most statements short in the sample programs +presented throughout the @value{DOCUMENT}. Backslash continuation is +most useful when your @command{awk} program is in a separate source file +instead of entered from the command line. You should also note that +many @command{awk} implementations are more particular about where you +may use backslash continuation. For example, they may not allow you to +split a string constant using backslash continuation. Thus, for maximum +portability of your @command{awk} programs, it is best not to split your +lines in the middle of a regular expression or a string. +@c 10/2000: gawk, mawk, and current bell labs awk allow it, +@c solaris 2.7 nawk does not. Solaris /usr/xpg4/bin/awk does though! sigh. + +@cindex @command{csh} utility +@cindex @command{csh}, backslash continuation +@cindex backslash continuation, in @command{csh} +@strong{Caution:} @emph{Backslash continuation does not work as described +above with the C shell.} It works for @command{awk} programs in files and +for one-shot programs, @emph{provided} you are using a POSIX-compliant +shell, such as the Unix Bourne shell or @command{bash}. But the C shell behaves differently! There, you must use two backslashes in a row, followed by a newline. Note also that when using the C shell, @emph{every} newline in your awk program must be escaped with a backslash. To illustrate: @@ -1735,185 +2550,117 @@ in your awk program must be escaped with a backslash. To illustrate: Here, the @samp{%} and @samp{?} are the C shell's primary and secondary prompts, analogous to the standard shell's @samp{$} and @samp{>}. -@code{awk} is a line-oriented language. Each rule's action has to +Compare the previous example to how it is done with a POSIX-compliant shell: + +@example +$ awk 'BEGIN @{ +> print \ +> "hello, world" +> @}' +@print{} hello, world +@end example + +@command{awk} is a line-oriented language. Each rule's action has to begin on the same line as the pattern. To have the pattern and action -on separate lines, you @emph{must} use backslash continuation---there +on separate lines, you @emph{must} use backslash continuation; there is no other way. -@cindex backslash continuation and comments +@cindex backslash continuation, and comments @cindex comments and backslash continuation -Note that backslash continuation and comments do not mix. As soon -as @code{awk} sees the @samp{#} that starts a comment, it ignores -@emph{everything} on the rest of the line. For example: +Another thing to keep in mind is that backslash continuation and +comments do not mix. As soon as @command{awk} sees the @samp{#} that +starts a comment, it ignores @emph{everything} on the rest of the +line. For example: @example -@group $ gawk 'BEGIN @{ print "dont panic" # a friendly \ > BEGIN rule > @}' @error{} gawk: cmd. line:2: BEGIN rule @error{} gawk: cmd. line:2: ^ parse error -@end group @end example @noindent -Here, it looks like the backslash would continue the comment onto the +In this case, it looks like the backslash would continue the comment onto the next line. However, the backslash-newline combination is never even -noticed, since it is ``hidden'' inside the comment. Thus, the -@samp{BEGIN} is noted as a syntax error. +noticed because it is ``hidden'' inside the comment. Thus, the +@code{BEGIN} is noted as a syntax error. @cindex multiple statements on one line -When @code{awk} statements within one rule are short, you might want to put -more than one of them on a line. You do this by separating the statements -with a semicolon, @samp{;}. - +When @command{awk} statements within one rule are short, you might want to put +more than one of them on a line. This is accomplished by separating the statements +with a semicolon (@samp{;}). This also applies to the rules themselves. -Thus, the previous program could have been written: +Thus, the program shown at the start of this @value{SECTION} +could also be written this way: @example /12/ @{ print $0 @} ; /21/ @{ print $0 @} @end example @noindent -@strong{Note:} the requirement that rules on the same line must be -separated with a semicolon was not in the original @code{awk} +@strong{Note:} The requirement that states that rules on the same line must be +separated with a semicolon was not in the original @command{awk} language; it was added for consistency with the treatment of statements within an action. @node Other Features, When, Statements/Lines, Getting Started -@section Other Features of @code{awk} +@section Other Features of @command{awk} -The @code{awk} language provides a number of predefined, or built-in variables, which -your programs can use to get information from @code{awk}. There are other -variables your program can set to control how @code{awk} processes your -data. +The @command{awk} language provides a number of predefined, or +@dfn{built-in}, variables that your programs can use to get information +from @command{awk}. There are other variables your program can set +as well to control how @command{awk} processes your data. -In addition, @code{awk} provides a number of built-in functions for doing +In addition, @command{awk} provides a number of built-in functions for doing common computational and string related operations. +@command{gawk} provides built-in functions for working with timestamps, +performing bit manipulation, and for runtime string translation. -As we develop our presentation of the @code{awk} language, we introduce +As we develop our presentation of the @command{awk} language, we introduce most of the variables and many of the functions. They are defined systematically in @ref{Built-in Variables}, and @ref{Built-in, ,Built-in Functions}. -@node When, , Other Features, Getting Started -@section When to Use @code{awk} +@node When, , Other Features, Getting Started +@section When to Use @command{awk} -@cindex when to use @code{awk} -@cindex applications of @code{awk} -You might wonder how @code{awk} might be useful for you. Using +@cindex uses of @command{awk} +@cindex applications of @command{awk} +Now that you've seen some of what @command{awk} can do, +you might wonder how @command{awk} could be useful for you. By using utility programs, advanced patterns, field separators, arithmetic statements, and other selection criteria, you can produce much more -complex output. The @code{awk} language is very useful for producing +complex output. The @command{awk} language is very useful for producing reports from large amounts of raw data, such as summarizing information -from the output of other utility programs like @code{ls}. +from the output of other utility programs like @command{ls}. (@xref{More Complex, ,A More Complex Example}.) -Programs written with @code{awk} are usually much smaller than they would -be in other languages. This makes @code{awk} programs easy to compose and -use. Often, @code{awk} programs can be quickly composed at your terminal, -used once, and thrown away. Since @code{awk} programs are interpreted, you +Programs written with @command{awk} are usually much smaller than they would +be in other languages. This makes @command{awk} programs easy to compose and +use. Often, @command{awk} programs can be quickly composed at your terminal, +used once, and thrown away. Because @command{awk} programs are interpreted, you can avoid the (usually lengthy) compilation part of the typical edit-compile-test-debug cycle of software development. -Complex programs have been written in @code{awk}, including a complete +Complex programs have been written in @command{awk}, including a complete retargetable assembler for eight-bit microprocessors (@pxref{Glossary}, for -more information) and a microcode assembler for a special purpose Prolog -computer. However, @code{awk}'s capabilities are strained by tasks of +more information), and a microcode assembler for a special purpose Prolog +computer. However, @command{awk}'s capabilities are strained by tasks of such complexity. -If you find yourself writing @code{awk} scripts of more than, say, a few +If you find yourself writing @command{awk} scripts of more than, say, a few hundred lines, you might consider using a different programming language. Emacs Lisp is a good choice if you need sophisticated string or pattern matching capabilities. The shell is also good at string and pattern matching; in addition, it allows powerful use of the system -utilities. More conventional languages, such as C, C++, and Lisp, offer +utilities. More conventional languages, such as C, C++, and Java, offer better facilities for system programming and for managing the complexity of large programs. Programs in these languages may require more lines -of source code than the equivalent @code{awk} programs, but they are +of source code than the equivalent @command{awk} programs, but they are easier to maintain and usually run more efficiently. -@node One-liners, Regexp, Getting Started, Top -@chapter Useful One Line Programs - -@cindex one-liners -Many useful @code{awk} programs are short, just a line or two. Here is a -collection of useful, short programs to get you started. Some of these -programs contain constructs that haven't been covered yet. The description -of the program will give you a good idea of what is going on, but please -read the rest of the @value{DOCUMENT} to become an @code{awk} expert! - -Most of the examples use a data file named @file{data}. This is just a -placeholder; if you were to use these programs yourself, you would substitute -your own file names for @file{data}. - -@ifinfo -Since you are reading this in Info, each line of the example code is -enclosed in quotes, to represent text that you would type literally. -The examples themselves represent shell commands that use single quotes -to keep the shell from interpreting the contents of the program. -When reading the examples, focus on the text between the open and close -quotes. -@end ifinfo - -@table @code -@item awk '@{ if (length($0) > max) max = length($0) @} -@itemx @ @ @ @ @ END @{ print max @}' data -This program prints the length of the longest input line. - -@item awk 'length($0) > 80' data -This program prints every line that is longer than 80 characters. The sole -rule has a relational expression as its pattern, and has no action (so the -default action, printing the record, is used). - -@item expand@ data@ |@ awk@ '@{ if (x < length()) x = length() @} -@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ END @{ print "maximum line length is " x @}' -This program prints the length of the longest line in @file{data}. The input -is processed by the @code{expand} program to change tabs into spaces, -so the widths compared are actually the right-margin columns. - -@item awk 'NF > 0' data -This program prints every line that has at least one field. This is an -easy way to delete blank lines from a file (or rather, to create a new -file similar to the old file but from which the blank lines have been -deleted). - -@c Karl Berry points out that new users probably don't want to see -@c multiple ways to do things, just the `best' way. He's probably -@c right. At some point it might be worth adding something about there -@c often being multiple ways to do things in awk, but for now we'll -@c just take this one out. -@ignore -@item awk '@{ if (NF > 0) print @}' data -This program also prints every line that has at least one field. Here we -allow the rule to match every line, and then decide in the action whether -to print. -@end ignore - -@item awk@ 'BEGIN@ @{@ for (i = 1; i <= 7; i++) -@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ print int(101 * rand()) @}' -This program prints seven random numbers from zero to 100, inclusive. - -@item ls -lg @var{files} | awk '@{ x += $5 @} ; END @{ print "total bytes: " x @}' -This program prints the total number of bytes used by @var{files}. - -@item ls -lg @var{files} | awk '@{ x += $5 @} -@itemx @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ @ END @{ print "total K-bytes: " (x + 1023)/1024 @}' -This program prints the total number of kilobytes used by @var{files}. - -@item awk -F: '@{ print $1 @}' /etc/passwd | sort -This program prints a sorted list of the login names of all users. - -@item awk 'END @{ print NR @}' data -This program counts lines in a file. - -@item awk 'NR % 2 == 0' data -This program prints the even numbered lines in the data file. -If you were to use the expression @samp{NR % 2 == 1} instead, -it would print the odd numbered lines. -@end table - -@node Regexp, Reading Files, One-liners, Top +@node Regexp, Reading Files, Getting Started, Top @chapter Regular Expressions @cindex pattern, regular expressions @cindex regexp @@ -1922,29 +2669,30 @@ it would print the odd numbered lines. A @dfn{regular expression}, or @dfn{regexp}, is a way of describing a set of strings. -Because regular expressions are such a fundamental part of @code{awk} -programming, their format and use deserve a separate chapter. +Because regular expressions are such a fundamental part of @command{awk} +programming, their format and use deserve a separate @value{CHAPTER}. A regular expression enclosed in slashes (@samp{/}) -is an @code{awk} pattern that matches every input record whose text +is an @command{awk} pattern that matches every input record whose text belongs to that set. - The simplest regular expression is a sequence of letters, numbers, or both. Such a regexp matches any string that contains that sequence. Thus, the regexp @samp{foo} matches any string containing @samp{foo}. Therefore, the pattern @code{/foo/} matches any input record containing -the three characters @samp{foo}, @emph{anywhere} in the record. Other +the three characters @samp{foo} @emph{anywhere} in the record. Other kinds of regexps let you specify more complicated classes of strings. -@iftex -Initially, the examples will be simple. As we explain more about how -regular expressions work, we will present more complicated examples. -@end iftex +@ifnotinfo +Initially, the examples in this @value{CHAPTER} are simple. +As we explain more about how +regular expressions work, we will present more complicated instances. +@end ifnotinfo @menu * Regexp Usage:: How to Use Regular Expressions. * Escape Sequences:: How to write non-printing characters. * Regexp Operators:: Regular Expression Operators. +* Character Lists:: What can go between @samp{[...]}. * GNU Regexp Operators:: Operators specific to GNU software. * Case-sensitivity:: How to do case-insensitive matching. * Leftmost Longest:: How much text matches. @@ -1957,53 +2705,49 @@ regular expressions work, we will present more complicated examples. A regular expression can be used as a pattern by enclosing it in slashes. Then the regular expression is tested against the entire text of each record. (Normally, it only needs -to match some part of the text in order to succeed.) For example, this -prints the second field of each record that contains the three -characters @samp{foo} anywhere in it: +to match some part of the text in order to succeed.) For example, the +following prints the second field of each record that contains the string +@samp{foo} anywhere in it: @example -@group $ awk '/foo/ @{ print $2 @}' BBS-list @print{} 555-1234 @print{} 555-6699 @print{} 555-6480 @print{} 555-2127 -@end group @end example -@cindex regexp matching operators +@cindex regexp operators @cindex string-matching operators @cindex operators, string-matching @cindex operators, regexp matching -@cindex regexp match/non-match operators @cindex @code{~} operator @cindex @code{!~} operator Regular expressions can also be used in matching expressions. These expressions allow you to specify the string to match against; it need -not be the entire current input record. The two operators, @samp{~} -and @samp{!~}, perform regular expression comparisons. Expressions -using these operators can be used as patterns or in @code{if}, +not be the entire current input record. The two operators @samp{~} +and @samp{!~} perform regular expression comparisons. Expressions +using these operators can be used as patterns, or in @code{if}, @code{while}, @code{for}, and @code{do} statements. -@ifinfo -@c adding this xref in TeX screws up the formatting too much (@xref{Statements, ,Control Statements in Actions}.) -@end ifinfo +For example: -@table @code -@item @var{exp} ~ /@var{regexp}/ -This is true if the expression @var{exp} (taken as a string) -is matched by @var{regexp}. The following example matches, or selects, -all input records with the upper-case letter @samp{J} somewhere in the +@example +@var{exp} ~ /@var{regexp}/ +@end example + +@noindent +is true if the expression @var{exp} (taken as a string) +matches @var{regexp}. The following example matches, or selects, +all input records with the uppercase letter @samp{J} somewhere in the first field: @example -@group $ awk '$1 ~ /J/' inventory-shipped @print{} Jan 13 25 15 115 @print{} Jun 31 42 75 492 @print{} Jul 24 34 67 436 @print{} Jan 21 36 64 620 -@end group @end example So does this: @@ -2012,27 +2756,30 @@ So does this: awk '@{ if ($1 ~ /J/) print @}' inventory-shipped @end example -@item @var{exp} !~ /@var{regexp}/ -This is true if the expression @var{exp} (taken as a character string) -is @emph{not} matched by @var{regexp}. The following example matches, +This next example is true if the expression @var{exp} +(taken as a character string) +does @emph{not} match @var{regexp}: + +@example +@var{exp} !~ /@var{regexp}/ +@end example + +The following example matches, or selects, all input records whose first field @emph{does not} contain -the upper-case letter @samp{J}: +the uppercase letter @samp{J}: @example -@group $ awk '$1 !~ /J/' inventory-shipped @print{} Feb 15 32 24 226 @print{} Mar 15 24 34 228 @print{} Apr 31 52 63 420 @print{} May 16 34 29 208 @dots{} -@end group @end example -@end table @cindex regexp constant -When a regexp is written enclosed in slashes, like @code{/foo/}, we call it -a @dfn{regexp constant}, much like @code{5.27} is a numeric constant, and +When a regexp is enclosed in slashes, such as @code{/foo/}, we call it +a @dfn{regexp constant}, much like @code{5.27} is a numeric constant and @code{"foo"} is a string constant. @node Escape Sequences, Regexp Operators, Regexp Usage, Regexp @@ -2040,13 +2787,12 @@ a @dfn{regexp constant}, much like @code{5.27} is a numeric constant, and @cindex escape sequence notation Some characters cannot be included literally in string constants -(@code{"foo"}) or regexp constants (@code{/foo/}). You represent them -instead with @dfn{escape sequences}, which are character sequences -beginning with a backslash (@samp{\}). - -One use of an escape sequence is to include a double-quote character in -a string constant. Since a plain double-quote would end the string, you -must use @samp{\"} to represent an actual double-quote character as a +(@code{"foo"}) or regexp constants (@code{/foo/}). +Instead, they should be represented with @dfn{escape sequences}, +which are character sequences beginning with a backslash (@samp{\}). +One use of an escape sequence is to include a double quote character in +a string constant. Because a plain double quote ends the string, you +must use @samp{\"} to represent an actual double quote character as a part of the string. For example: @example @@ -2055,7 +2801,7 @@ $ awk 'BEGIN @{ print "He said \"hi!\" to her." @}' @end example The backslash character itself is another character that cannot be -included normally; you write @samp{\\} to put one backslash in the +included normally; you must write @samp{\\} to put one backslash in the string or regexp. Thus, the string whose contents are the two characters @samp{"} and @samp{\} must be written @code{"\"\\"}. @@ -2064,264 +2810,392 @@ such as tab or newline. While there is nothing to stop you from entering most unprintable characters directly in a string constant or regexp constant, they may look ugly. -Here is a table of all the escape sequences used in @code{awk}, and -what they represent. Unless noted otherwise, all of these escape -sequences apply to both string constants and regexp constants. +The following table lists +all the escape sequences used in @command{awk} and +what they represent. Unless noted otherwise, all these escape +sequences apply to both string constants and regexp constants: -@c @cartouche @table @code @item \\ A literal backslash, @samp{\}. -@cindex @code{awk} language, V.4 version +@cindex @command{awk} language, V.4 version +@cindex @code{\a} escape sequence @item \a -The ``alert'' character, @kbd{Control-g}, ASCII code 7 (BEL). +The ``alert'' character, @kbd{Ctrl-g}, ASCII code 7 (BEL). +(This usually makes some sort of audible noise.) +@cindex @code{\b} escape sequence @item \b -Backspace, @kbd{Control-h}, ASCII code 8 (BS). +Backspace, @kbd{Ctrl-h}, ASCII code 8 (BS). +@cindex @code{\f} escape sequence @item \f -Formfeed, @kbd{Control-l}, ASCII code 12 (FF). +Formfeed, @kbd{Ctrl-l}, ASCII code 12 (FF). +@cindex @code{\n} escape sequence @item \n -Newline, @kbd{Control-j}, ASCII code 10 (LF). +Newline, @kbd{Ctrl-j}, ASCII code 10 (LF). +@cindex @code{\r} escape sequence @item \r -Carriage return, @kbd{Control-m}, ASCII code 13 (CR). +Carriage return, @kbd{Ctrl-m}, ASCII code 13 (CR). +@cindex @code{\t} escape sequence @item \t -Horizontal tab, @kbd{Control-i}, ASCII code 9 (HT). +Horizontal tab, @kbd{Ctrl-i}, ASCII code 9 (HT). -@cindex @code{awk} language, V.4 version +@cindex @command{awk} language, V.4 version +@cindex @code{\v} escape sequence @item \v -Vertical tab, @kbd{Control-k}, ASCII code 11 (VT). +Vertical tab, @kbd{Ctrl-k}, ASCII code 11 (VT). +@cindex @code{\}@var{nnn} escape sequence (octal) @item \@var{nnn} -The octal value @var{nnn}, where @var{nnn} are one to three digits +The octal value @var{nnn}, where @var{nnn} stands for 1 to 3 digits between @samp{0} and @samp{7}. For example, the code for the ASCII ESC (escape) character is @samp{\033}. -@cindex @code{awk} language, V.4 version -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} +@cindex @code{\x} escape sequence +@cindex @command{awk} language, V.4 version +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} @item \x@var{hh}@dots{} -The hexadecimal value @var{hh}, where @var{hh} are hexadecimal -digits (@samp{0} through @samp{9} and either @samp{A} through @samp{F} or -@samp{a} through @samp{f}). Like the same construct in ANSI C, the escape -sequence continues until the first non-hexadecimal digit is seen. However, -using more than two hexadecimal digits produces undefined results. (The -@samp{\x} escape sequence is not allowed in POSIX @code{awk}.) - +The hexadecimal value @var{hh}, where @var{hh} stands for a sequence +of hexadecimal digits (@samp{0} through @samp{9}, and either @samp{A} +through @samp{F} or @samp{a} through @samp{f}). Like the same construct +in ISO C, the escape sequence continues until the first non-hexadecimal +digit is seen. However, using more than two hexadecimal digits produces +undefined results. (The @samp{\x} escape sequence is not allowed in +POSIX @command{awk}.) + +@cindex @code{\/} escape sequence @item \/ A literal slash (necessary for regexp constants only). -You use this when you wish to write a regexp -constant that contains a slash. Since the regexp is delimited by +This expression is used when you want to write a regexp +constant that contains a slash. Because the regexp is delimited by slashes, you need to escape the slash that is part of the pattern, -in order to tell @code{awk} to keep processing the rest of the regexp. +in order to tell @command{awk} to keep processing the rest of the regexp. +@cindex @code{\"} escape sequence @item \" -A literal double-quote (necessary for string constants only). -You use this when you wish to write a string -constant that contains a double-quote. Since the string is delimited by -double-quotes, you need to escape the quote that is part of the string, -in order to tell @code{awk} to keep processing the rest of the string. +A literal double quote (necessary for string constants only). +This expression is used when you want to write a string +constant that contains a double quote. Because the string is delimited by +double quotes, you need to escape the quote that is part of the string, +in order to tell @command{awk} to keep processing the rest of the string. @end table -@c @end cartouche - -In @code{gawk}, there are additional two character sequences that begin -with backslash that have special meaning in regexps. -@xref{GNU Regexp Operators, ,Additional Regexp Operators Only in @code{gawk}}. - -In a string constant, -what happens if you place a backslash before something that is not one of -the characters listed above? POSIX @code{awk} purposely leaves this case -undefined. There are two choices. - -@itemize @bullet -@item -Strip the backslash out. This is what Unix @code{awk} and @code{gawk} both do. -For example, @code{"a\qc"} is the same as @code{"aqc"}. -@item -Leave the backslash alone. Some other @code{awk} implementations do this. -In such implementations, @code{"a\qc"} is the same as if you had typed -@code{"a\\qc"}. -@end itemize +In @command{gawk}, a number of additional two-character sequences that begin +with a backslash have special meaning in regexps. +@xref{GNU Regexp Operators, ,@command{gawk}-Specific Regexp Operators}. -In a regexp, a backslash before any character that is not in the above table, +In a regexp, a backslash before any character that is not in the above table and not listed in -@ref{GNU Regexp Operators, ,Additional Regexp Operators Only in @code{gawk}}, +@ref{GNU Regexp Operators, ,@command{gawk}-Specific Regexp Operators}, means that the next character should be taken literally, even if it would -normally be a regexp operator. E.g., @code{/a\+b/} matches the three +normally be a regexp operator. For example, @code{/a\+b/} matches the three characters @samp{a+b}. @cindex portability issues For complete portability, do not use a backslash before any character not -listed in the table above. - -Another interesting question arises. Suppose you use an octal or hexadecimal -escape to represent a regexp metacharacter -(@pxref{Regexp Operators, , Regular Expression Operators}). -Does @code{awk} treat the character as a literal character, or as a regexp -operator? - -@cindex dark corner -It turns out that historically, such characters were taken literally (d.c.). -However, the POSIX standard indicates that they should be treated -as real metacharacters, and this is what @code{gawk} does. -However, in compatibility mode (@pxref{Options, ,Command Line Options}), -@code{gawk} treats the characters represented by octal and hexadecimal -escape sequences literally when used in regexp constants. Thus, -@code{/a\52b/} is equivalent to @code{/a\*b/}. +shown in the table above. To summarize: -@enumerate 1 +@itemize @bullet @item The escape sequences in the table above are always processed first, for both string constants and regexp constants. This happens very early, -as soon as @code{awk} reads your program. +as soon as @command{awk} reads your program. @item -@code{gawk} processes both regexp constants and dynamic regexps +@command{gawk} processes both regexp constants and dynamic regexps (@pxref{Computed Regexps, ,Using Dynamic Regexps}), for the special operators listed in -@ref{GNU Regexp Operators, ,Additional Regexp Operators Only in @code{gawk}}. +@ref{GNU Regexp Operators, ,@command{gawk}-Specific Regexp Operators}. @item A backslash before any other character means to treat that character literally. -@end enumerate +@end itemize + +@c fakenode --- for prepinfo +@subheading Advanced Notes: Backslash Before Regular Characters +@cindex advanced notes + +@cindex common mistakes +@cindex mistakes, common +@cindex errors, common +If you place a backslash in a string constant before something that is +not one of the characters listed above, POSIX @command{awk} purposely +leaves what happens as undefined. There are two choices: + +@cindex automatic warnings +@cindex warnings, automatic +@table @asis +@item Strip the backslash out +This is what Unix @command{awk} and @command{gawk} both do. +For example, @code{"a\qc"} is the same as @code{"aqc"}. +(Because this is such an easy bug to both introduce and to miss, +@command{gawk} warns you about it.) +Consider @samp{FS = @w{"[ \t]+\|[ \t]+"}} to use vertical bars +surrounded by whitespace as the field separator. There should be +two backslashes in the string, @samp{FS = @w{"[ \t]+\\|[ \t]+"}}.) +@c I did this! This is why I added the warning. + +@item Leave the backslash alone +Some other @command{awk} implementations do this. +In such implementations, @code{"a\qc"} is the same as if you had typed +@code{"a\\qc"}. +@end table -@node Regexp Operators, GNU Regexp Operators, Escape Sequences, Regexp +@c fakenode --- for prepinfo +@subheading Advanced Notes: Escape Sequences for Metacharacters +@cindex advanced notes + +Suppose you use an octal or hexadecimal +escape to represent a regexp metacharacter +(@pxref{Regexp Operators, , Regular Expression Operators}). +Does @command{awk} treat the character as a literal character or as a regexp +operator? + +@cindex dark corner +Historically, such characters were taken literally. +@value{DARKCORNER} +However, the POSIX standard indicates that they should be treated +as real metacharacters, which is what @command{gawk} does. +In compatibility mode (@pxref{Options, ,Command-Line Options}), +@command{gawk} treats the characters represented by octal and hexadecimal +escape sequences literally when used in regexp constants. Thus, +@code{/a\52b/} is equivalent to @code{/a\*b/}. + +@node Regexp Operators, Character Lists, Escape Sequences, Regexp @section Regular Expression Operators @cindex metacharacters @cindex regular expression metacharacters @cindex regexp operators -You can combine regular expressions with the following characters, -called @dfn{regular expression operators}, or @dfn{metacharacters}, to +You can combine regular expressions with special characters, +called @dfn{regular expression operators} or @dfn{metacharacters}, to increase the power and versatility of regular expressions. The escape sequences described -@iftex -above -@end iftex +@ifnotinfo +earlier +@end ifnotinfo in @ref{Escape Sequences}, -are valid inside a regexp. They are introduced by a @samp{\}. They +are valid inside a regexp. They are introduced by a @samp{\}, and are recognized and converted into the corresponding real characters as the very first step in processing regexps. -Here is a table of metacharacters. All characters that are not escape -sequences and that are not listed in the table stand for themselves. +Here is a list of metacharacters. All characters that are not escape +sequences and that are not listed in the table stand for themselves: @table @code @item \ This is used to suppress the special meaning of a character when -matching. For example: - -@example -\$ -@end example - -@noindent +matching. For example, @samp{\$} matches the character @samp{$}. -@c NEEDED -@page @cindex anchors in regexps @cindex regexp, anchors +@cindex Texinfo @item ^ -This matches the beginning of a string. For example: - -@example -^@@chapter -@end example - -@noindent -matches the @samp{@@chapter} at the beginning of a string, and can be used +This matches the beginning of a string. For example, @samp{^@@chapter} +matches @samp{@@chapter} at the beginning of a string, and can be used to identify chapter beginnings in Texinfo source files. -The @samp{^} is known as an @dfn{anchor}, since it anchors the pattern to -matching only at the beginning of the string. +The @samp{^} is known as an @dfn{anchor}, because it anchors the pattern to +match only at the beginning of the string. It is important to realize that @samp{^} does not match the beginning of -a line embedded in a string. In this example the condition is not true: +a line embedded in a string. +The condition is not true in the following example: @example if ("line1\nLINE 2" ~ /^L/) @dots{} @end example @item $ -This is similar to @samp{^}, but it matches only at the end of a string. -For example: - -@example -p$ -@end example - -@noindent -matches a record that ends with a @samp{p}. The @samp{$} is also an anchor, -and also does not match the end of a line embedded in a string. In this -example the condition is not true: +This is similar to @samp{^} but it matches only at the end of a string. +For example, @samp{p$} +matches a record that ends with a @samp{p}. The @samp{$} is an anchor +and does not match the end of a line embedded in a string. +The condition is not true in the following example: @example if ("line1\nLINE 2" ~ /1$/) @dots{} @end example @item . -The period, or dot, matches any single character, -@emph{including} the newline character. For example: - -@example -.P -@end example - -@noindent +This matches any single character, +@emph{including} the newline character. For example, @samp{.P} matches any single character followed by a @samp{P} in a string. Using -concatenation we can make a regular expression like @samp{U.A}, which +concatenation, we can make a regular expression such as @samp{U.A}, that matches any three-character sequence that begins with @samp{U} and ends with @samp{A}. -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} -In strict POSIX mode (@pxref{Options, ,Command Line Options}), +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} +In strict POSIX mode (@pxref{Options, ,Command-Line Options}), @samp{.} does not match the @sc{nul} character, which is a character with all bits equal to zero. -Otherwise, @sc{nul} is just another character. Other versions of @code{awk} +Otherwise, @sc{nul} is just another character. Other versions of @command{awk} may not be able to match the @sc{nul} character. -@ignore -2e: Add stuff that character list is the POSIX terminology. In other - literature known as character set or character class. -@end ignore - @cindex character list +@cindex character set (regexp component) +@cindex character class +@cindex bracket expression @item [@dots{}] -This is called a @dfn{character list}. It matches any @emph{one} of the -characters that are enclosed in the square brackets. For example: +This is called a @dfn{character list}.@footnote{In other literature, +you may see a character list referred to as either a +@dfn{character set}, a @dfn{character class} or a @dfn{bracket expression}.} +It matches any @emph{one} of the characters that are enclosed in +the square brackets. For example, @samp{[MVX]} matches any one of +the characters @samp{M}, @samp{V}, or @samp{X}, in a string. A full +discussion of what can be inside the square brackets of a character list +is given in +@ref{Character Lists, ,Using Character Lists}. -@example -[MVX] -@end example +@cindex complemented character list +@cindex character list, complemented +@item [^ @dots{}] +This is a @dfn{complemented character list}. The first character after +the @samp{[} @emph{must} be a @samp{^}. It matches any characters +@emph{except} those in the square brackets. For example, @samp{[^awk]} +matches any character that is not an @samp{a}, a @samp{w}, +or a @samp{k}. -@noindent -matches any one of the characters @samp{M}, @samp{V}, or @samp{X} in a -string. +@item | +This is the @dfn{alternation operator} and it is used to specify +alternatives. +The @samp{|} has the lowest precedence of all the regular +expression operators. +For example, @samp{^P|[[:digit:]]} +matches any string that matches either @samp{^P} or @samp{[[:digit:]]}. This +means it matches any string that starts with @samp{P} or contains a digit. -Ranges of characters are indicated by using a hyphen between the beginning -and ending characters, and enclosing the whole thing in brackets. For -example: +The alternation applies to the largest possible regexps on either side. + +@cindex Texinfo +@item (@dots{}) +Parentheses are used for grouping in regular expressions, similar to +arithmetic. They can be used to concatenate regular expressions +containing the alternation operator, @samp{|}. For example, +@samp{@@(samp|code)\@{[^@}]+\@}} matches both @samp{@@code@{foo@}} and +@samp{@@samp@{bar@}}. +(These are Texinfo formatting control sequences.) + +@item * +This symbol means that the preceding regular expression should be +repeated as many times as necessary to find a match. For example, @samp{ph*} +applies the @samp{*} symbol to the preceding @samp{h} and looks for matches +of one @samp{p} followed by any number of @samp{h}s. This also matches +just @samp{p} if no @samp{h}s are present. + +The @samp{*} repeats the @emph{smallest} possible preceding expression. +(Use parentheses if you want to repeat a larger expression.) It finds +as many repetitions as possible. For example, +@samp{awk '/\(c[ad][ad]*r x\)/ @{ print @}' sample} +prints every record in @file{sample} containing a string of the form +@samp{(car x)}, @samp{(cdr x)}, @samp{(cadr x)}, and so on. +Notice the escaping of the parentheses by preceding them +with backslashes. + +@item + +This symbol is similar to @samp{*} except that the preceding expression must be +matched at least once. This means that @samp{wh+y} +would match @samp{why} and @samp{whhy}, but not @samp{wy}, whereas +@samp{wh*y} would match all three of these strings. +The following is a simpler +way of writing the last @samp{*} example: @example -[0-9] +awk '/\(c[ad]+r x\)/ @{ print @}' sample @end example -@noindent -matches any digit. -Multiple ranges are allowed. E.g., the list @code{@w{[A-Za-z0-9]}} is a -common way to express the idea of ``all alphanumeric characters.'' +@item ? +This symbol is similar to @samp{*} except that the preceding expression can be +matched either once or not at all. For example, @samp{fe?d} +matches @samp{fed} and @samp{fd}, but nothing else. + +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} +@cindex interval expressions +@item @{@var{n}@} +@itemx @{@var{n},@} +@itemx @{@var{n},@var{m}@} +One or two numbers inside braces denote an @dfn{interval expression}. +If there is one number in the braces, the preceding regexp is repeated +@var{n} times. +If there are two numbers separated by a comma, the preceding regexp is +repeated @var{n} to @var{m} times. +If there is one number followed by a comma, then the preceding regexp +is repeated at least @var{n} times: + +@table @code +@item wh@{3@}y +Matches @samp{whhhy}, but not @samp{why} or @samp{whhhhy}. + +@item wh@{3,5@}y +Matches @samp{whhhy}, @samp{whhhhy}, or @samp{whhhhhy}, only. + +@item wh@{2,@}y +Matches @samp{whhy} or @samp{whhhy}, and so on. +@end table + +Interval expressions were not traditionally available in @command{awk}. +They were added as part of the POSIX standard to make @command{awk} +and @command{egrep} consistent with each other. + +However, because old programs may use @samp{@{} and @samp{@}} in regexp +constants, by default @command{gawk} does @emph{not} match interval expressions +in regexps. If either @option{--posix} or @option{--re-interval} are specified +(@pxref{Options, , Command-Line Options}), then interval expressions +are allowed in regexps. + +For new programs that use @samp{@{} and @samp{@}} in regexp constants, +it is good practice to always escape them with a backslash. Then the +regexp constants are valid and work the way you want them to, using +any version of @command{awk}.@footnote{Use two backslashes if you're +using a string constant with a regexp operator or function.} +@end table + +@cindex precedence, regexp operators +@cindex regexp operators, precedence of +In regular expressions, the @samp{*}, @samp{+}, and @samp{?} operators, +as well as the braces @samp{@{} and @samp{@}}, +have +the highest precedence, followed by concatenation, and finally by @samp{|}. +As in arithmetic, parentheses can change how operators are grouped. + +In POSIX @command{awk} and @command{gawk}, the @samp{*}, @samp{+}, and @samp{?} operators +stand for themselves when there is nothing in the regexp that precedes them. +For example, @samp{/+/} matches a literal plus sign. However, many other versions of +@command{awk} treat such a usage as a syntax error. + +If @command{gawk} is in compatibility mode +(@pxref{Options, ,Command-Line Options}), +POSIX character classes and interval expressions are not available in +regular expressions. -To include one of the characters @samp{\}, @samp{]}, @samp{-} or @samp{^} in a +@node Character Lists, GNU Regexp Operators, Regexp Operators, Regexp +@section Using Character Lists + +Within a character list, a @dfn{range expression} consists of two +characters separated by a hyphen. It matches any single character that +sorts between the two characters, using the locale's +collating sequence and character set. For example, in the default C +locale, @samp{[a-dx-z]} is equivalent to @samp{[abcdxyz]}. Many locales +sort characters in dictionary order, and in these locales, +@samp{[a-dx-z]} is typically not equivalent to @samp{[abcdxyz]}; instead it +might be equivalent to @samp{[aBbCcDdxXyYz]}, for example. To obtain +the traditional interpretation of bracket expressions, you can use the C +locale by setting the @env{LC_ALL} environment variable to the value +@samp{C}. + +To include one of the characters @samp{\}, @samp{]}, @samp{-}, or @samp{^} in a character list, put a @samp{\} in front of it. For example: @example @@ -2329,32 +3203,37 @@ character list, put a @samp{\} in front of it. For example: @end example @noindent -matches either @samp{d}, or @samp{]}. +matches either @samp{d} or @samp{]}. -@cindex @code{egrep} +@cindex @command{egrep} utility This treatment of @samp{\} in character lists -is compatible with other @code{awk} -implementations, and is also mandated by POSIX. -The regular expressions in @code{awk} are a superset +is compatible with other @command{awk} +implementations and is also mandated by POSIX. +The regular expressions in @command{awk} are a superset of the POSIX specification for Extended Regular Expressions (EREs). POSIX EREs are based on the regular expressions accepted by the -traditional @code{egrep} utility. +traditional @command{egrep} utility. -@cindex character classes -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} +@cindex character class +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} @dfn{Character classes} are a new feature introduced in the POSIX standard. A character class is a special notation for describing -lists of characters that have a specific attribute, but where the -actual characters themselves can vary from country to country and/or +lists of characters that have a specific attribute, but the +actual characters can vary from country to country and/or from character set to character set. For example, the notion of what -is an alphabetic character differs in the USA and in France. +is an alphabetic character differs between the United States and France. A character class is only valid in a regexp @emph{inside} the brackets of a character list. Character classes consist of @samp{[:}, a keyword denoting the class, and @samp{:]}. Here are the character -classes defined by the POSIX standard. +classes defined by the POSIX standard: +@c the regular table is commented out while trying out the multitable. +@c leave it here in case we need to go back, but make sure the text +@c still corresponds! + +@ignore @table @code @item [:alnum:] Alphanumeric characters. @@ -2372,366 +3251,233 @@ Control characters. Numeric characters. @item [:graph:] -Characters that are printable and are also visible. -(A space is printable, but not visible, while an @samp{a} is both.) +Characters that are printable and visible. +(A space is printable but not visible, whereas an @samp{a} is both.) @item [:lower:] -Lower-case alphabetic characters. +Lowercase alphabetic characters. @item [:print:] -Printable characters (characters that are not control characters.) +Printable characters (characters that are not control characters). @item [:punct:] -Punctuation characters (characters that are not letter, digits, +Punctuation characters (characters that are not letters, digits, control characters, or space characters). @item [:space:] Space characters (such as space, tab, and formfeed, to name a few). @item [:upper:] -Upper-case alphabetic characters. +Uppercase alphabetic characters. @item [:xdigit:] Characters that are hexadecimal digits. @end table +@end ignore + +@multitable {@code{[:xdigit:]}} {Characters that are both printable and visible. (A space is} +@item @code{[:alnum:]} @tab Alphanumeric characters. +@item @code{[:alpha:]} @tab Alphabetic characters. +@item @code{[:blank:]} @tab Space and tab characters. +@item @code{[:cntrl:]} @tab Control characters. +@item @code{[:digit:]} @tab Numeric characters. +@item @code{[:graph:]} @tab Characters that are both printable and visible. +(A space is printable but not visible, whereas an @samp{a} is both.) +@item @code{[:lower:]} @tab Lowercase alphabetic characters. +@item @code{[:print:]} @tab Printable characters (characters that are not control characters). +@item @code{[:punct:]} @tab Punctuation characters (characters that are not letters, digits, +control characters, or space characters). +@item @code{[:space:]} @tab Space characters (such as space, tab, and formfeed, to name a few). +@item @code{[:upper:]} @tab Uppercase alphabetic characters. +@item @code{[:xdigit:]} @tab Characters that are hexadecimal digits. +@end multitable -For example, before the POSIX standard, to match alphanumeric -characters, you had to write @code{/[A-Za-z0-9]/}. If your +For example, before the POSIX standard, you had to write @code{/[A-Za-z0-9]/} +to match alphanumeric characters. If your character set had other alphabetic characters in it, this would not -match them. With the POSIX character classes, you can write -@code{/[[:alnum:]]/}, and this will match @emph{all} the alphabetic +match them, and if your character set collated differently from +ASCII, this might not even match the ASCII alphanumeric characters. +With the POSIX character classes, you can write +@code{/[[:alnum:]]/} to match the alphabetic and numeric characters in your character set. @cindex collating elements Two additional special sequences can appear in character lists. These apply to non-ASCII character sets, which can have single symbols (called @dfn{collating elements}) that are represented with more than one -character, as well as several characters that are equivalent for -@dfn{collating}, or sorting, purposes. (E.g., in French, a plain ``e'' +character. They can also have several characters that are equivalent for +@dfn{collating}, or sorting, purposes. (For example, in French, a plain ``e'' and a grave-accented ``@`e'' are equivalent.) @table @asis @cindex collating symbols @item Collating Symbols -A @dfn{collating symbol} is a multi-character collating element enclosed in +A @dfn{collating symbol} is a multicharacter collating element enclosed between @samp{[.} and @samp{.]}. For example, if @samp{ch} is a collating element, -then @code{[[.ch.]]} is a regexp that matches this collating element, while +then @code{[[.ch.]]} is a regexp that matches this collating element, whereas @code{[ch]} is a regexp that matches either @samp{c} or @samp{h}. @cindex equivalence classes @item Equivalence Classes An @dfn{equivalence class} is a locale-specific name for a list of -characters that are equivalent. The name is enclosed in +characters that are equal. The name is enclosed between @samp{[=} and @samp{=]}. For example, the name @samp{e} might be used to represent all of -``e,'' ``@`e,'' and ``@'e.'' In this case, @code{[[=e]]} is a regexp -that matches any of @samp{e}, @samp{@'e}, or @samp{@`e}. +``e,'' ``@`e,'' and ``@'e.'' In this case, @code{[[=e=]]} is a regexp +that matches any of @samp{e}, @samp{@'e}, or @samp{@`e}. @end table These features are very valuable in non-English speaking locales. -@strong{Caution:} The library functions that @code{gawk} uses for regular +@strong{Caution:} The library functions that @command{gawk} uses for regular expression matching currently only recognize POSIX character classes; they do not recognize collating symbols or equivalence classes. @c maybe one day ... -@cindex complemented character list -@cindex character list, complemented -@item [^ @dots{}] -This is a @dfn{complemented character list}. The first character after -the @samp{[} @emph{must} be a @samp{^}. It matches any characters -@emph{except} those in the square brackets. For example: +@node GNU Regexp Operators, Case-sensitivity, Character Lists, Regexp +@section @command{gawk}-Specific Regexp Operators -@example -[^0-9] -@end example +@c This section adapted (long ago) from the regex-0.12 manual -@noindent -matches any character that is not a digit. +@cindex regexp operators, GNU specific +@cindex word, regexp definition of +GNU software that deals with regular expressions provides a number of +additional regexp operators. These operators are described in this +@value{SECTION} and are specific to @command{gawk}; +they are not available in other @command{awk} implementations. +Most of the additional operators deal with word matching. +For our purposes, a @dfn{word} is a sequence of one or more letters, digits, +or underscores (@samp{_}): -@item | -This is the @dfn{alternation operator}, and it is used to specify -alternatives. For example: +@table @code +@cindex @code{\w} regexp operator +@item \w +Matches any word-constituent character---that is, it matches any +letter, digit, or underscore. Think of it as short-hand for +@w{@code{[[:alnum:]_]}}. -@example -^P|[0-9] -@end example +@cindex @code{\W} regexp operator +@item \W +Matches any character that is not word-constituent. +Think of it as short-hand for +@w{@code{[^[:alnum:]_]}}. -@noindent -matches any string that matches either @samp{^P} or @samp{[0-9]}. This -means it matches any string that starts with @samp{P} or contains a digit. +@cindex @code{\<} regexp operator +@item \< +Matches the empty string at the beginning of a word. +For example, @code{/\} regexp operator +@item \> +Matches the empty string at the end of a word. +For example, @code{/stow\>/} matches @samp{stow} but not @samp{stowaway}. -@item (@dots{}) -Parentheses are used for grouping in regular expressions as in -arithmetic. They can be used to concatenate regular expressions -containing the alternation operator, @samp{|}. For example, -@samp{@@(samp|code)\@{[^@}]+\@}} matches both @samp{@@code@{foo@}} and -@samp{@@samp@{bar@}}. (These are Texinfo formatting control sequences.) +@cindex @code{\y} regexp operator +@cindex word boundaries, matching +@item \y +Matches the empty string at either the beginning or the +end of a word (i.e., the word boundar@strong{y}). For example, @samp{\yballs?\y} +matches either @samp{ball} or @samp{balls}, as a separate word. -@item * -This symbol means that the preceding regular expression is to be -repeated as many times as necessary to find a match. For example: +@cindex @code{\B} regexp operator +@item \B +Matches the empty string that occurs between two +word-constituent characters. For example, +@code{/\Brat\B/} matches @samp{crate} but it does not match @samp{dirty rat}. +@samp{\B} is essentially the opposite of @samp{\y}. +@end table -@example -ph* -@end example +@cindex buffer matching operators +There are two other operators that work on buffers. In Emacs, a +@dfn{buffer} is, naturally, an Emacs buffer. For other programs, +@command{gawk}'s regexp library routines consider the entire +string to match as the buffer. -@noindent -applies the @samp{*} symbol to the preceding @samp{h} and looks for matches -of one @samp{p} followed by any number of @samp{h}s. This will also match -just @samp{p} if no @samp{h}s are present. +@table @code +@item \` +@cindex @code{\`} regexp operator +Matches the empty string at the +beginning of a buffer (string). -The @samp{*} repeats the @emph{smallest} possible preceding expression. -(Use parentheses if you wish to repeat a larger expression.) It finds -as many repetitions as possible. For example: +@cindex @code{\'} regexp operator +@item \' +Matches the empty string at the +end of a buffer (string). +@end table -@example -awk '/\(c[ad][ad]*r x\)/ @{ print @}' sample -@end example - -@noindent -prints every record in @file{sample} containing a string of the form -@samp{(car x)}, @samp{(cdr x)}, @samp{(cadr x)}, and so on. -Notice the escaping of the parentheses by preceding them -with backslashes. - -@item + -This symbol is similar to @samp{*}, but the preceding expression must be -matched at least once. This means that: - -@example -wh+y -@end example - -@noindent -would match @samp{why} and @samp{whhy} but not @samp{wy}, whereas -@samp{wh*y} would match all three of these strings. This is a simpler -way of writing the last @samp{*} example: - -@example -awk '/\(c[ad]+r x\)/ @{ print @}' sample -@end example - -@item ? -This symbol is similar to @samp{*}, but the preceding expression can be -matched either once or not at all. For example: - -@example -fe?d -@end example - -@noindent -will match @samp{fed} and @samp{fd}, but nothing else. - -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} -@cindex interval expressions -@item @{@var{n}@} -@itemx @{@var{n},@} -@itemx @{@var{n},@var{m}@} -One or two numbers inside braces denote an @dfn{interval expression}. -If there is one number in the braces, the preceding regexp is repeated -@var{n} times. -If there are two numbers separated by a comma, the preceding regexp is -repeated @var{n} to @var{m} times. -If there is one number followed by a comma, then the preceding regexp -is repeated at least @var{n} times. - -@table @code -@item wh@{3@}y -matches @samp{whhhy} but not @samp{why} or @samp{whhhhy}. - -@item wh@{3,5@}y -matches @samp{whhhy} or @samp{whhhhy} or @samp{whhhhhy}, only. - -@item wh@{2,@}y -matches @samp{whhy} or @samp{whhhy}, and so on. -@end table - -Interval expressions were not traditionally available in @code{awk}. -As part of the POSIX standard they were added, to make @code{awk} -and @code{egrep} consistent with each other. - -However, since old programs may use @samp{@{} and @samp{@}} in regexp -constants, by default @code{gawk} does @emph{not} match interval expressions -in regexps. If either @samp{--posix} or @samp{--re-interval} are specified -(@pxref{Options, , Command Line Options}), then interval expressions -are allowed in regexps. -@end table - -@cindex precedence, regexp operators -@cindex regexp operators, precedence of -In regular expressions, the @samp{*}, @samp{+}, and @samp{?} operators, -as well as the braces @samp{@{} and @samp{@}}, -have -the highest precedence, followed by concatenation, and finally by @samp{|}. -As in arithmetic, parentheses can change how operators are grouped. - -If @code{gawk} is in compatibility mode -(@pxref{Options, ,Command Line Options}), -character classes and interval expressions are not available in -regular expressions. - -The next -@ifinfo -node -@end ifinfo -@iftex -section -@end iftex -discusses the GNU-specific regexp operators, and provides -more detail concerning how command line options affect the way @code{gawk} -interprets the characters in regular expressions. - -@node GNU Regexp Operators, Case-sensitivity, Regexp Operators, Regexp -@section Additional Regexp Operators Only in @code{gawk} - -@c This section adapted from the regex-0.12 manual - -@cindex regexp operators, GNU specific -GNU software that deals with regular expressions provides a number of -additional regexp operators. These operators are described in this -section, and are specific to @code{gawk}; they are not available in other -@code{awk} implementations. - -@cindex word, regexp definition of -Most of the additional operators are for dealing with word matching. -For our purposes, a @dfn{word} is a sequence of one or more letters, digits, -or underscores (@samp{_}). - -@table @code -@cindex @code{\w} regexp operator -@item \w -This operator matches any word-constituent character, i.e.@: any -letter, digit, or underscore. Think of it as a short-hand for -@c @w{@code{[A-Za-z0-9_]}} or -@w{@code{[[:alnum:]_]}}. - -@cindex @code{\W} regexp operator -@item \W -This operator matches any character that is not word-constituent. -Think of it as a short-hand for -@c @w{@code{[^A-Za-z0-9_]}} or -@w{@code{[^[:alnum:]_]}}. - -@cindex @code{\<} regexp operator -@item \< -This operator matches the empty string at the beginning of a word. -For example, @code{/\} regexp operator -@item \> -This operator matches the empty string at the end of a word. -For example, @code{/stow\>/} matches @samp{stow}, but not @samp{stowaway}. - -@cindex @code{\y} regexp operator -@cindex word boundaries, matching -@item \y -This operator matches the empty string at either the beginning or the -end of a word (the word boundar@strong{y}). For example, @samp{\yballs?\y} -matches either @samp{ball} or @samp{balls} as a separate word. - -@cindex @code{\B} regexp operator -@item \B -This operator matches the empty string within a word. In other words, -@samp{\B} matches the empty string that occurs between two -word-constituent characters. For example, -@code{/\Brat\B/} matches @samp{crate}, but it does not match @samp{dirty rat}. -@samp{\B} is essentially the opposite of @samp{\y}. -@end table - -There are two other operators that work on buffers. In Emacs, a -@dfn{buffer} is, naturally, an Emacs buffer. For other programs, the -regexp library routines that @code{gawk} uses consider the entire -string to be matched as the buffer. - -For @code{awk}, since @samp{^} and @samp{$} always work in terms -of the beginning and end of strings, these operators don't add any -new capabilities. They are provided for compatibility with other GNU -software. - -@cindex buffer matching operators -@table @code -@cindex @code{\`} regexp operator -@item \` -This operator matches the empty string at the -beginning of the buffer. - -@cindex @code{\'} regexp operator -@item \' -This operator matches the empty string at the -end of the buffer. -@end table - -In other GNU software, the word boundary operator is @samp{\b}. However, -that conflicts with the @code{awk} language's definition of @samp{\b} -as backspace, so @code{gawk} uses a different letter. +Because @samp{^} and @samp{$} always work in terms of the beginning +and end of strings, these operators don't add any new capabilities +for @command{awk}. They are provided for compatibility with other +GNU software. +In other GNU software, the word-boundary operator is @samp{\b}. However, +that conflicts with the @command{awk} language's definition of @samp{\b} +as backspace, so @command{gawk} uses a different letter. An alternative method would have been to require two backslashes in the -GNU operators, but this was deemed to be too confusing, and the current +GNU operators, but this was deemed too confusing. The current method of using @samp{\y} for the GNU @samp{\b} appears to be the lesser of two evils. @c NOTE!!! Keep this in sync with the same table in the summary appendix! -@cindex regexp, effect of command line options -The various command line options -(@pxref{Options, ,Command Line Options}) -control how @code{gawk} interprets characters in regexps. +@c +@c Should really do this with file inclusion. +@cindex regexp, effect of command-line options +The various command-line options +(@pxref{Options, ,Command-Line Options}) +control how @command{gawk} interprets characters in regexps: @table @asis @item No options -In the default case, @code{gawk} provides all the facilities of -POSIX regexps and the GNU regexp operators described -@iftex -above. -@end iftex -@ifinfo +In the default case, @command{gawk} provides all the facilities of +POSIX regexps and the +@ifnotinfo +previously described +GNU regexp operators. +@end ifnotinfo +@ifnottex +GNU regexp operators described in @ref{Regexp Operators, ,Regular Expression Operators}. -@end ifinfo +@end ifnottex However, interval expressions are not supported. @item @code{--posix} -Only POSIX regexps are supported, the GNU operators are not special +Only POSIX regexps are supported; the GNU operators are not special (e.g., @samp{\w} matches a literal @samp{w}). Interval expressions are allowed. @item @code{--traditional} -Traditional Unix @code{awk} regexps are matched. The GNU operators -are not special, interval expressions are not available, and neither +Traditional Unix @command{awk} regexps are matched. The GNU operators +are not special, interval expressions are not available, nor are the POSIX character classes (@code{[[:alnum:]]} and so on). Characters described by octal and hexadecimal escape sequences are treated literally, even if they represent regexp metacharacters. @item @code{--re-interval} -Allow interval expressions in regexps, even if @samp{--traditional} +Allow interval expressions in regexps, even if @option{--traditional} has been provided. @end table @node Case-sensitivity, Leftmost Longest, GNU Regexp Operators, Regexp -@section Case-sensitivity in Matching +@section Case Sensitivity in Matching @cindex case sensitivity @cindex ignoring case Case is normally significant in regular expressions, both when matching -ordinary characters (i.e.@: not metacharacters), and inside character -sets. Thus a @samp{w} in a regular expression matches only a lower-case -@samp{w} and not an upper-case @samp{W}. +ordinary characters (i.e., not metacharacters) and inside character +sets. Thus, a @samp{w} in a regular expression matches only a lowercase +@samp{w} and not an uppercase @samp{W}. The simplest way to do a case-independent match is to use a character -list: @samp{[Ww]}. However, this can be cumbersome if you need to use it -often; and it can make the regular expressions harder to -read. There are two alternatives that you might prefer. +list---for example, @samp{[Ww]}. However, this can be cumbersome if +you need to use it often and it can make the regular expressions harder +to read. There are two alternatives that you might prefer. -One way to do a case-insensitive match at a particular point in the +One way to perform a case-insensitive match at a particular point in the program is to convert the data to a single case, using the @code{tolower} or @code{toupper} built-in string functions (which we haven't discussed yet; -@pxref{String Functions, ,Built-in Functions for String Manipulation}). +@pxref{String Functions, ,String Manipulation Functions}). For example: @example @@ -2739,75 +3485,66 @@ tolower($1) ~ /foo/ @{ @dots{} @} @end example @noindent -converts the first field to lower-case before matching against it. -This will work in any POSIX-compliant implementation of @code{awk}. +converts the first field to lowercase before matching against it. +This works in any POSIX-compliant @command{awk}. -@cindex differences between @code{gawk} and @code{awk} +@cindex differences between @command{gawk} and @command{awk} @cindex @code{~} operator @cindex @code{!~} operator -@vindex IGNORECASE -Another method, specific to @code{gawk}, is to set the variable -@code{IGNORECASE} to a non-zero value (@pxref{Built-in Variables}). +@cindex @code{IGNORECASE} variable +Another method, specific to @command{gawk}, is to set the variable +@code{IGNORECASE} to a nonzero value (@pxref{Built-in Variables}). When @code{IGNORECASE} is not zero, @emph{all} regexp and string operations ignore case. Changing the value of -@code{IGNORECASE} dynamically controls the case sensitivity of your +@code{IGNORECASE} dynamically controls the case sensitivity of the program as it runs. Case is significant by default because -@code{IGNORECASE} (like most variables) is initialized to zero. +@code{IGNORECASE} (like most variables) is initialized to zero: @example -@group x = "aB" if (x ~ /ab/) @dots{} # this test will fail -@end group -@group IGNORECASE = 1 if (x ~ /ab/) @dots{} # now it will succeed -@end group @end example In general, you cannot use @code{IGNORECASE} to make certain rules -case-insensitive and other rules case-sensitive, because there is no way -to set @code{IGNORECASE} just for the pattern of a particular rule. -@ignore -This isn't quite true. Consider: - - IGNORECASE=1 && /foObAr/ { .... } - IGNORECASE=0 || /foobar/ { .... } - -But that's pretty bad style and I don't want to get into it at this -late date. -@end ignore -To do this, you must use character lists or @code{tolower}. However, one -thing you can do only with @code{IGNORECASE} is turn case-sensitivity on -or off dynamically for all the rules at once. - -@code{IGNORECASE} can be set on the command line, or in a @code{BEGIN} rule -(@pxref{Other Arguments, ,Other Command Line Arguments}; also +case-insensitive and other rules case-sensitive, because there is no +straightforward way +to set @code{IGNORECASE} just for the pattern of +a particular rule.@footnote{Experienced C and C++ programmers will note +that it is possible, using something like +@samp{IGNORECASE = 1 && /foObAr/ @{ @dots{} @}} +and +@samp{IGNORECASE = 0 || /foobar/ @{ @dots{} @}}. +However, this is somewhat obscure and we don't recommend it.} +To do this, use either character lists or @code{tolower}. However, one +thing you can do with @code{IGNORECASE} only is dynamically turn +case-sensitivity on or off for all the rules at once. + +@code{IGNORECASE} can be set on the command line or in a @code{BEGIN} rule +(@pxref{Other Arguments, ,Other Command-Line Arguments}; also @pxref{Using BEGIN/END, ,Startup and Cleanup Actions}). Setting @code{IGNORECASE} from the command line is a way to make a program case-insensitive without having to edit it. -Prior to version 3.0 of @code{gawk}, the value of @code{IGNORECASE} -only affected regexp operations. It did not affect string comparison +Prior to @command{gawk} 3.0, the value of @code{IGNORECASE} +affected regexp operations only. It did not affect string comparison with @samp{==}, @samp{!=}, and so on. -Beginning with version 3.0, both regexp and string comparison -operations are affected by @code{IGNORECASE}. +Beginning with @value{PVERSION} 3.0, both regexp and string comparison +operations are also affected by @code{IGNORECASE}. @cindex ISO 8859-1 @cindex ISO Latin-1 -Beginning with version 3.0 of @code{gawk}, the equivalences between upper-case -and lower-case characters are based on the ISO-8859-1 (ISO Latin-1) +Beginning with @command{gawk} 3.0, +the equivalences between upper- +and lowercase characters are based on the ISO-8859-1 (ISO Latin-1) character set. This character set is a superset of the traditional 128 ASCII characters, that also provides a number of characters suitable for use with European languages. -@ignore -A pure ASCII character set can be used instead if @code{gawk} is compiled -with @samp{-DUSE_PURE_ASCII}. -@end ignore -The value of @code{IGNORECASE} has no effect if @code{gawk} is in -compatibility mode (@pxref{Options, ,Command Line Options}). +The value of @code{IGNORECASE} has no effect if @command{gawk} is in +compatibility mode (@pxref{Options, ,Command-Line Options}). Case is always significant in compatibility mode. @node Leftmost Longest, Computed Regexps, Case-sensitivity, Regexp @@ -2815,26 +3552,23 @@ Case is always significant in compatibility mode. @cindex leftmost longest match @cindex matching, leftmost longest -Consider the following example: +Consider the following: @example echo aaaabcd | awk '@{ sub(/a+/, ""); print @}' @end example -This example uses the @code{sub} function (which we haven't discussed yet, -@pxref{String Functions, ,Built-in Functions for String Manipulation}) +This example uses the @code{sub} function (which we haven't discussed yet; +@pxref{String Functions, ,String Manipulation Functions}) to make a change to the input record. Here, the regexp @code{/a+/} indicates ``one or more @samp{a} characters,'' and the replacement text is @samp{}. -The input contains four @samp{a} characters. What will the output be? -In other words, how many is ``one or more''---will @code{awk} match two, -three, or all four @samp{a} characters? - -The answer is, @code{awk} (and POSIX) regular expressions always match +The input contains four @samp{a} characters. +@command{awk} (and POSIX) regular expressions always match the leftmost, @emph{longest} sequence of input characters that can -match. Thus, in this example, all four @samp{a} characters are -replaced with @samp{}. +match. Thus, all four @samp{a} characters are +replaced with @samp{} in this example: @example $ echo aaaabcd | awk '@{ sub(/a+/, ""); print @}' @@ -2845,12 +3579,12 @@ For simple match/no-match tests, this is not so important. But when doing text matching and substitutions with the @code{match}, @code{sub}, @code{gsub}, and @code{gensub} functions, it is very important. @ifinfo -@xref{String Functions, ,Built-in Functions for String Manipulation}, +@xref{String Functions, ,String Manipulation Functions}, for more information on these functions. @end ifinfo Understanding this principle is also important for regexp-based record -and field splitting (@pxref{Records, ,How Input is Split into Records}, -and also @pxref{Field Separators, ,Specifying How Fields are Separated}). +and field splitting (@pxref{Records, ,How Input Is Split into Records}, +and also @pxref{Field Separators, ,Specifying How Fields Are Separated}). @node Computed Regexps, , Leftmost Longest, Regexp @section Using Dynamic Regexps @@ -2861,37 +3595,33 @@ and also @pxref{Field Separators, ,Specifying How Fields are Separated}). @cindex regexp, dynamic @cindex @code{~} operator @cindex @code{!~} operator -The right hand side of a @samp{~} or @samp{!~} operator need not be a -regexp constant (i.e.@: a string of characters between slashes). It may -be any expression. The expression is evaluated, and converted if -necessary to a string; the contents of the string are used as the +The righthand side of a @samp{~} or @samp{!~} operator need not be a +regexp constant (i.e., a string of characters between slashes). It may +be any expression. The expression is evaluated and converted to a string +if necessary; the contents of the string are used as the regexp. A regexp that is computed in this way is called a @dfn{dynamic -regexp}. For example: +regexp}: @example -BEGIN @{ identifier_regexp = "[A-Za-z_][A-Za-z_0-9]*" @} -$0 ~ identifier_regexp @{ print @} +BEGIN @{ digits_regexp = "[[:digit:]]+" @} +$0 ~ digits_regexp @{ print @} @end example @noindent -sets @code{identifier_regexp} to a regexp that describes @code{awk} -variable names, and tests if the input record matches this regexp. - -@ignore -Do we want to use "^[A-Za-z_][A-Za-z_0-9]*$" to restrict the entire -record to just identifiers? Doing that also would disrupt the flow of -the text. -@end ignore +This sets @code{digits_regexp} to a regexp that describes one or more digits, +and tests whether the input record matches this regexp. +@c @strong{Caution:} +When using the @samp{~} and @samp{!~} @strong{Caution:} When using the @samp{~} and @samp{!~} operators, there is a difference between a regexp constant -enclosed in slashes, and a string constant enclosed in double quotes. +enclosed in slashes and a string constant enclosed in double quotes. If you are going to use a string constant, you have to understand that -the string is in essence scanned @emph{twice}; the first time when -@code{awk} reads your program, and the second time when it goes to -match the string on the left-hand side of the operator with the pattern +the string is, in essence, scanned @emph{twice}: the first time when +@command{awk} reads your program, and the second time when it goes to +match the string on the lefthand side of the operator with the pattern on the right. This is true of any string valued expression (such as -@code{identifier_regexp} above), not just string constants. +@code{digits_regexp} shown previously), not just string constants. @cindex regexp constants, difference between slashes and quotes What difference does it make if the string is @@ -2901,8 +3631,8 @@ string, you have to type two backslashes. For example, @code{/\*/} is a regexp constant for a literal @samp{*}. Only one backslash is needed. To do the same thing with a string, -you would have to type @code{"\\*"}. The first backslash escapes the -second one, so that the string actually contains the +you have to type @code{"\\*"}. The first backslash escapes the +second one so that the string actually contains the two characters @samp{\} and @samp{*}. @cindex common mistakes @@ -2910,26 +3640,58 @@ two characters @samp{\} and @samp{*}. @cindex errors, common Given that you can use both regexp and string constants to describe regular expressions, which should you use? The answer is ``regexp -constants,'' for several reasons. +constants,'' for several reasons: -@enumerate 1 +@itemize @bullet @item -String constants are more complicated to write, and +String constants are more complicated to write and more difficult to read. Using regexp constants makes your programs less error-prone. Not understanding the difference between the two kinds of constants is a common source of errors. @item -It is also more efficient to use regexp constants: @code{awk} can note -that you have supplied a regexp and store it internally in a form that +It is more efficient to use regexp constants. @command{awk} can note +that you have supplied a regexp, and store it internally in a form that makes pattern matching more efficient. When using a string constant, -@code{awk} must first convert the string into this internal form, and +@command{awk} must first convert the string into this internal form and then perform the pattern matching. @item -Using regexp constants is better style; it shows clearly that you +Using regexp constants is better form; it shows clearly that you intend a regexp match. -@end enumerate +@end itemize + +@c fakenode --- for prepinfo +@subheading Advanced Notes: Using @code{\n} in Character Lists of Dynamic Regexps +@cindex advanced notes +@cindex dynamic regular expressions with embedded newlines +@cindex regexp, dynamic, with embedded newlines +@cindex newlines, embedded in dynamic regexps +@cindex embedded newlines, in dynamic regexps + +Some commercial versions of @command{awk} do not allow the newline +character to be used inside a character list for a dynamic regexp: + +@example +$ awk '$0 ~ "[ \t\n]"' +@error{} awk: newline in character class [ +@error{} ]... +@error{} source line number 1 +@error{} context is +@error{} >>> <<< +@end example + +But a newline in a regexp constant works with no problem: + +@example +$ awk '$0 ~ /[ \t\n]/' +here is a sample line +@print{} here is a sample line +@kbd{Ctrl-d} +@end example + +@command{gawk} does not have this problem, and it isn't likely to +occur often in practice, but it's worth noting for future reference. @node Reading Files, Printing, Regexp, Top @chapter Reading Input Files @@ -2937,25 +3699,26 @@ intend a regexp match. @cindex reading files @cindex input @cindex standard input -@vindex FILENAME -In the typical @code{awk} program, all input is read either from the -standard input (by default the keyboard, but often a pipe from another -command) or from files whose names you specify on the @code{awk} command -line. If you specify input files, @code{awk} reads them in order, reading -all the data from one before going on to the next. The name of the current -input file can be found in the built-in variable @code{FILENAME} +@cindex @code{FILENAME} variable +In the typical @command{awk} program, all input is read either from the +standard input (by default, this is the keyboard but often it is a pipe from another +command), or from files whose names you specify on the @command{awk} +command line. If you specify input files, @command{awk} reads them +in order, processing all the data from one before going on to the next. +The name of the current input file can be found in the built-in variable +@code{FILENAME} (@pxref{Built-in Variables}). -The input is read in units called @dfn{records}, and processed by the +The input is read in units called @dfn{records}, and is processed by the rules of your program one record at a time. By default, each record is one line. Each record is automatically split into chunks called @dfn{fields}. This makes it more convenient for programs to work on the parts of a record. -On rare occasions you will need to use the @code{getline} command. +On rare occasions, you may need to use the @code{getline} command. The @code{getline} command is valuable, both because it can do explicit input from any number of files, and because the files -used with it do not have to be named on the @code{awk} command line +used with it do not have to be named on the @command{awk} command line (@pxref{Getline, ,Explicit Input with @code{getline}}). @menu @@ -2971,49 +3734,62 @@ used with it do not have to be named on the @code{awk} command line @end menu @node Records, Fields, Reading Files, Reading Files -@section How Input is Split into Records +@section How Input Is Split into Records + +@cindex number of records, @code{NR}, @code{FNR} +@cindex @code{NR} variable +@cindex @code{FNR} variable +The @command{awk} utility divides the input for your @command{awk} +program into records and fields. +@command{awk} keeps track of the number of records that have +been read +so far +from the current input file. This value is stored in a +built-in variable called @code{FNR}. It is reset to zero when a new +file is started. Another built-in variable, @code{NR}, is the total +number of input records read so far from all @value{DF}s. It starts at zero, +but is never automatically reset to zero. @cindex record separator, @code{RS} @cindex changing the record separator @cindex record, definition of -@vindex RS -The @code{awk} utility divides the input for your @code{awk} -program into records and fields. +@cindex @code{RS} variable Records are separated by a character called the @dfn{record separator}. By default, the record separator is the newline character. This is why records are, by default, single lines. -You can use a different character for the record separator by +A different character can be used for the record separator by assigning the character to the built-in variable @code{RS}. -You can change the value of @code{RS} in the @code{awk} program, -like any other variable, with the -assignment operator, @samp{=} (@pxref{Assignment Ops, ,Assignment Expressions}). +Like any other variable, +the value of @code{RS} can be changed in the @command{awk} program +with the assignment operator, @samp{=} +(@pxref{Assignment Ops, ,Assignment Expressions}). The new record-separator character should be enclosed in quotation marks, -which indicate -a string constant. Often the right time to do this is at the beginning -of execution, before any input has been processed, so that the very -first record will be read with the proper separator. To do this, use -the special @code{BEGIN} pattern -(@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}). For -example: +which indicate a string constant. Often the right time to do this is +at the beginning of execution, before any input is processed, +so that the very first record is read with the proper separator. +To do this, use the special @code{BEGIN} pattern +(@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}). +For example: @example -awk 'BEGIN @{ RS = "/" @} ; @{ print $0 @}' BBS-list +awk 'BEGIN @{ RS = "/" @} + @{ print $0 @}' BBS-list @end example @noindent changes the value of @code{RS} to @code{"/"}, before reading any input. This is a string whose first character is a slash; as a result, records are separated by slashes. Then the input file is read, and the second -rule in the @code{awk} program (the action with no pattern) prints each -record. Since each @code{print} statement adds a newline at the end of -its output, the effect of this @code{awk} program is to copy the input +rule in the @command{awk} program (the action with no pattern) prints each +record. Because each @code{print} statement adds a newline at the end of +its output, the effect of this @command{awk} program is to copy the input with each slash changed to a newline. Here are the results of running the program on @file{BBS-list}: @example -@group -$ awk 'BEGIN @{ RS = "/" @} ; @{ print $0 @}' BBS-list +$ awk 'BEGIN @{ RS = "/" @} +> @{ print $0 @}' BBS-list @print{} aardvark 555-5553 1200 @print{} 300 B @print{} alpo-net 555-3412 2400 @@ -3040,13 +3816,12 @@ $ awk 'BEGIN @{ RS = "/" @} ; @{ print $0 @}' BBS-list @print{} sabafoo 555-2127 1200 @print{} 300 C @print{} -@end group @end example @noindent Note that the entry for the @samp{camelot} BBS is not split. -In the original data file -(@pxref{Sample Data Files, , Data Files for the Examples}), +In the original @value{DF} +(@pxref{Sample Data Files, ,@value{DDF}s for the Examples}), the line looks like this: @example @@ -3054,11 +3829,16 @@ camelot 555-0542 300 C @end example @noindent -It only has one baud rate; there are no slashes in the record. +It has one baud rate only, so there are no slashes in the record, +unlike the others which have two or more baud rates. +In fact, this record is treated as part of the record +for the @samp{core} BBS; the newline separating them in the output +is the original newline in the @value{DF}, not the one added by +@command{awk} when it printed the record! Another way to change the record separator is on the command line, using the variable-assignment feature -(@pxref{Other Arguments, ,Other Command Line Arguments}). +(@pxref{Other Arguments, ,Other Command-Line Arguments}): @example awk '@{ print $0 @}' RS="/" BBS-list @@ -3069,44 +3849,43 @@ This sets @code{RS} to @samp{/} before processing @file{BBS-list}. Using an unusual character such as @samp{/} for the record separator produces correct behavior in the vast majority of cases. However, -the following (extreme) pipeline prints a surprising @samp{1}. There -is one field, consisting of a newline. The value of the built-in -variable @code{NF} is the number of fields in the current record. +the following (extreme) pipeline prints a surprising @samp{1}: @example -@group $ echo | awk 'BEGIN @{ RS = "a" @} ; @{ print NF @}' @print{} 1 -@end group @end example +There is one field, consisting of a newline. The value of the built-in +variable @code{NF} is the number of fields in the current record. + @cindex dark corner -@noindent Reaching the end of an input file terminates the current input record, -even if the last character in the file is not the character in @code{RS} -(d.c.). +even if the last character in the file is not the character in @code{RS}. +@value{DARKCORNER} @cindex empty string -The empty string, @code{""} (a string of no characters), has a special meaning -as the value of @code{RS}: it means that records are separated -by one or more blank lines, and nothing else. +The empty string @code{""} (a string without any characters) +has a special meaning +as the value of @code{RS}. It means that records are separated +by one or more blank lines and nothing else. @xref{Multiple Line, ,Multiple-Line Records}, for more details. -If you change the value of @code{RS} in the middle of an @code{awk} run, +If you change the value of @code{RS} in the middle of an @command{awk} run, the new value is used to delimit subsequent records, but the record -currently being processed (and records already processed) are not +currently being processed, as well as records already processed, are not affected. -@vindex RT +@cindex @code{RT} variable @cindex record terminator, @code{RT} @cindex terminator, record -@cindex differences between @code{gawk} and @code{awk} -After the end of the record has been determined, @code{gawk} +@cindex differences between @command{gawk} and @command{awk} +@cindex regular expressions as record separators +After the end of the record has been determined, @command{gawk} sets the variable @code{RT} to the text in the input that matched @code{RS}. - -@cindex regular expressions as record separators -The value of @code{RS} is in fact not limited to a one-character +When using @command{gawk}, +the value of @code{RS} is not limited to a one-character string. It can be any regular expression (@pxref{Regexp, ,Regular Expressions}). In general, each record @@ -3116,18 +3895,17 @@ actually at work in the usual case, where @code{RS} contains just a newline: a record ends at the beginning of the next matching string (the next newline in the input) and the following record starts just after the end of this string (at the first character of the following line). -The newline, since it matches @code{RS}, is not part of either record. +The newline, because it matches @code{RS}, is not part of either record. -When @code{RS} is a single character, @code{RT} will -contain the same single character. However, when @code{RS} is a -regular expression, then @code{RT} becomes more useful; it contains +When @code{RS} is a single character, @code{RT} +contains the same single character. However, when @code{RS} is a +regular expression, @code{RT} contains the actual input text that matched the regular expression. The following example illustrates both of these features. It sets @code{RS} equal to a regular expression that -matches either a newline, or a series of one or more upper-case letters -with optional leading and/or trailing white space -(@pxref{Regexp, , Regular Expressions}). +matches either a newline or a series of one or more uppercase letters +with optional leading and/or trailing whitespace: @example $ echo record 1 AAAA record 2 BBBB record 3 | @@ -3141,29 +3919,55 @@ $ echo record 1 AAAA record 2 BBBB record 3 | @noindent The final line of output has an extra blank line. This is because the -value of @code{RT} is a newline, and then the @code{print} statement +value of @code{RT} is a newline, and the @code{print} statement supplies its own terminating newline. - @xref{Simple Sed, ,A Simple Stream Editor}, for a more useful example of @code{RS} as a regexp and @code{RT}. -@cindex differences between @code{gawk} and @code{awk} +@cindex differences between @command{gawk} and @command{awk} The use of @code{RS} as a regular expression and the @code{RT} -variable are @code{gawk} extensions; they are not available in +variable are @command{gawk} extensions; they are not available in compatibility mode -(@pxref{Options, ,Command Line Options}). +(@pxref{Options, ,Command-Line Options}). In compatibility mode, only the first character of the value of @code{RS} is used to determine the end of the record. -@cindex number of records, @code{NR}, @code{FNR} -@vindex NR -@vindex FNR -The @code{awk} utility keeps track of the number of records that have -been read so far from the current input file. This value is stored in a -built-in variable called @code{FNR}. It is reset to zero when a new -file is started. Another built-in variable, @code{NR}, is the total -number of input records read so far from all data files. It starts at zero -but is never automatically reset to zero. +@c fakenode --- for prepinfo +@subheading Advanced Notes: @code{RS = "\0"} Is Not Portable +@cindex advanced notes +@cindex portability issues + +There are times when you might want to treat an entire @value{DF} as a +single record. The only way to make this happen is to give @code{RS} +a value that you know doesn't occur in the input file. This is hard +to do in a general way, such that a program always works for arbitrary +input files. +@c can you say `understatement' boys and girls? + +You might think that for text files, the @sc{nul} character, which +consists of a character with all bits equal to zero, is a good +value to use for @code{RS} in this case: + +@example +BEGIN @{ RS = "\0" @} # whole file becomes one record? +@end example + +@cindex differences between @command{gawk} and @command{awk} +@command{gawk} in fact accepts this, and uses the @sc{nul} +character for the record separator. +However, this usage is @emph{not} portable +to other @command{awk} implementations. + +@cindex dark corner +All other @command{awk} implementations@footnote{At least that we know +about.} store strings internally as C-style strings. C strings use the +@sc{nul} character as the string terminator. In effect, this means that +@samp{RS = "\0"} is the same as @samp{RS = ""}. +@value{DARKCORNER} + +The best way to treat a whole file as a single record is to +simply read the file in, one record at a time, concatenating each +record onto the end of the previous ones. @node Fields, Non-Constant Fields, Records, Reading Files @section Examining Fields @@ -3171,72 +3975,65 @@ but is never automatically reset to zero. @cindex examining fields @cindex fields @cindex accessing fields -When @code{awk} reads an input record, the record is +When @command{awk} reads an input record, the record is automatically separated or @dfn{parsed} by the interpreter into chunks -called @dfn{fields}. By default, fields are separated by whitespace, +called @dfn{fields}. By default, fields are separated by @dfn{whitespace}, like words in a line. -Whitespace in @code{awk} means any string of one or more spaces, -tabs or newlines;@footnote{In POSIX @code{awk}, newlines are not -considered whitespace for separating fields.} other characters such as -formfeed, and so on, that are -considered whitespace by other languages are @emph{not} considered -whitespace by @code{awk}. +Whitespace in @command{awk} means any string of one or more spaces, +tabs, or newlines;@footnote{In POSIX @command{awk}, newlines are not +considered whitespace for separating fields.} other characters, such as +formfeed, vertical tab, etc.@: that are +considered whitespace by other languages, are @emph{not} considered +whitespace by @command{awk}. The purpose of fields is to make it more convenient for you to refer to these pieces of the record. You don't have to use them---you can -operate on the whole record if you wish---but fields are what make -simple @code{awk} programs so powerful. +operate on the whole record if you want---but fields are what make +simple @command{awk} programs so powerful. -@cindex @code{$} (field operator) +@cindex @code{$} field operator @cindex field operator @code{$} -To refer to a field in an @code{awk} program, you use a dollar-sign, -@samp{$}, followed by the number of the field you want. Thus, @code{$1} -refers to the first field, @code{$2} to the second, and so on. For -example, suppose the following is a line of input: +A dollar-sign (@samp{$}) is used +to refer to a field in an @command{awk} program, +followed by the number of the field you want. Thus, @code{$1} +refers to the first field, @code{$2} to the second, and so on. +(Unlike the Unix shells, the field numbers are not limited to single digits. +@code{$127} is the one hundred and twenty-seventh field in the record.) +For example, suppose the following is a line of input: @example This seems like a pretty nice example. @end example @noindent -Here the first field, or @code{$1}, is @samp{This}; the second field, or -@code{$2}, is @samp{seems}; and so on. Note that the last field, +Here the first field, or @code{$1}, is @samp{This}, the second field, or +@code{$2}, is @samp{seems}, and so on. Note that the last field, @code{$7}, is @samp{example.}. Because there is no space between the @samp{e} and the @samp{.}, the period is considered part of the seventh field. -@vindex NF +@cindex @code{NF} variable @cindex number of fields, @code{NF} -@code{NF} is a built-in variable whose value -is the number of fields in the current record. -@code{awk} updates the value of @code{NF} automatically, each time -a record is read. - -No matter how many fields there are, the last field in a record can be -represented by @code{$NF}. So, in the example above, @code{$NF} would -be the same as @code{$7}, which is @samp{example.}. Why this works is -explained below (@pxref{Non-Constant Fields, ,Non-constant Field Numbers}). -If you try to reference a field beyond the last one, such as @code{$8} -when the record has only seven fields, you get the empty string. -@c the empty string acts like 0 in some contexts, but I don't want to -@c get into that here.... - -@code{$0}, which looks like a reference to the ``zeroth'' field, is -a special case: it represents the whole input record. @code{$0} is -used when you are not interested in fields. - -@c NEEDED -@page +@code{NF} is a built-in variable whose value is the number of fields +in the current record. @command{awk} automatically updates the value +of @code{NF} each time it reads a record. No matter how many fields +there are, the last field in a record can be represented by @code{$NF}. +So, @code{$NF} is the same as @code{$7}, which is @samp{example.}. +If you try to reference a field beyond the last +one (such as @code{$8} when the record has only seven fields), you get +the empty string. (If used in a numeric operation, you get zero.) + +The use of @code{$0}, which looks like a reference to the ``zeroth'' field, is +a special case: it represents the whole input record +when you are not interested in specific fields. Here are some more examples: @example -@group $ awk '$1 ~ /foo/ @{ print $0 @}' BBS-list @print{} fooey 555-1234 2400/1200/300 B @print{} foot 555-6699 1200/300 B @print{} macfoo 555-6480 1200/300 A @print{} sabafoo 555-2127 1200/300 C -@end group @end example @noindent @@ -3249,24 +4046,21 @@ expression. By contrast, the following example looks for @samp{foo} in @emph{the entire record} and prints the first -field and the last field for each input record containing a -match. +field and the last field for each matching input record: @example -@group $ awk '/foo/ @{ print $1, $NF @}' BBS-list @print{} fooey B @print{} foot B @print{} macfoo A @print{} sabafoo C -@end group @end example @node Non-Constant Fields, Changing Fields, Fields, Reading Files -@section Non-constant Field Numbers +@section Non-Constant Field Numbers The number of a field does not need to be a constant. Any expression in -the @code{awk} language can be used after a @samp{$} to refer to a +the @command{awk} language can be used after a @samp{$} to refer to a field. The value of the expression specifies the field number. If the value is a string, rather than a number, it is converted to a number. Consider this example: @@ -3281,93 +4075,92 @@ first record, two in the second, etc. So this example prints the first field of the first record, the second field of the second record, and so on. For the twentieth record, field number 20 is printed; most likely, the record has fewer than 20 fields, so this prints a blank line. - Here is another example of using expressions as field numbers: @example awk '@{ print $(2*2) @}' BBS-list @end example -@code{awk} must evaluate the expression @samp{(2*2)} and use +@command{awk} evaluates the expression @samp{(2*2)} and uses its value as the number of the field to print. The @samp{*} sign represents multiplication, so the expression @samp{2*2} evaluates to four. The parentheses are used so that the multiplication is done before the @samp{$} operation; they are necessary whenever there is a binary operator in the field-number expression. This example, then, prints the hours of operation (the fourth field) for every line of the file -@file{BBS-list}. (All of the @code{awk} operators are listed, in +@file{BBS-list}. (All of the @command{awk} operators are listed, in order of decreasing precedence, in @ref{Precedence, , Operator Precedence (How Operators Nest)}.) If the field number you compute is zero, you get the entire record. -Thus, @code{$(2-2)} has the same value as @code{$0}. Negative field -numbers are not allowed; trying to reference one will usually terminate -your running @code{awk} program. (The POSIX standard does not define -what happens when you reference a negative field number. @code{gawk} -will notice this and terminate your program. Other @code{awk} +Thus, @samp{$(2-2)} has the same value as @code{$0}. Negative field +numbers are not allowed; trying to reference one usually terminates +the program. (The POSIX standard does not define +what happens when you reference a negative field number. @command{gawk} +notices this and terminates your program. Other @command{awk} implementations may behave differently.) As mentioned in @ref{Fields, ,Examining Fields}, -the number of fields in the current record is stored in the built-in +@command{awk} stores the current record's number of fields in the built-in variable @code{NF} (also @pxref{Built-in Variables}). The expression -@code{$NF} is not a special feature: it is the direct consequence of +@code{$NF} is not a special feature---it is the direct consequence of evaluating @code{NF} and using its value as a field number. @node Changing Fields, Field Separators, Non-Constant Fields, Reading Files @section Changing the Contents of a Field -@cindex field, changing contents of +@cindex fields, changing contents of @cindex changing contents of a field @cindex assignment to fields -You can change the contents of a field as seen by @code{awk} within an -@code{awk} program; this changes what @code{awk} perceives as the -current input record. (The actual input is untouched; @code{awk} @emph{never} +The contents of a field, as seen by @command{awk}, can be changed within an +@command{awk} program; this changes what @command{awk} perceives as the +current input record. (The actual input is untouched; @command{awk} @emph{never} modifies the input file.) - Consider this example and its output: @example -@group -$ awk '@{ $3 = $2 - 10; print $2, $3 @}' inventory-shipped +$ awk '@{ nboxes = $3 ; $3 = $3 - 10 +> print nboxes, $3 @}' inventory-shipped @print{} 13 3 @print{} 15 5 @print{} 15 5 @dots{} -@end group @end example @noindent +The program first saves the original value of field three in the variable +@code{nboxes}. The @samp{-} sign represents subtraction, so this program reassigns -field three, @code{$3}, to be the value of field two minus ten, -@samp{$2 - 10}. (@xref{Arithmetic Ops, ,Arithmetic Operators}.) -Then field two, and the new value for field three, are printed. - -In order for this to work, the text in field @code{$2} must make sense -as a number; the string of characters must be converted to a number in -order for the computer to do arithmetic on it. The number resulting -from the subtraction is converted back to a string of characters which +field three, @code{$3}, as the original value of field three minus ten: +@samp{$3 - 10}. (@xref{Arithmetic Ops, ,Arithmetic Operators}.) +Then it prints the original and new values for field three. +(Someone in the warehouse made a consistent mistake while inventorying +the red boxes.) + +For this to work, the text in field @code{$2} must make sense +as a number; the string of characters must be converted to a number +for the computer to do arithmetic on it. The number resulting +from the subtraction is converted back to a string of characters that then becomes field three. @xref{Conversion, ,Conversion of Strings and Numbers}. -When you change the value of a field (as perceived by @code{awk}), the +When the value of a field is changed (as perceived by @command{awk}), the text of the input record is recalculated to contain the new field where -the old one was. Therefore, @code{$0} changes to reflect the altered +the old one was. In other words, @code{$0} changes to reflect the altered field. Thus, this program prints a copy of the input file, with 10 subtracted from the second -field of each line. +field of each line: @example -@group $ awk '@{ $2 = $2 - 10; print $0 @}' inventory-shipped @print{} Jan 3 25 15 115 @print{} Feb 5 32 24 226 @print{} Mar 5 24 34 228 @dots{} -@end group @end example -You can also assign contents to fields that are out of range. For -example: +It is also possible to also assign contents to fields that are out +of range. For example: @example $ awk '@{ $6 = ($5 + $4 + $3 + $2) @@ -3384,17 +4177,17 @@ We've just created @code{$6}, whose value is the sum of fields represents addition. For the file @file{inventory-shipped}, @code{$6} represents the total number of parcels shipped for a particular month. -Creating a new field changes @code{awk}'s internal copy of the current -input record---the value of @code{$0}. Thus, if you do @samp{print $0} +Creating a new field changes @command{awk}'s internal copy of the current +input record, which is the value of @code{$0}. Thus, if you do @samp{print $0} after adding a field, the record printed includes the new field, with the appropriate number of field separators between it and the previously existing fields. This recomputation affects and is affected by -@code{NF} (the number of fields; @pxref{Fields, ,Examining Fields}), -and by a feature that has not been discussed yet, +@code{NF} (the number of fields; @pxref{Fields, ,Examining Fields}). +It is also affected by a feature that has not been discussed yet: the @dfn{output field separator}, @code{OFS}, -which is used to separate the fields (@pxref{Output Separators}). +used to separate the fields (@pxref{Output Separators}). For example, the value of @code{NF} is set to the number of the highest field you create. @@ -3413,29 +4206,26 @@ else @noindent should print @samp{everything is normal}, because @code{NF+1} is certain to be out of range. (@xref{If Statement, ,The @code{if}-@code{else} Statement}, -for more information about @code{awk}'s @code{if-else} statements. +for more information about @command{awk}'s @code{if-else} statements. @xref{Typing and Comparison, ,Variable Typing and Comparison Expressions}, for more information about the @samp{!=} operator.) It is important to note that making an assignment to an existing field -will change the -value of @code{$0}, but will not change the value of @code{NF}, +changes the +value of @code{$0} but does not change the value of @code{NF}, even when you assign the empty string to a field. For example: @example -@group $ echo a b c d | awk '@{ OFS = ":"; $2 = "" > print $0; print NF @}' @print{} a::c:d @print{} 4 -@end group @end example @noindent -The field is still there; it just has an empty value. You can tell -because there are two colons in a row. - -This example shows what happens if you create a new field. +The field is still there; it just has an empty value, denoted by +the two colons between @samp{a} and @samp{c}. +This example shows what happens if you create a new field: @example $ echo a b c d | awk '@{ OFS = ":"; $2 = ""; $6 = "new" @@ -3445,50 +4235,48 @@ $ echo a b c d | awk '@{ OFS = ":"; $2 = ""; $6 = "new" @end example @noindent -The intervening field, @code{$5} is created with an empty value +The intervening field, @code{$5}, is created with an empty value (indicated by the second pair of adjacent colons), and @code{NF} is updated with the value six. -Finally, decrementing @code{NF} will lose the values of the fields -after the new value of @code{NF}, and @code{$0} will be recomputed. +@c FIXME: Verify that this is in POSIX +@cindex dark corner +Decrementing @code{NF} throws away the values of the fields +after the new value of @code{NF} and recomputes @code{$0}. +@value{DARKCORNER} Here is an example: @example -$ echo a b c d e f | ../gawk '@{ print "NF =", NF; -> NF = 3; print $0 @}' +$ echo a b c d e f | awk '@{ print "NF =", NF; +> NF = 3; print $0 @}' @print{} NF = 6 @print{} a b c @end example -@node Field Separators, Constant Size, Changing Fields, Reading Files -@section Specifying How Fields are Separated +@cindex portability issues +@strong{Caution:} Some versions of @command{awk} don't +rebuild @code{$0} when @code{NF} is decremented. Caveat emptor. -This section is rather long; it describes one of the most fundamental -operations in @code{awk}. +@node Field Separators, Constant Size, Changing Fields, Reading Files +@section Specifying How Fields Are Separated @menu -* Basic Field Splitting:: How fields are split with single characters - or simple strings. * Regexp Field Splitting:: Using regexps as the field separator. * Single Character Fields:: Making each character a separate field. -* Command Line Field Separator:: Setting @code{FS} from the command line. +* Command Line Field Separator:: Setting @code{FS} from the command-line. * Field Splitting Summary:: Some final points and a summary table. @end menu -@node Basic Field Splitting, Regexp Field Splitting, Field Separators, Field Separators -@subsection The Basics of Field Separating -@vindex FS +@cindex @code{FS} variable @cindex fields, separating @cindex field separator, @code{FS} - The @dfn{field separator}, which is either a single character or a regular -expression, controls the way @code{awk} splits an input record into fields. -@code{awk} scans the input record for character sequences that +expression, controls the way @command{awk} splits an input record into fields. +@command{awk} scans the input record for character sequences that match the separator; the fields themselves are the text between the matches. -In the examples below, we use the bullet symbol ``@bullet{}'' to represent -spaces in the output. - +In the examples that follow, we use the bullet symbol (@bullet{}) to +represent spaces in the output. If the field separator is @samp{oo}, then the following line: @example @@ -3496,7 +4284,7 @@ moo goo gai pan @end example @noindent -would be split into three fields: @samp{m}, @samp{@bullet{}g} and +is split into three fields: @samp{m}, @samp{@bullet{}g}, and @samp{@bullet{}gai@bullet{}pan}. Note the leading spaces in the values of the second and third fields. @@ -3504,15 +4292,15 @@ Note the leading spaces in the values of the second and third fields. @cindex mistakes, common @cindex errors, common The field separator is represented by the built-in variable @code{FS}. -Shell programmers take note! @code{awk} does @emph{not} use the name @code{IFS} -which is used by the POSIX compatible shells (such as the Bourne shell, -@code{sh}, or the GNU Bourne-Again Shell, Bash). +Shell programmers take note: @command{awk} does @emph{not} use the +name @code{IFS} that is used by the POSIX-compliant shells (such as +the Unix Bourne shell, @command{sh}, or @command{bash}). -You can change the value of @code{FS} in the @code{awk} program with the +The value of @code{FS} can be changed in the @command{awk} program with the assignment operator, @samp{=} (@pxref{Assignment Ops, ,Assignment Expressions}). -Often the right time to do this is at the beginning of execution, +Often the right time to do this is at the beginning of execution before any input has been processed, so that the very first record -will be read with the proper separator. To do this, use the special +is read with the proper separator. To do this, use the special @code{BEGIN} pattern (@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}). For example, here we set the value of @code{FS} to the string @@ -3523,69 +4311,57 @@ awk 'BEGIN @{ FS = "," @} ; @{ print $2 @}' @end example @noindent -Given the input line, +Given the input line: @example John Q. Smith, 29 Oak St., Walamazoo, MI 42139 @end example @noindent -this @code{awk} program extracts and prints the string +this @command{awk} program extracts and prints the string @samp{@bullet{}29@bullet{}Oak@bullet{}St.}. @cindex field separator, choice of @cindex regular expressions as field separators -Sometimes your input data will contain separator characters that don't +Sometimes the input data contains separator characters that don't separate fields the way you thought they would. For instance, the person's name in the example we just used might have a title or -suffix attached, such as @samp{John Q. Smith, LXIX}. From input -containing such a name: +suffix attached, such as: @example John Q. Smith, LXIX, 29 Oak St., Walamazoo, MI 42139 @end example @noindent -@c careful of an overfull hbox here! -the above program would extract @samp{@bullet{}LXIX}, instead of +The same program would extract @samp{@bullet{}LXIX}, instead of @samp{@bullet{}29@bullet{}Oak@bullet{}St.}. If you were expecting the program to print the -address, you would be surprised. The moral is: choose your data layout and +address, you would be surprised. The moral is to choose your data layout and separator characters carefully to prevent such problems. +(If the data is not in a form that is easy to process, perhaps you +can massage it first with a separate @command{awk} program.) -@iftex -As you know, normally, -@end iftex -@ifinfo -Normally, -@end ifinfo -fields are separated by whitespace sequences -(spaces, tabs and newlines), not by single spaces: two spaces in a row do not +Fields are normally separated by whitespace sequences +(spaces, tabs, and newlines), not by single spaces. Two spaces in a row do not delimit an empty field. The default value of the field separator @code{FS} -is a string containing a single space, @w{@code{" "}}. If this value were -interpreted in the usual way, each space character would separate +is a string containing a single space, @w{@code{" "}}. If @command{awk} +interpreted this value in the usual way, each space character would separate fields, so two spaces in a row would make an empty field between them. The reason this does not happen is that a single space as the value of -@code{FS} is a special case: it is taken to specify the default manner +@code{FS} is a special case---it is taken to specify the default manner of delimiting fields. If @code{FS} is any other single character, such as @code{","}, then each occurrence of that character separates two fields. Two consecutive occurrences delimit an empty field. If the character occurs at the beginning or the end of the line, that too delimits an empty field. The -space character is the only single character which does not follow these +space character is the only single character that does not follow these rules. -@node Regexp Field Splitting, Single Character Fields, Basic Field Splitting, Field Separators +@node Regexp Field Splitting, Single Character Fields, Field Separators, Field Separators @subsection Using Regular Expressions to Separate Fields -The previous -@iftex -subsection -@end iftex -@ifinfo -node -@end ifinfo +The previous @value{SUBSECTION} discussed the use of single characters or simple strings as the value of @code{FS}. More generally, the value of @code{FS} may be a string containing any @@ -3598,33 +4374,33 @@ FS = ", \t" @noindent makes every area of an input line that consists of a comma followed by a -space and a tab, into a field separator. (@samp{\t} +space and a tab into a field separator. +@ifinfo +(@samp{\t} is an @dfn{escape sequence} that stands for a tab; @pxref{Escape Sequences}, for the complete list of similar escape sequences.) +@end ifinfo -For a less trivial example of a regular expression, suppose you want -single spaces to separate fields the way single commas were used above. -You can set @code{FS} to @w{@code{"[@ ]"}} (left bracket, space, right +For a less trivial example of a regular expression, try using +single spaces to separate fields the way single commas are used. +@code{FS} can be set to @w{@code{"[@ ]"}} (left bracket, space, right bracket). This regular expression matches a single space and nothing else (@pxref{Regexp, ,Regular Expressions}). There is an important difference between the two cases of @samp{FS = @w{" "}} -(a single space) and @samp{FS = @w{"[ \t\n]+"}} (left bracket, space, -backslash, ``t'', backslash, ``n'', right bracket, which is a regular -expression matching one or more spaces, tabs, or newlines). For both -values of @code{FS}, fields are separated by runs of spaces, tabs -and/or newlines. However, when the value of @code{FS} is @w{@code{" -"}}, @code{awk} will first strip leading and trailing whitespace from -the record, and then decide where the fields are. - +(a single space) and @samp{FS = @w{"[ \t\n]+"}} +(a regular expression matching one or more spaces, tabs, or newlines). +For both values of @code{FS}, fields are separated by @dfn{runs} +(multiple adjacent occurrences) of spaces, tabs, +and/or newlines. However, when the value of @code{FS} is @w{@code{" "}}, +@command{awk} first strips leading and trailing whitespace from +the record and then decides where the fields are. For example, the following pipeline prints @samp{b}: @example -@group $ echo ' a b c d ' | awk '@{ print $2 @}' @print{} b -@end group @end example @noindent @@ -3632,7 +4408,7 @@ However, this pipeline prints @samp{a} (note the extra spaces around each letter): @example -$ echo ' a b c d ' | awk 'BEGIN @{ FS = "[ \t]+" @} +$ echo ' a b c d ' | awk 'BEGIN @{ FS = "[ \t\n]+" @} > @{ print $2 @}' @print{} a @end example @@ -3640,7 +4416,7 @@ $ echo ' a b c d ' | awk 'BEGIN @{ FS = "[ \t]+" @} @noindent @cindex null string @cindex empty string -In this case, the first field is @dfn{null}, or empty. +In this case, the first field is @dfn{null} or empty. The stripping of leading and trailing whitespace also comes into play whenever @code{$0} is recomputed. For instance, study this pipeline: @@ -3655,49 +4431,50 @@ $ echo ' a b c d' | awk '@{ print; $2 = $2; print @}' The first @code{print} statement prints the record as it was read, with leading whitespace intact. The assignment to @code{$2} rebuilds @code{$0} by concatenating @code{$1} through @code{$NF} together, -separated by the value of @code{OFS}. Since the leading whitespace +separated by the value of @code{OFS}. Because the leading whitespace was ignored when finding @code{$1}, it is not part of the new @code{$0}. Finally, the last @code{print} statement prints the new @code{$0}. @node Single Character Fields, Command Line Field Separator, Regexp Field Splitting, Field Separators @subsection Making Each Character a Separate Field -@cindex differences between @code{gawk} and @code{awk} -@cindex single character fields +@cindex differences between @command{gawk} and @command{awk} +@cindex single-character fields There are times when you may want to examine each character -of a record separately. In @code{gawk}, this is easy to do, you -simply assign the null string (@code{""}) to @code{FS}. In this case, -each individual character in the record will become a separate field. -Here is an example: +of a record separately. This can be done in @command{gawk} by +simply assigning the null string (@code{""}) to @code{FS}. In this case, +each individual character in the record becomes a separate field. +For example: @example -@group $ echo a b | gawk 'BEGIN @{ FS = "" @} -> @{ +> @{ > for (i = 1; i <= NF; i = i + 1) > print "Field", i, "is", $i > @}' @print{} Field 1 is a @print{} Field 2 is @print{} Field 3 is b -@end group @end example @cindex dark corner -Traditionally, the behavior for @code{FS} equal to @code{""} was not defined. -In this case, Unix @code{awk} would simply treat the entire record -as only having one field (d.c.). In compatibility mode -(@pxref{Options, ,Command Line Options}), -if @code{FS} is the null string, then @code{gawk} will also -behave this way. +Traditionally, the behavior of @code{FS} equal to @code{""} was not defined. +In this case, most versions of Unix @command{awk} simply treat the entire record +as only having one field. +@value{DARKCORNER} +In compatibility mode +(@pxref{Options, ,Command-Line Options}), +if @code{FS} is the null string, then @command{gawk} also +behaves this way. @node Command Line Field Separator, Field Splitting Summary, Single Character Fields, Field Separators @subsection Setting @code{FS} from the Command Line @cindex @code{-F} option +@cindex command-line option, @code{-F} @cindex field separator, on command line @cindex command line, setting @code{FS} on -@code{FS} can be set on the command line. You use the @samp{-F} option to +@code{FS} can be set on the command line. Use the @option{-F} option to do so. For example: @example @@ -3705,64 +4482,59 @@ awk -F, '@var{program}' @var{input-files} @end example @noindent -sets @code{FS} to be the @samp{,} character. Notice that the option uses -a capital @samp{F}. Contrast this with @samp{-f}, which specifies a file -containing an @code{awk} program. Case is significant in command line options: -the @samp{-F} and @samp{-f} options have nothing to do with each other. +sets @code{FS} to the @samp{,} character. Notice that the option uses +a capital @samp{F} instead of a lowercase @option{-f}, which specifies a file +containing an @command{awk} program. Case is significant in command-line +options: +the @option{-F} and @option{-f} options have nothing to do with each other. You can use both options at the same time to set the @code{FS} variable -@emph{and} get an @code{awk} program from a file. +@emph{and} get an @command{awk} program from a file. -The value used for the argument to @samp{-F} is processed in exactly the -same way as assignments to the built-in variable @code{FS}. This means that -if the field separator contains special characters, they must be escaped -appropriately. For example, to use a @samp{\} as the field separator, you -would have to type: +The value used for the argument to @option{-F} is processed in exactly the +same way as assignments to the built-in variable @code{FS}. +Any special characters in the field separator must be escaped +appropriately. For example, to use a @samp{\} as the field separator +on the command line, you would have to type: @example -# same as FS = "\\" +# same as FS = "\\" awk -F\\\\ '@dots{}' files @dots{} @end example @noindent -Since @samp{\} is used for quoting in the shell, @code{awk} will see -@samp{-F\\}. Then @code{awk} processes the @samp{\\} for escape +Because @samp{\} is used for quoting in the shell, @command{awk} sees +@samp{-F\\}. Then @command{awk} processes the @samp{\\} for escape characters (@pxref{Escape Sequences}), finally yielding -a single @samp{\} to be used for the field separator. +a single @samp{\} to use for the field separator. @cindex historical features As a special case, in compatibility mode -(@pxref{Options, ,Command Line Options}), if the -argument to @samp{-F} is @samp{t}, then @code{FS} is set to the tab -character. This is because if you type @samp{-F\t} at the shell, -without any quotes, the @samp{\} gets deleted, so @code{awk} figures that you -really want your fields to be separated with tabs, and not @samp{t}s. -Use @samp{-v FS="t"} on the command line if you really do want to separate -your fields with @samp{t}s -(@pxref{Options, ,Command Line Options}). +(@pxref{Options, ,Command-Line Options}), +if the argument to @option{-F} is @samp{t}, then @code{FS} is set to +the tab character. If you type @samp{-F\t} at the +shell, without any quotes, the @samp{\} gets deleted, so @command{awk} +figures that you really want your fields to be separated with tabs and +not @samp{t}s. Use @samp{-v FS="t"} or @samp{-F"[t]"} on the command line +if you really do want to separate your fields with @samp{t}s. -For example, let's use an @code{awk} program file called @file{baud.awk} -that contains the pattern @code{/300/}, and the action @samp{print $1}. -Here is the program: +For example, let's use an @command{awk} program file called @file{baud.awk} +that contains the pattern @code{/300/} and the action @samp{print $1}: @example /300/ @{ print $1 @} @end example -Let's also set @code{FS} to be the @samp{-} character, and run the +Let's also set @code{FS} to be the @samp{-} character and run the program on the file @file{BBS-list}. The following command prints a list of the names of the bulletin boards that operate at 300 baud and the first three digits of their phone numbers: @c tweaked to make the tex output look better in @smallbook @example -@group $ awk -F- -f baud.awk BBS-list @print{} aardvark 555 @print{} alpo @print{} barfly 555 -@dots{} -@end group -@ignore @print{} bites 555 @print{} camelot 555 @print{} core 555 @@ -3771,13 +4543,11 @@ $ awk -F- -f baud.awk BBS-list @print{} macfoo 555 @print{} sdace 555 @print{} sabafoo 555 -@end ignore @end example @noindent -Note the second line of output. In the original file -(@pxref{Sample Data Files, ,Data Files for the Examples}), -the second line looked like this: +Note the second line of output. The second line +in the original file looked like this: @example alpo-net 555-3412 2400/1200/300 A @@ -3788,44 +4558,79 @@ separator, instead of the @samp{-} in the phone number that was originally intended. This demonstrates why you have to be careful in choosing your field and record separators. +Perhaps the most common use of a single character as the field +separator occurs when processing the Unix system password file. On many Unix systems, each user has a separate entry in the system password file, one line per user. The information in these lines is separated -by colons. The first field is the user's logon name, and the second is -the user's encrypted password. A password file entry might look like this: +by colons. The first field is the user's logon name and the second is +the user's (encrypted or shadow) password. A password file entry might look +like this: +@cindex Robbins, Arnold @example -arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/sh +arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/bash @end example -The following program searches the system password file, and prints +The following program searches the system password file and prints the entries for users who have no password: @example awk -F: '$2 == ""' /etc/passwd @end example -@node Field Splitting Summary, , Command Line Field Separator, Field Separators +@node Field Splitting Summary, , Command Line Field Separator, Field Separators @subsection Field Splitting Summary -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} -According to the POSIX standard, @code{awk} is supposed to behave -as if each record is split into fields at the time that it is read. -In particular, this means that you can change the value of @code{FS} -after a record is read, and the value of the fields (i.e.@: how they were split) +The following +table +summarizes how fields are split, based on the +value of @code{FS}. (@samp{==} means ``is equal to.'') + +@table @code +@item FS == " " +Fields are separated by runs of whitespace. Leading and trailing +whitespace are ignored. This is the default. + +@item FS == @var{any other single character} +Fields are separated by each occurrence of the character. Multiple +successive occurrences delimit empty fields, as do leading and +trailing occurrences. +The character can even be a regexp metacharacter; it does not need +to be escaped. + +@item FS == @var{regexp} +Fields are separated by occurrences of characters that match @var{regexp}. +Leading and trailing matches of @var{regexp} delimit empty fields. + +@item FS == "" +Each individual character in the record becomes a separate field. +(This is a @command{gawk} extension; it is not specified by the +POSIX standard.) +@end table + +@c fakenode --- for prepinfo +@subheading Advanced Notes: Changing @code{FS} Does Not Affect the Fields + +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} +According to the POSIX standard, @command{awk} is supposed to behave +as if each record is split into fields at the time it is read. +In particular, this means that if you change the value of @code{FS} +after a record is read, the value of the fields (i.e., how they were split) should reflect the old value of @code{FS}, not the new one. @cindex dark corner -@cindex @code{sed} utility +@cindex @command{sed} utility @cindex stream editor -However, many implementations of @code{awk} do not work this way. Instead, +However, many implementations of @command{awk} do not work this way. Instead, they defer splitting the fields until a field is actually -referenced. The fields will be split -using the @emph{current} value of @code{FS}! (d.c.) +referenced. The fields are split +using the @emph{current} value of @code{FS}! +@value{DARKCORNER} This behavior can be difficult to diagnose. The following example illustrates the difference between the two methods. -(The @code{sed}@footnote{The @code{sed} utility is a ``stream editor.'' +(The @command{sed}@footnote{The @command{sed} utility is a ``stream editor.'' Its behavior is also defined by the POSIX standard.} command prints just the first line of @file{/etc/passwd}.) @@ -3834,94 +4639,83 @@ sed 1q /etc/passwd | awk '@{ FS = ":" ; print $1 @}' @end example @noindent -will usually print +which usually prints: @example root @end example @noindent -on an incorrect implementation of @code{awk}, while @code{gawk} -will print something like +on an incorrect implementation of @command{awk}, while @command{gawk} +prints something like: @example root:nSijPlPhZZwgE:0:0:Root:/: @end example -The following table summarizes how fields are split, based on the -value of @code{FS}. (@samp{==} means ``is equal to.'') +@node Constant Size, Multiple Line, Field Separators, Reading Files +@section Reading Fixed-Width Data -@c @cartouche -@table @code -@item FS == " " -Fields are separated by runs of whitespace. Leading and trailing -whitespace are ignored. This is the default. - -@item FS == @var{any other single character} -Fields are separated by each occurrence of the character. Multiple -successive occurrences delimit empty fields, as do leading and -trailing occurrences. -The character can even be a regexp metacharacter; it does not need -to be escaped. - -@item FS == @var{regexp} -Fields are separated by occurrences of characters that match @var{regexp}. -Leading and trailing matches of @var{regexp} delimit empty fields. - -@item FS == "" -Each individual character in the record becomes a separate field. -@end table -@c @end cartouche +@ifnotinfo +@strong{Note:} This @value{SECTION} discusses an advanced +feature of @command{gawk}. If you are a novice @command{awk} user, +you might want to skip it on the first reading. +@end ifnotinfo -@node Constant Size, Multiple Line, Field Separators, Reading Files -@section Reading Fixed-width Data - -(This section discusses an advanced, experimental feature. If you are -a novice @code{awk} user, you may wish to skip it on the first reading.) +@ifinfo +(This @value{SECTION} discusses an advanced feature of @command{awk}. +If you are a novice @command{awk} user, you might want to skip it on +the first reading.) +@end ifinfo -@code{gawk} version 2.13 introduced a new facility for dealing with -fixed-width fields with no distinctive field separator. Data of this -nature arises, for example, in the input for old FORTRAN programs where -numbers are run together; or in the output of programs that did not +@command{gawk} @value{PVERSION} 2.13 introduced a facility for dealing with +fixed-width fields with no distinctive field separator. For example, +data of this nature arises in the input for old Fortran programs where +numbers are run together, or in the output of programs that did not anticipate the use of their output as input for other programs. An example of the latter is a table where all the columns are lined up by the use of a variable number of spaces and @emph{empty fields are just -spaces}. Clearly, @code{awk}'s normal field splitting based on @code{FS} -will not work well in this case. Although a portable @code{awk} program +spaces}. Clearly, @command{awk}'s normal field splitting based on @code{FS} +does not work well in this case. Although a portable @command{awk} program can use a series of @code{substr} calls on @code{$0} -(@pxref{String Functions, ,Built-in Functions for String Manipulation}), +(@pxref{String Functions, ,String Manipulation Functions}), this is awkward and inefficient for a large number of fields. +@cindex fatal errors +@cindex @command{w} utility The splitting of an input record into fixed-width fields is specified by assigning a string containing space-separated numbers to the built-in -variable @code{FIELDWIDTHS}. Each number specifies the width of the field +variable @code{FIELDWIDTHS}. Each number specifies the width of the field, @emph{including} columns between fields. If you want to ignore the columns between fields, you can specify the width as a separate field that is subsequently ignored. - -The following data is the output of the Unix @code{w} utility. It is useful -to illustrate the use of @code{FIELDWIDTHS}. +It is a fatal error to supply a field width that is not a positive number. +The following data is the output of the Unix @command{w} utility. It is useful +to illustrate the use of @code{FIELDWIDTHS}: @example @group 10:06pm up 21 days, 14:04, 23 users User tty login@ idle JCPU PCPU what -hzuo ttyV0 8:58pm 9 5 vi p24.tex -hzang ttyV3 6:37pm 50 -csh -eklye ttyV5 9:53pm 7 1 em thes.tex -dportein ttyV6 8:17pm 1:47 -csh -gierd ttyD3 10:00pm 1 elm -dave ttyD4 9:47pm 4 4 w -brent ttyp0 26Jun91 4:46 26:46 4:41 bash +hzuo ttyV0 8:58pm 9 5 vi p24.tex +hzang ttyV3 6:37pm 50 -csh +eklye ttyV5 9:53pm 7 1 em thes.tex +dportein ttyV6 8:17pm 1:47 -csh +gierd ttyD3 10:00pm 1 elm +dave ttyD4 9:47pm 4 4 w +brent ttyp0 26Jun91 4:46 26:46 4:41 bash dave ttyq4 26Jun9115days 46 46 wnewmail -@end group +@end group @end example The following program takes the above input, converts the idle time to -number of seconds and prints out the first two fields and the calculated -idle time. (This program uses a number of @code{awk} features that -haven't been introduced yet.) +number of seconds, and prints out the first two fields and the calculated +idle time. + +@strong{Note:} +This program uses a number of @command{awk} features that +haven't been introduced yet. @example BEGIN @{ FIELDWIDTHS = "9 6 10 6 7 7 35" @} @@ -3930,22 +4724,18 @@ NR > 2 @{ sub(/^ */, "", idle) # strip leading spaces if (idle == "") idle = 0 -@group if (idle ~ /:/) @{ split(idle, t, ":") idle = t[1] * 60 + t[2] @} -@end group -@group if (idle ~ /days/) idle *= 24 * 60 * 60 - + print $1, $2, idle @} -@end group @end example -Here is the result of running the program on the data: +Running the program on the data produces the following results: @example hzuo ttyV0 0 @@ -3959,26 +4749,40 @@ dave ttyq4 1296000 @end example Another (possibly more practical) example of fixed-width input data -would be the input from a deck of balloting cards. In some parts of +is the input from a deck of balloting cards. In some parts of the United States, voters mark their choices by punching holes in computer cards. These cards are then processed to count the votes for any particular -candidate or on any particular issue. Since a voter may choose not to -vote on some issue, any column on the card may be empty. An @code{awk} +candidate or on any particular issue. Because a voter may choose not to +vote on some issue, any column on the card may be empty. An @command{awk} program for processing such data could use the @code{FIELDWIDTHS} feature -to simplify reading the data. (Of course, getting @code{gawk} to run on +to simplify reading the data. (Of course, getting @command{gawk} to run on a system with card readers is another story!) @ignore Exercise: Write a ballot card reading program @end ignore -Assigning a value to @code{FS} causes @code{gawk} to return to using +Assigning a value to @code{FS} causes @command{gawk} to return to using @code{FS} for field splitting. Use @samp{FS = FS} to make this happen, without having to know the current value of @code{FS}. +In order to tell which kind of field splitting is in effect, +use @code{PROCINFO["FS"]} +(@pxref{Auto-set, ,Built-in Variables That Convey Information}). +The value is @code{"FS"} if regular field splitting is being used, +or it is @code{"FIELDWIDTHS"} if fixed-width field splitting is being used: + +@example +if (PROCINFO["FS"] == "FS") + @var{regular field splitting} @dots{} +else + @var{fixed-width field splitting} @dots{} +@end example -This feature is still experimental, and may evolve over time. -Note that in particular, @code{gawk} does not attempt to verify -the sanity of the values used in the value of @code{FIELDWIDTHS}. +This information is useful when writing a function +that needs to temporarily change @code{FS} or @code{FIELDWIDTHS}, +read some records, and then restore the original settings +(@pxref{Passwd Functions, ,Reading the User Database}, +for an example of such a function). @node Multiple Line, Getline, Constant Size, Reading Files @section Multiple-Line Records @@ -3987,17 +4791,13 @@ the sanity of the values used in the value of @code{FIELDWIDTHS}. @cindex input, multiple line records @cindex reading files, multiple line records @cindex records, multiple line -In some data bases, a single line cannot conveniently hold all the -information in one entry. In such cases, you can use multi-line -records. - -The first step in doing this is to choose your data format: when records -are not defined as single lines, how do you want to define them? -What should separate records? +In some databases, a single line cannot conveniently hold all the +information in one entry. In such cases, you can use multiline +records. The first step in doing this is to choose your data format. One technique is to use an unusual character or string to separate records. For example, you could use the formfeed character (written -@samp{\f} in @code{awk}, as in C) to separate them, making each record +@samp{\f} in @command{awk}, as in C) to separate them, making each record a page of the file. To do this, just set the variable @code{RS} to @code{"\f"} (a string containing the formfeed character). Any other character could equally well be used, as long as it won't be part @@ -4005,57 +4805,57 @@ of the data in a record. Another technique is to have blank lines separate records. By a special dispensation, an empty string as the value of @code{RS} indicates that -records are separated by one or more blank lines. If you set @code{RS} -to the empty string, a record always ends at the first blank line -encountered. And the next record doesn't start until the first non-blank -line that follows---no matter how many blank lines appear in a row, they -are considered one record-separator. +records are separated by one or more blank lines. When @code{RS} is set +to the empty string, each record always ends at the first blank line +encountered. The next record doesn't start until the first non-blank +line that follows. No matter how many blank lines appear in a row, they +all act as one record separator. +(Blank lines must be completely empty; lines that contain only +whitespace do not count.) @cindex leftmost longest match @cindex matching, leftmost longest You can achieve the same effect as @samp{RS = ""} by assigning the string @code{"\n\n+"} to @code{RS}. This regexp matches the newline -at the end of the record, and one or more blank lines after the record. +at the end of the record and one or more blank lines after the record. In addition, a regular expression always matches the longest possible sequence when there is a choice (@pxref{Leftmost Longest, ,How Much Text Matches?}). So the next record doesn't start until the first non-blank line that follows---no matter how many blank lines -appear in a row, they are considered one record-separator. +appear in a row, they are considered one record separator. @cindex dark corner There is an important difference between @samp{RS = ""} and @samp{RS = "\n\n+"}. In the first case, leading newlines in the input -data file are ignored, and if a file ends without extra blank lines +@value{DF} are ignored, and if a file ends without extra blank lines after the last record, the final newline is removed from the record. -In the second case, this special processing is not done (d.c.). +In the second case, this special processing is not done. +@value{DARKCORNER} Now that the input is separated into records, the second step is to separate the fields in the record. One way to do this is to divide each of the lines into fields in the normal manner. This happens by default -as the result of a special feature: when @code{RS} is set to the empty +as the result of a special feature. When @code{RS} is set to the empty string, the newline character @emph{always} acts as a field separator. This is in addition to whatever field separations result from @code{FS}. The original motivation for this special exception was probably to provide -useful behavior in the default case (i.e.@: @code{FS} is equal +useful behavior in the default case (i.e., @code{FS} is equal to @w{@code{" "}}). This feature can be a problem if you really don't -want the newline character to separate fields, since there is no way to +want the newline character to separate fields, because there is no way to prevent it. However, you can work around this by using the @code{split} function to break up the record manually -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). +(@pxref{String Functions, ,String Manipulation Functions}). Another way to separate fields is to put each field on a separate line: to do this, just set the variable @code{FS} to the string @code{"\n"}. (This simple regular expression matches a single newline.) - -A practical example of a data file organized this way might be a mailing -list, where each entry is separated by blank lines. If we have a mailing +A practical example of a @value{DF} organized this way might be a mailing +list, where each entry is separated by blank lines. Consider a mailing list in a file named @file{addresses}, that looks like this: -@c NEEDED -@page @example Jane Doe 123 Main Street @@ -4068,10 +4868,9 @@ Smallville, MW 98765-4321 @end example @noindent -A simple program to process this file would look like this: +A simple program to process this file is as follows: @example -@group # addrs.awk --- simple mailing list program # Records are separated by blank lines. @@ -4084,39 +4883,41 @@ BEGIN @{ RS = "" ; FS = "\n" @} print "City and State are:", $3 print "" @} -@end group @end example Running the program produces the following output: @example -@group $ awk -f addrs.awk addresses @print{} Name is: Jane Doe @print{} Address is: 123 Main Street @print{} City and State are: Anywhere, SE 12345-6789 @print{} -@end group -@group @print{} Name is: John Smith @print{} Address is: 456 Tree-lined Avenue @print{} City and State are: Smallville, MW 98765-4321 @print{} @dots{} -@end group @end example @xref{Labels Program, ,Printing Mailing Labels}, for a more realistic program that deals with address lists. +The following +table +summarizes how records are split, based on the +value of +@ifinfo +@code{RS}. +(@samp{==} means ``is equal to.'') +@end ifinfo +@ifnotinfo +@code{RS}: +@end ifnotinfo -The following table summarizes how records are split, based on the -value of @code{RS}. (@samp{==} means ``is equal to.'') - -@c @cartouche @table @code @item RS == "\n" Records are separated by the newline character (@samp{\n}). In effect, -every line in the data file is a separate record, including blank lines. +every line in the @value{DF} is a separate record, including blank lines. This is the default. @item RS == @var{any single character} @@ -4131,78 +4932,78 @@ always serves as a field separator, in addition to whatever value @item RS == @var{regexp} Records are separated by occurrences of characters that match @var{regexp}. Leading and trailing matches of @var{regexp} delimit empty records. +(This is a @command{gawk} extension, it is not specified by the +POSIX standard.) @end table -@c @end cartouche -@vindex RT -In all cases, @code{gawk} sets @code{RT} to the input text that matched the +@cindex @code{RT} variable +In all cases, @command{gawk} sets @code{RT} to the input text that matched the value specified by @code{RS}. @node Getline, , Multiple Line, Reading Files @section Explicit Input with @code{getline} -@findex getline +@cindex @code{getline} built-in function @cindex input, explicit @cindex explicit input @cindex input, @code{getline} command @cindex reading files, @code{getline} command -So far we have been getting our input data from @code{awk}'s main +So far we have been getting our input data from @command{awk}'s main input stream---either the standard input (usually your terminal, sometimes the output from another program) or from the -files specified on the command line. The @code{awk} language has a +files specified on the command line. The @command{awk} language has a special built-in command called @code{getline} that can be used to read input under your explicit control. -@menu -* Getline Intro:: Introduction to the @code{getline} function. -* Plain Getline:: Using @code{getline} with no arguments. -* Getline/Variable:: Using @code{getline} into a variable. -* Getline/File:: Using @code{getline} from a file. -* Getline/Variable/File:: Using @code{getline} into a variable from a - file. -* Getline/Pipe:: Using @code{getline} from a pipe. -* Getline/Variable/Pipe:: Using @code{getline} into a variable from a - pipe. -* Getline Summary:: Summary Of @code{getline} Variants. -@end menu - -@node Getline Intro, Plain Getline, Getline, Getline -@subsection Introduction to @code{getline} - -This command is used in several different ways, and should @emph{not} be -used by beginners. It is covered here because this is the chapter on input. +The @code{getline} command is used in several different ways and should +@emph{not} be used by beginners. The examples that follow the explanation of the @code{getline} command include material that has not been covered yet. Therefore, come back and study the @code{getline} command @emph{after} you have reviewed the -rest of this @value{DOCUMENT} and have a good knowledge of how @code{awk} works. +rest of this @value{DOCUMENT} and have a good knowledge of how @command{awk} works. -@vindex ERRNO -@cindex differences between @code{gawk} and @code{awk} +@cindex @code{ERRNO} variable +@cindex differences between @command{gawk} and @command{awk} @cindex @code{getline}, return values -@code{getline} returns one if it finds a record, and zero if the end of the -file is encountered. If there is some error in getting a record, such -as a file that cannot be opened, then @code{getline} returns @minus{}1. -In this case, @code{gawk} sets the variable @code{ERRNO} to a string -describing the error that occurred. +The @code{getline} command returns one if it finds a record and zero if +the end of the file is encountered. If there is some error in getting +a record, such as a file that cannot be opened, then @code{getline} +returns @minus{}1. In this case, @command{gawk} sets the variable +@code{ERRNO} to a string describing the error that occurred. In the following examples, @var{command} stands for a string value that represents a shell command. -@node Plain Getline, Getline/Variable, Getline Intro, Getline +@menu +* Plain Getline:: Using @code{getline} with no arguments. +* Getline/Variable:: Using @code{getline} into a variable. +* Getline/File:: Using @code{getline} from a file. +* Getline/Variable/File:: Using @code{getline} into a variable from a + file. +* Getline/Pipe:: Using @code{getline} from a pipe. +* Getline/Variable/Pipe:: Using @code{getline} into a variable from a + pipe. +* Getline/Coprocess:: Using @code{getline} from a coprocess. +* Getline/Variable/Coprocess:: Using @code{getline} into a variable from a + coprocess. +* Getline Notes:: Important things to know about @code{getline}. +* Getline Summary:: Summary of @code{getline} Variants. +@end menu + +@node Plain Getline, Getline/Variable, Getline, Getline @subsection Using @code{getline} with No Arguments The @code{getline} command can be used without arguments to read input from the current input file. All it does in this case is read the next input record and split it up into fields. This is useful if you've -finished processing the current record, but you want to do some special +finished processing the current record, but want to do some special processing @emph{right now} on the next record. Here's an example: @example -@group -awk '@{ +@{ if ((t = index($0, "/*")) != 0) @{ - # value will be "" if t is 1 + # value of `tmp' will be "" if t is 1 tmp = substr($0, 1, t - 1) u = index(substr($0, t + 2), "*/") while (u == 0) @{ @@ -4215,58 +5016,63 @@ awk '@{ t = -1 u = index($0, "*/") @} -@end group -@group # substr expression will be "" if */ # occurred at end of line - $0 = tmp substr($0, t + u + 3) + $0 = tmp substr($0, u + 2) @} print $0 -@}' -@end group +@} @end example -This @code{awk} program deletes all C-style comments, @samp{/* @dots{} -*/}, from the input. By replacing the @samp{print $0} with other +This @command{awk} program deletes all C-style comments (@samp{/* @dots{} +*/}) from the input. By replacing the @samp{print $0} with other statements, you could perform more complicated processing on the -decommented input, like searching for matches of a regular -expression. This program has a subtle problem---it does not work if one -comment ends and another begins on the same line. +decommented input, such as searching for matches of a regular +expression. (This program has a subtle problem---it does not work if one +comment ends and another begins on the same line.) @ignore Exercise, write a program that does handle multiple comments on the line. @end ignore -This form of the @code{getline} command sets @code{NF} (the number of -fields; @pxref{Fields, ,Examining Fields}), @code{NR} (the number of -records read so far; @pxref{Records, ,How Input is Split into Records}), -@code{FNR} (the number of records read from this input file), and the -value of @code{$0}. +This form of the @code{getline} command sets @code{NF}, +@code{NR}, @code{FNR}, and the value of @code{$0}. -@cindex dark corner -@strong{Note:} the new value of @code{$0} is used in testing +@strong{Note:} The new value of @code{$0} is used to test the patterns of any subsequent rules. The original value -of @code{$0} that triggered the rule which executed @code{getline} -is lost (d.c.). +of @code{$0} that triggered the rule that executed @code{getline} +is lost. By contrast, the @code{next} statement reads a new record but immediately begins processing it normally, starting with the first rule in the program. @xref{Next Statement, ,The @code{next} Statement}. @node Getline/Variable, Getline/File, Plain Getline, Getline -@subsection Using @code{getline} Into a Variable +@subsection Using @code{getline} into a Variable You can use @samp{getline @var{var}} to read the next record from -@code{awk}'s input into the variable @var{var}. No other processing is +@command{awk}'s input into the variable @var{var}. No other processing is done. - -For example, suppose the next line is a comment, or a special string, -and you want to read it, without triggering +For example, suppose the next line is a comment or a special string, +and you want to read it without triggering any rules. This form of @code{getline} allows you to read that line and store it in a variable so that the main -read-a-line-and-check-each-rule loop of @code{awk} never sees it. +read-a-line-and-check-each-rule loop of @command{awk} never sees it. +The following example swaps every two lines of input. +The program is as follows: + +@example +@{ + if ((getline tmp) > 0) @{ + print tmp + print $0 + @} else + print $0 +@} +@end example -The following example swaps every two lines of input. For example, given: +@noindent +It takes the following list: @example wan @@ -4276,7 +5082,7 @@ phore @end example @noindent -it outputs: +and produces these results: @example tew @@ -4285,21 +5091,6 @@ phore free @end example -@noindent -Here's the program: - -@example -@group -awk '@{ - if ((getline tmp) > 0) @{ - print tmp - print $0 - @} else - print $0 -@}' -@end group -@end example - The @code{getline} command used in this way sets only the variables @code{NR} and @code{FNR} (and of course, @var{var}). The record is not split into fields, so the values of the fields (including @code{$0}) and @@ -4310,80 +5101,66 @@ the value of @code{NF} do not change. @cindex input redirection @cindex redirection of input -Use @samp{getline < @var{file}} to read -the next record from the file -@var{file}. Here @var{file} is a string-valued expression that -specifies the file name. @samp{< @var{file}} is called a @dfn{redirection} -since it directs input to come from a different place. - +@cindex @code{<} I/O operator +Use @samp{getline < @var{file}} to read the next record from @var{file}. +Here @var{file} is a string-valued expression that +specifies the @value{FN}. @samp{< @var{file}} is called a @dfn{redirection} +because it directs input to come from a different place. For example, the following program reads its input record from the file @file{secondary.input} when it encounters a first field with a value equal to 10 in the current input -file. +file: @example -@group -awk '@{ +@{ if ($1 == 10) @{ getline < "secondary.input" print @} else print -@}' -@end group +@} @end example -Since the main input stream is not used, the values of @code{NR} and -@code{FNR} are not changed. But the record read is split into fields in -the normal manner, so the values of @code{$0} and other fields are -changed. So is the value of @code{NF}. +Because the main input stream is not used, the values of @code{NR} and +@code{FNR} are not changed. However, the record it reads is split into fields in +the normal manner, so the values of @code{$0} and the other fields are +changed, resulting in a new value of @code{NF}. @c Thanks to Paul Eggert for initial wording here According to POSIX, @samp{getline < @var{expression}} is ambiguous if @var{expression} contains unparenthesized operators other than @samp{$}; for example, @samp{getline < dir "/" file} is ambiguous -because the concatenation operator is not parenthesized, and you should +because the concatenation operator is not parenthesized. You should write it as @samp{getline < (dir "/" file)} if you want your program -to be portable to other @code{awk} implementations. +to be portable to other @command{awk} implementations. +(It happens that @command{gawk} gets it right, but you should not +rely on this. Parentheses make it easier to read.) @node Getline/Variable/File, Getline/Pipe, Getline/File, Getline -@subsection Using @code{getline} Into a Variable from a File +@subsection Using @code{getline} into a Variable from a File Use @samp{getline @var{var} < @var{file}} to read input -the file -@var{file} and put it in the variable @var{var}. As above, @var{file} +from the file +@var{file}, and put it in the variable @var{var}. As above, @var{file} is a string-valued expression that specifies the file from which to read. In this version of @code{getline}, none of the built-in variables are -changed, and the record is not split into fields. The only variable +changed and the record is not split into fields. The only variable changed is @var{var}. - -@ifinfo -@c Thanks to Paul Eggert for initial wording here -According to POSIX, @samp{getline @var{var} < @var{expression}} is ambiguous if -@var{expression} contains unparenthesized operators other than -@samp{$}; for example, @samp{getline < dir "/" file} is ambiguous -because the concatenation operator is not parenthesized, and you should -write it as @samp{getline < (dir "/" file)} if you want your program -to be portable to other @code{awk} implementations. -@end ifinfo - For example, the following program copies all the input files to the output, except for records that say @w{@samp{@@include @var{filename}}}. Such a record is replaced by the contents of the file -@var{filename}. +@var{filename}: @example -@group -awk '@{ +@{ if (NF == 2 && $1 == "@@include") @{ while ((getline line < $2) > 0) print line close($2) @} else print -@}' -@end group +@} @end example Note here how the name of the extra input file is not built into @@ -4393,11 +5170,11 @@ the @samp{@@include} line. The @code{close} function is called to ensure that if two identical @samp{@@include} lines appear in the input, the entire specified file is included twice. -@xref{Close Files And Pipes, ,Closing Input and Output Files and Pipes}. +@xref{Close Files And Pipes, ,Closing Input and Output Redirections}. One deficiency of this program is that it does not process nested @samp{@@include} statements -(@samp{@@include} statements in included files) +(i.e., @samp{@@include} statements in included files) the way a true macro preprocessor would. @xref{Igawk Program, ,An Easy Way to Use Library Functions}, for a program that does handle nested @samp{@@include} statements. @@ -4405,21 +5182,20 @@ that does handle nested @samp{@@include} statements. @node Getline/Pipe, Getline/Variable/Pipe, Getline/Variable/File, Getline @subsection Using @code{getline} from a Pipe +@cindex @code{|} I/O operator @cindex input pipeline @cindex pipeline, input -You can pipe the output of a command into @code{getline}, using +The output of a command can also be piped into @code{getline}, using @samp{@var{command} | getline}. In this case, the string @var{command} is run as a shell command and its output -is piped into @code{awk} to be used as input. This form of @code{getline} +is piped into @command{awk} to be used as input. This form of @code{getline} reads one record at a time from the pipe. - For example, the following program copies its input to its output, except for lines that begin with @samp{@@execute}, which are replaced by the output produced by running the rest of the line as a shell command: @example -@group -awk '@{ +@{ if ($1 == "@@execute") @{ tmp = substr($0, 10) while ((tmp | getline) > 0) @@ -4427,35 +5203,35 @@ awk '@{ close(tmp) @} else print -@}' -@end group +@} @end example @noindent The @code{close} function is called to ensure that if two identical @samp{@@execute} lines appear in the input, the command is run for each one. -@xref{Close Files And Pipes, ,Closing Input and Output Files and Pipes}. +@ifnottex +@xref{Close Files And Pipes, ,Closing Input and Output Redirections}. +@end ifnottex @c Exercise!! @c This example is unrealistic, since you could just use system - Given the input: @example -@group foo bar baz @@execute who bletch -@end group @end example @noindent the program might produce: +@cindex Robbins, Bill +@cindex Robbins, Miriam +@cindex Robbins, Arnold @example -@group foo bar baz @@ -4463,13 +5239,12 @@ arnold ttyv0 Jul 13 14:22 miriam ttyp0 Jul 13 14:23 (murphy:0) bill ttyp1 Jul 13 14:23 (murphy:0) bletch -@end group @end example @noindent -Notice that this program ran the command @code{who} and printed the result. +Notice that this program ran the command @command{who} and printed the result. (If you try this program yourself, you will of course get different results, -showing you who is logged in on your system.) +depending upon who is logged in on your system.) This variation of @code{getline} splits the record into fields, sets the value of @code{NF} and recomputes the value of @code{$0}. The values of @@ -4478,112 +5253,190 @@ value of @code{NF} and recomputes the value of @code{$0}. The values of @c Thanks to Paul Eggert for initial wording here According to POSIX, @samp{@var{expression} | getline} is ambiguous if @var{expression} contains unparenthesized operators other than -@samp{$}; for example, @samp{"echo " "date" | getline} is ambiguous -because the concatenation operator is not parenthesized, and you should -write it as @samp{("echo " "date") | getline} if you want your program -to be portable to other @code{awk} implementations. -(It happens that @code{gawk} gets it right, but you should not -rely on this. Parentheses make it easier to read, anyway.) +@samp{$}---for example, @samp{@w{"echo "} "date" | getline} is ambiguous +because the concatenation operator is not parenthesized. You should +write it as @samp{(@w{"echo "} "date") | getline} if you want your program +to be portable to other @command{awk} implementations. +@ifinfo +(It happens that @command{gawk} gets it right, but you should not +rely on this. Parentheses make it easier to read, anyway.) +@end ifinfo -@node Getline/Variable/Pipe, Getline Summary, Getline/Pipe, Getline -@subsection Using @code{getline} Into a Variable from a Pipe +@node Getline/Variable/Pipe, Getline/Coprocess, Getline/Pipe, Getline +@subsection Using @code{getline} into a Variable from a Pipe When you use @samp{@var{command} | getline @var{var}}, the -output of the command @var{command} is sent through a pipe to +output of @var{command} is sent through a pipe to @code{getline} and into the variable @var{var}. For example, the following program reads the current date and time into the variable -@code{current_time}, using the @code{date} utility, and then -prints it. +@code{current_time}, using the @command{date} utility, and then +prints it: @example -@group -awk 'BEGIN @{ +BEGIN @{ "date" | getline current_time close("date") print "Report printed on " current_time -@}' -@end group +@} @end example In this version of @code{getline}, none of the built-in variables are -changed, and the record is not split into fields. +changed and the record is not split into fields. @ifinfo @c Thanks to Paul Eggert for initial wording here According to POSIX, @samp{@var{expression} | getline @var{var}} is ambiguous if @var{expression} contains unparenthesized operators other than -@samp{$}; for example, @samp{"echo " "date" | getline @var{var}} is ambiguous -because the concatenation operator is not parenthesized, and you should -write it as @samp{("echo " "date") | getline @var{var}} if you want your -program to be portable to other @code{awk} implementations. -(It happens that @code{gawk} gets it right, but you should not -rely on this. Parentheses make it easier to read, anyway.) +@samp{$}; for example, @samp{@w{"echo "} "date" | getline @var{var}} is ambiguous +because the concatenation operator is not parenthesized. You should +write it as @samp{(@w{"echo "} "date") | getline @var{var}} if you want your +program to be portable to other @command{awk} implementations. +(It happens that @command{gawk} gets it right, but you should not +rely on this. Parentheses make it easier to read, anyway.) @end ifinfo -@node Getline Summary, , Getline/Variable/Pipe, Getline -@subsection Summary of @code{getline} Variants +@node Getline/Coprocess, Getline/Variable/Coprocess, Getline/Variable/Pipe, Getline +@subsection Using @code{getline} from a Coprocess +@cindex coprocess +@cindex @code{|&} I/O operator +@cindex differences between @command{gawk} and @command{awk} + +Input into @code{getline} from a pipe is a one-way operation. +The command that is started with @samp{@var{command} | getline} only +sends data @emph{to} your @command{awk} program. + +On occasion, you might want to send data to another program +for processing and then read the results back. +@command{gawk} allows you start a @dfn{coprocess}, with which two-way +communications are possible. This is done with the @samp{|&} +operator. +Typically, you write data to the coprocess first, and then +read results back, as shown in the following: -With all the forms of @code{getline}, even though @code{$0} and @code{NF}, -may be updated, the record will not be tested against all the patterns -in the @code{awk} program, in the way that would happen if the record -were read normally by the main processing loop of @code{awk}. However -the new record is tested against any subsequent rules. +@example +print "@var{some query}" |& "db_server" +"db_server" |& getline +@end example + +@noindent +which sends a query to @command{db_server} and then reads the results. + +The values of @code{NR} and +@code{FNR} are not changed, +because the main input stream is not used. +However, the record is split into fields in +the normal manner, thus changing the values of @code{$0}, the other fields, +and of @code{NF}. + +Coprocesses are an advanced feature. They are discussed here only because +this is the @value{SECTION} on @code{getline}. +@xref{Two-way I/O, ,Two-Way Communications with Another Process}, +where coprocesses are discussed in more detail. + +@node Getline/Variable/Coprocess, Getline Notes, Getline/Coprocess, Getline +@subsection Using @code{getline} into a Variable from a Coprocess + +When you use @samp{@var{command} |& getline @var{var}}, the output from +the coprocess @var{command} is sent through a two-way pipe to @code{getline} +and into the variable @var{var}. + +In this version of @code{getline}, none of the built-in variables are +changed and the record is not split into fields. The only variable +changed is @var{var}. + +@ifinfo +Coprocesses are an advanced feature. They are discussed here only because +this is the @value{SECTION} on @code{getline}. +@xref{Two-way I/O, ,Two-Way Communications with Another Process}, +where coprocesses are discussed in more detail. +@end ifinfo + +@node Getline Notes, Getline Summary, Getline/Variable/Coprocess, Getline +@subsection Points About @code{getline} to Remember +Here are some miscellaneous points about @code{getline} that +you should bear in mind: + +@itemize @bullet +@item +When @code{getline} changes the value of @code{$0} and @code{NF}, +@command{awk} does @emph{not} automatically jump to the start of the +program and start testing the new record against every pattern. +However, the new record is tested against any subsequent rules. -@cindex differences between @code{gawk} and @code{awk} +@cindex differences between @command{gawk} and @command{awk} @cindex limitations @cindex implementation limits -Many @code{awk} implementations limit the number of pipelines an @code{awk} -program may have open to just one! In @code{gawk}, there is no such limit. -You can open as many pipelines as the underlying operating system will -permit. +@item +Many @command{awk} implementations limit the number of pipelines that an @command{awk} +program may have open to just one. In @command{gawk}, there is no such limit. +You can open as many pipelines (and coprocesses) as the underlying operating +system permits. -@vindex FILENAME +@cindex side effects +@cindex @code{FILENAME} variable @cindex dark corner @cindex @code{getline}, setting @code{FILENAME} @cindex @code{FILENAME}, being set by @code{getline} -An interesting side-effect occurs if you use @code{getline} (without a -redirection) inside a @code{BEGIN} rule. Since an unredirected @code{getline} -reads from the command line data files, the first @code{getline} command -causes @code{awk} to set the value of @code{FILENAME}. Normally, -@code{FILENAME} does not have a value inside @code{BEGIN} rules, since you -have not yet started to process the command line data files (d.c.). +@item +An interesting side effect occurs if you use @code{getline} without a +redirection inside a @code{BEGIN} rule. Because an unredirected @code{getline} +reads from the command-line @value{DF}s, the first @code{getline} command +causes @command{awk} to set the value of @code{FILENAME}. Normally, +@code{FILENAME} does not have a value inside @code{BEGIN} rules, because you +have not yet started to process the command-line @value{DF}s. +@value{DARKCORNER} (@xref{BEGIN/END, , The @code{BEGIN} and @code{END} Special Patterns}, -also @pxref{Auto-set, , Built-in Variables that Convey Information}.) +also @pxref{Auto-set, ,Built-in Variables That Convey Information}.) +@end itemize + +@node Getline Summary, , Getline Notes, Getline +@subsection Summary of @code{getline} Variants -The following table summarizes the six variants of @code{getline}, +The following table summarizes the eight variants of @code{getline}, listing which built-in variables are set by each one. -@c @cartouche -@table @code -@item getline -sets @code{$0}, @code{NF}, @code{FNR}, and @code{NR}. +@multitable {@var{command} @code{|& getline} @var{var}} {1234567890123456789012345678901234567890} +@item @code{getline} @tab Sets @code{$0}, @code{NF}, @code{FNR} and @code{NR} -@item getline @var{var} -sets @var{var}, @code{FNR}, and @code{NR}. +@item @code{getline} @var{var} @tab Sets @var{var}, @code{FNR} and @code{NR} -@item getline < @var{file} -sets @code{$0}, and @code{NF}. +@item @code{getline <} @var{file} @tab Sets @code{$0} and @code{NF} -@item getline @var{var} < @var{file} -sets @var{var}. +@item @code{getline @var{var} < @var{file}} @tab Sets @var{var} -@item @var{command} | getline -sets @code{$0}, and @code{NF}. +@item @var{command} @code{| getline} @tab Sets @code{$0} and @code{NF} -@item @var{command} | getline @var{var} -sets @var{var}. -@end table -@c @end cartouche +@item @var{command} @code{| getline} @var{var} @tab Sets @var{var} + +@item @var{command} @code{|& getline} @tab Sets @code{$0} and @code{NF} +(this is a @command{gawk} extension) + +@item @var{command} @code{|& getline} @var{var} @tab Sets @var{var} +(this is a @command{gawk} extension) +@end multitable @node Printing, Expressions, Reading Files, Top @chapter Printing Output @cindex printing @cindex output -One of the most common actions is to @dfn{print}, or output, -some or all of the input. You use the @code{print} statement -for simple output. You use the @code{printf} statement -for fancier formatting. Both are described in this chapter. +One of the most common programming actions is to @dfn{print} or output, +some or all of the input. Use the @code{print} statement +for simple output, and the @code{printf} statement +for fancier formatting. +The @code{print} statement is not limited when +computing @emph{which} values to print. However, with two exceptions, +you cannot specify @emph{how} to print them---how many +columns, whether to use exponential notation or not, and so on. +(For the exceptions, @pxref{Output Separators}, and +@ref{OFMT, ,Controlling Numeric Output with @code{print}}.) +For that, you need the @code{printf} statement +(@pxref{Printf, ,Using @code{printf} Statements for Fancier Printing}). + +Besides basic and formatted printing, this @value{CHAPTER} +also covers I/O redirections to files and pipes, introduces +the special @value{FN}s that @command{gawk} processes internally, +and discusses the @code{close} built-in function. @menu * Print:: The @code{print} statement. @@ -4593,8 +5446,8 @@ for fancier formatting. Both are described in this chapter. * Printf:: The @code{printf} statement. * Redirection:: How to redirect output to multiple files and pipes. -* Special Files:: File name interpretation in @code{gawk}. - @code{gawk} allows access to inherited file +* Special Files:: File name interpretation in @command{gawk}. + @command{gawk} allows access to inherited file descriptors. * Close Files And Pipes:: Closing Input and Output Files and Pipes. @end menu @@ -4603,8 +5456,8 @@ for fancier formatting. Both are described in this chapter. @section The @code{print} Statement @cindex @code{print} statement -The @code{print} statement does output with simple, standardized -formatting. You specify only the strings or numbers to be printed, in a +The @code{print} statement is used to produce output with simple, standardized +formatting. Specify only the strings or numbers to print, in a list separated by commas. They are output, separated by single spaces, followed by a newline. The statement looks like this: @@ -4613,67 +5466,53 @@ print @var{item1}, @var{item2}, @dots{} @end example @noindent -The entire list of items may optionally be enclosed in parentheses. The +The entire list of items may be optionally enclosed in parentheses. The parentheses are necessary if any of the item expressions uses the @samp{>} relational operator; otherwise it could be confused with a redirection (@pxref{Redirection, ,Redirecting Output of @code{print} and @code{printf}}). -The items to be printed can be constant strings or numbers, fields of the -current record (such as @code{$1}), variables, or any @code{awk} -expressions. -Numeric values are converted to strings, and then printed. - -The @code{print} statement is completely general for -computing @emph{what} values to print. However, with two exceptions, -you cannot specify @emph{how} to print them---how many -columns, whether to use exponential notation or not, and so on. -(For the exceptions, @pxref{Output Separators}, and -@ref{OFMT, ,Controlling Numeric Output with @code{print}}.) -For that, you need the @code{printf} statement -(@pxref{Printf, ,Using @code{printf} Statements for Fancier Printing}). +The items to print can be constant strings or numbers, fields of the +current record (such as @code{$1}), variables, or any @command{awk} +expression. Numeric values are converted to strings and then printed. The simple statement @samp{print} with no items is equivalent to @samp{print $0}: it prints the entire current record. To print a blank line, use @samp{print ""}, where @code{""} is the empty string. - -To print a fixed piece of text, use a string constant such as -@w{@code{"Don't Panic"}} as one item. If you forget to use the -double-quote characters, your text will be taken as an @code{awk} -expression, and you will probably get an error. Keep in mind that a +To print a fixed piece of text, use a string constant, such as +@w{@code{"Don't Panic"}}, as one item. If you forget to use the +double quote characters, your text is taken as an @command{awk} +expression and you will probably get an error. Keep in mind that a space is printed between any two items. -Each @code{print} statement makes at least one line of output. But it -isn't limited to one line. If an item value is a string that contains a -newline, the newline is output along with the rest of the string. A -single @code{print} can make any number of lines this way. - @node Print Examples, Output Separators, Print, Printing @section Examples of @code{print} Statements -Here is an example of printing a string that contains embedded newlines +Each @code{print} statement makes at least one line of output. However, it +isn't limited to only one line. If an item value is a string that contains a +newline, the newline is output along with the rest of the string. A +single @code{print} statement can make any number of lines this way. + +The following is an example of printing a string that contains embedded newlines (the @samp{\n} is an escape sequence, used to represent the newline character; @pxref{Escape Sequences}): @example -@group $ awk 'BEGIN @{ print "line one\nline two\nline three" @}' @print{} line one @print{} line two @print{} line three -@end group @end example -Here is an example that prints the first two fields of each input record, -with a space between them: +The next example, which is run on the @file{inventory-shipped} file, +prints the first two fields of each input record, with a space between +them: @example -@group $ awk '@{ print $1, $2 @}' inventory-shipped @print{} Jan 13 @print{} Feb 15 @print{} Mar 15 @dots{} -@end group @end example @cindex common mistakes @@ -4682,26 +5521,24 @@ $ awk '@{ print $1, $2 @}' inventory-shipped A common mistake in using the @code{print} statement is to omit the comma between two items. This often has the effect of making the items run together in the output, with no space. The reason for this is that -juxtaposing two string expressions in @code{awk} means to concatenate +juxtaposing two string expressions in @command{awk} means to concatenate them. Here is the same program, without the comma: @example -@group $ awk '@{ print $1 $2 @}' inventory-shipped @print{} Jan13 @print{} Feb15 @print{} Mar15 @dots{} -@end group @end example -To someone unfamiliar with the file @file{inventory-shipped}, neither +To someone unfamiliar with the @file{inventory-shipped} file, neither example's output makes much sense. A heading line at the beginning would make it clearer. Let's add some headings to our table of months (@code{$1}) and green crates shipped (@code{$2}). We do this using the @code{BEGIN} pattern (@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}) -to force the headings to be printed only once: +so that the headings are only printed once: @example awk 'BEGIN @{ print "Month Crates" @@ -4710,77 +5547,79 @@ awk 'BEGIN @{ print "Month Crates" @end example @noindent -Did you already guess what happens? When run, the program prints -the following: +When run, the program prints the following: @example -@group Month Crates ----- ------ Jan 13 Feb 15 Mar 15 @dots{} -@end group @end example @noindent -The headings and the table data don't line up! We can fix this by printing -some spaces between the two fields: +The only problem, however, is that the headings and the table data +don't line up! We can fix this by printing some spaces between the +two fields: @example +@group awk 'BEGIN @{ print "Month Crates" print "----- ------" @} @{ print $1, " ", $2 @}' inventory-shipped +@end group @end example -You can imagine that this way of lining up columns can get pretty -complicated when you have many columns to fix. Counting spaces for two -or three columns can be simple, but more than this and you can get -lost quite easily. This is why the @code{printf} statement was +Lining up columns this way can get pretty +complicated when there are many columns to fix. Counting spaces for two +or three columns is simple, but any more than this can take up +a lot of time. This is why the @code{printf} statement was created (@pxref{Printf, ,Using @code{printf} Statements for Fancier Printing}); one of its specialties is lining up columns of data. @cindex line continuation -As a side point, -you can continue either a @code{print} or @code{printf} statement simply -by putting a newline after any comma -(@pxref{Statements/Lines, ,@code{awk} Statements Versus Lines}). +@strong{Note:} You can continue either a @code{print} or +@code{printf} statement simply by putting a newline after any comma +(@pxref{Statements/Lines, ,@command{awk} Statements Versus Lines}). @node Output Separators, OFMT, Print Examples, Printing @section Output Separators @cindex output field separator, @code{OFS} @cindex output record separator, @code{ORS} -@vindex OFS -@vindex ORS +@cindex @code{OFS} variable +@cindex @code{ORS} variable As mentioned previously, a @code{print} statement contains a list -of items, separated by commas. In the output, the items are normally -separated by single spaces. This need not be the case; a -single space is only the default. You can specify any string of -characters to use as the @dfn{output field separator} by setting the +of items separated by commas. In the output, the items are normally +separated by single spaces. However, this doesn't need to be the case; +a single space is only the default. Any string of +characters may be used as the @dfn{output field separator} by setting the built-in variable @code{OFS}. The initial value of this variable -is the string @w{@code{" "}}, that is, a single space. +is the string @w{@code{" "}}---that is, a single space. The output from an entire @code{print} statement is called an @dfn{output record}. Each @code{print} statement outputs one output -record and then outputs a string called the @dfn{output record separator}. -The built-in variable @code{ORS} specifies this string. The initial -value of @code{ORS} is the string @code{"\n"}, i.e.@: a newline -character; thus, normally each @code{print} statement makes a separate line. +record, and then outputs a string called the @dfn{output record separator} +(or @code{ORS}). The initial +value of @code{ORS} is the string @code{"\n"}; i.e., a newline +character. Thus, each @code{print} statement normally makes a separate line. -You can change how output fields and records are separated by assigning -new values to the variables @code{OFS} and/or @code{ORS}. The usual +In order to change how output fields and records are separated, assign +new values to the variables @code{OFS} and @code{ORS}. The usual place to do this is in the @code{BEGIN} rule (@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}), so -that it happens before any input is processed. You may also do this -with assignments on the command line, before the names of your input -files, or using the @samp{-v} command line option -(@pxref{Options, ,Command Line Options}). +that it happens before any input is processed. It can also be done +with assignments on the command line, before the names of the input +files, or using the @option{-v} command-line option +(@pxref{Options, ,Command-Line Options}). +The following example prints the first and second fields of each input +record, separated by a semicolon, with a blank line added after each +newline: @ignore Exercise, -Rewrite the +Rewrite the @example awk 'BEGIN @{ print "Month Crates" print "----- ------" @} @@ -4789,12 +5628,7 @@ awk 'BEGIN @{ print "Month Crates" program by using a new value of @code{OFS}. @end ignore -The following example prints the first and second fields of each input -record separated by a semicolon, with a blank line added after each -line: - @example -@group $ awk 'BEGIN @{ OFS = ";"; ORS = "\n\n" @} > @{ print $1, $2 @}' BBS-list @print{} aardvark;555-5553 @@ -4803,24 +5637,22 @@ $ awk 'BEGIN @{ OFS = ";"; ORS = "\n\n" @} @print{} @print{} barfly;555-7685 @dots{} -@end group @end example -If the value of @code{ORS} does not contain a newline, all your output -will be run together on a single line, unless you output newlines some -other way. +If the value of @code{ORS} does not contain a newline, the program's output +is run together on a single line. @node OFMT, Printf, Output Separators, Printing @section Controlling Numeric Output with @code{print} -@vindex OFMT +@cindex @code{OFMT} variable @cindex numeric output format @cindex format, numeric output @cindex output format specifier, @code{OFMT} -When you use the @code{print} statement to print numeric values, -@code{awk} internally converts the number to a string of characters, -and prints that string. @code{awk} uses the @code{sprintf} function +When the @code{print} statement is used to print numeric values, +@command{awk} internally converts the number to a string of characters +and prints that string. @command{awk} uses the @code{sprintf} function to do this conversion -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). +(@pxref{String Functions, ,String Manipulation Functions}). For now, it suffices to say that the @code{sprintf} function accepts a @dfn{format specification} that tells it how to format numbers (or strings), and that there are a number of different ways in which @@ -4832,39 +5664,39 @@ The built-in variable @code{OFMT} contains the default format specification that @code{print} uses with @code{sprintf} when it wants to convert a number to a string for printing. The default value of @code{OFMT} is @code{"%.6g"}. -By supplying different format specifications -as the value of @code{OFMT}, you can change how @code{print} will print -your numbers. As a brief example: +The way @code{print} prints numbers can be changed +by supplying different format specifications +as the value of @code{OFMT}, as shown in the following example: @example -@group $ awk 'BEGIN @{ > OFMT = "%.0f" # print numbers as integers (rounds) -> print 17.23 @}' -@print{} 17 -@end group +> print 17.23, 17.54 @}' +@print{} 17 18 @end example @noindent @cindex dark corner -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} -According to the POSIX standard, @code{awk}'s behavior will be undefined -if @code{OFMT} contains anything but a floating point conversion specification -(d.c.). +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} +According to the POSIX standard, @command{awk}'s behavior is undefined +if @code{OFMT} contains anything but a floating-point conversion specification. +@value{DARKCORNER} @node Printf, Redirection, OFMT, Printing @section Using @code{printf} Statements for Fancier Printing @cindex formatted output @cindex output, formatted +@cindex @code{printf} statement -If you want more precise control over the output format than -@code{print} gives you, use @code{printf}. With @code{printf} you can -specify the width to use for each item, and you can specify various -formatting choices for numbers (such as what radix to use, whether to +For more precise control over the output format than what is +normally provided by @code{print}, use @code{printf}. +@code{printf} can be used to +specify the width to use for each item, as well as various +formatting choices for numbers (such as what output base to use, whether to print an exponent, whether to print a sign, and how many digits to print -after the decimal point). You do this by supplying a string, called -the @dfn{format string}, which controls how and where to print the other +after the decimal point). This is done by supplying a string, called +the @dfn{format string}, that controls how and where to print the other arguments. @menu @@ -4878,7 +5710,7 @@ arguments. @subsection Introduction to the @code{printf} Statement @cindex @code{printf} statement, syntax of -The @code{printf} statement looks like this: +A simple @code{printf} statement looks like this: @example printf @var{format}, @var{item1}, @var{item2}, @dots{} @@ -4887,130 +5719,125 @@ printf @var{format}, @var{item1}, @var{item2}, @dots{} @noindent The entire list of arguments may optionally be enclosed in parentheses. The parentheses are necessary if any of the item expressions use the @samp{>} -relational operator; otherwise it could be confused with a redirection +relational operator; otherwise it can be confused with a redirection (@pxref{Redirection, ,Redirecting Output of @code{print} and @code{printf}}). @cindex format string The difference between @code{printf} and @code{print} is the @var{format} argument. This is an expression whose value is taken as a string; it -specifies how to output each of the other arguments. It is called -the @dfn{format string}. +specifies how to output each of the other arguments. It is called the +@dfn{format string}. -The format string is very similar to that in the ANSI C library function -@code{printf}. Most of @var{format} is text to be output verbatim. -Scattered among this text are @dfn{format specifiers}, one per item. -Each format specifier says to output the next item in the argument list +The format string is very similar to that in the ISO C library function +@code{printf}. Most of @var{format} is text to output verbatim. +Scattered among this text are @dfn{format specifiers}---one per item. +Each format specifier says to output the next item in the argument list at that place in the format. -The @code{printf} statement does not automatically append a newline to its -output. It outputs only what the format string specifies. So if you want -a newline, you must include one in the format string. The output separator -variables @code{OFS} and @code{ORS} have no effect on @code{printf} -statements. For example: +The @code{printf} statement does not automatically append a newline +to its output. It outputs only what the format string specifies. +So if a newline is needed, you must include one in the format string. +The output separator variables @code{OFS} and @code{ORS} have no effect +on @code{printf} statements. For example: @example -@group -BEGIN @{ - ORS = "\nOUCH!\n"; OFS = "!" - msg = "Don't Panic!"; printf "%s\n", msg -@} -@end group +$ awk 'BEGIN @{ +> ORS = "\nOUCH!\n"; OFS = "+" +> msg = "Dont Panic!" +> printf "%s\n", msg +> @}' +@print{} Dont Panic! @end example -This program still prints the familiar @samp{Don't Panic!} message. +@noindent +Here, neither the @samp{+} nor the @samp{OUCH} appear when +the message is printed. @node Control Letters, Format Modifiers, Basic Printf, Printf @subsection Format-Control Letters @cindex @code{printf}, format-control characters -@cindex format specifier - -A format specifier starts with the character @samp{%} and ends with a -@dfn{format-control letter}; it tells the @code{printf} statement how -to output one item. (If you actually want to output a @samp{%}, write -@samp{%%}.) The format-control letter specifies what kind of value to -print. The rest of the format specifier is made up of optional -@dfn{modifiers} which are parameters to use, such as the field width. +@cindex format specifier, @code{printf} -Here is a list of the format-control letters: +A format specifier starts with the character @samp{%} and ends with +a @dfn{format-control letter}---it tells the @code{printf} statement +how to output one item. The format-control letter specifies what @emph{kind} +of value to print. The rest of the format specifier is made up of +optional @dfn{modifiers} that control @emph{how} to print the value, such as +the field width. Here is a list of the format-control letters: @table @code -@item c -This prints a number as an ASCII character. Thus, @samp{printf "%c", -65} outputs the letter @samp{A}. The output for a string value is -the first character of the string. +@item %c +This prints a number as an ASCII character; thus, @samp{printf "%c", +65} outputs the letter @samp{A}. (The output for a string value is +the first character of the string.) -@item d -@itemx i -These are equivalent. They both print a decimal integer. -The @samp{%i} specification is for compatibility with ANSI C. +@item %d@r{,} %i +These are equivalent; they both print a decimal integer. +(The @samp{%i} specification is for compatibility with ISO C.) -@item e -@itemx E -This prints a number in scientific (exponential) notation. -For example, +@item %e@r{,} %E +These print a number in scientific (exponential) notation; +for example: @example printf "%4.3e\n", 1950 @end example @noindent -prints @samp{1.950e+03}, with a total of four significant figures of -which three follow the decimal point. The @samp{4.3} are modifiers, -discussed below. @samp{%E} uses @samp{E} instead of @samp{e} in the output. +prints @samp{1.950e+03}, with a total of four significant figures, three of +which follow the decimal point. +(The @samp{4.3} represents two modifiers, +discussed in the next @value{SUBSECTION}.) +@samp{%E} uses @samp{E} instead of @samp{e} in the output. -@item f -This prints a number in floating point notation. -For example, +@item %f +This prints a number in floating-point notation. +For example: @example printf "%4.3f", 1950 @end example @noindent -prints @samp{1950.000}, with a total of four significant figures of -which three follow the decimal point. The @samp{4.3} are modifiers, -discussed below. - -@item g -@itemx G -This prints a number in either scientific notation or floating point -notation, whichever uses fewer characters. If the result is printed in +prints @samp{1950.000}, with a total of four significant figures, three of +which follow the decimal point. +(The @samp{4.3} represents two modifiers, +discussed in the next @value{SUBSECTION}.) + +@item %g@r{,} %G +These print a number in either scientific notation or in floating-point +notation, whichever uses fewer characters; if the result is printed in scientific notation, @samp{%G} uses @samp{E} instead of @samp{e}. -@item o +@item %o This prints an unsigned octal integer. -(In octal, or base-eight notation, the digits run from @samp{0} to @samp{7}; -the decimal number eight is represented as @samp{10} in octal.) -@item s +@item %s This prints a string. -@item u -This prints an unsigned decimal number. -(This format is of marginal use, since all numbers in @code{awk} -are floating point. It is provided primarily for compatibility -with C.) - -@item x -@itemx X -This prints an unsigned hexadecimal integer. -(In hexadecimal, or base-16 notation, the digits are @samp{0} through @samp{9} -and @samp{a} through @samp{f}. The hexadecimal digit @samp{f} represents -the decimal number 15.) @samp{%X} uses the letters @samp{A} through @samp{F} +@item %u +This prints an unsigned decimal integer. +(This format is of marginal use, because all numbers in @command{awk} +are floating-point; it is provided primarily for compatibility with C.) + +@item %x@r{,} %X +These print an unsigned hexadecimal integer; +@samp{%X} uses the letters @samp{A} through @samp{F} instead of @samp{a} through @samp{f}. -@item % -This isn't really a format-control letter, but it does have a meaning -when used after a @samp{%}: the sequence @samp{%%} outputs one -@samp{%}. It does not consume an argument, and it ignores any -modifiers. +@item %% +This isn't a format-control letter but it does have meaning---the +sequence @samp{%%} outputs one @samp{%}; it does not consume an +argument and it ignores any modifiers. @end table @cindex dark corner +@strong{Note:} When using the integer format-control letters for values that are outside -the range of a C @code{long} integer, @code{gawk} will switch to the -@samp{%g} format specifier. Other versions of @code{awk} may print -invalid values, or do something else entirely (d.c.). +the range of a C @code{long} integer, @command{gawk} switches to the +@samp{%g} format specifier. Other versions of @command{awk} may print +invalid values or do something else entirely. +@value{DARKCORNER} @node Format Modifiers, Printf Examples, Control Letters, Printf @subsection Modifiers for @code{printf} Formats @@ -5018,18 +5845,46 @@ invalid values, or do something else entirely (d.c.). @cindex @code{printf}, modifiers @cindex modifiers (in format specifiers) A format specification can also include @dfn{modifiers} that can control -how much of the item's value is printed and how much space it gets. The -modifiers come between the @samp{%} and the format-control letter. -In the examples below, we use the bullet symbol ``@bullet{}'' to represent +how much of the item's value is printed, as well as how much space it gets. +The modifiers come between the @samp{%} and the format-control letter. +We will use the bullet symbol ``@bullet{}'' in the following examples to +represent spaces in the output. Here are the possible modifiers, in the order in which they may appear: @table @code +@cindex differences between @command{gawk} and @command{awk} +@cindex @code{printf}, positional specifier +@cindex positional specifier, @code{printf} +@item @var{N}$ +An integer constant followed by a @samp{$} is a @dfn{positional specifier}. +Normally, format specifications are applied to arguments in the order +given in the format string. With a positional specifier, the format +specification is applied to a specific argument, instead of what +would be the next argument in the list. Positional specifiers begin +counting with one: + +@example +printf "%s %s\n", "don't", "panic" +printf "%2$s %1$s\n", "panic", "don't" +@end example + +@noindent +prints the famous friendly message twice. + +At first glance, this feature doesn't seem to be of much use. +It is in fact a @command{gawk} extension, intended for use in translating +messages at runtime. +@xref{Printf Ordering, , Rearranging @code{printf} Arguments}, +which describes how and why to use positional specifiers. +For now, we will not use them. + @item - -The minus sign, used before the width modifier (see below), +The minus sign, used before the width modifier (see further on in +this table), says to left-justify -the argument within its specified width. Normally the argument -is printed right-justified in the specified width. Thus, +the argument within its specified width. Normally, the argument +is printed right-justified in the specified width. Thus: @example printf "%-4s", "foo" @@ -5039,36 +5894,38 @@ printf "%-4s", "foo" prints @samp{foo@bullet{}}. @item @var{space} -For numeric conversions, prefix positive values with a space, and +For numeric conversions, prefix positive values with a space and negative values with a minus sign. @item + -The plus sign, used before the width modifier (see below), +The plus sign, used before the width modifier (see further on in +this table), says to always supply a sign for numeric conversions, even if the data -to be formatted is positive. The @samp{+} overrides the space modifier. +to format is positive. The @samp{+} overrides the space modifier. @item # Use an ``alternate form'' for certain control letters. For @samp{%o}, supply a leading zero. -For @samp{%x}, and @samp{%X}, supply a leading @samp{0x} or @samp{0X} for -a non-zero result. -For @samp{%e}, @samp{%E}, and @samp{%f}, the result will always contain a +For @samp{%x} and @samp{%X}, supply a leading @samp{0x} or @samp{0X} for +a nonzero result. +For @samp{%e}, @samp{%E}, and @samp{%f}, the result always contains a decimal point. -For @samp{%g}, and @samp{%G}, trailing zeros are not removed from the result. +For @samp{%g} and @samp{%G}, trailing zeros are not removed from the result. @cindex dark corner @item 0 -A leading @samp{0} (zero) acts as a flag, that indicates output should be +A leading @samp{0} (zero) acts as a flag that indicates that output should be padded with zeros instead of spaces. -This applies even to non-numeric output formats (d.c.). +This applies even to non-numeric output formats. +@value{DARKCORNER} This flag only has an effect when the field width is wider than the -value to be printed. +value to print. @item @var{width} This is a number specifying the desired minimum width of a field. Inserting any -number between the @samp{%} sign and the format control character forces the -field to be expanded to this width. The default way to do this is to -pad with spaces on the left. For example, +number between the @samp{%} sign and the format-control character forces the +field to expand to this width. The default way to do this is to +pad with spaces on the left. For example: @example printf "%4s", "foo" @@ -5079,7 +5936,7 @@ prints @samp{@bullet{}foo}. The value of @var{width} is a minimum width, not a maximum. If the item value requires more than @var{width} characters, it can be as wide as -necessary. Thus, +necessary. Thus, the following: @example printf "%4s", "foobar" @@ -5092,14 +5949,25 @@ Preceding the @var{width} with a minus sign causes the output to be padded with spaces on the right, instead of on the left. @item .@var{prec} -This is a number that specifies the precision to use when printing. -For the @samp{e}, @samp{E}, and @samp{f} formats, this specifies the -number of digits you want printed to the right of the decimal point. -For the @samp{g}, and @samp{G} formats, it specifies the maximum number -of significant digits. For the @samp{d}, @samp{o}, @samp{i}, @samp{u}, -@samp{x}, and @samp{X} formats, it specifies the minimum number of -digits to print. For a string, it specifies the maximum number of -characters from the string that should be printed. Thus, +A period followed by an integer constant +specifies the precision to use when printing. +The meaning of the precision varies by control letter: + +@table @asis +@item @code{%e}, @code{%E}, @code{%f} +Number of digits to the right of the decimal point. + +@item @code{%g}, @code{%G} +Maximum number of significant digits. + +@item @code{%d}, @code{%i}, @code{%o}, @code{%u}, @code{%x}, @code{%X} +Minimum number of digits to print. + +@item @code{%s} +Maximum number of characters from the string that should print. +@end table + +Thus, the following: @example printf "%.4s", "foobar" @@ -5112,7 +5980,7 @@ prints @samp{foob}. The C library @code{printf}'s dynamic @var{width} and @var{prec} capability (for example, @code{"%*.*s"}) is supported. Instead of supplying explicit @var{width} and/or @var{prec} values in the format -string, you pass them in the argument list. For example: +string, they are passed in the argument list. For example: @example w = 5 @@ -5122,7 +5990,7 @@ printf "%*.*s\n", w, p, s @end example @noindent -is exactly equivalent to +is exactly equivalent to: @example s = "abcdefg" @@ -5131,8 +5999,7 @@ printf "%5.3s\n", s @noindent Both programs output @samp{@w{@bullet{}@bullet{}abc}}. - -Earlier versions of @code{awk} did not support this capability. +Earlier versions of @command{awk} did not support this capability. If you must use such a version, you may simulate this feature by using concatenation to build up the format string, like so: @@ -5144,35 +6011,40 @@ printf "%" w "." p "s\n", s @end example @noindent -This is not particularly easy to read, but it does work. - -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} -C programmers may be used to supplying additional @samp{l} and @samp{h} -flags in @code{printf} format strings. These are not valid in @code{awk}. -Most @code{awk} implementations silently ignore these flags. -If @samp{--lint} is provided on the command line -(@pxref{Options, ,Command Line Options}), -@code{gawk} will warn about their use. If @samp{--posix} is supplied, +This is not particularly easy to read but it does work. + +@cindex fatal errors +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} +@cindex lint checks +C programmers may be used to supplying additional +@samp{l}, @samp{L}, and @samp{h} +modifiers in @code{printf} format strings. These are not valid in @command{awk}. +Most @command{awk} implementations silently ignore these modifiers. +If @option{--lint} is provided on the command line +(@pxref{Options, ,Command-Line Options}), +@command{gawk} warns about their use. If @option{--posix} is supplied, their use is a fatal error. -@node Printf Examples, , Format Modifiers, Printf +@node Printf Examples, , Format Modifiers, Printf @subsection Examples Using @code{printf} -Here is how to use @code{printf} to make an aligned table: +The following is a simple example of +how to use @code{printf} to make an aligned table: @example awk '@{ printf "%-10s %s\n", $1, $2 @}' BBS-list @end example @noindent -prints the names of bulletin boards (@code{$1}) of the file -@file{BBS-list} as a string of 10 characters, left justified. It also -prints the phone numbers (@code{$2}) afterward on the line. This -produces an aligned two-column table of names and phone numbers: +This command +prints the names of the bulletin boards (@code{$1}) in the file +@file{BBS-list} as a string of 10 characters that are left-justified. It also +prints the phone numbers (@code{$2}) next on the line. This +produces an aligned two-column table of names and phone numbers, +as shown here: @example -@group $ awk '@{ printf "%-10s %s\n", $1, $2 @}' BBS-list @print{} aardvark 555-5553 @print{} alpo-net 555-3412 @@ -5185,66 +6057,59 @@ $ awk '@{ printf "%-10s %s\n", $1, $2 @}' BBS-list @print{} macfoo 555-6480 @print{} sdace 555-3430 @print{} sabafoo 555-2127 -@end group @end example -Did you notice that we did not specify that the phone numbers be printed -as numbers? They had to be printed as strings because the numbers are -separated by a dash. -If we had tried to print the phone numbers as numbers, all we would have -gotten would have been the first three digits, @samp{555}. +In this case, the phone numbers had to be printed as strings because +the numbers are separated by a dash. Printing the phone numbers as +numbers would have produced just the first three digits: @samp{555}. This would have been pretty confusing. -We did not specify a width for the phone numbers because they are the -last things on their lines. We don't need to put spaces after them. +It wasn't necessary to specify a width for the phone numbers because +they are last on their lines. They don't need to have spaces +after them. -We could make our table look even nicer by adding headings to the tops -of the columns. To do this, we use the @code{BEGIN} pattern +The table could be made to look even nicer by adding headings to the +tops of the columns. This is done using the @code{BEGIN} pattern (@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}) -to force the header to be printed only once, at the beginning of -the @code{awk} program: +so that the headers are only printed once, at the beginning of +the @command{awk} program: @example -@group awk 'BEGIN @{ print "Name Number" print "---- ------" @} @{ printf "%-10s %s\n", $1, $2 @}' BBS-list -@end group @end example -Did you notice that we mixed @code{print} and @code{printf} statements in -the above example? We could have used just @code{printf} statements to get -the same results: +The above example mixed @code{print} and @code{printf} statements in +the same program. Using just @code{printf} statements can produce the +same results: @example -@group awk 'BEGIN @{ printf "%-10s %s\n", "Name", "Number" printf "%-10s %s\n", "----", "------" @} @{ printf "%-10s %s\n", $1, $2 @}' BBS-list -@end group @end example @noindent -By printing each column heading with the same format specification -used for the elements of the column, we have made sure that the headings +Printing each column heading with the same format specification +used for the column elements ensures that the headings are aligned just like the columns. The fact that the same format specification is used three times can be emphasized by storing it in a variable, like this: @example -@group awk 'BEGIN @{ format = "%-10s %s\n" printf format, "Name", "Number" printf format, "----", "------" @} @{ printf format, $1, $2 @}' BBS-list -@end group @end example @c !!! exercise -See if you can use the @code{printf} statement to line up the headings and -table data for our @file{inventory-shipped} example covered earlier in the -section on the @code{print} statement +At this point, it would be a worthwhile exercise to use the +@code{printf} statement to line up the headings and table data for the +@file{inventory-shipped} example that was covered earlier in the @value{SECTION} +on the @code{print} statement (@pxref{Print, ,The @code{print} Statement}). @node Redirection, Special Files, Printf, Printing @@ -5252,82 +6117,84 @@ section on the @code{print} statement @cindex output redirection @cindex redirection of output -So far we have been dealing only with output that prints to the standard -output, usually your terminal. Both @code{print} and @code{printf} can +So far, the output from @code{print} and @code{printf} has gone +to the standard +output, usually the terminal. Both @code{print} and @code{printf} can also send their output to other places. This is called @dfn{redirection}. A redirection appears after the @code{print} or @code{printf} statement. -Redirections in @code{awk} are written just like redirections in shell -commands, except that they are written inside the @code{awk} program. +Redirections in @command{awk} are written just like redirections in shell +commands, except that they are written inside the @command{awk} program. -There are three forms of output redirection: output to a file, -output appended to a file, and output through a pipe to another -command. -They are all shown for -the @code{print} statement, but they work identically for @code{printf} -also. +There are four forms of output redirection: output to a file, output +appended to a file, output through a pipe to another command, and output +to a coprocess. They are all shown for the @code{print} statement, +but they work identically for @code{printf}: @table @code +@cindex @code{>} I/O operator @item print @var{items} > @var{output-file} -This type of redirection prints the items into the output file -@var{output-file}. The file name @var{output-file} can be any +This type of redirection prints the items into the output file named +@var{output-file}. The @value{FN} @var{output-file} can be any expression. Its value is changed to a string and then used as a -file name (@pxref{Expressions}). +@value{FN} (@pxref{Expressions}). When this type of redirection is used, the @var{output-file} is erased -before the first output is written to it. Subsequent writes -to the same @var{output-file} do not -erase @var{output-file}, but append to it. If @var{output-file} does -not exist, then it is created. - -For example, here is how an @code{awk} program can write a list of -BBS names to a file @file{name-list} and a list of phone numbers to a -file @file{phone-list}. Each output file contains one name or number -per line. +before the first output is written to it. Subsequent writes to the same +@var{output-file} do not erase @var{output-file}, but append to it. +(This is different from how you use redirections in shell scripts.) +If @var{output-file} does not exist, it is created. For example, here +is how an @command{awk} program can write a list of BBS names to one +file named @file{name-list}, and a list of phone numbers to another file +named @file{phone-list}: @example -@group $ awk '@{ print $2 > "phone-list" > print $1 > "name-list" @}' BBS-list -@end group -@group $ cat phone-list @print{} 555-5553 @print{} 555-3412 @dots{} -@end group -@group $ cat name-list @print{} aardvark @print{} alpo-net @dots{} -@end group @end example +@noindent +Each output file contains one name or number per line. + +@cindex @code{>>} I/O operator @item print @var{items} >> @var{output-file} This type of redirection prints the items into the pre-existing output file -@var{output-file}. The difference between this and the +named @var{output-file}. The difference between this and the single-@samp{>} redirection is that the old contents (if any) of -@var{output-file} are not erased. Instead, the @code{awk} output is +@var{output-file} are not erased. Instead, the @command{awk} output is appended to the file. If @var{output-file} does not exist, then it is created. +@cindex @code{|} I/O operator @cindex pipes for output @cindex output, piping @item print @var{items} | @var{command} It is also possible to send output to another program through a pipe -instead of into a -file. This type of redirection opens a pipe to @var{command} and writes -the values of @var{items} through this pipe, to another process created -to execute @var{command}. +instead of into a file. This type of redirection opens a pipe to +@var{command}, and writes the values of @var{items} through this pipe +to another process created to execute @var{command}. -The redirection argument @var{command} is actually an @code{awk} -expression. Its value is converted to a string, whose contents give the -shell command to be run. +The redirection argument @var{command} is actually an @command{awk} +expression. Its value is converted to a string whose contents give +the shell command to be run. For example, the following produces two +files, one unsorted list of BBS names, and one list sorted in reverse +alphabetical order: -For example, this produces two files, one unsorted list of BBS names -and one list sorted in reverse alphabetical order: +@ignore +10/2000: +This isn't the best style, since COMMAND is assigned for each +record. It's done to avoid overfull hboxes in TeX. Leave it +alone for now and let's hope no-one notices. +@end ignore @example awk '@{ print $1 > "names.unsorted" @@ -5335,12 +6202,12 @@ awk '@{ print $1 > "names.unsorted" print $1 | command @}' BBS-list @end example -Here the unsorted list is written with an ordinary redirection while -the sorted list is written by piping through the @code{sort} utility. +The unsorted list is written with an ordinary redirection, while +the sorted list is written by piping through the @command{sort} utility. -This example uses redirection to mail a message to a mailing +The next example uses redirection to mail a message to the mailing list @samp{bug-system}. This might be useful when trouble is encountered -in an @code{awk} script run periodically for system maintenance. +in an @command{awk} script run periodically for system maintenance: @example report = "mail bug-system" @@ -5351,42 +6218,121 @@ close(report) @end example The message is built using string concatenation and saved in the variable -@code{m}. It is then sent down the pipeline to the @code{mail} program. +@code{m}. It is then sent down the pipeline to the @command{mail} program. +(The parentheses group the items to concatenate---see +@ref{Concatenation, ,String Concatenation}.) -We call the @code{close} function here because it's a good idea to close +The @code{close} function is called here because it's a good idea to close the pipe as soon as all the intended output has been sent to it. -@xref{Close Files And Pipes, ,Closing Input and Output Files and Pipes}, -for more information -on this. This example also illustrates the use of a variable to represent -a @var{file} or @var{command}: it is not necessary to always +@xref{Close Files And Pipes, ,Closing Input and Output Redirections}, +for more information on this. + +This example also illustrates the use of a variable to represent +a @var{file} or @var{command}---it is not necessary to always use a string constant. Using a variable is generally a good idea, -since @code{awk} requires you to spell the string value identically +because @command{awk} requires that the string value be spelled identically every time. + +@cindex coprocess +@cindex @code{|&} I/O operator +@cindex differences between @command{gawk} and @command{awk} +@item print @var{items} |& @var{command} +This type of redirection prints the items to the input of @var{command}. +The difference between this and the +single-@samp{|} redirection is that the output from @var{command} +can be read with @code{getline}. +Thus @var{command} is a @dfn{coprocess}, that works together with, +but subsidiary to, the @command{awk} program. + +This feature is a @command{gawk} extension, and is not available in +POSIX @command{awk}. +@xref{Two-way I/O, ,Two-Way Communications with Another Process}, +for a more complete discussion. @end table -Redirecting output using @samp{>}, @samp{>>}, or @samp{|} asks the system -to open a file or pipe only if the particular @var{file} or @var{command} -you've specified has not already been written to by your program, or if -it has been closed since it was last written to. +Redirecting output using @samp{>}, @samp{>>}, @samp{|}, or @samp{|&} +asks the system to open a file, pipe, or coprocess, only if the particular +@var{file} or @var{command} you specify has not already been written +to by your program or if it has been closed since it was last written to. -@cindex differences between @code{gawk} and @code{awk} -@cindex limitations -@cindex implementation limits -@iftex -As mentioned earlier -(@pxref{Getline Summary, , Summary of @code{getline} Variants}), -many -@end iftex -@ifinfo -Many -@end ifinfo -@code{awk} implementations limit the number of pipelines an @code{awk} -program may have open to just one! In @code{gawk}, there is no such limit. -You can open as many pipelines as the underlying operating system will -permit. +@cindex common mistakes +@cindex mistakes, common +@cindex errors, common +It is a common error to use @samp{>} redirection for the first @code{print} +to a file, and then to use @samp{>>} for subsequent output: + +@example +# clear the file +print "Don't panic" > "guide.txt" +@dots{} +# append +print "Avoid improbability generators" >> "guide.txt" +@end example + +@noindent +This is indeed how redirections must be used from the shell. But in +@command{awk}, it isn't necessary. In this kind of case, a program should +use @samp{>} for all the @code{print} statements, since the output file +is only opened once. + +@cindex differences between @command{gawk} and @command{awk} +@cindex limitations +@cindex implementation limits +@ifnotinfo +As mentioned earlier +(@pxref{Getline Notes, ,Points About @code{getline} to Remember}), +many +@end ifnotinfo +@ifnottex +Many +@end ifnottex +@command{awk} implementations limit the number of pipelines that an @command{awk} +program may have open to just one! In @command{gawk}, there is no such limit. +@command{gawk} allows a program to +open as many pipelines as the underlying operating system permits. + +@c fakenode --- for prepinfo +@subheading Advanced Notes: Piping into @command{sh} +@cindex advanced notes +@cindex shell, piping commands into +@cindex piping commands into the shell + +A particularly powerful way to use redirection is to build command lines, +and pipe them into the shell, @command{sh}. For example, suppose you +have a list of files brought over from a system where all the @value{FN}s +are stored in uppercase, and you wish to rename them to have names in +all lowercase. The following program is both simple and efficient: + +@cindex @command{mv} utility +@example +@{ printf("mv %s %s\n", $0, tolower($0)) | "sh" @} + +END @{ close("sh") @} +@end example + +The @code{tolower} function returns its argument string with all +uppercase characters converted to lowercase +(@pxref{String Functions, ,String Manipulation Functions}). +The program builds up a list of command lines, +using the @command{mv} utility to rename the files. +It then sends the list to the shell for execution. + +@node Special Files, Close Files And Pipes, Redirection, Printing +@section Special @value{FFN}s in @command{gawk} -@node Special Files, Close Files And Pipes , Redirection, Printing -@section Special File Names in @code{gawk} +@command{gawk} provides a number of special @value{FN}s that it interprets +internally. These @value{FN}s provide access to standard file descriptors, +process-related information, and TCP/IP networking. + +@menu +* Special FD:: Special files for I/O. +* Special Process:: Special files for process information. +* Special Network:: Special files for network communications. +* Special Caveats:: Things to watch out for. +@end menu + +@node Special FD, Special Process, Special Files, Special Files +@subsection Special Files for Standard Descriptors @cindex standard input @cindex standard output @cindex standard error output @@ -5397,50 +6343,49 @@ already available to them for reading and writing. These are known as the @dfn{standard input}, @dfn{standard output}, and @dfn{standard error output}. These streams are, by default, connected to your terminal, but they are often redirected with the shell, via the @samp{<}, @samp{<<}, -@samp{>}, @samp{>>}, @samp{>&} and @samp{|} operators. Standard error -is typically used for writing error messages; the reason we have two separate -streams, standard output and standard error, is so that they can be +@samp{>}, @samp{>>}, @samp{>&}, and @samp{|} operators. Standard error +is typically used for writing error messages; the reason there are two separate +streams, standard output, and standard error, is so that they can be redirected separately. -@cindex differences between @code{gawk} and @code{awk} -In other implementations of @code{awk}, the only way to write an error -message to standard error in an @code{awk} program is as follows: +@cindex differences between @command{gawk} and @command{awk} +In other implementations of @command{awk}, the only way to write an error +message to standard error in an @command{awk} program is as follows: @example print "Serious error detected!" | "cat 1>&2" @end example @noindent -This works by opening a pipeline to a shell command which can access the -standard error stream which it inherits from the @code{awk} process. -This is far from elegant, and is also inefficient, since it requires a -separate process. So people writing @code{awk} programs often -neglect to do this. Instead, they send the error messages to the +This works by opening a pipeline to a shell command that can access the +standard error stream that it inherits from the @command{awk} process. +This is far from elegant, and it is also inefficient, because it requires a +separate process. So people writing @command{awk} programs often +don't do this. Instead, they send the error messages to the terminal, like this: @example -@group print "Serious error detected!" > "/dev/tty" -@end group @end example @noindent -This usually has the same effect, but not always: although the -standard error stream is usually the terminal, it can be redirected, and -when that happens, writing to the terminal is not correct. In fact, if -@code{awk} is run from a background job, it may not have a terminal at all. -Then opening @file{/dev/tty} will fail. - -@code{gawk} provides special file names for accessing the three standard -streams. When you redirect input or output in @code{gawk}, if the file name -matches one of these special names, then @code{gawk} directly uses the -stream it stands for. - -@cindex @file{/dev/stdin} -@cindex @file{/dev/stdout} -@cindex @file{/dev/stderr} -@cindex @file{/dev/fd} -@c @cartouche +This usually has the same effect but not always: although the +standard error stream is usually the terminal, it can be redirected; when +that happens, writing to the terminal is not correct. In fact, if +@command{awk} is run from a background job, it may not have a terminal at all. +Then opening @file{/dev/tty} fails. + +@command{gawk} provides special @value{FN}s for accessing the three standard +streams, as well as any other inherited open files. If the @value{FN} matches +one of these special names when @command{gawk} redirects input or output, +then it directly uses the stream that the @value{FN} stands for. +(These special @value{FN}s work for all operating systems that @command{gawk} +has been ported to, not just those that are POSIX-compliant.): + +@cindex @file{/dev/stdin} special file +@cindex @file{/dev/stdout} special file +@cindex @file{/dev/stderr} special file +@cindex @file{/dev/fd} special files @table @file @item /dev/stdin The standard input (file descriptor 0). @@ -5452,49 +6397,58 @@ The standard output (file descriptor 1). The standard error output (file descriptor 2). @item /dev/fd/@var{N} -The file associated with file descriptor @var{N}. Such a file must have -been opened by the program initiating the @code{awk} execution (typically -the shell). Unless you take special pains in the shell from which -you invoke @code{gawk}, only descriptors 0, 1 and 2 are available. +The file associated with file descriptor @var{N}. Such a file must +be opened by the program initiating the @command{awk} execution (typically +the shell). Unless special pains are taken in the shell from which +@command{gawk} is invoked, only descriptors 0, 1, and 2 are available. @end table -@c @end cartouche -The file names @file{/dev/stdin}, @file{/dev/stdout}, and @file{/dev/stderr} +The @value{FN}s @file{/dev/stdin}, @file{/dev/stdout}, and @file{/dev/stderr} are aliases for @file{/dev/fd/0}, @file{/dev/fd/1}, and @file{/dev/fd/2}, -respectively, but they are more self-explanatory. - -The proper way to write an error message in a @code{gawk} program +respectively. However, they are more self-explanatory. +The proper way to write an error message in a @command{gawk} program is to use @file{/dev/stderr}, like this: @example print "Serious error detected!" > "/dev/stderr" @end example -@code{gawk} also provides special file names that give access to information -about the running @code{gawk} process. Each of these ``files'' provides -a single record of information. To read them more than once, you must -first close them with the @code{close} function -(@pxref{Close Files And Pipes, ,Closing Input and Output Files and Pipes}). -The filenames are: +@cindex common mistakes +@cindex mistakes, common +@cindex errors, common +Note the use of quotes around the @value{FN}. +Like any other redirection, the value must be a string. +It is a common error to omit the quotes, which leads +to confusing results. +@c Exercise: What does it do? :-) + +@node Special Process, Special Network, Special FD, Special Files +@subsection Special Files for Process-Related Information + +@command{gawk} also provides special @value{FN}s that give access to information +about the running @command{gawk} process. Each of these ``files'' provides +a single record of information. To read them more than once, they must +first be closed with the @code{close} function +(@pxref{Close Files And Pipes, ,Closing Input and Output Redirections}). +The @value{FN}s are: @cindex process information -@cindex @file{/dev/pid} -@cindex @file{/dev/pgrpid} -@cindex @file{/dev/ppid} -@cindex @file{/dev/user} -@c @cartouche +@cindex @file{/dev/pid} special file +@cindex @file{/dev/pgrpid} special file +@cindex @file{/dev/ppid} special file +@cindex @file{/dev/user} special file @table @file @item /dev/pid Reading this file returns the process ID of the current process, -in decimal, terminated with a newline. +in decimal form, terminated with a newline. -@item /dev/ppid +@item /dev/ppid Reading this file returns the parent process ID of the current process, -in decimal, terminated with a newline. +in decimal form, terminated with a newline. -@item /dev/pgrpid +@item /dev/pgrpid Reading this file returns the process group ID of the current process, -in decimal, terminated with a newline. +in decimal form, terminated with a newline. @item /dev/user Reading this file returns a single record terminated with a newline. @@ -5520,64 +6474,126 @@ The return value of the @code{getegid} system call @end table If there are any additional fields, they are the group IDs returned by -@code{getgroups} system call. +the @code{getgroups} system call. (Multiple groups may not be supported on all systems.) @end table -@c @end cartouche -These special file names may be used on the command line as data -files, as well as for I/O redirections within an @code{awk} program. -They may not be used as source files with the @samp{-f} option. +These special @value{FN}s may be used on the command line as @value{DF}s, +as well as for I/O redirections within an @command{awk} program. +They may not be used as source files with the @option{-f} option. + +@cindex automatic warnings +@cindex warnings, automatic +@strong{Note:} +The special files that provide process-related information are now considered +obsolete and will disappear entirely +in the next release of @command{gawk}. +@command{gawk} prints a warning message every time you use one of +these files. +To obtain process-related information, use the @code{PROCINFO} array. +@xref{Auto-set, ,Built-in Variables That Convey Information}. + +@node Special Network, Special Caveats, Special Process, Special Files +@subsection Special Files for Network Communications + +Starting with @value{PVERSION} 3.1 of @command{gawk}, @command{awk} programs +can open a two-way +TCP/IP connection, acting as either a client or server. +This is done using a special @value{FN} of the form: + +@example +@file{/inet/@var{protocol}/@var{local-port}/@var{remote-host}/@var{remote-port}} +@end example + +The @var{protocol} is one of @samp{tcp}, @samp{udp}, or @samp{raw}, +and the other fields represent the other essential pieces of information +for making a networking connection. +These @value{FN}s are used with the @samp{|&} operator for communicating +with a coprocess +(@pxref{Two-way I/O, ,Two-Way Communications with Another Process}). +This is an advanced feature, mentioned here only for completeness. +Full discussion is delayed until +@ref{TCP/IP Networking, ,Using @command{gawk} for Network Programming}. + +@node Special Caveats, , Special Network, Special Files +@subsection Special @value{FFN} Caveats -Recognition of these special file names is disabled if @code{gawk} is in -compatibility mode (@pxref{Options, ,Command Line Options}). +Here is a list of things to bear in mind when using the +special @value{FN}s that @command{gawk} provides. + +@itemize @bullet +@item +Recognition of these special @value{FN}s is disabled if @command{gawk} is in +compatibility mode (@pxref{Options, ,Command-Line Options}). -@strong{Caution}: Unless your system actually has a @file{/dev/fd} directory -(or any of the other above listed special files), -the interpretation of these file names is done by @code{gawk} itself. -For example, using @samp{/dev/fd/4} for output will actually write on -file descriptor 4, and not on a new file descriptor that was @code{dup}'ed -from file descriptor 4. Most of the time this does not matter; however, it -is important to @emph{not} close any of the files related to file descriptors -0, 1, and 2. If you do close one of these files, unpredictable behavior -will result. +@cindex automatic warnings +@cindex warnings, automatic +@item +@ifnottex +The +@end ifnottex +@ifnotinfo +As mentioned earlier, the +@end ifnotinfo +special files that provide process-related information are now considered +obsolete and will disappear entirely +in the next release of @command{gawk}. +@command{gawk} prints a warning message every time you use one of +these files. +@ifnottex +To obtain process-related information, use the @code{PROCINFO} array. +@xref{Built-in Variables}. +@end ifnottex -The special files that provide process-related information will disappear -in a future version of @code{gawk}. -@xref{Future Extensions, ,Probable Future Extensions}. +@item +Starting with @value{PVERSION} 3.1, @command{gawk} @emph{always} +interprets these special @value{FN}s.@footnote{Older versions of +@command{gawk} would only interpret these names internally if the system +did not actually have a a @file{/dev/fd} directory or any of the other +above listed special files. Usually this didn't make a difference, +but sometimes it did; thus, it was decided to make @command{gawk}'s +behavior consistent on all systems and to have it always interpret +the special @value{FN}s itself.} +For example, using @samp{/dev/fd/4} +for output actually writes on file descriptor 4, and not on a new +file descriptor that is @code{dup}'ed from file descriptor 4. Most of +the time this does not matter; however, it is important to @emph{not} +close any of the files related to file descriptors 0, 1, and 2. +Doing so results in unpredictable behavior. +@end itemize @node Close Files And Pipes, , Special Files, Printing -@section Closing Input and Output Files and Pipes +@section Closing Input and Output Redirections @cindex closing input files and pipes @cindex closing output files and pipes -@findex close - -If the same file name or the same shell command is used with -@code{getline} -(@pxref{Getline, ,Explicit Input with @code{getline}}) -more than once during the execution of an @code{awk} -program, the file is opened (or the command is executed) only the first time. +@cindex closing coprocesses +@cindex coprocess +@cindex @code{close} built-in function + +If the same @value{FN} or the same shell command is used with @code{getline} +more than once during the execution of an @command{awk} program +(@pxref{Getline, ,Explicit Input with @code{getline}}), +the file is opened (or the command is executed) the first time only. At that time, the first record of input is read from that file or command. -The next time the same file or command is used in @code{getline}, another -record is read from it, and so on. +The next time the same file or command is used with @code{getline}, +another record is read from it, and so on. -Similarly, when a file or pipe is opened for output, the file name or command -associated with -it is remembered by @code{awk} and subsequent writes to the same file or -command are appended to the previous writes. The file or pipe stays -open until @code{awk} exits. +Similarly, when a file or pipe is opened for output, the @value{FN} or +command associated with it is remembered by @command{awk}, and subsequent +writes to the same file or command are appended to the previous writes. +The file or pipe stays open until @command{awk} exits. -This implies that if you want to start reading the same file again from -the beginning, or if you want to rerun a shell command (rather than -reading more output from the command), you must take special steps. -What you must do is use the @code{close} function, as follows: +This implies that special steps are necessary in order to read the same +file again from the beginning, or to rerun a shell command (rather than +reading more output from the same command). The @code{close} function +makes these things possible: @example close(@var{filename}) @end example @noindent -or +or: @example close(@var{command}) @@ -5601,12 +6617,11 @@ close("sort -r names") Once this function call is executed, the next @code{getline} from that file or command, or the next @code{print} or @code{printf} to that -file or command, will reopen the file or rerun the command. - +file or command, reopens the file or reruns the command. Because the expression that you use to close a file or pipeline must exactly match the expression used to open the file or run the command, -it is good practice to use a variable to store the file name or command. -The previous example would become +it is good practice to use a variable to store the @value{FN} or command. +The previous example becomes the following: @example sortcom = "sort -r names" @@ -5616,77 +6631,170 @@ close(sortcom) @end example @noindent -This helps avoid hard-to-find typographical errors in your @code{awk} -programs. - -Here are some reasons why you might need to close an output file: +This helps avoid hard-to-find typographical errors in your @command{awk} +programs. Here are some of the reasons for closing an output file: @itemize @bullet @item -To write a file and read it back later on in the same @code{awk} -program. Close the file when you are finished writing it; then -you can start reading it with @code{getline}. +To write a file and read it back later on in the same @command{awk} +program. Close the file after writing it, then +begin reading it with @code{getline}. @item -To write numerous files, successively, in the same @code{awk} -program. If you don't close the files, eventually you may exceed a -system limit on the number of open files in one process. So close -each one when you are finished writing it. +To write numerous files, successively, in the same @command{awk} +program. If the files aren't closed, eventually @command{awk} may exceed a +system limit on the number of open files in one process. It is best to +close each one when the program has finished writing it. @item -To make a command finish. When you redirect output through a pipe, +To make a command finish. When output is redirected through a pipe, the command reading the pipe normally continues to try to read input as long as the pipe is open. Often this means the command cannot -really do its work until the pipe is closed. For example, if you -redirect output to the @code{mail} program, the message is not +really do its work until the pipe is closed. For example, if +output is redirected to the @command{mail} program, the message is not actually sent until the pipe is closed. -@c NEEDED -@page @item To run the same program a second time, with the same arguments. This is not the same thing as giving more input to the first run! -For example, suppose you pipe output to the @code{mail} program. If you -output several lines redirected to this pipe without closing it, they make -a single message of several lines. By contrast, if you close the pipe -after each line of output, then each line makes a separate message. +For example, suppose a program pipes output to the @command{mail} program. +If it outputs several lines redirected to this pipe without closing +it, they make a single message of several lines. By contrast, if the +program closes the pipe after each line of output, then each line makes +a separate message. @end itemize -@vindex ERRNO -@cindex differences between @code{gawk} and @code{awk} -@code{close} returns a value of zero if the close succeeded. -Otherwise, the value will be non-zero. -In this case, @code{gawk} sets the variable @code{ERRNO} to a string -describing the error that occurred. - -@cindex differences between @code{gawk} and @code{awk} +@cindex differences between @command{gawk} and @command{awk} @cindex portability issues If you use more files than the system allows you to have open, -@code{gawk} will attempt to multiplex the available open files among -your data files. @code{gawk}'s ability to do this depends upon the -facilities of your operating system: it may not always work. It is +@command{gawk} attempts to multiplex the available open files among +your @value{DF}s. @command{gawk}'s ability to do this depends upon the +facilities of your operating system, so it may not always work. It is therefore both good practice and good portability advice to always use @code{close} on your files when you are done with them. +In fact, if you are using a lot of pipes, it is essential that +you close commands when done. For example, consider something like this: + +@example +@{ + @dots{} + command = ("grep " $1 " /some/file | my_prog -q " $3) + while ((command | getline) > 0) @{ + @var{process output of} command + @} + # need close(command) here +@} +@end example + +This example creates a new pipeline based on data in @emph{each} record. +Without the call to @code{close} indicated in the comment, @command{awk} +creates child processes to run the commands, until it eventually +runs out of file descriptors for more pipelines. + +Even though each command has finished (as indicated by the end-of-file +return status from @code{getline}), the child process is not +terminated;@footnote{The technical terminology is rather morbid. +The finished child is called a ``zombie,'' and cleaning up after +it is referred to as ``reaping.''} +@c Good old UNIX: give the marketing guys fits, that's the ticket +more importantly, the file descriptor for the pipe +is not closed and released until @code{close} is called or +@command{awk} exits. + +@code{close} will silently do nothing if given an argument that +does not represent a file, pipe or coprocess that was opened with +a redirection. + +When using the @samp{|&} operator to communicate with a coprocess, +it is occasionally useful to be able to close one end of the two-way +pipe without closing the other. +This is done by supplying a second argument to @code{close}. +As in any other call to @code{close}, +the first argument is the name of the command or special file used +to start the coprocess. +The second argument should be a string, with either of the values +@code{"to"} or @code{"from"}. Case does not matter. +As this is an advanced feature, a more complete discussion is +delayed until +@ref{Two-way I/O, ,Two-Way Communications with Another Process}, +which discusses it in more detail and gives an example. + +@c fakenode --- for prepinfo +@subheading Advanced Notes: Using @code{close}'s Return Value +@cindex advanced notes +@cindex dark corner +@cindex differences between @command{gawk} and @command{awk} +@cindex @code{close}, return value +@cindex return value from @code{close} + +In many versions of Unix @command{awk}, the @code{close} function +is actually a statement. It is a syntax error to try and use the return +value from @code{close}: +@value{DARKCORNER} + +@example +command = "@dots{}" +command | getline info +retval = close(command) # syntax error in most Unix awks +@end example + +@command{gawk} treats @code{close} as a function. +The return value is @minus{}1 if the argument names something +that was never opened with a redirection, or if there is +a system problem closing the file or process. +In these cases, @command{gawk} sets the built-in variable +@code{ERRNO} to a string describing the problem. + +In @command{gawk}, +when closing a pipe or coprocess, +the return value is the exit status of the command. +Otherwise, it is the return value from the system's @code{close} or +@code{fclose} C functions when closing input or output +files, respectively. +This value is zero if the close succeeds, or @minus{}1 if +it fails. + +The return value for closing a pipeline is particularly useful. +It allows you to get the output from a command as well as its +exit status. + +For POSIX-compliant systems, +if the exit status is a number above 128, then the program +was terminated by a signal. Subtract 128 to get the signal number: + +@example +exit_val = close(command) +if (exit_val > 128) + print command, "died with signal", exit_val - 128 +else + print command, "exited with code", exit_val +@end example + +Currently, in @command{gawk}, this only works for commands +piping into @code{getline}. For commands piped into +from @code{print} or @code{printf}, the +return value from @code{close} is that of the library's +@code{pclose} function. @node Expressions, Patterns and Actions, Printing, Top @chapter Expressions @cindex expression -Expressions are the basic building blocks of @code{awk} patterns -and actions. An expression evaluates to a value, which you can print, test, -store in a variable or pass to a function. Additionally, an expression -can assign a new value to a variable or a field, with an assignment operator. +Expressions are the basic building blocks of @command{awk} patterns +and actions. An expression evaluates to a value that you can print, test, +or pass to a function. Additionally, an expression +can assign a new value to a variable or a field by using an assignment operator. An expression can serve as a pattern or action statement on its own. Most other kinds of -statements contain one or more expressions which specify data on which to -operate. As in other languages, expressions in @code{awk} include +statements contain one or more expressions that specify the data on which to +operate. As in other languages, expressions in @command{awk} include variables, array references, constants, and function calls, as well as combinations of these with various operators. @menu -* Constants:: String, numeric, and regexp constants. +* Constants:: String, numeric and regexp constants. * Using Constant Regexps:: When and how to use a regexp constant. * Variables:: Variables give names to values for later use. * Conversion:: The conversion of strings to numbers and vice @@ -5697,7 +6805,7 @@ combinations of these with various operators. * Assignment Ops:: Changing the value of a variable or a field. * Increment Ops:: Incrementing the numeric value of a variable. * Truth Values:: What is ``true'' and what is ``false''. -* Typing and Comparison:: How variables acquire types, and how this +* Typing and Comparison:: How variables acquire types and how this affects comparison of numbers and strings with @samp{<}, etc. * Boolean Ops:: Combining comparison expressions using boolean @@ -5713,27 +6821,33 @@ combinations of these with various operators. @node Constants, Using Constant Regexps, Expressions, Expressions @section Constant Expressions @cindex constants, types of -@cindex string constants The simplest type of expression is the @dfn{constant}, which always has -the same value. There are three types of constants: numeric constants, -string constants, and regular expression constants. +the same value. There are three types of constants: numeric, +string, and regular expression. + +Each is used in the appropriate context when you need a data +value that isn't going to change. Numeric constants can +have different forms, but are stored identically internally. @menu * Scalar Constants:: Numeric and string constants. +* Non-decimal-numbers:: What are octal and hex numbers. * Regexp Constants:: Regular Expression constants. @end menu -@node Scalar Constants, Regexp Constants, Constants, Constants +@node Scalar Constants, Non-decimal-numbers, Constants, Constants @subsection Numeric and String Constants @cindex numeric constant @cindex numeric value A @dfn{numeric constant} stands for a number. This number can be an integer, a decimal fraction, or a number in scientific (exponential) -notation.@footnote{The internal representation uses double-precision -floating point numbers. If you don't know what that means, then don't -worry about it.} Here are some examples of numeric constants, which all +notation.@footnote{The internal representation of all numbers, +including integers, uses double-precision +floating-point numbers. +On most modern systems, these are in IEEE 754 standard format.} +Here are some examples of numeric constants that all have the same value: @example @@ -5742,46 +6856,143 @@ have the same value: 1050e-1 @end example +@cindex string constants A string constant consists of a sequence of characters enclosed in -double-quote marks. For example: +double quote marks. For example: @example "parrot" @end example @noindent -@cindex differences between @code{gawk} and @code{awk} +@cindex differences between @command{gawk} and @command{awk} represents the string whose contents are @samp{parrot}. Strings in -@code{gawk} can be of any length and they can contain any of the possible -eight-bit ASCII characters including ASCII NUL (character code zero). -Other @code{awk} +@command{gawk} can be of any length, and they can contain any of the possible +eight-bit ASCII characters including ASCII @sc{nul} (character code zero). +Other @command{awk} implementations may have difficulty with some character codes. -@node Regexp Constants, , Scalar Constants, Constants +@node Non-decimal-numbers, Regexp Constants, Scalar Constants, Constants +@subsection Octal and Hexadecimal Numbers +@cindex octal numbers +@cindex hexadecimal numbers +@cindex numbers, octal +@cindex numbers, hexadecimal + +In @command{awk}, all numbers are in decimal; i.e., base 10. Many other +programming languages allow you to specify numbers in other bases, often +octal (base 8) and hexadecimal (base 16). +In octal, the numbers go 0, 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, etc.. +Just as @samp{11} in decimal is 1 times 10 plus 1, so +@samp{11} in octal is 1 times 8, plus 1. This equals nine in decimal. +In hexadecimal, there are 16 digits. Since the everyday decimal +number system only has ten digits (@samp{0}---@samp{9}), the letters +@samp{a} through @samp{f} are used to represent the rest. +(Case in the letters is usually irrelevant; hexadecimal @samp{a} and @samp{A} +have the same value.) +Thus, @samp{11} in +hexadecimal is 1 times 16 plus 1, which equals 17 in decimal. + +Just by looking at plain @samp{11}, you can't tell what base it's in. +So, in C, C++, and other languages derived from C, +@c such as PERL, but we won't mention that.... +there is a special notation to help signify the base. +Octal numbers start with a leading @samp{0}, +and hexadecimal numbers start with a leading @samp{0x} or @samp{0X}: + +@table @code +@item 11 +Decimal 11. + +@item 011 +Octal 11, decimal value 9. + +@item 0x11 +Hexadecimal 11, decimal value 17. +@end table + +This example shows the difference: + +@example +$ gawk 'BEGIN @{ printf "%d, %d, %d\n", 011, 11, 0x11 @}' +@print{} 9, 11, 17 +@end example + +Being able to use octal and hexadecimal constants in your programs is most +useful when working with data that cannot be represented conveniently as +characters or as regular numbers, such as binary data of various sorts. + +@command{gawk} allows the use of octal and hexadecimal +constants in your program text. However, such numbers in the input data +are not treated differently; doing so by default would break old +programs. +(If you really need to do this, use the @option{--non-decimal-data} +command-line option, +@pxref{Non-decimal Data, ,Allowing Non-Decimal Input Data}.) +If you have octal or hexadecimal data, +you can use the @code{strtonum} function +(@pxref{String Functions, ,String Manipulation Functions}) +to convert the data into a number. +Most of the time, you will want to use octal or hexadecimal constants +when working with the built-in bit manipulation functions; +see @ref{Bitwise Functions, ,Using @command{gawk}'s Bit Manipulation Functions}, +for more information. + +Unlike some early C implementations, @samp{8} and @samp{9} are not valid +in octal constants; e.g., @command{gawk} treats @samp{018} as decimal 18. + +@example +$ gawk 'BEGIN @{ print "021 is", 021 ; print 018 @}' +@print{} 021 is 17 +@print{} 18 +@end example + +Octal and hexadecimal source code constants are a @command{gawk} extension. +If @command{gawk} is in compatibility mode +(@pxref{Options, ,Command-Line Options}), +they are not available. + +@c fakenode --- for prepinfo +@subheading Advanced Notes: A Constant's Base Does Not Affect Its Value +@cindex advanced notes + +Once a numeric constant has +been converted internally into a number, +@command{gawk} no longer remembers +what the original form of the constant was; the internal value is +always used. This has particular consequences for conversion of +numbers to strings: + +@example +$ gawk 'BEGIN @{ printf "0x11 is <%s>\n", 0x11 @}' +@print{} 0x11 is <17> +@end example + +@node Regexp Constants, , Non-decimal-numbers, Constants @subsection Regular Expression Constants @cindex @code{~} operator @cindex @code{!~} operator A regexp constant is a regular expression description enclosed in slashes, such as @code{@w{/^beginning and end$/}}. Most regexps used in -@code{awk} programs are constant, but the @samp{~} and @samp{!~} +@command{awk} programs are constant, but the @samp{~} and @samp{!~} matching operators can also match computed or ``dynamic'' regexps (which are just ordinary strings or variables that contain a regexp). @node Using Constant Regexps, Variables, Constants, Expressions @section Using Regular Expression Constants -When used on the right hand side of the @samp{~} or @samp{!~} +@cindex dark corner +When used on the righthand side of the @samp{~} or @samp{!~} operators, a regexp constant merely stands for the regexp that is to be matched. - -@cindex dark corner -Regexp constants (such as @code{/foo/}) may be used like simple expressions. +However, regexp constants (such as @code{/foo/}) may be used like simple expressions. When a regexp constant appears by itself, it has the same meaning as if it appeared -in a pattern, i.e.@: @samp{($0 ~ /foo/)} (d.c.) -(@pxref{Expression Patterns, ,Expressions as Patterns}). -This means that the two code segments, +in a pattern, i.e.; @samp{($0 ~ /foo/)} +@value{DARKCORNER} +@xref{Expression Patterns, ,Expressions as Patterns}. +This means that the following two code segments: @example if ($0 ~ /barfly/ || $0 ~ /camelot/) @@ -5789,7 +7000,7 @@ if ($0 ~ /barfly/ || $0 ~ /camelot/) @end example @noindent -and +and: @example if (/barfly/ || /camelot/) @@ -5798,9 +7009,8 @@ if (/barfly/ || /camelot/) @noindent are exactly equivalent. - One rather bizarre consequence of this rule is that the following -boolean expression is valid, but does not do what the user probably +Boolean expression is valid, but does not do what the user probably intended: @example @@ -5808,48 +7018,46 @@ intended: if (/foo/ ~ $1) print "found foo" @end example +@cindex automatic warnings +@cindex warnings, automatic @noindent This code is ``obviously'' testing @code{$1} for a match against the regexp @code{/foo/}. But in fact, the expression @samp{/foo/ ~ $1} actually means @samp{($0 ~ /foo/) ~ $1}. In other words, first match the input record -against the regexp @code{/foo/}. The result will be either zero or one, -depending upon the success or failure of the match. Then match that result -against the first field in the record. - -Since it is unlikely that you would ever really wish to make this kind of -test, @code{gawk} will issue a warning when it sees this construct in +against the regexp @code{/foo/}. The result is either zero or one, +depending upon the success or failure of the match. That result +is then matched against the first field in the record. +Because it is unlikely that you would ever really want to make this kind of +test, @command{gawk} issues a warning when it sees this construct in a program. - -Another consequence of this rule is that the assignment statement +Another consequence of this rule is that the assignment statement: @example matches = /foo/ @end example @noindent -will assign either zero or one to the variable @code{matches}, depending +assigns either zero or one to the variable @code{matches}, depending upon the contents of the current input record. - -This feature of the language was never well documented until the +This feature of the language has never been well documented until the POSIX specification. -@cindex differences between @code{gawk} and @code{awk} +@cindex differences between @command{gawk} and @command{awk} @cindex dark corner Constant regular expressions are also used as the first argument for -the @code{gensub}, @code{sub} and @code{gsub} functions, and as the +the @code{gensub}, @code{sub}, and @code{gsub} functions, and as the second argument of the @code{match} function -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). -Modern implementations of @code{awk}, including @code{gawk}, allow -the third argument of @code{split} to be a regexp constant, while some -older implementations do not (d.c.). - +(@pxref{String Functions, ,String Manipulation Functions}). +Modern implementations of @command{awk}, including @command{gawk}, allow +the third argument of @code{split} to be a regexp constant, but some +older implementations do not. +@value{DARKCORNER} This can lead to confusion when attempting to use regexp constants as arguments to user defined functions -(@pxref{User-defined, , User-defined Functions}). +(@pxref{User-defined, ,User-Defined Functions}). For example: @example -@group function mysub(pat, repl, str, global) @{ if (global) @@ -5858,40 +7066,38 @@ function mysub(pat, repl, str, global) sub(pat, repl, str) return str @} -@end group -@group @{ @dots{} text = "hi! hi yourself!" mysub(/hi/, "howdy", text, 1) @dots{} @} -@end group @end example -In this example, the programmer wishes to pass a regexp constant to the -user-defined function @code{mysub}, which will in turn pass it on to +@cindex automatic warnings +@cindex warnings, automatic +In this example, the programmer wants to pass a regexp constant to the +user-defined function @code{mysub}, which in turn passes it on to either @code{sub} or @code{gsub}. However, what really happens is that -the @code{pat} parameter will be either one or zero, depending upon whether +the @code{pat} parameter is either one or zero, depending upon whether or not @code{$0} matches @code{/hi/}. - -As it is unlikely that you would ever really wish to pass a truth value -in this way, @code{gawk} will issue a warning when it sees a regexp -constant used as a parameter to a user-defined function. +@command{gawk} issues a warning when it sees a regexp constant used as +a parameter to a user-defined function, since passing a truth value in +this way is probably not what was intended. @node Variables, Conversion, Using Constant Regexps, Expressions @section Variables Variables are ways of storing values at one point in your program for -use later in another part of your program. You can manipulate them -entirely within your program text, and you can also assign values to -them on the @code{awk} command line. +use later in another part of your program. They can be manipulated +entirely within the program text, and they can also be assigned values +on the @command{awk} command line. @menu * Using Variables:: Using variables in your programs. -* Assignment Options:: Setting variables on the command line and a - summary of command line syntax. This is an +* Assignment Options:: Setting variables on the command-line and a + summary of command-line syntax. This is an advanced method of input. @end menu @@ -5900,62 +7106,63 @@ them on the @code{awk} command line. @cindex variables, user-defined @cindex user-defined variables -Variables let you give names to values and refer to them later. You have -already seen variables in many of the examples. The name of a variable -must be a sequence of letters, digits and underscores, but it may not begin +Variables let you give names to values and refer to them later. Variables +have already been used in many of the examples. The name of a variable +must be a sequence of letters, digits, or underscores, and it may not begin with a digit. Case is significant in variable names; @code{a} and @code{A} are distinct variables. A variable name is a valid expression by itself; it represents the variable's current value. Variables are given new values with -@dfn{assignment operators}, @dfn{increment operators} and +@dfn{assignment operators}, @dfn{increment operators}, and @dfn{decrement operators}. @xref{Assignment Ops, ,Assignment Expressions}. +@c NEXT ED: Can also be changed by sub, gsub, split -A few variables have special built-in meanings, such as @code{FS}, the -field separator, and @code{NF}, the number of fields in the current -input record. @xref{Built-in Variables}, for a list of them. These -built-in variables can be used and assigned just like all other +A few variables have special built-in meanings, such as @code{FS} (the +field separator), and @code{NF} (the number of fields in the current input +record). @xref{Built-in Variables}, for a list of the built-in variables. +These built-in variables can be used and assigned just like all other variables, but their values are also used or changed automatically by -@code{awk}. All built-in variables names are entirely upper-case. +@command{awk}. All built-in variables' names are entirely uppercase. -Variables in @code{awk} can be assigned either numeric or string -values. By default, variables are initialized to the empty string, which +Variables in @command{awk} can be assigned either numeric or string values. +The kind of value a variable holds can change over the life of a program. +By default, variables are initialized to the empty string, which is zero if converted to a number. There is no need to -``initialize'' each variable explicitly in @code{awk}, -the way you would in C and in most other traditional languages. +``initialize'' each variable explicitly in @command{awk}, +which is what you would do in C and in most other traditional languages. -@node Assignment Options, , Using Variables, Variables +@node Assignment Options, , Using Variables, Variables @subsection Assigning Variables on the Command Line -You can set any @code{awk} variable by including a @dfn{variable assignment} -among the arguments on the command line when you invoke @code{awk} -(@pxref{Other Arguments, ,Other Command Line Arguments}). Such an assignment has -this form: +Any @command{awk} variable can be set by including a @dfn{variable assignment} +among the arguments on the command line when @command{awk} is invoked +(@pxref{Other Arguments, ,Other Command-Line Arguments}). +Such an assignment has the following form: @example @var{variable}=@var{text} @end example @noindent -With it, you can set a variable either at the beginning of the -@code{awk} run or in between input files. - -If you precede the assignment with the @samp{-v} option, like this: +With it, a variable is set either at the beginning of the +@command{awk} run or in between input files. +When the assignment is preceded with the @option{-v} option, +as in the following: @example -v @var{variable}=@var{text} @end example @noindent -then the variable is set at the very beginning, before even the -@code{BEGIN} rules are run. The @samp{-v} option and its assignment -must precede all the file name arguments, as well as the program text. -(@xref{Options, ,Command Line Options}, for more information about -the @samp{-v} option.) - +the variable is set at the very beginning, even before the +@code{BEGIN} rules are run. The @option{-v} option and its assignment +must precede all the @value{FN} arguments, as well as the program text. +(@xref{Options, ,Command-Line Options}, for more information about +the @option{-v} option.) Otherwise, the variable assignment is performed at a time determined by -its position among the input file arguments: after the processing of the +its position among the input file arguments---after the processing of the preceding input file argument. For example: @example @@ -5968,10 +7175,9 @@ the first file is read, the command line sets the variable @code{n} equal to four. This causes the fourth field to be printed in lines from the file @file{inventory-shipped}. After the first file has finished, but before the second file is started, @code{n} is set to two, so that the -second field is printed in lines from @file{BBS-list}. +second field is printed in lines from @file{BBS-list}: @example -@group $ awk '@{ print $n @}' n=4 inventory-shipped n=2 BBS-list @print{} 15 @print{} 24 @@ -5979,27 +7185,27 @@ $ awk '@{ print $n @}' n=4 inventory-shipped n=2 BBS-list @print{} 555-5553 @print{} 555-3412 @dots{} -@end group @end example -Command line arguments are made available for explicit examination by -the @code{awk} program in an array named @code{ARGV} -(@pxref{ARGC and ARGV, ,Using @code{ARGC} and @code{ARGV}}). - @cindex dark corner -@code{awk} processes the values of command line assignments for escape -sequences (d.c.) (@pxref{Escape Sequences}). +Command-line arguments are made available for explicit examination by +the @command{awk} program in an array named @code{ARGV} +(@pxref{ARGC and ARGV, ,Using @code{ARGC} and @code{ARGV}}). +@command{awk} processes the values of command-line assignments for escape +sequences +@value{DARKCORNER} +(@pxref{Escape Sequences}). @node Conversion, Arithmetic Ops, Variables, Expressions @section Conversion of Strings and Numbers @cindex conversion of strings and numbers -Strings are converted to numbers, and numbers to strings, if the context -of the @code{awk} program demands it. For example, if the value of +Strings are converted to numbers and numbers are converted to strings, if the context +of the @command{awk} program demands it. For example, if the value of either @code{foo} or @code{bar} in the expression @samp{foo + bar} happens to be a string, it is converted to a number before the addition is performed. If numeric values appear in string concatenation, they -are converted to strings. Consider this: +are converted to strings. Consider the following: @example two = 2; three = 3 @@ -6009,7 +7215,7 @@ print (two three) + 4 @noindent This prints the (numeric) value 27. The numeric values of the variables @code{two} and @code{three} are converted to strings and -concatenated together, and the resulting string is converted back to the +concatenated together. The resulting string is converted back to the number 23, to which four is then added. @cindex null string @@ -6018,33 +7224,34 @@ number 23, to which four is then added. If, for some reason, you need to force a number to be converted to a string, concatenate the empty string, @code{""}, with that number. To force a string to be converted to a number, add zero to that string. - A string is converted to a number by interpreting any numeric prefix of the string as numerals: @code{"2.5"} converts to 2.5, @code{"1e3"} converts to 1000, and @code{"25fix"} has a numeric value of 25. -Strings that can't be interpreted as valid numbers are converted to -zero. +Strings that can't be interpreted as valid numbers convert to zero. -@vindex CONVFMT +@cindex @code{CONVFMT} variable The exact manner in which numbers are converted into strings is controlled -by the @code{awk} built-in variable @code{CONVFMT} (@pxref{Built-in Variables}). +by the @command{awk} built-in variable @code{CONVFMT} (@pxref{Built-in Variables}). Numbers are converted using the @code{sprintf} function -(@pxref{String Functions, ,Built-in Functions for String Manipulation}) with @code{CONVFMT} as the format -specifier. +specifier +(@pxref{String Functions, ,String Manipulation Functions}). @code{CONVFMT}'s default value is @code{"%.6g"}, which prints a value with -at least six significant digits. For some applications you will want to -change it to specify more precision. On most modern machines, you must -print 17 digits to capture a floating point number's value exactly. - -Strange results can happen if you set @code{CONVFMT} to a string that doesn't -tell @code{sprintf} how to format floating point numbers in a useful way. -For example, if you forget the @samp{%} in the format, all numbers will be -converted to the same constant string. +at least six significant digits. For some applications, you might want to +change it to specify more precision. +On most modern machines, +17 digits is enough to capture a floating-point number's +value exactly, +most of the time.@footnote{Pathological cases can require up to +752 digits (!), but we doubt that you need to worry about this.} @cindex dark corner +Strange results can occur if you set @code{CONVFMT} to a string that doesn't +tell @code{sprintf} how to format floating-point numbers in a useful way. +For example, if you forget the @samp{%} in the format, @command{awk} converts +all numbers to the same constant string. As a special case, if a number is an integer, then the result of converting it to a string is @emph{always} an integer, no matter what the value of @code{CONVFMT} may be. Given the following code fragment: @@ -6056,21 +7263,23 @@ b = a "" @end example @noindent -@code{b} has the value @code{"12"}, not @code{"12.00"} (d.c.). - -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} -@vindex OFMT -Prior to the POSIX standard, @code{awk} specified that the value -of @code{OFMT} was used for converting numbers to strings. @code{OFMT} +@code{b} has the value @code{"12"}, not @code{"12.00"}. +@value{DARKCORNER} + +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} +@cindex @code{OFMT} variable +Prior to the POSIX standard, @command{awk} used the value +of @code{OFMT} for converting numbers to strings. @code{OFMT} specifies the output format to use when printing numbers with @code{print}. @code{CONVFMT} was introduced in order to separate the semantics of conversion from the semantics of printing. Both @code{CONVFMT} and @code{OFMT} have the same default value: @code{"%.6g"}. In the vast majority -of cases, old @code{awk} programs will not change their behavior. -However, this use of @code{OFMT} is something to keep in mind if you must -port your program to other implementations of @code{awk}; we recommend -that instead of changing your programs, you just port @code{gawk} itself! +of cases, old @command{awk} programs do not change their behavior. +However, these semantics for @code{OFMT} are something to keep in mind if you must +port your new style program to older implementations of @command{awk}. +We recommend +that instead of changing your programs, just port @command{gawk} itself. @xref{Print, ,The @code{print} Statement}, for more information on the @code{print} statement. @@ -6086,17 +7295,13 @@ for more information on the @code{print} statement. @cindex quotient @cindex exponentiation -The @code{awk} language uses the common arithmetic operators when +The @command{awk} language uses the common arithmetic operators when evaluating expressions. All of these arithmetic operators follow normal -precedence rules, and work as you would expect them to. Arithmetic -operations are evaluated using double precision floating point, which -has the usual problems of inexactness and exceptions.@footnote{David -Goldberg, @uref{http://www.validgh.com/goldberg/paper.ps, @cite{What Every -Computer Scientist Should Know About Floating-point Arithmetic}}, -@cite{ACM Computing Surveys} @strong{23}, 1 (1991-03), 5-48.} +precedence rules and work as you would expect them to. -Here is a file @file{grades} containing a list of student names and -three test scores per student (it's a small class): +The following example uses a file named @file{grades}, which contains +a list of student names as well as three test scores per student (it's +a small class): @example Pat 100 97 58 @@ -6105,8 +7310,8 @@ Chris 72 92 89 @end example @noindent -This programs takes the file @file{grades}, and prints the average -of the scores. +This programs takes the file @file{grades} and prints the average +of the scores: @example $ awk '@{ sum = $2 + $3 + $4 ; avg = sum / 3 @@ -6116,39 +7321,58 @@ $ awk '@{ sum = $2 + $3 + $4 ; avg = sum / 3 @print{} Chris 84.3333 @end example -This table lists the arithmetic operators in @code{awk}, in order from -highest precedence to lowest: +The following list provides the arithmetic operators in @command{awk}, in order from +the highest precedence to the lowest: -@c @cartouche @table @code @item - @var{x} Negation. @item + @var{x} -Unary plus. The expression is converted to a number. +Unary plus; the expression is converted to a number. -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} @item @var{x} ^ @var{y} @itemx @var{x} ** @var{y} -Exponentiation: @var{x} raised to the @var{y} power. @samp{2 ^ 3} has -the value eight. The character sequence @samp{**} is equivalent to -@samp{^}. (The POSIX standard only specifies the use of @samp{^} -for exponentiation.) +Exponentiation; @var{x} raised to the @var{y} power. @samp{2 ^ 3} has +the value eight; the character sequence @samp{**} is equivalent to +@samp{^}. @item @var{x} * @var{y} Multiplication. +@cindex common mistakes +@cindex mistakes, common +@cindex errors, common @item @var{x} / @var{y} -Division. Since all numbers in @code{awk} are -floating point numbers, the result is not rounded to an integer: @samp{3 / 4} -has the value 0.75. +Division; because all numbers in @command{awk} are floating-point +numbers, the result is @emph{not} rounded to an integer---@samp{3 / 4} has +the value 0.75. (It is a common mistake, especially for C programmers, +to forget that @emph{all} numbers in @command{awk} are floating-point, +and that division of integer-looking constants produces a real number, +not an integer.) @item @var{x} % @var{y} -@cindex differences between @code{gawk} and @code{awk} -Remainder. The quotient is rounded toward zero to an integer, -multiplied by @var{y} and this result is subtracted from @var{x}. -This operation is sometimes known as ``trunc-mod.'' The following +Remainder; further discussion is provided in the text, just +after this list. + +@item @var{x} + @var{y} +Addition. + +@item @var{x} - @var{y} +Subtraction. +@end table + +Unary plus and minus have the same precedence, +the multiplication operators all have the same precedence, and +addition and subtraction have the same precedence. + +@cindex differences between @command{gawk} and @command{awk} +When computing the remainder of @code{@var{x} % @var{y}}, +the quotient is rounded toward zero to an integer and +multiplied by @var{y}. This result is subtracted from @var{x}; +this operation is sometimes known as ``trunc-mod.'' The following relation always holds: @example @@ -6156,38 +7380,29 @@ b * int(a / b) + (a % b) == a @end example One possibly undesirable effect of this definition of remainder is that -@code{@var{x} % @var{y}} is negative if @var{x} is negative. Thus, +@code{@var{x} % @var{y}} is negative if @var{x} is negative. Thus: @example -17 % 8 = -1 @end example -In other @code{awk} implementations, the signedness of the remainder +In other @command{awk} implementations, the signedness of the remainder may be machine dependent. @c !!! what does posix say? -@item @var{x} + @var{y} -Addition. - -@item @var{x} - @var{y} -Subtraction. -@end table -@c @end cartouche - +@cindex portability issues +@strong{Note:} +The POSIX standard only specifies the use of @samp{^} +for exponentiation. For maximum portability, do not use the @samp{**} operator. -Unary plus and minus have the same precedence, -the multiplication operators all have the same precedence, and -addition and subtraction have the same precedence. - @node Concatenation, Assignment Ops, Arithmetic Ops, Expressions @section String Concatenation @cindex Kernighan, Brian -@display -@i{It seemed like a good idea at the time.} +@quotation +@i{It seemed like a good idea at the time.}@* Brian Kernighan -@end display -@sp 1 +@end quotation @cindex string operators @cindex operators, string @@ -6197,39 +7412,35 @@ specific operator to represent it. Instead, concatenation is performed by writing expressions next to one another, with no operator. For example: @example -@group $ awk '@{ print "Field number one: " $1 @}' BBS-list @print{} Field number one: aardvark @print{} Field number one: alpo-net @dots{} -@end group @end example Without the space in the string constant after the @samp{:}, the line -would run together. For example: +runs together. For example: @example -@group $ awk '@{ print "Field number one:" $1 @}' BBS-list @print{} Field number one:aardvark @print{} Field number one:alpo-net @dots{} -@end group @end example -Since string concatenation does not have an explicit operator, it is -often necessary to insure that it happens where you want it to by -using parentheses to enclose -the items to be concatenated. For example, the +@cindex common mistakes +@cindex mistakes, common +@cindex errors, common +Because string concatenation does not have an explicit operator, it is +often necessary to insure that it happens at the right time by using +parentheses to enclose the items to concatenate. For example, the following code fragment does not concatenate @code{file} and @code{name} as you might expect: @example -@group file = "file" name = "name" print "something meaningful" > file name -@end group @end example @noindent @@ -6239,8 +7450,84 @@ It is necessary to use the following: print "something meaningful" > (file name) @end example -We recommend that you use parentheses around concatenation in all but the -most common contexts (such as on the right-hand side of @samp{=}). +@cindex order of evaluation, concatenation +@cindex concatenation evaluation order +@cindex evaluation, order of +@cindex side effects +Parentheses should be used around concatenation in all but the +most common contexts, such as on the righthand side of @samp{=}. +Be careful about the kinds of expressions used in string concatenation. +In particular, the order of evaluation of expressions used for concatenation +is undefined in the @command{awk} language. Consider this example: + +@example +BEGIN @{ + a = "don't" + print (a " " (a = "panic")) +@} +@end example + +@noindent +It is not defined whether the assignment to @code{a} happens +before or after the value of @code{a} is retrieved for producing the +concatenated value. The result could be either @samp{don't panic}, +or @samp{panic panic}. +@c see test/nasty.awk for a worse example +The precedence of concatenation, when mixed with other operators, is often +counter-intuitive. Consider this example: + +@ignore +> To: bug-gnu-utils@@gnu.org +> CC: arnold@gnu.org +> Subject: gawk 3.0.4 bug with {print -12 " " -24} +> From: Russell Schulz +> Date: Tue, 8 Feb 2000 19:56:08 -0700 +> +> gawk 3.0.4 on NT gives me: +> +> prompt> cat bad.awk +> BEGIN { print -12 " " -24; } +> +> prompt> gawk -f bad.awk +> -12-24 +> +> when I would expect +> +> -12 -24 +> +> I have not investigated the source, or other implementations. The +> bug is there on my NT and DOS versions 2.15.6 . +@end ignore + +@example +$ awk 'BEGIN @{ print -12 " " -24 @}' +@print{} -12-24 +@end example + +This ``obviously'' is concatenating @minus{}12, a space, and @minus{}24. +But where did the space disappear to? +The answer lies in the combination of operator precedences and +@command{awk}'s automatic conversion rules. To get the desired result, +write the program in the following manner: + +@example +$ awk 'BEGIN @{ print -12 " " (-24) @}' +@print{} -12 -24 +@end example + +This forces @command{awk} to treat the @samp{-} on the @samp{-24} as unary. +Otherwise, it's parsed as follows: + +@display + @minus{}12 (@code{"@ "} @minus{} 24) +@result{} @minus{}12 (0 @minus{} 24) +@result{} @minus{}12 (@minus{}24) +@result{} @minus{}12@minus{}24 +@end display + +As mentioned earlier, +when doing concatenation, @emph{parenthesize}. Otherwise, +you're never quite sure what you'll get. @node Assignment Ops, Increment Ops, Concatenation, Expressions @section Assignment Expressions @@ -6248,8 +7535,9 @@ most common contexts (such as on the right-hand side of @samp{=}). @cindex operators, assignment @cindex expression, assignment -An @dfn{assignment} is an expression that stores a new value into a -variable. For example, let's assign the value one to the variable +@cindex @code{=} operator +An @dfn{assignment} is an expression that stores a (usually different) +value into a variable. For example, let's assign the value one to the variable @code{z}: @example @@ -6259,7 +7547,8 @@ z = 1 After this expression is executed, the variable @code{z} has the value one. Whatever old value @code{z} had before the assignment is forgotten. -Assignments can store string values also. For example, this would store +Assignments can also store string values. For example, the +following stores the value @code{"this food is good"} in the variable @code{message}: @example @@ -6269,45 +7558,41 @@ message = "this " thing " is " predicate @end example @noindent -(This also illustrates string concatenation.) - +@cindex side effects +This also illustrates string concatenation. The @samp{=} sign is called an @dfn{assignment operator}. It is the -simplest assignment operator because the value of the right-hand +simplest assignment operator because the value of the righthand operand is stored unchanged. - -@cindex side effect Most operators (addition, concatenation, and so on) have no effect -except to compute a value. If you ignore the value, you might as well -not use the operator. An assignment operator is different; it does -produce a value, but even if you ignore the value, the assignment still +except to compute a value. If the value isn't used, there's no reason to +use the operator. An assignment operator is different; it does +produce a value, but even if you ignore it, the assignment still makes itself felt through the alteration of the variable. We call this a @dfn{side effect}. @cindex lvalue @cindex rvalue -The left-hand operand of an assignment need not be a variable +The lefthand operand of an assignment need not be a variable (@pxref{Variables}); it can also be a field (@pxref{Changing Fields, ,Changing the Contents of a Field}) or -an array element (@pxref{Arrays, ,Arrays in @code{awk}}). +an array element (@pxref{Arrays, ,Arrays in @command{awk}}). These are all called @dfn{lvalues}, -which means they can appear on the left-hand side of an assignment operator. -The right-hand operand may be any expression; it produces the new value -which the assignment stores in the specified variable, field or array +which means they can appear on the lefthand side of an assignment operator. +The righthand operand may be any expression; it produces the new value +that the assignment stores in the specified variable, field, or array element. (Such values are called @dfn{rvalues}). @cindex types of variables It is important to note that variables do @emph{not} have permanent types. -The type of a variable is simply the type of whatever value it happens +A variable's type is simply the type of whatever value it happens to hold at the moment. In the following program fragment, the variable @code{foo} has a numeric value at first, and a string value later on: @example -@group foo = 1 print foo foo = "bar" print foo -@end group @end example @noindent @@ -6315,7 +7600,7 @@ When the second assignment gives @code{foo} a string value, the fact that it previously had a numeric value is forgotten. String values that do not begin with a digit have a numeric value of -zero. After executing this code, the value of @code{foo} is five: +zero. After executing the following code, the value of @code{foo} is five: @example foo = "a string" @@ -6323,32 +7608,36 @@ foo = foo + 5 @end example @noindent -(Note that using a variable as a number and then later as a string can -be confusing and is poor programming style. The above examples illustrate how -@code{awk} works, @emph{not} how you should write your own programs!) +@strong{Note:} Using a variable as a number and then later as a string +can be confusing and is poor programming style. The previous two examples +illustrate how @command{awk} works, @emph{not} how you should write your +own programs! -An assignment is an expression, so it has a value: the same value that -is assigned. Thus, @samp{z = 1} as an expression has the value one. -One consequence of this is that you can write multiple assignments together: +An assignment is an expression, so it has a value---the same value that +is assigned. Thus, @samp{z = 1} is an expression with the value one. +One consequence of this is that you can write multiple assignments together, +such as: @example -x = y = z = 0 +x = y = z = 5 @end example @noindent -stores the value zero in all three variables. It does this because the -value of @samp{z = 0}, which is zero, is stored into @code{y}, and then -the value of @samp{y = z = 0}, which is zero, is stored into @code{x}. - -You can use an assignment anywhere an expression is called for. For -example, it is valid to write @samp{x != (y = 1)} to set @code{y} to one +This example stores the value five in all three variables +(@code{x}, @code{y}, and @code{z}). +It does so because the +value of @samp{z = 5}, which is five, is stored into @code{y} and then +the value of @samp{y = z = 5}, which is five, is stored into @code{x}. + +Assignments may be used anywhere an expression is called for. For +example, it is valid to write @samp{x != (y = 1)} to set @code{y} to one, and then test whether @code{x} equals one. But this style tends to make -programs hard to read; except in a one-shot program, you should -not use such nesting of assignments. +programs hard to read; such nesting of assignments should be avoided, +except perhaps in a one-shot program. Aside from @samp{=}, there are several other assignment operators that do arithmetic with the old value of the variable. For example, the -operator @samp{+=} computes a new value by adding the right-hand value +operator @samp{+=} computes a new value by adding the righthand value to the old value of the variable. Thus, the following assignment adds five to the value of @code{foo}: @@ -6364,15 +7653,14 @@ foo = foo + 5 @end example @noindent -Use whichever one makes the meaning of your program clearer. +Use whichever makes the meaning of your program clearer. There are situations where using @samp{+=} (or any assignment operator) -is @emph{not} the same as simply repeating the left-hand operand in the -right-hand expression. For example: +is @emph{not} the same as simply repeating the lefthand operand in the +righthand expression. For example: @cindex Rankin, Pat @example -@group # Thanks to Pat Rankin for this example BEGIN @{ foo[rand()] += 5 @@ -6383,20 +7671,18 @@ BEGIN @{ for (x in bar) print x, bar[x] @} -@end group @end example @noindent -The indices of @code{bar} are guaranteed to be different, because -@code{rand} will return different values each time it is called. +The indices of @code{bar} are practically guaranteed to be different, because +@code{rand} returns different values each time it is called. (Arrays and the @code{rand} function haven't been covered yet. -@xref{Arrays, ,Arrays in @code{awk}}, -and see @ref{Numeric Functions, ,Numeric Built-in Functions}, for more information). -This example illustrates an important fact about the assignment -operators: the left-hand expression is only evaluated @emph{once}. - -It is also up to the implementation as to which expression is evaluated -first, the left-hand one or the right-hand one. +@xref{Arrays, ,Arrays in @command{awk}}, +and see @ref{Numeric Functions}, for more information). +This example illustrates an important fact about assignment +operators: the lefthand expression is only evaluated @emph{once}. +It is up to the implementation as to which expression is evaluated +first, the lefthand or the righthand. Consider this example: @example @@ -6408,14 +7694,13 @@ a[i += 2] = i + 1 The value of @code{a[3]} could be either two or four. Here is a table of the arithmetic assignment operators. In each -case, the right-hand operand is an expression whose value is converted +case, the righthand operand is an expression whose value is converted to a number. -@c @cartouche +@ignore @table @code @item @var{lvalue} += @var{increment} -Adds @var{increment} to the value of @var{lvalue} to make the new value -of @var{lvalue}. +Adds @var{increment} to the value of @var{lvalue}. @item @var{lvalue} -= @var{decrement} Subtracts @var{decrement} from the value of @var{lvalue}. @@ -6429,102 +7714,212 @@ Divides the value of @var{lvalue} by @var{divisor}. @item @var{lvalue} %= @var{modulus} Sets @var{lvalue} to its remainder by @var{modulus}. -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} @item @var{lvalue} ^= @var{power} @itemx @var{lvalue} **= @var{power} Raises @var{lvalue} to the power @var{power}. (Only the @samp{^=} operator is specified by POSIX.) @end table -@c @end cartouche +@end ignore + +@cindex @code{+=} operator +@cindex @code{-=} operator +@cindex @code{*=} operator +@cindex @code{/=} operator +@cindex @code{%=} operator +@cindex @code{^=} operator +@cindex @code{**=} operator +@multitable {@var{lvalue} *= @var{coefficient}} {Subtracts @var{decrement} from the value of @var{lvalue}.} +@item @var{lvalue} @code{+=} @var{increment} @tab Adds @var{increment} to the value of @var{lvalue}. + +@item @var{lvalue} @code{-=} @var{decrement} @tab Subtracts @var{decrement} from the value of @var{lvalue}. + +@item @var{lvalue} @code{*=} @var{coefficient} @tab Multiplies the value of @var{lvalue} by @var{coefficient}. +@item @var{lvalue} @code{/=} @var{divisor} @tab Divides the value of @var{lvalue} by @var{divisor}. + +@item @var{lvalue} @code{%=} @var{modulus} @tab Sets @var{lvalue} to its remainder by @var{modulus}. + +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} +@item @var{lvalue} @code{^=} @var{power} @tab +@item @var{lvalue} @code{**=} @var{power} @tab Raises @var{lvalue} to the power @var{power}. +@end multitable + +@cindex portability issues +@strong{Note:} +Only the @samp{^=} operator is specified by POSIX. For maximum portability, do not use the @samp{**=} operator. +@c fakenode --- for prepinfo +@subheading Advanced Notes: Syntactic Ambiguities Between @samp{/=} and Regular Expressions +@cindex advanced notes + +@c derived from email from "Nelson H. F. Beebe" +@c Date: Mon, 1 Sep 1997 13:38:35 -0600 (MDT) + +@cindex dark corner +@cindex ambiguity, syntactic: @code{/=} operator vs. @code{/=@dots{}/} regexp constant +@cindex syntactic ambiguity: @code{/=} operator vs. @code{/=@dots{}/} regexp constant +@cindex @code{/=} operator vs. @code{/=@dots{}/} regexp constant +There is a syntactic ambiguity between the @samp{/=} assignment +operator and regexp constants whose first character is an @samp{=}. +@value{DARKCORNER} +This is most notable in commercial @command{awk} versions. +For example: + +@example +$ awk /==/ /dev/null +@error{} awk: syntax error at source line 1 +@error{} context is +@error{} >>> /= <<< +@error{} awk: bailing out at source line 1 +@end example + +@noindent +A workaround is: + +@example +awk '/[=]=/' /dev/null +@end example + +@command{gawk} does not have this problem, +nor do the other +freely-available versions described in +@ref{Other Versions, , Other Freely Available @command{awk} Implementations}. + @node Increment Ops, Truth Values, Assignment Ops, Expressions @section Increment and Decrement Operators @cindex increment operators @cindex operators, increment @dfn{Increment} and @dfn{decrement operators} increase or decrease the value of -a variable by one. You could do the same thing with an assignment operator, so -the increment operators add no power to the @code{awk} language; but they +a variable by one. An assignment operator can do the same thing, so +the increment operators add no power to the @command{awk} language; however they are convenient abbreviations for very common operations. -The operator to add one is written @samp{++}. It can be used to increment +@cindex side effects +The operator used for adding one is written @samp{++}. It can be used to increment a variable either before or after taking its value. - -To pre-increment a variable @var{v}, write @samp{++@var{v}}. This adds -one to the value of @var{v} and that new value is also the value of this -expression. The assignment expression @samp{@var{v} += 1} is completely -equivalent. - +To pre-increment a variable @code{v}, write @samp{++v}. This adds +one to the value of @code{v}---that new value is also the value of the +expression. (The assignment expression @samp{v += 1} is completely +equivalent.) Writing the @samp{++} after the variable specifies post-increment. This increments the variable value just the same; the difference is that the value of the increment expression itself is the variable's @emph{old} value. Thus, if @code{foo} has the value four, then the expression @samp{foo++} has the value four, but it changes the value of @code{foo} to five. +In other words, the operator returns the old value of the variable, +but with the side effect of incrementing it. -The post-increment @samp{foo++} is nearly equivalent to writing @samp{(foo +The post-increment @samp{foo++} is nearly the same as writing @samp{(foo += 1) - 1}. It is not perfectly equivalent because all numbers in -@code{awk} are floating point: in floating point, @samp{foo + 1 - 1} does +@command{awk} are floating-point---in floating-point, @samp{foo + 1 - 1} does not necessarily equal @code{foo}. But the difference is minute as long as you stick to numbers that are fairly small (less than 10e12). -Any lvalue can be incremented. Fields and array elements are incremented -just like variables. (Use @samp{$(i++)} when you wish to do a field reference +Fields and array elements are incremented +just like variables. (Use @samp{$(i++)} when you want to do a field reference and a variable increment at the same time. The parentheses are necessary -because of the precedence of the field reference operator, @samp{$}.) +because of the precedence of the field reference operator @samp{$}.) @cindex decrement operators @cindex operators, decrement -The decrement operator @samp{--} works just like @samp{++} except that -it subtracts one instead of adding. Like @samp{++}, it can be used before +The decrement operator @samp{--} works just like @samp{++}, except that +it subtracts one instead of adding it. As with @samp{++}, it can be used before the lvalue to pre-decrement or after it to post-decrement. +Following is a summary of increment and decrement expressions: -Here is a summary of increment and decrement expressions. - -@c @cartouche @table @code +@cindex @code{++} operator @item ++@var{lvalue} -This expression increments @var{lvalue} and the new value becomes the +This expression increments @var{lvalue}, and the new value becomes the value of the expression. @item @var{lvalue}++ This expression increments @var{lvalue}, but the value of the expression is the @emph{old} value of @var{lvalue}. +@cindex @code{--} operator @item --@var{lvalue} -Like @samp{++@var{lvalue}}, but instead of adding, it subtracts. It -decrements @var{lvalue} and delivers the value that results. +This expression is +like @samp{++@var{lvalue}}, but instead of adding, it subtracts. It +decrements @var{lvalue} and delivers the value that is the result. @item @var{lvalue}-- -Like @samp{@var{lvalue}++}, but instead of adding, it subtracts. It +This expression is +like @samp{@var{lvalue}++}, but instead of adding, it subtracts. It decrements @var{lvalue}. The value of the expression is the @emph{old} value of @var{lvalue}. @end table -@c @end cartouche + +@c fakenode --- for prepinfo +@subheading Advanced Notes: Operator Evaluation Order +@cindex advanced notes +@cindex precedence +@cindex operator precedence +@cindex portability issues +@cindex evaluation, order of +@cindex Marx, Groucho +@quotation +@i{Doctor, doctor! It hurts when I do this!@* +So don't do that!}@* +Groucho Marx +@end quotation + +@noindent +What happens for something like the following? + +@example +b = 6 +print b += b++ +@end example + +@noindent +Or something even stranger? + +@example +b = 6 +b += ++b + b++ +print b +@end example + +@cindex side effects +In other words, when do the various side effects prescribed by the +postfix operators (@samp{b++}) take effect? +When side effects happen is @dfn{implementation defined}. +In other words, it is up to the particular version of @command{awk}. +The result for the first example may be 12 or 13, and for the second, it +may be 22 or 23. + +In short, doing things like this is not recommended and definitely +not anything that you can rely upon for portability. +You should avoid such things in your own programs. +@c You'll sleep better at night and be able to look at yourself +@c in the mirror in the morning. @node Truth Values, Typing and Comparison, Increment Ops, Expressions -@section True and False in @code{awk} +@section True and False in @command{awk} @cindex truth values @cindex logical true @cindex logical false -Many programming languages have a special representation for the concepts -of ``true'' and ``false.'' Such languages usually use the special -constants @code{true} and @code{false}, or perhaps their upper-case -equivalents. - @cindex null string @cindex empty string -@code{awk} is different. It borrows a very simple concept of true and -false from C. In @code{awk}, any non-zero numeric value, @emph{or} any +Many programming languages have a special representation for the concepts +of ``true'' and ``false.'' Such languages usually use the special +constants @code{true} and @code{false}, or perhaps their uppercase +equivalents. +However, @command{awk} is different. +It borrows a very simple concept of true and +false from C. In @command{awk}, any nonzero numeric value @emph{or} any non-empty string value is true. Any other value (zero or the null -string, @code{""}) is false. The following program will print @samp{A strange +string @code{""}) is false. The following program prints @samp{A strange truth value} three times: @example -@group BEGIN @{ if (3.1415927) print "A strange truth value" @@ -6533,12 +7928,12 @@ BEGIN @{ if (j = 57) print "A strange truth value" @} -@end group @end example @cindex dark corner -There is a surprising consequence of the ``non-zero or non-null'' rule: -The string constant @code{"0"} is actually true, since it is non-null (d.c.). +There is a surprising consequence of the ``nonzero or non-null'' rule: +the string constant @code{"0"} is actually true, because it is non-null. +@value{DARKCORNER} @node Typing and Comparison, Boolean Ops, Truth Values, Expressions @section Variable Typing and Comparison Expressions @@ -6547,60 +7942,56 @@ The string constant @code{"0"} is actually true, since it is non-null (d.c.). @cindex expression, matching @cindex relational operators @cindex operators, relational -@cindex regexp match/non-match operators +@cindex regexp operators @cindex variable typing @cindex types of variables -@c 2e: consider splitting this section into subsections -@display -@i{The Guide is definitive. Reality is frequently inaccurate.} +@quotation +@i{The Guide is definitive. Reality is frequently inaccurate.}@* The Hitchhiker's Guide to the Galaxy -@end display -@sp 1 +@end quotation -Unlike other programming languages, @code{awk} variables do not have a +Unlike other programming languages, @command{awk} variables do not have a fixed type. Instead, they can be either a number or a string, depending upon the value that is assigned to them. @cindex numeric string The 1992 POSIX standard introduced the concept of a @dfn{numeric string}, which is simply a string that looks -like a number, for example, @code{@w{" +2"}}. This concept is used +like a number---for example, @code{@w{" +2"}}. This concept is used for determining the type of a variable. - -The type of the variable is important, since the types of two variables +The type of the variable is important because the types of two variables determine how they are compared. +In @command{gawk}, variable typing follows these rules: -In @code{gawk}, variable typing follows these rules. - -@enumerate 1 +@itemize @bullet @item -A numeric literal or the result of a numeric operation has the @var{numeric} +A numeric constant or the result of a numeric operation has the @var{numeric} attribute. @item -A string literal or the result of a string operation has the @var{string} +A string constant or the result of a string operation has the @var{string} attribute. @item Fields, @code{getline} input, @code{FILENAME}, @code{ARGV} elements, -@code{ENVIRON} elements and the +@code{ENVIRON} elements, and the elements of an array created by @code{split} that are numeric strings have the @var{strnum} attribute. Otherwise, they have the @var{string} attribute. Uninitialized variables also have the @var{strnum} attribute. @item -Attributes propagate across assignments, but are not changed by +Attributes propagate across assignments but are not changed by any use. -@c (Although a use may cause the entity to acquire an additional -@c value such that it has both a numeric and string value -- this leaves the +@c (Although a use may cause the entity to acquire an additional +@c value such that it has both a numeric and string value, this leaves the @c attribute unchanged.) @c This is important but not relevant -@end enumerate +@end itemize The last rule is particularly important. In the following program, @code{a} has numeric type, even though it is later used in a string -operation. +operation: @example BEGIN @{ @@ -6611,8 +8002,8 @@ BEGIN @{ @end example When two operands are compared, either string comparison or numeric comparison -may be used, depending on the attributes of the operands, according to the -following, symmetric, matrix: +may be used. This depends upon the attributes of the operands, according to the +following symmetric matrix: @c thanks to Karl Berry, kb@cs.umb.edu, for major help with TeX tables @tex @@ -6657,24 +8048,34 @@ NUMERIC &&string &numeric &numeric\cr STRNUM &&string &numeric &numeric\cr }}} @end tex -@ifinfo +@ifnottex @display - +---------------------------------------------- - | STRING NUMERIC STRNUM + +---------------------------------------------- + | STRING NUMERIC STRNUM --------+---------------------------------------------- - | -STRING | string string string - | -NUMERIC | string numeric numeric - | -STRNUM | string numeric numeric + | +STRING | string string string + | +NUMERIC | string numeric numeric + | +STRNUM | string numeric numeric --------+---------------------------------------------- @end display -@end ifinfo - -The basic idea is that user input that looks numeric, and @emph{only} -user input, should be treated as numeric, even though it is actually -made of characters, and is therefore also a string. +@end ifnottex + +The basic idea is that user input that looks numeric---and @emph{only} +user input---should be treated as numeric, even though it is actually +made of characters and is therefore also a string. +Thus, for example, the string constant @w{@code{" +3.14"}} +is a string, even though it looks numeric, +and is @emph{never} treated as number for comparison +purposes. + +In short, when one operand is a ``pure'' string, such as a string +constant, then a string comparison is performed. Otherwise, a +numeric comparison is performed.@footnote{The POSIX standard is under +revision. The revised standard's rules for typing and comparison are +the same as just described for @command{gawk}.} @dfn{Comparison expressions} compare strings or numbers for relationships such as equality. They are written using @dfn{relational @@ -6692,7 +8093,6 @@ them: @cindex @code{~} operator @cindex @code{!~} operator @cindex @code{in} operator -@c @cartouche @table @code @item @var{x} < @var{y} True if @var{x} is less than @var{y}. @@ -6721,26 +8121,24 @@ True if the string @var{x} does not match the regexp denoted by @var{y}. @item @var{subscript} in @var{array} True if the array @var{array} has an element with the subscript @var{subscript}. @end table -@c @end cartouche Comparison expressions have the value one if true and zero if false. - When comparing operands of mixed types, numeric operands are converted to strings using the value of @code{CONVFMT} (@pxref{Conversion, ,Conversion of Strings and Numbers}). Strings are compared by comparing the first character of each, then the second character of each, -and so on. Thus @code{"10"} is less than @code{"9"}. If there are two +and so on. Thus, @code{"10"} is less than @code{"9"}. If there are two strings where one is a prefix of the other, the shorter string is less than -the longer one. Thus @code{"abc"} is less than @code{"abcd"}. +the longer one. Thus, @code{"abc"} is less than @code{"abcd"}. @cindex common mistakes @cindex mistakes, common @cindex errors, common -It is very easy to accidentally mistype the @samp{==} operator, and -leave off one of the @samp{=}s. The result is still valid @code{awk} -code, but the program will not do what you mean: +It is very easy to accidentally mistype the @samp{==} operator and +leave off one of the @samp{=} characters. The result is still valid @command{awk} +code, but the program does not do what is intended: @example if (a = b) # oops! should be a == b @@ -6751,12 +8149,12 @@ else @noindent Unless @code{b} happens to be zero or the null string, the @code{if} -part of the test will always succeed. Because the operators are +part of the test always succeeds. Because the operators are so similar, this kind of error is very difficult to spot when scanning the source code. -Here are some sample expressions, how @code{gawk} compares them, and what -the result of the comparison is. +The following table of expressions illustrates the kind of comparison +@command{gawk} performs, as well as what the result of the comparison is: @table @code @item 1.5 <= 2.0 @@ -6776,41 +8174,37 @@ string comparison (true) string comparison (true) @item a = 2; b = " +2" -@itemx a == b +@item a == b string comparison (false) @end table -In this example, +In the next example: @example -@group $ echo 1e2 3 | awk '@{ print ($1 < $2) ? "true" : "false" @}' @print{} false -@end group @end example +@cindex comparisons, string vs. regexp +@cindex string comparison vs. regexp comparison +@cindex regexp comparison vs. string comparison @noindent -the result is @samp{false} since both @code{$1} and @code{$2} are numeric -strings and thus both have the @var{strnum} attribute, -dictating a numeric comparison. - +the result is @samp{false} because both @code{$1} and @code{$2} +are user input. They are numeric strings---therefore both have +the @var{strnum} attribute, dictating a numeric comparison. The purpose of the comparison rules and the use of numeric strings is to attempt to produce the behavior that is ``least surprising,'' while still ``doing the right thing.'' - -@cindex comparisons, string vs. regexp -@cindex string comparison vs. regexp comparison -@cindex regexp comparison vs. string comparison String comparisons and regular expression comparisons are very different. -For example, +For example: @example x == "foo" @end example @noindent -has the value of one, or is true, if the variable @code{x} -is precisely @samp{foo}. By contrast, +has the value one, or is true if the variable @code{x} +is precisely @samp{foo}. By contrast: @example x ~ /foo/ @@ -6820,97 +8214,86 @@ x ~ /foo/ has the value one if @code{x} contains @samp{foo}, such as @code{"Oh, what a fool am I!"}. -The right hand operand of the @samp{~} and @samp{!~} operators may be -either a regexp constant (@code{/@dots{}/}), or an ordinary -expression, in which case the value of the expression as a string is used as a +The righthand operand of the @samp{~} and @samp{!~} operators may be +either a regexp constant (@code{/@dots{}/}) or an ordinary +expression. In the latter case, the value of the expression as a string is used as a dynamic regexp (@pxref{Regexp Usage, ,How to Use Regular Expressions}; also @pxref{Computed Regexps, ,Using Dynamic Regexps}). @cindex regexp as expression -In recent implementations of @code{awk}, a constant regular +In modern implementations of @command{awk}, a constant regular expression in slashes by itself is also an expression. The regexp -@code{/@var{regexp}/} is an abbreviation for this comparison expression: +@code{/@var{regexp}/} is an abbreviation for the following comparison expression: @example $0 ~ /@var{regexp}/ @end example One special place where @code{/foo/} is @emph{not} an abbreviation for -@samp{$0 ~ /foo/} is when it is the right-hand operand of @samp{~} or -@samp{!~}! +@samp{$0 ~ /foo/} is when it is the righthand operand of @samp{~} or +@samp{!~}. @xref{Using Constant Regexps, ,Using Regular Expression Constants}, where this is discussed in more detail. -@c This paragraph has been here since day 1, and has always bothered -@c me, especially since the expression doesn't really make a lot of -@c sense. So, just take it out. -@ignore -In some contexts it may be necessary to write parentheses around the -regexp to avoid confusing the @code{gawk} parser. For example, -@samp{(/x/ - /y/) > threshold} is not allowed, but @samp{((/x/) - (/y/)) -> threshold} parses properly. -@end ignore - @node Boolean Ops, Conditional Exp, Typing and Comparison, Expressions @section Boolean Expressions @cindex expression, boolean @cindex boolean expressions @cindex operators, boolean @cindex boolean operators -@cindex logical operations -@cindex operations, logical +@cindex logical operators +@cindex operators, logical @cindex short-circuit operators @cindex operators, short-circuit -@cindex and operator -@cindex or operator -@cindex not operator +@cindex AND logical operator +@cindex OR logical operator +@cindex NOT logical operator @cindex @code{&&} operator @cindex @code{||} operator @cindex @code{!} operator -A @dfn{boolean expression} is a combination of comparison expressions or -matching expressions, using the boolean operators ``or'' +A @dfn{Boolean expression} is a combination of comparison expressions or +matching expressions, using the Boolean operators ``or'' (@samp{||}), ``and'' (@samp{&&}), and ``not'' (@samp{!}), along with -parentheses to control nesting. The truth value of the boolean expression is +parentheses to control nesting. The truth value of the Boolean expression is computed by combining the truth values of the component expressions. Boolean expressions are also referred to as @dfn{logical expressions}. The terms are equivalent. Boolean expressions can be used wherever comparison and matching expressions can be used. They can be used in @code{if}, @code{while}, -@code{do} and @code{for} statements +@code{do}, and @code{for} statements (@pxref{Statements, ,Control Statements in Actions}). -They have numeric values (one if true, zero if false), which come into play -if the result of the boolean expression is stored in a variable, or +They have numeric values (one if true, zero if false), that come into play +if the result of the Boolean expression is stored in a variable or used in arithmetic. -In addition, every boolean expression is also a valid pattern, so +In addition, every Boolean expression is also a valid pattern, so you can use one as a pattern to control the execution of rules. +The Boolean operators are: -Here are descriptions of the three boolean operators, with examples. - -@c @cartouche @table @code @item @var{boolean1} && @var{boolean2} True if both @var{boolean1} and @var{boolean2} are true. For example, the following statement prints the current input record if it contains -both @samp{2400} and @samp{foo}. +both @samp{2400} and @samp{foo}: @example if ($0 ~ /2400/ && $0 ~ /foo/) print @end example +@cindex side effects The subexpression @var{boolean2} is evaluated only if @var{boolean1} is true. This can make a difference when @var{boolean2} contains -expressions that have side effects: in the case of @samp{$0 ~ /foo/ && +expressions that have side effects. In the case of @samp{$0 ~ /foo/ && ($2 == bar++)}, the variable @code{bar} is not incremented if there is -no @samp{foo} in the record. +no substring @samp{foo} in the record. @item @var{boolean1} || @var{boolean2} True if at least one of @var{boolean1} or @var{boolean2} is true. For example, the following statement prints all records in the input that contain @emph{either} @samp{2400} or -@samp{foo}, or both. +@samp{foo} or both: @example if ($0 ~ /2400/ || $0 ~ /foo/) print @@ -6921,17 +8304,19 @@ is false. This can make a difference when @var{boolean2} contains expressions that have side effects. @item ! @var{boolean} -True if @var{boolean} is false. For example, the following program prints -all records in the input file @file{BBS-list} that do @emph{not} contain the -string @samp{foo}. +True if @var{boolean} is false. For example, +the following program prints @samp{no home!} in +the unusual event that the @env{HOME} environment +variable is not defined: -@c A better example would be `if (! (subscript in array)) ...' but we -@c haven't done anything with arrays or `in' yet. Sigh. @example -awk '@{ if (! ($0 ~ /foo/)) print @}' BBS-list +BEGIN @{ if (! ("HOME" in ENVIRON)) + print "no home!" @} @end example + +(The @code{in} operator is described in +@ref{Reference to Elements, ,Referring to an Array Element}.) @end table -@c @end cartouche The @samp{&&} and @samp{||} operators are called @dfn{short-circuit} operators because of the way they work. Evaluation of the full expression @@ -6939,48 +8324,56 @@ is ``short-circuited'' if the result can be determined part way through its evaluation. @cindex line continuation -You can continue a statement that uses @samp{&&} or @samp{||} simply +Statements that use @samp{&&} or @samp{||} can be continued simply by putting a newline after them. But you cannot put a newline in front of either of these operators without using backslash continuation -(@pxref{Statements/Lines, ,@code{awk} Statements Versus Lines}). +(@pxref{Statements/Lines, ,@command{awk} Statements Versus Lines}). -The actual value of an expression using the @samp{!} operator will be +@cindex flag variables +The actual value of an expression using the @samp{!} operator is either one or zero, depending upon the truth value of the expression it is applied to. - The @samp{!} operator is often useful for changing the sense of a flag variable from false to true and back again. For example, the following program is one way to print lines in between special bracketing lines: @example -$1 == "START" @{ interested = ! interested @} +$1 == "START" @{ interested = ! interested; next @} interested == 1 @{ print @} -$1 == "END" @{ interested = ! interested @} +$1 == "END" @{ interested = ! interested; next @} @end example @noindent -The variable @code{interested}, like all @code{awk} variables, starts +The variable @code{interested}, as with all @command{awk} variables, starts out initialized to zero, which is also false. When a line is seen whose first field is @samp{START}, the value of @code{interested} is toggled to true, using @samp{!}. The next rule prints lines as long as @code{interested} is true. When a line is seen whose first field is @samp{END}, @code{interested} is toggled back to false. + @ignore -We should discuss using `next' in the two rules that toggle the -variable, to avoid printing the bracketing lines, but that's more -distraction than really needed. +Scott Deifik points out that this program isn't robust against +bogus input data, but the point is to illustrate the use of `!', +so we'll leave well enough alone. @end ignore +@strong{Note:} The @code{next} statement is discussed in +@ref{Next Statement, ,The @code{next} Statement}. +@code{next} tells @command{awk} to skip the rest of the rules, get the +next record, and start processing the rules over again at the top. +The reason it's there is to avoid printing the bracketing +@samp{START} and @samp{END} lines. + @node Conditional Exp, Function Calls, Boolean Ops, Expressions @section Conditional Expressions @cindex conditional expression @cindex expression, conditional -A @dfn{conditional expression} is a special kind of expression with +A @dfn{conditional expression} is a special kind of expression that has three operands. It allows you to use one expression's value to select one of two other expressions. - -The conditional expression is the same as in the C language: +The conditional expression is the same as in the C language, +as shown here: @example @var{selector} ? @var{if-true-exp} : @var{if-false-exp} @@ -6988,22 +8381,22 @@ The conditional expression is the same as in the C language: @noindent There are three subexpressions. The first, @var{selector}, is always -computed first. If it is ``true'' (not zero and not null) then +computed first. If it is ``true'' (not zero or not null), then @var{if-true-exp} is computed next and its value becomes the value of the whole expression. Otherwise, @var{if-false-exp} is computed next and its value becomes the value of the whole expression. - -For example, this expression produces the absolute value of @code{x}: +For example, the following expression produces the absolute value of @code{x}: @example -x > 0 ? x : -x +x >= 0 ? x : -x @end example -Each time the conditional expression is computed, exactly one of +@cindex side effects +Each time the conditional expression is computed, only one of @var{if-true-exp} and @var{if-false-exp} is used; the other is ignored. This is important when the expressions have side effects. For example, this conditional expression examines element @code{i} of either array -@code{a} or array @code{b}, and increments @code{i}. +@code{a} or array @code{b}, and increments @code{i}: @example x == y ? a[i++] : b[i++] @@ -7011,46 +8404,48 @@ x == y ? a[i++] : b[i++] @noindent This is guaranteed to increment @code{i} exactly once, because each time -only one of the two increment expressions is executed, +only one of the two increment expressions is executed and the other is not. -@xref{Arrays, ,Arrays in @code{awk}}, +@xref{Arrays, ,Arrays in @command{awk}}, for more information about arrays. -@cindex differences between @code{gawk} and @code{awk} +@cindex differences between @command{gawk} and @command{awk} @cindex line continuation -As a minor @code{gawk} extension, -you can continue a statement that uses @samp{?:} simply +As a minor @command{gawk} extension, +a statement that uses @samp{?:} can be continued simply by putting a newline after either character. -However, you cannot put a newline in front -of either character without using backslash continuation -(@pxref{Statements/Lines, ,@code{awk} Statements Versus Lines}). -If @samp{--posix} is specified -(@pxref{Options, , Command Line Options}), then this extension is disabled. +However, putting a newline in front +of either character does not work without using backslash continuation +(@pxref{Statements/Lines, ,@command{awk} Statements Versus Lines}). +If @option{--posix} is specified +(@pxref{Options, , Command-Line Options}), then this extension is disabled. @node Function Calls, Precedence, Conditional Exp, Expressions @section Function Calls @cindex function call @cindex calling a function -A @dfn{function} is a name for a particular calculation. Because it has -a name, you can ask for it by name at any point in the program. For +A @dfn{function} is a name for a particular calculation. +This enables you to +ask for it by name at any point in the program. For example, the function @code{sqrt} computes the square root of a number. A fixed set of functions are @dfn{built-in}, which means they are -available in every @code{awk} program. The @code{sqrt} function is one +available in every @command{awk} program. The @code{sqrt} function is one of these. @xref{Built-in, ,Built-in Functions}, for a list of built-in -functions and their descriptions. In addition, you can define your own +functions and their descriptions. In addition, you can define functions for use in your program. -@xref{User-defined, ,User-defined Functions}, for how to do this. +@xref{User-defined, ,User-Defined Functions}, +for instructions on how to do this. @cindex arguments in function call The way to use a function is with a @dfn{function call} expression, which consists of the function name followed immediately by a list of -@dfn{arguments} in parentheses. The arguments are expressions which +@dfn{arguments} in parentheses. The arguments are expressions that provide the raw materials for the function's calculations. When there is more than one argument, they are separated by commas. If -there are no arguments, write just @samp{()} after the function name. -Here are some examples: +there are no arguments, just write @samp{()} after the function name. +The following examples show function calls with and without arguments: @example sqrt(x^2 + y^2) @i{one argument} @@ -7058,40 +8453,41 @@ atan2(y, x) @i{two arguments} rand() @i{no arguments} @end example -@strong{Do not put any space between the function name and the -open-parenthesis!} A user-defined function name looks just like the name of -a variable, and space would make the expression look like concatenation -of a variable with an expression inside parentheses. Space before the -parenthesis is harmless with built-in functions, but it is best not to get -into the habit of using space to avoid mistakes with user-defined -functions. +@strong{Caution:} +Do not put any space between the function name and the open-parenthesis! +A user-defined function name looks just like the name of a +variable---a space would make the expression look like concatenation of +a variable with an expression inside parentheses. -Each function expects a particular number of arguments. For example, the -@code{sqrt} function must be called with a single argument, the number -to take the square root of: +With built-in functions, space before the parenthesis is harmless, but +it is best not to get into the habit of using space to avoid mistakes +with user-defined functions. Each function expects a particular number +of arguments. For example, the @code{sqrt} function must be called with +a single argument: the number to take the square root of: @example sqrt(@var{argument}) @end example -Some of the built-in functions allow you to omit the final argument. -If you do so, they use a reasonable default. +Some of the built-in functions have one or +more optional arguments. +If those arguments are not supplied, the functions +use a reasonable default value. @xref{Built-in, ,Built-in Functions}, for full details. If arguments are omitted in calls to user-defined functions, then those arguments are -treated as local variables, initialized to the empty string -(@pxref{User-defined, ,User-defined Functions}). +treated as local variables and initialized to the empty string +(@pxref{User-defined, ,User-Defined Functions}). +@cindex side effects Like every other expression, the function call has a value, which is computed by the function based on the arguments you give it. In this example, the value of @samp{sqrt(@var{argument})} is the square root of @var{argument}. A function can also have side effects, such as assigning values to certain variables or doing I/O. - -Here is a command to read numbers, one number per line, and print the +The following program reads numbers, one number per line, and prints the square root of each one: @example -@group $ awk '@{ print "The square root of", $1, "is", sqrt($1) @}' 1 @print{} The square root of 1 is 1 @@ -7099,48 +8495,83 @@ $ awk '@{ print "The square root of", $1, "is", sqrt($1) @}' @print{} The square root of 3 is 1.73205 5 @print{} The square root of 5 is 2.23607 -@kbd{Control-d} -@end group +@kbd{Ctrl-d} @end example -@node Precedence, , Function Calls, Expressions +@node Precedence, , Function Calls, Expressions @section Operator Precedence (How Operators Nest) @cindex precedence @cindex operator precedence -@dfn{Operator precedence} determines how operators are grouped, when +@dfn{Operator precedence} determines how operators are grouped when different operators appear close by in one expression. For example, @samp{*} has higher precedence than @samp{+}; thus, @samp{a + b * c} means to multiply @code{b} and @code{c}, and then add @code{a} to the -product (i.e.@: @samp{a + (b * c)}). +product (i.e., @samp{a + (b * c)}). -You can overrule the precedence of the operators by using parentheses. -You can think of the precedence rules as saying where the -parentheses are assumed to be if you do not write parentheses yourself. In -fact, it is wise to always use parentheses whenever you have an unusual +The normal precedence of the operators can be overruled by using parentheses. +Think of the precedence rules as saying where the +parentheses are assumed to be. In +fact, it is wise to always use parentheses whenever there is an unusual combination of operators, because other people who read the program may -not remember what the precedence is in this case. You might forget, -too; then you could make a mistake. Explicit parentheses will help prevent -any such mistake. +not remember what the precedence is in this case. +Even experienced programmers occasionally forget the exact rules, +which leads to mistakes. +Explicit parentheses help prevent +any such mistakes. When operators of equal precedence are used together, the leftmost -operator groups first, except for the assignment, conditional and +operator groups first, except for the assignment, conditional, and exponentiation operators, which group in the opposite order. -Thus, @samp{a - b + c} groups as @samp{(a - b) + c}, and +Thus, @samp{a - b + c} groups as @samp{(a - b) + c} and @samp{a = b = c} groups as @samp{a = (b = c)}. The precedence of prefix unary operators does not matter as long as only unary operators are involved, because there is only one way to interpret -them---innermost first. Thus, @samp{$++i} means @samp{$(++i)} and +them: innermost first. Thus, @samp{$++i} means @samp{$(++i)} and @samp{++$x} means @samp{++($x)}. However, when another operator follows the operand, then the precedence of the unary operators can matter. -Thus, @samp{$x^2} means @samp{($x)^2}, but @samp{-x^2} means -@samp{-(x^2)}, because @samp{-} has lower precedence than @samp{^} -while @samp{$} has higher precedence. - -Here is a table of @code{awk}'s operators, in order from highest +@samp{$x^2} means @samp{($x)^2}, but @samp{-x^2} means +@samp{-(x^2)}, because @samp{-} has lower precedence than @samp{^}, +whereas @samp{$} has higher precedence. +This table presents @command{awk}'s operators, in order of highest precedence to lowest: +@page + +@cindex @code{$} field operator +@cindex @code{+} operator +@cindex @code{-} operator +@cindex @code{!} operator +@cindex @code{*} operator +@cindex @code{/} operator +@cindex @code{%} operator +@cindex @code{^} operator +@cindex @code{**} operator +@cindex @code{++} operator +@cindex @code{--} operator +@cindex @code{<} operator +@cindex @code{<=} operator +@cindex @code{==} operator +@cindex @code{!=} operator +@cindex @code{>} operator +@cindex @code{>=} operator +@cindex @code{>>} I/O operator +@cindex @code{|} I/O operator +@cindex @code{|&} I/O operator +@cindex @code{~} operator +@cindex @code{!~} operator +@cindex @code{in} operator +@cindex @code{&&} operator +@cindex @code{||} operator +@cindex @code{?:} operator +@cindex @code{+=} operator +@cindex @code{-=} operator +@cindex @code{*=} operator +@cindex @code{/=} operator +@cindex @code{%=} operator +@cindex @code{^=} operator +@cindex @code{**=} operator @c use @code in the items, looks better in TeX w/o all the quotes @table @code @item (@dots{}) @@ -7152,14 +8583,11 @@ Field. @item ++ -- Increment, decrement. -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} @item ^ ** Exponentiation. These operators group right-to-left. -(The @samp{**} operator is not specified by POSIX.) @item + - ! -Unary plus, minus, logical ``not''. +Unary plus, minus, logical ``not.'' @item * / % Multiplication, division, modulus. @@ -7167,23 +8595,24 @@ Multiplication, division, modulus. @item + - Addition, subtraction. -@item @r{Concatenation} -No special token is used to indicate concatenation. -The operands are simply written side by side. +@item @r{String Concatenation} +No special symbol is used to indicate concatenation. +The operands are simply written side by side +(@pxref{Concatenation, ,String Concatenation}). @item < <= == != -@itemx > >= >> | -Relational, and redirection. +@itemx > >= >> | |& +Relational and redirection. The relational operators and the redirections have the same precedence level. Characters such as @samp{>} serve both as relationals and as redirections; the context distinguishes between the two meanings. Note that the I/O redirection operators in @code{print} and @code{printf} statements belong to the statement level, not to expressions. The -redirection does not produce an expression which could be the operand of +redirection does not produce an expression that could be the operand of another operator. As a result, it does not make sense to use a -redirection operator near another operator of lower precedence, without -parentheses. Such combinations, for example @samp{print foo > a ? b : c}, +redirection operator near another operator of lower precedence without +parentheses. Such combinations (for example @samp{print foo > a ? b : c}), result in syntax errors. The correct way to write this statement is @samp{print foo > (a ? b : c)}. @@ -7202,36 +8631,47 @@ Logical ``or''. @item ?: Conditional. This operator groups right-to-left. -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} @item = += -= *= @itemx /= %= ^= **= Assignment. These operators group right-to-left. -(The @samp{**=} operator is not specified by POSIX.) @end table -@node Patterns and Actions, Statements, Expressions, Top -@chapter Patterns and Actions +@cindex portability issues +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} +@strong{Note:} +The @samp{|&}, @samp{**}, and @samp{**=} operators are not specified by POSIX. +For maximum portability, do not use them. + +@node Patterns and Actions, Arrays, Expressions, Top +@chapter Patterns, Actions, and Variables @cindex pattern, definition of -As you have already seen, each @code{awk} statement consists of -a pattern with an associated action. This chapter describes how -you build patterns and actions. +As you have already seen, each @command{awk} statement consists of +a pattern with an associated action. This @value{CHAPTER} describes how +you build patterns and actions, what kinds of things you can do within +actions, and @command{awk}'s built-in variables. + +The pattern-action rules and the statements available for use +within actions form the core of @command{awk} programming. +In a sense, everything covered +up to here has been the foundation +that programs are built on top of. Now it's time to start +building something useful. @menu * Pattern Overview:: What goes into a pattern. +* Using Shell Variables:: How to use shell variables with @command{awk}. * Action Overview:: What goes into an action. +* Statements:: Describes the various control statements in + detail. +* Built-in Variables:: Summarizes the built-in variables. @end menu -@node Pattern Overview, Action Overview, Patterns and Actions, Patterns and Actions +@node Pattern Overview, Using Shell Variables, Patterns and Actions, Patterns and Actions @section Pattern Elements -Patterns in @code{awk} control the execution of rules: a rule is -executed when its pattern matches the current input record. This -section explains all about how to write patterns. - @menu -* Kinds of Patterns:: A list of all kinds of patterns. * Regexp Patterns:: Using regexps as patterns. * Expression Patterns:: Any expression can be used as a pattern. * Ranges:: Pairs of patterns specify record ranges. @@ -7239,33 +8679,32 @@ section explains all about how to write patterns. * Empty:: The empty pattern, which matches every record. @end menu -@node Kinds of Patterns, Regexp Patterns, Pattern Overview, Pattern Overview -@subsection Kinds of Patterns @cindex patterns, types of - -Here is a summary of the types of patterns supported in @code{awk}. +Patterns in @command{awk} control the execution of rules---a rule is +executed when its pattern matches the current input record. +The following is a summary of the types of patterns in @command{awk}: @table @code @item /@var{regular expression}/ -A regular expression as a pattern. It matches when the text of the +A regular expression. It matches when the text of the input record fits the regular expression. (@xref{Regexp, ,Regular Expressions}.) @item @var{expression} A single expression. It matches when its value -is non-zero (if a number) or non-null (if a string). +is nonzero (if a number) or non-null (if a string). (@xref{Expression Patterns, ,Expressions as Patterns}.) @item @var{pat1}, @var{pat2} A pair of patterns separated by a comma, specifying a range of records. -The range includes both the initial record that matches @var{pat1}, and +The range includes both the initial record that matches @var{pat1} and the final record that matches @var{pat2}. (@xref{Ranges, ,Specifying Record Ranges with Patterns}.) @item BEGIN @itemx END -Special patterns for you to supply start-up or clean-up actions for your -@code{awk} program. +Special patterns for you to supply startup or cleanup actions for your +@command{awk} program. (@xref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}.) @item @var{empty} @@ -7273,10 +8712,11 @@ The empty pattern matches every input record. (@xref{Empty, ,The Empty Pattern}.) @end table -@node Regexp Patterns, Expression Patterns, Kinds of Patterns, Pattern Overview +@node Regexp Patterns, Expression Patterns, Pattern Overview, Pattern Overview @subsection Regular Expressions as Patterns -We have been using regular expressions as patterns since our early examples. +Regular expressions are one of the first kinds of patterns presented +in this book. This kind of pattern is simply a regexp constant in the pattern part of a rule. Its meaning is @samp{$0 ~ /@var{pattern}/}. The pattern matches when the input record matches the regexp. @@ -7290,55 +8730,54 @@ END @{ print buzzwords, "buzzwords seen" @} @node Expression Patterns, Ranges, Regexp Patterns, Pattern Overview @subsection Expressions as Patterns -Any @code{awk} expression is valid as an @code{awk} pattern. -Then the pattern matches if the expression's value is non-zero (if a +Any @command{awk} expression is valid as an @command{awk} pattern. +The pattern matches if the expression's value is nonzero (if a number) or non-null (if a string). - The expression is reevaluated each time the rule is tested against a new input record. If the expression uses fields such as @code{$1}, the -value depends directly on the new input record's text; otherwise, it -depends only on what has happened so far in the execution of the -@code{awk} program, but that may still be useful. - -A very common kind of expression used as a pattern is the comparison -expression, using the comparison operators described in -@ref{Typing and Comparison, ,Variable Typing and Comparison Expressions}. +value depends directly on the new input record's text; otherwise it +depends on only what has happened so far in the execution of the +@command{awk} program. +Comparison expressions, using the comparison operators described in +@ref{Typing and Comparison, ,Variable Typing and Comparison Expressions}, +are a very common kind of pattern. Regexp matching and non-matching are also very common expressions. The left operand of the @samp{~} and @samp{!~} operators is a string. The right operand is either a constant regular expression enclosed in -slashes (@code{/@var{regexp}/}), or any expression, whose string value +slashes (@code{/@var{regexp}/}), or any expression whose string value is used as a dynamic regular expression (@pxref{Computed Regexps, , Using Dynamic Regexps}). - The following example prints the second field of each input record -whose first field is precisely @samp{foo}. +whose first field is precisely @samp{foo}: @example $ awk '$1 == "foo" @{ print $2 @}' BBS-list @end example @noindent -(There is no output, since there is no BBS site named ``foo''.) -Contrast this with the following regular expression match, which would -accept any record with a first field that contains @samp{foo}: +(There is no output, because there is no BBS site with the exact name @samp{foo}.) +Contrast this with the following regular expression match, which +accepts any record with a first field that contains @samp{foo}: @example -@group $ awk '$1 ~ /foo/ @{ print $2 @}' BBS-list @print{} 555-1234 @print{} 555-6699 @print{} 555-6480 @print{} 555-2127 -@end group @end example +A regexp constant as a pattern is also a special case of an expression +pattern. The expression @code{/foo/} has the value one if @samp{foo} +appears in the current input record. Thus, as a pattern, @code{/foo/} +matches any record containing @samp{foo}. + Boolean expressions are also commonly used as patterns. Whether the pattern matches an input record depends on whether its subexpressions match. - -For example, the following command prints all records in -@file{BBS-list} that contain both @samp{2400} and @samp{foo}. +For example, the following command prints all the records in +@file{BBS-list} that contain both @samp{2400} and @samp{foo}: @example $ awk '/2400/ && /foo/' BBS-list @@ -7346,11 +8785,10 @@ $ awk '/2400/ && /foo/' BBS-list @end example The following command prints all records in -@file{BBS-list} that contain @emph{either} @samp{2400} or @samp{foo}, or -both. +@file{BBS-list} that contain @emph{either} @samp{2400} or @samp{foo} +(or both, of course): @example -@group $ awk '/2400/ || /foo/' BBS-list @print{} alpo-net 555-3412 2400/1200/300 A @print{} bites 555-1675 2400/1200/300 A @@ -7359,14 +8797,12 @@ $ awk '/2400/ || /foo/' BBS-list @print{} macfoo 555-6480 1200/300 A @print{} sdace 555-3430 2400/1200/300 A @print{} sabafoo 555-2127 1200/300 C -@end group @end example The following command prints all records in -@file{BBS-list} that do @emph{not} contain the string @samp{foo}. +@file{BBS-list} that do @emph{not} contain the string @samp{foo}: @example -@group $ awk '! /foo/' BBS-list @print{} aardvark 555-5553 1200/300 B @print{} alpo-net 555-3412 2400/1200/300 A @@ -7375,20 +8811,14 @@ $ awk '! /foo/' BBS-list @print{} camelot 555-0542 300 C @print{} core 555-2912 1200/300 C @print{} sdace 555-3430 2400/1200/300 A -@end group @end example -The subexpressions of a boolean operator in a pattern can be constant regular -expressions, comparisons, or any other @code{awk} expressions. Range -patterns are not expressions, so they cannot appear inside boolean +The subexpressions of a Boolean operator in a pattern can be constant regular +expressions, comparisons, or any other @command{awk} expressions. Range +patterns are not expressions, so they cannot appear inside Boolean patterns. Likewise, the special patterns @code{BEGIN} and @code{END}, which never match any input record, are not expressions and cannot -appear inside boolean patterns. - -A regexp constant as a pattern is also a special case of an expression -pattern. @code{/foo/} as an expression has the value one if @samp{foo} -appears in the current input record; thus, as a pattern, @code{/foo/} -matches any record containing @samp{foo}. +appear inside Boolean patterns. @node Ranges, BEGIN/END, Expression Patterns, Pattern Overview @subsection Specifying Record Ranges with Patterns @@ -7396,26 +8826,26 @@ matches any record containing @samp{foo}. @cindex range pattern @cindex pattern, range @cindex matching ranges of lines -A @dfn{range pattern} is made of two patterns separated by a comma, of -the form @samp{@var{begpat}, @var{endpat}}. It matches ranges of +A @dfn{range pattern} is made of two patterns separated by a comma, in +the form @samp{@var{begpat}, @var{endpat}}. It is used to match ranges of consecutive input records. The first pattern, @var{begpat}, controls -where the range begins, and the second one, @var{endpat}, controls where -it ends. For example, +where the range begins, while @var{endpat} controls where +the pattern ends. For example, the following: @example -awk '$1 == "on", $1 == "off"' +awk '$1 == "on", $1 == "off"' myfile @end example @noindent -prints every record between @samp{on}/@samp{off} pairs, inclusive. - -A range pattern starts out by matching @var{begpat} -against every input record; when a record matches @var{begpat}, the -range pattern becomes @dfn{turned on}. The range pattern matches this -record. As long as it stays turned on, it automatically matches every -input record read. It also matches @var{endpat} against -every input record; when that succeeds, the range pattern is turned -off again for the following record. Then it goes back to checking +prints every record in @file{myfile} between @samp{on}/@samp{off} pairs, inclusive. + +A range pattern starts out by matching @var{begpat} against every +input record. When a record matches @var{begpat}, the range pattern is +@dfn{turned on} and the range pattern matches this record as well. As long as +the range pattern stays turned on, it automatically matches every input +record read. The range pattern also matches @var{endpat} against every +input record; when this succeeds, the range pattern is turned off again +for the following record. Then the range pattern goes back to checking @var{begpat} against each record. The record that turns on the range pattern and the one that turns it @@ -7423,18 +8853,18 @@ off both match the range pattern. If you don't want to operate on these records, you can write @code{if} statements in the rule's action to distinguish them from the records you are interested in. -It is possible for a pattern to be turned both on and off by the same -record, if the record satisfies both conditions. Then the action is +It is possible for a pattern to be turned on and off by the same +record. If the record satisfies both conditions, then the action is executed for just that record. - -For example, suppose you have text between two identical markers (say -the @samp{%} symbol) that you wish to ignore. You might try to +For example, suppose there is text between two identical markers (say +the @samp{%} symbol), each on its own line, that should be ignored. +A first attempt would be to combine a range pattern that describes the delimited text with the @code{next} statement -(not discussed yet, @pxref{Next Statement, , The @code{next} Statement}), -which causes @code{awk} to skip any further processing of the current +(not discussed yet, @pxref{Next Statement, , The @code{next} Statement}). +This causes @command{awk} to skip any further processing of the current record and start over again with the next input record. Such a program -would look like this: +looks like this: @example /^%$/,/^%$/ @{ next @} @@ -7443,28 +8873,37 @@ would look like this: @noindent @cindex skipping lines between markers +@cindex flag variables This program fails because the range pattern is both turned on and turned off -by the first line with just a @samp{%} on it. To accomplish this task, you -must write the program this way, using a flag: +by the first line, which just has a @samp{%} on it. To accomplish this task, +write the program in the following manner, using a flag: +@cindex @code{!} operator @example /^%$/ @{ skip = ! skip; next @} skip == 1 @{ next @} # skip lines with `skip' set @end example -Note that in a range pattern, the @samp{,} has the lowest precedence -(is evaluated last) of all the operators. Thus, for example, the -following program attempts to combine a range pattern with another, -simpler test. +In a range pattern, the comma (@samp{,}) has the lowest precedence of +all the operators (i.e., it is evaluated last). Thus, the following +program attempts to combine a range pattern with another simpler test: @example echo Yes | awk '/1/,/2/ || /Yes/' @end example -The author of this program intended it to mean @samp{(/1/,/2/) || /Yes/}. -However, @code{awk} interprets this as @samp{/1/, (/2/ || /Yes/)}. +The intent of this program is @samp{(/1/,/2/) || /Yes/}. +However, @command{awk} interprets this as @samp{/1/, (/2/ || /Yes/)}. This cannot be changed or worked around; range patterns do not combine -with other patterns. +with other patterns: + +@example +$ echo yes | gawk '(/1/,/2/) || /Yes/' +@error{} gawk: cmd. line:1: (/1/,/2/) || /Yes/ +@error{} gawk: cmd. line:1: ^ parse error +@error{} gawk: cmd. line:2: (/1/,/2/) || /Yes/ +@error{} gawk: cmd. line:2: ^ unexpected newline +@end example @node BEGIN/END, Empty, Ranges, Pattern Overview @subsection The @code{BEGIN} and @code{END} Special Patterns @@ -7473,9 +8912,15 @@ with other patterns. @cindex pattern, @code{BEGIN} @cindex @code{END} special pattern @cindex pattern, @code{END} -@code{BEGIN} and @code{END} are special patterns. They are not used to -match input records. Rather, they supply start-up or -clean-up actions for your @code{awk} script. +@cindex blocks, @code{BEGIN} and @code{END} +All the patterns described so far are for matching input records. +The @code{BEGIN} and @code{END} special patterns are different. +They supply startup and cleanup actions for @command{awk} programs. +@code{BEGIN} and @code{END} rules must have actions; there is no default +action for these rules because there is no current record when they run. +@code{BEGIN} and @code{END} rules are often referred to as +``@code{BEGIN} and @code{END} blocks'' by long-time @command{awk} +programmers. @menu * Using BEGIN/END:: How and why to use BEGIN/END rules. @@ -7485,115 +8930,113 @@ clean-up actions for your @code{awk} script. @node Using BEGIN/END, I/O And BEGIN/END, BEGIN/END, BEGIN/END @subsubsection Startup and Cleanup Actions -A @code{BEGIN} rule is executed, once, before the first input record -has been read. An @code{END} rule is executed, once, after all the -input has been read. For example: +A @code{BEGIN} rule is executed once only, before the first input record +is read. Likewise, an @code{END} rule is executed once only, after all the +input is read. For example: @example -@group $ awk ' > BEGIN @{ print "Analysis of \"foo\"" @} > /foo/ @{ ++n @} -> END @{ print "\"foo\" appears " n " times." @}' BBS-list +> END @{ print "\"foo\" appears", n, "times." @}' BBS-list @print{} Analysis of "foo" @print{} "foo" appears 4 times. -@end group @end example This program finds the number of records in the input file @file{BBS-list} that contain the string @samp{foo}. The @code{BEGIN} rule prints a title for the report. There is no need to use the @code{BEGIN} rule to -initialize the counter @code{n} to zero, as @code{awk} does this +initialize the counter @code{n} to zero, since @command{awk} does this automatically (@pxref{Variables}). - The second rule increments the variable @code{n} every time a record containing the pattern @samp{foo} is read. The @code{END} rule prints the value of @code{n} at the end of the run. The special patterns @code{BEGIN} and @code{END} cannot be used in ranges -or with boolean operators (indeed, they cannot be used with any operators). - -An @code{awk} program may have multiple @code{BEGIN} and/or @code{END} -rules. They are executed in the order they appear, all the @code{BEGIN} -rules at start-up and all the @code{END} rules at termination. +or with Boolean operators (indeed, they cannot be used with any operators). +An @command{awk} program may have multiple @code{BEGIN} and/or @code{END} +rules. They are executed in the order in which they appear: all the @code{BEGIN} +rules at startup and all the @code{END} rules at termination. @code{BEGIN} and @code{END} rules may be intermixed with other rules. -This feature was added in the 1987 version of @code{awk}, and is included -in the POSIX standard. The original (1978) version of @code{awk} -required you to put the @code{BEGIN} rule at the beginning of the -program, and the @code{END} rule at the end, and only allowed one of -each. This is no longer required, but it is a good idea in terms of -program organization and readability. +This feature was added in the 1987 version of @command{awk} and is included +in the POSIX standard. +The original (1978) version of @command{awk} +required the @code{BEGIN} rule to be placed at the beginning of the +program, the @code{END} rule to be placed at the end, and only allowed one of +each. +This is no longer required, but it is a good idea to follow this template +in terms of program organization and readability. Multiple @code{BEGIN} and @code{END} rules are useful for writing -library functions, since each library file can have its own @code{BEGIN} and/or -@code{END} rule to do its own initialization and/or cleanup. Note that -the order in which library functions are named on the command line +library functions, because each library file can have its own @code{BEGIN} and/or +@code{END} rule to do its own initialization and/or cleanup. +The order in which library functions are named on the command line controls the order in which their @code{BEGIN} and @code{END} rules are -executed. Therefore you have to be careful to write such rules in +executed. Therefore you have to be careful when writing such rules in library files so that the order in which they are executed doesn't matter. -@xref{Options, ,Command Line Options}, for more information on +@xref{Options, ,Command-Line Options}, for more information on using library functions. -@xref{Library Functions, ,A Library of @code{awk} Functions}, +@xref{Library Functions, ,A Library of @command{awk} Functions}, for a number of useful library functions. -@cindex dark corner -If an @code{awk} program only has a @code{BEGIN} rule, and no other -rules, then the program exits after the @code{BEGIN} rule has been run. -(The original version of @code{awk} used to keep reading and ignoring input -until end of file was seen.) However, if an @code{END} rule exists, -then the input will be read, even if there are no other rules in -the program. This is necessary in case the @code{END} rule checks the -@code{FNR} and @code{NR} variables (d.c.). - -@code{BEGIN} and @code{END} rules must have actions; there is no default -action for these rules since there is no current record when they run. +If an @command{awk} program only has a @code{BEGIN} rule and no +other rules, then the program exits after the @code{BEGIN} rule is +run.@footnote{The original version of @command{awk} used to keep +reading and ignoring input until end of file was seen.} However, if an +@code{END} rule exists, then the input is read, even if there are +no other rules in the program. This is necessary in case the @code{END} +rule checks the @code{FNR} and @code{NR} variables. @node I/O And BEGIN/END, , Using BEGIN/END, BEGIN/END @subsubsection Input/Output from @code{BEGIN} and @code{END} Rules -@cindex I/O from @code{BEGIN} and @code{END} -There are several (sometimes subtle) issues involved when doing I/O +@cindex I/O, from @code{BEGIN} and @code{END} +There are several (sometimes subtle) points to remember when doing I/O from a @code{BEGIN} or @code{END} rule. - The first has to do with the value of @code{$0} in a @code{BEGIN} -rule. Since @code{BEGIN} rules are executed before any input is read, +rule. Because @code{BEGIN} rules are executed before any input is read, there simply is no input record, and therefore no fields, when executing @code{BEGIN} rules. References to @code{$0} and the fields yield a null string or zero, depending upon the context. One way to give @code{$0} a real value is to execute a @code{getline} command without a variable (@pxref{Getline, ,Explicit Input with @code{getline}}). -Another way is to simply assign a value to it. +Another way is to simply assign a value to @code{$0}. -@cindex differences between @code{gawk} and @code{awk} -The second point is similar to the first, but from the other direction. -Inside an @code{END} rule, what is the value of @code{$0} and @code{NF}? +@cindex differences between @command{gawk} and @command{awk} +The second point is similar to the first but from the other direction. Traditionally, due largely to implementation issues, @code{$0} and @code{NF} were @emph{undefined} inside an @code{END} rule. -The POSIX standard specified that @code{NF} was available in an @code{END} -rule, containing the number of fields from the last input record. -Due most probably to an oversight, the standard does not say that @code{$0} +The POSIX standard specifies that @code{NF} is available in an @code{END} +rule. It contains the number of fields from the last input record. +Most probably due to an oversight, the standard does not say that @code{$0} is also preserved, although logically one would think that it should be. -In fact, @code{gawk} does preserve the value of @code{$0} for use in -@code{END} rules. Be aware, however, that Unix @code{awk}, and possibly +In fact, @command{gawk} does preserve the value of @code{$0} for use in +@code{END} rules. Be aware, however, that Unix @command{awk}, and possibly other implementations, do not. -The third point follows from the first two. What is the meaning of -@samp{print} inside a @code{BEGIN} or @code{END} rule? The meaning is -the same as always, @samp{print $0}. If @code{$0} is the null string, -then this prints an empty line. Many long time @code{awk} programmers -use @samp{print} in @code{BEGIN} and @code{END} rules, to mean -@samp{@w{print ""}}, relying on @code{$0} being null. While you might -generally get away with this in @code{BEGIN} rules, in @code{gawk} at -least, it is a very bad idea in @code{END} rules. It is also poor -style, since if you want an empty line in the output, you -should say so explicitly in your program. - -@node Empty, , BEGIN/END, Pattern Overview +The third point follows from the first two. The meaning of @samp{print} +inside a @code{BEGIN} or @code{END} rule is the same as always: +@samp{print $0}. If @code{$0} is the null string, then this prints an +empty line. Many long time @command{awk} programmers use an unadorned +@samp{print} in @code{BEGIN} and @code{END} rules, to mean @samp{@w{print ""}}, +relying on @code{$0} being null. Although one might generally get away with +this in @code{BEGIN} rules, it is a very bad idea in @code{END} rules, +at least in @command{gawk}. It is also poor style, since if an empty +line is needed in the output, the program should print one explicitly. + +Finally, the @code{next} and @code{nextfile} statements are not allowed +in a @code{BEGIN} rule, because the implicit +read-a-record-and-match-against-the-rules loop has not started yet. Similarly, those statements +are not valid in an @code{END} rule, since all the input has been read. +(@xref{Next Statement, ,The @code{next} Statement}, and see +@ref{Nextfile Statement, ,Using @command{gawk}'s @code{nextfile} Statement}.) + +@node Empty, , BEGIN/END, Pattern Overview @subsection The Empty Pattern @cindex empty pattern @cindex pattern, empty -An empty (i.e.@: non-existent) pattern is considered to match @emph{every} +An empty (i.e., non-existent) pattern is considered to match @emph{every} input record. For example, the program: @example @@ -7603,22 +9046,82 @@ awk '@{ print $1 @}' BBS-list @noindent prints the first field of every record. -@node Action Overview, , Pattern Overview, Patterns and Actions -@section Overview of Actions +@node Using Shell Variables, Action Overview, Pattern Overview, Patterns and Actions +@section Using Shell Variables in Programs +@cindex shell varibles, using in @command{awk} programs +@cindex using shell variables in @command{awk} programs +@cindex shell and @command{awk} interaction + +@command{awk} programs are often used as components in larger +programs written in shell. +For example, it is very common to use a shell variable to +hold a pattern that the @command{awk} program searches for. +There are two ways to get the value of the shell variable +into the body of the @command{awk} program. + +The most common method is to use shell quoting to substitute +the variable's value into the program inside the script. +For example, in the following program: + +@example +echo -n "Enter search pattern: " +read pattern +awk "/$pattern/ "'@{ nmatches++ @} + END @{ print nmatches, "found" @}' /path/to/data +@end example + +@noindent +the @command{awk} program consists of two pieces of quoted text +that are concatenated together to form the program. +The first part is double-quoted, which allows substitution of +the @code{pattern} variable inside the quotes. +The second part is single-quoted. + +Variable substitution via quoting works, but can be potentially +messy. It requires a good understanding of the shell's quoting rules +(@pxref{Quoting, ,Shell Quoting Issues}), +and it's often difficult to correctly +match up the quotes when reading the program. + +A better method is to use @command{awk}'s variable assignment feature +(@pxref{Assignment Options, ,Assigning Variables on the Command Line}) +to assign the shell variable's value to an @command{awk} variable's +value. Then use dynamic regexps to match the pattern +(@pxref{Computed Regexps, ,Using Dynamic Regexps}). +The following shows how to redo the +previous example using this technique: + +@example +echo -n "Enter search pattern: " +read pattern +awk -v pat="$pattern" '$0 ~ pat @{ nmatches++ @} + END @{ print nmatches, "found" @}' /path/to/data +@end example + +@noindent +Now, the @command{awk} program is just one single-quoted string. +The assignment @samp{-v pat="$pattern"} still requires double quotes, +in case there is whitespace in the value of @code{$pattern}. +The @command{awk} variable @code{pat} could be named @code{pattern} +too, but that would be more confusing. Using a variable also +provides more flexibility, since the variable can be used anywhere inside +the program---for printing, as an array subscript, or for any other +use---without requiring the quoting tricks at every point in the program. + +@node Action Overview, Statements, Using Shell Variables, Patterns and Actions +@section Actions @cindex action, definition of @cindex curly braces @cindex action, curly braces @cindex action, separating statements -An @code{awk} program or script consists of a series of -rules and function definitions, interspersed. (Functions are -described later. @xref{User-defined, ,User-defined Functions}.) - +An @command{awk} program or script consists of a series of +rules and function definitions interspersed. (Functions are +described later. @xref{User-defined, ,User-Defined Functions}.) A rule contains a pattern and an action, either of which (but not -both) may be -omitted. The purpose of the @dfn{action} is to tell @code{awk} what to do -once a match for the pattern is found. Thus, in outline, an @code{awk} -program generally looks like this: +both) may be omitted. The purpose of the @dfn{action} is to tell +@command{awk} what to do once a match for the pattern is found. Thus, +in outline, an @command{awk} program generally looks like this: @example @r{[}@var{pattern}@r{]} @r{[}@{ @var{action} @}@r{]} @@ -7628,24 +9131,23 @@ function @var{name}(@var{args}) @{ @dots{} @} @dots{} @end example -An action consists of one or more @code{awk} @dfn{statements}, enclosed +An action consists of one or more @command{awk} @dfn{statements}, enclosed in curly braces (@samp{@{} and @samp{@}}). Each statement specifies one -thing to be done. The statements are separated by newlines or -semicolons. - +thing to do. The statements are separated by newlines or semicolons. The curly braces around an action must be used even if the action -contains only one statement, or even if it contains no statements at +contains only one statement, or if it contains no statements at all. However, if you omit the action entirely, omit the curly braces as -well. An omitted action is equivalent to @samp{@{ print $0 @}}. +well. An omitted action is equivalent to @samp{@{ print $0 @}}: @example -/foo/ @{ @} # match foo, do nothing - empty action -/foo/ # match foo, print the record - omitted action +/foo/ @{ @} @i{match @code{foo}, do nothing --- empty action} +/foo/ @i{match @code{foo}, print the record --- omitted action} @end example -Here are the kinds of statements supported in @code{awk}: +The following types of statements are supported in @command{awk}: @itemize @bullet +@cindex side effects @item Expressions, which can call functions or assign values to variables (@pxref{Expressions}). Executing @@ -7654,60 +9156,54 @@ This is useful when the expression has side effects (@pxref{Assignment Ops, ,Assignment Expressions}). @item -Control statements, which specify the control flow of @code{awk} -programs. The @code{awk} language gives you C-like constructs +Control statements, which specify the control flow of @command{awk} +programs. The @command{awk} language gives you C-like constructs (@code{if}, @code{for}, @code{while}, and @code{do}) as well as a few special ones (@pxref{Statements, ,Control Statements in Actions}). @item Compound statements, which consist of one or more statements enclosed in curly braces. A compound statement is used in order to put several -statements together in the body of an @code{if}, @code{while}, @code{do} +statements together in the body of an @code{if}, @code{while}, @code{do}, or @code{for} statement. @item -Input statements, using the @code{getline} command +Input statements using the @code{getline} command (@pxref{Getline, ,Explicit Input with @code{getline}}), the @code{next} statement (@pxref{Next Statement, ,The @code{next} Statement}), and the @code{nextfile} statement -(@pxref{Nextfile Statement, ,The @code{nextfile} Statement}). +(@pxref{Nextfile Statement, ,Using @command{gawk}'s @code{nextfile} Statement}). @item -Output statements, @code{print} and @code{printf}. +Output statements, such as @code{print} and @code{printf}. @xref{Printing, ,Printing Output}. @item -Deletion statements, for deleting array elements. +Deletion statements for deleting array elements. @xref{Delete, ,The @code{delete} Statement}. @end itemize -@iftex -The next chapter covers control statements in detail. -@end iftex - -@node Statements, Built-in Variables, Patterns and Actions, Top -@chapter Control Statements in Actions +@node Statements, Built-in Variables, Action Overview, Patterns and Actions +@section Control Statements in Actions @cindex control statement -@dfn{Control statements} such as @code{if}, @code{while}, and so on -control the flow of execution in @code{awk} programs. Most of the -control statements in @code{awk} are patterned on similar statements in -C. - -All the control statements start with special keywords such as @code{if} -and @code{while}, to distinguish them from simple expressions. +@dfn{Control statements}, such as @code{if}, @code{while}, and so on, +control the flow of execution in @command{awk} programs. Most of the +control statements in @command{awk} are patterned on similar statements in C. @cindex compound statement @cindex statement, compound -Many control statements contain other statements; for example, the -@code{if} statement contains another statement which may or may not be -executed. The contained statement is called the @dfn{body}. If you -want to include more than one statement in the body, group them into a +All the control statements start with special keywords, such as @code{if} +and @code{while}, to distinguish them from simple expressions. +Many control statements contain other statements. For example, the +@code{if} statement contains another statement that may or may not be +executed. The contained statement is called the @dfn{body}. +To include more than one statement in the body, group them into a single @dfn{compound statement} with curly braces, separating them with newlines or semicolons. @menu -* If Statement:: Conditionally execute some @code{awk} +* If Statement:: Conditionally execute some @command{awk} statements. * While Statement:: Loop until some condition is satisfied. * Do Statement:: Do specified action while looping until some @@ -7719,14 +9215,14 @@ newlines or semicolons. loop. * Next Statement:: Stop processing the current input record. * Nextfile Statement:: Stop processing the current file. -* Exit Statement:: Stop execution of @code{awk}. +* Exit Statement:: Stop execution of @command{awk}. @end menu @node If Statement, While Statement, Statements, Statements -@section The @code{if}-@code{else} Statement +@subsection The @code{if}-@code{else} Statement @cindex @code{if}-@code{else} statement -The @code{if}-@code{else} statement is @code{awk}'s decision-making +The @code{if}-@code{else} statement is @command{awk}'s decision-making statement. It looks like this: @example @@ -7735,13 +9231,12 @@ if (@var{condition}) @var{then-body} @r{[}else @var{else-body}@r{]} @noindent The @var{condition} is an expression that controls what the rest of the -statement will do. If @var{condition} is true, @var{then-body} is +statement does. If the @var{condition} is true, @var{then-body} is executed; otherwise, @var{else-body} is executed. The @code{else} part of the statement is optional. The condition is considered false if its value is zero or -the null string, and true otherwise. - -Here is an example: +the null string; otherwise the condition is true. +Refer to the following: @example if (x % 2 == 0) @@ -7751,14 +9246,14 @@ else @end example In this example, if the expression @samp{x % 2 == 0} is true (that is, -the value of @code{x} is evenly divisible by two), then the first @code{print} -statement is executed, otherwise the second @code{print} statement is -executed. - -If the @code{else} appears on the same line as @var{then-body}, and -@var{then-body} is not a compound statement (i.e.@: not surrounded by +if the value of @code{x} is evenly divisible by two), then the first +@code{print} statement is executed; otherwise the second @code{print} +statement is executed. +If the @code{else} keyword appears on the same line as @var{then-body} and +@var{then-body} is not a compound statement (i.e., not surrounded by curly braces), then a semicolon must separate @var{then-body} from -@code{else}. To illustrate this, let's rewrite the previous example: +the @code{else}. +To illustrate this, the previous example can be rewritten as: @example if (x % 2 == 0) print "x is even"; else @@ -7766,25 +9261,22 @@ if (x % 2 == 0) print "x is even"; else @end example @noindent -If you forget the @samp{;}, @code{awk} won't be able to interpret the -statement, and you will get a syntax error. - -We would not actually write this example this way, because a human -reader might fail to see the @code{else} if it were not the first thing -on its line. +If the @samp{;} is left out, @command{awk} can't interpret the statement and +it produces a syntax error. Don't actually write programs this way, +because a human reader might fail to see the @code{else} if it is not +the first thing on its line. @node While Statement, Do Statement, If Statement, Statements -@section The @code{while} Statement +@subsection The @code{while} Statement @cindex @code{while} statement @cindex loop @cindex body of a loop -In programming, a @dfn{loop} means a part of a program that can +In programming, a @dfn{loop} is a part of a program that can be executed two or more times in succession. - The @code{while} statement is the simplest looping statement in -@code{awk}. It repeatedly executes a statement as long as a condition is -true. It looks like this: +@command{awk}. It repeatedly executes a statement as long as a condition is +true. For example: @example while (@var{condition}) @@ -7792,24 +9284,22 @@ while (@var{condition}) @end example @noindent -Here @var{body} is a statement that we call the @dfn{body} of the loop, +@var{body} is a statement called the @dfn{body} of the loop, and @var{condition} is an expression that controls how long the loop keeps running. - -The first thing the @code{while} statement does is test @var{condition}. -If @var{condition} is true, it executes the statement @var{body}. +The first thing the @code{while} statement does is test the @var{condition}. +If the @var{condition} is true, it executes the statement @var{body}. @ifinfo -(The @var{condition} is true when the value +(The @var{condition} is true when the value is not zero and not a null string.) @end ifinfo After @var{body} has been executed, @var{condition} is tested again, and if it is still true, @var{body} is -executed again. This process repeats until @var{condition} is no longer -true. If @var{condition} is initially false, the body of the loop is -never executed, and @code{awk} continues with the statement following +executed again. This process repeats until the @var{condition} is no longer +true. If the @var{condition} is initially false, the body of the loop is +never executed and @command{awk} continues with the statement following the loop. - -This example prints the first three fields of each record, one per line. +This example prints the first three fields of each record, one per line: @example awk '@{ i = 1 @@ -7821,39 +9311,37 @@ awk '@{ i = 1 @end example @noindent -Here the body of the loop is a compound statement enclosed in braces, +The body of this loop is a compound statement enclosed in braces, containing two statements. - -The loop works like this: first, the value of @code{i} is set to one. -Then, the @code{while} tests whether @code{i} is less than or equal to +The loop works in the following manner: first, the value of @code{i} is set to one. +Then, the @code{while} statement tests whether @code{i} is less than or equal to three. This is true when @code{i} equals one, so the @code{i}-th field is printed. Then the @samp{i++} increments the value of @code{i} and the loop repeats. The loop terminates when @code{i} reaches four. -As you can see, a newline is not required between the condition and the -body; but using one makes the program clearer unless the body is a -compound statement or is very simple. The newline after the open-brace +A newline is not required between the condition and the +body; however using one makes the program clearer unless the body is a +compound statement or else is very simple. The newline after the open-brace that begins the compound statement is not required either, but the -program would be harder to read without it. +program is harder to read without it. @node Do Statement, For Statement, While Statement, Statements -@section The @code{do}-@code{while} Statement +@subsection The @code{do}-@code{while} Statement +@cindex @code{do}-@code{while} statement The @code{do} loop is a variation of the @code{while} looping statement. -The @code{do} loop executes the @var{body} once, and then repeats @var{body} -as long as @var{condition} is true. It looks like this: +The @code{do} loop executes the @var{body} once and then repeats the +@var{body} as long as the @var{condition} is true. It looks like this: @example -@group do @var{body} while (@var{condition}) -@end group @end example -Even if @var{condition} is false at the start, @var{body} is executed at -least once (and only once, unless executing @var{body} makes -@var{condition} true). Contrast this with the corresponding +Even if the @var{condition} is false at the start, the @var{body} is +executed at least once (and only once, unless executing @var{body} +makes @var{condition} true). Contrast this with the corresponding @code{while} statement: @example @@ -7862,28 +9350,27 @@ while (@var{condition}) @end example @noindent -This statement does not execute @var{body} even once if @var{condition} +This statement does not execute @var{body} even once if the @var{condition} is false to begin with. - -Here is an example of a @code{do} statement: +The following is an example of a @code{do} statement: @example -awk '@{ i = 1 +@{ i = 1 do @{ print $0 i++ @} while (i <= 10) -@}' +@} @end example @noindent -This program prints each input record ten times. It isn't a very +This program prints each input record ten times. However, it isn't a very realistic example, since in this case an ordinary @code{while} would do -just as well. But this reflects actual experience; there is only -occasionally a real use for a @code{do} statement. +just as well. This situation reflects actual experience; only +occasionally is there a real use for a @code{do} statement. @node For Statement, Break Statement, Do Statement, Statements -@section The @code{for} Statement +@subsection The @code{for} Statement @cindex @code{for} statement The @code{for} statement makes it more convenient to count iterations of a @@ -7895,58 +9382,56 @@ for (@var{initialization}; @var{condition}; @var{increment}) @end example @noindent -The @var{initialization}, @var{condition} and @var{increment} parts are -arbitrary @code{awk} expressions, and @var{body} stands for any -@code{awk} statement. +The @var{initialization}, @var{condition}, and @var{increment} parts are +arbitrary @command{awk} expressions, and @var{body} stands for any +@command{awk} statement. The @code{for} statement starts by executing @var{initialization}. Then, as long -as @var{condition} is true, it repeatedly executes @var{body} and then -@var{increment}. Typically @var{initialization} sets a variable to +as the @var{condition} is true, it repeatedly executes @var{body} and then +@var{increment}. Typically, @var{initialization} sets a variable to either zero or one, @var{increment} adds one to it, and @var{condition} compares it against the desired number of iterations. - -Here is an example of a @code{for} statement: +For example: @example -@group awk '@{ for (i = 1; i <= 3; i++) print $i @}' inventory-shipped -@end group @end example @noindent -This prints the first three fields of each input record, one field per +This prints the first three fields of each input record, with one field per line. -You cannot set more than one variable in the -@var{initialization} part unless you use a multiple assignment statement -such as @samp{x = y = 0}, which is possible only if all the initial values -are equal. (But you can initialize additional variables by writing +It isn't possible to +set more than one variable in the +@var{initialization} part without using a multiple assignment statement +such as @samp{x = y = 0}. This makes sense only if all the initial values +are equal. (But it is possible to initialize additional variables by writing their assignments as separate statements preceding the @code{for} loop.) -The same is true of the @var{increment} part; to increment additional -variables, you must write separate statements at the end of the loop. -The C compound expression, using C's comma operator, would be useful in -this context, but it is not supported in @code{awk}. +@cindex comma operator, not supported +The same is true of the @var{increment} part. Incrementing additional +variables requires separate statements at the end of the loop. +The C compound expression, using C's comma operator, is useful in +this context but it is not supported in @command{awk}. -Most often, @var{increment} is an increment expression, as in the -example above. But this is not required; it can be any expression -whatever. For example, this statement prints all the powers of two -between one and 100: +Most often, @var{increment} is an increment expression, as in the previous +example. But this is not required; it can be any expression +whatsoever. For example, the following statement prints all the powers of two +between 1 and 100: @example for (i = 1; i <= 100; i *= 2) print i @end example -Any of the three expressions in the parentheses following the @code{for} may -be omitted if there is nothing to be done there. Thus, @w{@samp{for (; x -> 0;)}} is equivalent to @w{@samp{while (x > 0)}}. If the -@var{condition} is omitted, it is treated as @var{true}, effectively -yielding an @dfn{infinite loop} (i.e.@: a loop that will never -terminate). +If there is nothing to be done, any of the three expressions in the +parentheses following the @code{for} keyword may be omitted. Thus, +@w{@samp{for (; x > 0;)}} is equivalent to @w{@samp{while (x > 0)}}. If the +@var{condition} is omitted, it is treated as true, effectively +yielding an @dfn{infinite loop} (i.e., a loop that never terminates). In most cases, a @code{for} loop is an abbreviation for a @code{while} loop, as shown here: @@ -7962,10 +9447,18 @@ while (@var{condition}) @{ @noindent The only exception is when the @code{continue} statement (@pxref{Continue Statement, ,The @code{continue} Statement}) is used -inside the loop; changing a @code{for} statement to a @code{while} +inside the loop. Changing a @code{for} statement to a @code{while} statement in this way can change the effect of the @code{continue} statement inside the loop. +The @command{awk} language has a @code{for} statement in addition to a +@code{while} statement because a @code{for} loop is often both less work to +type and more natural to think of. Counting the number of iterations is +very common in loops. It can be easier to think of this counting as part +of looping rather than as something to do inside the loop. + +@ifinfo +@cindex @code{in} operator There is an alternate version of the @code{for} loop, for iterating over all the indices of an array: @@ -7977,157 +9470,114 @@ for (i in array) @noindent @xref{Scanning an Array, ,Scanning All Elements of an Array}, for more information on this version of the @code{for} loop. - -The @code{awk} language has a @code{for} statement in addition to a -@code{while} statement because often a @code{for} loop is both less work to -type and more natural to think of. Counting the number of iterations is -very common in loops. It can be easier to think of this counting as part -of looping rather than as something to do inside the loop. - -The next section has more complicated examples of @code{for} loops. +@end ifinfo @node Break Statement, Continue Statement, For Statement, Statements -@section The @code{break} Statement +@subsection The @code{break} Statement @cindex @code{break} statement @cindex loops, exiting The @code{break} statement jumps out of the innermost @code{for}, -@code{while}, or @code{do} loop that encloses it. The -following example finds the smallest divisor of any integer, and also -identifies prime numbers: +@code{while}, or @code{do} loop that encloses it. The following example +finds the smallest divisor of any integer, and also identifies prime +numbers: @example -awk '# find smallest divisor of num - @{ num = $1 -@group - for (div = 2; div*div <= num; div++) - if (num % div == 0) - break -@end group - if (num % div == 0) - printf "Smallest divisor of %d is %d\n", num, div - else - printf "%d is prime\n", num - @}' +# find smallest divisor of num +@{ + num = $1 + for (div = 2; div*div <= num; div++) + if (num % div == 0) + break + if (num % div == 0) + printf "Smallest divisor of %d is %d\n", num, div + else + printf "%d is prime\n", num +@} @end example -When the remainder is zero in the first @code{if} statement, @code{awk} +When the remainder is zero in the first @code{if} statement, @command{awk} immediately @dfn{breaks out} of the containing @code{for} loop. This means -that @code{awk} proceeds immediately to the statement following the loop +that @command{awk} proceeds immediately to the statement following the loop and continues processing. (This is very different from the @code{exit} -statement which stops the entire @code{awk} program. +statement, which stops the entire @command{awk} program. @xref{Exit Statement, ,The @code{exit} Statement}.) -Here is another program equivalent to the previous one. It illustrates how -the @var{condition} of a @code{for} or @code{while} could just as well be -replaced with a @code{break} inside an @code{if}: +Th following program illustrates how the @var{condition} of a @code{for} +or @code{while} statement could be replaced with a @code{break} inside +an @code{if}: @example -@group -awk '# find smallest divisor of num - @{ num = $1 - for (div = 2; ; div++) @{ - if (num % div == 0) @{ - printf "Smallest divisor of %d is %d\n", num, div - break - @} - if (div*div > num) @{ - printf "%d is prime\n", num - break - @} - @} -@}' -@end group +# find smallest divisor of num +@{ + num = $1 + for (div = 2; ; div++) @{ + if (num % div == 0) @{ + printf "Smallest divisor of %d is %d\n", num, div + break + @} + if (div*div > num) @{ + printf "%d is prime\n", num + break + @} + @} +@} @end example @cindex @code{break}, outside of loops @cindex historical features -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} @cindex dark corner -As described above, the @code{break} statement has no meaning when +The @code{break} statement has no meaning when used outside the body of a loop. However, although it was never documented, -historical implementations of @code{awk} have treated the @code{break} +historical implementations of @command{awk} treated the @code{break} statement outside of a loop as if it were a @code{next} statement (@pxref{Next Statement, ,The @code{next} Statement}). -Recent versions of Unix @code{awk} no longer allow this usage. -@code{gawk} will support this use of @code{break} only if @samp{--traditional} +Recent versions of Unix @command{awk} no longer allow this usage. +@command{gawk} supports this use of @code{break} only +if @option{--traditional} has been specified on the command line -(@pxref{Options, ,Command Line Options}). -Otherwise, it will be treated as an error, since the POSIX standard +(@pxref{Options, ,Command-Line Options}). +Otherwise, it is treated as an error, since the POSIX standard specifies that @code{break} should only be used inside the body of a -loop (d.c.). +loop. +@value{DARKCORNER} @node Continue Statement, Next Statement, Break Statement, Statements -@section The @code{continue} Statement +@subsection The @code{continue} Statement @cindex @code{continue} statement -The @code{continue} statement, like @code{break}, is used only inside +As with @code{break}, the @code{continue} statement is used only inside @code{for}, @code{while}, and @code{do} loops. It skips over the rest of the loop body, causing the next cycle around the loop to begin immediately. Contrast this with @code{break}, which jumps out of the loop altogether. -@c The point of this program was to illustrate the use of continue with -@c a while loop. But Karl Berry points out that that is done adequately -@c below, and that this example is very un-awk-like. So for now, we'll -@c omit it. -@ignore -In Texinfo source files, text that the author wishes to ignore can be -enclosed between lines that start with @samp{@@ignore} and end with -@samp{@atend ignore}. Here is a program that strips out lines between -@samp{@@ignore} and @samp{@atend ignore} pairs. - -@example -BEGIN @{ - while (getline > 0) @{ - if (/^@@ignore/) - ignoring = 1 - else if (/^@@end[ \t]+ignore/) @{ - ignoring = 0 - continue - @} - if (ignoring) - continue - print - @} -@} -@end example - -When an @samp{@@ignore} is seen, the @code{ignoring} flag is set to one (true). -When @samp{@atend ignore} is seen, the flag is reset to zero (false). As long -as the flag is true, the input record is not printed, because the -@code{continue} restarts the @code{while} loop, skipping over the @code{print} -statement. - -@c Exercise!!! -@c How could this program be written to make better use of the awk language? -@end ignore - -The @code{continue} statement in a @code{for} loop directs @code{awk} to -skip the rest of the body of the loop, and resume execution with the +The @code{continue} statement in a @code{for} loop directs @command{awk} to +skip the rest of the body of the loop and resume execution with the increment-expression of the @code{for} statement. The following program illustrates this fact: @example -awk 'BEGIN @{ +BEGIN @{ for (x = 0; x <= 20; x++) @{ if (x == 5) continue printf "%d ", x @} print "" -@}' +@} @end example @noindent -This program prints all the numbers from zero to 20, except for five, for -which the @code{printf} is skipped. Since the increment @samp{x++} +This program prints all the numbers from 0 to 20---except for five, for +which the @code{printf} is skipped. Because the increment @samp{x++} is not skipped, @code{x} does not remain stuck at five. Contrast the -@code{for} loop above with this @code{while} loop: +@code{for} loop from the previous example with the following @code{while} loop: @example -awk 'BEGIN @{ +BEGIN @{ x = 0 while (x <= 20) @{ if (x == 5) @@ -8136,186 +9586,203 @@ awk 'BEGIN @{ x++ @} print "" -@}' +@} @end example @noindent -This program loops forever once @code{x} gets to five. +This program loops forever once @code{x} reaches five. @cindex @code{continue}, outside of loops @cindex historical features -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} @cindex dark corner -As described above, the @code{continue} statement has no meaning when -used outside the body of a loop. However, although it was never documented, -historical implementations of @code{awk} have treated the @code{continue} -statement outside of a loop as if it were a @code{next} statement +The @code{continue} statement has no meaning when used outside the body of +a loop. Historical versions of @command{awk} treated a @code{continue} +statement outside a loop the same way they treated a @code{break} +statement outside a loop: as if it were a @code{next} +statement (@pxref{Next Statement, ,The @code{next} Statement}). -Recent versions of Unix @code{awk} no longer allow this usage. -@code{gawk} will support this use of @code{continue} only if -@samp{--traditional} has been specified on the command line -(@pxref{Options, ,Command Line Options}). -Otherwise, it will be treated as an error, since the POSIX standard -specifies that @code{continue} should only be used inside the body of a -loop (d.c.). +Recent versions of Unix @command{awk} no longer work this way, and +@command{gawk} allows it only if @option{--traditional} is specified on +the command line (@pxref{Options, ,Command-Line Options}). Just like the +@code{break} statement, the POSIX standard specifies that @code{continue} +should only be used inside the body of a loop. +@value{DARKCORNER} @node Next Statement, Nextfile Statement, Continue Statement, Statements -@section The @code{next} Statement +@subsection The @code{next} Statement @cindex @code{next} statement -The @code{next} statement forces @code{awk} to immediately stop processing +The @code{next} statement forces @command{awk} to immediately stop processing the current record and go on to the next record. This means that no -further rules are executed for the current record. The rest of the -current rule's action is not executed either. +further rules are executed for the current record, and the rest of the +current rule's action isn't executed. Contrast this with the effect of the @code{getline} function -(@pxref{Getline, ,Explicit Input with @code{getline}}). That too causes -@code{awk} to read the next record immediately, but it does not alter the -flow of control in any way. So the rest of the current action executes -with a new input record. +(@pxref{Getline, ,Explicit Input with @code{getline}}). That also causes +@command{awk} to read the next record immediately, but it does not alter the +flow of control in any way (i.e., the rest of the current action executes +with a new input record). -At the highest level, @code{awk} program execution is a loop that reads +At the highest level, @command{awk} program execution is a loop that reads an input record and then tests each rule's pattern against it. If you think of this loop as a @code{for} statement whose body contains the rules, then the @code{next} statement is analogous to a @code{continue} -statement: it skips to the end of the body of this implicit loop, and +statement. It skips to the end of the body of this implicit loop and executes the increment (which reads another record). -For example, if your @code{awk} program works only on records with four -fields, and you don't want it to fail when given bad input, you might -use this rule near the beginning of the program: +For example, suppose an @command{awk} program works only on records +with four fields, and it shouldn't fail when given bad input. To avoid +complicating the rest of the program, write a ``weed out'' rule near +the beginning, in the following manner: @example -@group NF != 4 @{ err = sprintf("%s:%d: skipped: NF != 4\n", FILENAME, FNR) print err > "/dev/stderr" next @} -@end group @end example @noindent -so that the following rules will not see the bad record. The error +Because of the @code{next} statement, +the program's subsequent rules won't see the bad record. The error message is redirected to the standard error output stream, as error -messages should be. @xref{Special Files, ,Special File Names in @code{gawk}}. +messages should be. +@xref{Special Files, ,Special @value{FFN}s in @command{gawk}}. -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} +@cindex @code{next}, inside a user-defined function According to the POSIX standard, the behavior is undefined if the @code{next} statement is used in a @code{BEGIN} or @code{END} rule. -@code{gawk} will treat it as a syntax error. +@command{gawk} treats it as a syntax error. Although POSIX permits it, -some other @code{awk} implementations don't allow the @code{next} +some other @command{awk} implementations don't allow the @code{next} statement inside function bodies -(@pxref{User-defined, ,User-defined Functions}). -Just as any other @code{next} statement, a @code{next} inside a +(@pxref{User-defined, ,User-Defined Functions}). +Just as with any other @code{next} statement, a @code{next} statement inside a function body reads the next record and starts processing it with the first rule in the program. - If the @code{next} statement causes the end of the input to be reached, -then the code in any @code{END} rules will be executed. +then the code in any @code{END} rules is executed. @xref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}. -@cindex @code{next}, inside a user-defined function -@strong{Caution:} Some @code{awk} implementations generate a run-time -error if you use the @code{next} statement inside a user-defined function -(@pxref{User-defined, , User-defined Functions}). -@code{gawk} does not have this problem. - @node Nextfile Statement, Exit Statement, Next Statement, Statements -@section The @code{nextfile} Statement +@subsection Using @command{gawk}'s @code{nextfile} Statement @cindex @code{nextfile} statement -@cindex differences between @code{gawk} and @code{awk} +@cindex differences between @command{gawk} and @command{awk} -@code{gawk} provides the @code{nextfile} statement, +@command{gawk} provides the @code{nextfile} statement, which is similar to the @code{next} statement. However, instead of abandoning processing of the current record, the -@code{nextfile} statement instructs @code{gawk} to stop processing the -current data file. +@code{nextfile} statement instructs @command{gawk} to stop processing the +current @value{DF}. + +The @code{nextfile} statement is a @command{gawk} extension. +In most other @command{awk} implementations, +or if @command{gawk} is in compatibility mode +(@pxref{Options, ,Command-Line Options}), +@code{nextfile} is not special. Upon execution of the @code{nextfile} statement, @code{FILENAME} is -updated to the name of the next data file listed on the command line, +updated to the name of the next @value{DF} listed on the command line, @code{FNR} is reset to one, @code{ARGIND} is incremented, and processing -starts over with the first rule in the progam. @xref{Built-in Variables}. - +starts over with the first rule in the program. +(@code{ARGIND} hasn't been introduced yet. @xref{Built-in Variables}.) If the @code{nextfile} statement causes the end of the input to be reached, -then the code in any @code{END} rules will be executed. +then the code in any @code{END} rules is executed. @xref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}. -The @code{nextfile} statement is a @code{gawk} extension; it is not -(currently) available in any other @code{awk} implementation. -@xref{Nextfile Function, ,Implementing @code{nextfile} as a Function}, -for a user-defined function you can use to simulate the @code{nextfile} +The @code{nextfile} statement is useful when there are many @value{DF}s +to process but it isn't necessary to process every record in every file. +Normally, in order to move on to the next @value{DF}, a program +has to continue scanning the unwanted records. The @code{nextfile} +statement accomplishes this much more efficiently. + +While one might think that @samp{close(FILENAME)} would accomplish +the same as @code{nextfile}, this isn't true. @code{close} is +reserved for closing files, pipes, and coprocesses that are +opened with redirections. It is not related to the main processing that +@command{awk} does with the files listed in @code{ARGV}. + +If it's necessary to use an @command{awk} version that doesn't support +@code{nextfile}, see +@ref{Nextfile Function, ,Implementing @code{nextfile} as a Function}, +for a user-defined function that simulates the @code{nextfile} statement. -The @code{nextfile} statement would be useful if you have many data -files to process, and you expect that you -would not want to process every record in every file. -Normally, in order to move on to -the next data file, you would have to continue scanning the unwanted -records. The @code{nextfile} statement accomplishes this much more -efficiently. +@cindex @code{nextfile}, inside a user-defined function +The current version of the Bell Laboratories @command{awk} +(@pxref{Other Versions, ,Other Freely Available @command{awk} Implementations}) +also supports @code{nextfile}. However, it doesn't allow the @code{nextfile} +statement inside function bodies +(@pxref{User-defined, ,User-Defined Functions}). +@command{gawk} does; a @code{nextfile} inside a +function body reads the next record and starts processing it with the +first rule in the program, just as any other @code{nextfile} statement. @cindex @code{next file} statement -@strong{Caution:} Versions of @code{gawk} prior to 3.0 used two -words (@samp{next file}) for the @code{nextfile} statement. This was -changed in 3.0 to one word, since the treatment of @samp{file} was -inconsistent. When it appeared after @code{next}, it was a keyword. -Otherwise, it was a regular identifier. The old usage is still -accepted. However, @code{gawk} will generate a warning message, and -support for @code{next file} will eventually be discontinued in a -future version of @code{gawk}. - -@node Exit Statement, , Nextfile Statement, Statements -@section The @code{exit} Statement +@strong{Caution:} Versions of @command{gawk} prior to 3.0 used two +words (@samp{next file}) for the @code{nextfile} statement. +In @value{PVERSION} 3.0, this was changed +to one word, because the treatment of @samp{file} was +inconsistent. When it appeared after @code{next}, @samp{file} was a keyword; +otherwise, it was a regular identifier. The old usage is no longer +accepted; @samp{next file} generates a syntax error. + +@node Exit Statement, , Nextfile Statement, Statements +@subsection The @code{exit} Statement @cindex @code{exit} statement -The @code{exit} statement causes @code{awk} to immediately stop +The @code{exit} statement causes @command{awk} to immediately stop executing the current rule and to stop processing input; any remaining input -is ignored. It looks like this: +is ignored. The @code{exit} statement is written as follows: @example exit @r{[}@var{return code}@r{]} @end example -If an @code{exit} statement is executed from a @code{BEGIN} rule the +When an @code{exit} statement is executed from a @code{BEGIN} rule, the program stops processing everything immediately. No input records are -read. However, if an @code{END} rule is present, it is executed +read. However, if an @code{END} rule is present, +as part of executing the @code{exit} statement, +the @code{END} rule is executed (@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}). - If @code{exit} is used as part of an @code{END} rule, it causes the program to stop immediately. -An @code{exit} statement that is not part -of a @code{BEGIN} or @code{END} rule stops the execution of any further -automatic rules for the current record, skips reading any remaining input -records, and executes -the @code{END} rule if there is one. +An @code{exit} statement that is not part of a @code{BEGIN} or @code{END} +rule stops the execution of any further automatic rules for the current +record, skips reading any remaining input records, and executes the +@code{END} rule if there is one. -If you do not want the @code{END} rule to do its job in this case, you -can set a variable to non-zero before the @code{exit} statement, and check -that variable in the @code{END} rule. +In such a case, +if you don't want the @code{END} rule to do its job, set a variable +to nonzero before the @code{exit} statement and check that variable in +the @code{END} rule. @xref{Assert Function, ,Assertions}, for an example that does this. @cindex dark corner If an argument is supplied to @code{exit}, its value is used as the exit -status code for the @code{awk} process. If no argument is supplied, +status code for the @command{awk} process. If no argument is supplied, @code{exit} returns status zero (success). In the case where an argument is supplied to a first @code{exit} statement, and then @code{exit} is -called a second time with no argument, the previously supplied exit value -is used (d.c.). +called a second time from an @code{END} rule with no argument, +@command{awk} uses the previously supplied exit value. +@value{DARKCORNER} -For example, let's say you've discovered an error condition you really -don't know how to handle. Conventionally, programs report this by -exiting with a non-zero status. Your @code{awk} program can do this -using an @code{exit} statement with a non-zero argument. Here is an -example: +@cindex conventions, programming +@cindex programming conventions +For example, suppose an error condition occurs that is difficult or +impossible to handle. Conventionally, programs report this by +exiting with a nonzero status. An @command{awk} program can do this +using an @code{exit} statement with a nonzero argument, as shown +in the following example: @example -@group BEGIN @{ if (("date" | getline date_now) <= 0) @{ print "Can't get system date" > "/dev/stderr" @@ -8324,317 +9791,452 @@ BEGIN @{ print "current date is", date_now close("date") @} -@end group @end example -@node Built-in Variables, Arrays, Statements, Top -@chapter Built-in Variables +@node Built-in Variables, , Statements, Patterns and Actions +@section Built-in Variables @cindex built-in variables -Most @code{awk} variables are available for you to use for your own -purposes; they never change except when your program assigns values to -them, and never affect anything except when your program examines them. -However, a few variables in @code{awk} have special built-in meanings. -Some of them @code{awk} examines automatically, so that they enable you -to tell @code{awk} how to do certain things. Others are set -automatically by @code{awk}, so that they carry information from the -internal workings of @code{awk} to your program. +Most @command{awk} variables are available for you to use for your own +purposes; they never change unless your program assigns values to +them, and they never affect anything unless your program examines them. +However, a few variables in @command{awk} have special built-in meanings. +@command{awk} examines some of these automatically, so that they enable you +to tell @command{awk} how to do certain things. Others are set +automatically by @command{awk}, so that they carry information from the +internal workings of @command{awk} to your program. -This chapter documents all the built-in variables of @code{gawk}. Most -of them are also documented in the chapters describing their areas of -activity. +This @value{SECTION} documents all the built-in variables of +@command{gawk}, most of which are also documented in the chapters +describing their areas of activity. @menu * User-modified:: Built-in variables that you change to control - @code{awk}. -* Auto-set:: Built-in variables where @code{awk} gives you - information. + @command{awk}. +* Auto-set:: Built-in variables where @command{awk} gives + you information. * ARGC and ARGV:: Ways to use @code{ARGC} and @code{ARGV}. @end menu @node User-modified, Auto-set, Built-in Variables, Built-in Variables -@section Built-in Variables that Control @code{awk} +@subsection Built-in Variables That Control @command{awk} @cindex built-in variables, user modifiable -This is an alphabetical list of the variables which you can change to -control how @code{awk} does certain things. Those variables that are -specific to @code{gawk} are marked with an asterisk, @samp{*}. +The following is an alphabetical list of variables that you can change to +control how @command{awk} does certain things. The variables that are +specific to @command{gawk} are marked with a pound sign (@samp{#}). @table @code -@vindex CONVFMT -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} +@cindex @code{BINMODE} variable +@cindex binary I/O +@cindex I/O, binary +@cindex differences between @command{gawk} and @command{awk} +@item BINMODE # +On non-POSIX systems, this variable specifies use of ``binary'' mode for all I/O. +Numeric values of one, two, or three, specify that input files, output files, or +all files, respectively, should use binary I/O. +Alternatively, +string values of @code{"r"} or @code{"w"} specify that input files and +output files, respectively, should use binary I/O. +A string value of @code{"rw"} or @code{"wr"} indicates that all +files should use binary I/O. +Any other string value is equivalent to @code{"rw"}, but @command{gawk} +generates a warning message. +@code{BINMODE} is described in more detail in +@ref{PC Using, ,Using @command{gawk} on PC Operating Systems}. + +This variable is a @command{gawk} extension. +In other @command{awk} implementations +(except @command{mawk}, +@pxref{Other Versions, , Other Freely Available @command{awk} Implementations}), +or if @command{gawk} is in compatibility mode +(@pxref{Options, ,Command-Line Options}), +it is not special. + +@cindex @code{CONVFMT} variable +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} @item CONVFMT This string controls conversion of numbers to strings (@pxref{Conversion, ,Conversion of Strings and Numbers}). It works by being passed, in effect, as the first argument to the @code{sprintf} function -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). +(@pxref{String Functions, ,String Manipulation Functions}). Its default value is @code{"%.6g"}. @code{CONVFMT} was introduced by the POSIX standard. -@vindex FIELDWIDTHS -@item FIELDWIDTHS * -This is a space separated list of columns that tells @code{gawk} -how to split input with fixed, columnar boundaries. It is an -experimental feature. Assigning to @code{FIELDWIDTHS} +@cindex @code{FIELDWIDTHS} variable +@item FIELDWIDTHS # +This is a space-separated list of columns that tells @command{gawk} +how to split input with fixed columnar boundaries. +Assigning a value to @code{FIELDWIDTHS} overrides the use of @code{FS} for field splitting. -@xref{Constant Size, ,Reading Fixed-width Data}, for more information. +@xref{Constant Size, ,Reading Fixed-Width Data}, for more information. -If @code{gawk} is in compatibility mode -(@pxref{Options, ,Command Line Options}), then @code{FIELDWIDTHS} -has no special meaning, and field splitting operations are done based +If @command{gawk} is in compatibility mode +(@pxref{Options, ,Command-Line Options}), then @code{FIELDWIDTHS} +has no special meaning, and field-splitting operations occur based exclusively on the value of @code{FS}. -@vindex FS +@cindex @code{FS} variable @item FS -@code{FS} is the input field separator -(@pxref{Field Separators, ,Specifying How Fields are Separated}). +This is the input field separator +(@pxref{Field Separators, ,Specifying How Fields Are Separated}). The value is a single-character string or a multi-character regular expression that matches the separations between fields in an input record. If the value is the null string (@code{""}), then each character in the record becomes a separate field. +(This behavior is a @command{gawk} extension. POSIX @command{awk} does not +specify the behavior when @code{FS} is the null string.) +@c NEXT ED: Mark as common extension The default value is @w{@code{" "}}, a string consisting of a single space. As a special exception, this value means that any sequence of spaces, tabs, and/or newlines is a single separator.@footnote{In -POSIX @code{awk}, newline does not count as whitespace.} It also causes +POSIX @command{awk}, newline does not count as whitespace.} It also causes spaces, tabs, and newlines at the beginning and end of a record to be ignored. You can set the value of @code{FS} on the command line using the -@samp{-F} option: +@option{-F} option: @example awk -F, '@var{program}' @var{input-files} @end example -If @code{gawk} is using @code{FIELDWIDTHS} for field-splitting, -assigning a value to @code{FS} will cause @code{gawk} to return to -the normal, @code{FS}-based, field splitting. An easy way to do this +If @command{gawk} is using @code{FIELDWIDTHS} for field splitting, +assigning a value to @code{FS} causes @command{gawk} to return to +the normal, @code{FS}-based field splitting. An easy way to do this is to simply say @samp{FS = FS}, perhaps with an explanatory comment. -@vindex IGNORECASE -@item IGNORECASE * -If @code{IGNORECASE} is non-zero or non-null, then all string comparisons, +@cindex @code{IGNORECASE} variable +@item IGNORECASE # +If @code{IGNORECASE} is nonzero or non-null, then all string comparisons and all regular expression matching are case-independent. Thus, regexp -matching with @samp{~} and @samp{!~}, and the @code{gensub}, -@code{gsub}, @code{index}, @code{match}, @code{split} and @code{sub} +matching with @samp{~} and @samp{!~}, as well as the @code{gensub}, +@code{gsub}, @code{index}, @code{match}, @code{split}, and @code{sub} functions, record termination with @code{RS}, and field splitting with -@code{FS} all ignore case when doing their particular regexp operations. -The value of @code{IGNORECASE} does @emph{not} affect array subscripting. -@xref{Case-sensitivity, ,Case-sensitivity in Matching}. +@code{FS}, all ignore case when doing their particular regexp operations. +However, the value of @code{IGNORECASE} does @emph{not} affect array subscripting. +@xref{Case-sensitivity, ,Case Sensitivity in Matching}. -If @code{gawk} is in compatibility mode -(@pxref{Options, ,Command Line Options}), -then @code{IGNORECASE} has no special meaning, and string +If @command{gawk} is in compatibility mode +(@pxref{Options, ,Command-Line Options}), +then @code{IGNORECASE} has no special meaning. Thus, string and regexp operations are always case-sensitive. -@vindex OFMT +@cindex @code{LINT} variable +@cindex differences between @command{gawk} and @command{awk} +@cindex lint checks +@item LINT # +When this variable is true (nonzero or non-null), @command{gawk} +behaves as if the @option{--lint} command-line option is in effect. +(@pxref{Options, ,Command-Line Options}). +With a value of @code{"fatal"}, lint warnings become fatal errors. +Any other true value prints non-fatal warnings. +Assigning a false value to @code{LINT} turns off the lint warnings. + +This variable is a @command{gawk} extension. It is not special +in other @command{awk} implementations. Unlike the other special variables, +changing @code{LINT} does affect the production of lint warnings, +even if @command{gawk} is in compatibility mode. Much as +the @option{--lint} and @option{--traditional} options independently +control different aspects of @command{gawk}'s behavior, the control +of lint warnings during program execution is independent of the flavor +of @command{awk} being executed. + +@cindex @code{OFMT} variable @item OFMT This string controls conversion of numbers to strings (@pxref{Conversion, ,Conversion of Strings and Numbers}) for -printing with the @code{print} statement. It works by being passed, in -effect, as the first argument to the @code{sprintf} function -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). -Its default value is @code{"%.6g"}. Earlier versions of @code{awk} +printing with the @code{print} statement. It works by being passed +as the first argument to the @code{sprintf} function +(@pxref{String Functions, ,String Manipulation Functions}). +Its default value is @code{"%.6g"}. Earlier versions of @command{awk} also used @code{OFMT} to specify the format for converting numbers to strings in general expressions; this is now done by @code{CONVFMT}. -@vindex OFS +@cindex @code{OFS} variable @item OFS This is the output field separator (@pxref{Output Separators}). It is -output between the fields output by a @code{print} statement. Its +output between the fields printed by a @code{print} statement. Its default value is @w{@code{" "}}, a string consisting of a single space. -@vindex ORS +@cindex @code{ORS} variable @item ORS This is the output record separator. It is output at the end of every -@code{print} statement. Its default value is @code{"\n"}. -(@xref{Output Separators}.) +@code{print} statement. Its default value is @code{"\n"}, the newline +character. (@xref{Output Separators}.) -@vindex RS +@cindex @code{RS} variable @item RS -This is @code{awk}'s input record separator. Its default value is a string +This is @command{awk}'s input record separator. Its default value is a string containing a single newline character, which means that an input record consists of a single line of text. It can also be the null string, in which case records are separated by -runs of blank lines, or a regexp, in which case records are separated by +runs of blank lines. +If it is a regexp, records are separated by matches of the regexp in the input text. -(@xref{Records, ,How Input is Split into Records}.) +(@xref{Records, ,How Input Is Split into Records}.) -@vindex SUBSEP +The ability for @code{RS} to be a regular expression +is a @command{gawk} extension. +In most other @command{awk} implementations, +or if @command{gawk} is in compatibility mode +(@pxref{Options, ,Command-Line Options}), +just the first character of @code{RS}'s value is used. + +@cindex @code{SUBSEP} variable @item SUBSEP -@code{SUBSEP} is the subscript separator. It has the default value of -@code{"\034"}, and is used to separate the parts of the indices of a -multi-dimensional array. Thus, the expression @code{@w{foo["A", "B"]}} +This is the subscript separator. It has the default value of +@code{"\034"} and is used to separate the parts of the indices of a +multidimensional array. Thus, the expression @code{@w{foo["A", "B"]}} really accesses @code{foo["A\034B"]} -(@pxref{Multi-dimensional, ,Multi-dimensional Arrays}). +(@pxref{Multi-dimensional, ,Multidimensional Arrays}). + +@cindex @code{TEXTDOMAIN} variable +@cindex internationalization +@item TEXTDOMAIN # +This variable is used for internationalization of programs at the +@command{awk} level. It sets the default text domain for specially +marked string constants in the source text, as well as for the +@code{dcgettext} and @code{bindtextdomain} functions +(@pxref{Internationalization, ,Internationalization with @command{gawk}}). +The default value of @code{TEXTDOMAIN} is @code{"messages"}. + +This variable is a @command{gawk} extension. +In other @command{awk} implementations, +or if @command{gawk} is in compatibility mode +(@pxref{Options, ,Command-Line Options}), +it is not special. @end table @node Auto-set, ARGC and ARGV, User-modified, Built-in Variables -@section Built-in Variables that Convey Information +@subsection Built-in Variables That Convey Information @cindex built-in variables, convey information -This is an alphabetical list of the variables that are set -automatically by @code{awk} on certain occasions in order to provide -information to your program. Those variables that are specific to -@code{gawk} are marked with an asterisk, @samp{*}. +The following is an alphabetical list of variables that @command{awk} +sets automatically on certain occasions in order to provide +information to your program. The variables that are specific to +@command{gawk} are marked with an asterisk (@samp{*}). @table @code -@vindex ARGC -@vindex ARGV -@item ARGC -@itemx ARGV -The command-line arguments available to @code{awk} programs are stored in +@cindex @code{ARGC} variable +@cindex @code{ARGV} variable +@item ARGC@r{,} ARGV +The command-line arguments available to @command{awk} programs are stored in an array called @code{ARGV}. @code{ARGC} is the number of command-line -arguments present. @xref{Other Arguments, ,Other Command Line Arguments}. -Unlike most @code{awk} arrays, -@code{ARGV} is indexed from zero to @code{ARGC} @minus{} 1. For example: +arguments present. @xref{Other Arguments, ,Other Command-Line Arguments}. +Unlike most @command{awk} arrays, +@code{ARGV} is indexed from 0 to @code{ARGC} @minus{} 1. +In the following example: @example -@group $ awk 'BEGIN @{ -> for (i = 0; i < ARGC; i++) -> print ARGV[i] +> for (i = 0; i < ARGC; i++) +> print ARGV[i] > @}' inventory-shipped BBS-list @print{} awk @print{} inventory-shipped @print{} BBS-list -@end group @end example @noindent -In this example, @code{ARGV[0]} contains @code{"awk"}, @code{ARGV[1]} -contains @code{"inventory-shipped"}, and @code{ARGV[2]} contains +@code{ARGV[0]} contains @code{"awk"}, @code{ARGV[1]} +contains @code{"inventory-shipped"} and @code{ARGV[2]} contains @code{"BBS-list"}. The value of @code{ARGC} is three, one more than the -index of the last element in @code{ARGV}, since the elements are numbered +index of the last element in @code{ARGV}, because the elements are numbered from zero. +@cindex conventions, programming +@cindex programming conventions The names @code{ARGC} and @code{ARGV}, as well as the convention of indexing -the array from zero to @code{ARGC} @minus{} 1, are derived from the C language's -method of accessing command line arguments. +the array from 0 to @code{ARGC} @minus{} 1, are derived from the C language's +method of accessing command-line arguments. + +The value of @code{ARGV[0]} can vary from system to system. +Also, you should note that the program text is @emph{not} included in +@code{ARGV}, nor are any of @command{awk}'s command-line options. @xref{ARGC and ARGV, , Using @code{ARGC} and @code{ARGV}}, for information -about how @code{awk} uses these variables. +about how @command{awk} uses these variables. -@vindex ARGIND -@item ARGIND * -The index in @code{ARGV} of the current file being processed. -Every time @code{gawk} opens a new data file for processing, it sets -@code{ARGIND} to the index in @code{ARGV} of the file name. -When @code{gawk} is processing the input files, it is always -true that @samp{FILENAME == ARGV[ARGIND]}. +@cindex @code{ARGIND} variable +@item ARGIND # +This is the index in @code{ARGV} of the current file being processed. +Every time @command{gawk} opens a new @value{DF} for processing, it sets +@code{ARGIND} to the index in @code{ARGV} of the @value{FN}. +When @command{gawk} is processing the input files, +@samp{FILENAME == ARGV[ARGIND]} is always true. This variable is useful in file processing; it allows you to tell how far -along you are in the list of data files, and to distinguish between -successive instances of the same filename on the command line. +along you are in the list of @value{DF}s as well as to distinguish between +successive instances of the same @value{FN} on the command line. -While you can change the value of @code{ARGIND} within your @code{awk} -program, @code{gawk} will automatically set it to a new value when the +While you can change the value of @code{ARGIND} within your @command{awk} +program, @command{gawk} automatically sets it to a new value when the next file is opened. -This variable is a @code{gawk} extension. In other @code{awk} implementations, -or if @code{gawk} is in compatibility mode -(@pxref{Options, ,Command Line Options}), +This variable is a @command{gawk} extension. +In other @command{awk} implementations, +or if @command{gawk} is in compatibility mode +(@pxref{Options, ,Command-Line Options}), it is not special. -@vindex ENVIRON +@cindex @code{ENVIRON} variable @item ENVIRON An associative array that contains the values of the environment. The array -indices are the environment variable names; the values are the values of +indices are the environment variable names; the elements are the values of the particular environment variables. For example, @code{ENVIRON["HOME"]} might be @file{/home/arnold}. Changing this array does not affect the environment passed on to any programs that -@code{awk} may spawn via redirection or the @code{system} function. -(In a future version of @code{gawk}, it may do so.) +@command{awk} may spawn via redirection or the @code{system} function. +@c (In a future version of @command{gawk}, it may do so.) Some operating systems may not have environment variables. On such systems, the @code{ENVIRON} array is empty (except for -@w{@code{ENVIRON["AWKPATH"]}}). +@w{@code{ENVIRON["AWKPATH"]}}, +@pxref{AWKPATH Variable, ,The @env{AWKPATH} Environment Variable}). -@vindex ERRNO -@item ERRNO * -If a system error occurs either doing a redirection for @code{getline}, +@cindex @code{ERRNO} variable +@item ERRNO # +If a system error occurs during a redirection for @code{getline}, during a read for @code{getline}, or during a @code{close} operation, -then @code{ERRNO} will contain a string describing the error. +then @code{ERRNO} contains a string describing the error. -This variable is a @code{gawk} extension. In other @code{awk} implementations, -or if @code{gawk} is in compatibility mode -(@pxref{Options, ,Command Line Options}), +This variable is a @command{gawk} extension. +In other @command{awk} implementations, +or if @command{gawk} is in compatibility mode +(@pxref{Options, ,Command-Line Options}), it is not special. @cindex dark corner -@vindex FILENAME +@cindex @code{FILENAME} variable @item FILENAME -This is the name of the file that @code{awk} is currently reading. -When no data files are listed on the command line, @code{awk} reads -from the standard input, and @code{FILENAME} is set to @code{"-"}. +This is the name of the file that @command{awk} is currently reading. +When no @value{DF}s are listed on the command line, @command{awk} reads +from the standard input and @code{FILENAME} is set to @code{"-"}. @code{FILENAME} is changed each time a new file is read (@pxref{Reading Files, ,Reading Input Files}). Inside a @code{BEGIN} rule, the value of @code{FILENAME} is @code{""}, since there are no input files being processed -yet.@footnote{Some early implementations of Unix @code{awk} initialized -@code{FILENAME} to @code{"-"}, even if there were data files to be -processed. This behavior was incorrect, and should not be relied -upon in your programs.} (d.c.) +yet.@footnote{Some early implementations of Unix @command{awk} initialized +@code{FILENAME} to @code{"-"}, even if there were @value{DF}s to be +processed. This behavior was incorrect and should not be relied +upon in your programs.} +@value{DARKCORNER} +Note though, that using @code{getline} +(@pxref{Getline, ,Explicit Input with @code{getline}}) +inside a @code{BEGIN} rule can give +@code{FILENAME} a value. -@vindex FNR +@cindex @code{FNR} variable @item FNR -@code{FNR} is the current record number in the current file. @code{FNR} is +This is the current record number in the current file. @code{FNR} is incremented each time a new record is read (@pxref{Getline, ,Explicit Input with @code{getline}}). It is reinitialized to zero each time a new input file is started. -@vindex NF +@cindex @code{NF} variable @item NF -@code{NF} is the number of fields in the current input record. +This is the number of fields in the current input record. @code{NF} is set each time a new record is read, when a new field is -created, or when @code{$0} changes (@pxref{Fields, ,Examining Fields}). +created or when @code{$0} changes (@pxref{Fields, ,Examining Fields}). -@vindex NR +@cindex @code{NR} variable @item NR -This is the number of input records @code{awk} has processed since +This is the number of input records @command{awk} has processed since the beginning of the program's execution -(@pxref{Records, ,How Input is Split into Records}). -@code{NR} is set each time a new record is read. +(@pxref{Records, ,How Input Is Split into Records}). +@code{NR} is incremented each time a new record is read. -@vindex RLENGTH +@cindex @code{PROCINFO} variable +@item PROCINFO # +The elements of this array provide access to information about the +running @command{awk} program. +The following elements (listed alphabetically) +are guaranteed to be available: + +@table @code +@item PROCINFO["egid"] +The value of the @code{getegid} system call. + +@item PROCINFO["euid"] +The value of the @code{geteuid} system call. + +@item PROCINFO["FS"] +This is +@code{"FS"} if field splitting with @code{FS} is in effect, or it is +@code{"FIELDWIDTHS"} if field splitting with @code{FIELDWIDTHS} is in effect. + +@item PROCINFO["gid"] +The value of the @code{getgid} system call. + +@item PROCINFO["pgrpid"] +The process group ID of the current process. + +@item PROCINFO["pid"] +The process ID of the current process. + +@item PROCINFO["ppid"] +The parent process ID of the current process. + +@item PROCINFO["uid"] +The value of the @code{getuid} system call. +@end table + +On some systems, there may be elements in the array, @code{"group1"} +through @code{"group@var{N}"} for some @var{N}. @var{N} is the number of +supplementary groups that the process has. Use the @code{in} operator +to test for these elements +(@pxref{Reference to Elements, , Referring to an Array Element}). + +This array is a @command{gawk} extension. +In other @command{awk} implementations, +or if @command{gawk} is in compatibility mode +(@pxref{Options, ,Command-Line Options}), +it is not special. + +@cindex @code{RLENGTH} variable @item RLENGTH -@code{RLENGTH} is the length of the substring matched by the +This is the length of the substring matched by the @code{match} function -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). +(@pxref{String Functions, ,String Manipulation Functions}). @code{RLENGTH} is set by invoking the @code{match} function. Its value -is the length of the matched string, or @minus{}1 if no match was found. +is the length of the matched string, or @minus{}1 if no match is found. -@vindex RSTART +@cindex @code{RSTART} variable @item RSTART -@code{RSTART} is the start-index in characters of the substring matched by the +This is the start-index in characters of the substring that is matched by the @code{match} function -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). +(@pxref{String Functions, ,String Manipulation Functions}). @code{RSTART} is set by invoking the @code{match} function. Its value is the position of the string where the matched substring starts, or zero if no match was found. -@vindex RT -@item RT * -@code{RT} is set each time a record is read. It contains the input text +@cindex @code{RT} variable +@item RT # +This is set each time a record is read. It contains the input text that matched the text denoted by @code{RS}, the record separator. -This variable is a @code{gawk} extension. In other @code{awk} implementations, -or if @code{gawk} is in compatibility mode -(@pxref{Options, ,Command Line Options}), +This variable is a @command{gawk} extension. +In other @command{awk} implementations, +or if @command{gawk} is in compatibility mode +(@pxref{Options, ,Command-Line Options}), it is not special. @end table +@c fakenode --- for prepinfo +@subheading Advanced Notes: Changing @code{NR} and @code{FNR} +@cindex advanced notes @cindex dark corner -A side note about @code{NR} and @code{FNR}. -@code{awk} simply increments both of these variables +@command{awk} increments @code{NR} and @code{FNR} each time it reads a record, instead of setting them to the absolute -value of the number of records read. This means that your program can -change these variables, and their new values will be incremented for -each record (d.c.). For example: +value of the number of records read. This means that a program can +change these variables and their new values are incremented for +each record. +@value{DARKCORNER} +This is demonstrated in the following example: @example -@group $ echo '1 > 2 > 3 @@ -8644,46 +10246,42 @@ $ echo '1 @print{} 17 @print{} 18 @print{} 19 -@end group @end example @noindent -Before @code{FNR} was added to the @code{awk} language -(@pxref{V7/SVR3.1, ,Major Changes between V7 and SVR3.1}), -many @code{awk} programs used this feature to track the number of +Before @code{FNR} was added to the @command{awk} language +(@pxref{V7/SVR3.1, ,Major Changes Between V7 and SVR3.1}), +many @command{awk} programs used this feature to track the number of records in a file by resetting @code{NR} to zero when @code{FILENAME} changed. @node ARGC and ARGV, , Auto-set, Built-in Variables -@section Using @code{ARGC} and @code{ARGV} +@subsection Using @code{ARGC} and @code{ARGV} -In @ref{Auto-set, , Built-in Variables that Convey Information}, -you saw this program describing the information contained in @code{ARGC} +@ref{Auto-set, ,Built-in Variables That Convey Information}, +presented the following program describing the information contained in @code{ARGC} and @code{ARGV}: @example -@group $ awk 'BEGIN @{ -> for (i = 0; i < ARGC; i++) -> print ARGV[i] +> for (i = 0; i < ARGC; i++) +> print ARGV[i] > @}' inventory-shipped BBS-list @print{} awk @print{} inventory-shipped @print{} BBS-list -@end group @end example @noindent -In this example, @code{ARGV[0]} contains @code{"awk"}, @code{ARGV[1]} -contains @code{"inventory-shipped"}, and @code{ARGV[2]} contains -@code{"BBS-list"}. - -Notice that the @code{awk} program is not entered in @code{ARGV}. The -other special command line options, with their arguments, are also not -entered. This includes variable assignments done with the @samp{-v} -option (@pxref{Options, ,Command Line Options}). +In this example, @code{ARGV[0]} contains @samp{awk}, @code{ARGV[1]} +contains @samp{inventory-shipped}, and @code{ARGV[2]} contains +@samp{BBS-list}. +Notice that the @command{awk} program is not entered in @code{ARGV}. The +other special command-line options, with their arguments, are also not +entered. This includes variable assignments done with the @option{-v} +option (@pxref{Options, ,Command-Line Options}). Normal variable assignments on the command line @emph{are} -treated as arguments, and do show up in the @code{ARGV} array. +treated as arguments and do show up in the @code{ARGV} array: @example $ cat showargs.awk @@ -8695,51 +10293,49 @@ $ cat showargs.awk @print{} END @{ printf "A=%d, B=%d\n", A, B @} $ awk -v A=1 -f showargs.awk B=2 /dev/null @print{} A=1, B=0 -@print{} ARGV[0] = awk -@print{} ARGV[1] = B=2 -@print{} ARGV[2] = /dev/null +@print{} ARGV[0] = awk +@print{} ARGV[1] = B=2 +@print{} ARGV[2] = /dev/null @print{} A=1, B=2 @end example -Your program can alter @code{ARGC} and the elements of @code{ARGV}. -Each time @code{awk} reaches the end of an input file, it uses the next +A program can alter @code{ARGC} and the elements of @code{ARGV}. +Each time @command{awk} reaches the end of an input file, it uses the next element of @code{ARGV} as the name of the next input file. By storing a -different string there, your program can change which files are read. -You can use @code{"-"} to represent the standard input. By storing -additional elements and incrementing @code{ARGC} you can cause +different string there, a program can change which files are read. +Use @code{"-"} to represent the standard input. Storing +additional elements and incrementing @code{ARGC} causes additional files to be read. -If you decrease the value of @code{ARGC}, that eliminates input files +If the value of @code{ARGC} is decreased, that eliminates input files from the end of the list. By recording the old value of @code{ARGC} -elsewhere, your program can treat the eliminated arguments as -something other than file names. +elsewhere, a program can treat the eliminated arguments as +something other than @value{FN}s. To eliminate a file from the middle of the list, store the null string (@code{""}) into @code{ARGV} in place of the file's name. As a -special feature, @code{awk} ignores file names that have been +special feature, @command{awk} ignores @value{FN}s that have been replaced with the null string. -You may also use the @code{delete} statement to remove elements from +Another option is to +use the @code{delete} statement to remove elements from @code{ARGV} (@pxref{Delete, ,The @code{delete} Statement}). -All of these actions are typically done from the @code{BEGIN} rule, +All of these actions are typically done in the @code{BEGIN} rule, before actual processing of the input begins. -@xref{Split Program, ,Splitting a Large File Into Pieces}, and see -@ref{Tee Program, ,Duplicating Output Into Multiple Files}, for an example +@xref{Split Program, ,Splitting a Large File into Pieces}, and see +@ref{Tee Program, ,Duplicating Output into Multiple Files}, for examples of each way of removing elements from @code{ARGV}. - The following fragment processes @code{ARGV} in order to examine, and -then remove, command line options. +then remove, command-line options: +@c NEXT ED: Add xref to rewind() function @example -@group BEGIN @{ for (i = 1; i < ARGC; i++) @{ if (ARGV[i] == "-v") verbose = 1 else if (ARGV[i] == "-d") debug = 1 -@end group -@group else if (ARGV[i] ~ /^-?/) @{ e = sprintf("%s: unrecognized option -- %c", ARGV[0], substr(ARGV[i], 1, ,1)) @@ -8749,44 +10345,55 @@ BEGIN @{ delete ARGV[i] @} @} -@end group @end example -To actually get the options into the @code{awk} program, you have to -end the @code{awk} options with @samp{--}, and then supply your options, -like so: +To actually get the options into the @command{awk} program, +end the @command{awk} options with @option{--} and then supply +the @command{awk} program's options, in the following manner: @example awk -f myprog -- -v -d file1 file2 @dots{} @end example -@cindex differences between @code{gawk} and @code{awk} -This is not necessary in @code{gawk}: Unless @samp{--posix} has been -specified, @code{gawk} silently puts any unrecognized options into -@code{ARGV} for the @code{awk} program to deal with. - -As soon as it -sees an unknown option, @code{gawk} stops looking for other options it might -otherwise recognize. The above example with @code{gawk} would be: +@cindex differences between @command{gawk} and @command{awk} +This is not necessary in @command{gawk}. Unless @option{--posix} has +been specified, @command{gawk} silently puts any unrecognized options +into @code{ARGV} for the @command{awk} program to deal with. As soon +as it sees an unknown option, @command{gawk} stops looking for other +options that it might otherwise recognize. The previous example with +@command{gawk} would be: @example gawk -f myprog -d -v file1 file2 @dots{} @end example @noindent -Since @samp{-d} is not a valid @code{gawk} option, the following @samp{-v} -is passed on to the @code{awk} program. +Because @option{-d} is not a valid @command{gawk} option, +it and the following @option{-v} +are passed on to the @command{awk} program. -@node Arrays, Built-in, Built-in Variables, Top -@chapter Arrays in @code{awk} +@node Arrays, Functions, Patterns and Actions, Top +@chapter Arrays in @command{awk} -An @dfn{array} is a table of values, called @dfn{elements}. The +An @dfn{array} is a table of values called @dfn{elements}. The elements of an array are distinguished by their indices. @dfn{Indices} -may be either numbers or strings. @code{awk} maintains a single set -of names that may be used for naming variables, arrays and functions -(@pxref{User-defined, ,User-defined Functions}). +may be either numbers or strings. + +This @value{CHAPTER} describes how arrays work in @command{awk}, +how to use array elements, how to scan through every element in an array, +and how to remove array elements. +It also describes how @command{awk} simulates multidimensional +arrays, as well as some of the less obvious points about array usage. +The @value{CHAPTER} finishes with a discussion of @command{gawk}'s facility +for sorting an array based on its indices. + +@cindex names, use of +@cindex namespace issues in @command{awk} +@command{awk} maintains a single set +of names that may be used for naming variables, arrays, and functions +(@pxref{User-defined, ,User-Defined Functions}). Thus, you cannot have a variable and an array with the same name in the -same @code{awk} program. +same @command{awk} program. @menu * Array Intro:: Introduction to Arrays @@ -8799,49 +10406,51 @@ same @code{awk} program. * Delete:: The @code{delete} statement removes an element from an array. * Numeric Array Subscripts:: How to use numbers as subscripts in - @code{awk}. + @command{awk}. * Uninitialized Subscripts:: Using Uninitialized variables as subscripts. -* Multi-dimensional:: Emulating multi-dimensional arrays in - @code{awk}. -* Multi-scanning:: Scanning multi-dimensional arrays. -* Array Efficiency:: Implementation-specific tips. +* Multi-dimensional:: Emulating multidimensional arrays in + @command{awk}. +* Multi-scanning:: Scanning multidimensional arrays. +* Array Sorting:: Sorting array values and indices. @end menu @node Array Intro, Reference to Elements, Arrays, Arrays @section Introduction to Arrays @cindex arrays -The @code{awk} language provides one-dimensional @dfn{arrays} for storing groups -of related strings or numbers. - -Every @code{awk} array must have a name. Array names have the same +The @command{awk} language provides one-dimensional arrays +for storing groups of related strings or numbers. +Every @command{awk} array must have a name. Array names have the same syntax as variable names; any valid variable name would also be a valid -array name. But you cannot use one name in both ways (as an array and -as a variable) in one @code{awk} program. - -Arrays in @code{awk} superficially resemble arrays in other programming -languages; but there are fundamental differences. In @code{awk}, you -don't need to specify the size of an array before you start to use it. -Additionally, any number or string in @code{awk} may be used as an -array index, not just consecutive integers. - -In most other languages, you have to @dfn{declare} an array and specify -how many elements or components it contains. In such languages, the +array name. But one name cannot be used in both ways (as an array and +as a variable) in the same @command{awk} program. + +Arrays in @command{awk} superficially resemble arrays in other programming +languages, but there are fundamental differences. In @command{awk}, it +isn't necessary to specify the size of an array before starting to use it. +Additionally, any number or string in @command{awk}, not just consecutive integers, +may be used as an array index. + +In most other languages, arrays must be @dfn{declared} before use, +including a specification of +how many elements or components they contain. In such languages, the declaration causes a contiguous block of memory to be allocated for that -many elements. An index in the array usually must be a positive integer; for -example, the index zero specifies the first element in the array, which is +many elements. Usually, an index in the array must be a positive integer. +For example, the index zero specifies the first element in the array, which is actually stored at the beginning of the block of memory. Index one specifies the second element, which is stored in memory right after the first element, and so on. It is impossible to add more elements to the -array, because it has room for only as many elements as you declared. -(Some languages allow arbitrary starting and ending indices, -e.g., @samp{15 .. 27}, but the size of the array is still fixed when +array, because it has room only for as many elements as given in +the declaration. +(Some languages allow arbitrary starting and ending +indices---e.g., @samp{15 .. 27}---but the size of the array is still fixed when the array is declared.) -A contiguous array of four elements might look like this, -conceptually, if the element values are eight, @code{"foo"}, -@code{""} and 30: +A contiguous array of four elements might look like the following example, +conceptually, if the element values are 8, @code{"foo"}, +@code{""}, and 30: +@c NEXT ED: Use real images here @iftex @c from Karl Berry, much thanks for the help. @tex @@ -8852,10 +10461,10 @@ conceptually, if the element values are eight, @code{"foo"}, \centerline{\vbox{ \halign{\strut\hfil\ignorespaces#&&\vrule#&\hbox to\width{\hfil#\unskip\hfil}\cr \noalign{\hrule width\hwidth} - &&{\tt 8} &&{\tt "foo"} &&{\tt ""} &&{\tt 30} &&\quad value\cr + &&{\tt 8} &&{\tt "foo"} &&{\tt ""} &&{\tt 30} &&\quad Value\cr \noalign{\hrule width\hwidth} \noalign{\smallskip} - &\omit&0&\omit &1 &\omit&2 &\omit&3 &\omit&\quad index\cr + &\omit&0&\omit &1 &\omit&2 &\omit&3 &\omit&\quad Index\cr } }} @end tex @@ -8863,56 +10472,55 @@ conceptually, if the element values are eight, @code{"foo"}, @ifinfo @example +---------+---------+--------+---------+ -| 8 | "foo" | "" | 30 | @r{value} +| 8 | "foo" | "" | 30 | @r{Value} +---------+---------+--------+---------+ - 0 1 2 3 @r{index} + 0 1 2 3 @r{Index} @end example @end ifinfo @noindent Only the values are stored; the indices are implicit from the order of -the values. Eight is the value at index zero, because eight appears in the +the values. 8 is the value at index zero, because 8 appears in the position with zero elements before it. @cindex arrays, definition of @cindex associative arrays @cindex arrays, associative -Arrays in @code{awk} are different: they are @dfn{associative}. This means +Arrays in @command{awk} are different---they are @dfn{associative}. This means that each array is a collection of pairs: an index, and its corresponding array element value: @example -@r{Element} 4 @r{Value} 30 -@r{Element} 2 @r{Value} "foo" -@r{Element} 1 @r{Value} 8 -@r{Element} 3 @r{Value} "" +@r{Element} 3 @r{Value} 30 +@r{Element} 1 @r{Value} "foo" +@r{Element} 0 @r{Value} 8 +@r{Element} 2 @r{Value} "" @end example @noindent -We have shown the pairs in jumbled order because their order is irrelevant. +The pairs are shown in jumbled order because their order is irrelevant. One advantage of associative arrays is that new pairs can be added -at any time. For example, suppose we add to the above array a tenth element -whose value is @w{@code{"number ten"}}. The result is this: +at any time. For example, suppose a tenth element is added to the array +whose value is @w{@code{"number ten"}}. The result is: @example @r{Element} 10 @r{Value} "number ten" -@r{Element} 4 @r{Value} 30 -@r{Element} 2 @r{Value} "foo" -@r{Element} 1 @r{Value} 8 -@r{Element} 3 @r{Value} "" +@r{Element} 3 @r{Value} 30 +@r{Element} 1 @r{Value} "foo" +@r{Element} 0 @r{Value} 8 +@r{Element} 2 @r{Value} "" @end example @noindent @cindex sparse arrays @cindex arrays, sparse -Now the array is @dfn{sparse}, which just means some indices are missing: -it has elements 1--4 and 10, but doesn't have elements 5, 6, 7, 8, or 9. -@c ok, I should spell out the above, but ... +Now the array is @dfn{sparse}, which just means some indices are missing. +It has elements 0--3 and 10, but doesn't have elements 4, 5, 6, 7, 8, or 9. Another consequence of associative arrays is that the indices don't have to be positive integers. Any number, or even a string, can be -an index. For example, here is an array which translates words from +an index. For example, the following is an array that translates words from English into French: @example @@ -8926,21 +10534,25 @@ English into French: Here we decided to translate the number one in both spelled-out and numeric form---thus illustrating that a single array can have both numbers and strings as indices. -(In fact, array subscripts are always strings; this is discussed +In fact, array subscripts are always strings; this is discussed in more detail in -@ref{Numeric Array Subscripts, ,Using Numbers to Subscript Arrays}.) +@ref{Numeric Array Subscripts, ,Using Numbers to Subscript Arrays}. +Here, the number @code{1} isn't double-quoted, since @command{awk} +automatically converts it to a string. -@cindex Array subscripts and @code{IGNORECASE} -@cindex @code{IGNORECASE} and array subscripts -@vindex IGNORECASE +@cindex arrays, subscripts, and @code{IGNORECASE} +@cindex @code{IGNORECASE}, and array subscripts +@cindex @code{IGNORECASE} variable The value of @code{IGNORECASE} has no effect upon array subscripting. -You must use the exact same string value to retrieve an array element -as you used to store it. - -When @code{awk} creates an array for you, e.g., with the @code{split} -built-in function, +The identical string value used to store an array element must be used +to retrieve it. +When @command{awk} creates an array (e.g., with the @code{split} +built-in function), that array's indices are consecutive integers starting at one. -(@xref{String Functions, ,Built-in Functions for String Manipulation}.) +(@xref{String Functions, ,String Manipulation Functions}.) + +@command{awk}'s arrays are efficient---the time to access an element +is independent of the number of elements in the array. @node Reference to Elements, Assigning Elements, Array Intro, Arrays @section Referring to an Array Element @@ -8948,8 +10560,8 @@ that array's indices are consecutive integers starting at one. @cindex element of array @cindex reference to array -The principal way of using an array is to refer to one of its elements. -An array reference is an expression which looks like this: +The principal way to use an array is to refer to one of its elements. +An array reference is an expression as follows: @example @var{array}[@var{index}] @@ -8957,48 +10569,48 @@ An array reference is an expression which looks like this: @noindent Here, @var{array} is the name of an array. The expression @var{index} is -the index of the element of the array that you want. +the index of the desired element of the array. The value of the array reference is the current value of that array element. For example, @code{foo[4.3]} is an expression for the element of array @code{foo} at index @samp{4.3}. -If you refer to an array element that has no recorded value, the value -of the reference is @code{""}, the null string. This includes elements -to which you have not assigned any value, and elements that have been +A reference to an array element that has no recorded value yields a value of +@code{""}, the null string. This includes elements +that have not been assigned any value as well as elements that have been deleted (@pxref{Delete, ,The @code{delete} Statement}). Such a reference automatically creates that array element, with the null string as its value. (In some cases, this is unfortunate, because it might waste memory inside -@code{awk}.) +@command{awk}.) @cindex arrays, presence of elements @cindex arrays, the @code{in} operator -You can find out if an element exists in an array at a certain index with -the expression: +To determine whether an element exists in an array at a certain index, use +the following expression: @example @var{index} in @var{array} @end example +@cindex side effects @noindent This expression tests whether or not the particular index exists, without the side effect of creating that element if it is not present. The expression has the value one (true) if @code{@var{array}[@var{index}]} -exists, and zero (false) if it does not exist. - -For example, to test whether the array @code{frequencies} contains the -index @samp{2}, you could write this statement: +exists and zero (false) if it does not exist. +For example, this statement tests whether the array @code{frequencies} +contains the index @samp{2}: @example if (2 in frequencies) print "Subscript 2 is present." @end example -Note that this is @emph{not} a test of whether or not the array +Note that this is @emph{not} a test of whether the array @code{frequencies} contains an element whose @emph{value} is two. -(There is no way to do that except to scan all the elements.) Also, this +There is no way to do that except to scan all the elements. Also, this @emph{does not} create @code{frequencies[2]}, while the following -(incorrect) alternative would do so: +(incorrect) alternative does: @example if (frequencies[2] != "") @@ -9010,39 +10622,38 @@ if (frequencies[2] != "") @cindex array assignment @cindex element assignment -Array elements are lvalues: they can be assigned values just like -@code{awk} variables: +Array elements can be assigned values just like +@command{awk} variables: @example @var{array}[@var{subscript}] = @var{value} @end example @noindent -Here @var{array} is the name of your array. The expression -@var{subscript} is the index of the element of the array that you want -to assign a value. The expression @var{value} is the value you are -assigning to that element of the array. +@var{array} is the name of an array. The expression +@var{subscript} is the index of the element of the array that is +assigned a value. The expression @var{value} is the value to +assign to that element of the array. @node Array Example, Scanning an Array, Assigning Elements, Arrays @section Basic Array Example The following program takes a list of lines, each beginning with a line -number, and prints them out in order of line number. The line numbers are -not in order, however, when they are first read: they are scrambled. This -program sorts the lines by making an array using the line numbers as -subscripts. It then prints out the lines in sorted order of their numbers. -It is a very simple program, and gets confused if it encounters repeated -numbers, gaps, or lines that don't begin with a number. +number, and prints them out in order of line number. The line numbers +are not in order when they are first read---instead they +are scrambled. This program sorts the lines by making an array using +the line numbers as subscripts. The program then prints out the lines +in sorted order of their numbers. It is a very simple program and gets +confused upon encountering repeated numbers, gaps, or lines that don't +begin with a number: @example -@group @c file eg/misc/arraymax.awk @{ if ($1 > max) max = $1 arr[$1] = $0 @} -@end group END @{ for (x = 1; x <= max; x++) @@ -9054,14 +10665,11 @@ END @{ The first rule keeps track of the largest line number seen so far; it also stores each line into the array @code{arr}, at an index that is the line's number. - The second rule runs after all the input has been read, to print out all the lines. - When this program is run with the following input: @example -@group @c file eg/misc/arraymax.data 5 I am the Five man 2 Who are you? The new number two! @@ -9069,11 +10677,10 @@ When this program is run with the following input: 1 Who is number one? 3 I three you. @c endfile -@end group @end example @noindent -its output is this: +its output is: @example 1 Who is number one? @@ -9085,9 +10692,8 @@ its output is this: If a line number is repeated, the last line with a given number overrides the others. - Gaps in the line numbers can be handled with an easy improvement to the -program's @code{END} rule: +program's @code{END} rule, as follows: @example END @{ @@ -9099,19 +10705,19 @@ END @{ @node Scanning an Array, Delete, Array Example, Arrays @section Scanning All Elements of an Array -@cindex @code{for (x in @dots{})} +@cindex @code{for (x in @dots{})} statement @cindex arrays, special @code{for} statement @cindex scanning an array +@cindex @code{in} operator -In programs that use arrays, you often need a loop that executes -once for each element of an array. In other languages, where arrays are -contiguous and indices are limited to positive integers, this is -easy: you can -find all the valid indices by counting from the lowest index -up to the highest. This -technique won't do the job in @code{awk}, since any number or string -can be an array index. So @code{awk} has a special kind of @code{for} -statement for scanning an array: +In programs that use arrays, it is often necessary to use a loop that +executes once for each element of an array. In other languages, where +arrays are contiguous and indices are limited to positive integers, +this is easy: all the valid indices can be found by counting from +the lowest index up to the highest. This technique won't do the job +in @command{awk}, because any number or string can be an array index. +So @command{awk} has a special kind of @code{for} statement for scanning +an array: @example for (@var{var} in @var{array}) @@ -9119,27 +10725,27 @@ for (@var{var} in @var{array}) @end example @noindent -This loop executes @var{body} once for each index in @var{array} that your -program has previously used, with the -variable @var{var} set to that index. +This loop executes @var{body} once for each index in @var{array} that the +program has previously used, with the variable @var{var} set to that index. -Here is a program that uses this form of the @code{for} statement. The +The following program uses this form of the @code{for} statement. The first rule scans the input records and notes which words appear (at least once) in the input, by storing a one into the array @code{used} with the word as index. The second rule scans the elements of @code{used} to find all the distinct words that appear in the input. It prints each -word that is more than 10 characters long, and also prints the number of -such words. @xref{String Functions, ,Built-in Functions for String Manipulation}, for more information -on the built-in function @code{length}. +word that is more than 10 characters long and also prints the number of +such words. +@xref{String Functions, ,String Manipulation Functions}, +for more information on the built-in function @code{length}. @example -# Record a 1 for each word that is used at least once. +# Record a 1 for each word that is used at least once @{ for (i = 1; i <= NF; i++) used[$i] = 1 @} -# Find number of distinct words more than 10 characters long. +# Find number of distinct words more than 10 characters long END @{ for (x in used) if (length(x) > 10) @{ @@ -9156,9 +10762,9 @@ for a more detailed example of this type. The order in which elements of the array are accessed by this statement is determined by the internal arrangement of the array elements within -@code{awk} and cannot be controlled or changed. This can lead to +@command{awk} and cannot be controlled or changed. This can lead to problems if new elements are added to @var{array} by statements in -the loop body; you cannot predict whether or not the @code{for} loop will +the loop body; it is not predictable whether or not the @code{for} loop will reach them. Similarly, changing @var{var} inside the loop may produce strange results. It is best to avoid such things. @@ -9169,18 +10775,17 @@ strange results. It is best to avoid such things. @cindex removing elements of arrays @cindex arrays, deleting an element -You can remove an individual element of an array using the @code{delete} +To remove an individual element of an array, use the @code{delete} statement: @example delete @var{array}[@var{index}] @end example -Once you have deleted an array element, you can no longer obtain any -value the element once had. It is as if you had never referred -to it and had never given it any value. - -Here is an example of deleting elements in an array: +Once an array element has been deleted, any value the element once +had is no longer available. It is as if the element had never +been referred to or had been given a value. +The following is an example of deleting elements in an array: @example for (i in frequencies) @@ -9189,10 +10794,9 @@ for (i in frequencies) @noindent This example removes all the elements from the array @code{frequencies}. - -If you delete an element, a subsequent @code{for} statement to scan the array -will not report that element, and the @code{in} operator to check for -the presence of that element will return zero (i.e.@: false): +Once an element is deleted, a subsequent @code{for} statement to scan the array +does not report that element and the @code{in} operator to check for +the presence of that element returns zero (i.e., false): @example delete foo[4] @@ -9202,6 +10806,7 @@ if (4 in foo) It is important to note that deleting an element is @emph{not} the same as assigning it a null value (the empty string, @code{""}). +For example: @example foo[4] = "" @@ -9209,46 +10814,49 @@ if (4 in foo) print "This is printed, even though foo[4] is empty" @end example +@cindex lint checks It is not an error to delete an element that does not exist. +If @option{--lint} is provided on the command line +(@pxref{Options, ,Command-Line Options}), +@command{gawk} issues a warning message when an element that +is not in the array is deleted. @cindex arrays, deleting entire contents @cindex deleting entire arrays -@cindex differences between @code{gawk} and @code{awk} -You can delete all the elements of an array with a single statement, -by leaving off the subscript in the @code{delete} statement. +@cindex differences between @command{gawk} and @command{awk} +All the elements of an array may be deleted with a single statement +by leaving off the subscript in the @code{delete} statement, +as follows: @example delete @var{array} @end example -This ability is a @code{gawk} extension; it is not available in -compatibility mode (@pxref{Options, ,Command Line Options}). +This ability is a @command{gawk} extension; it is not available in +compatibility mode (@pxref{Options, ,Command-Line Options}). Using this version of the @code{delete} statement is about three times more efficient than the equivalent loop that deletes each element one at a time. @cindex portability issues -The following statement provides a portable, but non-obvious way to clear -out an array. - @cindex Brennan, Michael +The following statement provides a portable but non-obvious way to clear +out an array:@footnote{Thanks to Michael Brennan for pointing this out.} + @example -@group -# thanks to Michael Brennan for pointing this out split("", array) -@end group @end example The @code{split} function -(@pxref{String Functions, ,Built-in Functions for String Manipulation}) +(@pxref{String Functions, ,String Manipulation Functions}) clears out the target array first. This call asks it to split -apart the null string. Since there is no data to split out, the +apart the null string. Because there is no data to split out, the function simply clears the array and then returns. @strong{Caution:} Deleting an array does not change its type; you cannot -delete an array and then use the array's name as a scalar. For -example, this will not work: +delete an array and then use the array's name as a scalar +(i.e., a regular variable). For example, the following does not work: @example a[1] = 3; delete a; a = 3 @@ -9257,69 +10865,78 @@ a[1] = 3; delete a; a = 3 @node Numeric Array Subscripts, Uninitialized Subscripts, Delete, Arrays @section Using Numbers to Subscript Arrays -An important aspect of arrays to remember is that @emph{array subscripts -are always strings}. If you use a numeric value as a subscript, -it will be converted to a string value before it is used for subscripting -(@pxref{Conversion, ,Conversion of Strings and Numbers}). - @cindex conversions, during subscripting @cindex numbers, used as subscripts -@vindex CONVFMT -This means that the value of the built-in variable @code{CONVFMT} can potentially +@cindex @code{CONVFMT} variable +An important aspect about arrays to remember is that @emph{array subscripts +are always strings}. When a numeric value is used as a subscript, +it is converted to a string value before being used for subscripting +(@pxref{Conversion, ,Conversion of Strings and Numbers}). +This means that the value of the built-in variable @code{CONVFMT} can affect how your program accesses elements of an array. For example: @example xyz = 12.153 data[xyz] = 1 CONVFMT = "%2.2f" -@group if (xyz in data) printf "%s is in data\n", xyz else printf "%s is not in data\n", xyz -@end group @end example @noindent This prints @samp{12.15 is not in data}. The first statement gives @code{xyz} a numeric value. Assigning to @code{data[xyz]} subscripts @code{data} with the string value @code{"12.153"} -(using the default conversion value of @code{CONVFMT}, @code{"%.6g"}), -and assigns one to @code{data["12.153"]}. The program then changes +(using the default conversion value of @code{CONVFMT}, @code{"%.6g"}). +Thus, the array element @code{data["12.153"]} is assigned the value one. +The program then changes the value of @code{CONVFMT}. The test @samp{(xyz in data)} generates a new -string value from @code{xyz}, this time @code{"12.15"}, since the value of +string value from @code{xyz}---this time @code{"12.15"}---because the value of @code{CONVFMT} only allows two significant digits. This test fails, since @code{"12.15"} is a different string from @code{"12.153"}. According to the rules for conversions (@pxref{Conversion, ,Conversion of Strings and Numbers}), integer values are always converted to strings as integers, no matter what the -value of @code{CONVFMT} may happen to be. So the usual case of: +value of @code{CONVFMT} may happen to be. So the usual case of +the following works: @example for (i = 1; i <= maxsub; i++) @i{do something with} array[i] @end example -@noindent -will work, no matter what the value of @code{CONVFMT}. +The ``integer values always convert to strings as integers'' rule +has an additional consequence for array indexing. +Octal and hexadecimal constants +(@pxref{Non-decimal-numbers, ,Octal and Hexadecimal Numbers}) +are converted internally into numbers and their original form +is forgotten. +This means, for example, that +@code{array[17]}, +@code{array[021]}, +and +@code{array[0x11]} +all refer to the same element! -Like many things in @code{awk}, the majority of the time things work -as you would expect them to work. But it is useful to have a precise -knowledge of the actual rules, since sometimes they can have a subtle +As with many things in @command{awk}, the majority of the time +things work as one would expect them to. But it is useful to have a precise +knowledge of the actual rules which sometimes can have a subtle effect on your programs. @node Uninitialized Subscripts, Multi-dimensional, Numeric Array Subscripts, Arrays @section Using Uninitialized Variables as Subscripts @cindex uninitialized variables, as array subscripts -@cindex array subscripts, uninitialized variables -Suppose you want to print your input data in reverse order. -A reasonable attempt at a program to do so (with some test +@cindex arrays, subscripts, uninitialized variables +Suppose it's necessary to write a program +to print the input data in reverse order. +A reasonable attempt to do so (with some test data) might look like this: @example -@group $ echo 'line 1 > line 2 > line 3' | awk '@{ l[lines] = $0; ++lines @} @@ -9329,7 +10946,6 @@ $ echo 'line 1 > @}' @print{} line 3 @print{} line 2 -@end group @end example Unfortunately, the very first line of input data did not come out in the @@ -9337,13 +10953,12 @@ output! At first glance, this program should have worked. The variable @code{lines} is uninitialized, and uninitialized variables have the numeric value zero. -So, @code{awk} should have printed the value of @code{l[0]}. +So, @command{awk} should have printed the value of @code{l[0]}. -The issue here is that subscripts for @code{awk} arrays are @strong{always} -strings. And uninitialized variables, when used as strings, have the -value @code{""}, not zero. Thus, @samp{line 1} ended up stored in +The issue here is that subscripts for @command{awk} arrays are @emph{always} +strings. Uninitialized variables, when used as strings, have the +value @code{""}, not zero. Thus, @samp{line 1} ends up stored in @code{l[""]}. - The following version of the program works correctly: @example @@ -9355,33 +10970,36 @@ END @{ @end example Here, the @samp{++} forces @code{lines} to be numeric, thus making -the ``old value'' numeric zero, which is then converted to @code{"0"} +the ``old value'' numeric zero. This is then converted to @code{"0"} as the array subscript. @cindex null string, as array subscript @cindex dark corner -As we have just seen, even though it is somewhat unusual, the null string -(@code{""}) is a valid array subscript (d.c.). If @samp{--lint} is provided -on the command line (@pxref{Options, ,Command Line Options}), -@code{gawk} will warn about the use of the null string as a subscript. +@cindex lint checks +Even though it is somewhat unusual, the null string +(@code{""}) is a valid array subscript. +@value{DARKCORNER} +@command{gawk} warns about the use of the null string as a subscript +if @option{--lint} is provided +on the command line (@pxref{Options, ,Command-Line Options}). @node Multi-dimensional, Multi-scanning, Uninitialized Subscripts, Arrays -@section Multi-dimensional Arrays +@section Multidimensional Arrays @cindex subscripts in arrays -@cindex arrays, multi-dimensional subscripts -@cindex multi-dimensional subscripts -A multi-dimensional array is an array in which an element is identified -by a sequence of indices, instead of a single index. For example, a +@cindex arrays, multidimensional subscripts +@cindex multidimensional subscripts +A multidimensional array is an array in which an element is identified +by a sequence of indices instead of a single index. For example, a two-dimensional array requires two indices. The usual way (in most -languages, including @code{awk}) to refer to an element of a +languages, including @command{awk}) to refer to an element of a two-dimensional array named @code{grid} is with @code{grid[@var{x},@var{y}]}. -@vindex SUBSEP -Multi-dimensional arrays are supported in @code{awk} through -concatenation of indices into one string. What happens is that -@code{awk} converts the indices into strings +@cindex @code{SUBSEP} variable +Multidimensional arrays are supported in @command{awk} through +concatenation of indices into one string. +@command{awk} converts the indices into strings (@pxref{Conversion, ,Conversion of Strings and Numbers}) and concatenates them together, with a separator between them. This creates a single string that describes the values of the separate indices. The @@ -9390,32 +11008,30 @@ one-dimensional array. The separator used is the value of the built-in variable @code{SUBSEP}. For example, suppose we evaluate the expression @samp{foo[5,12] = "value"} -when the value of @code{SUBSEP} is @code{"@@"}. The numbers five and 12 are +when the value of @code{SUBSEP} is @code{"@@"}. The numbers 5 and 12 are converted to strings and concatenated with an @samp{@@} between them, yielding @code{"5@@12"}; thus, the array element @code{foo["5@@12"]} is set to @code{"value"}. -Once the element's value is stored, @code{awk} has no record of whether +Once the element's value is stored, @command{awk} has no record of whether it was stored with a single index or a sequence of indices. The two expressions @samp{foo[5,12]} and @w{@samp{foo[5 SUBSEP 12]}} are always equivalent. The default value of @code{SUBSEP} is the string @code{"\034"}, which contains a non-printing character that is unlikely to appear in an -@code{awk} program or in most input data. - +@command{awk} program or in most input data. The usefulness of choosing an unlikely character comes from the fact -that index values that contain a string matching @code{SUBSEP} lead to -combined strings that are ambiguous. Suppose that @code{SUBSEP} were +that index values that contain a string matching @code{SUBSEP} can lead to +combined strings that are ambiguous. Suppose that @code{SUBSEP} is @code{"@@"}; then @w{@samp{foo["a@@b", "c"]}} and @w{@samp{foo["a", -"b@@c"]}} would be indistinguishable because both would actually be +"b@@c"]}} are indistinguishable because both are actually stored as @samp{foo["a@@b@@c"]}. -You can test whether a particular index-sequence exists in a -``multi-dimensional'' array with the same operator @samp{in} used for single -dimensional arrays. Instead of a single index as the left-hand operand, -write the whole sequence of indices, separated by commas, in -parentheses: +To test whether a particular index sequence exists in a +``multidimensional'' array, use the same operator (@samp{in}) that is +used for single dimensional arrays. Write the whole sequence of indices +in parentheses, separated by commas, as the left operand: @example (@var{subscript1}, @var{subscript2}, @dots{}) in @var{array} @@ -9427,190 +11043,260 @@ result. It assumes that all lines have the same number of elements. @example -@group -awk '@{ +@{ if (max_nf < NF) max_nf = NF max_nr = NR for (x = 1; x <= NF; x++) vector[x, NR] = $x @} -@end group -@group END @{ for (x = 1; x <= max_nf; x++) @{ for (y = max_nr; y >= 1; --y) printf("%s ", vector[x, y]) printf("\n") @} -@}' -@end group +@} @end example @noindent When given the input: @example -@group 1 2 3 4 5 6 2 3 4 5 6 1 3 4 5 6 1 2 4 5 6 1 2 3 -@end group @end example @noindent -it produces: +the program produces the following output: @example -@group 4 3 2 1 5 4 3 2 6 5 4 3 1 6 5 4 2 1 6 5 3 2 1 6 -@end group @end example -@node Multi-scanning, Array Efficiency, Multi-dimensional, Arrays -@section Scanning Multi-dimensional Arrays +@node Multi-scanning, Array Sorting, Multi-dimensional, Arrays +@section Scanning Multidimensional Arrays There is no special @code{for} statement for scanning a -``multi-dimensional'' array; there cannot be one, because in truth there -are no multi-dimensional arrays or elements; there is only a -multi-dimensional @emph{way of accessing} an array. +``multidimensional'' array. There cannot be one, because in truth there +are no multidimensional arrays or elements---there is only a +multidimensional @emph{way of accessing} an array. However, if your program has an array that is always accessed as -multi-dimensional, you can get the effect of scanning it by combining +multidimensional, you can get the effect of scanning it by combining the scanning @code{for} statement (@pxref{Scanning an Array, ,Scanning All Elements of an Array}) with the -@code{split} built-in function -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). -It works like this: +built-in @code{split} function +(@pxref{String Functions, ,String Manipulation Functions}). +It works in the following manner: @example for (combined in array) @{ - split(combined, separate, SUBSEP) - @dots{} + split(combined, separate, SUBSEP) + @dots{} @} @end example @noindent -This sets @code{combined} to -each concatenated, combined index in the array, and splits it +This sets the variable @code{combined} to +each concatenated combined index in the array, and splits it into the individual indices by breaking it apart where the value of -@code{SUBSEP} appears. The split-out indices become the elements of +@code{SUBSEP} appears. The individual indices then become the elements of the array @code{separate}. -Thus, suppose you have previously stored a value in @code{array[1, "foo"]}; -then an element with index @code{"1\034foo"} exists in -@code{array}. (Recall that the default value of @code{SUBSEP} is -the character with code 034.) Sooner or later the @code{for} statement -will find that index and do an iteration with @code{combined} set to -@code{"1\034foo"}. Then the @code{split} function is called as -follows: +Thus, if a value is previously stored in @code{array[1, "foo"]}; then +an element with index @code{"1\034foo"} exists in @code{array}. (Recall +that the default value of @code{SUBSEP} is the character with code 034.) +Sooner or later, the @code{for} statement finds that index and does an +iteration with the variable @code{combined} set to @code{"1\034foo"}. +Then the @code{split} function is called as follows: @example split("1\034foo", separate, "\034") @end example @noindent -The result of this is to set @code{separate[1]} to @code{"1"} and -@code{separate[2]} to @code{"foo"}. Presto, the original sequence of -separate indices has been recovered. +The result is to set @code{separate[1]} to @code{"1"} and +@code{separate[2]} to @code{"foo"}. Presto! The original sequence of +separate indices is recovered. + +@node Array Sorting, , Multi-scanning, Arrays +@section Sorting Array Values and Indices with @command{gawk} + +@cindex arrays, sorting +@cindex @code{asort} built-in function +The order in which an array is scanned with a @samp{for (i in array)} +loop is essentially arbitrary. +In most @command{awk} implementations, sorting an array requires +writing a @code{sort} function. +While this can be educational for exploring different sorting algorithms, +usually that's not the point of the program. +@command{gawk} provides the built-in @code{asort} function +(@pxref{String Functions, ,String Manipulation Functions}) +that sorts an array. For example: + +@example +@var{populate the array} data +n = asort(data) +for (i = 1; i <= n; i++) + @var{do something with} data[i] +@end example + +After the call to @code{asort}, the array @code{data} is indexed from 1 +to some number @var{n}, the total number of elements in @code{data}. +(This count is @code{asort}'s return value.) +@code{data[1]} @value{LEQ} @code{data[2]} @value{LEQ} @code{data[3]}, and so on. +The comparison of array elements is done +using @command{gawk}'s usual comparison rules +(@pxref{Typing and Comparison, ,Variable Typing and Comparison Expressions}). + +@cindex side effects +An important side effect of calling @code{asort} is that +@emph{the array's original indices are irrevocably lost}. +As this isn't always desirable, @code{asort} accepts a +second argument: + +@example +@var{populate the array} source +n = asort(source, dest) +for (i = 1; i <= n; i++) + @var{do something with} dest[i] +@end example + +In this case, @command{gawk} copies the @code{source} array into the +@code{dest} array and then sorts @code{dest}, destroying its indices. +However, the @code{source} array is not affected. + +Often, what's needed is to sort on the values of the @emph{indices} +instead of the values of the elements. To do this, use a helper array +to hold the sorted index values, and then access the original array's +elements. It works in the following way: + +@example +@var{populate the array} data +# copy indices +j = 1 +for (i in data) @{ + ind[j] = i # index value becomes element value + j++ +@} +n = asort(ind) # index values are now sorted +for (i = 1; i <= n; i++) + @var{do something with} data[ind[i]] +@end example + +Sorting the array by replacing the indices provides maximal flexibility. +To traverse the elements in decreasing order, use a loop that goes from +@var{n} down to 1, either over the elements or over the indices. + +@cindex reference counting +Copying array indices and elements isn't expensive in terms of memory. +Internally, @command{gawk} maintains @dfn{reference counts} to data. +For example, when @code{asort} copies the first array to the second one, +there is only one copy of the original array elements' data, even though +both arrays use the values. Similarly, when copying the indices from +@code{data} to @code{ind}, there is only one copy of the actual index +strings. -@node Array Efficiency, , Multi-scanning, Arrays -@section Using Array Memory Efficiently +@cindex arrays, sorting and @code{IGNORECASE} +@cindex @code{IGNORECASE}, and array sorting +@cindex @code{IGNORECASE} variable +As with array subscripts, the value of @code{IGNORECASE} +does not affect array sorting. -This section applies just to @code{gawk}. +@node Functions, Internationalization, Arrays, Top +@chapter Functions -It is often useful to use the same bit of data as an index -into multiple arrays. -Due to the way @code{gawk} implements associative arrays, -when you need to use input data as an index for multiple -arrays, it is much more effecient to assign the input field -to a separate variable, and then use that variable as the index. +This @value{CHAPTER} describes @command{awk}'s built-in functions, +which fall into three categories: numeric, string, and I/O. +@command{gawk} provides additional groups of functions +to work with values that represent time, do +bit manipulation, and to internationalize and localize programs. -@example -@{ - name = $1 - ssn = $2 - nkids = $3 - @dots{} - seniority[name]++ # better than seniority[$1]++ - kids[name] = nkids # better than kids[$1] = nkids -@} -@end example +Besides the built-in functions, @command{awk} has provisions for +writing new functions that the rest of a program can use. +The second half of this @value{CHAPTER} describes these +@dfn{user-defined} functions. -Using separate variables with mnemonic names for the input fields -makes programs more readable, in any case. -It is an eventual goal to make @code{gawk}'s array indexing as efficient -as possible, no matter what the source of the index value. +@menu +* Built-in:: Summarizes the built-in functions. +* User-defined:: Describes User-defined functions in detail. +@end menu -@node Built-in, User-defined, Arrays, Top -@chapter Built-in Functions +@node Built-in, User-defined, Functions, Functions +@section Built-in Functions @c 2e: USE TEXINFO-2 FUNCTION DEFINITION STUFF!!!!!!!!!!!!! @cindex built-in functions -@dfn{Built-in} functions are functions that are always available for -your @code{awk} program to call. This chapter defines all the built-in -functions in @code{awk}; some of them are mentioned in other sections, -but they are summarized here for your convenience. (You can also define -new functions yourself. @xref{User-defined, ,User-defined Functions}.) +@dfn{Built-in} functions are always available for +your @command{awk} program to call. This @value{SECTION} defines all +the built-in +functions in @command{awk}; some of these are mentioned in other sections +but are summarized here for your convenience. @menu * Calling Built-in:: How to call built-in functions. * Numeric Functions:: Functions that work with numbers, including @code{int}, @code{sin} and @code{rand}. * String Functions:: Functions for string manipulation, such as - @code{split}, @code{match}, and - @code{sprintf}. + @code{split}, @code{match} and @code{sprintf}. * I/O Functions:: Functions for files and shell commands. -* Time Functions:: Functions for dealing with time stamps. +* Time Functions:: Functions for dealing with timestamps. +* Bitwise Functions:: Functions for bitwise operations. +* I18N Functions:: Functions for string translation. @end menu @node Calling Built-in, Numeric Functions, Built-in, Built-in -@section Calling Built-in Functions +@subsection Calling Built-in Functions -To call a built-in function, write the name of the function followed +To call one of @command{awk}'s built-in functions, write the name of +the function followed by arguments in parentheses. For example, @samp{atan2(y + z, 1)} -is a call to the function @code{atan2}, with two arguments. +is a call to the function @code{atan2}, and has two arguments. +@cindex conventions, programming +@cindex programming conventions Whitespace is ignored between the built-in function name and the -open-parenthesis, but we recommend that you avoid using whitespace +open parenthesis, and it is good practice to avoid using whitespace there. User-defined functions do not permit whitespace in this way, and -you will find it easier to avoid mistakes by following a simple -convention which always works: no whitespace after a function name. +it is easier to avoid mistakes by following a simple +convention that always works---no whitespace after a function name. -@cindex differences between @code{gawk} and @code{awk} +@cindex fatal errors +@cindex differences between @command{gawk} and @command{awk} Each built-in function accepts a certain number of arguments. In some cases, arguments can be omitted. The defaults for omitted arguments vary from function to function and are described under the -individual functions. In some @code{awk} implementations, extra -arguments given to built-in functions are ignored. However, in @code{gawk}, +individual functions. In some @command{awk} implementations, extra +arguments given to built-in functions are ignored. However, in @command{gawk}, it is a fatal error to give extra arguments to a built-in function. When a function is called, expressions that create the function's actual -parameters are evaluated completely before the function call is performed. -For example, in the code fragment: +parameters are evaluated completely before the call is performed. +For example, in the following code fragment: @example i = 4 j = sqrt(i++) @end example -@noindent -the variable @code{i} is set to five before @code{sqrt} is called -with a value of four for its actual parameter. - @cindex evaluation, order of @cindex order of evaluation +@noindent +the variable @code{i} is incremented to the value five before @code{sqrt} +is called with a value of four for its actual parameter. The order of evaluation of the expressions used for the function's -parameters is undefined. Thus, you should not write programs that +parameters is undefined. Thus, avoid writing programs that assume that parameters are evaluated from left to right or from -right to left. For example, +right to left. For example: @example i = 5 @@ -9618,62 +11304,69 @@ j = atan2(i++, i *= 2) @end example If the order of evaluation is left to right, then @code{i} first becomes -six, and then 12, and @code{atan2} is called with the two arguments six +six, and then 12, and @code{atan2} is called with the two arguments 6 and 12. But if the order of evaluation is right to left, @code{i} -first becomes 10, and then 11, and @code{atan2} is called with the +first becomes 10, then 11, and @code{atan2} is called with the two arguments 11 and 10. @node Numeric Functions, String Functions, Calling Built-in, Built-in -@section Numeric Built-in Functions +@subsection Numeric Functions -Here is a full list of built-in functions that work with numbers. -Optional parameters are enclosed in square brackets (``['' and ``]''). +The following list describes all of +the built-in functions that work with numbers. +Optional parameters are enclosed in square brackets ([ and ]): @table @code @item int(@var{x}) -@findex int -This produces the nearest integer to @var{x}, located between @var{x} and zero, +@cindex @code{int} built-in function +This returns the nearest integer to @var{x}, located between @var{x} and zero and truncated toward zero. For example, @code{int(3)} is three, @code{int(3.9)} is three, @code{int(-3.9)} is @minus{}3, and @code{int(-3)} is @minus{}3 as well. @item sqrt(@var{x}) -@findex sqrt -This gives you the positive square root of @var{x}. It reports an error +@cindex @code{sqrt} built-in function +This returns the positive square root of @var{x}. +@command{gawk} reports an error if @var{x} is negative. Thus, @code{sqrt(4)} is two. @item exp(@var{x}) -@findex exp -This gives you the exponential of @var{x} (@code{e ^ @var{x}}), or reports +@cindex @code{exp} built-in function +This returns the exponential of @var{x} (@code{e ^ @var{x}}) or reports an error if @var{x} is out of range. The range of values @var{x} can have -depends on your machine's floating point representation. +depends on your machine's floating-point representation. @item log(@var{x}) -@findex log -This gives you the natural logarithm of @var{x}, if @var{x} is positive; +@cindex @code{log} built-in function +This returns the natural logarithm of @var{x}, if @var{x} is positive; otherwise, it reports an error. @item sin(@var{x}) -@findex sin -This gives you the sine of @var{x}, with @var{x} in radians. +@cindex @code{sin} built-in function +This returns the sine of @var{x}, with @var{x} in radians. @item cos(@var{x}) -@findex cos -This gives you the cosine of @var{x}, with @var{x} in radians. +@cindex @code{cos} built-in function +This returns the cosine of @var{x}, with @var{x} in radians. @item atan2(@var{y}, @var{x}) -@findex atan2 -This gives you the arctangent of @code{@var{y} / @var{x}} in radians. +@cindex @code{atan2} built-in function +This returns the arctangent of @code{@var{y} / @var{x}} in radians. @item rand() -@findex rand -This gives you a random number. The values of @code{rand} are -uniformly-distributed between zero and one. -The value is never zero and never one. +@cindex @code{rand} built-in function +This returns a random number. The values of @code{rand} are +uniformly distributed between zero and one. +The value is never zero and never one.@footnote{The C version of @code{rand} +is known to produce fairly poor sequences of random numbers. +However, nothing requires that an @command{awk} implementation use the C +@code{rand} to implement the @command{awk} version of @code{rand}. +In fact, @command{gawk} uses the BSD @code{random} function, which is +considerably better than @code{rand}, to produce random numbers.} -Often you want random integers instead. Here is a user-defined function -you can use to obtain a random non-negative integer less than @var{n}: +Often random integers are needed instead. Following is a user-defined function +that can be used to obtain a random non-negative integer less than @var{n}: @example function randint(n) @{ @@ -9683,45 +11376,40 @@ function randint(n) @{ @noindent The multiplication produces a random number greater than zero and less -than @code{n}. We then make it an integer (using @code{int}) between zero -and @code{n} @minus{} 1, inclusive. +than @code{n}. Using @code{int}, this result is made into +an integer between zero and @code{n} @minus{} 1, inclusive. -Here is an example where a similar function is used to produce -random integers between one and @var{n}. This program -prints a new random number for each input record. +The following example uses a similar function to produce random integers +between one and @var{n}. This program prints a new random number for +each input record. @example -@group -awk ' # Function to roll a simulated die. function roll(n) @{ return 1 + int(rand() * n) @} -@end group -@group # Roll 3 six-sided dice and # print total number of points. @{ printf("%d points\n", roll(6)+roll(6)+roll(6)) -@}' -@end group +@} @end example @cindex seed for random numbers @cindex random numbers, seed of -@comment MAWK uses a different seed each time. -@strong{Caution:} In most @code{awk} implementations, including @code{gawk}, +@c MAWK uses a different seed each time. +@strong{Caution:} In most @command{awk} implementations, including @command{gawk}, @code{rand} starts generating numbers from the same -starting number, or @dfn{seed}, each time you run @code{awk}. Thus, -a program will generate the same results each time you run it. -The numbers are random within one @code{awk} run, but predictable +starting number, or @dfn{seed}, each time you run @command{awk}. Thus, +a program generates the same results each time you run it. +The numbers are random within one @command{awk} run but predictable from run to run. This is convenient for debugging, but if you want a program to do different things each time it is used, you must change -the seed to a value that will be different in each run. To do this, +the seed to a value that is different in each run. To do this, use @code{srand}. @item srand(@r{[}@var{x}@r{]}) -@findex srand +@cindex @code{srand} built-in function The function @code{srand} sets the starting point, or seed, for generating random numbers to the value @var{x}. @@ -9730,31 +11418,83 @@ numbers.@footnote{Computer generated random numbers really are not truly random. They are technically known as ``pseudo-random.'' This means that while the numbers in a sequence appear to be random, you can in fact generate the same sequence of random numbers over and over again.} -Thus, if you set the seed to the same value a second time, you will get -the same sequence of random numbers again. +Thus, if the seed is set to the same value a second time, +the same sequence of random numbers is produced again. -If you omit the argument @var{x}, as in @code{srand()}, then the current +Different @command{awk} implementations use different random number +generators internally. Don't expect the same @command{awk} program +to produce the same series of random numbers when executed by +different versions of @command{awk}. + +If the argument @var{x} is omitted, as in @samp{srand()}, then the current date and time of day are used for a seed. This is the way to get random numbers that are truly unpredictable. The return value of @code{srand} is the previous seed. This makes it -easy to keep track of the seeds for use in consistently reproducing +easy to keep track of the seeds in case you need to consistently reproduce sequences of random numbers. @end table @node String Functions, I/O Functions, Numeric Functions, Built-in -@section Built-in Functions for String Manipulation +@subsection String Manipulation Functions -The functions in this section look at or change the text of one or more +The functions in this @value{SECTION} look at or change the text of one or more strings. -Optional parameters are enclosed in square brackets (``['' and ``]''). +Optional parameters are enclosed in square brackets ([ and ]). +Those functions that are +specific to @command{gawk} are marked with a pound sign (@samp{#}): + +@menu +* Gory Details:: More than you want to know about @samp{\} and + @samp{&} with @code{sub}, @code{gsub}, and + @code{gensub}. +@end menu @table @code +@item asort(@var{source} @r{[}, @var{dest}@r{]}) # +@cindex @code{asort} built-in function +@code{asort} is a @command{gawk}-specific extension, returning the number of +elements in the array @var{source}. The contents of @var{source} are +sorted using @command{gawk}'s normal rules for comparing values, and the indices +of the sorted values of @var{source} are replaced with sequential +integers starting with one. If the optional array @var{dest} is specified, +then @var{source} is duplicated into @var{dest}. @var{dest} is then +sorted, leaving the indices of @var{source} unchanged. +For example, if the contents of @code{a} are as follows: + +@example +a["last"] = "de" +a["first"] = "sac" +a["middle"] = "cul" +@end example + +@noindent +A call to @code{asort}: + +@example +asort(a) +@end example + +@noindent +results in the following contents of @code{a}: + +@example +a[1] = "cul" +a[2] = "de" +a[3] = "sac" +@end example + +@cindex differences between @command{gawk} and @command{awk} +The @code{asort} function is described in more detail in +@ref{Array Sorting, ,Sorting Array Values and Indices with @command{gawk}}. +@code{asort} is a @command{gawk} extension; it is not available +in compatibility mode (@pxref{Options, ,Command-Line Options}). + @item index(@var{in}, @var{find}) -@findex index +@cindex @code{index} built-in function This searches the string @var{in} for the first occurrence of the string @var{find}, and returns the position in characters where that occurrence -begins in the string @var{in}. For example: +begins in the string @var{in}. Consider the following example: @example $ awk 'BEGIN @{ print index("peanut", "an") @}' @@ -9763,14 +11503,14 @@ $ awk 'BEGIN @{ print index("peanut", "an") @}' @noindent If @var{find} is not found, @code{index} returns zero. -(Remember that string indices in @code{awk} start at one.) +(Remember that string indices in @command{awk} start at one.) @item length(@r{[}@var{string}@r{]}) -@findex length -This gives you the number of characters in @var{string}. If +@cindex @code{length} built-in function +This returns the number of characters in @var{string}. If @var{string} is a number, the length of the digit string representing -that number is returned. For example, @code{length("abcde")} is five. By -contrast, @code{length(15 * 35)} works out to three. How? Well, 15 * 35 = +that number is returned. For example, @code{length("abcde")} is 5. By +contrast, @code{length(15 * 35)} works out to 3. In this example, 15 * 35 = 525, and 525 is then converted to the string @code{"525"}, which has three characters. @@ -9778,25 +11518,33 @@ If no argument is supplied, @code{length} returns the length of @code{$0}. @cindex historical features @cindex portability issues -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} -In older versions of @code{awk}, you could call the @code{length} function +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} +@strong{Note:} +In older versions of @command{awk}, the @code{length} function could +be called without any parentheses. Doing so is marked as ``deprecated'' in the -POSIX standard. This means that while you can do this in your -programs, it is a feature that can eventually be removed from a future -version of the standard. Therefore, for maximal portability of your -@code{awk} programs, you should always supply the parentheses. - -@item match(@var{string}, @var{regexp}) -@findex match -The @code{match} function searches the string, @var{string}, for the -longest, leftmost substring matched by the regular expression, -@var{regexp}. It returns the character position, or @dfn{index}, of +POSIX standard. This means that while a program can do this, +it is a feature that can eventually be removed from a future +version of the standard. Therefore, for programs to be maximally portable, +always supply the parentheses. + +@item match(@var{string}, @var{regexp} @r{[}, @var{array}@r{]}) +@cindex @code{match} built-in function +The @code{match} function searches @var{string} for the +longest leftmost substring matched by the regular expression, +@var{regexp}. It returns the character position, or @dfn{index}, where that substring begins (one, if it starts at the beginning of @var{string}). If no match is found, it returns zero. -@vindex RSTART -@vindex RLENGTH +The order of the first two arguments is backwards from most other string +functions that work with regular expressions, such as +@code{sub} and @code{gsub}. It might help to remember that +for @code{match}, the order is the same as for the @samp{~} operator: +@samp{@var{string} ~ @var{regexp}}. + +@cindex @code{RSTART} variable +@cindex @code{RLENGTH} variable The @code{match} function sets the built-in variable @code{RSTART} to the index. It also sets the built-in variable @code{RLENGTH} to the length in characters of the matched substring. If no match is found, @@ -9805,27 +11553,25 @@ length in characters of the matched substring. If no match is found, For example: @example -@group -@c file eg/misc/findpat.sh -awk '@{ +@c file eg/misc/findpat.awk +@{ if ($1 == "FIND") regex = $2 else @{ where = match($0, regex) if (where != 0) - print "Match of", regex, "found at", \ + print "Match of", regex, "found at", where, "in", $0 @} -@}' +@} @c endfile -@end group @end example @noindent This program looks for lines that match the regular expression stored in the variable @code{regex}. This regular expression can be changed. If the first word on a line is @samp{FIND}, @code{regex} is changed to be the -second word on that line. Therefore, given: +second word on that line. Therefore, if given: @example @c file eg/misc/findpat.data @@ -9840,16 +11586,38 @@ Melvin was here. @end example @noindent -@code{awk} prints: +@command{awk} prints: @example Match of ru+n found at 12 in My program runs Match of Melvin found at 1 in Melvin was here. @end example +@cindex differences between @command{gawk} and @command{awk} +If @var{array} is present, it is cleared, and then the 0'th element +of @var{array} is set to the entire portion of @var{string} +matched by @var{regexp}. If @var{regexp} contains parentheses, +the integer-indexed elements of @var{array} are set to contain the +portion of @var{string} matching the corresponding parenthesized +sub-expression. +For example: + +@example +$ echo foooobazbarrrrr | +> gawk '@{ match($0, /(fo+).+(ba*r)/, arr) +> print arr[1], arr[2] @}' +@print{} foooo barrrrr +@end example + +@cindex fatal errors +The @var{array} argument to @code{match} is a +@command{gawk} extension. In compatibility mode +(@pxref{Options, ,Command-Line Options}), +using a third argument is a fatal error. + @item split(@var{string}, @var{array} @r{[}, @var{fieldsep}@r{]}) -@findex split -This divides @var{string} into pieces separated by @var{fieldsep}, +@cindex @code{split} built-in function +This function divides @var{string} into pieces separated by @var{fieldsep}, and stores the pieces in @var{array}. The first piece is stored in @code{@var{array}[1]}, the second piece in @code{@var{array}[2]}, and so forth. The string value of the third argument, @var{fieldsep}, is @@ -9857,6 +11625,8 @@ a regexp describing where to split @var{string} (much as @code{FS} can be a regexp describing where to split input records). If the @var{fieldsep} is omitted, the value of @code{FS} is used. @code{split} returns the number of elements created. +If @var{string} does not match @var{fieldsep}, @var{array} is empty +and @code{split} returns zero. The @code{split} function splits strings into pieces in a manner similar to the way input lines are split into fields. For example: @@ -9878,68 +11648,78 @@ a[3] = "sac" @noindent The value returned by this call to @code{split} is three. +@cindex differences between @command{gawk} and @command{awk} As with input field-splitting, when the value of @var{fieldsep} is -@w{@code{" "}}, leading and trailing whitespace is ignored, and the elements +@w{@code{" "}}, leading and trailing whitespace is ignored and the elements are separated by runs of whitespace. - -@cindex differences between @code{gawk} and @code{awk} Also as with input field-splitting, if @var{fieldsep} is the null string, each individual character in the string is split into its own array element. -(This is a @code{gawk}-specific extension.) +(This is a @command{gawk}-specific extension.) @cindex dark corner -Recent implementations of @code{awk}, including @code{gawk}, allow -the third argument to be a regexp constant (@code{/abc/}), as well as a -string (d.c.). The POSIX standard allows this as well. +Modern implementations of @command{awk}, including @command{gawk}, allow +the third argument to be a regexp constant (@code{/abc/}) as well as a +string. +@value{DARKCORNER} +The POSIX standard allows this as well. Before splitting the string, @code{split} deletes any previously existing -elements in the array @var{array} (d.c.). - -If @var{string} does not match @var{fieldsep} at all, @var{array} will have -one element. The value of that element will be the original -@var{string}. +elements in the array @var{array}. +If @var{string} does not match @var{fieldsep} at all, @var{array} has +one element only. The value of that element is the original @var{string}. -@item sprintf(@var{format}, @var{expression1},@dots{}) -@findex sprintf +@item sprintf(@var{format}, @var{expression1}, @dots{}) +@cindex @code{sprintf} built-in function This returns (without printing) the string that @code{printf} would have printed out with the same arguments (@pxref{Printf, ,Using @code{printf} Statements for Fancier Printing}). For example: @example -sprintf("pi = %.2f (approx.)", 22/7) +pival = sprintf("pi = %.2f (approx.)", 22/7) @end example @noindent -returns the string @w{@code{"pi = 3.14 (approx.)"}}. +assigns the string @w{@code{"pi = 3.14 (approx.)"}} to the variable @code{pival}. + +@cindex @code{strtonum} built-in function +@item strtonum(@var{str}) # +Examines @var{str} and returns its numeric value. If @var{str} +begins with a leading @samp{0}, @code{strtonum} assumes that @var{str} +is an octal number. If @var{str} begins with a leading @samp{0x} or +@samp{0X}, @code{strtonum} assumes that @var{str} is a hexadecimal number. +For example: -@ignore -2e: For sub, gsub, and gensub, either here or in the "how much matches" - section, we need some explanation that it is possible to match the - null string when using closures like *. E.g., +@example +$ echo 0x11 | +> gawk '@{ printf "%d\n", strtonum($1) @}' +@print{} 17 +@end example - $ echo abc | awk '{ gsub(/m*/, "X"); print }' - @print{} XaXbXcX +Using the @code{strtonum} function is @emph{not} the same as adding zero +to a string value; the automatic coercion of strings to numbers +works only for decimal data, not for octal or hexadecimal.@footnote{Unless +you use the @option{--non-decimal-data} option, which isn't recommended. +@xref{Non-decimal Data, ,Allowing Non-Decimal Input Data}, for more information.} - Although this makes a certain amount of sense, it can be very - suprising. -@end ignore +@cindex differences between @command{gawk} and @command{awk} +@code{strtonum} is a @command{gawk} extension; it is not available +in compatibility mode (@pxref{Options, ,Command-Line Options}). @item sub(@var{regexp}, @var{replacement} @r{[}, @var{target}@r{]}) -@findex sub +@cindex @code{sub} built-in function The @code{sub} function alters the value of @var{target}. It searches this value, which is treated as a string, for the -leftmost longest substring matched by the regular expression, @var{regexp}, -extending this match as far as possible. Then the entire string is +leftmost longest substring matched by the regular expression @var{regexp}. +Then the entire string is changed by replacing the matched text with @var{replacement}. The modified string becomes the new value of @var{target}. This function is peculiar because @var{target} is not simply -used to compute a value, and not just any expression will do: it -must be a variable, field or array element, so that @code{sub} can +used to compute a value, and not just any expression will do---it +must be a variable, field, or array element so that @code{sub} can store a modified value there. If this argument is omitted, then the default is to use and alter @code{$0}. - For example: @example @@ -9949,7 +11729,7 @@ sub(/at/, "ith", str) @noindent sets @code{str} to @w{@code{"wither, water, everywhere"}}, by replacing the -leftmost, longest occurrence of @samp{at} with @samp{ith}. +leftmost longest occurrence of @samp{at} with @samp{ith}. The @code{sub} function returns the number of substitutions made (either one or zero). @@ -9960,26 +11740,25 @@ the regexp can match more than one string, then this precise substring may vary.) For example: @example -awk '@{ sub(/candidate/, "& and his wife"); print @}' +@{ sub(/candidate/, "& and his wife"); print @} @end example @noindent changes the first occurrence of @samp{candidate} to @samp{candidate and his wife} on each input line. - Here is another example: @example -awk 'BEGIN @{ - str = "daabaaa" - sub(/a+/, "C&C", str) - print str -@}' +$ awk 'BEGIN @{ +> str = "daabaaa" +> sub(/a+/, "C&C", str) +> print str +> @}' @print{} dCaaCbaaa @end example @noindent -This shows how @samp{&} can represent a non-constant string, and also +This shows how @samp{&} can represent a non-constant string and also illustrates the ``leftmost, longest'' rule in regexp matching (@pxref{Leftmost Longest, ,How Much Text Matches?}). @@ -9987,46 +11766,47 @@ The effect of this special character (@samp{&}) can be turned off by putting a backslash before it in the string. As usual, to insert one backslash in the string, you must write two backslashes. Therefore, write @samp{\\&} in a string constant to include a literal @samp{&} in the replacement. -For example, here is how to replace the first @samp{|} on each line with +For example, following is shown how to replace the first @samp{|} on each line with an @samp{&}: @example -awk '@{ sub(/\|/, "\\&"); print @}' +@{ sub(/\|/, "\\&"); print @} @end example @cindex @code{sub}, third argument of @cindex @code{gsub}, third argument of -@strong{Note:} As mentioned above, the third argument to @code{sub} must +As mentioned, the third argument to @code{sub} must be a variable, field or array reference. -Some versions of @code{awk} allow the third argument to -be an expression which is not an lvalue. In such a case, @code{sub} -would still search for the pattern and return zero or one, but the result of -the substitution (if any) would be thrown away because there is no place -to put it. Such versions of @code{awk} accept expressions like -this: +Some versions of @command{awk} allow the third argument to +be an expression that is not an lvalue. In such a case, @code{sub} +still searches for the pattern and returns zero or one, but the result of +the substitution (if any) is thrown away because there is no place +to put it. Such versions of @command{awk} accept expressions +such as the following: @example sub(/USA/, "United States", "the USA and Canada") @end example @noindent -For historical compatibility, @code{gawk} will accept erroneous code, -such as in the above example. However, using any other non-changeable -object as the third parameter will cause a fatal error, and your program +@cindex fatal errors +For historical compatibility, @command{gawk} accepts erroneous code, +such as in the previous example. However, using any other non-changeable +object as the third parameter causes a fatal error and your program will not run. Finally, if the @var{regexp} is not a regexp constant, it is converted into a -string and then the value of that string is treated as the regexp to match. +string, and then the value of that string is treated as the regexp to match. @item gsub(@var{regexp}, @var{replacement} @r{[}, @var{target}@r{]}) -@findex gsub +@cindex @code{gsub} built-in function This is similar to the @code{sub} function, except @code{gsub} replaces @emph{all} of the longest, leftmost, @emph{non-overlapping} matching substrings it can find. The @samp{g} in @code{gsub} stands for ``global,'' which means replace everywhere. For example: @example -awk '@{ gsub(/Britain/, "United Kingdom"); print @}' +@{ gsub(/Britain/, "United Kingdom"); print @} @end example @noindent @@ -10034,35 +11814,31 @@ replaces all occurrences of the string @samp{Britain} with @samp{United Kingdom} for all input records. The @code{gsub} function returns the number of substitutions made. If -the variable to be searched and altered, @var{target}, is -omitted, then the entire input record, @code{$0}, is used. - +the variable to search and alter (@var{target}) is +omitted, then the entire input record (@code{$0}) is used. As in @code{sub}, the characters @samp{&} and @samp{\} are special, -and the third argument must be an lvalue. -@end table +and the third argument must be assignable. -@table @code -@item gensub(@var{regexp}, @var{replacement}, @var{how} @r{[}, @var{target}@r{]}) -@findex gensub +@item gensub(@var{regexp}, @var{replacement}, @var{how} @r{[}, @var{target}@r{]}) # +@cindex @code{gensub} built-in function @code{gensub} is a general substitution function. Like @code{sub} and @code{gsub}, it searches the target string @var{target} for matches of -the regular expression @var{regexp}. Unlike @code{sub} and -@code{gsub}, the modified string is returned as the result of the -function, and the original target string is @emph{not} changed. If -@var{how} is a string beginning with @samp{g} or @samp{G}, then it -replaces all matches of @var{regexp} with @var{replacement}. -Otherwise, @var{how} is a number indicating which match of @var{regexp} -to replace. If no @var{target} is supplied, @code{$0} is used instead. +the regular expression @var{regexp}. Unlike @code{sub} and @code{gsub}, +the modified string is returned as the result of the function and the +original target string is @emph{not} changed. If @var{how} is a string +beginning with @samp{g} or @samp{G}, then it replaces all matches of +@var{regexp} with @var{replacement}. Otherwise, @var{how} is treated +as a number that indicates which match of @var{regexp} to replace. If +no @var{target} is supplied, @code{$0} is used. @code{gensub} provides an additional feature that is not available -in @code{sub} or @code{gsub}: the ability to specify components of -a regexp in the replacement text. This is done by using parentheses -in the regexp to mark the components, and then specifying @samp{\@var{n}} -in the replacement text, where @var{n} is a digit from one to nine. +in @code{sub} or @code{gsub}: the ability to specify components of a +regexp in the replacement text. This is done by using parentheses in +the regexp to mark the components and then specifying @samp{\@var{N}} +in the replacement text, where @var{N} is a digit from 1 to 9. For example: @example -@group $ gawk ' > BEGIN @{ > a = "abc def" @@ -10070,18 +11846,17 @@ $ gawk ' > print b > @}' @print{} def abc -@end group @end example @noindent -As described above for @code{sub}, you must type two backslashes in order +As with @code{sub}, you must type two backslashes in order to get one into the string. In the replacement text, the sequence @samp{\0} represents the entire matched text, as does the character @samp{&}. -This example shows how you can use the third argument to control -which match of the regexp should be changed. +The following example shows how you can use the third argument to control +which match of the regexp should be changed: @example $ echo a b c a b c | @@ -10093,23 +11868,27 @@ In this case, @code{$0} is used as the default target string. @code{gensub} returns the new string as its result, which is passed directly to @code{print} for printing. +@cindex automatic warnings +@cindex warnings, automatic If the @var{how} argument is a string that does not begin with @samp{g} or -@samp{G}, or if it is a number that is less than zero, only one -substitution is performed. +@samp{G}, or if it is a number that is less than or equal to zero, only one +substitution is performed. If @var{how} is zero, @command{gawk} issues +a warning message. If @var{regexp} does not match @var{target}, @code{gensub}'s return value -is the original, unchanged value of @var{target}. +is the original unchanged value of @var{target}. -@cindex differences between @code{gawk} and @code{awk} -@code{gensub} is a @code{gawk} extension; it is not available -in compatibility mode (@pxref{Options, ,Command Line Options}). +@cindex differences between @command{gawk} and @command{awk} +@code{gensub} is a @command{gawk} extension; it is not available +in compatibility mode (@pxref{Options, ,Command-Line Options}). @item substr(@var{string}, @var{start} @r{[}, @var{length}@r{]}) -@findex substr +@cindex @code{substr} built-in function This returns a @var{length}-character-long substring of @var{string}, starting at character number @var{start}. The first character of a -string is character number one. For example, -@code{substr("washington", 5, 3)} returns @code{"ing"}. +string is character number one.@footnote{This is different from +C and C++, where the first character is number zero.} +For example, @code{substr("washington", 5, 3)} returns @code{"ing"}. If @var{length} is not present, this function returns the whole suffix of @var{string} that begins at character number @var{start}. For example, @@ -10118,9 +11897,12 @@ suffix is also returned if @var{length} is greater than the number of characters remaining in the string, counting from character number @var{start}. -@strong{Note:} The string returned by @code{substr} @emph{cannot} be -assigned to. Thus, it is a mistake to attempt to change a portion of -a string, like this: +@cindex common mistakes +@cindex mistakes, common +@cindex errors, common +The string returned by @code{substr} @emph{cannot} be +assigned. Thus, it is a mistake to attempt to change a portion of +a string, as shown in the following example: @example string = "abcdef" @@ -10129,57 +11911,72 @@ substr(string, 3, 3) = "CDE" @end example @noindent -or to use @code{substr} as the third agument of @code{sub} or @code{gsub}: +It is also a mistake to use @code{substr} as the third argument +of @code{sub} or @code{gsub}: @example gsub(/xyz/, "pdq", substr($0, 5, 20)) # WRONG @end example +@cindex portability issues +(Some commercial versions of @command{awk} do in fact let you use +@code{substr} this way, but doing so is not portable.) + +If you need to replace bits and pieces of a string, combine @code{substr} +with string concatenation, in the following manner: + +@example +string = "abcdef" +@dots{} +string = substr(string, 1, 2) "CDE" substr(string, 6) +@end example + @cindex case conversion @cindex conversion of case @item tolower(@var{string}) -@findex tolower -This returns a copy of @var{string}, with each upper-case character -in the string replaced with its corresponding lower-case character. +@cindex @code{tolower} built-in function +This returns a copy of @var{string}, with each uppercase character +in the string replaced with its corresponding lowercase character. Non-alphabetic characters are left unchanged. For example, @code{tolower("MiXeD cAsE 123")} returns @code{"mixed case 123"}. @item toupper(@var{string}) -@findex toupper -This returns a copy of @var{string}, with each lower-case character -in the string replaced with its corresponding upper-case character. +@cindex @code{toupper} built-in function +This returns a copy of @var{string}, with each lowercase character +in the string replaced with its corresponding uppercase character. Non-alphabetic characters are left unchanged. For example, @code{toupper("MiXeD cAsE 123")} returns @code{"MIXED CASE 123"}. @end table -@c fakenode --- for prepinfo -@subheading More About @samp{\} and @samp{&} with @code{sub}, @code{gsub} and @code{gensub} +@node Gory Details, , String Functions, String Functions +@subsubsection More About @samp{\} and @samp{&} with @code{sub}, @code{gsub}, and @code{gensub} @cindex escape processing, @code{sub} et. al. -When using @code{sub}, @code{gsub} or @code{gensub}, and trying to get literal +@cindex @code{sub}, escape processing +@cindex @code{gsub}, escape processing +@cindex @code{gensub}, escape processing +When using @code{sub}, @code{gsub}, or @code{gensub}, and trying to get literal backslashes and ampersands into the replacement text, you need to remember that there are several levels of @dfn{escape processing} going on. -First, there is the @dfn{lexical} level, which is when @code{awk} reads -your program, and builds an internal copy of your program that can -be executed. - -Then there is the run-time level, when @code{awk} actually scans the +First, there is the @dfn{lexical} level, which is when @command{awk} reads +your program +and builds an internal copy of it that can be executed. +Then there is the runtime level, which is when @command{awk} actually scans the replacement string to determine what to generate. -At both levels, @code{awk} looks for a defined set of characters that +At both levels, @command{awk} looks for a defined set of characters that can come after a backslash. At the lexical level, it looks for the escape sequences listed in @ref{Escape Sequences}. -Thus, for every @samp{\} that @code{awk} will process at the run-time -level, you type two @samp{\}s at the lexical level. +Thus, for every @samp{\} that @command{awk} processes at the runtime +level, type two backslashes at the lexical level. When a character that is not valid for an escape sequence follows the -@samp{\}, Unix @code{awk} and @code{gawk} both simply remove the initial -@samp{\}, and put the following character into the string. Thus, for +@samp{\}, Unix @command{awk} and @command{gawk} both simply remove the initial +@samp{\} and put the next character into the string. Thus, for example, @code{"a\qb"} is treated as @code{"aqb"}. -At the run-time level, the various functions handle sequences of +At the runtime level, the various functions handle sequences of @samp{\} and @samp{&} differently. The situation is (sadly) somewhat complex. - Historically, the @code{sub} and @code{gsub} functions treated the two character sequence @samp{\&} specially; this sequence was replaced in the generated text with a single @samp{&}. Any other @samp{\} within @@ -10206,7 +12003,7 @@ through unchanged. To illustrate with a table: } @bigskip} @end tex -@ifinfo +@ifnottex @display You type @code{sub} sees @code{sub} generates -------- ---------- --------------- @@ -10218,25 +12015,24 @@ through unchanged. To illustrate with a table: @code{\\\\\\&} @code{\\\&} a literal @samp{\\&} @code{\\q} @code{\q} a literal @samp{\q} @end display -@end ifinfo +@end ifnottex @noindent -This table shows both the lexical level processing, where -an odd number of backslashes becomes an even number at the run time level, -and the run-time processing done by @code{sub}. +This table shows both the lexical-level processing, where +an odd number of backslashes becomes an even number at the runtime level, +as well as the runtime processing done by @code{sub}. (For the sake of simplicity, the rest of the tables below only show the -case of even numbers of @samp{\}s entered at the lexical level.) +case of even numbers of backslashes entered at the lexical level.) The problem with the historical approach is that there is no way to get a literal @samp{\} followed by the matched text. -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} The 1992 POSIX standard attempted to fix this problem. The standard says that @code{sub} and @code{gsub} look for either a @samp{\} or an @samp{&} after the @samp{\}. If either one follows a @samp{\}, that character is -output literally. The interpretation of @samp{\} and @samp{&} then becomes -like this: +output literally. The interpretation of @samp{\} and @samp{&} then becomes: @c thanks to Karl Berry for formatting this table @tex @@ -10255,7 +12051,7 @@ like this: } @bigskip} @end tex -@ifinfo +@ifnottex @display You type @code{sub} sees @code{sub} generates -------- ---------- --------------- @@ -10264,34 +12060,32 @@ like this: @code{\\\\&} @code{\\&} a literal @samp{\}, then the matched text @code{\\\\\\&} @code{\\\&} a literal @samp{\&} @end display -@end ifinfo +@end ifnottex @noindent -This would appear to solve the problem. +This appears to solve the problem. Unfortunately, the phrasing of the standard is unusual. It says, in effect, that @samp{\} turns off the special meaning of any -following character, but that for anything other than @samp{\} and @samp{&}, -such special meaning is undefined. This wording leads to two problems. +following character, but for anything other than @samp{\} and @samp{&}, +such special meaning is undefined. This wording leads to two problems: -@enumerate +@itemize @bullet @item Backslashes must now be doubled in the @var{replacement} string, breaking -historical @code{awk} programs. +historical @command{awk} programs. @item -To make sure that an @code{awk} program is portable, @emph{every} character +To make sure that an @command{awk} program is portable, @emph{every} character in the @var{replacement} string must be preceded with a backslash.@footnote{This consequence was certainly unintended.} @c I can say that, 'cause I was involved in making this change -@end enumerate +@end itemize -The POSIX standard is under revision.@footnote{As of @value{UPDATE-MONTH}, -with final approval and publication as part of the Austin Group -Standards hopefully sometime in 2001.} -Because of the above problems, proposed text for the revised standard +The POSIX standard is under revision. +Because of the problems just listed, proposed text for the revised standard reverts to rules that correspond more closely to the original existing practice. The proposed rules have special cases that make it possible -to produce a @samp{\} preceding the matched text. +to produce a @samp{\} preceding the matched text: @tex \vbox{\bigskip @@ -10320,26 +12114,30 @@ to produce a @samp{\} preceding the matched text. @end display @end ifinfo -In a nutshell, at the run-time level, there are now three special sequences -of characters, @samp{\\\&}, @samp{\\&} and @samp{\&}, whereas historically, +In a nutshell, at the runtime level, there are now three special sequences +of characters (@samp{\\\&}, @samp{\\&} and @samp{\&}) whereas historically there was only one. However, as in the historical case, any @samp{\} that -is not part of one of these three sequences is not special, and appears +is not part of one of these three sequences is not special and appears in the output literally. -@code{gawk} 3.0 follows these proposed POSIX rules for @code{sub} and +@command{gawk} 3.0 and 3.1 follow these proposed POSIX rules for @code{sub} and @code{gsub}. @c As much as we think it's a lousy idea. You win some, you lose some. Sigh. Whether these proposed rules will actually become codified into the -standard is unknown at this point. Subsequent @code{gawk} releases will +standard is unknown at this point. Subsequent @command{gawk} releases will track the standard and implement whatever the final version specifies; -this @value{DOCUMENT} will be updated as well. - -The rules for @code{gensub} are considerably simpler. At the run-time -level, whenever @code{gawk} sees a @samp{\}, if the following character +this @value{DOCUMENT} will be updated as +well.@footnote{As this @value{DOCUMENT} was being finalized, +we learned that the POSIX standard will not use these rules. +However, it was too late to change @command{gawk} for the 3.1 release. +@command{gawk} behaves as described here.} + +The rules for @code{gensub} are considerably simpler. At the runtime +level, whenever @command{gawk} sees a @samp{\}, if the following character is a digit, then the text that matched the corresponding parenthesized subexpression is placed in the generated output. Otherwise, -no matter what the character after the @samp{\} is, that character will -appear in the generated text, and the @samp{\} will not. +no matter what the character after the @samp{\} is, it +appears in the generated text and the @samp{\} does not: @tex \vbox{\bigskip @@ -10359,7 +12157,7 @@ appear in the generated text, and the @samp{\} will not. } @bigskip} @end tex -@ifinfo +@ifnottex @display You type @code{gensub} sees @code{gensub} generates -------- ------------- ------------------ @@ -10370,73 +12168,110 @@ appear in the generated text, and the @samp{\} will not. @code{\\\\\\&} @code{\\\&} a literal @samp{\&} @code{\\q} @code{\q} a literal @samp{q} @end display -@end ifinfo +@end ifnottex -Because of the complexity of the lexical and run-time level processing, +Because of the complexity of the lexical and runtime level processing and the special cases for @code{sub} and @code{gsub}, -we recommend the use of @code{gawk} and @code{gensub} for when you have +we recommend the use of @command{gawk} and @code{gensub} when you have to do substitutions. +@c fakenode --- for prepinfo +@subheading Advanced Notes: Matching the Null String +@cindex advanced notes +@cindex matching, the null string + +In @command{awk}, the @samp{*} operator can match the null string. +This is particularly important for the @code{sub}, @code{gsub}, +and @code{gensub} functions. For example: + +@example +$ echo abc | awk '@{ gsub(/m*/, "X"); print @}' +@print{} XaXbXcX +@end example + +@noindent +Although this makes a certain amount of sense, it can be surprising. + @node I/O Functions, Time Functions, String Functions, Built-in -@section Built-in Functions for Input/Output +@subsection Input/Output Functions -The following functions are related to Input/Output (I/O). -Optional parameters are enclosed in square brackets (``['' and ``]''). +The following functions relate to Input/Output (I/O). +Optional parameters are enclosed in square brackets ([ and ]): @table @code -@item close(@var{filename}) -@findex close -Close the file @var{filename}, for input or output. The argument may -alternatively be a shell command that was used for redirecting to or -from a pipe; then the pipe is closed. -@xref{Close Files And Pipes, ,Closing Input and Output Files and Pipes}, +@item close(@var{filename} @r{[}, @var{how}@r{]}) +@cindex @code{close} built-in function +Close the file @var{filename} for input or output. Alternatively, the +argument may be a shell command that was used for creating a coprocess, or +for redirecting to or from a pipe; then the coprocess or pipe is closed. +@xref{Close Files And Pipes, ,Closing Input and Output Redirections}, for more information. +When closing a coprocess, it is occasionally useful to first close +one end of the two-way pipe, and then to close the other. This is done +by providing a second argument to @code{close}. This second argument +should be one of the two string values @code{"to"} or @code{"from"}, +indicating which end of the pipe to close. Case in the string does +not matter. +@xref{Two-way I/O, ,Two-Way Communications with Another Process}, +which discusses this feature in more detail and gives an example. + @item fflush(@r{[}@var{filename}@r{]}) -@findex fflush +@cindex @code{fflush} built-in function @cindex portability issues @cindex flushing buffers @cindex buffers, flushing @cindex buffering output @cindex output, buffering -Flush any buffered output associated @var{filename}, which is either a -file opened for writing, or a shell command for redirecting output to -a pipe. +Flush any buffered output associated with @var{filename}, which is either a +file opened for writing or a shell command for redirecting output to +a pipe or coprocess. -Many utility programs will @dfn{buffer} their output; they save information -to be written to a disk file or terminal in memory, until there is enough -for it to be worthwhile to send the data to the ouput device. +Many utility programs @dfn{buffer} their output; i.e., they save information +to write to a disk file or terminal in memory, until there is enough +for it to be worthwhile to send the data to the output device. This is often more efficient than writing every little bit of information as soon as it is ready. However, sometimes it is necessary to force a program to @dfn{flush} its buffers; that is, write the information to its destination, even if a buffer is not full. -This is the purpose of the @code{fflush} function; @code{gawk} too -buffers its output, and the @code{fflush} function can be used to force -@code{gawk} to flush its buffers. +This is the purpose of the @code{fflush} function---@command{gawk} also +buffers its output and the @code{fflush} function forces +@command{gawk} to flush its buffers. -@code{fflush} is a recent (1994) addition to the Bell Labs research -version of @code{awk}; it is not part of the POSIX standard, and will -not be available if @samp{--posix} has been specified on the command -line (@pxref{Options, ,Command Line Options}). +@code{fflush} was added to the Bell Laboratories research +version of @command{awk} in 1994; it is not part of the POSIX standard and is +not available if @option{--posix} has been specified on the +command line (@pxref{Options, ,Command-Line Options}). -@code{gawk} extends the @code{fflush} function in two ways. The first +@command{gawk} extends the @code{fflush} function in two ways. The first is to allow no argument at all. In this case, the buffer for the -standard output is flushed. The second way is to allow the null string +standard output is flushed. The second is to allow the null string (@w{@code{""}}) as the argument. In this case, the buffers for @emph{all} open output files and pipes are flushed. -@code{fflush} returns zero if the buffer was successfully flushed, -and nonzero otherwise. +@cindex automatic warnings +@cindex warnings, automatic +@code{fflush} returns zero if the buffer is successfully flushed; +otherwise it returns @minus{}1. +In the case where all buffers are flushed, the return value is zero +only if all buffers were flushed successfully. Otherwise, it is +@minus{}1, and @command{gawk} warns about the @var{filename} that had the problem. + +@command{gawk} also issues a warning message if you attempt to flush +a file or pipe that was opened for reading (such as with @code{getline}), +or if @var{filename} is not an open file, pipe, or coprocess. +In such a case, @code{fflush} returns @minus{}1 as well. @item system(@var{command}) -@findex system -@cindex interaction, @code{awk} and other programs -The @code{system} function allows the user to execute operating system commands -and then return to the @code{awk} program. The @code{system} function -executes the command given by the string @var{command}. It returns, as -its value, the status returned by the command that was executed. - -For example, if the following fragment of code is put in your @code{awk} +@cindex @code{system} built-in function +@cindex interaction, @command{awk} and other programs +The @code{system} function allows the user to execute operating system +commands and then return to the @command{awk} program. The @code{system} +function executes the command given by the string @var{command}. +It returns the status returned by the command that was executed as +its value. + +For example, if the following fragment of code is put in your @command{awk} program: @example @@ -10446,12 +12281,12 @@ END @{ @end example @noindent -the system administrator will be sent mail when the @code{awk} program +the system administrator is sent mail when the @command{awk} program finishes processing input and begins its end-of-input processing. Note that redirecting @code{print} or @code{printf} into a pipe is often enough to accomplish your task. If you need to run many commands, it -will be more efficient to simply print them to a pipe to the shell: +is more efficient to simply print them down a pipeline to the shell: @example while (@var{more stuff to do}) @@ -10460,34 +12295,34 @@ close("/bin/sh") @end example @noindent -However, if your @code{awk} +@cindex fatal errors +However, if your @command{awk} program is interactive, @code{system} is useful for cranking up large self-contained programs, such as a shell or an editor. - Some operating systems cannot implement the @code{system} function. @code{system} causes a fatal error if it is not supported. @end table @c fakenode --- for prepinfo -@subheading Interactive vs. Non-Interactive Buffering +@subheading Advanced Notes: Interactive Versus Non-Interactive Buffering +@cindex advanced notes @cindex buffering, interactive vs. non-interactive @cindex buffering, non-interactive vs. interactive @cindex interactive buffering vs. non-interactive @cindex non-interactive buffering vs. interactive -As a side point, buffering issues can be even more confusing depending -upon whether or not your program is @dfn{interactive}, i.e., communicating +As a side point, buffering issues can be even more confusing, depending +upon whether your program is @dfn{interactive}; i.e., communicating with a user sitting at a keyboard.@footnote{A program is interactive if the standard output is connected to a terminal device.} -Interactive programs generally @dfn{line buffer} their output; they -write out every line. Non-interactive programs wait until they have -a full buffer, which may be many lines of output. - @c Thanks to Walter.Mecky@dresdnerbank.de for this example, and for @c motivating me to write this section. -Here is an example of the difference. +Interactive programs generally @dfn{line buffer} their output; i.e., they +write out every line. Non-interactive programs wait until they have +a full buffer, which may be many lines of output. +Here is an example of the difference: @example $ awk '@{ print $1 + $2 @}' @@ -10495,28 +12330,29 @@ $ awk '@{ print $1 + $2 @}' @print{} 2 2 3 @print{} 5 -@kbd{Control-d} +@kbd{Ctrl-d} @end example @noindent Each line of output is printed immediately. Compare that behavior -with this example. +with this example: @example $ awk '@{ print $1 + $2 @}' | cat 1 1 2 3 -@kbd{Control-d} +@kbd{Ctrl-d} @print{} 2 @print{} 5 @end example @noindent -Here, no output is printed until after the @kbd{Control-d} is typed, since -it is all buffered, and sent down the pipe to @code{cat} in one shot. +Here, no output is printed until after the @kbd{Ctrl-d} is typed, because +it is all buffered and sent down the pipe to @command{cat} in one shot. @c fakenode --- for prepinfo -@subheading Controlling Output Buffering with @code{system} +@subheading Advanced Notes: Controlling Output Buffering with @code{system} +@cindex advanced notes @cindex flushing buffers @cindex buffers, flushing @cindex buffering output @@ -10524,21 +12360,21 @@ it is all buffered, and sent down the pipe to @code{cat} in one shot. The @code{fflush} function provides explicit control over output buffering for individual files and pipes. However, its use is not portable to many other -@code{awk} implementations. An alternative method to flush output -buffers is by calling @code{system} with a null string as its argument: +@command{awk} implementations. An alternative method to flush output +buffers is to call @code{system} with a null string as its argument: @example system("") # flush output @end example @noindent -@code{gawk} treats this use of the @code{system} function as a special -case, and is smart enough not to run a shell (or other command -interpreter) with the empty command. Therefore, with @code{gawk}, this -idiom is not only useful, it is efficient. While this method should work -with other @code{awk} implementations, it will not necessarily avoid +@command{gawk} treats this use of the @code{system} function as a special +case and is smart enough not to run a shell (or other command +interpreter) with the empty command. Therefore, with @command{gawk}, this +idiom is not only useful, it is also efficient. While this method should work +with other @command{awk} implementations, it does not necessarily avoid starting an unnecessary shell. (Other implementations may only -flush the buffer associated with the standard output, and not necessarily +flush the buffer associated with the standard output and not necessarily all buffered output.) If you think about what a programmer expects, it makes sense that @@ -10553,7 +12389,7 @@ BEGIN @{ @end example @noindent -must print +must print: @example first print @@ -10562,7 +12398,7 @@ second print @end example @noindent -and not +and not: @example system echo @@ -10570,67 +12406,114 @@ first print second print @end example -If @code{awk} did not flush its buffers before calling @code{system}, the -latter (undesirable) output is what you would see. +If @command{awk} did not flush its buffers before calling @code{system}, the +latter (undesirable) output is what you see. -@node Time Functions, , I/O Functions, Built-in -@section Functions for Dealing with Time Stamps +@node Time Functions, Bitwise Functions, I/O Functions, Built-in +@subsection Using @command{gawk}'s Timestamp Functions @cindex timestamps @cindex time of day -A common use for @code{awk} programs is the processing of log files -containing time stamp information, indicating when a -particular log record was written. Many programs log their time stamp +A common use for @command{awk} programs is the processing of log files +containing timestamp information, indicating when a +particular log record was written. Many programs log their timestamp in the form returned by the @code{time} system call, which is the -number of seconds since a particular epoch. On POSIX systems, -it is the number of seconds since Midnight, January 1, 1970, UTC. - -In order to make it easier to process such log files, and to produce -useful reports, @code{gawk} provides two functions for working with time -stamps. Both of these are @code{gawk} extensions; they are not specified -in the POSIX standard, nor are they in any other known version -of @code{awk}. - -Optional parameters are enclosed in square brackets (``['' and ``]''). +number of seconds since a particular epoch. On POSIX-compliant systems, +it is the number of seconds since +1970-01-01 00:00:00 UTC, not counting leap seconds.@footnote{@xref{Glossary}, +especially the entries for ``Epoch'' and ``UTC.''} +All known POSIX-compliant systems support timestamps from 0 through +@math{2^31 - 1}, which is sufficient to represent times through +2038-01-19 03:14:07 UTC. Many systems support a wider range of timestamps, +including negative timestamps that represent times before the +epoch. + +In order to make it easier to process such log files and to produce +useful reports, @command{gawk} provides the following functions for +working with timestamps. They are @command{gawk} extensions; they are +not specified in the POSIX standard, nor are they in any other known +version of @command{awk}.@footnote{The GNU @command{date} utility can +also do many of the things described here. It's use may be preferable +for simple time-related operations in shell scripts.} +Optional parameters are enclosed in square brackets ([ and ]): @table @code @item systime() -@findex systime +@cindex @code{systime} built-in function This function returns the current time as the number of seconds since the system epoch. On POSIX systems, this is the number of seconds -since Midnight, January 1, 1970, UTC. It may be a different number on +since 1970-01-01 00:00:00 UTC, not counting leap seconds. +It may be a different number on other systems. +@item mktime(@var{datespec}) +@cindex @code{mktime} built-in function +This function turns @var{datespec} into a timestamp in the same form +as is returned by @code{systime}. It is similar to the function of the +same name in ISO C. The argument, @var{datespec}, is a string of the form +@w{@code{"@var{YYYY} @var{MM} @var{DD} @var{HH} @var{MM} @var{SS} [@var{DST}]"}}. +The string consists of six or seven numbers representing, respectively, +the full year including century, the month from 1 to 12, the day of the month +from 1 to 31, the hour of the day from 0 to 23, the minute from 0 to +59, the second from 0 to 60,@footnote{Occasionally there are +minutes in a year with a leap second, which is why the +seconds can go up to 60.} +and an optional daylight savings flag. + +The values of these numbers need not be within the ranges specified; +for example, an hour of @minus{}1 means 1 hour before midnight. +The origin-zero Gregorian calendar is assumed, with year 0 preceding +year 1 and year @minus{}1 preceding year 0. +The time is assumed to be in the local timezone. +If the daylight savings flag is positive, the time is assumed to be +daylight savings time; if zero, the time is assumed to be standard +time; and if negative (the default), @code{mktime} attempts to determine +whether daylight savings time is in effect for the specified time. + +If @var{datespec} does not contain enough elements or if the resulting time +is out of range, @code{mktime} returns @minus{}1. + @item strftime(@r{[}@var{format} @r{[}, @var{timestamp}@r{]]}) -@findex strftime +@cindex @code{strftime} built-in function This function returns a string. It is similar to the function of the -same name in ANSI C. The time specified by @var{timestamp} is used to +same name in ISO C. The time specified by @var{timestamp} is used to produce a string, based on the contents of the @var{format} string. The @var{timestamp} is in the same format as the value returned by the @code{systime} function. If no @var{timestamp} argument is supplied, -@code{gawk} will use the current time of day as the time stamp. +@command{gawk} uses the current time of day as the timestamp. If no @var{format} argument is supplied, @code{strftime} uses @code{@w{"%a %b %d %H:%M:%S %Z %Y"}}. This format string produces -output (almost) equivalent to that of the @code{date} utility. -(Versions of @code{gawk} prior to 3.0 require the @var{format} argument.) +output that is (almost) equivalent to that of the @command{date} utility. +(Versions of @command{gawk} prior to 3.0 require the @var{format} argument.) @end table -The @code{systime} function allows you to compare a time stamp from a +The @code{systime} function allows you to compare a timestamp from a log file with the current time of day. In particular, it is easy to determine how long ago a particular record was logged. It also allows you to produce log records using the ``seconds since the epoch'' format. -The @code{strftime} function allows you to easily turn a time stamp +@cindex converting dates to timestamps +@cindex dates, converting to timestamps +@cindex timestamps, converting from dates +The @code{mktime} function allows you to convert a textual representation +of a date and time into a timestamp. This makes it easy to do before/after +comparisons of dates and times, particularly when dealing with date and +time data coming from an external source, such as a log file. + +The @code{strftime} function allows you to easily turn a timestamp into human-readable information. It is similar in nature to the @code{sprintf} function -(@pxref{String Functions, ,Built-in Functions for String Manipulation}), +(@pxref{String Functions, ,String Manipulation Functions}), in that it copies non-format specification characters verbatim to the returned string, while substituting date and time values for format specifications in the @var{format} string. -@code{strftime} is guaranteed by the ANSI C standard to support -the following date format specifications: +@code{strftime} is guaranteed by the 1999 ISO C standard@footnote{As this +is a recent standard, not every system's @code{strftime} necessarily +supports all of the conversions listed here.} +to support the following date format specifications: +@cindex format specifier, @code{strftime} @table @code @item %a The locale's abbreviated weekday name. @@ -10646,10 +12529,38 @@ The locale's full month name. @item %c The locale's ``appropriate'' date and time representation. +(This is @samp{%A %B %d %T %Y} in the @code{"C"} locale.) + +@item %C +The century. This is the year divided by 100 and truncated to the next +lower integer. @item %d The day of the month as a decimal number (01--31). +@item %D +Equivalent to specifying @samp{%m/%d/%y}. + +@item %e +The day of the month, padded with a space if it is only one digit. + +@item %F +Equivalent to specifying @samp{%Y-%m-%d}. +This is the ISO 8601 date format. + +@item %g +The year modulo 100 of the ISO week number, as a decimal number (00--99). +For example, January 1, 1993, is in week 53 of 1992. Thus, the year +of its ISO week number is 1992, even though its year is 1993. +Similarly, December 31, 1973, is in week 1 of 1974. Thus, the year +of its ISO week number is 1974, even though its year is 1973. + +@item %G +The full year of the ISO week number, as a decimal number. + +@item %h +Equivalent to @samp{%b}. + @item %H The hour (24-hour clock) as a decimal number (00--23). @@ -10665,19 +12576,45 @@ The month as a decimal number (01--12). @item %M The minute as a decimal number (00--59). +@item %n +A newline character (ASCII LF). + @item %p The locale's equivalent of the AM/PM designations associated with a 12-hour clock. +@item %r +The locale's 12-hour clock time. +(This is @samp{%I:%M:%S %p} in the @code{"C"} locale.) + +@item %R +Equivalent to specifying @samp{%H:%M}. + @item %S -The second as a decimal number (00--60).@footnote{Occasionally there are -minutes in a year with a leap second, which is why the -seconds can go up to 60.} +The second as a decimal number (00--60). + +@item %t +A tab character. + +@item %T +Equivalent to specifying @samp{%H:%M:%S}. + +@item %u +The weekday as a decimal number (1--7). Monday is day one. @item %U The week number of the year (the first Sunday as the first day of week one) as a decimal number (00--53). +@cindex ISO 8601 +@item %V +The week number of the year (the first Monday as the first +day of week one) as a decimal number (01--53). +The method for determining the week number is as specified by ISO 8601. +(To wit: if the week containing January 1 has four or more days in the +new year, then it is week one, otherwise it is week 53 of the previous year +and the next week is week one.) + @item %w The weekday as a decimal number (0--6). Sunday is day zero. @@ -10687,165 +12624,129 @@ as a decimal number (00--53). @item %x The locale's ``appropriate'' date representation. +(This is @samp{%A %B %d %Y} in the @code{"C"} locale.) @item %X The locale's ``appropriate'' time representation. +(This is @samp{%T} in the @code{"C"} locale.) @item %y -The year without century as a decimal number (00--99). +The year modulo 100 as a decimal number (00--99). @item %Y -The year with century as a decimal number (e.g., 1995). +The full year as a decimal number (e.g., 1995). + +@cindex RFC 822 +@cindex RFC 1036 +@item %z +The timezone offset in a +HHMM format (e.g., the format necessary to +produce RFC 822/RFC 1036 date headers). @item %Z -The time zone name or abbreviation, or no characters if +The time zone name or abbreviation; no characters if no time zone is determinable. +@item %Ec %EC %Ex %EX %Ey %EY %Od %Oe %OH +@itemx %OI %Om %OM %OS %Ou %OU %OV %Ow %OW %Oy +These are ``alternate representations'' for the specifications +that use only the second letter (@samp{%c}, @samp{%C}, +and so on).@footnote{If you don't understand any of this, don't worry about +it; these facilities are meant to make it easier to ``internationalize'' +programs. +Other internationalization features are described in +@ref{Internationalization, ,Internationalization with @command{gawk}}.} +(These facilitate compliance with the POSIX @command{date} utility.) + @item %% A literal @samp{%}. @end table If a conversion specifier is not one of the above, the behavior is -undefined.@footnote{This is because ANSI C leaves the -behavior of the C version of @code{strftime} undefined, and @code{gawk} -will use the system's version of @code{strftime} if it's there. -Typically, the conversion specifier will either not appear in the -returned string, or it will appear literally.} +undefined.@footnote{This is because ISO C leaves the +behavior of the C version of @code{strftime} undefined and @command{gawk} +uses the system's version of @code{strftime} if it's there. +Typically, the conversion specifier either does not appear in the +returned string or it appears literally.} @cindex locale, definition of Informally, a @dfn{locale} is the geographic place in which a program is meant to run. For example, a common way to abbreviate the date -September 4, 1991 in the United States would be ``9/4/91''. -In many countries in Europe, however, it would be abbreviated ``4.9.91''. +September 4, 1991 in the United States is ``9/4/91.'' +In many countries in Europe, however, it is abbreviated ``4.9.91.'' Thus, the @samp{%x} specification in a @code{"US"} locale might produce @samp{9/4/91}, while in a @code{"EUROPE"} locale, it might produce -@samp{4.9.91}. The ANSI C standard defines a default @code{"C"} +@samp{4.9.91}. The ISO C standard defines a default @code{"C"} locale, which is an environment that is typical of what most C programmers are used to. -A public-domain C version of @code{strftime} is supplied with @code{gawk} -for systems that are not yet fully ANSI-compliant. If that version is -used to compile @code{gawk} (@pxref{Installation, ,Installing @code{gawk}}), +A public-domain C version of @code{strftime} is supplied with @command{gawk} +for systems that are not yet fully standards-compliant. +It supports all of the just listed format specifications. +If that version is +used to compile @command{gawk} (@pxref{Installation, ,Installing @command{gawk}}), then the following additional format specifications are available: @table @code -@item %D -Equivalent to specifying @samp{%m/%d/%y}. - -@item %e -The day of the month, padded with a space if it is only one digit. - -@item %h -Equivalent to @samp{%b}, above. - -@item %n -A newline character (ASCII LF). - -@item %r -Equivalent to specifying @samp{%I:%M:%S %p}. - -@item %R -Equivalent to specifying @samp{%H:%M}. - -@item %T -Equivalent to specifying @samp{%H:%M:%S}. - -@item %t -A tab character. - @item %k -The hour (24-hour clock) as a decimal number (0-23). +The hour (24-hour clock) as a decimal number (0--23). Single digit numbers are padded with a space. @item %l -The hour (12-hour clock) as a decimal number (1-12). +The hour (12-hour clock) as a decimal number (1--12). Single digit numbers are padded with a space. -@item %C -The century, as a number between 00 and 99. - -@item %u -The weekday as a decimal number -[1 (Monday)--7]. - -@cindex ISO 8601 -@item %V -The week number of the year (the first Monday as the first -day of week one) as a decimal number (01--53). -The method for determining the week number is as specified by ISO 8601 -(to wit: if the week containing January 1 has four or more days in the -new year, then it is week one, otherwise it is week 53 of the previous year -and the next week is week one). - -@item %G -The year with century of the ISO week number, as a decimal number. - -For example, January 1, 1993, is in week 53 of 1992. Thus, the year -of its ISO week number is 1992, even though its year is 1993. -Similarly, December 31, 1973, is in week 1 of 1974. Thus, the year -of its ISO week number is 1974, even though its year is 1973. +@item %N +The ``Emperor/Era'' name. +Equivalent to @code{%C}. -@item %g -The year without century of the ISO week number, as a decimal number (00--99). +@item %o +The ``Emperor/Era'' year. +Equivalent to @code{%y}. -@item %Ec %EC %Ex %Ey %EY %Od %Oe %OH %OI -@itemx %Om %OM %OS %Ou %OU %OV %Ow %OW %Oy -These are ``alternate representations'' for the specifications -that use only the second letter (@samp{%c}, @samp{%C}, and so on). -They are recognized, but their normal representations are -used.@footnote{If you don't understand any of this, don't worry about -it; these facilities are meant to make it easier to ``internationalize'' -programs.} -(These facilitate compliance with the POSIX @code{date} utility.) +@item %s +The time as a decimal timestamp in seconds since the epoch. @item %v -The date in VMS format (e.g., 20-JUN-1991). - -@cindex RFC-822 -@cindex RFC-1036 -@item %z -The timezone offset in a +HHMM format (e.g., the format necessary to -produce RFC-822/RFC-1036 date headers). +The date in VMS format (e.g., @samp{20-JUN-1991}). @end table -This example is an @code{awk} implementation of the POSIX -@code{date} utility. Normally, the @code{date} utility prints the -current date and time of day in a well known format. However, if you -provide an argument to it that begins with a @samp{+}, @code{date} -will copy non-format specifier characters to the standard output, and -will interpret the current time according to the format specifiers in +Additionally, the alternate representations are recognized but their +normal representations are used. + +This example is an @command{awk} implementation of the POSIX +@command{date} utility. Normally, the @command{date} utility prints the +current date and time of day in a well-known format. However, if you +provide an argument to it that begins with a @samp{+}, @command{date} +copies non-format specifier characters to the standard output and +interprets the current time according to the format specifiers in the string. For example: @example $ date '+Today is %A, %B %d, %Y.' -@print{} Today is Thursday, July 11, 1991. +@print{} Today is Thursday, September 14, 2000. @end example -Here is the @code{gawk} version of the @code{date} utility. -It has a shell ``wrapper'', to handle the @samp{-u} option, -which requires that @code{date} run as if the time zone -was set to UTC. +Here is the @command{gawk} version of the @command{date} utility. +It has a shell ``wrapper'' to handle the @option{-u} option, +which requires that @command{date} run as if the time zone +is set to UTC: @example -@group #! /bin/sh # # date --- approximate the P1003.2 'date' command case $1 in --u) TZ=GMT0 # use UTC +-u) TZ=UTC0 # use UTC export TZ shift ;; esac -@end group -@group +@c FIXME: One day, change %d to %e, when C 99 is common. gawk 'BEGIN @{ format = "%a %b %d %H:%M:%S %Z %Y" exitval = 0 -@end group -@group if (ARGC > 2) exitval = 1 else if (ARGC == 2) @{ @@ -10856,41 +12757,316 @@ gawk 'BEGIN @{ print strftime(format) exit exitval @}' "$@@" -@end group @end example -@node User-defined, Invoking Gawk, Built-in, Top -@chapter User-defined Functions +@node Bitwise Functions, I18N Functions, Time Functions, Built-in +@subsection Using @command{gawk}'s Bit Manipulation Functions +@cindex bitwise operations +@quotation +@i{I can explain it for you, but I can't understand it for you.}@* +Anonymous +@end quotation -@cindex user-defined functions -@cindex functions, user-defined -Complicated @code{awk} programs can often be simplified by defining -your own functions. User-defined functions can be called just like -built-in ones (@pxref{Function Calls}), but it is up to you to define -them---to tell @code{awk} what they should do. +@cindex AND bitwise operation +@cindex OR bitwise operation +@cindex XOR bitwise operation +Many languages provide the ability to perform @dfn{bitwise} operations +on two integer numbers. In other words, the operation is performed on +each successive pair of bits in the operands. +Three common operations are bitwise AND, OR, and XOR. +The operations are described by the following table: -@menu -* Definition Syntax:: How to write definitions and what they mean. -* Function Example:: An example function definition and what it - does. +@ifnottex +@display + Bit Operator + | AND | OR | XOR + |---+---+---+---+---+--- +Operands | 0 | 1 | 0 | 1 | 0 | 1 +----------+---+---+---+---+---+--- + 0 | 0 0 | 0 1 | 0 1 + 1 | 0 1 | 1 1 | 1 0 +@end display +@end ifnottex +@tex +\centerline{ +\vbox{\bigskip % space above the table (about 1 linespace) +% Because we have vertical rules, we can't let TeX insert interline space +% in its usual way. +\offinterlineskip +\halign{\strut\hfil#\quad\hfil % operands + &\vrule#&\quad#\quad % rule, 0 (of and) + &\vrule#&\quad#\quad % rule, 1 (of and) + &\vrule# % rule between and and or + &\quad#\quad % 0 (of or) + &\vrule#&\quad#\quad % rule, 1 (of of) + &\vrule# % rule between or and xor + &\quad#\quad % 0 of xor + &\vrule#&\quad#\quad % rule, 1 of xor + \cr +&\omit&\multispan{11}\hfil\bf Bit operator\hfil\cr +\noalign{\smallskip} +& &\multispan3\hfil AND\hfil&&\multispan3\hfil OR\hfil + &&\multispan3\hfil XOR\hfil\cr +\bf Operands&&0&&1&&0&&1&&0&&1\cr +\noalign{\hrule} +\omit&height 2pt&&\omit&&&&\omit&&&&\omit\cr +\noalign{\hrule height0pt}% without this the rule does not extend; why? +0&&0&\omit&0&&0&\omit&1&&0&\omit&1\cr +1&&0&\omit&1&&1&\omit&1&&1&\omit&0\cr +}}} +@end tex + +@cindex bitwise complement +@cindex complement, bitwise +As you can see, the result of an AND operation is 1 only when @emph{both} +bits are 1. +The result of an OR operation is 1 if @emph{either} bit is 1. +The result of an XOR operation is 1 if either bit is 1, +but not both. +The next operation is the @dfn{complement}; the complement of 1 is 0 and +the complement of 0 is 1. Thus, this operation ``flips'' all the bits +of a given value. + +@cindex bitwise shift +@cindex left shift, bitwise +@cindex right shift, bitwise +@cindex shift, bitwise +Finally, two other common operations are to shift the bits left or right. +For example, if you have a bit string @samp{10111001} and you shift it +right by three bits, you end up with @samp{00010111}.@footnote{This example +shows that 0's come in on the left side. For @command{gawk}, this is +always true, but in some languages, it's possible to have the left side +fill with 1's. Caveat emptor.} +@c Purposely decided to use 0's and 1's here. 2/2001. +If you start over +again with @samp{10111001} and shift it left by three bits, you end up +with @samp{11001000}. +@command{gawk} provides built-in functions that implement the +bitwise operations just described. They are: + +@ignore +@table @code +@cindex @code{and} built-in function +@item and(@var{v1}, @var{v2}) +Return the bitwise AND of the values provided by @var{v1} and @var{v2}. + +@cindex @code{or} built-in function +@item or(@var{v1}, @var{v2}) +Return the bitwise OR of the values provided by @var{v1} and @var{v2}. + +@cindex @code{xor} built-in function +@item xor(@var{v1}, @var{v2}) +Return the bitwise XOR of the values provided by @var{v1} and @var{v2}. + +@cindex @code{compl} built-in function +@item compl(@var{val}) +Return the bitwise complement of @var{val}. + +@cindex @code{lshift} built-in function +@item lshift(@var{val}, @var{count}) +Return the value of @var{val}, shifted left by @var{count} bits. + +@cindex @code{rshift} built-in function +@item rshift(@var{val}, @var{count}) +Return the value of @var{val}, shifted right by @var{count} bits. +@end table +@end ignore + +@multitable {@code{rshift(@var{val}, @var{count})}} {Return the value of @var{val}, shifted right by @var{count} bits.} +@cindex @code{and} built-in function +@item @code{and(@var{v1}, @var{v2})} +@tab Return the bitwise AND of the values provided by @var{v1} and @var{v2}. + +@cindex @code{or} built-in function +@item @code{or(@var{v1}, @var{v2})} +@tab Return the bitwise OR of the values provided by @var{v1} and @var{v2}. + +@cindex @code{xor} built-in function +@item @code{xor(@var{v1}, @var{v2})} +@tab Return the bitwise XOR of the values provided by @var{v1} and @var{v2}. + +@cindex @code{compl} built-in function +@item @code{compl(@var{val})} +@tab Return the bitwise complement of @var{val}. + +@cindex @code{lshift} built-in function +@item @code{lshift(@var{val}, @var{count})} +@tab Return the value of @var{val}, shifted left by @var{count} bits. + +@cindex @code{rshift} built-in function +@item @code{rshift(@var{val}, @var{count})} +@tab Return the value of @var{val}, shifted right by @var{count} bits. +@end multitable + +For all of these functions, first the double-precision floating-point value is +converted to a C @code{unsigned long}, then the bitwise operation is +performed and then the result is converted back into a C @code{double}. (If +you don't understand this paragraph, don't worry about it.) + +Here is a user-defined function +(@pxref{User-defined, ,User-Defined Functions}) +that illustrates the use of these functions: + +@cindex @code{bits2str} user-defined function +@cindex @code{testbits.awk} program +@smallexample +@group +@c file eg/lib/bits2str.awk +# bits2str --- turn a byte into readable 1's and 0's + +function bits2str(bits, data, mask) +@{ + if (bits == 0) + return "0" + + mask = 1 + for (; bits != 0; bits = rshift(bits, 1)) + data = (and(bits, mask) ? "1" : "0") data + + while ((length(data) % 8) != 0) + data = "0" data + + return data +@} +@c endfile +@end group + +@c this is a hack to make testbits.awk self-contained +@ignore +@c file eg/prog/testbits.awk +# bits2str --- turn a byte into readable 1's and 0's + +function bits2str(bits, data, mask) +@{ + if (bits == 0) + return "0" + + mask = 1 + for (; bits != 0; bits = rshift(bits, 1)) + data = (and(bits, mask) ? "1" : "0") data + + while ((length(data) % 8) != 0) + data = "0" data + + return data +@} +@c endfile +@end ignore +@c file eg/prog/testbits.awk +BEGIN @{ + printf "123 = %s\n", bits2str(123) + printf "0123 = %s\n", bits2str(0123) + printf "0x99 = %s\n", bits2str(0x99) + comp = compl(0x99) + printf "compl(0x99) = %#x = %s\n", comp, bits2str(comp) + shift = lshift(0x99, 2) + printf "lshift(0x99, 2) = %#x = %s\n", shift, bits2str(shift) + shift = rshift(0x99, 2) + printf "rshift(0x99, 2) = %#x = %s\n", shift, bits2str(shift) +@} +@c endfile +@end smallexample + +@noindent +This program produces the following output when run: + +@smallexample +$ gawk -f testbits.awk +@print{} 123 = 01111011 +@print{} 0123 = 01010011 +@print{} 0x99 = 10011001 +@print{} compl(0x99) = 0xffffff66 = 11111111111111111111111101100110 +@print{} lshift(0x99, 2) = 0x264 = 0000001001100100 +@print{} rshift(0x99, 2) = 0x26 = 00100110 +@end smallexample + +The @code{bits2str} function turns a binary number into a string. +The number @code{1} represents a binary value where the rightmost bit +is set to 1. Using this mask, +the function repeatedly checks the rightmost bit. +AND-ing the mask with the value indicates whether the +rightmost bit is 1 or not. If so, a @code{"1"} is concatenated onto the front +of the string. +Otherwise, a @code{"0"} is added. +The value is then shifted right by one bit and the loop continues +until there are no more 1 bits. + +If the initial value is zero it returns a simple @code{"0"}. +Otherwise, at the end, it pads the value with zeros to represent multiples +of eight-bit quantities. This is typical in modern computers. + +The main code in the @code{BEGIN} rule shows the difference between the +decimal and octal values for the same numbers +(@pxref{Non-decimal-numbers, ,Octal and Hexadecimal Numbers}), +and then demonstrates the +results of the @code{compl}, @code{lshift}, and @code{rshift} functions. + +@node I18N Functions, , Bitwise Functions, Built-in +@subsection Using @command{gawk}'s String Translation Functions + +@command{gawk} provides facilities for internationalizing @command{awk} programs. +These include the functions described in the following list. +The description here is purposely brief. +@xref{Internationalization, ,Internationalization with @command{gawk}}, +for the full story. +Optional parameters are enclosed in square brackets ([ and ]): + +@table @code +@cindex @code{dcgettext} built-in function +@item dcgettext(@var{string} @r{[}, @var{domain} @r{[}, @var{category}@r{]]}) +This function returns the translation of @var{string} in +text domain @var{domain} for locale category @var{category}. +The default value for @var{domain} is the current value of @code{TEXTDOMAIN}. +The default value for @var{category} is @code{"LC_MESSAGES"}. + +@cindex @code{bindtextdomain} built-in function +@item bindtextdomain(@var{directory} @r{[}, @var{domain}@r{]}) +This function allows you to specify the directory where +@command{gawk} will look for message translation files, in case they +will not or cannot be placed in the ``standard'' locations +(e.g., during testing). +It returns the directory where @var{domain} is ``bound.'' + +The default @var{domain} is the value of @code{TEXTDOMAIN}. +If @var{directory} is the null string (@code{""}), then +@code{bindtextdomain} returns the current binding for the +given @var{domain}. +@end table + +@node User-defined, , Built-in, Functions +@section User-Defined Functions + +@cindex user-defined functions +@cindex function, user-defined +Complicated @command{awk} programs can often be simplified by defining +your own functions. User-defined functions can be called just like +built-in ones (@pxref{Function Calls}), but it is up to you to define +them; i.e., to tell @command{awk} what they should do. + +@menu +* Definition Syntax:: How to write definitions and what they mean. +* Function Example:: An example function definition and what it + does. * Function Caveats:: Things to watch out for. * Return Statement:: Specifying the value a function returns. +* Dynamic Typing:: How variable types can change at runtime. @end menu @node Definition Syntax, Function Example, User-defined, User-defined -@section Function Definition Syntax +@subsection Function Definition Syntax @cindex defining functions @cindex function definition Definitions of functions can appear anywhere between the rules of an -@code{awk} program. Thus, the general form of an @code{awk} program is +@command{awk} program. Thus, the general form of an @command{awk} program is extended to include sequences of rules @emph{and} user-defined function definitions. -There is no need in @code{awk} to put the definition of a function -before all uses of the function. This is because @code{awk} reads the +There is no need to put the definition of a function +before all uses of the function. This is because @command{awk} reads the entire program before starting to execute any of it. The definition of a function named @var{name} looks like this: +@c NEXT ED: put [ ] around parameter list @example function @var{name}(@var{parameter-list}) @@ -10900,31 +13076,33 @@ function @var{name}(@var{parameter-list}) @end example @cindex names, use of -@cindex namespaces +@cindex namespace issues in @command{awk} @noindent -@var{name} is the name of the function to be defined. A valid function -name is like a valid variable name: a sequence of letters, digits and -underscores, not starting with a digit. -Within a single @code{awk} program, any particular name can only be -used as a variable, array or function. +@var{name} is the name of the function to define. A valid function +name is like a valid variable name: a sequence of letters, digits, and +underscores, that doesn't start with a digit. +Within a single @command{awk} program, any particular name can only be +used as a variable, array, or function. +@c NEXT ED: parameter-list is an OPTIONAL list of ... @var{parameter-list} is a list of the function's arguments and local variable names, separated by commas. When the function is called, the argument names are used to hold the argument values given in the call. The local variables are initialized to the empty string. -A function cannot have two parameters with the same name. +A function cannot have two parameters with the same name, nor may it +have a parameter with the same name as the function itself. -The @var{body-of-function} consists of @code{awk} statements. It is the +The @var{body-of-function} consists of @command{awk} statements. It is the most important part of the definition, because it says what the function should actually @emph{do}. The argument names exist to give the body a -way to talk about the arguments; local variables, to give the body +way to talk about the arguments; local variables exist to give the body places to keep temporary values. Argument names are not distinguished syntactically from local variable -names; instead, the number of arguments supplied when the function is +names. Instead, the number of arguments supplied when the function is called determines how many argument variables there are. Thus, if three argument values are given, the first three names in @var{parameter-list} -are arguments, and the rest are local variables. +are arguments and the rest are local variables. It follows that if the number of arguments is not the same in all calls to the function, some of the names in @var{parameter-list} may be @@ -10932,10 +13110,12 @@ arguments on some occasions and local variables on others. Another way to think of this is that omitted arguments default to the null string. -Usually when you write a function you know how many names you intend to +@cindex conventions, programming +@cindex programming conventions +Usually when you write a function, you know how many names you intend to use for arguments and how many you intend to use as local variables. It is conventional to place some extra space between the arguments and -the local variables, to document how your function is supposed to be used. +the local variables, in order to document how your function is supposed to be used. @cindex variable shadowing During execution of the function body, the arguments and local variable @@ -10943,7 +13123,7 @@ values hide or @dfn{shadow} any variables of the same names used in the rest of the program. The shadowed variables are not accessible in the function definition, because there is no way to name them while their names have been taken away for the local variables. All other variables -used in the @code{awk} program can be referenced or set normally in the +used in the @command{awk} program can be referenced or set normally in the function's body. The arguments and local variables last only as long as the function body @@ -10952,19 +13132,20 @@ variables that were shadowed while the function was running. @cindex recursive function @cindex function, recursive -The function body can contain expressions which call functions. They +The function body can contain expressions that call functions. They can even call this function, either directly or by way of another function. When this happens, we say the function is @dfn{recursive}. +The act of a function calling itself is called @dfn{recursion}. -@cindex @code{awk} language, POSIX version -@cindex POSIX @code{awk} -In many @code{awk} implementations, including @code{gawk}, +@cindex @command{awk} language, POSIX version +@cindex POSIX @command{awk} +In many @command{awk} implementations, including @command{gawk}, the keyword @code{function} may be abbreviated @code{func}. However, POSIX only specifies the use of the keyword @code{function}. This actually has some practical implications. -If @code{gawk} is in POSIX-compatibility mode -(@pxref{Options, ,Command Line Options}), then the following -statement will @emph{not} define a function: +If @command{gawk} is in POSIX-compatibility mode +(@pxref{Options, ,Command-Line Options}), then the following +statement does @emph{not} define a function: @example func foo() @{ a = sqrt($1) ; print a @} @@ -10974,19 +13155,20 @@ func foo() @{ a = sqrt($1) ; print a @} Instead it defines a rule that, for each record, concatenates the value of the variable @samp{func} with the return value of the function @samp{foo}. If the resulting string is non-null, the action is executed. -This is probably not what was desired. (@code{awk} accepts this input as -syntactically valid, since functions may be used before they are defined -in @code{awk} programs.) +This is probably not what is desired. (@command{awk} accepts this input as +syntactically valid, because functions may be used before they are defined +in @command{awk} programs.) +@c NEXT ED: This won't actually run, since foo() is undefined ... @cindex portability issues -To ensure that your @code{awk} programs are portable, always use the +To ensure that your @command{awk} programs are portable, always use the keyword @code{function} when defining a function. @node Function Example, Function Caveats, Definition Syntax, User-defined -@section Function Definition Examples +@subsection Function Definition Examples Here is an example of a user-defined function, called @code{myprint}, that -takes a number and prints it in a specific format. +takes a number and prints it in a specific format: @example function myprint(num) @@ -10996,7 +13178,7 @@ function myprint(num) @end example @noindent -To illustrate, here is an @code{awk} rule which uses our @code{myprint} +To illustrate, here is an @command{awk} rule that uses our @code{myprint} function: @example @@ -11005,14 +13187,12 @@ $3 > 0 @{ myprint($3) @} @noindent This program prints, in our special format, all the third fields that -contain a positive number in our input. Therefore, when given: +contain a positive number in our input. Therefore, when given the following: @example -@group 1.2 3.4 5.6 7.8 9.10 11.12 -13.14 15.16 17.18 19.20 21.22 23.24 -@end group @end example @noindent @@ -11023,7 +13203,8 @@ this program, using our function to format the results, prints: 21.2 @end example -This function deletes all the elements in an array. +@page +This function deletes all the elements in an array: @example function delarray(a, i) @@ -11037,13 +13218,16 @@ When working with arrays, it is often necessary to delete all the elements in an array and start over with a new list of elements (@pxref{Delete, ,The @code{delete} Statement}). Instead of having -to repeat this loop everywhere in your program that you need to clear out +to repeat this loop everywhere that you need to clear out an array, your program can just call @code{delarray}. -(This guarantees portability. The usage @samp{delete @var{array}} to delete +(This guarantees portability. The use of @samp{delete @var{array}} to delete the contents of an entire array is a non-standard extension.) -Here is an example of a recursive function. It takes a string -as an input parameter, and returns the string in backwards order. +The following is an example of a recursive function. It takes a string +as an input parameter and returns the string in backwards order. +Recursive functions must always have a test that stops the recursion. +In this case, the recursion terminates when the starting position +is zero; i.e., when there are no more characters left in the string. @example function rev(str, start) @@ -11055,7 +13239,7 @@ function rev(str, start) @} @end example -If this function is in a file named @file{rev.awk}, we can test it +If this function is in a file named @file{rev.awk}, it can be tested this way: @example @@ -11064,19 +13248,19 @@ $ echo "Don't Panic!" | @print{} !cinaP t'noD @end example -Here is an example that uses the built-in function @code{strftime}. -(@xref{Time Functions, ,Functions for Dealing with Time Stamps}, -for more information on @code{strftime}.) The C @code{ctime} function takes a timestamp and returns it in a string, -formatted in a well known fashion. Here is an @code{awk} version: +formatted in a well-known fashion. +The following example uses the built-in @code{strftime} function +(@pxref{Time Functions, ,Using @command{gawk}'s Timestamp Functions}) +to create an @command{awk} version of @code{ctime}: +@c FIXME: One day, change %d to %e, when C 99 is common. @example @c file eg/lib/ctime.awk # ctime.awk # # awk version of C ctime(3) function -@group function ctime(ts, format) @{ format = "%a %b %d %H:%M:%S %Z %Y" @@ -11085,23 +13269,20 @@ function ctime(ts, format) return strftime(format, ts) @} @c endfile -@end group @end example @node Function Caveats, Return Statement, Function Example, User-defined -@section Calling User-defined Functions +@subsection Calling User-Defined Functions -@cindex call by value -@cindex call by reference @cindex calling a function @cindex function call @dfn{Calling a function} means causing the function to run and do its job. -A function call is an expression, and its value is the value returned by +A function call is an expression and its value is the value returned by the function. A function call consists of the function name followed by the arguments -in parentheses. What you write in the call for the arguments are -@code{awk} expressions; each time the call is executed, these +in parentheses. @command{awk} expressions are what you write in the +call for the arguments. Each time the call is executed, these expressions are evaluated, and the values are the actual arguments. For example, here is a call to @code{foo} with three arguments (the first being a string concatenation): @@ -11110,9 +13291,9 @@ being a string concatenation): foo(x y, "lose", 4 * z) @end example -@strong{Caution:} whitespace characters (spaces and tabs) are not allowed +@strong{Caution:} Whitespace characters (spaces and tabs) are not allowed between the function name and the open-parenthesis of the argument list. -If you write whitespace by mistake, @code{awk} might think that you mean +If you write whitespace by mistake, @command{awk} might think that you mean to concatenate a variable with an expression in parentheses. However, it notices that you used a function name and not a variable name, and reports an error. @@ -11121,8 +13302,8 @@ an error. When a function is called, it is given a @emph{copy} of the values of its arguments. This is known as @dfn{call by value}. The caller may use a variable as the expression for the argument, but the called function -does not know this: it only knows what value the argument had. For -example, if you write this code: +does not know this---it only knows what value the argument had. For +example, if you write the following code: @example foo = "bar" @@ -11132,27 +13313,24 @@ z = myfunc(foo) @noindent then you should not think of the argument to @code{myfunc} as being ``the variable @code{foo}.'' Instead, think of the argument as the -string value, @code{"bar"}. - +string value @code{"bar"}. If the function @code{myfunc} alters the values of its local variables, this has no effect on any other variables. Thus, if @code{myfunc} does this: @example -@group function myfunc(str) @{ print str str = "zzz" print str @} -@end group @end example @noindent -to change its first argument variable @code{str}, this @emph{does not} +to change its first argument variable @code{str}, it @emph{does not} change the value of @code{foo} in the caller. The role of @code{foo} in -calling @code{myfunc} ended when its value, @code{"bar"}, was computed. +calling @code{myfunc} ended when its value (@code{"bar"}) was computed. If @code{str} also exists outside of @code{myfunc}, the function body cannot alter this outer value, because it is shadowed during the execution of @code{myfunc} and cannot be seen or changed from there. @@ -11162,23 +13340,17 @@ However, when arrays are the parameters to functions, they are @emph{not} copied. Instead, the array itself is made available for direct manipulation by the function. This is usually called @dfn{call by reference}. Changes made to an array parameter inside the body of a function @emph{are} -visible outside that function. -@ifinfo -This can be @strong{very} dangerous if you do not watch what you are -doing. For example: -@end ifinfo -@iftex -@emph{This can be very dangerous if you do not watch what you are -doing.} For example: -@end iftex +visible outside that function. + +@strong{Note:} Changing an array parameter inside a function +can be very dangerous if you do not watch what you are doing. +For example: @example -@group function changeit(array, ind, nvalue) @{ array[ind] = nvalue @} -@end group BEGIN @{ a[1] = 1; a[2] = 2; a[3] = 3 @@ -11194,12 +13366,11 @@ This program prints @samp{a[1] = 1, a[2] = two, a[3] = 3}, because @cindex undefined functions @cindex functions, undefined -Some @code{awk} implementations allow you to call a function that -has not been defined, and only report a problem at run-time when the +Some @command{awk} implementations allow you to call a function that +has not been defined. They only report a problem at runtime when the program actually tries to call the function. For example: @example -@group BEGIN @{ if (0) foo() @@ -11208,36 +13379,32 @@ BEGIN @{ @} function bar() @{ @dots{} @} # note that `foo' is not defined -@end group @end example @noindent -Since the @samp{if} statement will never be true, it is not really a +Because the @samp{if} statement will never be true, it is not really a problem that @code{foo} has not been defined. Usually though, it is a problem if a program calls an undefined function. -@ignore -At one point, I had gawk dieing on this, but later decided that this might -break old programs and/or test suites. -@end ignore - -If @samp{--lint} has been specified -(@pxref{Options, ,Command Line Options}), -@code{gawk} will report about calls to undefined functions. +@cindex lint checks +If @option{--lint} is specified +(@pxref{Options, ,Command-Line Options}), +@command{gawk} reports calls to undefined functions. -Some @code{awk} implementations generate a run-time +@cindex portability issues +Some @command{awk} implementations generate a runtime error if you use the @code{next} statement (@pxref{Next Statement, , The @code{next} Statement}) inside a user-defined function. -@code{gawk} does not have this problem. +@command{gawk} does not have this limitation. -@node Return Statement, , Function Caveats, User-defined -@section The @code{return} Statement +@node Return Statement, Dynamic Typing, Function Caveats, User-defined +@subsection The @code{return} Statement @cindex @code{return} statement The body of a user-defined function can contain a @code{return} statement. -This statement returns control to the rest of the @code{awk} program. It -can also be used to return a value for use in the rest of the @code{awk} +This statement returns control to the calling part of the @command{awk} program. It +can also be used to return a value for use in the rest of the @command{awk} program. It looks like this: @example @@ -11245,24 +13412,23 @@ return @r{[}@var{expression}@r{]} @end example The @var{expression} part is optional. If it is omitted, then the returned -value is undefined and, therefore, unpredictable. +value is undefined, and therefore, unpredictable. A @code{return} statement with no value expression is assumed at the end of every function definition. So if control reaches the end of the function -body, then the function returns an unpredictable value. @code{awk} -will @emph{not} warn you if you use the return value of such a function. +body, then the function returns an unpredictable value. @command{awk} +does @emph{not} warn you if you use the return value of such a function. Sometimes, you want to write a function for what it does, not for what it returns. Such a function corresponds to a @code{void} function in C or to a @code{procedure} in Pascal. Thus, it may be appropriate to not -return any value; you should simply bear in mind that if you use the return +return any value; simply bear in mind that if you use the return value of such a function, you do so at your own risk. -Here is an example of a user-defined function that returns a value +The following is an example of a user-defined function that returns a value for the largest number among the elements of an array: @example -@group function maxelt(vec, i, ret) @{ for (i in vec) @{ @@ -11271,9 +13437,10 @@ function maxelt(vec, i, ret) @} return ret @} -@end group @end example +@cindex conventions, programming +@cindex programming conventions @noindent You call @code{maxelt} with one argument, which is an array name. The local variables @code{i} and @code{ret} are not intended to be arguments; @@ -11283,13 +13450,11 @@ to @code{maxelt}, the results would be strange. The extra space before @code{ret} are not supposed to be arguments. This is a convention that you should follow when you define functions. -Here is a program that uses our @code{maxelt} function. It loads an +The following program uses the @code{maxelt} function. It loads an array, calls @code{maxelt}, and then reports the maximum number in that array: @example -@group -awk ' function maxelt(vec, i, ret) @{ for (i in vec) @{ @@ -11298,9 +13463,7 @@ function maxelt(vec, i, ret) @} return ret @} -@end group -@group # Load all fields of each record into nums. @{ for(i = 1; i <= NF; i++) @@ -11309,7334 +13472,8069 @@ function maxelt(vec, i, ret) END @{ print maxelt(nums) -@}' -@end group +@} @end example Given the following input: @example -@group 1 5 23 8 16 44 3 5 2 8 26 256 291 1396 2962 100 -6 467 998 1101 99385 11 0 225 -@end group @end example @noindent -our program tells us (predictably) that @code{99385} is the largest number -in our array. - -@node Invoking Gawk, Library Functions, User-defined, Top -@chapter Running @code{awk} -@cindex command line -@cindex invocation of @code{gawk} -@cindex arguments, command line -@cindex options, command line -@cindex long options -@cindex options, long +the program reports (predictably) that @code{99385} is the largest number +in the array. -There are two ways to run @code{awk}: with an explicit program, or with -one or more program files. Here are templates for both of them; items -enclosed in @samp{@r{[}@dots{}@r{]}} in these templates are optional. +@node Dynamic Typing, , Return Statement, User-defined +@subsection Functions and Their Effect on Variable Typing -Besides traditional one-letter POSIX-style options, @code{gawk} also -supports GNU long options. +@command{awk} is a very fluid language. +It is possible that @command{awk} can't tell if an identifier +represents a regular variable or an array until runtime. +Here is an annotated sample program: @example -awk @r{[@var{options}]} -f progfile @r{[@code{--}]} @var{file} @dots{} -awk @r{[@var{options}]} @r{[@code{--}]} '@var{program}' @var{file} @dots{} -@end example +function foo(a) +@{ + a[1] = 1 # parameter is an array +@} -@cindex empty program -@cindex dark corner -It is possible to invoke @code{awk} with an empty program: +BEGIN @{ + b = 1 + foo(b) # invalid: fatal type mismatch -@example -$ awk '' datafile1 datafile2 + foo(x) # x uninitialized, becomes an array dynamically + x = 1 # now not allowed, runtime error +@} @end example -@noindent -Doing so makes little sense though; @code{awk} will simply exit -silently when given an empty program (d.c.). If @samp{--lint} has -been specified on the command line, @code{gawk} will issue a -warning that the program is empty. +Usually, such things aren't a big issue, but it's worth +being aware of them. + +@node Internationalization, Advanced Features, Functions, Top +@chapter Internationalization with @command{gawk} + +Once upon a time, computer makers +wrote software that only worked in English. +Eventually, hardware and software vendors noticed that if their +systems worked in the native languages of non-English-speaking +countries, they were able to sell more systems. +As a result, internationalization and localization +of programs and software systems became a common practice. + +@cindex internationalization features in @command{gawk} +Until recently, the ability to provide internationalization +was largely restricted to programs written in C and C++. +This @value{CHAPTER} describes the underlying library @command{gawk} +uses for internationalization, as well as how +@command{gawk} makes internationalization +features available at the @command{awk} program level. +Having internationalization available at the @command{awk} level +gives software developers additional flexibility---they are no +longer required to write in C when internationalization is +a requirement. @menu -* Options:: Command line options and their meanings. -* Other Arguments:: Input file names and variable assignments. -* AWKPATH Variable:: Searching directories for @code{awk} programs. -* Obsolete:: Obsolete Options and/or features. -* Undocumented:: Undocumented Options and Features. -* Known Bugs:: Known Bugs in @code{gawk}. +* I18N and L10N:: Internationalization and Localization. +* Explaining gettext:: How GNU @code{gettext} works. +* Programmer i18n:: Features for the programmer. +* Translator i18n:: Features for the translator. +* I18N Example:: A simple i18n example. +* Gawk I18N:: @command{gawk} is also internationalized. @end menu -@node Options, Other Arguments, Invoking Gawk, Invoking Gawk -@section Command Line Options +@node I18N and L10N, Explaining gettext, Internationalization, Internationalization +@section Internationalization and Localization + +@cindex internationalization +@cindex localization +@dfn{Internationalization} means writing (or modifying) a program once, +in such a way that it can use multiple languages without requiring +further source code changes. +@dfn{Localization} means providing the data necessary for an +internationalized program to work in a particular language. +Most typically, these terms refer to features such as the language +used for printing error messages, the language used to read +responses, and information related to how numerical and +monetary values are printed and read. + +@node Explaining gettext, Programmer i18n, I18N and L10N, Internationalization +@section GNU @code{gettext} + +@cindex @code{gettext}, how it works +@cindex internationalizing a program +The facilities in GNU @code{gettext} focus on messages; strings printed +by a program, either directly or via formatting with @code{printf} or +@code{sprintf}.@footnote{For some operating systems, the @command{gawk} +port doesn't support GNU @code{gettext}. This applies most notably to +the PC operating systems. As such, these features are not available +if you are using one of those operating systems. Sorry.} + +When using GNU @code{gettext}, each application has its own +@dfn{text domain}. This is a unique name such as @samp{kpilot} or @samp{gawk}, +that identifies the application. +A complete application may have multiple components---programs written +in C or C++, as well as scripts written in @command{sh} or @command{awk}. +All of the components use the same text domain. + +To make the discussion concrete, assume we're writing an application +named @command{guide}. Internationalization consists of the +following steps, in this order: -Options begin with a dash, and consist of a single character. -GNU style long options consist of two dashes and a keyword. -The keyword can be abbreviated, as long the abbreviation allows the option -to be uniquely identified. If the option takes an argument, then the -keyword is either immediately followed by an equals sign (@samp{=}) and the -argument's value, or the keyword and the argument's value are separated -by whitespace. For brevity, the discussion below only refers to the -traditional short options; however the long and short options are -interchangeable in all contexts. +@enumerate +@item +The programmer goes +through the source for all of @command{guide}'s components +and marks each string that is a candidate for translation. +For example, @code{"`-F': option required"} is a good candidate for translation. +A table with strings of option names is not (e.g., @command{gawk}'s +@option{--profile} option should remain the same, no matter what the local +language). + +@cindex @code{textdomain} C library function +@item +The programmer indicates the application's text domain +(@code{"guide"}) to the @code{gettext} library, +by calling the @code{textdomain} function. -Each long option for @code{gawk} has a corresponding -POSIX-style option. The options and their meanings are as follows: +@item +Messages from the application are extracted from the source code and +collected into a Portable Object file (@file{guide.po}), +which lists the strings and their translations. +The translations are initially empty. +The original (usually English) messages serve as the key for +lookup of the translations. + +@cindex portable object files (@code{gettext}) +@item +For each language with a translator, @file{guide.po} +is copied and translations are created and shipped with the application. -@table @code -@item -F @var{fs} -@itemx --field-separator @var{fs} -@cindex @code{-F} option -@cindex @code{--field-separator} option -Sets the @code{FS} variable to @var{fs} -(@pxref{Field Separators, ,Specifying How Fields are Separated}). +@cindex message object files (@code{gettext}) +@item +Each language's @file{.po} file is converted into a binary +message object (@file{.mo}) file. +A message object file contains the original messages and their +translations in a binary format that allows fast lookup of translations +at runtime. -@item -f @var{source-file} -@itemx --file @var{source-file} -@cindex @code{-f} option -@cindex @code{--file} option -Indicates that the @code{awk} program is to be found in @var{source-file} -instead of in the first non-option argument. +@item +When @command{guide} is built and installed, the binary translation files +are installed in a standard place. -@item -v @var{var}=@var{val} -@itemx --assign @var{var}=@var{val} -@cindex @code{-v} option -@cindex @code{--assign} option -Sets the variable @var{var} to the value @var{val} @strong{before} -execution of the program begins. Such variable values are available -inside the @code{BEGIN} rule -(@pxref{Other Arguments, ,Other Command Line Arguments}). +@cindex @code{bindtextdomain} C library function +@item +For testing and development, it is possible to tell @code{gettext} +to use @file{.mo} files in a different directory than the standard +one by using the @code{bindtextdomain} function. -The @samp{-v} option can only set one variable, but you can use -it more than once, setting another variable each time, like this: -@samp{awk @w{-v foo=1} @w{-v bar=2} @dots{}}. +@item +At runtime, @command{guide} looks up each string via a call +to @code{gettext}. The returned string is the translated string +if available, or the original string if not. -@strong{Caution:} Using @samp{-v} to set the values of the builtin -variables may lead to suprising results. @code{awk} will reset the -values of those variables as it needs to, possibly ignoring any -predefined value you may have given. +@item +If necessary, it is possible to access messages from a different +text domain than the one belonging to the application, without +having to switch the application's default text domain back +and forth. +@end enumerate -@item -mf @var{NNN} -@itemx -mr @var{NNN} -Set various memory limits to the value @var{NNN}. The @samp{f} flag sets -the maximum number of fields, and the @samp{r} flag sets the maximum -record size. These two flags and the @samp{-m} option are from the -Bell Labs research version of Unix @code{awk}. They are provided -for compatibility, but otherwise ignored by -@code{gawk}, since @code{gawk} has no predefined limits. +@cindex @code{gettext} C library function +In C (or C++), the string marking and dynamic translation lookup +are accomplished by wrapping each string in a call to @code{gettext}: -@item -W @var{gawk-opt} -@cindex @code{-W} option -Following the POSIX standard, options that are implementation -specific are supplied as arguments to the @samp{-W} option. These options -also have corresponding GNU style long options. -See below. +@example +printf(gettext("Don't Panic!\n")); +@end example -@item -- -Signals the end of the command line options. The following arguments -are not treated as options even if they begin with @samp{-}. This -interpretation of @samp{--} follows the POSIX argument parsing -conventions. +The tools that extract messages from source code pull out all +strings enclosed in calls to @code{gettext}. -This is useful if you have file names that start with @samp{-}, -or in shell scripts, if you have file names that will be specified -by the user which could start with @samp{-}. -@end table +@cindex @code{_} C macro (@code{gettext}) +The GNU @code{gettext} developers, recognizing that typing +@samp{gettext} over and over again is both painful and ugly to look +at, use the macro @samp{_} (an underscore) to make things easier: -The following @code{gawk}-specific options are available: +@example +/* In the standard header file: */ +#define _(str) gettext(str) -@table @code -@item -W traditional -@itemx -W compat -@itemx --traditional -@itemx --compat -@cindex @code{--compat} option -@cindex @code{--traditional} option -@cindex compatibility mode -Specifies @dfn{compatibility mode}, in which the GNU extensions to -the @code{awk} language are disabled, so that @code{gawk} behaves just -like the Bell Labs research version of Unix @code{awk}. -@samp{--traditional} is the preferred form of this option. -@xref{POSIX/GNU, ,Extensions in @code{gawk} Not in POSIX @code{awk}}, -which summarizes the extensions. Also see -@ref{Compatibility Mode, ,Downward Compatibility and Debugging}. +/* In the program text: */ +printf(_("Don't Panic!\n")); +@end example -@item -W copyleft -@itemx -W copyright -@itemx --copyleft -@itemx --copyright -@cindex @code{--copyleft} option -@cindex @code{--copyright} option -Print the short version of the General Public License, and then exit. -This option may disappear in a future version of @code{gawk}. +@cindex locale categories +@noindent +This reduces the typing overhead to just three extra characters per string +and is considerably easier to read as well. +There are locale @dfn{categories} +for different types of locale-related information. +The defined locale categories that @code{gettext} knows about are: -@item -W help -@itemx -W usage -@itemx --help -@itemx --usage -@cindex @code{--help} option -@cindex @code{--usage} option -Print a ``usage'' message summarizing the short and long style options -that @code{gawk} accepts, and then exit. +@table @code +@cindex @code{LC_MESSAGES} locale category +@item LC_MESSAGES +Text messages. This is the default category for @code{gettext} +operations, but it is possible to supply a different one explicitly, +if necessary. (It is almost never necessary to supply a different category.) + +@cindex @code{LC_COLLATE} locale category +@item LC_COLLATE +Text collation information; i.e., how different characters +and/or groups of characters sort in a given language. + +@cindex @code{LC_CTYPE} locale category +@item LC_CTYPE +Character type information (alphabetic, digit, upper- or lowercase, and +so on). +This information is accessed via the +POSIX character classes in regular expressions, +such as @code{/[[:alnum:]]/} +(@pxref{Regexp Operators, ,Regular Expression Operators}). + +@cindex @code{LC_MONETARY} locale category +@item LC_MONETARY +Monetary information, such as the currency symbol, and whether the +symbol goes before or after a number. + +@cindex @code{LC_NUMERIC} locale category +@item LC_NUMERIC +Numeric information, such as which characters to use for the decimal +point and the thousands separator.@footnote{Americans +use a comma every three decimal places and a period for the decimal +point, while many Europeans do exactly the opposite: +@code{1,234.56} vs.@: @code{1.234,56}.} + +@cindex @code{LC_RESPONSE} locale category +@item LC_RESPONSE +Response information, such as how ``yes'' and ``no'' appear in the +local language, and possibly other information as well. + +@cindex @code{LC_TIME} locale category +@item LC_TIME +Time and date related information, such as 12- or 24-hour clock, month printed +before or after day in a date, local month abbreviations, and so on. + +@cindex @code{LC_ALL} locale category +@item LC_ALL +All of the above. (Not too useful in the context of @code{gettext}.) +@end table -@item -W lint -@itemx --lint -@cindex @code{--lint} option -Warn about constructs that are dubious or non-portable to -other @code{awk} implementations. -Some warnings are issued when @code{gawk} first reads your program. Others -are issued at run-time, as your program executes. +@node Programmer i18n, Translator i18n, Explaining gettext, Internationalization +@section Internationalizing @command{awk} Programs -@item -W lint-old -@itemx --lint-old -@cindex @code{--lint-old} option -Warn about constructs that are not available in -the original Version 7 Unix version of @code{awk} -(@pxref{V7/SVR3.1, , Major Changes between V7 and SVR3.1}). +@command{gawk} provides the following variables and functions for +internationalization: -@item -W posix -@itemx --posix -@cindex @code{--posix} option -@cindex POSIX mode -Operate in strict POSIX mode. This disables all @code{gawk} -extensions (just like @samp{--traditional}), and adds the following additional -restrictions: +@table @code +@cindex @code{TEXTDOMAIN} variable +@item TEXTDOMAIN +This variable indicates the application's text domain. +For compatibility with GNU @code{gettext}, the default +value is @code{"messages"}. + +@cindex internationalization, marked strings +@cindex marked strings for internationalization +@item _"your message here" +String constants marked with a leading underscore +are candidates for translation at runtime. +String constants without a leading underscore are not translated. + +@cindex @code{dcgettext} built-in function +@item dcgettext(@var{string} @r{[}, @var{domain} @r{[}, @var{category}@r{]]}) +This built-in function returns the translation of @var{string} in +text domain @var{domain} for locale category @var{category}. +The default value for @var{domain} is the current value of @code{TEXTDOMAIN}. +The default value for @var{category} is @code{"LC_MESSAGES"}. + +If you supply a value for @var{category}, it must be a string equal to +one of the known locale categories described in +@ifnotinfo +the previous @value{SECTION}. +@end ifnotinfo +@ifinfo +@ref{Explaining gettext, ,GNU @code{gettext}}. +@end ifinfo +You must also supply a text domain. Use @code{TEXTDOMAIN} if +you want to use the current domain. + +@strong{Caution:} The order of arguments to the @command{awk} version +of the @code{dcgettext} function is purposely different from the order for +the C version. The @command{awk} version's order was +chosen to be simple and to allow for reasonable @command{awk}-style +default arguments. + +@cindex @code{bindtextdomain} built-in function +@item bindtextdomain(@var{directory} @r{[}, @var{domain}@r{]}) +This built-in function allows you to specify the directory where +@code{gettext} looks for @file{.mo} files, in case they +will not or cannot be placed in the standard locations +(e.g., during testing). +It returns the directory where @var{domain} is ``bound.'' + +The default @var{domain} is the value of @code{TEXTDOMAIN}. +If @var{directory} is the null string (@code{""}), then +@code{bindtextdomain} returns the current binding for the +given @var{domain}. +@end table -@c IMPORTANT! Keep this list in sync with the one in node POSIX +To use these facilities in your @command{awk} program, follow the steps +outlined in +@ifnotinfo +the previous @value{SECTION}, +@end ifnotinfo +@ifinfo +@ref{Explaining gettext, ,GNU @code{gettext}}, +@end ifinfo +like so: -@itemize @bullet +@enumerate @item -@code{\x} escape sequences are not recognized -(@pxref{Escape Sequences}). +Set the variable @code{TEXTDOMAIN} to the text domain of +your program. This is best done in a @code{BEGIN} rule +(@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}), +or it can also be done via the @option{-v} command-line +option (@pxref{Options, ,Command-Line Options}): -@item -Newlines do not act as whitespace to separate fields when @code{FS} is -equal to a single space. +@example +BEGIN @{ + TEXTDOMAIN = "guide" + @dots{} +@} +@end example @item -The synonym @code{func} for the keyword @code{function} is not -recognized (@pxref{Definition Syntax, ,Function Definition Syntax}). +Mark all translatable strings with a leading underscore (@samp{_}) +character. It @emph{must} be adjacent to the opening +quote of the string. For example: -@item -The operators @samp{**} and @samp{**=} cannot be used in -place of @samp{^} and @samp{^=} (@pxref{Arithmetic Ops, ,Arithmetic Operators}, -and also @pxref{Assignment Ops, ,Assignment Expressions}). +@example +print _"hello, world" +x = _"you goofed" +printf(_"Number of users is %d\n", nusers) +@end example @item -Specifying @samp{-Ft} on the command line does not set the value -of @code{FS} to be a single tab character -(@pxref{Field Separators, ,Specifying How Fields are Separated}). +If you are creating strings dynamically, you can +still translate them, using the @code{dcgettext} +built-in function. + +@example +message = nusers " users logged in" +message = dcgettext(message, "adminprog") +print message +@end example + +Here, the call to @code{dcgettext} supplies a different +text domain (@code{"adminprog"}) in which to find the +message, but it uses the default @code{"LC_MESSAGES"} category. @item -The @code{fflush} built-in function is not supported -(@pxref{I/O Functions, , Built-in Functions for Input/Output}). -@end itemize +During development, you might want to put the @file{.mo} +file in a private directory for testing. This is done +with the @code{bindtextdomain} built-in function: -If you supply both @samp{--traditional} and @samp{--posix} on the -command line, @samp{--posix} will take precedence. @code{gawk} -will also issue a warning if both options are supplied. +@example +BEGIN @{ + TEXTDOMAIN = "guide" # our text domain + if (Testing) @{ + # where to find our files + bindtextdomain("testdir") + # joe is in charge of adminprog + bindtextdomain("../joe/testdir", "adminprog") + @} + @dots{} +@} +@end example -@item -W re-interval -@itemx --re-interval -Allow interval expressions -(@pxref{Regexp Operators, , Regular Expression Operators}), -in regexps. -Because interval expressions were traditionally not available in @code{awk}, -@code{gawk} does not provide them by default. This prevents old @code{awk} -programs from breaking. +@end enumerate -@item -W source @var{program-text} -@itemx --source @var{program-text} -@cindex @code{--source} option -Program source code is taken from the @var{program-text}. This option -allows you to mix source code in files with source -code that you enter on the command line. This is particularly useful -when you have library functions that you wish to use from your command line -programs (@pxref{AWKPATH Variable, ,The @code{AWKPATH} Environment Variable}). +@xref{I18N Example, ,A Simple Internationalization Example}, +for an example program showing the steps necessary to create +and use translations from @command{awk}. -@item -W version -@itemx --version -@cindex @code{--version} option -Prints version information for this particular copy of @code{gawk}. -This allows you to determine if your copy of @code{gawk} is up to date -with respect to whatever the Free Software Foundation is currently -distributing. -It is also useful for bug reports -(@pxref{Bugs, , Reporting Problems and Bugs}). -@end table +@node Translator i18n, I18N Example, Programmer i18n, Internationalization +@section Translating @command{awk} Programs -Any other options are flagged as invalid with a warning message, but -are otherwise ignored. +Once a program's translatable strings have been marked, they must +be extracted to create the initial @file{.po} file. +As part of translation, it is often helpful to rearrange the order +in which arguments to @code{printf} are output. -In compatibility mode, as a special case, if the value of @var{fs} supplied -to the @samp{-F} option is @samp{t}, then @code{FS} is set to the tab -character (@code{"\t"}). This is only true for @samp{--traditional}, and not -for @samp{--posix} -(@pxref{Field Separators, ,Specifying How Fields are Separated}). +@command{gawk}'s @option{--gen-po} command-line option extracts +the messages and is discussed next. +After that, @code{printf}'s ability to +rearrange the order for @code{printf} arguments at runtime +is covered. -The @samp{-f} option may be used more than once on the command line. -If it is, @code{awk} reads its program source from all of the named files, as -if they had been concatenated together into one big file. This is -useful for creating libraries of @code{awk} functions. Useful functions -can be written once, and then retrieved from a standard place, instead -of having to be included into each individual program. +@menu +* String Extraction:: Extracting marked strings. +* Printf Ordering:: Rearranging @code{printf} arguments. +* I18N Portability:: @command{awk}-level portability issues. +@end menu -You can type in a program at the terminal and still use library functions, -by specifying @samp{-f /dev/tty}. @code{awk} will read a file from the terminal -to use as part of the @code{awk} program. After typing your program, -type @kbd{Control-d} (the end-of-file character) to terminate it. -(You may also use @samp{-f -} to read program source from the standard -input, but then you will not be able to also use the standard input as a -source of data.) +@node String Extraction, Printf Ordering, Translator i18n, Translator i18n +@subsection Extracting Marked Strings +@cindex string extraction (internationalization) +@cindex marked string extraction (internationalization) +@cindex extraction, of marked strings (internationalization) -Because it is clumsy using the standard @code{awk} mechanisms to mix source -file and command line @code{awk} programs, @code{gawk} provides the -@samp{--source} option. This does not require you to pre-empt the standard -input for your source code, and allows you to easily mix command line -and library source code -(@pxref{AWKPATH Variable, ,The @code{AWKPATH} Environment Variable}). +@cindex @code{--gen-po} option +@cindex command-line option, @code{--gen-po} +Once your @command{awk} program is working, and all the strings have +been marked and you've set (and perhaps bound) the text domain, +it is time to produce translations. +First, use the @option{--gen-po} command-line option to create +the initial @file{.po} file: -If no @samp{-f} or @samp{--source} option is specified, then @code{gawk} -will use the first non-option command line argument as the text of the -program source code. +@example +$ gawk --gen-po -f guide.awk > guide.po +@end example -@cindex @code{POSIXLY_CORRECT} environment variable -@cindex environment variable, @code{POSIXLY_CORRECT} -If the environment variable @code{POSIXLY_CORRECT} exists, -then @code{gawk} will behave in strict POSIX mode, exactly as if -you had supplied the @samp{--posix} command line option. -Many GNU programs look for this environment variable to turn on -strict POSIX mode. If you supply @samp{--lint} on the command line, -and @code{gawk} turns on POSIX mode because of @code{POSIXLY_CORRECT}, -then it will print a warning message indicating that POSIX -mode is in effect. +@cindex @code{xgettext} utility +When run with @option{--gen-po}, @command{gawk} does not execute your +program. Instead, it parses it as usual and prints all marked strings +to standard output in the format of a GNU @code{gettext} Portable Object +file. Also included in the output are any constant strings that +appear as the first argument to @code{dcgettext}.@footnote{Eventually, +the @command{xgettext} utility that comes with GNU @code{gettext} will be +taught to automatically run @samp{gawk --gen-po} for @file{.awk} files, +freeing the translator from having to do it manually.} +@xref{I18N Example, ,A Simple Internationalization Example}, +for the full list of steps to go through to create and test +translations for @command{guide}. -You would typically set this variable in your shell's startup file. -For a Bourne compatible shell (such as Bash), you would add these -lines to the @file{.profile} file in your home directory. +@node Printf Ordering, I18N Portability, String Extraction, Translator i18n +@subsection Rearranging @code{printf} Arguments +@cindex @code{printf}, positional specifier +@cindex positional specifier, @code{printf} +Format strings for @code{printf} and @code{sprintf} +(@pxref{Printf, ,Using @code{printf} Statements for Fancier Printing}) +present a special problem for translation. +Consider the following:@footnote{This example is borrowed +from the GNU @code{gettext} manual.} + +@c line broken here only for smallbook format @example -@group -POSIXLY_CORRECT=true -export POSIXLY_CORRECT -@end group +printf(_"String `%s' has %d characters\n", + string, length(string))) @end example -For a @code{csh} compatible shell,@footnote{Not recommended.} -you would add this line to the @file{.login} file in your home directory. +A possible German translation for this might be: @example -setenv POSIXLY_CORRECT true +"%d Zeichen lang ist die Zeichenkette `%s'\n" @end example -@node Other Arguments, AWKPATH Variable, Options, Invoking Gawk -@section Other Command Line Arguments +The problem should be obvious: the order of the format +specifications is different from the original! +Even though @code{gettext} can return the translated string +at runtime, +it cannot change the argument order in the call to @code{printf}. -Any additional arguments on the command line are normally treated as -input files to be processed in the order specified. However, an -argument that has the form @code{@var{var}=@var{value}}, assigns -the value @var{value} to the variable @var{var}---it does not specify a -file at all. +To solve this problem, @code{printf} format specificiers may have +an additional optional element, which we call a @dfn{positional specifier}. +For example: -@vindex ARGIND -@vindex ARGV -All these arguments are made available to your @code{awk} program in the -@code{ARGV} array (@pxref{Built-in Variables}). Command line options -and the program text (if present) are omitted from @code{ARGV}. -All other arguments, including variable assignments, are -included. As each element of @code{ARGV} is processed, @code{gawk} -sets the variable @code{ARGIND} to the index in @code{ARGV} of the -current element. +@example +"%2$d Zeichen lang ist die Zeichenkette `%1$s'\n" +@end example -The distinction between file name arguments and variable-assignment -arguments is made when @code{awk} is about to open the next input file. -At that point in execution, it checks the ``file name'' to see whether -it is really a variable assignment; if so, @code{awk} sets the variable -instead of reading a file. +Here, the positional specifier consists of an integer count, which indicates which +argument to use, and a @samp{$}. Counts are one-based, and the +format string itself is @emph{not} included. Thus, in the following +example, @samp{string} is the first argument and @samp{length(string)} is the second. -Therefore, the variables actually receive the given values after all -previously specified files have been read. In particular, the values of -variables assigned in this fashion are @emph{not} available inside a -@code{BEGIN} rule -(@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}), -since such rules are run before @code{awk} begins scanning the argument list. +@example +$ gawk 'BEGIN @{ +> string = "Dont Panic" +> printf _"%2$d characters live in \"%1$s\"\n", +> string, length(string) +> @}' +@print{} 10 characters live in "Dont Panic" +@end example -@cindex dark corner -The variable values given on the command line are processed for escape -sequences (d.c.) (@pxref{Escape Sequences}). - -In some earlier implementations of @code{awk}, when a variable assignment -occurred before any file names, the assignment would happen @emph{before} -the @code{BEGIN} rule was executed. @code{awk}'s behavior was thus -inconsistent; some command line assignments were available inside the -@code{BEGIN} rule, while others were not. However, -some applications came to depend -upon this ``feature.'' When @code{awk} was changed to be more consistent, -the @samp{-v} option was added to accommodate applications that depended -upon the old behavior. +If present, positional specifiers come first in the format specification, +before the flags, the field width, and/or the precision. -The variable assignment feature is most useful for assigning to variables -such as @code{RS}, @code{OFS}, and @code{ORS}, which control input and -output formats, before scanning the data files. It is also useful for -controlling state if multiple passes are needed over a data file. For -example: +Positional specifiers can be used with the dynamic field width and +precision capability: -@cindex multiple passes over data -@cindex passes, multiple @example -awk 'pass == 1 @{ @var{pass 1 stuff} @} - pass == 2 @{ @var{pass 2 stuff} @}' pass=1 mydata pass=2 mydata +$ gawk 'BEGIN @{ +> printf("%*.*s\n", 10, 20, "hello") +> printf("%3$*2$.*1$s\n", 20, 10, "hello") +> @}' +@print{} hello +@print{} hello @end example -Given the variable assignment feature, the @samp{-F} option for setting -the value of @code{FS} is not -strictly necessary. It remains for historical compatibility. - -@node AWKPATH Variable, Obsolete, Other Arguments, Invoking Gawk -@section The @code{AWKPATH} Environment Variable -@cindex @code{AWKPATH} environment variable -@cindex environment variable, @code{AWKPATH} -@cindex search path -@cindex directory search -@cindex path, search -@cindex differences between @code{gawk} and @code{awk} +@noindent +@strong{Note:} When using @samp{*} with a positional specifier, the @samp{*} +comes first, then the integer position, and then the @samp{$}. +This is somewhat counter-intutive. -The previous section described how @code{awk} program files can be named -on the command line with the @samp{-f} option. In most @code{awk} -implementations, you must supply a precise path name for each program -file, unless the file is in the current directory. +@cindex @code{printf}, mixing positional specifiers with regular formats +@cindex positional specifiers, mixing with regular formats (@code{printf}) +@cindex format specifiers, mixing regular with positional specifiers (@code{printf}) +@command{gawk} does not allow you to mix regular format specifiers +and those with positional specifiers in the same string: -@cindex search path, for source files -But in @code{gawk}, if the file name supplied to the @samp{-f} option -does not contain a @samp{/}, then @code{gawk} searches a list of -directories (called the @dfn{search path}), one by one, looking for a -file with the specified name. +@smallexample +$ gawk 'BEGIN @{ printf _"%d %3$s\n", 1, 2, "hi" @}' +@error{} gawk: cmd. line:1: fatal: must use `count$' on all formats or none +@end smallexample -The search path is a string consisting of directory names -separated by colons. @code{gawk} gets its search path from the -@code{AWKPATH} environment variable. If that variable does not exist, -@code{gawk} uses a default path, which is -@samp{.:/usr/local/share/awk}.@footnote{Your version of @code{gawk} -may use a different directory; it -will depend upon how @code{gawk} was built and installed. The actual -directory will be the value of @samp{$(datadir)} generated when -@code{gawk} was configured. You probably don't need to worry about this -though.} (Programs written for use by -system administrators should use an @code{AWKPATH} variable that -does not include the current directory, @file{.}.) +@strong{Note:} There are some pathological cases that @command{gawk} may fail to +diagnose. In such cases, the output may not be what you expect. +It's still a bad idea to try mixing them, even if @command{gawk} +doesn't detect it. -The search path feature is particularly useful for building up libraries -of useful @code{awk} functions. The library files can be placed in a -standard directory that is in the default path, and then specified on -the command line with a short file name. Otherwise, the full file name -would have to be typed for each file. +Although positional specifiers can be used directly in @command{awk} programs, +their primary purpose is to help in producing correct translations of +format strings into languages different from the one in which the program +is first written. -By using both the @samp{--source} and @samp{-f} options, your command line -@code{awk} programs can use facilities in @code{awk} library files. -@xref{Library Functions, , A Library of @code{awk} Functions}. +@node I18N Portability, , Printf Ordering, Translator i18n +@subsection @command{awk} Portability Issues -Path searching is not done if @code{gawk} is in compatibility mode. -This is true for both @samp{--traditional} and @samp{--posix}. -@xref{Options, ,Command Line Options}. +@cindex portability issues +@cindex portability issues, internationalization of @command{awk} programs +@cindex internationalization of @command{awk} programs, portability issues +@command{gawk}'s internationalization features were purposely chosen to +have as little impact as possible on the portability of @command{awk} +programs that use them to other versions of @command{awk}. +Consider this program: -@strong{Note:} if you want files in the current directory to be found, -you must include the current directory in the path, either by including -@file{.} explicitly in the path, or by writing a null entry in the -path. (A null entry is indicated by starting or ending the path with a -colon, or by placing two colons next to each other (@samp{::}).) If the -current directory is not included in the path, then files cannot be -found in the current directory. This path search mechanism is identical -to the shell's. -@c someday, @cite{The Bourne Again Shell}.... +@example +BEGIN @{ + TEXTDOMAIN = "guide" + if (Test_Guide) # set with -v + bindtextdomain("/test/guide/messages") + print _"don't panic!" +@} +@end example -Starting with version 3.0, if @code{AWKPATH} is not defined in the -environment, @code{gawk} will place its default search path into -@code{ENVIRON["AWKPATH"]}. This makes it easy to determine -the actual search path @code{gawk} will use. +@noindent +As written, it won't work on other versions of @command{awk}. +However, it is actually almost portable, requiring very little +change. -@node Obsolete, Undocumented, AWKPATH Variable, Invoking Gawk -@section Obsolete Options and/or Features +@itemize @bullet +@item +Assignments to @code{TEXTDOMAIN} won't have any effect, +since @code{TEXTDOMAIN} is not special in other @command{awk} implementations. -@cindex deprecated options -@cindex obsolete options -@cindex deprecated features -@cindex obsolete features -This section describes features and/or command line options from -previous releases of @code{gawk} that are either not available in the -current version, or that are still supported but deprecated (meaning that -they will @emph{not} be in the next release). +@item +Non-GNU versions of @command{awk} treat marked strings +as the concatenation of a variable named @code{_} with the string +following it.@footnote{This is good fodder for an ``Obfuscated +@command{awk}'' contest.} Typically, the variable @code{_} has +the null string (@code{""}) as its value, leaving the original string constant as +the result. -@c update this section for each release! +@item +By defining ``dummy'' functions to replace @code{dcgettext} +and @code{bindtextdomain}, the @command{awk} program can be made to run, but +all the messages are output in the original language. +For example: -For version @value{VERSION}.@value{PATCHLEVEL} of @code{gawk}, there are no -command line options -or other deprecated features from the previous version of @code{gawk}. -@iftex -This section -@end iftex -@ifinfo -This node -@end ifinfo -is thus essentially a place holder, -in case some option becomes obsolete in a future version of @code{gawk}. +@cindex @code{bindtextdomain} user-defined function +@cindex @code{dcgettext} user-defined function +@example +@c file eg/lib/libintl.awk +function bindtextdomain(dir, domain) +@{ + return dir +@} -@ignore -@c This is pretty old news... -The public-domain version of @code{strftime} that is distributed with -@code{gawk} changed for the 2.14 release. The @samp{%V} conversion specifier -that used to generate the date in VMS format was changed to @samp{%v}. -This is because the POSIX standard for the @code{date} utility now -specifies a @samp{%V} conversion specifier. -@xref{Time Functions, ,Functions for Dealing with Time Stamps}, for details. -@end ignore +function dcgettext(string, domain, category) +@{ + return string +@} +@c endfile +@end example -@node Undocumented, Known Bugs, Obsolete, Invoking Gawk -@section Undocumented Options and Features -@cindex undocumented features -@display -@i{Use the Source, Luke!} -Obi-Wan -@end display -@sp 1 +@item +The use of positional specifications in @code{printf} or +@code{sprintf} is @emph{not} portable. +To support @code{gettext} at the C level, many systems' C versions of +@code{sprintf} do support positional specifiers. But it works only if +enough arguments are supplied in the function call. Many versions of +@command{awk} pass @code{printf} formats and arguments unchanged to the +underlying C library version of @code{sprintf}, but only one format and +argument at a time. What happens if a positional specification is +used is anybody's guess. +However, since the positional specifications are primarily for use in +@emph{translated} format strings, and since non-GNU @command{awk}s never +retrieve the translated string, this should not be a problem in practice. +@end itemize -This section intentionally left blank. +@node I18N Example, Gawk I18N, Translator i18n, Internationalization +@section A Simple Internationalization Example -@c Read The Source, Luke! +Now let's look at a step-by-step example of how to internationalize and +localize a simple @command{awk} program, using @file{guide.awk} as our +original source: -@ignore -@c If these came out in the Info file or TeX document, then they wouldn't -@c be undocumented, would they? +@example +@c file eg/prog/guide.awk +BEGIN @{ + TEXTDOMAIN = "guide" + bindtextdomain(".") # for testing + print _"Don't Panic" + print _"The Answer Is", 42 + print "Pardon me, Zaphod who?" +@} +@c endfile +@end example -@code{gawk} has one undocumented option: +@noindent +Run @samp{gawk --gen-po} to create the @file{.po} file: -@table @code -@item -W nostalgia -@itemx --nostalgia -Print the message @code{"awk: bailing out near line 1"} and dump core. -This option was inspired by the common behavior of very early versions of -Unix @code{awk}, and by a t--shirt. -@end table +@example +$ gawk --gen-po -f guide.awk > guide.po +@end example -Early versions of @code{awk} used to not require any separator (either -a newline or @samp{;}) between the rules in @code{awk} programs. Thus, -it was common to see one-line programs like: +@noindent +This produces: @example -awk '@{ sum += $1 @} END @{ print sum @}' +@c file eg/data/guide.po +#: guide.awk:4 +msgid "Don't Panic" +msgstr "" + +#: guide.awk:5 +msgid "The Answer Is" +msgstr "" + +@c endfile @end example -@code{gawk} actually supports this, but it is purposely undocumented -since it is considered bad style. The correct way to write such a program -is either +This original portable object file is saved and reused for each language +into which the application is translated. The @code{msgid} +is the original string and the @code{msgstr} is the translation. + +@strong{Note:} Strings not marked with a leading underscore do not +appear in the @file{guide.po} file. + +Next, the messages must be translated. +Here is a translation to a hypothetical dialect of English, +called ``Mellow'':@footnote{Perhaps it would be better if it were +called ``Hippy.'' Ah, well.} @example -awk '@{ sum += $1 @} ; END @{ print sum @}' +@group +$ cp guide.po guide-mellow.po +@var{Add translations to} guide-mellow.po @dots{} +@end group @end example @noindent -or +Following are the translations: @example -awk '@{ sum += $1 @} - END @{ print sum @}' data +@c file eg/data/guide-mellow.po +#: guide.awk:4 +msgid "Don't Panic" +msgstr "Hey man, relax!" + +#: guide.awk:5 +msgid "The Answer Is" +msgstr "Like, the scoop is" + +@c endfile @end example -@noindent -@xref{Statements/Lines, ,@code{awk} Statements Versus Lines}, for a fuller -explanation. +@cindex Linux +@cindex GNU/Linux +The next step is to make the directory to hold the binary message object +file and then to create the @file{guide.mo} file. +The directory layout shown here is standard for GNU @code{gettext} on +GNU/Linux systems. Other versions of @code{gettext} may use a different +layout: -@end ignore +@example +$ mkdir en_US en_US/LC_MESSAGES +@end example -@node Known Bugs, , Undocumented, Invoking Gawk -@section Known Bugs in @code{gawk} -@cindex bugs, known in @code{gawk} -@cindex known bugs +@cindex @command{msgfmt} utility +The @command{msgfmt} utility does the conversion from human-readable +@file{.po} file to machine-readable @file{.mo} file. +By default, @command{msgfmt} creates a file named @file{messages}. +This file must be renamed and placed in the proper directory so that +@command{gawk} can find it: -@itemize @bullet -@item -The @samp{-F} option for changing the value of @code{FS} -(@pxref{Options, ,Command Line Options}) -is not necessary given the command line variable -assignment feature; it remains only for backwards compatibility. +@example +$ msgfmt guide-mellow.po +$ mv messages en_US/LC_MESSAGES/guide.mo +@end example -@item -If your system actually has support for @file{/dev/fd} and the -associated @file{/dev/stdin}, @file{/dev/stdout}, and -@file{/dev/stderr} files, you may get different output from @code{gawk} -than you would get on a system without those files. When @code{gawk} -interprets these files internally, it synchronizes output to the -standard output with output to @file{/dev/stdout}, while on a system -with those files, the output is actually to different open files -(@pxref{Special Files, ,Special File Names in @code{gawk}}). +Finally, we run the program to test it: -@item -Syntactically invalid single character programs tend to overflow -the parse stack, generating a rather unhelpful message. Such programs -are surprisingly difficult to diagnose in the completely general case, -and the effort to do so really is not worth it. -@end itemize +@example +$ gawk -f guide.awk +@print{} Hey man, relax! +@print{} Like, the scoop is 42 +@print{} Pardon me, Zaphod who? +@end example -@node Library Functions, Sample Programs, Invoking Gawk, Top -@chapter A Library of @code{awk} Functions +If the two replacement functions for @code{dcgettext} +and @code{bindtextdomain} +(@pxref{I18N Portability, ,@command{awk} Portability Issues}) +are in a file named @file{libintl.awk}, +then we can run @file{guide.awk} unchanged as follows: -@c 2e: USE TEXINFO-2 FUNCTION DEFINITION STUFF!!!!!!!!!!!!! -This chapter presents a library of useful @code{awk} functions. The -sample programs presented later -(@pxref{Sample Programs, ,Practical @code{awk} Programs}) -use these functions. -The functions are presented here in a progression from simple to complex. +@example +$ gawk --posix -f guide.awk -f libintl.awk +@print{} Don't Panic +@print{} The Answer Is 42 +@print{} Pardon me, Zaphod who? +@end example -@ref{Extract Program, ,Extracting Programs from Texinfo Source Files}, -presents a program that you can use to extract the source code for -these example library functions and programs from the Texinfo source -for this @value{DOCUMENT}. -(This has already been done as part of the @code{gawk} distribution.) +@node Gawk I18N, , I18N Example, Internationalization +@section @command{gawk} Can Speak Your Language -If you have written one or more useful, general purpose @code{awk} functions, -and would like to contribute them for a subsequent edition of this @value{DOCUMENT}, -please contact the author. @xref{Bugs, ,Reporting Problems and Bugs}, -for information on doing this. Don't just send code, as you will be -required to either place your code in the public domain, -publish it under the GPL (@pxref{Copying, ,GNU GENERAL PUBLIC LICENSE}), -or assign the copyright in it to the Free Software Foundation. +As of @value{PVERSION} 3.1, @command{gawk} itself has been internationalized +using the GNU @code{gettext} package. +@ifinfo +(GNU @code{gettext} is described in +complete detail in +@ref{Top}.) +@end ifinfo +@ifnotinfo +(GNU @code{gettext} is described in +complete detail in +@cite{GNU gettext tools}.) +@end ifnotinfo +As of this writing, the latest version of GNU @code{gettext} is +@uref{ftp://gnudist.gnu.org/gnu/gettext/gettext-0.10.37.tar.gz, @value{PVERSION} 0.10.37}. + +If a translation of @command{gawk}'s messages exists, +then @command{gawk} produces usage messages, warnings, +and fatal errors in the local language. + +@cindex @code{--with-included-gettext} configuration option +@cindex configuration option, @code{--with-included-gettext} +On systems that do not use @value{PVERSION} 2 (or later) of the GNU C library, you should +configure @command{gawk} with the @option{--with-included-gettext} option +before compiling and installing it. +@xref{Additional Configuration Options}, +for more information. -@menu -* Portability Notes:: What to do if you don't have @code{gawk}. -* Nextfile Function:: Two implementations of a @code{nextfile} - function. -* Assert Function:: A function for assertions in @code{awk} - programs. -* Round Function:: A function for rounding if @code{sprintf} does - not do it correctly. -* Ordinal Functions:: Functions for using characters as numbers and - vice versa. -* Join Function:: A function to join an array into a string. -* Mktime Function:: A function to turn a date into a timestamp. -* Gettimeofday Function:: A function to get formatted times. -* Filetrans Function:: A function for handling data file transitions. -* Getopt Function:: A function for processing command line - arguments. -* Passwd Functions:: Functions for getting user information. -* Group Functions:: Functions for getting group information. -* Library Names:: How to best name private global variables in - library functions. -@end menu +@node Advanced Features, Invoking Gawk, Internationalization, Top +@chapter Advanced Features of @command{gawk} +@cindex advanced features +@cindex features, advanced +@ignore +Contributed by: Peter Langston -@node Portability Notes, Nextfile Function, Library Functions, Library Functions -@section Simulating @code{gawk}-specific Features -@cindex portability issues + Found in Steve English's "signature" line: -The programs in this chapter and in -@ref{Sample Programs, ,Practical @code{awk} Programs}, -freely use features that are specific to @code{gawk}. -This section briefly discusses how you can rewrite these programs for -different implementations of @code{awk}. +"Write documentation as if whoever reads it is a violent psychopath +who knows where you live." +@end ignore +@quotation +@i{Write documentation as if whoever reads it is +a violent psychopath who knows where you live.}@* +Steve English, as quoted by Peter Langston +@end quotation -Diagnostic error messages are sent to @file{/dev/stderr}. -Use @samp{| "cat 1>&2"} instead of @samp{> "/dev/stderr"}, if your system -does not have a @file{/dev/stderr}, or if you cannot use @code{gawk}. +This @value{CHAPTER} discusses advanced features in @command{gawk}. +It's a bit of a ``grab bag'' of items that are otherwise unrelated +to each other. +First, a command-line option allows @command{gawk} to recognize +non-decimal numbers in input data, not just in @command{awk} +programs. Next, two-way I/O, discussed briefly in earlier parts of this +@value{DOCUMENT}, is described in full detail, along with the basics +of TCP/IP networking and BSD portal files. Finally, @command{gawk} +can @dfn{profile} an @command{awk} program, making it possible to tune +it for performance. + +@ref{Dynamic Extensions, ,Adding New Built-in Functions to @command{gawk}}, +discusses the ability to dynamically add new built-in functions to +@command{gawk}. As this feature is still immature and likely to change, +its description is relegated to an appendix. -A number of programs use @code{nextfile} -(@pxref{Nextfile Statement, ,The @code{nextfile} Statement}), -to skip any remaining input in the input file. -@ref{Nextfile Function, ,Implementing @code{nextfile} as a Function}, -shows you how to write a function that will do the same thing. +@menu +* Non-decimal Data:: Allowing non-decimal input data. +* Two-way I/O:: Two-way communications with another process. +* TCP/IP Networking:: Using @command{gawk} for network programming. +* Portal Files:: Using @command{gawk} with BSD portals. +* Profiling:: Profiling your @command{awk} programs. +@end menu -Finally, some of the programs choose to ignore upper-case and lower-case -distinctions in their input. They do this by assigning one to @code{IGNORECASE}. -You can achieve the same effect by adding the following rule to the -beginning of the program: +@node Non-decimal Data, Two-way I/O, Advanced Features, Advanced Features +@section Allowing Non-Decimal Input Data +@cindex @code{--non-decimal-data} option +@cindex command-line option, @code{--non-decimal-data} +If you run @command{gawk} with the @option{--non-decimal-data} option, +you can have non-decimal constants in your input data: + +@c line break here for small book format @example -# ignore case -@{ $0 = tolower($0) @} +$ echo 0123 123 0x123 | +> gawk --non-decimal-data '@{ printf "%d, %d, %d\n", +> $1, $2, $3 @}' +@print{} 83, 123, 291 @end example -@noindent -Also, verify that all regexp and string constants used in -comparisons only use lower-case letters. +For this feature to work, write your program so that +@command{gawk} treats your data as numeric: -@node Nextfile Function, Assert Function, Portability Notes, Library Functions -@section Implementing @code{nextfile} as a Function +@example +$ echo 0123 123 0x123 | gawk '@{ print $1, $2, $3 @}' +@print{} 0123 123 0x123 +@end example -@cindex skipping input files -@cindex input files, skipping -The @code{nextfile} statement presented in -@ref{Nextfile Statement, ,The @code{nextfile} Statement}, -is a @code{gawk}-specific extension. It is not available in other -implementations of @code{awk}. This section shows two versions of a -@code{nextfile} function that you can use to simulate @code{gawk}'s -@code{nextfile} statement if you cannot use @code{gawk}. +@noindent +The @code{print} statement treats its expressions as strings. +Although the fields can act as numbers when necessary, +they are still strings, so @code{print} does not try to treat them +numerically. You may need to add zero to a field to force it to +be treated as a number. For example: + +@example +$ echo 0123 123 0x123 | gawk --non-decimal-data ' +> @{ print $1, $2, $3 +> print $1 + 0, $2 + 0, $3 + 0 @}' +@print{} 0123 123 0x123 +@print{} 83 123 291 +@end example + +Because it is common to have decimal data with leading zeros, and because +using it could lead to surprising results, the default is to leave this +facility disabled. If you want it, you must explicitly request it. + +@cindex conventions, programming +@cindex programming conventions +@strong{Caution:} +@emph{Use of this option is not recommended.} +It can break old programs very badly. +Instead, use the @code{strtonum} function to convert your data +(@pxref{Non-decimal-numbers, ,Octal and Hexadecimal Numbers}). +This makes your programs easier to write and easier to read, and +leads to less surprising results. + +@node Two-way I/O, TCP/IP Networking, Non-decimal Data, Advanced Features +@section Two-Way Communications with Another Process +@cindex Brennan, Michael +@cindex sex, programmer attractiveness +@smallexample +@c Path: cssun.mathcs.emory.edu!gatech!newsxfer3.itd.umich.edu!news-peer.sprintlink.net!news-sea-19.sprintlink.net!news-in-west.sprintlink.net!news.sprintlink.net!Sprint!204.94.52.5!news.whidbey.com!brennan +From: brennan@@whidbey.com (Mike Brennan) +Newsgroups: comp.lang.awk +Subject: Re: Learn the SECRET to Attract Women Easily +Date: 4 Aug 1997 17:34:46 GMT +@c Organization: WhidbeyNet +@c Lines: 12 +Message-ID: <5s53rm$eca@@news.whidbey.com> +@c References: <5s20dn$2e1@chronicle.concentric.net> +@c Reply-To: brennan@whidbey.com +@c NNTP-Posting-Host: asn202.whidbey.com +@c X-Newsreader: slrn (0.9.4.1 UNIX) +@c Xref: cssun.mathcs.emory.edu comp.lang.awk:5403 + +On 3 Aug 1997 13:17:43 GMT, Want More Dates??? + wrote: +>Learn the SECRET to Attract Women Easily +> +>The SCENT(tm) Pheromone Sex Attractant For Men to Attract Women + +The scent of awk programmers is a lot more attractive to women than +the scent of perl programmers. +-- +Mike Brennan +@c brennan@@whidbey.com +@end smallexample -Here is a first attempt at writing a @code{nextfile} function. +It is often useful to be able to +send data to a separate program for +processing and then read the result. This can always be +done with temporary files: @example -@group -# nextfile --- skip remaining records in current file +# write the data for processing +tempfile = ("/tmp/mydata." PROCINFO["pid"]) +while (@var{not done with data}) + print @var{data} | ("subprogram > " tempfile) +close("subprogram > " tempfile) -# this should be read in before the "main" awk program +# read the results, remove tempfile when done +while ((getline newdata < tempfile) > 0) + @var{process} newdata @var{appropriately} +close(tempfile) +system("rm " tempfile) +@end example -function nextfile() @{ _abandon_ = FILENAME; next @} +@noindent +This works, but not elegantly. + +@cindex coprocess +@cindex two-way I/O +@cindex I/O, two-way +@cindex @code{|&} I/O operator +@cindex @command{csh} utility +Starting with @value{PVERSION} 3.1 of @command{gawk}, it is possible to +open a @emph{two-way} pipe to another process. The second process is +termed a @dfn{coprocess}, since it runs in parallel with @command{gawk}. +The two-way connection is created using the new @samp{|&} operator +(borrowed from the Korn Shell, @command{ksh}):@footnote{This is very +different from the same operator in the C shell, @command{csh}.} + +@example +do @{ + print @var{data} |& "subprogram" + "subprogram" |& getline results +@} while (@var{data left to process}) +close("subprogram") +@end example + +The first time an I/O operation is executed using the @samp{|&} +operator, @command{gawk} creates a two-way pipeline to a child process +that runs the other program. Output created with @code{print} +or @code{printf} is written to the program's standard input, and +output from the program's standard output can be read by the @command{gawk} +program using @code{getline}. +As is the case with processes started by @samp{|}, the subprogram +can be any program, or pipeline of programs, that can be started by +the shell. + +There are some cautionary items to be aware of: -_abandon_ == FILENAME @{ next @} -@end group -@end example - -This file should be included before the main program, because it supplies -a rule that must be executed first. This rule compares the current data -file's name (which is always in the @code{FILENAME} variable) to a private -variable named @code{_abandon_}. If the file name matches, then the action -part of the rule executes a @code{next} statement, to go on to the next -record. (The use of @samp{_} in the variable name is a convention. -It is discussed more fully in -@ref{Library Names, , Naming Library Function Global Variables}.) +@itemize @bullet +@item +As the code inside @command{gawk} currently stands, the coprocess's +standard error goes to the same place that the parent @command{gawk}'s +standard error goes. It is not possible to read the child's +standard error separately. -The use of the @code{next} statement effectively creates a loop that reads -all the records from the current data file. -Eventually, the end of the file is reached, and -a new data file is opened, changing the value of @code{FILENAME}. -Once this happens, the comparison of @code{_abandon_} to @code{FILENAME} -fails, and execution continues with the first rule of the ``real'' program. +@cindex deadlock +@item +I/O buffering may be a problem. @command{gawk} automatically +flushes all output down the pipe to the child process. +However, if the coprocess does not flush its output, +@command{gawk} may hang when doing a @code{getline} in order to read +the coprocess's results. This could lead to a situation +known as @dfn{deadlock}, where each process is waiting for the +other one to do something. +@end itemize -The @code{nextfile} function itself simply sets the value of @code{_abandon_} -and then executes a @code{next} statement to start the loop -going.@footnote{Some implementations of @code{awk} do not allow you to -execute @code{next} from within a function body. Some other work-around -will be necessary if you use such a version.} -@c mawk is what we're talking about. - -This initial version has a subtle problem. What happens if the same data -file is listed @emph{twice} on the command line, one right after the other, -or even with just a variable assignment between the two occurrences of -the file name? - -@c @findex nextfile -@c do it this way, since all the indices are merged -@cindex @code{nextfile} function -In such a case, -this code will skip right through the file, a second time, even though -it should stop when it gets to the end of the first occurrence. -Here is a second version of @code{nextfile} that remedies this problem. +It is possible to close just one end of the two-way pipe to +a coprocess, by supplying a second argument to the @code{close} +function of either @code{"to"} or @code{"from"} +(@pxref{Close Files And Pipes, ,Closing Input and Output Redirections}). +These strings tell @command{gawk} to close the end of the pipe +that sends data to the process or the end that reads from it, +respectively. + +This is particularly necessary in order to use +the system @command{sort} utility as part of a coprocess; +@command{sort} must read @emph{all} of its input +data before it can produce any output. +The @command{sort} program does not receive an end-of-file indication +until @command{gawk} closes the write end of the pipe. + +When you have finished writing data to the @command{sort} +utility, you can close the @code{"to"} end of the pipe, and +then start reading sorted data via @code{getline}. +For example: @example -@c file eg/lib/nextfile.awk -# nextfile --- skip remaining records in current file -# correctly handle successive occurrences of the same file -# Arnold Robbins, arnold@@gnu.org, Public Domain -# May, 1993 - -# this should be read in before the "main" awk program +BEGIN @{ + command = "LC_ALL=C sort" + n = split("abcdefghijklmnopqrstuvwxyz", a, "") -function nextfile() @{ _abandon_ = FILENAME; next @} + for (i = n; i > 0; i--) + print a[i] |& command + close(command, "to") -@group -_abandon_ == FILENAME @{ - if (FNR == 1) - _abandon_ = "" - else - next + while ((command |& getline line) > 0) + print "got", line + close(command) @} -@end group -@c endfile @end example -The @code{nextfile} function has not changed. It sets @code{_abandon_} -equal to the current file name and then executes a @code{next} satement. -The @code{next} statement reads the next record and increments @code{FNR}, -so @code{FNR} is guaranteed to have a value of at least two. -However, if @code{nextfile} is called for the last record in the file, -then @code{awk} will close the current data file and move on to the next -one. Upon doing so, @code{FILENAME} will be set to the name of the new file, -and @code{FNR} will be reset to one. If this next file is the same as -the previous one, @code{_abandon_} will still be equal to @code{FILENAME}. -However, @code{FNR} will be equal to one, telling us that this is a new -occurrence of the file, and not the one we were reading when the -@code{nextfile} function was executed. In that case, @code{_abandon_} -is reset to the empty string, so that further executions of this rule -will fail (until the next time that @code{nextfile} is called). - -If @code{FNR} is not one, then we are still in the original data file, -and the program executes a @code{next} statement to skip through it. +This program writes the letters of the alphabet in reverse order, one +per line, down the two-way pipe to @command{sort}. It then closes the +write end of the pipe, so that @command{sort} receives an end-of-file +indication. This causes @command{sort} to sort the data and write the +sorted data back to the @command{gawk} program. Once all of the data +has been read, @command{gawk} terminates the coprocess and exits. -An important question to ask at this point is: ``Given that the -functionality of @code{nextfile} can be provided with a library file, -why is it built into @code{gawk}?'' This is an important question. Adding -features for little reason leads to larger, slower programs that are -harder to maintain. +As a side note, the assignment @samp{LC_ALL=C} in the @command{sort} +command ensures traditional Unix (ASCII) sorting from @command{sort}. -The answer is that building @code{nextfile} into @code{gawk} provides -significant gains in efficiency. If the @code{nextfile} function is executed -at the beginning of a large data file, @code{awk} still has to scan the entire -file, splitting it up into records, just to skip over it. The built-in -@code{nextfile} can simply close the file immediately and proceed to the -next one, saving a lot of time. This is particularly important in -@code{awk}, since @code{awk} programs are generally I/O bound (i.e.@: -they spend most of their time doing input and output, instead of performing -computations). +@node TCP/IP Networking, Portal Files, Two-way I/O, Advanced Features +@section Using @command{gawk} for Network Programming +@cindex networking, TCP/IP +@cindex TCP/IP networking +@cindex @file{/inet} special files +@cindex @code{EMISTERED} +@quotation +@code{EMISTERED}: @i{A host is a host from coast to coast,@* +and no-one can talk to host that's close,@* +unless the host that isn't close@* +is busy hung or dead.} +@end quotation -@node Assert Function, Round Function, Nextfile Function, Library Functions -@section Assertions +In addition to being able to open a two-way pipeline to a coprocess +on the same system +(@pxref{Two-way I/O, ,Two-Way Communications with Another Process}), +it is possible to make a two-way connection to +another process on another system across an IP networking connection. + +You can think of this as just a @emph{very long} two-way pipeline to +a coprocess. +The way @command{gawk} decides that you want to use TCP/IP networking is +by recognizing special @value{FN}s that begin with @samp{/inet/}. + +The full syntax of the special @value{FN} is +@file{/inet/@var{protocol}/@var{local-port}/@var{remote-host}/@var{remote-port}}. +The meaning of the components are: + +@table @var +@item protocol +The protocol to use over IP. This must be either @samp{tcp}, +@samp{udp}, or @samp{raw}, for a TCP, UDP, or raw IP connection, +respectively. The use of TCP is recommended for most applications. + +@strong{Caution:} The use of raw sockets is not currently supported +in @value{PVERSION} 3.1 of @command{gawk}. + +@item local-port +@cindex @code{getservbyname} C library function +The local TCP or UDP port number to use. Use a port number of @samp{0} +when you want the system to pick a port. This is what you should do +when writing a TCP or UDP client. +You may also use a well-known service name, such as @samp{smtp} +or @samp{http}, in which case @command{gawk} attempts to determine +the pre-defined port number using the C @code{getservbyname} function. + +@item remote-host +The IP address or fully-qualified domain name of the Internet +host to which you want to connect. + +@item remote-port +The TCP or UDP port number to use on the given @var{remote-host}. +Again, use @samp{0} if you don't care, or else a well-known +service name. +@end table -@cindex assertions -@cindex @code{assert}, C version -When writing large programs, it is often useful to be able to know -that a condition or set of conditions is true. Before proceeding with a -particular computation, you make a statement about what you believe to be -the case. Such a statement is known as an -``assertion.'' The C language provides an @code{} header file -and corresponding @code{assert} macro that the programmer can use to make -assertions. If an assertion fails, the @code{assert} macro arranges to -print a diagnostic message describing the condition that should have -been true but was not, and then it kills the program. In C, using -@code{assert} looks this: +Consider the following very simple example: -@c NEEDED -@page @example -#include - -int myfunc(int a, double b) -@{ - assert(a <= 5 && b >= 17); - @dots{} +BEGIN @{ + Service = "/inet/tcp/0/localhost/daytime" + Service |& getline + print $0 + close(Service) @} @end example -If the assertion failed, the program would print a message similar to -this: +This program reads the current date and time from the local system's +TCP @samp{daytime} server. +It then prints the results and closes the connection. -@example -prog.c:5: assertion failed: a <= 5 && b >= 17 +Because this topic is extensive, the use of @command{gawk} for +TCP/IP programming is documented separately. +@ifinfo +@xref{Top}, +@end ifinfo +@ifnotinfo +See @cite{TCP/IP Internetworking with @command{gawk}}, +which comes as part of the @command{gawk} distribution, +@end ifnotinfo +for a much more complete introduction and discussion, as well as +extensive examples. + +@node Portal Files, Profiling, TCP/IP Networking, Advanced Features +@section Using @command{gawk} with BSD Portals +@cindex portal files +@cindex BSD portal files +@cindex TCP/IP networking +@cindex @file{/p} special files +@cindex @code{--enable-portals} configuration option +@cindex configuration option, @code{--enable-portals} +@cindex BSD-based operating systems + +Similar to the @file{/inet} special files, if @command{gawk} +is configured with the @option{--enable-portals} option +(@pxref{Quick Installation, , Compiling @command{gawk} for Unix}), +then @command{gawk} treats +files whose pathnames begin with @code{/p} as 4.4 BSD-style portals. + +When used with the @samp{|&} operator, @command{gawk} opens the file +for two-way communications. The operating system's portal mechanism +then manages creating the process associated with the portal and +the corresponding communications with the portal's process. + +@node Profiling, , Portal Files, Advanced Features +@section Profiling Your @command{awk} Programs +@cindex profiling @command{awk} programs +@cindex @command{pgawk} program + +Beginning with @value{PVERSION} 3.1 of @command{gawk}, you may produce execution +traces of your @command{awk} programs. +This is done with a specially compiled version of @command{gawk}, +called @command{pgawk} (``profiling @command{gawk}''). + +@cindex @file{awkprof.out} profiling output file +@cindex profiling output file (@file{awkprof.out}) +@command{pgawk} is identical in every way to @command{gawk}, except that when +it has finished running, it creates a profile of your program in a file +named @file{awkprof.out}. +Because it is profiling, it also executes up to 45 percent slower than +@command{gawk} normally does. + +As shown in the following example, +the @option{--profile} option can be used to change the name of the file +where @command{pgawk} will write the profile: + +@example +$ pgawk --profile=myprog.prof -f myprog.awk data1 data2 @end example -@findex assert -The ANSI C language makes it possible to turn the condition into a string for use -in printing the diagnostic message. This is not possible in @code{awk}, so -this @code{assert} function also requires a string version of the condition -that is being tested. +@noindent +In the above example, @command{pgawk} places the profile in +@file{myprog.prof} instead of in @file{awkprof.out}. + +Regular @command{gawk} also accepts this option. When called with just +@option{--profile}, @command{gawk} ``pretty prints'' the program into +@file{awkprof.out}, without any execution counts. You may supply an +option to @option{--profile} to change the @value{FN}. Here is a sample +session showing a simple @command{awk} program, its input data, and the +results from running @command{pgawk}. First, the @command{awk} program: @example -@c @group -@c file eg/lib/assert.awk -# assert --- assert that a condition is true. Otherwise exit. -# Arnold Robbins, arnold@@gnu.org, Public Domain -# May, 1993 +BEGIN @{ print "First BEGIN rule" @} -function assert(condition, string) -@{ - if (! condition) @{ - printf("%s:%d: assertion failed: %s\n", - FILENAME, FNR, string) > "/dev/stderr" - _assert_exit = 1 - exit 1 - @} -@} +END @{ print "First END rule" @} -END @{ - if (_assert_exit) - exit 1 +/foo/ @{ + print "matched /foo/, gosh" + for (i = 1; i <= 3; i++) + sing() @} -@c endfile -@c @end group -@end example -The @code{assert} function tests the @code{condition} parameter. If it -is false, it prints a message to standard error, using the @code{string} -parameter to describe the failed condition. It then sets the variable -@code{_assert_exit} to one, and executes the @code{exit} statement. -The @code{exit} statement jumps to the @code{END} rule. If the @code{END} -rules finds @code{_assert_exit} to be true, then it exits immediately. +@{ + if (/foo/) + print "if is true" + else + print "else is true" +@} -The purpose of the @code{END} rule with its test is to -keep any other @code{END} rules from running. When an assertion fails, the -program should exit immediately. -If no assertions fail, then @code{_assert_exit} will still be -false when the @code{END} rule is run normally, and the rest of the -program's @code{END} rules will execute. -For all of this to work correctly, @file{assert.awk} must be the -first source file read by @code{awk}. +BEGIN @{ print "Second BEGIN rule" @} -@c NEEDED -@page -You would use this function in your programs this way: +END @{ print "Second END rule" @} -@example -function myfunc(a, b) +function sing( dummy) @{ - assert(a <= 5 && b >= 17, "a <= 5 && b >= 17") - @dots{} + print "I gotta be me!" @} @end example -@noindent -If the assertion failed, you would see a message like this: +Following is the input data: @example -mydata:1357: assertion failed: a <= 5 && b >= 17 +foo +bar +baz +foo +junk @end example -There is a problem with this version of @code{assert}, that it may not -be possible to work around with standard @code{awk}. -An @code{END} rule is automatically added -to the program calling @code{assert}. Normally, if a program consists -of just a @code{BEGIN} rule, the input files and/or standard input are -not read. However, now that the program has an @code{END} rule, @code{awk} -will attempt to read the input data files, or standard input -(@pxref{Using BEGIN/END, , Startup and Cleanup Actions}), -most likely causing the program to hang, waiting for input. - -@node Round Function, Ordinal Functions, Assert Function, Library Functions -@section Rounding Numbers +Here is the @file{awkprof.out} that results from running @command{pgawk} +on this program and data. (This example also illustrates that @command{awk} +programmers sometimes have to work late.): -@cindex rounding -The way @code{printf} and @code{sprintf} -(@pxref{Printf, , Using @code{printf} Statements for Fancier Printing}) -do rounding will often depend -upon the system's C @code{sprintf} subroutine. -On many machines, -@code{sprintf} rounding is ``unbiased,'' which means it doesn't always -round a trailing @samp{.5} up, contrary to naive expectations. In unbiased -rounding, @samp{.5} rounds to even, rather than always up, so 1.5 rounds to -2 but 4.5 rounds to 4. -The result is that if you are using a format that does -rounding (e.g., @code{"%.0f"}) you should check what your system does. -The following function does traditional rounding; -it might be useful if your awk's @code{printf} does unbiased rounding. - -@findex round +@cindex blocks, @code{BEGIN} and @code{END} @example -@c file eg/lib/round.awk -# round --- do normal rounding -# -# Arnold Robbins, arnold@@gnu.org, August, 1996 -# Public Domain + # gawk profile, created Sun Aug 13 00:00:15 2000 -function round(x, ival, aval, fraction) -@{ - ival = int(x) # integer part, int() truncates + # BEGIN block(s) - # see if fractional part - if (ival == x) # no fraction - return x + BEGIN @{ + 1 print "First BEGIN rule" + 1 print "Second BEGIN rule" + @} - if (x < 0) @{ - aval = -x # absolute value - ival = int(aval) - fraction = aval - ival -@group - if (fraction >= .5) - return int(x) - 1 # -2.5 --> -3 - else - return int(x) # -2.3 --> -2 -@end group - @} else @{ - fraction = x - ival - if (fraction >= .5) - return ival + 1 - else - return ival - @} -@} + # Rule(s) -# test harness -@{ print $0, round($0) @} -@c endfile + 5 /foo/ @{ # 2 + 2 print "matched /foo/, gosh" + 6 for (i = 1; i <= 3; i++) @{ + 6 sing() + @} + @} + + 5 @{ + 5 if (/foo/) @{ # 2 + 2 print "if is true" + 3 @} else @{ + 3 print "else is true" + @} + @} + + # END block(s) + + END @{ + 1 print "First END rule" + 1 print "Second END rule" + @} + + # Functions, listed alphabetically + + 6 function sing(dummy) + @{ + 6 print "I gotta be me!" + @} @end example -@node Ordinal Functions, Join Function, Round Function, Library Functions -@section Translating Between Characters and Numbers +The previous example illustrates many of the basic rules for profiling output. +The rules are as follows: -@cindex numeric character values -@cindex values of characters as numbers -One commercial implementation of @code{awk} supplies a built-in function, -@code{ord}, which takes a character and returns the numeric value for that -character in the machine's character set. If the string passed to -@code{ord} has more than one character, only the first one is used. +@itemize @bullet +@item +The program is printed in the order @code{BEGIN} rule, +pattern/action rules, @code{END} rule and functions, listed +alphabetically. +Multiple @code{BEGIN} and @code{END} rules are merged together. -The inverse of this function is @code{chr} (from the function of the same -name in Pascal), which takes a number and returns the corresponding character. +@item +Pattern-action rules have two counts. +The first count, to the left of the rule, shows how many times +the rule's pattern was @emph{tested}. +The second count, to the right of the rule's opening left brace +in a comment, +shows how many times the rule's action was @emph{executed}. +The difference between the two indicates how many times the rule's +pattern evaluated to false. -Both functions can be written very nicely in @code{awk}; there is no real -reason to build them into the @code{awk} interpreter. +@item +Similarly, +the count for an @code{if}-@code{else} statement shows how many times +the condition was tested. +To the right of the opening left brace for the @code{if}'s body +is a count showing how many times the condition was true. +The count for the @code{else} +indicates how many times the test failed. -@findex ord -@findex chr -@example -@group -@c file eg/lib/ord.awk -# ord.awk --- do ord and chr -# -# Global identifiers: -# _ord_: numerical values indexed by characters -# _ord_init: function to initialize _ord_ -# -# Arnold Robbins -# arnold@@gnu.org -# Public Domain -# 16 January, 1992 -# 20 July, 1992, revised +@item +The count for a loop header (such as @code{for} +or @code{while}) shows how many times the loop test was executed. +(Because of this, you can't just look at the count on the first +statement in a rule to determine how many times the rule was executed. +If the first statement is a loop, the count is misleading.) -BEGIN @{ _ord_init() @} -@c endfile -@end group +@item +For user-defined functions, the count next to the @code{function} +keyword indicates how many times the function was called. +The counts next to the statements in the body show how many times +those statements were executed. -@c @group -@c file eg/lib/ord.awk -function _ord_init( low, high, i, t) -@{ - low = sprintf("%c", 7) # BEL is ascii 7 - if (low == "\a") @{ # regular ascii - low = 0 - high = 127 - @} else if (sprintf("%c", 128 + 7) == "\a") @{ - # ascii, mark parity - low = 128 - high = 255 - @} else @{ # ebcdic(!) - low = 0 - high = 255 - @} +@item +The layout uses ``K&R'' style using tabs. +Braces are used everywhere, even when +the body of an @code{if}, @code{else}, or loop is only a single statement. - for (i = low; i <= high; i++) @{ - t = sprintf("%c", i) - _ord_[t] = i - @} -@} -@c endfile -@c @end group +@item +Parentheses are used only where needed, as indicated by the structure +of the program and the precedence rules. +@c extra verbiage here satisfies the copyeditor. ugh. +For example, @samp{(3 + 5) * 4} means add three plus five, then multiply +the total by four. However, @samp{3 + 5 * 4} has no parentheses, and +means @samp{3 + (5 * 4)}. + +@item +All string concatenations are parenthesized too. +(This could be made a bit smarter.) + +@item +Parentheses are used around the arguments to @code{print} +and @code{printf} only when +the @code{print} or @code{printf} statement is followed by a redirection. +Similarly, if +the target of a redirection isn't a scalar, it gets parenthesized. + +@item +@command{pgawk} supplies leading comments in +front of the @code{BEGIN} and @code{END} rules, +the pattern/action rules, and the functions. + +@end itemize + +The profiled version of your program may not look exactly like what you +typed when you wrote it. This is because @command{pgawk} creates the +profiled version by ``pretty printing'' its internal representation of +the program. The advantage to this is that @command{pgawk} can produce +a standard representation. The disadvantage is that all source code +comments are lost, as are the distinctions among multiple @code{BEGIN} +and @code{END} rules. Also, things such as: + +@example +/foo/ @end example -@cindex character sets -@cindex character encodings -@cindex ASCII -@cindex EBCDIC -@cindex mark parity -Some explanation of the numbers used by @code{chr} is worthwhile. -The most prominent character set in use today is ASCII. Although an -eight-bit byte can hold 256 distinct values (from zero to 255), ASCII only -defines characters that use the values from zero to 127.@footnote{ASCII -has been extended in many countries to use the values from 128 to 255 -for country-specific characters. If your system uses these extensions, -you can simplify @code{_ord_init} to simply loop from zero to 255.} -At least one computer manufacturer that we know of -@c Pr1me, blech -uses ASCII, but with mark parity, meaning that the leftmost bit in the byte -is always one. What this means is that on those systems, characters -have numeric values from 128 to 255. -Finally, large mainframe systems use the EBCDIC character set, which -uses all 256 values. -While there are other character sets in use on some older systems, -they are not really worth worrying about. +@noindent +come out as: @example -@group -@c file eg/lib/ord.awk -function ord(str, c) -@{ - # only first character is of interest - c = substr(str, 1, 1) - return _ord_[c] +/foo/ @{ + print $0 @} -@c endfile -@end group +@end example -@group -@c file eg/lib/ord.awk -function chr(c) -@{ - # force c to be numeric by adding 0 - return sprintf("%c", c + 0) -@} -@c endfile -@end group +@noindent +which is correct, but possibly surprising. -@group -@c file eg/lib/ord.awk -#### test code #### -# BEGIN \ -# @{ -# for (;;) @{ -# printf("enter a character: ") -# if (getline var <= 0) -# break -# printf("ord(%s) = %d\n", var, ord(var)) -# @} -# @} -@c endfile -@end group -@end example +@cindex dynamic profiling +@cindex profiling, dynamic +Besides creating profiles when a program has completed, +@command{pgawk} can produce a profile while it is running. +This is useful if your @command{awk} program goes into an +infinite loop and you want to see what has been executed. +To use this feature, run @command{pgawk} in the background: -An obvious improvement to these functions would be to move the code for the -@code{@w{_ord_init}} function into the body of the @code{BEGIN} rule. It was -written this way initially for ease of development. +@example +$ pgawk -f myprog & +[1] 13992 +@end example -There is a ``test program'' in a @code{BEGIN} rule, for testing the -function. It is commented out for production use. +@cindex @command{kill} command +@cindex @code{SIGUSR1} signal +@cindex @code{USR1} signal +@cindex signals, @code{SIGUSR1} +@noindent +The shell prints a job number and process ID number, in this case, 13992. +Use the @command{kill} command to send the @code{USR1} signal +to @command{pgawk}: -@node Join Function, Mktime Function, Ordinal Functions, Library Functions -@section Merging an Array Into a String +@example +$ kill -USR1 13992 +@end example -@cindex merging strings -When doing string processing, it is often useful to be able to join -all the strings in an array into one long string. The following function, -@code{join}, accomplishes this task. It is used later in several of -the application programs -(@pxref{Sample Programs, ,Practical @code{awk} Programs}). +@noindent +As usual, the profiled version of the program is written to +@file{awkprof.out}, or to a different file if you use the @option{--profile} +option. -Good function design is important; this function needs to be general, but it -should also have a reasonable default behavior. It is called with an array -and the beginning and ending indices of the elements in the array to be -merged. This assumes that the array indices are numeric---a reasonable -assumption since the array was likely created with @code{split} -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). +Along with the regular profile, as shown earlier, the profile +includes a trace of any active functions: -@findex join @example -@group -@c file eg/lib/join.awk -# join.awk --- join an array into a string -# Arnold Robbins, arnold@@gnu.org, Public Domain -# May 1993 +# Function Call Stack: -function join(array, start, end, sep, result, i) -@{ - if (sep == "") - sep = " " - else if (sep == SUBSEP) # magic value - sep = "" - result = array[start] - for (i = start + 1; i <= end; i++) - result = result sep array[i] - return result -@} -@c endfile -@end group +# 3. baz +# 2. bar +# 1. foo +# -- main -- @end example -An optional additional argument is the separator to use when joining the -strings back together. If the caller supplies a non-empty value, -@code{join} uses it. If it is not supplied, it will have a null -value. In this case, @code{join} uses a single blank as a default -separator for the strings. If the value is equal to @code{SUBSEP}, -then @code{join} joins the strings with no separator between them. -@code{SUBSEP} serves as a ``magic'' value to indicate that there should -be no separation between the component strings. +You may send @command{pgawk} the @code{USR1} signal as many times as you like. +Each time, the profile and function call trace are appended to the output +profile file. -It would be nice if @code{awk} had an assignment operator for concatenation. -The lack of an explicit operator for concatenation makes string operations -more difficult than they really need to be. +@cindex @code{SIGHUP} signal +@cindex @code{HUP} signal +@cindex signals, @code{SIGHUP} +If you use the @code{HUP} signal instead of the @code{USR1} signal, +@command{pgawk} produces the profile and the function call trace, and then exits. -@node Mktime Function, Gettimeofday Function, Join Function, Library Functions -@section Turning Dates Into Timestamps +@node Invoking Gawk, Library Functions, Advanced Features, Top +@chapter Running @command{awk} and @command{gawk} -The @code{systime} function built in to @code{gawk} -returns the current time of day as -a timestamp in ``seconds since the Epoch.'' This timestamp -can be converted into a printable date of almost infinitely variable -format using the built-in @code{strftime} function. -(For more information on @code{systime} and @code{strftime}, -@pxref{Time Functions, ,Functions for Dealing with Time Stamps}.) +This @value{CHAPTER} covers how to run awk, both POSIX-standard +and @command{gawk}-specific command-line options, and what +@command{awk} and +@command{gawk} do with non-option arguments. +It then proceeds to cover how @command{gawk} searches for source files, +obsolete options and/or features, and known bugs in @command{gawk}. +This @value{CHAPTER} rounds out the discussion of @command{awk} +as a program and as a language. -@cindex converting dates to timestamps -@cindex dates, converting to timestamps -@cindex timestamps, converting from dates -An interesting but difficult problem is to convert a readable representation -of a date back into a timestamp. The ANSI C library provides a @code{mktime} -function that does the basic job, converting a canonical representation of a -date into a timestamp. - -It would appear at first glance that @code{gawk} would have to supply a -@code{mktime} built-in function that was simply a ``hook'' to the C language -version. In fact though, @code{mktime} can be implemented entirely in -@code{awk}.@footnote{@value{UPDATE-MONTH}: Actually, I was mistaken when -I wrote this. The version presented here doesn't always work correctly, -and the next major version of @code{gawk} will provide @code{mktime} -as a built-in function.} -@c sigh. - -Here is a version of @code{mktime} for @code{awk}. It takes a simple -representation of the date and time, and converts it into a timestamp. - -The code is presented here intermixed with explanatory prose. In -@ref{Extract Program, ,Extracting Programs from Texinfo Source Files}, -you will see how the Texinfo source file for this @value{DOCUMENT} -can be processed to extract the code into a single source file. +While a number of the options and features described here were +discussed in passing earlier in the book, this @value{CHAPTER} provides the +full details. -The program begins with a descriptive comment and a @code{BEGIN} rule -that initializes a table @code{_tm_months}. This table is a two-dimensional -array that has the lengths of the months. The first index is zero for -regular years, and one for leap years. The values are the same for all the -months in both kinds of years, except for February; thus the use of multiple -assignment. +@menu +* Command Line:: How to run @command{awk}. +* Options:: Command-line options and their meanings. +* Other Arguments:: Input file names and variable assignments. +* AWKPATH Variable:: Searching directories for @command{awk} + programs. +* Obsolete:: Obsolete Options and/or features. +* Undocumented:: Undocumented Options and Features. +* Known Bugs:: Known Bugs in @command{gawk}. +@end menu -@example -@c @group -@c file eg/lib/mktime.awk -# mktime.awk --- convert a canonical date representation -# into a timestamp -# Arnold Robbins, arnold@@gnu.org, Public Domain -# May 1993 +@node Command Line, Options, Invoking Gawk, Invoking Gawk +@section Invoking @command{awk} +@cindex command line +@cindex invocation of @command{gawk} +@cindex arguments, command-line +@cindex options, command-line +@cindex long options +@cindex options, long -BEGIN \ -@{ - # Initialize table of month lengths - _tm_months[0,1] = _tm_months[1,1] = 31 - _tm_months[0,2] = 28; _tm_months[1,2] = 29 - _tm_months[0,3] = _tm_months[1,3] = 31 - _tm_months[0,4] = _tm_months[1,4] = 30 - _tm_months[0,5] = _tm_months[1,5] = 31 - _tm_months[0,6] = _tm_months[1,6] = 30 - _tm_months[0,7] = _tm_months[1,7] = 31 - _tm_months[0,8] = _tm_months[1,8] = 31 - _tm_months[0,9] = _tm_months[1,9] = 30 - _tm_months[0,10] = _tm_months[1,10] = 31 - _tm_months[0,11] = _tm_months[1,11] = 30 - _tm_months[0,12] = _tm_months[1,12] = 31 -@} -@c endfile -@c @end group +There are two ways to run @command{awk}---with an explicit program or with +one or more program files. Here are templates for both of them; items +enclosed in [@dots{}] in these templates are optional: + +@example +awk @r{[@var{options}]} -f progfile @r{[@code{--}]} @var{file} @dots{} +awk @r{[@var{options}]} @r{[@code{--}]} '@var{program}' @var{file} @dots{} @end example -The benefit of merging multiple @code{BEGIN} rules -(@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}) -is particularly clear when writing library files. Functions in library -files can cleanly initialize their own private data and also provide clean-up -actions in private @code{END} rules. +Besides traditional one-letter POSIX-style options, @command{gawk} also +supports GNU long options. -The next function is a simple one that computes whether a given year is or -is not a leap year. If a year is evenly divisible by four, but not evenly -divisible by 100, or if it is evenly divisible by 400, then it is a leap -year. Thus, 1904 was a leap year, 1900 was not, but 2000 will be. -@c Change this after the year 2000 to ``2000 was'' (:-) +@cindex empty program +@cindex dark corner +@cindex lint checks +It is possible to invoke @command{awk} with an empty program: -@findex _tm_isleap @example -@group -@c file eg/lib/mktime.awk -# decide if a year is a leap year -function _tm_isleap(year, ret) -@{ - ret = (year % 4 == 0 && year % 100 != 0) || - (year % 400 == 0) - - return ret -@} -@c endfile -@end group +awk '' datafile1 datafile2 @end example -This function is only used a few times in this file, and its computation -could have been written @dfn{in-line} (at the point where it's used). -Making it a separate function made the original development easier, and also -avoids the possibility of typing errors when duplicating the code in -multiple places. - -The next function is more interesting. It does most of the work of -generating a timestamp, which is converting a date and time into some number -of seconds since the Epoch. The caller passes an array (rather -imaginatively named @code{a}) containing six -values: the year including century, the month as a number between one and 12, -the day of the month, the hour as a number between zero and 23, the minute in -the hour, and the seconds within the minute. - -The function uses several local variables to precompute the number of -seconds in an hour, seconds in a day, and seconds in a year. Often, -similar C code simply writes out the expression in-line, expecting the -compiler to do @dfn{constant folding}. E.g., most C compilers would -turn @samp{60 * 60} into @samp{3600} at compile time, instead of recomputing -it every time at run time. Precomputing these values makes the -function more efficient. - -@findex _tm_addup -@example -@c @group -@c file eg/lib/mktime.awk -# convert a date into seconds -function _tm_addup(a, total, yearsecs, daysecs, - hoursecs, i, j) -@{ - hoursecs = 60 * 60 - daysecs = 24 * hoursecs - yearsecs = 365 * daysecs +@noindent +Doing so makes little sense though; @command{awk} exits +silently when given an empty program. +@value{DARKCORNER} +If @option{--lint} has +been specified on the command-line, @command{gawk} issues a +warning that the program is empty. - total = (a[1] - 1970) * yearsecs +@node Options, Other Arguments, Command Line, Invoking Gawk +@section Command-Line Options -@group - # extra day for leap years - for (i = 1970; i < a[1]; i++) - if (_tm_isleap(i)) - total += daysecs -@end group +Options begin with a dash and consist of a single character. +GNU-style long options consist of two dashes and a keyword. +The keyword can be abbreviated, as long as the abbreviation allows the option +to be uniquely identified. If the option takes an argument, then the +keyword is either immediately followed by an equals sign (@samp{=}) and the +argument's value, or the keyword and the argument's value are separated +by whitespace. +If a particular option with a value is given more than once, it is the +last value that counts. -@group - j = _tm_isleap(a[1]) - for (i = 1; i < a[2]; i++) - total += _tm_months[j, i] * daysecs -@end group +Each long option for @command{gawk} has a corresponding +POSIX-style option. +The long and short options are +interchangeable in all contexts. +The options and their meanings are as follows: - total += (a[3] - 1) * daysecs - total += a[4] * hoursecs - total += a[5] * 60 - total += a[6] +@table @code +@item -F @var{fs} +@itemx --field-separator @var{fs} +@cindex @code{-F} option +@cindex command-line option, @code{-F} +@cindex @code{--field-separator} option +@cindex command-line option, @code{--field-separator} +Sets the @code{FS} variable to @var{fs} +(@pxref{Field Separators, ,Specifying How Fields Are Separated}). - return total -@} -@c endfile -@c @end group -@end example +@item -f @var{source-file} +@itemx --file @var{source-file} +@cindex @code{-f} option +@cindex command-line option, @code{-f} +@cindex @code{--file} option +@cindex command-line option, @code{--file} +Indicates that the @command{awk} program is to be found in @var{source-file} +instead of in the first non-option argument. -The function starts with a first approximation of all the seconds between -Midnight, January 1, 1970,@footnote{This is the Epoch on POSIX systems. -It may be different on other systems.} and the beginning of the current -year. It then goes through all those years, and for every leap year, -adds an additional day's worth of seconds. +@item -v @var{var}=@var{val} +@itemx --assign @var{var}=@var{val} +@cindex @code{-v} option +@cindex command-line option, @code{-v} +@cindex @code{--assign} option +@cindex command-line option, @code{--assign} +Sets the variable @var{var} to the value @var{val} @emph{before} +execution of the program begins. Such variable values are available +inside the @code{BEGIN} rule +(@pxref{Other Arguments, ,Other Command-Line Arguments}). -The variable @code{j} holds either one or zero, if the current year is or is not -a leap year. -For every month in the current year prior to the current month, it adds -the number of seconds in the month, using the appropriate entry in the -@code{_tm_months} array. +The @option{-v} option can only set one variable, but it can be used +more than once, setting another variable each time, like this: +@samp{awk @w{-v foo=1} @w{-v bar=2} @dots{}}. -Finally, it adds in the seconds for the number of days prior to the current -day, and the number of hours, minutes, and seconds in the current day. +@strong{Caution:} Using @option{-v} to set the values of the built-in +variables may lead to surprising results. @command{awk} will reset the +values of those variables as it needs to, possibly ignoring any +predefined value you may have given. -The result is a count of seconds since January 1, 1970. This value is not -yet what is needed though. The reason why is described shortly. +@item -mf @var{N} +@itemx -mr @var{N} +@cindex @code{-mf} option +@cindex command-line option, @code{-mf} +@cindex @code{-mr} option +@cindex command-line option, @code{-mr} +Set various memory limits to the value @var{N}. The @samp{f} flag sets +the maximum number of fields and the @samp{r} flag sets the maximum +record size. These two flags and the @option{-m} option are from the +Bell Laboratories research version of Unix @command{awk}. They are provided +for compatibility but otherwise ignored by +@command{gawk}, since @command{gawk} has no predefined limits. +(The Bell Laboratories @command{awk} no longer needs these options; +it continues to accept them to avoid breaking old programs.) -The main @code{mktime} function takes a single character string argument. -This string is a representation of a date and time in a ``canonical'' -(fixed) form. This string should be -@code{"@var{year} @var{month} @var{day} @var{hour} @var{minute} @var{second}"}. +@item -W @var{gawk-opt} +@cindex @code{-W} option +@cindex command-line option, @code{-W} +Following the POSIX standard, implementation-specific +options are supplied as arguments to the @option{-W} option. These options +also have corresponding GNU-style long options. +Note that the long options may be abbreviated, as long as +the abbreviations remain unique. +The full list of @command{gawk}-specific options is provided next. -@findex mktime -@example -@c @group -@c file eg/lib/mktime.awk -# mktime --- convert a date into seconds, -# compensate for time zone +@item -- +Signals the end of the command-line options. The following arguments +are not treated as options even if they begin with @samp{-}. This +interpretation of @option{--} follows the POSIX argument parsing +conventions. -function mktime(str, res1, res2, a, b, i, j, t, diff) -@{ - i = split(str, a, " ") # don't rely on FS +This is useful if you have @value{FN}s that start with @samp{-}, +or in shell scripts, if you have @value{FN}s that will be specified +by the user that could start with @samp{-}. +@end table - if (i != 6) - return -1 +The previous list described options mandated by the POSIX standard, +as well as options available in the Bell Laboratories version of @command{awk}. +The following list describes @command{gawk}-specific options: - # force numeric - for (j in a) - a[j] += 0 +@table @code +@item -W compat +@itemx -W traditional +@itemx --compat +@itemx --traditional +@cindex @code{--compat} option +@cindex command-line option, @code{--compat} +@cindex @code{--traditional} option +@cindex command-line option, @code{--traditional} +@cindex compatibility mode +Specifies @dfn{compatibility mode}, in which the GNU extensions to +the @command{awk} language are disabled, so that @command{gawk} behaves just +like the Bell Laboratories research version of Unix @command{awk}. +@option{--traditional} is the preferred form of this option. +@xref{POSIX/GNU, ,Extensions in @command{gawk} Not in POSIX @command{awk}}, +which summarizes the extensions. Also see +@ref{Compatibility Mode, ,Downward Compatibility and Debugging}. -@group - # validate - if (a[1] < 1970 || - a[2] < 1 || a[2] > 12 || - a[3] < 1 || a[3] > 31 || - a[4] < 0 || a[4] > 23 || - a[5] < 0 || a[5] > 59 || - a[6] < 0 || a[6] > 60 ) - return -1 -@end group +@item -W copyright +@itemx --copyright +@cindex @code{--copyright} option +@cindex command-line option, @code{--copyright} +Print the short version of the General Public License and then exit. - res1 = _tm_addup(a) - t = strftime("%Y %m %d %H %M %S", res1) +@item -W copyleft +@itemx --copyleft +@cindex @code{--copyleft} option +@cindex command-line option, @code{--copyleft} +Just like @option{--copyright}. +This option may disappear in a future version of @command{gawk}. + +@cindex @code{--dump-variables} option +@cindex command-line option, @code{--dump-variables} +@cindex @file{awkvars.out} global variable list output file +@item -W dump-variables@r{[}=@var{file}@r{]} +@itemx --dump-variables@r{[}=@var{file}@r{]} +Print a sorted list of global variables, their types, and final values +to @var{file}. If no @var{file} is provided, @command{gawk} prints this +list to a file named @file{awkvars.out} in the current directory. - if (_tm_debug) - printf("(%s) -> (%s)\n", str, t) > "/dev/stderr" +@cindex common mistakes +@cindex mistakes, common +@cindex errors, common +Having a list of all the global variables is a good way to look for +typographical errors in your programs. +You would also use this option if you have a large program with a lot of +functions, and you want to be sure that your functions don't +inadvertently use global variables that you meant to be local. +(This is a particularly easy mistake to make with simple variable +names like @code{i}, @code{j}, and so on.) + +@item -W gen-po +@itemx --gen-po +@cindex @code{--gen-po} option +@cindex command-line option, @code{--gen-po} +Analyze the source program and +generate a GNU @code{gettext} Portable Object file on standard +output for all string constants that have been marked for translation. +@xref{Internationalization, ,Internationalization with @command{gawk}}, +for information about this option. - split(t, b, " ") - res2 = _tm_addup(b) +@item -W help +@itemx -W usage +@itemx --help +@itemx --usage +@cindex @code{--help} option +@cindex command-line option, @code{--help} +@cindex @code{--usage} option +@cindex command-line option, @code{--usage} +Print a ``usage'' message summarizing the short and long style options +that @command{gawk} accepts and then exit. - diff = res1 - res2 +@item -W lint@r{[}=fatal@r{]} +@itemx --lint@r{[}=fatal@r{]} +@cindex @code{--lint} option +@cindex command-line option, @code{--lint} +@cindex lint checks +@cindex fatal errors +Warn about constructs that are dubious or non-portable to +other @command{awk} implementations. +Some warnings are issued when @command{gawk} first reads your program. Others +are issued at runtime, as your program executes. +With an optional argument of @samp{fatal}, +lint warnings become fatal errors. +This may be drastic but its use will certainly encourage the +development of cleaner @command{awk} programs. - if (_tm_debug) - printf("diff = %d seconds\n", diff) > "/dev/stderr" +@item -W lint-old +@itemx --lint-old +@cindex @code{--lint-old} option +@cindex command-line option, @code{--lint-old} +@cindex lint checks +Warn about constructs that are not available in the original version of +@command{awk} from Version 7 Unix +(@pxref{V7/SVR3.1, ,Major Changes Between V7 and SVR3.1}). + +@item -W non-decimal-data +@itemx --non-decimal-data +@cindex @code{--non-decimal-data} option +@cindex command-line option, @code{--non-decimal-data} +Enable automatic interpretation of octal and hexadecimal +values in input data +(@pxref{Non-decimal Data, ,Allowing Non-Decimal Input Data}). + +@strong{Caution:} This option can severely break old programs. +Use with care. - res1 += diff +@item -W posix +@itemx --posix +@cindex @code{--posix} option +@cindex command-line option, @code{--posix} +@cindex POSIX mode +Operate in strict POSIX mode. This disables all @command{gawk} +extensions (just like @option{--traditional}) and adds the following additional +restrictions: - return res1 -@} -@c endfile -@c @end group -@end example - -The function first splits the string into an array, using spaces and tabs as -separators. If there are not six elements in the array, it returns an -error, signaled as the value @minus{}1. -Next, it forces each element of the array to be numeric, by adding zero to it. -The following @samp{if} statement then makes sure that each element is -within an allowable range. (This checking could be extended further, e.g., -to make sure that the day of the month is within the correct range for the -particular month supplied.) All of this is essentially preliminary set-up -and error checking. - -Recall that @code{_tm_addup} generated a value in seconds since Midnight, -January 1, 1970. This value is not directly usable as the result we want, -@emph{since the calculation does not account for the local timezone}. In other -words, the value represents the count in seconds since the Epoch, but only -for UTC (Universal Coordinated Time). If the local timezone is east or west -of UTC, then some number of hours should be either added to, or subtracted from -the resulting timestamp. - -For example, 6:23 p.m. in Atlanta, Georgia (USA), is normally five hours west -of (behind) UTC. It is only four hours behind UTC if daylight savings -time is in effect. -If you are calling @code{mktime} in Atlanta, with the argument -@code{@w{"1993 5 23 18 23 12"}}, the result from @code{_tm_addup} will be -for 6:23 p.m. UTC, which is only 2:23 p.m. in Atlanta. It is necessary to -add another four hours worth of seconds to the result. - -How can @code{mktime} determine how far away it is from UTC? This is -surprisingly easy. The returned timestamp represents the time passed to -@code{mktime} @emph{as UTC}. This timestamp can be fed back to -@code{strftime}, which will format it as a @emph{local} time; i.e.@: as -if it already had the UTC difference added in to it. This is done by -giving @code{@w{"%Y %m %d %H %M %S"}} to @code{strftime} as the format -argument. It returns the computed timestamp in the original string -format. The result represents a time that accounts for the UTC -difference. When the new time is converted back to a timestamp, the -difference between the two timestamps is the difference (in seconds) -between the local timezone and UTC. This difference is then added back -to the original result. An example demonstrating this is presented below. - -Finally, there is a ``main'' program for testing the function. - -@example -@c there used to be a blank line after the getline, -@c squished out for page formatting reasons -@c @group -@c file eg/lib/mktime.awk -BEGIN @{ - if (_tm_test) @{ - printf "Enter date as yyyy mm dd hh mm ss: " - getline _tm_test_date - t = mktime(_tm_test_date) - r = strftime("%Y %m %d %H %M %S", t) - printf "Got back (%s)\n", r - @} -@} -@c endfile -@c @end group -@end example +@c IMPORTANT! Keep this list in sync with the one in node POSIX -The entire program uses two variables that can be set on the command -line to control debugging output and to enable the test in the final -@code{BEGIN} rule. Here is the result of a test run. (Note that debugging -output is to standard error, and test output is to standard output.) +@itemize @bullet +@item +@code{\x} escape sequences are not recognized +(@pxref{Escape Sequences}). -@example -@c @group -$ gawk -f mktime.awk -v _tm_test=1 -v _tm_debug=1 -@print{} Enter date as yyyy mm dd hh mm ss: 1993 5 23 15 35 10 -@error{} (1993 5 23 15 35 10) -> (1993 05 23 11 35 10) -@error{} diff = 14400 seconds -@print{} Got back (1993 05 23 15 35 10) -@c @end group -@end example +@item +Newlines do not act as whitespace to separate fields when @code{FS} is +equal to a single space +(@pxref{Fields, , Examining Fields}). -The time entered was 3:35 p.m. (15:35 on a 24-hour clock), on May 23, 1993. -The first line -of debugging output shows the resulting time as UTC---four hours ahead of -the local time zone. The second line shows that the difference is 14400 -seconds, which is four hours. (The difference is only four hours, since -daylight savings time is in effect during May.) -The final line of test output shows that the timezone compensation -algorithm works; the returned time is the same as the entered time. +@item +Newlines are not allowed after @samp{?} or @samp{:} +(@pxref{Conditional Exp, ,Conditional Expressions}). -This program does not solve the general problem of turning an arbitrary date -representation into a timestamp. That problem is very involved. However, -the @code{mktime} function provides a foundation upon which to build. Other -software can convert month names into numeric months, and AM/PM times into -24-hour clocks, to generate the ``canonical'' format that @code{mktime} -requires. +@item +The synonym @code{func} for the keyword @code{function} is not +recognized (@pxref{Definition Syntax, ,Function Definition Syntax}). -@node Gettimeofday Function, Filetrans Function, Mktime Function, Library Functions -@section Managing the Time of Day +@item +The @samp{**} and @samp{**=} operators cannot be used in +place of @samp{^} and @samp{^=} (@pxref{Arithmetic Ops, ,Arithmetic Operators}, +and also @pxref{Assignment Ops, ,Assignment Expressions}). -@cindex formatted timestamps -@cindex timestamps, formatted -The @code{systime} and @code{strftime} functions described in -@ref{Time Functions, ,Functions for Dealing with Time Stamps}, -provide the minimum functionality necessary for dealing with the time of day -in human readable form. While @code{strftime} is extensive, the control -formats are not necessarily easy to remember or intuitively obvious when -reading a program. +@item +Specifying @samp{-Ft} on the command-line does not set the value +of @code{FS} to be a single tab character +(@pxref{Field Separators, ,Specifying How Fields Are Separated}). -The following function, @code{gettimeofday}, populates a user-supplied array -with pre-formatted time information. It returns a string with the current -time formatted in the same way as the @code{date} utility. +@item +The @code{fflush} built-in function is not supported +(@pxref{I/O Functions, ,Input/Output Functions}). +@end itemize -@findex gettimeofday -@example -@c @group -@c file eg/lib/gettime.awk -# gettimeofday --- get the time of day in a usable format -# Arnold Robbins, arnold@@gnu.org, Public Domain, May 1993 -# -# Returns a string in the format of output of date(1) -# Populates the array argument time with individual values: -# time["second"] -- seconds (0 - 59) -# time["minute"] -- minutes (0 - 59) -# time["hour"] -- hours (0 - 23) -# time["althour"] -- hours (0 - 12) -# time["monthday"] -- day of month (1 - 31) -# time["month"] -- month of year (1 - 12) -# time["monthname"] -- name of the month -# time["shortmonth"] -- short name of the month -# time["year"] -- year within century (0 - 99) -# time["fullyear"] -- year with century (19xx or 20xx) -# time["weekday"] -- day of week (Sunday = 0) -# time["altweekday"] -- day of week (Monday = 0) -# time["weeknum"] -- week number, Sunday first day -# time["altweeknum"] -- week number, Monday first day -# time["dayname"] -- name of weekday -# time["shortdayname"] -- short name of weekday -# time["yearday"] -- day of year (0 - 365) -# time["timezone"] -- abbreviation of timezone name -# time["ampm"] -- AM or PM designation +@cindex automatic warnings +@cindex warnings, automatic +If you supply both @option{--traditional} and @option{--posix} on the +command-line, @option{--posix} takes precedence. @command{gawk} +also issues a warning if both options are supplied. + +@item -W profile@r{[}=@var{file}@r{]} +@itemx --profile@r{[}=@var{file}@r{]} +@cindex @code{--profile} option +@cindex command-line option, @code{--profile} +Enable profiling of @command{awk} programs +(@pxref{Profiling, ,Profiling Your @command{awk} Programs}). +By default, profiles are created in a file named @file{awkprof.out}. +The optional @var{file} argument allows you to specify a different +@value{FN} for the profile file. + +When run with @command{gawk}, the profile is just a ``pretty printed'' version +of the program. When run with @command{pgawk}, the profile contains execution +counts for each statement in the program in the left margin, and function +call counts for each function. -function gettimeofday(time, ret, now, i) -@{ - # get time once, avoids unnecessary system calls - now = systime() +@item -W re-interval +@itemx --re-interval +@cindex @code{--re-interval} option +@cindex command-line option, @code{--re-interval} +Allow interval expressions +(@pxref{Regexp Operators, , Regular Expression Operators}) +in regexps. +Because interval expressions were traditionally not available in @command{awk}, +@command{gawk} does not provide them by default. This prevents old @command{awk} +programs from breaking. - # return date(1)-style output - ret = strftime("%a %b %d %H:%M:%S %Z %Y", now) +@item -W source @var{program-text} +@itemx --source @var{program-text} +@cindex @code{--source} option +@cindex command-line option, @code{--source} +Program source code is taken from the @var{program-text}. This option +allows you to mix source code in files with source +code that you enter on the command-line. This is particularly useful +when you have library functions that you want to use from your command-line +programs (@pxref{AWKPATH Variable, ,The @env{AWKPATH} Environment Variable}). - # clear out target array - for (i in time) - delete time[i] +@item -W version +@itemx --version +@cindex @code{--version} option +@cindex command-line option, @code{--version} +Print version information for this particular copy of @command{gawk}. +This allows you to determine if your copy of @command{gawk} is up to date +with respect to whatever the Free Software Foundation is currently +distributing. +It is also useful for bug reports +(@pxref{Bugs, , Reporting Problems and Bugs}). +@end table - # fill in values, force numeric values to be - # numeric by adding 0 - time["second"] = strftime("%S", now) + 0 - time["minute"] = strftime("%M", now) + 0 - time["hour"] = strftime("%H", now) + 0 - time["althour"] = strftime("%I", now) + 0 - time["monthday"] = strftime("%d", now) + 0 - time["month"] = strftime("%m", now) + 0 - time["monthname"] = strftime("%B", now) - time["shortmonth"] = strftime("%b", now) - time["year"] = strftime("%y", now) + 0 - time["fullyear"] = strftime("%Y", now) + 0 - time["weekday"] = strftime("%w", now) + 0 - time["altweekday"] = strftime("%u", now) + 0 - time["dayname"] = strftime("%A", now) - time["shortdayname"] = strftime("%a", now) - time["yearday"] = strftime("%j", now) + 0 - time["timezone"] = strftime("%Z", now) - time["ampm"] = strftime("%p", now) - time["weeknum"] = strftime("%U", now) + 0 - time["altweeknum"] = strftime("%W", now) + 0 +As long as program text has been supplied, +any other options are flagged as invalid with a warning message but +are otherwise ignored. - return ret -@} -@c endfile -@end example +In compatibility mode, as a special case, if the value of @var{fs} supplied +to the @option{-F} option is @samp{t}, then @code{FS} is set to the tab +character (@code{"\t"}). This is only true for @option{--traditional} and not +for @option{--posix} +(@pxref{Field Separators, ,Specifying How Fields Are Separated}). -The string indices are easier to use and read than the various formats -required by @code{strftime}. The @code{alarm} program presented in -@ref{Alarm Program, ,An Alarm Clock Program}, -uses this function. +The @option{-f} option may be used more than once on the command-line. +If it is, @command{awk} reads its program source from all of the named files, as +if they had been concatenated together into one big file. This is +useful for creating libraries of @command{awk} functions. These functions +can be written once and then retrieved from a standard place, instead +of having to be included into each individual program. +(As mentioned in +@ref{Definition Syntax, ,Function Definition Syntax}, +function names must be unique.) -@c exercise!!! -The @code{gettimeofday} function is presented above as it was written. A -more general design for this function would have allowed the user to supply -an optional timestamp value that would have been used instead of the current -time. +Library functions can still be used, even if the program is entered at the terminal, +by specifying @samp{-f /dev/tty}. After typing your program, +type @kbd{Ctrl-d} (the end-of-file character) to terminate it. +(You may also use @samp{-f -} to read program source from the standard +input but then you will not be able to also use the standard input as a +source of data.) -@node Filetrans Function, Getopt Function, Gettimeofday Function, Library Functions -@section Noting Data File Boundaries +Because it is clumsy using the standard @command{awk} mechanisms to mix source +file and command-line @command{awk} programs, @command{gawk} provides the +@option{--source} option. This does not require you to pre-empt the standard +input for your source code; it allows you to easily mix command-line +and library source code +(@pxref{AWKPATH Variable, ,The @env{AWKPATH} Environment Variable}). -@cindex per file initialization and clean-up -The @code{BEGIN} and @code{END} rules are each executed exactly once, at -the beginning and end respectively of your @code{awk} program -(@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}). -We (the @code{gawk} authors) once had a user who mistakenly thought that the -@code{BEGIN} rule was executed at the beginning of each data file and the -@code{END} rule was executed at the end of each data file. When informed -that this was not the case, the user requested that we add new special -patterns to @code{gawk}, named @code{BEGIN_FILE} and @code{END_FILE}, that -would have the desired behavior. He even supplied us the code to do so. +If no @option{-f} or @option{--source} option is specified, then @command{gawk} +uses the first non-option command-line argument as the text of the +program source code. -However, after a little thought, I came up with the following library program. -It arranges to call two user-supplied functions, @code{beginfile} and -@code{endfile}, at the beginning and end of each data file. -Besides solving the problem in only nine(!) lines of code, it does so -@emph{portably}; this will work with any implementation of @code{awk}. +@cindex @code{POSIXLY_CORRECT} environment variable +@cindex environment variable, @code{POSIXLY_CORRECT} +@cindex lint checks +If the environment variable @env{POSIXLY_CORRECT} exists, +then @command{gawk} behaves in strict POSIX mode, exactly as if +you had supplied the @option{--posix} command-line option. +Many GNU programs look for this environment variable to turn on +strict POSIX mode. If @option{--lint} is supplied on the command-line +and @command{gawk} turns on POSIX mode because of @env{POSIXLY_CORRECT}, +then it issues a warning message indicating that POSIX +mode is in effect. +You would typically set this variable in your shell's startup file. +For a Bourne-compatible shell (such as @command{bash}), you would add these +lines to the @file{.profile} file in your home directory: @example -@c @group -# transfile.awk -# -# Give the user a hook for filename transitions -# -# The user must supply functions beginfile() and endfile() -# that each take the name of the file being started or -# finished, respectively. -# -# Arnold Robbins, arnold@@gnu.org, January 1992 -# Public Domain +POSIXLY_CORRECT=true +export POSIXLY_CORRECT +@end example -FILENAME != _oldfilename \ -@{ - if (_oldfilename != "") - endfile(_oldfilename) - _oldfilename = FILENAME - beginfile(FILENAME) -@} +@cindex @command{csh} utility +For a @command{csh} compatible +shell,@footnote{Not recommended.} +you would add this line to the @file{.login} file in your home directory: -END @{ endfile(FILENAME) @} -@c @end group +@example +setenv POSIXLY_CORRECT true @end example -This file must be loaded before the user's ``main'' program, so that the -rule it supplies will be executed first. +Having @env{POSIXLY_CORRECT} set is not recommended for daily use, +but it is good for testing the portability of your programs to other +environments. -This rule relies on @code{awk}'s @code{FILENAME} variable that -automatically changes for each new data file. The current file name is -saved in a private variable, @code{_oldfilename}. If @code{FILENAME} does -not equal @code{_oldfilename}, then a new data file is being processed, and -it is necessary to call @code{endfile} for the old file. Since -@code{endfile} should only be called if a file has been processed, the -program first checks to make sure that @code{_oldfilename} is not the null -string. The program then assigns the current file name to -@code{_oldfilename}, and calls @code{beginfile} for the file. -Since, like all @code{awk} variables, @code{_oldfilename} will be -initialized to the null string, this rule executes correctly even for the -first data file. +@node Other Arguments, AWKPATH Variable, Options, Invoking Gawk +@section Other Command-Line Arguments -The program also supplies an @code{END} rule, to do the final processing for -the last file. Since this @code{END} rule comes before any @code{END} rules -supplied in the ``main'' program, @code{endfile} will be called first. Once -again the value of multiple @code{BEGIN} and @code{END} rules should be clear. +Any additional arguments on the command-line are normally treated as +input files to be processed in the order specified. However, an +argument that has the form @code{@var{var}=@var{value}}, assigns +the value @var{value} to the variable @var{var}---it does not specify a +file at all. +(This was discussed earlier in +@ref{Assignment Options, ,Assigning Variables on the Command Line}.) -@findex beginfile -@findex endfile -This version has same problem as the first version of @code{nextfile} -(@pxref{Nextfile Function, ,Implementing @code{nextfile} as a Function}). -If the same data file occurs twice in a row on command line, then -@code{endfile} and @code{beginfile} will not be executed at the end of the -first pass and at the beginning of the second pass. -This version solves the problem. +@cindex @code{ARGIND} variable +@cindex @code{ARGV} variable +All these arguments are made available to your @command{awk} program in the +@code{ARGV} array (@pxref{Built-in Variables}). Command-line options +and the program text (if present) are omitted from @code{ARGV}. +All other arguments, including variable assignments, are +included. As each element of @code{ARGV} is processed, @command{gawk} +sets the variable @code{ARGIND} to the index in @code{ARGV} of the +current element. -@example -@c @group -@c file eg/lib/ftrans.awk -# ftrans.awk --- handle data file transitions -# -# user supplies beginfile() and endfile() functions -# -# Arnold Robbins, arnold@@gnu.org, November 1992 -# Public Domain +The distinction between @value{FN} arguments and variable-assignment +arguments is made when @command{awk} is about to open the next input file. +At that point in execution, it checks the @value{FN} to see whether +it is really a variable assignment; if so, @command{awk} sets the variable +instead of reading a file. -FNR == 1 @{ - if (_filename_ != "") - endfile(_filename_) - _filename_ = FILENAME - beginfile(FILENAME) -@} +Therefore, the variables actually receive the given values after all +previously specified files have been read. In particular, the values of +variables assigned in this fashion are @emph{not} available inside a +@code{BEGIN} rule +(@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}), +because such rules are run before @command{awk} begins scanning the argument list. -END @{ endfile(_filename_) @} -@c endfile -@c @end group -@end example +@cindex dark corner +The variable values given on the command-line are processed for escape +sequences (@pxref{Escape Sequences}). +@value{DARKCORNER} + +In some earlier implementations of @command{awk}, when a variable assignment +occurred before any @value{FN}s, the assignment would happen @emph{before} +the @code{BEGIN} rule was executed. @command{awk}'s behavior was thus +inconsistent; some command-line assignments were available inside the +@code{BEGIN} rule, while others were not. Unfortunately, +some applications came to depend +upon this ``feature.'' When @command{awk} was changed to be more consistent, +the @option{-v} option was added to accommodate applications that depended +upon the old behavior. -In @ref{Wc Program, ,Counting Things}, -you will see how this library function can be used, and -how it simplifies writing the main program. +The variable assignment feature is most useful for assigning to variables +such as @code{RS}, @code{OFS}, and @code{ORS}, which control input and +output formats before scanning the @value{DF}s. It is also useful for +controlling state if multiple passes are needed over a @value{DF}. For +example: -@node Getopt Function, Passwd Functions, Filetrans Function, Library Functions -@section Processing Command Line Options +@cindex multiple passes over data +@cindex passes, multiple +@example +awk 'pass == 1 @{ @var{pass 1 stuff} @} + pass == 2 @{ @var{pass 2 stuff} @}' pass=1 mydata pass=2 mydata +@end example -@cindex @code{getopt}, C version -@cindex processing arguments -@cindex argument processing -Most utilities on POSIX compatible systems take options or ``switches'' on -the command line that can be used to change the way a program behaves. -@code{awk} is an example of such a program -(@pxref{Options, ,Command Line Options}). -Often, options take @dfn{arguments}, data that the program needs to -correctly obey the command line option. For example, @code{awk}'s -@samp{-F} option requires a string to use as the field separator. -The first occurrence on the command line of either @samp{--} or a -string that does not begin with @samp{-} ends the options. +Given the variable assignment feature, the @option{-F} option for setting +the value of @code{FS} is not +strictly necessary. It remains for historical compatibility. -Most Unix systems provide a C function named @code{getopt} for processing -command line arguments. The programmer provides a string describing the one -letter options. If an option requires an argument, it is followed in the -string with a colon. @code{getopt} is also passed the -count and values of the command line arguments, and is called in a loop. -@code{getopt} processes the command line arguments for option letters. -Each time around the loop, it returns a single character representing the -next option letter that it found, or @samp{?} if it found an invalid option. -When it returns @minus{}1, there are no options left on the command line. +@node AWKPATH Variable, Obsolete, Other Arguments, Invoking Gawk +@section The @env{AWKPATH} Environment Variable +@cindex @env{AWKPATH} environment variable +@cindex environment variable, @env{AWKPATH} +@cindex search path +@cindex directory search +@cindex path, search +@cindex search path, for source files +@cindex differences between @command{gawk} and @command{awk} +@ifinfo +The previous @value{SECTION} described how @command{awk} program files can be named +on the command-line with the @option{-f} option. +@end ifinfo +In most @command{awk} +implementations, you must supply a precise path name for each program +file, unless the file is in the current directory. +But in @command{gawk}, if the @value{FN} supplied to the @option{-f} option +does not contain a @samp{/}, then @command{gawk} searches a list of +directories (called the @dfn{search path}), one by one, looking for a +file with the specified name. -When using @code{getopt}, options that do not take arguments can be -grouped together. Furthermore, options that take arguments require that the -argument be present. The argument can immediately follow the option letter, -or it can be a separate command line argument. +The search path is a string consisting of directory names +separated by colons. @command{gawk} gets its search path from the +@env{AWKPATH} environment variable. If that variable does not exist, +@command{gawk} uses a default path, which is +@samp{.:/usr/local/share/awk}.@footnote{Your version of @command{gawk} +may use a different directory; it +will depend upon how @command{gawk} was built and installed. The actual +directory is the value of @samp{$(datadir)} generated when +@command{gawk} was configured. You probably don't need to worry about this +though.} (Programs written for use by +system administrators should use an @env{AWKPATH} variable that +does not include the current directory, @file{.}.) -Given a hypothetical program that takes -three command line options, @samp{-a}, @samp{-b}, and @samp{-c}, and -@samp{-b} requires an argument, all of the following are valid ways of -invoking the program: +The search path feature is particularly useful for building libraries +of useful @command{awk} functions. The library files can be placed in a +standard directory in the default path and then specified on +the command-line with a short @value{FN}. Otherwise, the full @value{FN} +would have to be typed for each file. -@example -@c @group -prog -a -b foo -c data1 data2 data3 -prog -ac -bfoo -- data1 data2 data3 -prog -acbfoo data1 data2 data3 -@c @end group -@end example +By using both the @option{--source} and @option{-f} options, your command-line +@command{awk} programs can use facilities in @command{awk} library files. +@xref{Library Functions, , A Library of @command{awk} Functions}. +Path searching is not done if @command{gawk} is in compatibility mode. +This is true for both @option{--traditional} and @option{--posix}. +@xref{Options, ,Command-Line Options}. -Notice that when the argument is grouped with its option, the rest of -the command line argument is considered to be the option's argument. -In the above example, @samp{-acbfoo} indicates that all of the -@samp{-a}, @samp{-b}, and @samp{-c} options were supplied, -and that @samp{foo} is the argument to the @samp{-b} option. +@strong{Note:} If you want files in the current directory to be found, +you must include the current directory in the path, either by including +@file{.} explicitly in the path or by writing a null entry in the +path. (A null entry is indicated by starting or ending the path with a +colon or by placing two colons next to each other (@samp{::}).) If the +current directory is not included in the path, then files cannot be +found in the current directory. This path search mechanism is identical +to the shell's. +@c someday, @cite{The Bourne Again Shell}.... -@code{getopt} provides four external variables that the programmer can use. +Starting with @value{PVERSION} 3.0, if @env{AWKPATH} is not defined in the +environment, @command{gawk} places its default search path into +@code{ENVIRON["AWKPATH"]}. This makes it easy to determine +the actual search path that @command{gawk} will use +from within an @command{awk} program. -@table @code -@item optind -The index in the argument value array (@code{argv}) where the first -non-option command line argument can be found. +While you can change @code{ENVIRON["AWKPATH"]} within your @command{awk} +program, this has no effect on the running program's behavior. This makes +sense: the @env{AWKPATH} environment variable is used to find the program +source files. Once your program is running, all the files have been +found, and @command{gawk} no longer needs to use @env{AWKPATH}. -@item optarg -The string value of the argument to an option. +@node Obsolete, Undocumented, AWKPATH Variable, Invoking Gawk +@section Obsolete Options and/or Features -@item opterr -Usually @code{getopt} prints an error message when it finds an invalid -option. Setting @code{opterr} to zero disables this feature. (An -application might wish to print its own error message.) +@cindex deprecated options +@cindex obsolete options +@cindex deprecated features +@cindex obsolete features +This @value{SECTION} describes features and/or command-line options from +previous releases of @command{gawk} that are either not available in the +current version or that are still supported but deprecated (meaning that +they will @emph{not} be in the next release). -@item optopt -The letter representing the command line option. -While not usually documented, most versions supply this variable. -@end table +@c update this section for each release! -The following C fragment shows how @code{getopt} might process command line -arguments for @code{awk}. +For @value{PVERSION} @value{VERSION} of @command{gawk}, there are no +deprecated command-line options +@c or other deprecated features +from the previous version of @command{gawk}. +The use of @samp{next file} (two words) for @code{nextfile} was deprecated +in @command{gawk} 3.0 but still worked. Starting with @value{PVERSION} 3.1, the +two word usage is no longer accepted. + +The process-related special files described in +@ref{Special Process, ,Special Files for Process-Related Information}, +work as described, but +are now considered deprecated. +@command{gawk} prints a warning message every time they are used. +(Use @code{PROCINFO} instead; see +@ref{Auto-set, ,Built-in Variables That Convey Information}.) +They will be removed from the next release of @command{gawk}. -@example -@group -int -main(int argc, char *argv[]) -@{ - @dots{} - /* print our own message */ - opterr = 0; -@end group -@group - while ((c = getopt(argc, argv, "v:f:F:W:")) != -1) @{ - switch (c) @{ - case 'f': /* file */ - @dots{} - break; - case 'F': /* field separator */ - @dots{} - break; - case 'v': /* variable assignment */ - @dots{} - break; - case 'W': /* extension */ - @dots{} - break; - case '?': - default: - usage(); - break; - @} - @} - @dots{} -@} -@end group -@end example +@ignore +This @value{SECTION} +is thus essentially a place holder, +in case some option becomes obsolete in a future version of @command{gawk}. +@end ignore -As a side point, @code{gawk} actually uses the GNU @code{getopt_long} -function to process both normal and GNU-style long options -(@pxref{Options, ,Command Line Options}). +@node Undocumented, Known Bugs, Obsolete, Invoking Gawk +@section Undocumented Options and Features +@cindex undocumented features +@cindex features, undocumented +@cindex Skywalker, Luke +@cindex Kenobi, Obi-Wan +@cindex Jedi knights +@cindex Knights, jedi +@quotation +@i{Use the Source, Luke!}@* +Obi-Wan +@end quotation -The abstraction provided by @code{getopt} is very useful, and would be quite -handy in @code{awk} programs as well. Here is an @code{awk} version of -@code{getopt}. This function highlights one of the greatest weaknesses in -@code{awk}, which is that it is very poor at manipulating single characters. -Repeated calls to @code{substr} are necessary for accessing individual -characters (@pxref{String Functions, ,Built-in Functions for String Manipulation}). +This @value{SECTION} intentionally left +blank. -The discussion walks through the code a bit at a time. +@ignore +@c If these came out in the Info file or TeX document, then they wouldn't +@c be undocumented, would they? -@example -@c @group -@c file eg/lib/getopt.awk -# getopt --- do C library getopt(3) function in awk -# -# arnold@@gnu.org -# Public domain -# -# Initial version: March, 1991 -# Revised: May, 1993 +@command{gawk} has one undocumented option: -@group -# External variables: -# Optind -- index of ARGV for first non-option argument -# Optarg -- string value of argument to current option -# Opterr -- if non-zero, print our own diagnostic -# Optopt -- current option letter -@end group +@table @code +@item -W nostalgia +@itemx --nostalgia +Print the message @code{"awk: bailing out near line 1"} and dump core. +This option was inspired by the common behavior of very early versions of +Unix @command{awk} and by a t--shirt. +The message is @emph{not} subject to translation in non-English locales. +@c so there! nyah, nyah. +@end table -# Returns -# -1 at end of options -# ? for unrecognized option -# a character representing the current option +Early versions of @command{awk} used to not require any separator (either +a newline or @samp{;}) between the rules in @command{awk} programs. Thus, +it was common to see one-line programs like: -# Private Data -# _opti index in multi-flag option, e.g., -abc -@c endfile -@c @end group +@example +awk '@{ sum += $1 @} END @{ print sum @}' @end example -The function starts out with some documentation: who wrote the code, -and when it was revised, followed by a list of the global variables it uses, -what the return values are and what they mean, and any global variables that -are ``private'' to this library function. Such documentation is essential -for any program, and particularly for library functions. +@command{gawk} actually supports this but it is purposely undocumented +because it is considered bad style. The correct way to write such a program +is either -@findex getopt @example -@c @group -@c file eg/lib/getopt.awk -function getopt(argc, argv, options, optl, thisopt, i) -@{ - optl = length(options) - if (optl == 0) # no options given - return -1 - - if (argv[Optind] == "--") @{ # all done - Optind++ - _opti = 0 - return -1 - @} else if (argv[Optind] !~ /^-[^: \t\n\f\r\v\b]/) @{ - _opti = 0 - return -1 - @} -@c endfile -@c @end group +awk '@{ sum += $1 @} ; END @{ print sum @}' @end example -The function first checks that it was indeed called with a string of options -(the @code{options} parameter). If @code{options} has a zero length, -@code{getopt} immediately returns @minus{}1. - -The next thing to check for is the end of the options. A @samp{--} ends the -command line options, as does any command line argument that does not begin -with a @samp{-}. @code{Optind} is used to step through the array of command -line arguments; it retains its value across calls to @code{getopt}, since it -is a global variable. - -The regexp used, @code{@w{/^-[^: \t\n\f\r\v\b]/}}, is -perhaps a bit of overkill; it checks for a @samp{-} followed by anything -that is not whitespace and not a colon. -If the current command line argument does not match this pattern, -it is not an option, and it ends option processing. +@noindent +or @example -@group -@c file eg/lib/getopt.awk - if (_opti == 0) - _opti = 2 - thisopt = substr(argv[Optind], _opti, 1) - Optopt = thisopt - i = index(options, thisopt) - if (i == 0) @{ - if (Opterr) - printf("%c -- invalid option\n", - thisopt) > "/dev/stderr" - if (_opti >= length(argv[Optind])) @{ - Optind++ - _opti = 0 - @} else - _opti++ - return "?" - @} -@c endfile -@end group +awk '@{ sum += $1 @} + END @{ print sum @}' data @end example -The @code{_opti} variable tracks the position in the current command line -argument (@code{argv[Optind]}). In the case that multiple options were -grouped together with one @samp{-} (e.g., @samp{-abx}), it is necessary -to return them to the user one at a time. +@noindent +@xref{Statements/Lines, ,@command{awk} Statements Versus Lines}, for a fuller +explanation. -If @code{_opti} is equal to zero, it is set to two, the index in the string -of the next character to look at (we skip the @samp{-}, which is at position -one). The variable @code{thisopt} holds the character, obtained with -@code{substr}. It is saved in @code{Optopt} for the main program to use. +You can insert newlines after the @samp{;} in @code{for} loops. +This seems to have been a long-undocumented feature in Unix @command{awk}. -If @code{thisopt} is not in the @code{options} string, then it is an -invalid option. If @code{Opterr} is non-zero, @code{getopt} prints an error -message on the standard error that is similar to the message from the C -version of @code{getopt}. +If the environment variable @env{WHINY_USERS} exists +when @command{gawk} is run, +then the associative @code{for} loop will go through the array +indices in sorted order. +The comparison used for sorting is simple string comparison; +any non-English or non-ASCII locales are not taken into account. +@code{IGNORECASE} does not affect the comparison either. -Since the option is invalid, it is necessary to skip it and move on to the -next option character. If @code{_opti} is greater than or equal to the -length of the current command line argument, then it is necessary to move on -to the next one, so @code{Optind} is incremented and @code{_opti} is reset -to zero. Otherwise, @code{Optind} is left alone and @code{_opti} is merely -incremented. +@end ignore -In any case, since the option was invalid, @code{getopt} returns @samp{?}. -The main program can examine @code{Optopt} if it needs to know what the -invalid option letter actually was. +@node Known Bugs, , Undocumented, Invoking Gawk +@section Known Bugs in @command{gawk} +@cindex bugs, known in @command{gawk} +@cindex known bugs -@example -@group -@c file eg/lib/getopt.awk - if (substr(options, i + 1, 1) == ":") @{ - # get option argument - if (length(substr(argv[Optind], _opti + 1)) > 0) - Optarg = substr(argv[Optind], _opti + 1) - else - Optarg = argv[++Optind] - _opti = 0 - @} else - Optarg = "" -@c endfile -@end group -@end example +@itemize @bullet +@item +The @option{-F} option for changing the value of @code{FS} +(@pxref{Options, ,Command-Line Options}) +is not necessary given the command-line variable +assignment feature; it remains only for backwards compatibility. -If the option requires an argument, the option letter is followed by a colon -in the @code{options} string. If there are remaining characters in the -current command line argument (@code{argv[Optind]}), then the rest of that -string is assigned to @code{Optarg}. Otherwise, the next command line -argument is used (@samp{-xFOO} vs. @samp{@w{-x FOO}}). In either case, -@code{_opti} is reset to zero, since there are no more characters left to -examine in the current command line argument. +@item +Syntactically invalid single character programs tend to overflow +the parse stack, generating a rather unhelpful message. Such programs +are surprisingly difficult to diagnose in the completely general case +and the effort to do so really is not worth it. +@end itemize -@example -@c @group -@c file eg/lib/getopt.awk - if (_opti == 0 || _opti >= length(argv[Optind])) @{ - Optind++ - _opti = 0 - @} else - _opti++ - return thisopt -@} -@c endfile -@c @end group -@end example +@ignore +@c Try this +@iftex +@page +@headings off +@majorheading II@ @ @ Using @command{awk} and @command{gawk} +Part II shows how to use @command{awk} and @command{gawk} for problem solving. +There is lots of code here for you to read and learn from. +It contains the following chapters: -Finally, if @code{_opti} is either zero or greater than the length of the -current command line argument, it means this element in @code{argv} is -through being processed, so @code{Optind} is incremented to point to the -next element in @code{argv}. If neither condition is true, then only -@code{_opti} is incremented, so that the next option letter can be processed -on the next call to @code{getopt}. +@itemize @bullet +@item +@ref{Library Functions, ,A Library of @command{awk} Functions}. -@example -@c @group -@c file eg/lib/getopt.awk -BEGIN @{ - Opterr = 1 # default is to diagnose - Optind = 1 # skip ARGV[0] +@item +@ref{Sample Programs, ,Practical @command{awk} Programs}. - # test program - if (_getopt_test) @{ - while ((_go_c = getopt(ARGC, ARGV, "ab:cd")) != -1) - printf("c = <%c>, optarg = <%s>\n", - _go_c, Optarg) - printf("non-option arguments:\n") - for (; Optind < ARGC; Optind++) - printf("\tARGV[%d] = <%s>\n", - Optind, ARGV[Optind]) - @} -@} -@c endfile -@c @end group -@end example +@end itemize -The @code{BEGIN} rule initializes both @code{Opterr} and @code{Optind} to one. -@code{Opterr} is set to one, since the default behavior is for @code{getopt} -to print a diagnostic message upon seeing an invalid option. @code{Optind} -is set to one, since there's no reason to look at the program name, which is -in @code{ARGV[0]}. +@page +@evenheading @thispage@ @ @ @strong{@value{TITLE}} @| @| +@oddheading @| @| @strong{@thischapter}@ @ @ @thispage +@end iftex +@end ignore -The rest of the @code{BEGIN} rule is a simple test program. Here is the -result of two sample runs of the test program. +@node Library Functions, Sample Programs, Invoking Gawk, Top +@chapter A Library of @command{awk} Functions -@example -@group -$ awk -f getopt.awk -v _getopt_test=1 -- -a -cbARG bax -x -@print{} c = , optarg = <> -@print{} c = , optarg = <> -@print{} c = , optarg = -@print{} non-option arguments: -@print{} ARGV[3] = -@print{} ARGV[4] = <-x> -@end group +@ref{User-defined, ,User-Defined Functions}, describes how to write +your own @command{awk} functions. Writing functions is important, because +it allows you to encapsulate algorithms and program tasks in a single +place. It simplifies programming, making program development more +manageable, and making programs more readable. -@group -$ awk -f getopt.awk -v _getopt_test=1 -- -a -x -- xyz abc -@print{} c = , optarg = <> -@error{} x -- invalid option -@print{} c = , optarg = <> -@print{} non-option arguments: -@print{} ARGV[4] = -@print{} ARGV[5] = -@end group -@end example +One valuable way to learn a new programming language is to @emph{read} +programs in that language. To that end, this @value{CHAPTER} +and @ref{Sample Programs, ,Practical @command{awk} Programs}, +provide a good-sized body of code for you to read, +and hopefully, to learn from. -The first @samp{--} terminates the arguments to @code{awk}, so that it does -not try to interpret the @samp{-a} etc. as its own options. +@c 2e: USE TEXINFO-2 FUNCTION DEFINITION STUFF!!!!!!!!!!!!! +This @value{CHAPTER} presents a library of useful @command{awk} functions. +Many of the sample programs presented later in this @value{DOCUMENT} +use these functions. +The functions are presented here in a progression from simple to complex. -Several of the sample programs presented in -@ref{Sample Programs, ,Practical @code{awk} Programs}, -use @code{getopt} to process their arguments. +@cindex Texinfo +@ref{Extract Program, ,Extracting Programs from Texinfo Source Files}, +presents a program that you can use to extract the source code for +these example library functions and programs from the Texinfo source +for this @value{DOCUMENT}. +(This has already been done as part of the @command{gawk} distribution.) -@node Passwd Functions, Group Functions, Getopt Function, Library Functions -@section Reading the User Database +If you have written one or more useful, general purpose @command{awk} functions +and would like to contribute them to the author's collection of @command{awk} +programs, see +@ref{How To Contribute, ,How to Contribute}, for more information. -@cindex @file{/dev/user} -The @file{/dev/user} special file -(@pxref{Special Files, ,Special File Names in @code{gawk}}) -provides access to the current user's real and effective user and group id -numbers, and if available, the user's supplementary group set. -However, since these are numbers, they do not provide very useful -information to the average user. There needs to be some way to find the -user information associated with the user and group numbers. This -section presents a suite of functions for retrieving information from the -user database. @xref{Group Functions, ,Reading the Group Database}, -for a similar suite that retrieves information from the group database. +@cindex portability issues +The programs in this @value{CHAPTER} and in +@ref{Sample Programs, ,Practical @command{awk} Programs}, +freely use features that are @command{gawk}-specific. +It is straightforward to rewrite these programs for +different implementations of @command{awk}. -@cindex @code{getpwent}, C version -@cindex user information -@cindex login information -@cindex account information -@cindex password file -The POSIX standard does not define the file where user information is -kept. Instead, it provides the @code{} header file -and several C language subroutines for obtaining user information. -The primary function is @code{getpwent}, for ``get password entry.'' -The ``password'' comes from the original user database file, -@file{/etc/passwd}, which kept user information, along with the -encrypted passwords (hence the name). +Diagnostic error messages are sent to @file{/dev/stderr}. +Use @samp{| "cat 1>&2"} instead of @samp{> "/dev/stderr"}, if your system +does not have a @file{/dev/stderr} or if you cannot use @command{gawk}. -While an @code{awk} program could simply read @file{/etc/passwd} directly -(the format is well known), because of the way password -files are handled on networked systems, -this file may not contain complete information about the system's set of users. - -@cindex @code{pwcat} program -To be sure of being -able to produce a readable, complete version of the user database, it is -necessary to write a small C program that calls @code{getpwent}. -@code{getpwent} is defined to return a pointer to a @code{struct passwd}. -Each time it is called, it returns the next entry in the database. -When there are no more entries, it returns @code{NULL}, the null pointer. -When this happens, the C program should call @code{endpwent} to close the -database. -Here is @code{pwcat}, a C program that ``cats'' the password database. - -@findex pwcat.c -@example -@c @group -@c file eg/lib/pwcat.c -/* - * pwcat.c - * - * Generate a printable version of the password database - * - * Arnold Robbins - * arnold@@gnu.org - * May 1993 - * Public Domain - */ +A number of programs use @code{nextfile} +(@pxref{Nextfile Statement, ,Using @command{gawk}'s @code{nextfile} Statement}) +to skip any remaining input in the input file. +@ref{Nextfile Function, ,Implementing @code{nextfile} as a Function}, +shows you how to write a function that does the same thing. + +@c 12/2000: Thanks to Nelson Beebe for pointing out the output issue. +Finally, some of the programs choose to ignore upper- and lowercase +distinctions in their input. They do so by assigning one to @code{IGNORECASE}. +You can achieve almost the same effect@footnote{The effects are +not identical. Output of the transformed +record will be in all lowercase, while @code{IGNORECASE} preserves the original +contents of the input record.} by adding the following rule to the +beginning of the program: -#include -#include +@example +# ignore case +@{ $0 = tolower($0) @} +@end example -int -main(argc, argv) -int argc; -char **argv; -@{ - struct passwd *p; +@noindent +Also, verify that all regexp and string constants used in +comparisons only use lowercase letters. - while ((p = getpwent()) != NULL) - printf("%s:%s:%d:%d:%s:%s:%s\n", - p->pw_name, p->pw_passwd, p->pw_uid, - p->pw_gid, p->pw_gecos, p->pw_dir, p->pw_shell); +@menu +* Library Names:: How to best name private global variables in + library functions. +* General Functions:: Functions that are of general use. +* Data File Management:: Functions for managing command-line data + files. +* Getopt Function:: A function for processing command-line + arguments. +* Passwd Functions:: Functions for getting user information. +* Group Functions:: Functions for getting group information. +@end menu - endpwent(); - exit(0); -@} -@c endfile -@c @end group -@end example +@node Library Names, General Functions, Library Functions, Library Functions +@section Naming Library Function Global Variables -If you don't understand C, don't worry about it. -The output from @code{pwcat} is the user database, in the traditional -@file{/etc/passwd} format of colon-separated fields. The fields are: +@cindex names, use of +@cindex namespace issues in @command{awk} +@cindex documenting @command{awk} programs +@cindex programs, documenting +Due to the way the @command{awk} language evolved, variables are either +@dfn{global} (usable by the entire program) or @dfn{local} (usable just by +a specific function). There is no intermediate state analogous to +@code{static} variables in C. -@table @asis -@item Login name -The user's login name. +Library functions often need to have global variables that they can use to +preserve state information between calls to the function---for example, +@code{getopt}'s variable @code{_opti} +(@pxref{Getopt Function, ,Processing Command-Line Options}). +Such variables are called @dfn{private}, since the only functions that need to +use them are the ones in the library. -@item Encrypted password -The user's encrypted password. This may not be available on some systems. +When writing a library function, you should try to choose names for your +private variables that will not conflict with any variables used by +either another library function or a user's main program. For example, a +name like @samp{i} or @samp{j} is not a good choice, because user programs +often use variable names like these for their own purposes. -@item User-ID -The user's numeric user-id number. +@cindex conventions, programming +@cindex programming conventions +The example programs shown in this @value{CHAPTER} all start the names of their +private variables with an underscore (@samp{_}). Users generally don't use +leading underscores in their variable names, so this convention immediately +decreases the chances that the variable name will be accidentally shared +with the user's program. -@item Group-ID -The user's numeric group-id number. +In addition, several of the library functions use a prefix that helps +indicate what function or set of functions use the variables---for example, +@code{_pw_byname} in the user database routines +(@pxref{Passwd Functions, ,Reading the User Database}). +This convention is recommended, since it even further decreases the +chance of inadvertent conflict among variable names. Note that this +convention is used equally well for variable names and for private +function names as well.@footnote{While all the library routines could have +been rewritten to use this convention, this was not done, in order to +show how my own @command{awk} programming style has evolved, and to +provide some basis for this discussion.} -@item Full name -The user's full name, and perhaps other information associated with the -user. +As a final note on variable naming, if a function makes global variables +available for use by a main program, it is a good convention to start that +variable's name with a capital letter---for +example, @code{getopt}'s @code{Opterr} and @code{Optind} variables +(@pxref{Getopt Function, ,Processing Command-Line Options}). +The leading capital letter indicates that it is global, while the fact that +the variable name is not all capital letters indicates that the variable is +not one of @command{awk}'s built-in variables, such as @code{FS}. -@item Home directory -The user's login, or ``home'' directory (familiar to shell programmers as -@code{$HOME}). +It is also important that @emph{all} variables in library +functions that do not need to save state are, in fact, declared +local.@footnote{@command{gawk}'s @option{--dump-variables} command-line +option is useful for verifying this.} If this is not done, the variable +could accidentally be used in the user's program, leading to bugs that +are very difficult to track down: -@item Login shell -The program that will be run when the user logs in. This is usually a -shell, such as Bash (the Gnu Bourne-Again shell). -@end table +@example +function lib_func(x, y, l1, l2) +@{ + @dots{} + @var{use variable} some_var # some_var should be local + @dots{} # but is not by oversight +@} +@end example + +@cindex Tcl +A different convention, common in the Tcl community, is to use a single +associative array to hold the values needed by the library function(s), or +``package.'' This significantly decreases the number of actual global names +in use. For example, the functions described in +@ref{Passwd Functions, , Reading the User Database}, +might have used array elements @code{@w{PW_data["inited"]}}, @code{@w{PW_data["total"]}}, +@code{@w{PW_data["count"]}}, and @code{@w{PW_data["awklib"]}}, instead of +@code{@w{_pw_inited}}, @code{@w{_pw_awklib}}, @code{@w{_pw_total}}, +and @code{@w{_pw_count}}. + +The conventions presented in this @value{SECTION} are exactly +that: conventions. You are not required to write your programs this +way---we merely recommend that you do so. + +@node General Functions, Data File Management, Library Names, Library Functions +@section General Programming + +This @value{SECTION} presents a number of functions that are of general +programming use. + +@menu +* Nextfile Function:: Two implementations of a @code{nextfile} + function. +* Assert Function:: A function for assertions in @command{awk} + programs. +* Round Function:: A function for rounding if @code{sprintf} does + not do it correctly. +* Cliff Random Function:: The Cliff Random Number Generator. +* Ordinal Functions:: Functions for using characters as numbers and + vice versa. +* Join Function:: A function to join an array into a string. +* Gettimeofday Function:: A function to get formatted times. +@end menu -Here are a few lines representative of @code{pwcat}'s output. +@node Nextfile Function, Assert Function, General Functions, General Functions +@subsection Implementing @code{nextfile} as a Function + +@cindex skipping input files +@cindex input files, skipping +The @code{nextfile} statement presented in +@ref{Nextfile Statement, ,Using @command{gawk}'s @code{nextfile} Statement}, +is a @command{gawk}-specific extension---it is not available in most other +implementations of @command{awk}. This @value{SECTION} shows two versions of a +@code{nextfile} function that you can use to simulate @command{gawk}'s +@code{nextfile} statement if you cannot use @command{gawk}. + +A first attempt at writing a @code{nextfile} function is as follows: @example -@c @group -$ pwcat -@print{} root:3Ov02d5VaUPB6:0:1:Operator:/:/bin/sh -@print{} nobody:*:65534:65534::/: -@print{} daemon:*:1:1::/: -@print{} sys:*:2:2::/:/bin/csh -@print{} bin:*:3:3::/bin: -@print{} arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/sh -@print{} miriam:yxaay:112:10:Miriam Robbins:/home/miriam:/bin/sh -@print{} andy:abcca2:113:10:Andy Jacobs:/home/andy:/bin/sh -@dots{} -@c @end group +# nextfile --- skip remaining records in current file +# this should be read in before the "main" awk program + +function nextfile() @{ _abandon_ = FILENAME; next @} +_abandon_ == FILENAME @{ next @} @end example -With that introduction, here is a group of functions for getting user -information. There are several functions here, corresponding to the C -functions of the same name. +@cindex conventions, programming +@cindex programming conventions +Because it supplies a rule that must be executed first, this file should +be included before the main program. This rule compares the current +@value{DF}'s name (which is always in the @code{FILENAME} variable) to +a private variable named @code{_abandon_}. If the @value{FN} matches, +then the action part of the rule executes a @code{next} statement to +go on to the next record. (The use of @samp{_} in the variable name is +a convention. It is discussed more fully in +@ref{Library Names, , Naming Library Function Global Variables}.) + +The use of the @code{next} statement effectively creates a loop that reads +all the records from the current @value{DF}. +The end of the file is eventually reached and +a new @value{DF} is opened, changing the value of @code{FILENAME}. +Once this happens, the comparison of @code{_abandon_} to @code{FILENAME} +fails and execution continues with the first rule of the ``real'' program. + +The @code{nextfile} function itself simply sets the value of @code{_abandon_} +and then executes a @code{next} statement to start the +loop. +@ignore +@c If the function can't be used on other versions of awk, this whole +@c section is pointless, no? Sigh. +@footnote{@command{gawk} is the only known @command{awk} implementation +that allows you to +execute @code{next} from within a function body. Some other workaround +is necessary if you are not using @command{gawk}.} +@end ignore + +@cindex @code{nextfile} user-defined function +This initial version has a subtle problem. +If the same @value{DF} is listed @emph{twice} on the commandline, +one right after the other +or even with just a variable assignment between them, +this code skips right through the file, a second time, even though +it should stop when it gets to the end of the first occurrence. +A second version of @code{nextfile} that remedies this problem +is shown here: -@findex _pw_init @example -@c file eg/lib/passwdawk.in -@group -# passwd.awk --- access password file information +@c file eg/lib/nextfile.awk +# nextfile --- skip remaining records in current file +# correctly handle successive occurrences of the same file +@c endfile +@ignore +@c file eg/lib/nextfile.awk +# # Arnold Robbins, arnold@@gnu.org, Public Domain -# May 1993 +# May, 1993 -BEGIN @{ - # tailor this to suit your system - _pw_awklib = "/usr/local/libexec/awk/" -@} -@end group +@c endfile +@end ignore +@c file eg/lib/nextfile.awk +# this should be read in before the "main" awk program -@group -function _pw_init( oldfs, oldrs, olddol0, pwcat) -@{ - if (_pw_inited) - return - oldfs = FS - oldrs = RS - olddol0 = $0 - FS = ":" - RS = "\n" - pwcat = _pw_awklib "pwcat" - while ((pwcat | getline) > 0) @{ - _pw_byname[$1] = $0 - _pw_byuid[$3] = $0 - _pw_bycount[++_pw_total] = $0 - @} - close(pwcat) - _pw_count = 0 - _pw_inited = 1 - FS = oldfs - RS = oldrs - $0 = olddol0 +function nextfile() @{ _abandon_ = FILENAME; next @} + +_abandon_ == FILENAME @{ + if (FNR == 1) + _abandon_ = "" + else + next @} @c endfile -@end group @end example -The @code{BEGIN} rule sets a private variable to the directory where -@code{pwcat} is stored. Since it is used to help out an @code{awk} library -routine, we have chosen to put it in @file{/usr/local/libexec/awk}. -You might want it to be in a different directory on your system. +The @code{nextfile} function has not changed. It makes @code{_abandon_} +equal to the current @value{FN} and then executes a @code{next} statement. +The @code{next} statement reads the next record and increments @code{FNR} +so that @code{FNR} is guaranteed to have a value of at least two. +However, if @code{nextfile} is called for the last record in the file, +then @command{awk} closes the current @value{DF} and moves on to the next +one. Upon doing so, @code{FILENAME} is set to the name of the new file +and @code{FNR} is reset to one. If this next file is the same as +the previous one, @code{_abandon_} is still equal to @code{FILENAME}. +However, @code{FNR} is equal to one, telling us that this is a new +occurrence of the file and not the one we were reading when the +@code{nextfile} function was executed. In that case, @code{_abandon_} +is reset to the empty string, so that further executions of this rule +fail (until the next time that @code{nextfile} is called). -The function @code{_pw_init} keeps three copies of the user information -in three associative arrays. The arrays are indexed by user name -(@code{_pw_byname}), by user-id number (@code{_pw_byuid}), and by order of -occurrence (@code{_pw_bycount}). +If @code{FNR} is not one, then we are still in the original @value{DF} +and the program executes a @code{next} statement to skip through it. -The variable @code{_pw_inited} is used for efficiency; @code{_pw_init} only -needs to be called once. +An important question to ask at this point is: given that the +functionality of @code{nextfile} can be provided with a library file, +why is it built into @command{gawk}? Adding +features for little reason leads to larger, slower programs that are +harder to maintain. +The answer is that building @code{nextfile} into @command{gawk} provides +significant gains in efficiency. If the @code{nextfile} function is executed +at the beginning of a large @value{DF}, @command{awk} still has to scan the entire +file, splitting it up into records, +@c at least conceptually +just to skip over it. The built-in +@code{nextfile} can simply close the file immediately and proceed to the +next one, which saves a lot of time. This is particularly important in +@command{awk}, because @command{awk} programs are generally I/O-bound (i.e., +they spend most of their time doing input and output, instead of performing +computations). -Since this function uses @code{getline} to read information from -@code{pwcat}, it first saves the values of @code{FS}, @code{RS}, and -@code{$0}. Doing so is necessary, since these functions could be called -from anywhere within a user's program, and the user may have his or her -own values for @code{FS} and @code{RS}. -@ignore -Problem, what if FIELDWIDTHS is in use? Sigh. -@end ignore +@node Assert Function, Round Function, Nextfile Function, General Functions +@subsection Assertions -The main part of the function uses a loop to read database lines, split -the line into fields, and then store the line into each array as necessary. -When the loop is done, @code{@w{_pw_init}} cleans up by closing the pipeline, -setting @code{@w{_pw_inited}} to one, and restoring @code{FS}, @code{RS}, and -@code{$0}. The use of @code{@w{_pw_count}} will be explained below. +@cindex assertions +@cindex @code{assert} C library function +When writing large programs, it is often useful to know +that a condition or set of conditions is true. Before proceeding with a +particular computation, you make a statement about what you believe to be +the case. Such a statement is known as an +@dfn{assertion}. The C language provides an @code{} header file +and corresponding @code{assert} macro that the programmer can use to make +assertions. If an assertion fails, the @code{assert} macro arranges to +print a diagnostic message describing the condition that should have +been true but was not, and then it kills the program. In C, using +@code{assert} looks this: -@findex getpwnam @example -@group -@c file eg/lib/passwdawk.in -function getpwnam(name) +#include + +int myfunc(int a, double b) @{ - _pw_init() - if (name in _pw_byname) - return _pw_byname[name] - return "" + assert(a <= 5 && b >= 17.1); + @dots{} @} -@c endfile -@end group @end example -The @code{getpwnam} function takes a user name as a string argument. If that -user is in the database, it returns the appropriate line. Otherwise it -returns the null string. +If the assertion fails, the program prints a message similar to this: -@findex getpwuid @example -@group -@c file eg/lib/passwdawk.in -function getpwuid(uid) -@{ - _pw_init() - if (uid in _pw_byuid) - return _pw_byuid[uid] - return "" -@} -@c endfile -@end group +prog.c:5: assertion failed: a <= 5 && b >= 17.1 @end example -Similarly, -the @code{getpwuid} function takes a user-id number argument. If that -user number is in the database, it returns the appropriate line. Otherwise it -returns the null string. +@cindex @code{assert} user-defined function +The C language makes it possible to turn the condition into a string for use +in printing the diagnostic message. This is not possible in @command{awk}, so +this @code{assert} function also requires a string version of the condition +that is being tested. +Following is the function: -@findex getpwent @example -@c @group -@c file eg/lib/passwdawk.in -function getpwent() +@c file eg/lib/assert.awk +# assert --- assert that a condition is true. Otherwise exit. +@c endfile +@ignore +@c file eg/lib/assert.awk + +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# May, 1993 + +@c endfile +@end ignore +@c file eg/lib/assert.awk +function assert(condition, string) @{ - _pw_init() - if (_pw_count < _pw_total) - return _pw_bycount[++_pw_count] - return "" + if (! condition) @{ + printf("%s:%d: assertion failed: %s\n", + FILENAME, FNR, string) > "/dev/stderr" + _assert_exit = 1 + exit 1 + @} +@} + +@group +END @{ + if (_assert_exit) + exit 1 @} +@end group @c endfile -@c @end group @end example -The @code{getpwent} function simply steps through the database, one entry at -a time. It uses @code{_pw_count} to track its current position in the -@code{_pw_bycount} array. +The @code{assert} function tests the @code{condition} parameter. If it +is false, it prints a message to standard error, using the @code{string} +parameter to describe the failed condition. It then sets the variable +@code{_assert_exit} to one and executes the @code{exit} statement. +The @code{exit} statement jumps to the @code{END} rule. If the @code{END} +rules finds @code{_assert_exit} to be true, it then exits immediately. + +The purpose of the test in the @code{END} rule is to +keep any other @code{END} rules from running. When an assertion fails, the +program should exit immediately. +If no assertions fail, then @code{_assert_exit} is still +false when the @code{END} rule is run normally, and the rest of the +program's @code{END} rules execute. +For all of this to work correctly, @file{assert.awk} must be the +first source file read by @command{awk}. +The function can be used in a program in the following way: -@findex endpwent @example -@c @group -@c file eg/lib/passwdawk.in -function endpwent() +function myfunc(a, b) @{ - _pw_count = 0 + assert(a <= 5 && b >= 17.1, "a <= 5 && b >= 17.1") + @dots{} @} -@c endfile -@c @end group @end example -The @code{@w{endpwent}} function resets @code{@w{_pw_count}} to zero, so that -subsequent calls to @code{getpwent} will start over again. +@noindent +If the assertion fails, you see a message similar to the following: -A conscious design decision in this suite is that each subroutine calls -@code{@w{_pw_init}} to initialize the database arrays. The overhead of running -a separate process to generate the user database, and the I/O to scan it, -will only be incurred if the user's main program actually calls one of these -functions. If this library file is loaded along with a user's program, but -none of the routines are ever called, then there is no extra run-time overhead. -(The alternative would be to move the body of @code{@w{_pw_init}} into a -@code{BEGIN} rule, which would always run @code{pwcat}. This simplifies the -code but runs an extra process that may never be needed.) +@example +mydata:1357: assertion failed: a <= 5 && b >= 17.1 +@end example -In turn, calling @code{_pw_init} is not too expensive, since the -@code{_pw_inited} variable keeps the program from reading the data more than -once. If you are worried about squeezing every last cycle out of your -@code{awk} program, the check of @code{_pw_inited} could be moved out of -@code{_pw_init} and duplicated in all the other functions. In practice, -this is not necessary, since most @code{awk} programs are I/O bound, and it -would clutter up the code. +There is a small problem with this version of @code{assert}. +An @code{END} rule is automatically added +to the program calling @code{assert}. Normally, if a program consists +of just a @code{BEGIN} rule, the input files and/or standard input are +not read. However, now that the program has an @code{END} rule, @command{awk} +attempts to read the input @value{DF}s or standard input +(@pxref{Using BEGIN/END, , Startup and Cleanup Actions}), +most likely causing the program to hang as it waits for input. -The @code{id} program in @ref{Id Program, ,Printing Out User Information}, -uses these functions. +There is a simple workaround to this: +make sure the @code{BEGIN} rule always ends +with an @code{exit} statement. -@node Group Functions, Library Names, Passwd Functions, Library Functions -@section Reading the Group Database +@node Round Function, Cliff Random Function, Assert Function, General Functions +@subsection Rounding Numbers -@cindex @code{getgrent}, C version -@cindex group information -@cindex account information -@cindex group file -Much of the discussion presented in -@ref{Passwd Functions, ,Reading the User Database}, -applies to the group database as well. Although there has traditionally -been a well known file, @file{/etc/group}, in a well known format, the POSIX -standard only provides a set of C library routines -(@code{} and @code{getgrent}) -for accessing the information. -Even though this file may exist, it likely does not have -complete information. Therefore, as with the user database, it is necessary -to have a small C program that generates the group database as its output. - -@cindex @code{grcat} program -Here is @code{grcat}, a C program that ``cats'' the group database. - -@findex grcat.c +@cindex rounding +The way @code{printf} and @code{sprintf} +(@pxref{Printf, , Using @code{printf} Statements for Fancier Printing}) +perform rounding often depends upon the system's C @code{sprintf} +subroutine. On many machines, @code{sprintf} rounding is ``unbiased,'' +which means it doesn't always round a trailing @samp{.5} up, contrary +to naive expectations. In unbiased rounding, @samp{.5} rounds to even, +rather than always up, so 1.5 rounds to 2 but 4.5 rounds to 4. This means +that if you are using a format that does rounding (e.g., @code{"%.0f"}), +you should check what your system does. The following function does +traditional rounding; it might be useful if your awk's @code{printf} +does unbiased rounding: + +@cindex @code{round} user-defined function @example -@c @group -@c file eg/lib/grcat.c -/* - * grcat.c - * - * Generate a printable version of the group database - * - * Arnold Robbins, arnold@@gnu.org - * May 1993 - * Public Domain - */ - -#include -#include +@c file eg/lib/round.awk +# round --- do normal rounding +@c endfile +@ignore +@c file eg/lib/round.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# August, 1996 -@group -int -main(argc, argv) -int argc; -char **argv; +@c endfile +@end ignore +@c file eg/lib/round.awk +function round(x, ival, aval, fraction) @{ - struct group *g; - int i; -@end group + ival = int(x) # integer part, int() truncates -@group - while ((g = getgrent()) != NULL) @{ - printf("%s:%s:%d:", g->gr_name, g->gr_passwd, - g->gr_gid); -@end group - for (i = 0; g->gr_mem[i] != NULL; i++) @{ - printf("%s", g->gr_mem[i]); - if (g->gr_mem[i+1] != NULL) - putchar(','); - @} - putchar('\n'); - @} - endgrent(); - exit(0); + # see if fractional part + if (ival == x) # no fraction + return x + + if (x < 0) @{ + aval = -x # absolute value + ival = int(aval) + fraction = aval - ival + if (fraction >= .5) + return int(x) - 1 # -2.5 --> -3 + else + return int(x) # -2.3 --> -2 + @} else @{ + fraction = x - ival + if (fraction >= .5) + return ival + 1 + else + return ival + @} @} + +# test harness +@{ print $0, round($0) @} @c endfile -@c @end group @end example -Each line in the group database represent one group. The fields are -separated with colons, and represent the following information. - -@table @asis -@item Group Name -The name of the group. - -@item Group Password -The encrypted group password. In practice, this field is never used. It is -usually empty, or set to @samp{*}. - -@item Group ID Number -The numeric group-id number. This number should be unique within the file. - -@item Group Member List -A comma-separated list of user names. These users are members of the group. -Most Unix systems allow users to be members of several groups -simultaneously. If your system does, then reading @file{/dev/user} will -return those group-id numbers in @code{$5} through @code{$NF}. -(Note that @file{/dev/user} is a @code{gawk} extension; -@pxref{Special Files, ,Special File Names in @code{gawk}}.) -@end table - -Here is what running @code{grcat} might produce: - -@example -@group -$ grcat -@print{} wheel:*:0:arnold -@print{} nogroup:*:65534: -@print{} daemon:*:1: -@print{} kmem:*:2: -@print{} staff:*:10:arnold,miriam,andy -@print{} other:*:20: -@dots{} -@end group -@end example +@node Cliff Random Function, Ordinal Functions, Round Function, General Functions +@subsection The Cliff Random Number Generator +@cindex random numbers, Cliff +@cindex Cliff random numbers -Here are the functions for obtaining information from the group database. -There are several, modeled after the C library functions of the same names. +The Cliff random number +generator@footnote{@uref{http://mathworld.wolfram.com/CliffRandomNumberGenerator.hmtl}} +is a very simple random number generator that ``passes the noise sphere test +for randomness by showing no structure.'' +It is easily programmed, in less than 10 lines of @command{awk} code: -@findex _gr_init +@cindex @code{cliff_rand} user-defined function @example -@group -@c file eg/lib/groupawk.in -# group.awk --- functions for dealing with the group file +@c file eg/lib/cliff_rand.awk +# cliff_rand.awk --- generate Cliff random numbers +@c endfile +@ignore +@c file eg/lib/cliff_rand.awk +# # Arnold Robbins, arnold@@gnu.org, Public Domain -# May 1993 +# December 2000 -BEGIN \ -@{ - # Change to suit your system - _gr_awklib = "/usr/local/libexec/awk/" -@} @c endfile -@end group +@end ignore +@c file eg/lib/cliff_rand.awk +BEGIN @{ _cliff_seed = 0.1 @} -@group -@c file eg/lib/groupawk.in -function _gr_init( oldfs, oldrs, olddol0, grcat, n, a, i) +function cliff_rand() @{ - if (_gr_inited) - return -@end group - -@group - oldfs = FS - oldrs = RS - olddol0 = $0 - FS = ":" - RS = "\n" -@end group - -@group - grcat = _gr_awklib "grcat" - while ((grcat | getline) > 0) @{ - if ($1 in _gr_byname) - _gr_byname[$1] = _gr_byname[$1] "," $4 - else - _gr_byname[$1] = $0 - if ($3 in _gr_bygid) - _gr_bygid[$3] = _gr_bygid[$3] "," $4 - else - _gr_bygid[$3] = $0 - - n = split($4, a, "[ \t]*,[ \t]*") -@end group -@group - for (i = 1; i <= n; i++) - if (a[i] in _gr_groupsbyuser) - _gr_groupsbyuser[a[i]] = \ - _gr_groupsbyuser[a[i]] " " $1 - else - _gr_groupsbyuser[a[i]] = $1 -@end group - -@group - _gr_bycount[++_gr_count] = $0 - @} -@end group -@group - close(grcat) - _gr_count = 0 - _gr_inited++ - FS = oldfs - RS = oldrs - $0 = olddol0 + _cliff_seed = (100 * log(_cliff_seed)) % 1 + if (_cliff_seed < 0) + _cliff_seed = - _cliff_seed + return _cliff_seed @} @c endfile -@end group @end example -The @code{BEGIN} rule sets a private variable to the directory where -@code{grcat} is stored. Since it is used to help out an @code{awk} library -routine, we have chosen to put it in @file{/usr/local/libexec/awk}. You might -want it to be in a different directory on your system. +This algorithm requires an initial ``seed'' of 0.1. Each new value +uses the current seed as input for the calculation. +If the built-in @code{rand} function +(@pxref{Numeric Functions}) +isn't random enough, you might try using this function instead. -These routines follow the same general outline as the user database routines -(@pxref{Passwd Functions, ,Reading the User Database}). -The @code{@w{_gr_inited}} variable is used to -ensure that the database is scanned no more than once. -The @code{@w{_gr_init}} function first saves @code{FS}, @code{RS}, and -@code{$0}, and then sets @code{FS} and @code{RS} to the correct values for -scanning the group information. +@node Ordinal Functions, Join Function, Cliff Random Function, General Functions +@subsection Translating Between Characters and Numbers -The group information is stored is several associative arrays. -The arrays are indexed by group name (@code{@w{_gr_byname}}), by group-id number -(@code{@w{_gr_bygid}}), and by position in the database (@code{@w{_gr_bycount}}). -There is an additional array indexed by user name (@code{@w{_gr_groupsbyuser}}), -that is a space separated list of groups that each user belongs to. +@cindex numeric character values +@cindex values of characters as numbers +One commercial implementation of @command{awk} supplies a built-in function, +@code{ord}, which takes a character and returns the numeric value for that +character in the machine's character set. If the string passed to +@code{ord} has more than one character, only the first one is used. -Unlike the user database, it is possible to have multiple records in the -database for the same group. This is common when a group has a large number -of members. Such a pair of entries might look like: +The inverse of this function is @code{chr} (from the function of the same +name in Pascal), which takes a number and returns the corresponding character. +Both functions are written very nicely in @command{awk}; there is no real +reason to build them into the @command{awk} interpreter: +@cindex @code{ord} user-defined function +@cindex @code{chr} user-defined function @example -tvpeople:*:101:johny,jay,arsenio -tvpeople:*:101:david,conan,tom,joan -@end example +@c file eg/lib/ord.awk +# ord.awk --- do ord and chr -For this reason, @code{_gr_init} looks to see if a group name or -group-id number has already been seen. If it has, then the user names are -simply concatenated onto the previous list of users. (There is actually a -subtle problem with the code presented above. Suppose that -the first time there were no names. This code adds the names with -a leading comma. It also doesn't check that there is a @code{$4}.) +# Global identifiers: +# _ord_: numerical values indexed by characters +# _ord_init: function to initialize _ord_ +@c endfile +@ignore +@c file eg/lib/ord.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# 16 January, 1992 +# 20 July, 1992, revised -Finally, @code{_gr_init} closes the pipeline to @code{grcat}, restores -@code{FS}, @code{RS}, and @code{$0}, initializes @code{_gr_count} to zero -(it is used later), and makes @code{_gr_inited} non-zero. +@c endfile +@end ignore +@c file eg/lib/ord.awk +BEGIN @{ _ord_init() @} -@findex getgrnam -@example -@c @group -@c file eg/lib/groupawk.in -function getgrnam(group) +function _ord_init( low, high, i, t) @{ - _gr_init() - if (group in _gr_byname) - return _gr_byname[group] - return "" + low = sprintf("%c", 7) # BEL is ascii 7 + if (low == "\a") @{ # regular ascii + low = 0 + high = 127 + @} else if (sprintf("%c", 128 + 7) == "\a") @{ + # ascii, mark parity + low = 128 + high = 255 + @} else @{ # ebcdic(!) + low = 0 + high = 255 + @} + + for (i = low; i <= high; i++) @{ + t = sprintf("%c", i) + _ord_[t] = i + @} @} @c endfile -@c @end group @end example -The @code{getgrnam} function takes a group name as its argument, and if that -group exists, it is returned. Otherwise, @code{getgrnam} returns the null -string. +@cindex character sets (machine character encodings) +@cindex character encodings +@cindex ASCII +@cindex EBCDIC +@cindex mark parity +Some explanation of the numbers used by @code{chr} is worthwhile. +The most prominent character set in use today is ASCII. Although an +eight-bit byte can hold 256 distinct values (from 0 to 255), ASCII only +defines characters that use the values from 0 to 127.@footnote{ASCII +has been extended in many countries to use the values from 128 to 255 +for country-specific characters. If your system uses these extensions, +you can simplify @code{_ord_init} to simply loop from 0 to 255.} +In the now distant past, +at least one minicomputer manufacturer +@c Pr1me, blech +used ASCII, but with mark parity, meaning that the leftmost bit in the byte +is always 1. This means that on those systems, characters +have numeric values from 128 to 255. +Finally, large mainframe systems use the EBCDIC character set, which +uses all 256 values. +While there are other character sets in use on some older systems, +they are not really worth worrying about: -@findex getgrgid @example -@c @group -@c file eg/lib/groupawk.in -function getgrgid(gid) +@c file eg/lib/ord.awk +function ord(str, c) @{ - _gr_init() - if (gid in _gr_bygid) - return _gr_bygid[gid] - return "" + # only first character is of interest + c = substr(str, 1, 1) + return _ord_[c] @} -@c endfile -@c @end group -@end example -The @code{getgrgid} function is similar, it takes a numeric group-id, and -looks up the information associated with that group-id. - -@findex getgruser -@example -@group -@c file eg/lib/groupawk.in -function getgruser(user) +function chr(c) @{ - _gr_init() - if (user in _gr_groupsbyuser) - return _gr_groupsbyuser[user] - return "" + # force c to be numeric by adding 0 + return sprintf("%c", c + 0) @} @c endfile -@end group -@end example - -The @code{getgruser} function does not have a C counterpart. It takes a -user name, and returns the list of groups that have the user as a member. -@findex getgrent -@example -@c @group -@c file eg/lib/groupawk.in -function getgrent() -@{ - _gr_init() - if (++_gr_count in _gr_bycount) - return _gr_bycount[_gr_count] - return "" -@} +#### test code #### +# BEGIN \ +# @{ +# for (;;) @{ +# printf("enter a character: ") +# if (getline var <= 0) +# break +# printf("ord(%s) = %d\n", var, ord(var)) +# @} +# @} @c endfile -@c @end group @end example -The @code{getgrent} function steps through the database one entry at a time. -It uses @code{_gr_count} to track its position in the list. +An obvious improvement to these functions is to move the code for the +@code{@w{_ord_init}} function into the body of the @code{BEGIN} rule. It was +written this way initially for ease of development. +There is a ``test program'' in a @code{BEGIN} rule, to test the +function. It is commented out for production use. + +@node Join Function, Gettimeofday Function, Ordinal Functions, General Functions +@subsection Merging an Array into a String -@findex endgrent +@cindex merging strings +When doing string processing, it is often useful to be able to join +all the strings in an array into one long string. The following function, +@code{join}, accomplishes this task. It is used later in several of +the application programs +(@pxref{Sample Programs, ,Practical @command{awk} Programs}). + +Good function design is important; this function needs to be general but it +should also have a reasonable default behavior. It is called with an array +as well as the beginning and ending indices of the elements in the array to be +merged. This assumes that the array indices are numeric---a reasonable +assumption since the array was likely created with @code{split} +(@pxref{String Functions, ,String Manipulation Functions}): + +@cindex @code{join} user-defined function @example -@group -@c file eg/lib/groupawk.in -function endgrent() +@c file eg/lib/join.awk +# join.awk --- join an array into a string +@c endfile +@ignore +@c file eg/lib/join.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# May 1993 + +@c endfile +@end ignore +@c file eg/lib/join.awk +function join(array, start, end, sep, result, i) @{ - _gr_count = 0 + if (sep == "") + sep = " " + else if (sep == SUBSEP) # magic value + sep = "" + result = array[start] + for (i = start + 1; i <= end; i++) + result = result sep array[i] + return result @} @c endfile -@end group @end example -@code{endgrent} resets @code{_gr_count} to zero so that @code{getgrent} can -start over again. - -As with the user database routines, each function calls @code{_gr_init} to -initialize the arrays. Doing so only incurs the extra overhead of running -@code{grcat} if these functions are used (as opposed to moving the body of -@code{_gr_init} into a @code{BEGIN} rule). - -Most of the work is in scanning the database and building the various -associative arrays. The functions that the user calls are themselves very -simple, relying on @code{awk}'s associative arrays to do work. - -The @code{id} program in @ref{Id Program, ,Printing Out User Information}, -uses these functions. +An optional additional argument is the separator to use when joining the +strings back together. If the caller supplies a non-empty value, +@code{join} uses it; if it is not supplied, it has a null +value. In this case, @code{join} uses a single blank as a default +separator for the strings. If the value is equal to @code{SUBSEP}, +then @code{join} joins the strings with no separator between them. +@code{SUBSEP} serves as a ``magic'' value to indicate that there should +be no separation between the component strings.@footnote{It would +be nice if @command{awk} had an assignment operator for concatenation. +The lack of an explicit operator for concatenation makes string operations +more difficult than they really need to be.} -@node Library Names, , Group Functions, Library Functions -@section Naming Library Function Global Variables +@node Gettimeofday Function, , Join Function, General Functions +@subsection Managing the Time of Day -@cindex namespace issues in @code{awk} -@cindex documenting @code{awk} programs -@cindex programs, documenting -Due to the way the @code{awk} language evolved, variables are either -@dfn{global} (usable by the entire program), or @dfn{local} (usable just by -a specific function). There is no intermediate state analogous to -@code{static} variables in C. +@cindex formatted timestamps +@cindex timestamps, formatted +The @code{systime} and @code{strftime} functions described in +@ref{Time Functions, ,Using @command{gawk}'s Timestamp Functions}, +provide the minimum functionality necessary for dealing with the time of day +in human readable form. While @code{strftime} is extensive, the control +formats are not necessarily easy to remember or intuitively obvious when +reading a program. -Library functions often need to have global variables that they can use to -preserve state information between calls to the function. For example, -@code{getopt}'s variable @code{_opti} -(@pxref{Getopt Function, ,Processing Command Line Options}), -and the @code{_tm_months} array used by @code{mktime} -(@pxref{Mktime Function, ,Turning Dates Into Timestamps}). -Such variables are called @dfn{private}, since the only functions that need to -use them are the ones in the library. +The following function, @code{gettimeofday}, populates a user-supplied array +with preformatted time information. It returns a string with the current +time formatted in the same way as the @command{date} utility: -When writing a library function, you should try to choose names for your -private variables so that they will not conflict with any variables used by -either another library function or a user's main program. For example, a -name like @samp{i} or @samp{j} is not a good choice, since user programs -often use variable names like these for their own purposes. +@cindex @code{gettimeofday} user-defined function +@example +@c file eg/lib/gettime.awk +# gettimeofday.awk --- get the time of day in a usable format +@c endfile +@ignore +@c file eg/lib/gettime.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain, May 1993 +# +@c endfile +@end ignore +@c file eg/lib/gettime.awk -The example programs shown in this chapter all start the names of their -private variables with an underscore (@samp{_}). Users generally don't use -leading underscores in their variable names, so this convention immediately -decreases the chances that the variable name will be accidentally shared -with the user's program. +# Returns a string in the format of output of date(1) +# Populates the array argument time with individual values: +# time["second"] -- seconds (0 - 59) +# time["minute"] -- minutes (0 - 59) +# time["hour"] -- hours (0 - 23) +# time["althour"] -- hours (0 - 12) +# time["monthday"] -- day of month (1 - 31) +# time["month"] -- month of year (1 - 12) +# time["monthname"] -- name of the month +# time["shortmonth"] -- short name of the month +# time["year"] -- year modulo 100 (0 - 99) +# time["fullyear"] -- full year +# time["weekday"] -- day of week (Sunday = 0) +# time["altweekday"] -- day of week (Monday = 0) +# time["dayname"] -- name of weekday +# time["shortdayname"] -- short name of weekday +# time["yearday"] -- day of year (0 - 365) +# time["timezone"] -- abbreviation of timezone name +# time["ampm"] -- AM or PM designation +# time["weeknum"] -- week number, Sunday first day +# time["altweeknum"] -- week number, Monday first day -In addition, several of the library functions use a prefix that helps -indicate what function or set of functions uses the variables. For example, -@code{_tm_months} in @code{mktime} -(@pxref{Mktime Function, ,Turning Dates Into Timestamps}), and -@code{_pw_byname} in the user data base routines -(@pxref{Passwd Functions, ,Reading the User Database}). -This convention is recommended, since it even further decreases the chance -of inadvertent conflict among variable names. -Note that this convention can be used equally well both for variable names -and for private function names too. +function gettimeofday(time, ret, now, i) +@{ + # get time once, avoids unnecessary system calls + now = systime() -While I could have re-written all the library routines to use this -convention, I did not do so, in order to show how my own @code{awk} -programming style has evolved, and to provide some basis for this -discussion. + # return date(1)-style output + ret = strftime("%a %b %d %H:%M:%S %Z %Y", now) -As a final note on variable naming, if a function makes global variables -available for use by a main program, it is a good convention to start that -variable's name with a capital letter. -For example, @code{getopt}'s @code{Opterr} and @code{Optind} variables -(@pxref{Getopt Function, ,Processing Command Line Options}). -The leading capital letter indicates that it is global, while the fact that -the variable name is not all capital letters indicates that the variable is -not one of @code{awk}'s built-in variables, like @code{FS}. + # clear out target array + delete time -It is also important that @emph{all} variables in library functions -that do not need to save state are in fact declared local. If this is -not done, the variable could accidentally be used in the user's program, -leading to bugs that are very difficult to track down. + # fill in values, force numeric values to be + # numeric by adding 0 + time["second"] = strftime("%S", now) + 0 + time["minute"] = strftime("%M", now) + 0 + time["hour"] = strftime("%H", now) + 0 + time["althour"] = strftime("%I", now) + 0 + time["monthday"] = strftime("%d", now) + 0 + time["month"] = strftime("%m", now) + 0 + time["monthname"] = strftime("%B", now) + time["shortmonth"] = strftime("%b", now) + time["year"] = strftime("%y", now) + 0 + time["fullyear"] = strftime("%Y", now) + 0 + time["weekday"] = strftime("%w", now) + 0 + time["altweekday"] = strftime("%u", now) + 0 + time["dayname"] = strftime("%A", now) + time["shortdayname"] = strftime("%a", now) + time["yearday"] = strftime("%j", now) + 0 + time["timezone"] = strftime("%Z", now) + time["ampm"] = strftime("%p", now) + time["weeknum"] = strftime("%U", now) + 0 + time["altweeknum"] = strftime("%W", now) + 0 -@example -function lib_func(x, y, l1, l2) -@{ - @dots{} - @var{use variable} some_var # some_var could be local - @dots{} # but is not by oversight + return ret @} +@c endfile @end example -@cindex Tcl -A different convention, common in the Tcl community, is to use a single -associative array to hold the values needed by the library function(s), or -``package.'' This significantly decreases the number of actual global names -in use. For example, the functions described in -@ref{Passwd Functions, , Reading the User Database}, -might have used @code{@w{PW_data["inited"]}}, @code{@w{PW_data["total"]}}, -@code{@w{PW_data["count"]}} and @code{@w{PW_data["awklib"]}}, instead of -@code{@w{_pw_inited}}, @code{@w{_pw_awklib}}, @code{@w{_pw_total}}, -and @code{@w{_pw_count}}. - -The conventions presented in this section are exactly that, conventions. You -are not required to write your programs this way, we merely recommend that -you do so. - -@node Sample Programs, Language History, Library Functions, Top -@chapter Practical @code{awk} Programs +The string indices are easier to use and read than the various formats +required by @code{strftime}. The @code{alarm} program presented in +@ref{Alarm Program, ,An Alarm Clock Program}, +uses this function. +A more general design for the @code{gettimeofday} function would have +allowed the user to supply an optional timestamp value to use instead +of the current time. -This chapter presents a potpourri of @code{awk} programs for your reading -enjoyment. -@iftex -There are two sections. The first presents @code{awk} -versions of several common POSIX utilities. -The second is a grab-bag of interesting programs. -@end iftex +@node Data File Management, Getopt Function, General Functions, Library Functions +@section @value{DDF} Management -Many of these programs use the library functions presented in -@ref{Library Functions, ,A Library of @code{awk} Functions}. +This @value{SECTION} presents functions that are useful for managing +command-line datafiles. @menu -* Clones:: Clones of common utilities. -* Miscellaneous Programs:: Some interesting @code{awk} programs. +* Filetrans Function:: A function for handling data file transitions. +* Rewind Function:: A function for rereading the current file. +* File Checking:: Checking that data files are readable. +* Ignoring Assigns:: Treating assignments as file names. @end menu -@node Clones, Miscellaneous Programs, Sample Programs, Sample Programs -@section Re-inventing Wheels for Fun and Profit - -This section presents a number of POSIX utilities that are implemented in -@code{awk}. Re-inventing these programs in @code{awk} is often enjoyable, -since the algorithms can be very clearly expressed, and usually the code is -very concise and simple. This is true because @code{awk} does so much for you. +@node Filetrans Function, Rewind Function, Data File Management, Data File Management +@subsection Noting @value{DDF} Boundaries -It should be noted that these programs are not necessarily intended to -replace the installed versions on your system. Instead, their -purpose is to illustrate @code{awk} language programming for ``real world'' -tasks. +@cindex per file initialization and cleanup +The @code{BEGIN} and @code{END} rules are each executed exactly once, at +the beginning and end of your @command{awk} program, respectively +(@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}). +We (the @command{gawk} authors) once had a user who mistakenly thought that the +@code{BEGIN} rule is executed at the beginning of each @value{DF} and the +@code{END} rule is executed at the end of each @value{DF}. When informed +that this was not the case, the user requested that we add new special +patterns to @command{gawk}, named @code{BEGIN_FILE} and @code{END_FILE}, that +would have the desired behavior. He even supplied us the code to do so. -The programs are presented in alphabetical order. +Adding these special patterns to @command{gawk} wasn't necessary; +the job can be done cleanly in @command{awk} itself, as illustrated +by the following library program. +It arranges to call two user-supplied functions, @code{beginfile} and +@code{endfile}, at the beginning and end of each @value{DF}. +Besides solving the problem in only nine(!) lines of code, it does so +@emph{portably}; this works with any implementation of @command{awk}: -@menu -* Cut Program:: The @code{cut} utility. -* Egrep Program:: The @code{egrep} utility. -* Id Program:: The @code{id} utility. -* Split Program:: The @code{split} utility. -* Tee Program:: The @code{tee} utility. -* Uniq Program:: The @code{uniq} utility. -* Wc Program:: The @code{wc} utility. -@end menu +@example +# transfile.awk +# +# Give the user a hook for filename transitions +# +# The user must supply functions beginfile() and endfile() +# that each take the name of the file being started or +# finished, respectively. +@c # +@c # Arnold Robbins, arnold@@gnu.org, Public Domain +@c # January 1992 -@node Cut Program, Egrep Program, Clones, Clones -@subsection Cutting Out Fields and Columns +FILENAME != _oldfilename \ +@{ + if (_oldfilename != "") + endfile(_oldfilename) + _oldfilename = FILENAME + beginfile(FILENAME) +@} -@cindex @code{cut} utility -The @code{cut} utility selects, or ``cuts,'' either characters or fields -from its standard -input and sends them to its standard output. @code{cut} can cut out either -a list of characters, or a list of fields. By default, fields are separated -by tabs, but you may supply a command line option to change the field -@dfn{delimiter}, i.e.@: the field separator character. @code{cut}'s definition -of fields is less general than @code{awk}'s. +END @{ endfile(FILENAME) @} +@end example -A common use of @code{cut} might be to pull out just the login name of -logged-on users from the output of @code{who}. For example, the following -pipeline generates a sorted, unique list of the logged on users: +This file must be loaded before the user's ``main'' program, so that the +rule it supplies is executed first. -@example -who | cut -c1-8 | sort | uniq -@end example +This rule relies on @command{awk}'s @code{FILENAME} variable that +automatically changes for each new @value{DF}. The current @value{FN} is +saved in a private variable, @code{_oldfilename}. If @code{FILENAME} does +not equal @code{_oldfilename}, then a new @value{DF} is being processed and +it is necessary to call @code{endfile} for the old file. Because +@code{endfile} should only be called if a file has been processed, the +program first checks to make sure that @code{_oldfilename} is not the null +string. The program then assigns the current @value{FN} to +@code{_oldfilename} and calls @code{beginfile} for the file. +Because, like all @command{awk} variables, @code{_oldfilename} is +initialized to the null string, this rule executes correctly even for the +first @value{DF}. -The options for @code{cut} are: +The program also supplies an @code{END} rule to do the final processing for +the last file. Because this @code{END} rule comes before any @code{END} rules +supplied in the ``main'' program, @code{endfile} is called first. Once +again the value of multiple @code{BEGIN} and @code{END} rules should be clear. -@table @code -@item -c @var{list} -Use @var{list} as the list of characters to cut out. Items within the list -may be separated by commas, and ranges of characters can be separated with -dashes. The list @samp{1-8,15,22-35} specifies characters one through -eight, 15, and 22 through 35. +@cindex @code{beginfile} user-defined function +@cindex @code{endfile} user-defined function +This version has same problem as the first version of @code{nextfile} +(@pxref{Nextfile Function, ,Implementing @code{nextfile} as a Function}). +If the same @value{DF} occurs twice in a row on the command line, then +@code{endfile} and @code{beginfile} are not executed at the end of the +first pass and at the beginning of the second pass. +The following version solves the problem: -@item -f @var{list} -Use @var{list} as the list of fields to cut out. +@example +@c file eg/lib/ftrans.awk +# ftrans.awk --- handle data file transitions +# +# user supplies beginfile() and endfile() functions +@c endfile +@ignore +@c file eg/lib/ftrans.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# November 1992 -@item -d @var{delim} -Use @var{delim} as the field separator character instead of the tab -character. +@c endfile +@end ignore +@c file eg/lib/ftrans.awk +FNR == 1 @{ + if (_filename_ != "") + endfile(_filename_) + _filename_ = FILENAME + beginfile(FILENAME) +@} -@item -s -Suppress printing of lines that do not contain the field delimiter. -@end table +END @{ endfile(_filename_) @} +@c endfile +@end example -The @code{awk} implementation of @code{cut} uses the @code{getopt} library -function (@pxref{Getopt Function, ,Processing Command Line Options}), -and the @code{join} library function -(@pxref{Join Function, ,Merging an Array Into a String}). +@ref{Wc Program, ,Counting Things}, +shows how this library function can be used and +how it simplifies writing the main program. -The program begins with a comment describing the options and a @code{usage} -function which prints out a usage message and exits. @code{usage} is called -if invalid arguments are supplied. +@node Rewind Function, File Checking, Filetrans Function, Data File Management +@subsection Rereading the Current File -@findex cut.awk -@example -@c @group -@c file eg/prog/cut.awk -# cut.awk --- implement cut in awk -# Arnold Robbins, arnold@@gnu.org, Public Domain -# May 1993 +Another request for a new built-in function was for a @code{rewind} +function that would make it possible to reread the current file. +The requesting user didn't want to have to use @code{getline} +(@pxref{Getline, , Explicit Input with @code{getline}}) +inside a loop. -# Options: -# -f list Cut fields -# -d c Field delimiter character -# -c list Cut characters +However, as long as you are not in the @code{END} rule, it is +quite easy to arrange to immediately close the current input file +and then start over with it from the top. +For lack of a better name, we'll call it @code{rewind}: + +@cindex @code{rewind} user-defined function +@example +@c file eg/lib/rewind.awk +# rewind.awk --- rewind the current file and start over +@c endfile +@ignore +@c file eg/lib/rewind.awk # -# -s Suppress lines without the delimiter character +# Arnold Robbins, arnold@@gnu.org, Public Domain +# September 2000 -function usage( e1, e2) +@c endfile +@end ignore +@c file eg/lib/rewind.awk +function rewind( i) @{ - e1 = "usage: cut [-f list] [-d c] [-s] [files...]" - e2 = "usage: cut [-c list] [files...]" - print e1 > "/dev/stderr" - print e2 > "/dev/stderr" - exit 1 + # shift remaining arguments up + for (i = ARGC; i > ARGIND; i--) + ARGV[i] = ARGV[i-1] + + # make sure gawk knows to keep going + ARGC++ + + # make current file next to get done + ARGV[ARGIND+1] = FILENAME + + # do it + nextfile @} @c endfile -@c @end group @end example -@noindent -The variables @code{e1} and @code{e2} are used so that the function -fits nicely on the +This code relies on the @code{ARGIND} variable +(@pxref{Auto-set, ,Built-in Variables That Convey Information}), +which is specific to @command{gawk}. +If you are not using +@command{gawk}, you can use ideas presented in @iftex -page. +the previous @value{SECTION} @end iftex -@ifinfo -screen. -@end ifinfo - -Next comes a @code{BEGIN} rule that parses the command line options. -It sets @code{FS} to a single tab character, since that is @code{cut}'s -default field separator. The output field separator is also set to be the -same as the input field separator. Then @code{getopt} is used to step -through the command line options. One or the other of the variables -@code{by_fields} or @code{by_chars} is set to true, to indicate that -processing should be done by fields or by characters respectively. -When cutting by characters, the output field separator is set to the null -string. +@ifnottex +@ref{Filetrans Function, ,Noting @value{DDF} Boundaries}, +@end ifnottex +to either update @code{ARGIND} on your own +or modify this code as appropriate. + +The @code{rewind} function also relies on the @code{nextfile} keyword +(@pxref{Nextfile Statement, ,Using @command{gawk}'s @code{nextfile} Statement}). +@xref{Nextfile Function, ,Implementing @code{nextfile} as a Function}, +for a function version of @code{nextfile}. + +@node File Checking, Ignoring Assigns, Rewind Function, Data File Management +@subsection Checking for Readable @value{DDF}s + +@cindex fatal errors +@cindex readable @value{DF}s, checking +@cindex non-readable @value{DF}s, skipping +@cindex @value{DF}s, non-readable, skipping +@cindex @value{DF}s, readable, checking +Normally, if you give @command{awk} a @value{DF} that isn't readable, +it stops with a fatal error. There are times when you +might want to just ignore such files and keep going. You can +do this by prepending the following program to your @command{awk} +program: +@cindex @code{readable.awk} program @example -@c @group -@c file eg/prog/cut.awk -BEGIN \ -@{ - FS = "\t" # default - OFS = FS - while ((c = getopt(ARGC, ARGV, "sf:c:d:")) != -1) @{ - if (c == "f") @{ - by_fields = 1 - fieldlist = Optarg - @} else if (c == "c") @{ - by_chars = 1 - fieldlist = Optarg - OFS = "" -@group - @} else if (c == "d") @{ - if (length(Optarg) > 1) @{ - printf("Using first character of %s" \ - " for delimiter\n", Optarg) > "/dev/stderr" - Optarg = substr(Optarg, 1, 1) - @} - FS = Optarg - OFS = FS - if (FS == " ") # defeat awk semantics - FS = "[ ]" - @} else if (c == "s") - suppress++ +@c file eg/lib/readable.awk +# readable.awk --- library file to skip over unreadable files +@c endfile +@ignore +@c file eg/lib/readable.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# October 2000 + +@c endfile +@end ignore +@c file eg/lib/readable.awk +BEGIN @{ + for (i = 1; i < ARGC; i++) @{ + if (ARGV[i] ~ /^[A-Za-z_][A-Za-z0-9_]*=.*/ \ + || ARGV[i] == "-") + continue # assignment or standard input + else if ((getline junk < ARGV[i]) < 0) # unreadable + delete ARGV[i] else - usage() + close(ARGV[i]) @} -@end group - - for (i = 1; i < Optind; i++) - ARGV[i] = "" +@} @c endfile -@c @end group @end example -Special care is taken when the field delimiter is a space. Using -@code{@w{" "}} (a single space) for the value of @code{FS} is -incorrect---@code{awk} would -separate fields with runs of spaces, tabs and/or newlines, and we want them to be -separated with individual spaces. Also, note that after @code{getopt} is -through, we have to clear out all the elements of @code{ARGV} from one to -@code{Optind}, so that @code{awk} will not try to process the command line -options as file names. +@cindex fatal errors +In @command{gawk}, the @code{getline} won't be fatal (unless +@option{--posix} is in force). +Removing the element from @code{ARGV} with @code{delete} +skips the file (since it's no longer in the list). -After dealing with the command line options, the program verifies that the -options make sense. Only one or the other of @samp{-c} and @samp{-f} should -be used, and both require a field list. Then either @code{set_fieldlist} or -@code{set_charlist} is called to pull apart the list of fields or -characters. +@c This doesn't handle /dev/stdin etc. Not worth the hassle to mention or fix. -@example -@c @group -@c file eg/prog/cut.awk - if (by_fields && by_chars) - usage() +@node Ignoring Assigns, , File Checking, Data File Management +@subsection Treating Assignments as @value{FFN}s - if (by_fields == 0 && by_chars == 0) - by_fields = 1 # default +Occasionally, you might not want @command{awk} to process command-line +variable assignments +(@pxref{Assignment Options, ,Assigning Variables on the Command Line}). +In particular, if you have @value{FN}s that contain an @samp{=} character, +@command{awk} treats the @value{FN} as an assignment, and does not process it. - if (fieldlist == "") @{ - print "cut: needs list for -c or -f" > "/dev/stderr" - exit 1 - @} +Some users have suggested an additional command-line option for @command{gawk} +to disable command-line assignments. However, some simple programming with +a library file does the trick: -@group - if (by_fields) - set_fieldlist() - else - set_charlist() -@} +@cindex @code{noassign.awk} program +@example +@c file eg/lib/noassign.awk +# noassign.awk --- library file to avoid the need for a +# special option that disables command-line assignments @c endfile -@end group -@end example - -Here is @code{set_fieldlist}. It first splits the field list apart -at the commas, into an array. Then, for each element of the array, it -looks to see if it is actually a range, and if so splits it apart. The range -is verified to make sure the first number is smaller than the second. -Each number in the list is added to the @code{flist} array, which simply -lists the fields that will be printed. -Normal field splitting is used. -The program lets @code{awk} -handle the job of doing the field splitting. +@ignore +@c file eg/lib/noassign.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# October 1999 -@example -@c @group -@c file eg/prog/cut.awk -function set_fieldlist( n, m, i, j, k, f, g) +@c endfile +@end ignore +@c file eg/lib/noassign.awk +function disable_assigns(argc, argv, i) @{ - n = split(fieldlist, f, ",") - j = 1 # index in flist - for (i = 1; i <= n; i++) @{ - if (index(f[i], "-") != 0) @{ # a range - m = split(f[i], g, "-") - if (m != 2 || g[1] >= g[2]) @{ - printf("bad field list: %s\n", - f[i]) > "/dev/stderr" - exit 1 - @} - for (k = g[1]; k <= g[2]; k++) - flist[j++] = k - @} else - flist[j++] = f[i] - @} - nfields = j - 1 + for (i = 1; i < argc; i++) + if (argv[i] ~ /^[A-Za-z_][A-Za-z_0-9]*=.*/) + argv[i] = ("./" argv[i]) +@} + +BEGIN @{ + if (No_command_assign) + disable_assigns(ARGC, ARGV) @} @c endfile -@c @end group @end example -The @code{set_charlist} function is more complicated than @code{set_fieldlist}. -The idea here is to use @code{gawk}'s @code{FIELDWIDTHS} variable -(@pxref{Constant Size, ,Reading Fixed-width Data}), -which describes constant width input. When using a character list, that is -exactly what we have. - -Setting up @code{FIELDWIDTHS} is more complicated than simply listing the -fields that need to be printed. We have to keep track of the fields to be -printed, and also the intervening characters that have to be skipped. -For example, suppose you wanted characters one through eight, 15, and -22 through 35. You would use @samp{-c 1-8,15,22-35}. The necessary value -for @code{FIELDWIDTHS} would be @code{@w{"8 6 1 6 14"}}. This gives us five -fields, and what should be printed are @code{$1}, @code{$3}, and @code{$5}. -The intermediate fields are ``filler,'' stuff in between the desired data. - -@code{flist} lists the fields to be printed, and @code{t} tracks the -complete field list, including filler fields. +You then run your program this way: @example -@c @group -@c file eg/prog/cut.awk -function set_charlist( field, i, j, f, g, t, - filler, last, len) -@{ - field = 1 # count total fields - n = split(fieldlist, f, ",") - j = 1 # index in flist - for (i = 1; i <= n; i++) @{ - if (index(f[i], "-") != 0) @{ # range - m = split(f[i], g, "-") - if (m != 2 || g[1] >= g[2]) @{ - printf("bad character list: %s\n", - f[i]) > "/dev/stderr" - exit 1 - @} - len = g[2] - g[1] + 1 - if (g[1] > 1) # compute length of filler - filler = g[1] - last - 1 - else - filler = 0 - if (filler) - t[field++] = filler - t[field++] = len # length of field - last = g[2] - flist[j++] = field - 1 - @} else @{ - if (f[i] > 1) - filler = f[i] - last - 1 - else - filler = 0 - if (filler) - t[field++] = filler - t[field++] = 1 - last = f[i] - flist[j++] = field - 1 - @} - @} -@group - FIELDWIDTHS = join(t, 1, field - 1) - nfields = j - 1 -@} -@end group -@c endfile +awk -v No_command_assign=1 -f noassign.awk -f yourprog.awk * @end example -Here is the rule that actually processes the data. If the @samp{-s} option -was given, then @code{suppress} will be true. The first @code{if} statement -makes sure that the input record does have the field separator. If -@code{cut} is processing fields, @code{suppress} is true, and the field -separator character is not in the record, then the record is skipped. - -If the record is valid, then at this point, @code{gawk} has split the data -into fields, either using the character in @code{FS} or using fixed-length -fields and @code{FIELDWIDTHS}. The loop goes through the list of fields -that should be printed. If the corresponding field has data in it, it is -printed. If the next field also has data, then the separator character is -written out in between the fields. +The function works by looping through the arguments. +It prepends @samp{./} to +any argument that matches the form +of a variable assignment, turning that argument into a @value{FN}. -@c 2e: Could use `index($0, FS) != 0' instead of `$0 !~ FS', below +The use of @code{No_command_assign} allows you to disable command-line +assignments at invocation time, by giving the variable a true value. +When not set, it is initially zero (i.e., false), so the command-line arguments +are left alone. -@example -@c @group -@c file eg/prog/cut.awk -@{ - if (by_fields && suppress && $0 !~ FS) - next +@node Getopt Function, Passwd Functions, Data File Management, Library Functions +@section Processing Command-Line Options - for (i = 1; i <= nfields; i++) @{ - if ($flist[i] != "") @{ - printf "%s", $flist[i] - if (i < nfields && $flist[i+1] != "") - printf "%s", OFS - @} - @} - print "" -@} -@c endfile -@c @end group -@end example +@cindex @code{getopt} C library function +@cindex processing arguments +@cindex argument processing +Most utilities on POSIX compatible systems take options, or ``switches,'' on +the command line that can be used to change the way a program behaves. +@command{awk} is an example of such a program +(@pxref{Options, ,Command-Line Options}). +Often, options take @dfn{arguments}; i.e., data that the program needs to +correctly obey the command-line option. For example, @command{awk}'s +@option{-F} option requires a string to use as the field separator. +The first occurrence on the command line of either @option{--} or a +string that does not begin with @samp{-} ends the options. -This version of @code{cut} relies on @code{gawk}'s @code{FIELDWIDTHS} -variable to do the character-based cutting. While it would be possible in -other @code{awk} implementations to use @code{substr} -(@pxref{String Functions, ,Built-in Functions for String Manipulation}), -it would also be extremely painful to do so. -The @code{FIELDWIDTHS} variable supplies an elegant solution to the problem -of picking the input line apart by characters. +Modern Unix systems provide a C function named @code{getopt} for processing +command-line arguments. The programmer provides a string describing the +one-letter options. If an option requires an argument, it is followed in the +string with a colon. @code{getopt} is also passed the +count and values of the command-line arguments and is called in a loop. +@code{getopt} processes the command-line arguments for option letters. +Each time around the loop, it returns a single character representing the +next option letter that it finds, or @samp{?} if it finds an invalid option. +When it returns @minus{}1, there are no options left on the command line. -@node Egrep Program, Id Program, Cut Program, Clones -@subsection Searching for Regular Expressions in Files +When using @code{getopt}, options that do not take arguments can be +grouped together. Furthermore, options that take arguments require that the +argument is present. The argument can immediately follow the option letter +or it can be a separate command-line argument. -@cindex @code{egrep} utility -The @code{egrep} utility searches files for patterns. It uses regular -expressions that are almost identical to those available in @code{awk} -(@pxref{Regexp Constants, ,Regular Expression Constants}). It is used this way: +Given a hypothetical program that takes +three command-line options, @option{-a}, @option{-b}, and @option{-c}, where +@option{-b} requires an argument, all of the following are valid ways of +invoking the program: @example -egrep @r{[} @var{options} @r{]} '@var{pattern}' @var{files} @dots{} +prog -a -b foo -c data1 data2 data3 +prog -ac -bfoo -- data1 data2 data3 +prog -acbfoo data1 data2 data3 @end example -The @var{pattern} is a regexp. -In typical usage, the regexp is quoted to prevent the shell from expanding -any of the special characters as file name wildcards. -Normally, @code{egrep} prints the -lines that matched. If multiple file names are provided on the command -line, each output line is preceded by the name of the file and a colon. +Notice that when the argument is grouped with its option, the rest of +the argument is considered to be the option's argument. +In this example, @option{-acbfoo} indicates that all of the +@option{-a}, @option{-b}, and @option{-c} options were supplied, +and that @samp{foo} is the argument to the @option{-b} option. -The options are: +@code{getopt} provides four external variables that the programmer can use: @table @code -@item -c -Print out a count of the lines that matched the pattern, instead of the -lines themselves. - -@item -s -Be silent. No output is produced, and the exit value indicates whether -or not the pattern was matched. - -@item -v -Invert the sense of the test. @code{egrep} prints the lines that do -@emph{not} match the pattern, and exits successfully if the pattern was not -matched. +@item optind +The index in the argument value array (@code{argv}) where the first +non-option command-line argument can be found. -@item -i -Ignore case distinctions in both the pattern and the input data. +@item optarg +The string value of the argument to an option. -@item -l -Only print the names of the files that matched, not the lines that matched. +@item opterr +Usually @code{getopt} prints an error message when it finds an invalid +option. Setting @code{opterr} to zero disables this feature. (An +application might want to print its own error message.) -@item -e @var{pattern} -Use @var{pattern} as the regexp to match. The purpose of the @samp{-e} -option is to allow patterns that start with a @samp{-}. +@item optopt +The letter representing the command-line option. +@c While not usually documented, most versions supply this variable. @end table -This version uses the @code{getopt} library function -(@pxref{Getopt Function, ,Processing Command Line Options}), -and the file transition library program -(@pxref{Filetrans Function, ,Noting Data File Boundaries}). - -The program begins with a descriptive comment, and then a @code{BEGIN} rule -that processes the command line arguments with @code{getopt}. The @samp{-i} -(ignore case) option is particularly easy with @code{gawk}; we just use the -@code{IGNORECASE} built in variable -(@pxref{Built-in Variables}). +The following C fragment shows how @code{getopt} might process command-line +arguments for @command{awk}: -@findex egrep.awk @example -@c @group -@c file eg/prog/egrep.awk -# egrep.awk --- simulate egrep in awk -# Arnold Robbins, arnold@@gnu.org, Public Domain -# May 1993 - -# Options: -# -c count of lines -# -s silent - use exit value -# -v invert test, success if no match -# -i ignore case -# -l print filenames only -# -e argument is pattern - -BEGIN @{ - while ((c = getopt(ARGC, ARGV, "ce:svil")) != -1) @{ - if (c == "c") - count_only++ - else if (c == "s") - no_print++ - else if (c == "v") - invert++ - else if (c == "i") - IGNORECASE = 1 - else if (c == "l") - filenames_only++ - else if (c == "e") - pattern = Optarg - else - usage() +int +main(int argc, char *argv[]) +@{ + @dots{} + /* print our own message */ + opterr = 0; + while ((c = getopt(argc, argv, "v:f:F:W:")) != -1) @{ + switch (c) @{ + case 'f': /* file */ + @dots{} + break; + case 'F': /* field separator */ + @dots{} + break; + case 'v': /* variable assignment */ + @dots{} + break; + case 'W': /* extension */ + @dots{} + break; + case '?': + default: + usage(); + break; + @} @} -@c endfile -@c @end group + @dots{} +@} @end example -Next comes the code that handles the @code{egrep} specific behavior. If no -pattern was supplied with @samp{-e}, the first non-option on the command -line is used. The @code{awk} command line arguments up to @code{ARGV[Optind]} -are cleared, so that @code{awk} won't try to process them as files. If no -files were specified, the standard input is used, and if multiple files were -specified, we make sure to note this so that the file names can precede the -matched lines in the output. - -The last two lines are commented out, since they are not needed in -@code{gawk}. They should be uncommented if you have to use another version -of @code{awk}. +As a side point, @command{gawk} actually uses the GNU @code{getopt_long} +function to process both normal and GNU-style long options +(@pxref{Options, ,Command-Line Options}). -@example -@c @group -@c file eg/prog/egrep.awk - if (pattern == "") - pattern = ARGV[Optind++] +The abstraction provided by @code{getopt} is very useful and is quite +handy in @command{awk} programs as well. Following is an @command{awk} +version of @code{getopt}. This function highlights one of the +greatest weaknesses in @command{awk}, which is that it is very poor at +manipulating single characters. Repeated calls to @code{substr} are +necessary for accessing individual characters +(@pxref{String Functions, ,String Manipulation Functions}).@footnote{This +function was written before @command{gawk} acquired the ability to +split strings into single characters using @code{""} as the separator. +We have left it alone, since using @code{substr} is more portable.} - for (i = 1; i < Optind; i++) - ARGV[i] = "" - if (Optind >= ARGC) @{ - ARGV[1] = "-" - ARGC = 2 - @} else if (ARGC - Optind > 1) - do_filenames++ +The discussion that follows walks through the code a bit at a time: -# if (IGNORECASE) -# pattern = tolower(pattern) -@} +@example +@c file eg/lib/getopt.awk +# getopt.awk --- do C library getopt(3) function in awk @c endfile -@c @end group -@end example - -The next set of lines should be uncommented if you are not using -@code{gawk}. This rule translates all the characters in the input line -into lower-case if the @samp{-i} option was specified. The rule is -commented out since it is not necessary with @code{gawk}. -@c bug: if a match happens, we output the translated line, not the original +@ignore +@c file eg/lib/getopt.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# +# Initial version: March, 1991 +# Revised: May, 1993 -@example -@c @group -@c file eg/prog/egrep.awk -#@{ -# if (IGNORECASE) -# $0 = tolower($0) -#@} @c endfile -@c @end group -@end example +@end ignore +@c file eg/lib/getopt.awk +# External variables: +# Optind -- index in ARGV of first non-option argument +# Optarg -- string value of argument to current option +# Opterr -- if nonzero, print our own diagnostic +# Optopt -- current option letter -The @code{beginfile} function is called by the rule in @file{ftrans.awk} -when each new file is processed. In this case, it is very simple; all it -does is initialize a variable @code{fcount} to zero. @code{fcount} tracks -how many lines in the current file matched the pattern. +# Returns: +# -1 at end of options +# ? for unrecognized option +# a character representing the current option -@example -@group -@c file eg/prog/egrep.awk -function beginfile(junk) -@{ - fcount = 0 -@} +# Private Data: +# _opti -- index in multi-flag option, e.g., -abc @c endfile -@end group @end example -The @code{endfile} function is called after each file has been processed. -It is used only when the user wants a count of the number of lines that -matched. @code{no_print} will be true only if the exit status is desired. -@code{count_only} will be true if line counts are desired. @code{egrep} -will therefore only print line counts if printing and counting are enabled. -The output format must be adjusted depending upon the number of files to be -processed. Finally, @code{fcount} is added to @code{total}, so that we -know how many lines altogether matched the pattern. +The function starts out with +a list of the global variables it uses, +what the return values are, what they mean, and any global variables that +are ``private'' to this library function. Such documentation is essential +for any program, and particularly for library functions. + +The @code{getopt} function first checks that it was indeed called with a string of options +(the @code{options} parameter). If @code{options} has a zero length, +@code{getopt} immediately returns @minus{}1: +@cindex @code{getopt} user-defined function @example -@group -@c file eg/prog/egrep.awk -function endfile(file) +@c file eg/lib/getopt.awk +function getopt(argc, argv, options, thisopt, i) @{ - if (! no_print && count_only) - if (do_filenames) - print file ":" fcount - else - print fcount + if (length(options) == 0) # no options given + return -1 - total += fcount -@} -@c endfile +@group + if (argv[Optind] == "--") @{ # all done + Optind++ + _opti = 0 + return -1 @end group + @} else if (argv[Optind] !~ /^-[^: \t\n\f\r\v\b]/) @{ + _opti = 0 + return -1 + @} +@c endfile @end example -This rule does most of the work of matching lines. The variable -@code{matches} will be true if the line matched the pattern. If the user -wants lines that did not match, the sense of the @code{matches} is inverted -using the @samp{!} operator. @code{fcount} is incremented with the value of -@code{matches}, which will be either one or zero, depending upon a -successful or unsuccessful match. If the line did not match, the -@code{next} statement just moves on to the next record. - -There are several optimizations for performance in the following few lines -of code. If the user only wants exit status (@code{no_print} is true), and -we don't have to count lines, then it is enough to know that one line in -this file matched, and we can skip on to the next file with @code{nextfile}. -Along similar lines, if we are only printing file names, and we -don't need to count lines, we can print the file name, and then skip to the -next file with @code{nextfile}. - -Finally, each line is printed, with a leading filename and colon if -necessary. +The next thing to check for is the end of the options. A @option{--} +ends the command-line options, as does any command-line argument that +does not begin with a @samp{-}. @code{Optind} is used to step through +the array of command-line arguments; it retains its value across calls +to @code{getopt}, because it is a global variable. -@ignore -2e: note, probably better to recode the last few lines as - if (! count_only) @{ - if (no_print) - nextfile - - if (filenames_only) @{ - print FILENAME - nextfile - @} +The regular expression that is used, @code{@w{/^-[^: \t\n\f\r\v\b]/}}, is +perhaps a bit of overkill; it checks for a @samp{-} followed by anything +that is not whitespace and not a colon. +If the current command-line argument does not match this pattern, +it is not an option, and it ends option processing. - if (do_filenames) - print FILENAME ":" $0 - else - print +@example +@c file eg/lib/getopt.awk + if (_opti == 0) + _opti = 2 + thisopt = substr(argv[Optind], _opti, 1) + Optopt = thisopt + i = index(options, thisopt) + if (i == 0) @{ + if (Opterr) + printf("%c -- invalid option\n", + thisopt) > "/dev/stderr" + if (_opti >= length(argv[Optind])) @{ + Optind++ + _opti = 0 + @} else + _opti++ + return "?" @} -@end ignore +@c endfile +@end example -@example -@c @group -@c file eg/prog/egrep.awk -@{ - matches = ($0 ~ pattern) - if (invert) - matches = ! matches +The @code{_opti} variable tracks the position in the current command-line +argument (@code{argv[Optind]}). If multiple options are +grouped together with one @samp{-} (e.g., @option{-abx}), it is necessary +to return them to the user one at a time. - fcount += matches # 1 or 0 +If @code{_opti} is equal to zero, it is set to two, which is the index in +the string of the next character to look at (we skip the @samp{-}, which +is at position one). The variable @code{thisopt} holds the character, +obtained with @code{substr}. It is saved in @code{Optopt} for the main +program to use. - if (! matches) - next +If @code{thisopt} is not in the @code{options} string, then it is an +invalid option. If @code{Opterr} is nonzero, @code{getopt} prints an error +message on the standard error that is similar to the message from the C +version of @code{getopt}. - if (no_print && ! count_only) - nextfile +Because the option is invalid, it is necessary to skip it and move on to the +next option character. If @code{_opti} is greater than or equal to the +length of the current command-line argument, it is necessary to move on +to the next argument, so @code{Optind} is incremented and @code{_opti} is reset +to zero. Otherwise, @code{Optind} is left alone and @code{_opti} is merely +incremented. - if (filenames_only && ! count_only) @{ - print FILENAME - nextfile - @} +In any case, because the option is invalid, @code{getopt} returns @samp{?}. +The main program can examine @code{Optopt} if it needs to know what the +invalid option letter actually is. Continuing on: - if (do_filenames && ! count_only) - print FILENAME ":" $0 -@group - else if (! count_only) - print -@end group -@} +@example +@c file eg/lib/getopt.awk + if (substr(options, i + 1, 1) == ":") @{ + # get option argument + if (length(substr(argv[Optind], _opti + 1)) > 0) + Optarg = substr(argv[Optind], _opti + 1) + else + Optarg = argv[++Optind] + _opti = 0 + @} else + Optarg = "" @c endfile -@c @end group @end example -@c @strong{Exercise}: rearrange the code inside @samp{if (! count_only)}. - -The @code{END} rule takes care of producing the correct exit status. If -there were no matches, the exit status is one, otherwise it is zero. +If the option requires an argument, the option letter is followed by a colon +in the @code{options} string. If there are remaining characters in the +current command-line argument (@code{argv[Optind]}), then the rest of that +string is assigned to @code{Optarg}. Otherwise, the next command-line +argument is used (@samp{-xFOO} vs.@: @samp{@w{-x FOO}}). In either case, +@code{_opti} is reset to zero, because there are no more characters left to +examine in the current command-line argument. Continuing: @example -@c @group -@c file eg/prog/egrep.awk -END \ -@{ - if (total == 0) - exit 1 - exit 0 +@c file eg/lib/getopt.awk + if (_opti == 0 || _opti >= length(argv[Optind])) @{ + Optind++ + _opti = 0 + @} else + _opti++ + return thisopt @} @c endfile -@c @end group @end example -The @code{usage} function prints a usage message in case of invalid options -and then exits. - -@example -@c @group -@c file eg/prog/egrep.awk -function usage( e) -@{ - e = "Usage: egrep [-csvil] [-e pat] [files ...]" - print e > "/dev/stderr" - exit 1 +Finally, if @code{_opti} is either zero or greater than the length of the +current command-line argument, it means this element in @code{argv} is +through being processed, so @code{Optind} is incremented to point to the +next element in @code{argv}. If neither condition is true, then only +@code{_opti} is incremented, so that the next option letter can be processed +on the next call to @code{getopt}. + +The @code{BEGIN} rule initializes both @code{Opterr} and @code{Optind} to one. +@code{Opterr} is set to one, since the default behavior is for @code{getopt} +to print a diagnostic message upon seeing an invalid option. @code{Optind} +is set to one, since there's no reason to look at the program name, which is +in @code{ARGV[0]}: + +@example +@c file eg/lib/getopt.awk +BEGIN @{ + Opterr = 1 # default is to diagnose + Optind = 1 # skip ARGV[0] + + # test program + if (_getopt_test) @{ + while ((_go_c = getopt(ARGC, ARGV, "ab:cd")) != -1) + printf("c = <%c>, optarg = <%s>\n", + _go_c, Optarg) + printf("non-option arguments:\n") + for (; Optind < ARGC; Optind++) + printf("\tARGV[%d] = <%s>\n", + Optind, ARGV[Optind]) + @} @} @c endfile -@c @end group @end example -The variable @code{e} is used so that the function fits nicely -on the printed page. +The rest of the @code{BEGIN} rule is a simple test program. Here is the +result of two sample runs of the test program: -@cindex backslash continuation -Just a note on programming style. You may have noticed that the @code{END} -rule uses backslash continuation, with the open brace on a line by -itself. This is so that it more closely resembles the way functions -are written. Many of the examples -@iftex -in this chapter -@end iftex -use this style. You can decide for yourself if you like writing -your @code{BEGIN} and @code{END} rules this way, -or not. +@example +$ awk -f getopt.awk -v _getopt_test=1 -- -a -cbARG bax -x +@print{} c = , optarg = <> +@print{} c = , optarg = <> +@print{} c = , optarg = +@print{} non-option arguments: +@print{} ARGV[3] = +@print{} ARGV[4] = <-x> -@node Id Program, Split Program, Egrep Program, Clones -@subsection Printing Out User Information +$ awk -f getopt.awk -v _getopt_test=1 -- -a -x -- xyz abc +@print{} c = , optarg = <> +@error{} x -- invalid option +@print{} c = , optarg = <> +@print{} non-option arguments: +@print{} ARGV[4] = +@print{} ARGV[5] = +@end example -@cindex @code{id} utility -The @code{id} utility lists a user's real and effective user-id numbers, -real and effective group-id numbers, and the user's group set, if any. -@code{id} will only print the effective user-id and group-id if they are -different from the real ones. If possible, @code{id} will also supply the -corresponding user and group names. The output might look like this: +In both runs, +the first @option{--} terminates the arguments to @command{awk}, so that it does +not try to interpret the @option{-a}, etc., as its own options. +Several of the sample programs presented in +@ref{Sample Programs, ,Practical @command{awk} Programs}, +use @code{getopt} to process their arguments. -@example -$ id -@print{} uid=2076(arnold) gid=10(staff) groups=10(staff),4(tty) -@end example +@node Passwd Functions, Group Functions, Getopt Function, Library Functions +@section Reading the User Database -This information is exactly what is provided by @code{gawk}'s -@file{/dev/user} special file (@pxref{Special Files, ,Special File Names in @code{gawk}}). -However, the @code{id} utility provides a more palatable output than just a -string of numbers. +The @code{PROCINFO} array +(@pxref{Built-in Variables}) +provides access to the current user's real and effective user and group id +numbers, and if available, the user's supplementary group set. +However, because these are numbers, they do not provide very useful +information to the average user. There needs to be some way to find the +user information associated with the user and group numbers. This +@value{SECTION} presents a suite of functions for retrieving information from the +user database. @xref{Group Functions, ,Reading the Group Database}, +for a similar suite that retrieves information from the group database. -Here is a simple version of @code{id} written in @code{awk}. -It uses the user database library functions -(@pxref{Passwd Functions, ,Reading the User Database}), -and the group database library functions -(@pxref{Group Functions, ,Reading the Group Database}). +@cindex @code{getpwent} C library function +@cindex user information +@cindex login information +@cindex account information +@cindex password file +The POSIX standard does not define the file where user information is +kept. Instead, it provides the @code{} header file +and several C language subroutines for obtaining user information. +The primary function is @code{getpwent}, for ``get password entry.'' +The ``password'' comes from the original user database file, +@file{/etc/passwd}, which stores user information, along with the +encrypted passwords (hence the name). -The program is fairly straightforward. All the work is done in the -@code{BEGIN} rule. The user and group id numbers are obtained from -@file{/dev/user}. If there is no support for @file{/dev/user}, the program -gives up. +@cindex @command{pwcat} program +While an @command{awk} program could simply read @file{/etc/passwd} +directly, this file may not contain complete information about the +system's set of users.@footnote{It is often the case that password +information is stored in a network database.} To be sure you are able to +produce a readable and complete version of the user database, it is necessary +to write a small C program that calls @code{getpwent}. @code{getpwent} +is defined as returning a pointer to a @code{struct passwd}. Each time it +is called, it returns the next entry in the database. When there are +no more entries, it returns @code{NULL}, the null pointer. When this +happens, the C program should call @code{endpwent} to close the database. +Following is @command{pwcat}, a C program that ``cats'' the password database. -The code is repetitive. The entry in the user database for the real user-id -number is split into parts at the @samp{:}. The name is the first field. -Similar code is used for the effective user-id number, and the group -numbers. +@c Use old style function header for portability to old systems (SunOS, HP/UX). -@findex id.awk @example -@c @group -@c file eg/prog/id.awk -# id.awk --- implement id in awk -# Arnold Robbins, arnold@@gnu.org, Public Domain -# May 1993 +@c file eg/lib/pwcat.c +/* + * pwcat.c + * + * Generate a printable version of the password database + */ +@c endfile +@ignore +@c file eg/lib/pwcat.c +/* + * Arnold Robbins, arnold@@gnu.org, May 1993 + * Public Domain + */ -# output is: -# uid=12(foo) euid=34(bar) gid=3(baz) \ -# egid=5(blat) groups=9(nine),2(two),1(one) +@c endfile +@end ignore +@c file eg/lib/pwcat.c +#include +#include -BEGIN \ +int +main(argc, argv) +int argc; +char **argv; @{ - if ((getline < "/dev/user") < 0) @{ - err = "id: no /dev/user support - cannot run" - print err > "/dev/stderr" - exit 1 - @} - close("/dev/user") - - uid = $1 - euid = $2 - gid = $3 - egid = $4 - - printf("uid=%d", uid) - pw = getpwuid(uid) -@group - if (pw != "") @{ - split(pw, a, ":") - printf("(%s)", a[1]) - @} -@end group - - if (euid != uid) @{ - printf(" euid=%d", euid) - pw = getpwuid(euid) - if (pw != "") @{ - split(pw, a, ":") - printf("(%s)", a[1]) - @} - @} - - printf(" gid=%d", gid) - pw = getgrgid(gid) - if (pw != "") @{ - split(pw, a, ":") - printf("(%s)", a[1]) - @} + struct passwd *p; - if (egid != gid) @{ - printf(" egid=%d", egid) - pw = getgrgid(egid) - if (pw != "") @{ - split(pw, a, ":") - printf("(%s)", a[1]) - @} - @} + while ((p = getpwent()) != NULL) + printf("%s:%s:%d:%d:%s:%s:%s\n", + p->pw_name, p->pw_passwd, p->pw_uid, + p->pw_gid, p->pw_gecos, p->pw_dir, p->pw_shell); - if (NF > 4) @{ - printf(" groups="); - for (i = 5; i <= NF; i++) @{ - printf("%d", $i) - pw = getgrgid($i) - if (pw != "") @{ - split(pw, a, ":") - printf("(%s)", a[1]) - @} -@group - if (i < NF) - printf(",") -@end group - @} - @} - print "" + endpwent(); + exit(0); @} @c endfile -@c @end group @end example -@c exercise!!! +If you don't understand C, don't worry about it. +The output from @command{pwcat} is the user database, in the traditional +@file{/etc/passwd} format of colon-separated fields. The fields are: + @ignore -The POSIX version of @code{id} takes arguments that control which -information is printed. Modify this version to accept the same -arguments and perform in the same way. -@end ignore +@table @asis +@item Login name +The user's login name. -@node Split Program, Tee Program, Id Program, Clones -@subsection Splitting a Large File Into Pieces +@item Encrypted password +The user's encrypted password. This may not be available on some systems. -@cindex @code{split} utility -The @code{split} program splits large text files into smaller pieces. By default, -the output files are named @file{xaa}, @file{xab}, and so on. Each file has -1000 lines in it, with the likely exception of the last file. To change the -number of lines in each file, you supply a number on the command line -preceded with a minus, e.g., @samp{-500} for files with 500 lines in them -instead of 1000. To change the name of the output files to something like -@file{myfileaa}, @file{myfileab}, and so on, you supply an additional -argument that specifies the filename. +@item User-ID +The user's numeric user-id number. -Here is a version of @code{split} in @code{awk}. It uses the @code{ord} and -@code{chr} functions presented in -@ref{Ordinal Functions, ,Translating Between Characters and Numbers}. +@item Group-ID +The user's numeric group-id number. -The program first sets its defaults, and then tests to make sure there are -not too many arguments. It then looks at each argument in turn. The -first argument could be a minus followed by a number. If it is, this happens -to look like a negative number, so it is made positive, and that is the -count of lines. The data file name is skipped over, and the final argument -is used as the prefix for the output file names. +@item Full name +The user's full name, and perhaps other information associated with the +user. -@findex split.awk -@example -@c @group -@c file eg/prog/split.awk -# split.awk --- do split in awk -# Arnold Robbins, arnold@@gnu.org, Public Domain -# May 1993 +@item Home directory +The user's login (or ``home'') directory (familiar to shell programmers as +@code{$HOME}). -# usage: split [-num] [file] [outname] +@item Login shell +The program that is run when the user logs in. This is usually a +shell, such as @command{bash}. +@end table +@end ignore -BEGIN @{ - outfile = "x" # default - count = 1000 - if (ARGC > 4) - usage() +@multitable {Encrypted password} {1234567890123456789012345678901234567890123456} +@item Login name @tab The user's login name. - i = 1 - if (ARGV[i] ~ /^-[0-9]+$/) @{ - count = -ARGV[i] - ARGV[i] = "" - i++ - @} - # test argv in case reading from stdin instead of file - if (i in ARGV) - i++ # skip data file name - if (i in ARGV) @{ - outfile = ARGV[i] - ARGV[i] = "" - @} +@item Encrypted password @tab The user's encrypted password. This may not be available on some systems. - s1 = s2 = "a" - out = (outfile s1 s2) -@} -@c endfile -@c @end group -@end example +@item User-ID @tab The user's numeric user-id number. -The next rule does most of the work. @code{tcount} (temporary count) tracks -how many lines have been printed to the output file so far. If it is greater -than @code{count}, it is time to close the current file and start a new one. -@code{s1} and @code{s2} track the current suffixes for the file name. If -they are both @samp{z}, the file is just too big. Otherwise, @code{s1} -moves to the next letter in the alphabet and @code{s2} starts over again at -@samp{a}. +@item Group-ID @tab The user's numeric group-id number. +@item Full name @tab The user's full name, and perhaps other information associated with the +user. + +@item Home directory @tab The user's login (or ``home'') directory (familiar to shell programmers as +@code{$HOME}). + +@item Login shell @tab The program that is run when the user logs in. This is usually a +shell, such as @command{bash}. +@end multitable + +A few lines representative of @command{pwcat}'s output are as follows: + +@cindex Jacobs, Andrew +@cindex Robbins, Arnold +@cindex Robbins, Miriam @example -@c @group -@c file eg/prog/split.awk -@{ - if (++tcount > count) @{ - close(out) - if (s2 == "z") @{ - if (s1 == "z") @{ - printf("split: %s is too large to split\n", \ - FILENAME) > "/dev/stderr" - exit 1 - @} - s1 = chr(ord(s1) + 1) - s2 = "a" - @} else - s2 = chr(ord(s2) + 1) - out = (outfile s1 s2) - tcount = 1 - @} - print > out -@} -@c endfile -@c @end group +$ pwcat +@print{} root:3Ov02d5VaUPB6:0:1:Operator:/:/bin/sh +@print{} nobody:*:65534:65534::/: +@print{} daemon:*:1:1::/: +@print{} sys:*:2:2::/:/bin/csh +@print{} bin:*:3:3::/bin: +@print{} arnold:xyzzy:2076:10:Arnold Robbins:/home/arnold:/bin/sh +@print{} miriam:yxaay:112:10:Miriam Robbins:/home/miriam:/bin/sh +@print{} andy:abcca2:113:10:Andy Jacobs:/home/andy:/bin/sh +@dots{} @end example -The @code{usage} function simply prints an error message and exits. +With that introduction, following is a group of functions for getting user +information. There are several functions here, corresponding to the C +functions of the same names: + +@c Exercise: simplify all these functions that return values. +@c Answer: return foo[key] returns "" if key not there, no need to check with `in'. +@cindex @code{_pw_init} user-defined function @example -@c @group -@c file eg/prog/split.awk -function usage( e) -@{ - e = "usage: split [-num] [file] [outname]" - print e > "/dev/stderr" - exit 1 -@} +@c file eg/lib/passwdawk.in +# passwd.awk --- access password file information @c endfile -@c @end group -@end example - -@noindent -The variable @code{e} is used so that the function -fits nicely on the -@iftex -page. -@end iftex -@ifinfo -screen. -@end ifinfo +@ignore +@c file eg/lib/passwdawk.in +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# May 1993 +# Revised October 2000 -This program is a bit sloppy; it relies on @code{awk} to close the last file -for it automatically, instead of doing it in an @code{END} rule. +@c endfile +@end ignore +@c file eg/lib/passwdawk.in +BEGIN @{ + # tailor this to suit your system + _pw_awklib = "/usr/local/libexec/awk/" +@} -@node Tee Program, Uniq Program, Split Program, Clones -@subsection Duplicating Output Into Multiple Files +function _pw_init( oldfs, oldrs, olddol0, pwcat, using_fw) +@{ + if (_pw_inited) + return -@cindex @code{tee} utility -The @code{tee} program is known as a ``pipe fitting.'' @code{tee} copies -its standard input to its standard output, and also duplicates it to the -files named on the command line. Its usage is: + oldfs = FS + oldrs = RS + olddol0 = $0 + using_fw = (PROCINFO["FS"] == "FIELDWIDTHS") + FS = ":" + RS = "\n" -@example -tee @r{[}-a@r{]} file @dots{} + pwcat = _pw_awklib "pwcat" + while ((pwcat | getline) > 0) @{ + _pw_byname[$1] = $0 + _pw_byuid[$3] = $0 + _pw_bycount[++_pw_total] = $0 + @} + close(pwcat) + _pw_count = 0 + _pw_inited = 1 + FS = oldfs + if (using_fw) + FIELDWIDTHS = FIELDWIDTHS + RS = oldrs + $0 = olddol0 +@} +@c endfile @end example -The @samp{-a} option tells @code{tee} to append to the named files, instead of -truncating them and starting over. +The @code{BEGIN} rule sets a private variable to the directory where +@command{pwcat} is stored. Because it is used to help out an @command{awk} library +routine, we have chosen to put it in @file{/usr/local/libexec/awk}; +however, you might want it to be in a different directory on your system. -The @code{BEGIN} rule first makes a copy of all the command line arguments, -into an array named @code{copy}. -@code{ARGV[0]} is not copied, since it is not needed. -@code{tee} cannot use @code{ARGV} directly, since @code{awk} will attempt to -process each file named in @code{ARGV} as input data. +The function @code{_pw_init} keeps three copies of the user information +in three associative arrays. The arrays are indexed by username +(@code{_pw_byname}), by user-id number (@code{_pw_byuid}), and by order of +occurrence (@code{_pw_bycount}). +The variable @code{_pw_inited} is used for efficiency; @code{_pw_init} +needs only to be called once. + +Because this function uses @code{getline} to read information from +@command{pwcat}, it first saves the values of @code{FS}, @code{RS}, and @code{$0}. +It notes in the variable @code{using_fw} whether field splitting +with @code{FIELDWIDTHS} is in effect or not. +Doing so is necessary, since these functions could be called +from anywhere within a user's program, and the user may have his +or her +own way of splitting records and fields. + +The @code{using_fw} variable checks @code{PROCINFO["FS"]}, which +is @code{"FIELDWIDTHS"} if field splitting is being done with +@code{FIELDWIDTHS}. This makes it possible to restore the correct +field-splitting mechanism later. The test can only be true for +@command{gawk}. It is false if using @code{FS} or on some other +@command{awk} implementation. -If the first argument is @samp{-a}, then the flag variable -@code{append} is set to true, and both @code{ARGV[1]} and -@code{copy[1]} are deleted. If @code{ARGC} is less than two, then no file -names were supplied, and @code{tee} prints a usage message and exits. -Finally, @code{awk} is forced to read the standard input by setting -@code{ARGV[1]} to @code{"-"}, and @code{ARGC} to two. +The main part of the function uses a loop to read database lines, split +the line into fields, and then store the line into each array as necessary. +When the loop is done, @code{@w{_pw_init}} cleans up by closing the pipeline, +setting @code{@w{_pw_inited}} to one, and restoring @code{FS} (and @code{FIELDWIDTHS} +if necessary), @code{RS}, and @code{$0}. +The use of @code{@w{_pw_count}} is explained shortly. -@c 2e: the `ARGC--' in the `if (ARGV[1] == "-a")' isn't needed. +@c NEXT ED: All of these functions don't need the ... in ... test. Just +@c return the array element, which will be "" if not already there. Duh. +The @code{getpwnam} function takes a username as a string argument. If that +user is in the database, it returns the appropriate line. Otherwise it +returns the null string: -@findex tee.awk +@cindex @code{getpwnam} user-defined function @example @group -@c file eg/prog/tee.awk -# tee.awk --- tee in awk -# Arnold Robbins, arnold@@gnu.org, Public Domain -# May 1993 -# Revised December 1995 -@end group - -@group -BEGIN \ +@c file eg/lib/passwdawk.in +function getpwnam(name) @{ - for (i = 1; i < ARGC; i++) - copy[i] = ARGV[i] -@end group - -@group - if (ARGV[1] == "-a") @{ - append = 1 - delete ARGV[1] - delete copy[1] - ARGC-- - @} -@end group -@group - if (ARGC < 2) @{ - print "usage: tee [-a] file ..." > "/dev/stderr" - exit 1 - @} -@end group -@group - ARGV[1] = "-" - ARGC = 2 + _pw_init() + if (name in _pw_byname) + return _pw_byname[name] + return "" @} @c endfile @end group @end example -The single rule does all the work. Since there is no pattern, it is -executed for each line of input. The body of the rule simply prints the -line into each file on the command line, and then to the standard output. +Similarly, +the @code{getpwuid} function takes a user-id number argument. If that +user number is in the database, it returns the appropriate line. Otherwise it +returns the null string: +@cindex @code{getpwuid} user-defined function @example -@group -@c file eg/prog/tee.awk +@c file eg/lib/passwdawk.in +function getpwuid(uid) @{ - # moving the if outside the loop makes it run faster - if (append) - for (i in copy) - print >> copy[i] - else - for (i in copy) - print > copy[i] - print + _pw_init() + if (uid in _pw_byuid) + return _pw_byuid[uid] + return "" @} @c endfile -@end group -@end example - -It would have been possible to code the loop this way: - -@example -for (i in copy) - if (append) - print >> copy[i] - else - print > copy[i] @end example -@noindent -This is more concise, but it is also less efficient. The @samp{if} is -tested for each record and for each output file. By duplicating the loop -body, the @samp{if} is only tested once for each input record. If there are -@var{N} input records and @var{M} input files, the first method only -executes @var{N} @samp{if} statements, while the second would execute -@var{N}@code{*}@var{M} @samp{if} statements. - -Finally, the @code{END} rule cleans up, by closing all the output files. +The @code{getpwent} function simply steps through the database, one entry at +a time. It uses @code{_pw_count} to track its current position in the +@code{_pw_bycount} array: +@cindex @code{getpwent} user-defined function @example -@c @group -@c file eg/prog/tee.awk -END \ +@c file eg/lib/passwdawk.in +function getpwent() @{ - for (i in copy) - close(copy[i]) + _pw_init() + if (_pw_count < _pw_total) + return _pw_bycount[++_pw_count] + return "" @} @c endfile -@c @end group @end example -@node Uniq Program, Wc Program, Tee Program, Clones -@subsection Printing Non-duplicated Lines of Text - -@cindex @code{uniq} utility -The @code{uniq} utility reads sorted lines of data on its standard input, -and (by default) removes duplicate lines. In other words, only unique lines -are printed, hence the name. @code{uniq} has a number of options. The usage is: +The @code{@w{endpwent}} function resets @code{@w{_pw_count}} to zero, so that +subsequent calls to @code{getpwent} start over again: +@cindex @code{endpwent} user-defined function @example -uniq @r{[}-udc @r{[}-@var{n}@r{]]} @r{[}+@var{n}@r{]} @r{[} @var{input file} @r{[} @var{output file} @r{]]} +@c file eg/lib/passwdawk.in +function endpwent() +@{ + _pw_count = 0 +@} +@c endfile @end example -The option meanings are: +A conscious design decision in this suite is that each subroutine calls +@code{@w{_pw_init}} to initialize the database arrays. The overhead of running +a separate process to generate the user database, and the I/O to scan it, +are only incurred if the user's main program actually calls one of these +functions. If this library file is loaded along with a user's program, but +none of the routines are ever called, then there is no extra runtime overhead. +(The alternative is move the body of @code{@w{_pw_init}} into a +@code{BEGIN} rule, which always runs @command{pwcat}. This simplifies the +code but runs an extra process that may never be needed.) -@table @code -@item -d -Only print repeated lines. +In turn, calling @code{_pw_init} is not too expensive, because the +@code{_pw_inited} variable keeps the program from reading the data more than +once. If you are worried about squeezing every last cycle out of your +@command{awk} program, the check of @code{_pw_inited} could be moved out of +@code{_pw_init} and duplicated in all the other functions. In practice, +this is not necessary, since most @command{awk} programs are I/O-bound, and it +clutters up the code. -@item -u -Only print non-repeated lines. +The @command{id} program in @ref{Id Program, ,Printing out User Information}, +uses these functions. -@item -c -Count lines. This option overrides @samp{-d} and @samp{-u}. Both repeated -and non-repeated lines are counted. +@node Group Functions, , Passwd Functions, Library Functions +@section Reading the Group Database -@item -@var{n} -Skip @var{n} fields before comparing lines. The definition of fields -is similar to @code{awk}'s default: non-whitespace characters separated -by runs of spaces and/or tabs. +@cindex @code{getgrent} C library function +@cindex group information +@cindex account information +@cindex group file +Much of the discussion presented in +@ref{Passwd Functions, ,Reading the User Database}, +applies to the group database as well. Although there has traditionally +been a well-known file (@file{/etc/group}) in a well-known format, the POSIX +standard only provides a set of C library routines +(@code{} and @code{getgrent}) +for accessing the information. +Even though this file may exist, it likely does not have +complete information. Therefore, as with the user database, it is necessary +to have a small C program that generates the group database as its output. -@item +@var{n} -Skip @var{n} characters before comparing lines. Any fields specified with -@samp{-@var{n}} are skipped first. +@cindex @command{grcat} program +@command{grcat}, a C program that ``cats'' the group database, +is as follows: -@item @var{input file} -Data is read from the input file named on the command line, instead of from -the standard input. +@example +@c file eg/lib/grcat.c +/* + * grcat.c + * + * Generate a printable version of the group database + */ +@c endfile +@ignore +@c file eg/lib/grcat.c +/* + * Arnold Robbins, arnold@@gnu.org, May 1993 + * Public Domain + */ -@item @var{output file} -The generated output is sent to the named output file, instead of to the -standard output. -@end table +@c endfile +@end ignore +@c file eg/lib/grcat.c +#include +#include -Normally @code{uniq} behaves as if both the @samp{-d} and @samp{-u} options -had been provided. +int +main(argc, argv) +int argc; +char **argv; +@{ + struct group *g; + int i; -Here is an @code{awk} implementation of @code{uniq}. It uses the -@code{getopt} library function -(@pxref{Getopt Function, ,Processing Command Line Options}), -and the @code{join} library function -(@pxref{Join Function, ,Merging an Array Into a String}). + while ((g = getgrent()) != NULL) @{ + printf("%s:%s:%d:", g->gr_name, g->gr_passwd, + g->gr_gid); + for (i = 0; g->gr_mem[i] != NULL; i++) @{ + printf("%s", g->gr_mem[i]); +@group + if (g->gr_mem[i+1] != NULL) + putchar(','); + @} +@end group + putchar('\n'); + @} + endgrent(); + exit(0); +@} +@c endfile +@end example -The program begins with a @code{usage} function and then a brief outline of -the options and their meanings in a comment. +Each line in the group database represents one group. The fields are +separated with colons and represent the following information: -The @code{BEGIN} rule deals with the command line arguments and options. It -uses a trick to get @code{getopt} to handle options of the form @samp{-25}, -treating such an option as the option letter @samp{2} with an argument of -@samp{5}. If indeed two or more digits were supplied (@code{Optarg} looks -like a number), @code{Optarg} is -concatenated with the option digit, and then result is added to zero to make -it into a number. If there is only one digit in the option, then -@code{Optarg} is not needed, and @code{Optind} must be decremented so that -@code{getopt} will process it next time. This code is admittedly a bit -tricky. +@ignore +@table @asis +@item Group Name +The name of the group. -If no options were supplied, then the default is taken, to print both -repeated and non-repeated lines. The output file, if provided, is assigned -to @code{outputfile}. Earlier, @code{outputfile} was initialized to the -standard output, @file{/dev/stdout}. +@item Group Password +The encrypted group password. In practice, this field is never used. It is +usually empty or set to @samp{*}. + +@item Group ID Number +The numeric group-id number. This number should be unique within the file. + +@item Group Member List +A comma-separated list of usernames. These users are members of the group. +Modern Unix systems allow users to be members of several groups +simultaneously. If your system does, then there are elements +@code{"group1"} through @code{"group@var{N}"} in @code{PROCINFO} +for those group-id numbers. +(Note that @code{PROCINFO} is a @command{gawk} extension; +@pxref{Built-in Variables}.) +@end table +@end ignore + +@multitable {Encrypted password} {1234567890123456789012345678901234567890123456} +@item Group name @tab The group's name. + +@item Group password @tab The group's encrypted password. In practice, this field is never used; +it is usually empty or set to @samp{*}. + +@item Group-ID @tab +The group's numeric group-id number; this number should be unique within the file. + +@item Group member list @tab +A comma-separated list of usernames. These users are members of the group. +Modern Unix systems allow users to be members of several groups +simultaneously. If your system does, then there are elements +@code{"group1"} through @code{"group@var{N}"} in @code{PROCINFO} +for those group-id numbers. +(Note that @code{PROCINFO} is a @command{gawk} extension; +@pxref{Built-in Variables}.) +@end multitable + +Here is what running @command{grcat} might produce: -@findex uniq.awk @example -@c file eg/prog/uniq.awk -# uniq.awk --- do uniq in awk +$ grcat +@print{} wheel:*:0:arnold +@print{} nogroup:*:65534: +@print{} daemon:*:1: +@print{} kmem:*:2: +@print{} staff:*:10:arnold,miriam,andy +@print{} other:*:20: +@dots{} +@end example + +Here are the functions for obtaining information from the group database. +There are several, modeled after the C library functions of the same names: + +@cindex @code{_gr_init} user-defined function +@example +@c file eg/lib/groupawk.in +# group.awk --- functions for dealing with the group file +@c endfile +@ignore +@c file eg/lib/groupawk.in +# # Arnold Robbins, arnold@@gnu.org, Public Domain # May 1993 +# Revised October 2000 -@group -function usage( e) +@c endfile +@end ignore +@c line break on _gr_init for smallbook +@c file eg/lib/groupawk.in +BEGIN \ @{ - e = "Usage: uniq [-udc [-n]] [+n] [ in [ out ]]" - print e > "/dev/stderr" - exit 1 + # Change to suit your system + _gr_awklib = "/usr/local/libexec/awk/" @} -@end group - -# -c count lines. overrides -d and -u -# -d only repeated lines -# -u only non-repeated lines -# -n skip n fields -# +n skip n characters, skip fields first -BEGIN \ +function _gr_init( oldfs, oldrs, olddol0, grcat, + using_fw, n, a, i) @{ - count = 1 - outputfile = "/dev/stdout" - opts = "udc0:1:2:3:4:5:6:7:8:9:" - while ((c = getopt(ARGC, ARGV, opts)) != -1) @{ - if (c == "u") - non_repeated_only++ - else if (c == "d") - repeated_only++ - else if (c == "c") - do_count++ - else if (index("0123456789", c) != 0) @{ - # getopt requires args to options - # this messes us up for things like -5 - if (Optarg ~ /^[0-9]+$/) - fcount = (c Optarg) + 0 -@group - else @{ - fcount = c + 0 - Optind-- - @} -@end group - @} else - usage() - @} + if (_gr_inited) + return - if (ARGV[Optind] ~ /^\+[0-9]+$/) @{ - charcount = substr(ARGV[Optind], 2) + 0 - Optind++ - @} + oldfs = FS + oldrs = RS + olddol0 = $0 + using_fw = (PROCINFO["FS"] == "FIELDWIDTHS") + FS = ":" + RS = "\n" - for (i = 1; i < Optind; i++) - ARGV[i] = "" + grcat = _gr_awklib "grcat" + while ((grcat | getline) > 0) @{ + if ($1 in _gr_byname) + _gr_byname[$1] = _gr_byname[$1] "," $4 + else + _gr_byname[$1] = $0 + if ($3 in _gr_bygid) + _gr_bygid[$3] = _gr_bygid[$3] "," $4 + else + _gr_bygid[$3] = $0 - if (repeated_only == 0 && non_repeated_only == 0) - repeated_only = non_repeated_only = 1 + n = split($4, a, "[ \t]*,[ \t]*") + for (i = 1; i <= n; i++) + if (a[i] in _gr_groupsbyuser) + _gr_groupsbyuser[a[i]] = \ + _gr_groupsbyuser[a[i]] " " $1 + else + _gr_groupsbyuser[a[i]] = $1 - if (ARGC - Optind == 2) @{ - outputfile = ARGV[ARGC - 1] - ARGV[ARGC - 1] = "" + _gr_bycount[++_gr_count] = $0 @} + close(grcat) + _gr_count = 0 + _gr_inited++ + FS = oldfs + if (using_fw) + FIELDWIDTHS = FIELDWIDTHS + RS = oldrs + $0 = olddol0 @} @c endfile @end example -The following function, @code{are_equal}, compares the current line, -@code{$0}, to the -previous line, @code{last}. It handles skipping fields and characters. +The @code{BEGIN} rule sets a private variable to the directory where +@command{grcat} is stored. Because it is used to help out an @command{awk} library +routine, we have chosen to put it in @file{/usr/local/libexec/awk}. You might +want it to be in a different directory on your system. -If no field count and no character count were specified, @code{are_equal} -simply returns one or zero depending upon the result of a simple string -comparison of @code{last} and @code{$0}. Otherwise, things get more -complicated. +These routines follow the same general outline as the user database routines +(@pxref{Passwd Functions, ,Reading the User Database}). +The @code{@w{_gr_inited}} variable is used to +ensure that the database is scanned no more than once. +The @code{@w{_gr_init}} function first saves @code{FS}, @code{FIELDWIDTHS}, @code{RS}, and +@code{$0}, and then sets @code{FS} and @code{RS} to the correct values for +scanning the group information. -If fields have to be skipped, each line is broken into an array using -@code{split} -(@pxref{String Functions, ,Built-in Functions for String Manipulation}), -and then the desired fields are joined back into a line using @code{join}. -The joined lines are stored in @code{clast} and @code{cline}. -If no fields are skipped, @code{clast} and @code{cline} are set to -@code{last} and @code{$0} respectively. +The group information is stored is several associative arrays. +The arrays are indexed by group name (@code{@w{_gr_byname}}), by group-id number +(@code{@w{_gr_bygid}}), and by position in the database (@code{@w{_gr_bycount}}). +There is an additional array indexed by username (@code{@w{_gr_groupsbyuser}}), +which is a space-separated list of groups that each user belongs to. -Finally, if characters are skipped, @code{substr} is used to strip off the -leading @code{charcount} characters in @code{clast} and @code{cline}. The -two strings are then compared, and @code{are_equal} returns the result. +Unlike the user database, it is possible to have multiple records in the +database for the same group. This is common when a group has a large number +of members. A pair of such entries might look like the following: @example -@c @group -@c file eg/prog/uniq.awk -function are_equal( n, m, clast, cline, alast, aline) -@{ - if (fcount == 0 && charcount == 0) - return (last == $0) +tvpeople:*:101:johnny,jay,arsenio +tvpeople:*:101:david,conan,tom,joan +@end example - if (fcount > 0) @{ - n = split(last, alast) - m = split($0, aline) - clast = join(alast, fcount+1, n) - cline = join(aline, fcount+1, m) - @} else @{ - clast = last - cline = $0 - @} - if (charcount) @{ - clast = substr(clast, charcount + 1) - cline = substr(cline, charcount + 1) - @} +For this reason, @code{_gr_init} looks to see if a group name or +group-id number is already seen. If it is, then the usernames are +simply concatenated onto the previous list of users. (There is actually a +subtle problem with the code just presented. Suppose that +the first time there were no names. This code adds the names with +a leading comma. It also doesn't check that there is a @code{$4}.) - return (clast == cline) +Finally, @code{_gr_init} closes the pipeline to @command{grcat}, restores +@code{FS} (and @code{FIELDWIDTHS} if necessary), @code{RS}, and @code{$0}, +initializes @code{_gr_count} to zero +(it is used later), and makes @code{_gr_inited} nonzero. + +The @code{getgrnam} function takes a group name as its argument, and if that +group exists, it is returned. Otherwise, @code{getgrnam} returns the null +string: + +@cindex @code{getgrnam} user-defined function +@example +@c file eg/lib/groupawk.in +function getgrnam(group) +@{ + _gr_init() + if (group in _gr_byname) + return _gr_byname[group] + return "" @} @c endfile -@c @end group @end example -The following two rules are the body of the program. The first one is -executed only for the very first line of data. It sets @code{last} equal to -@code{$0}, so that subsequent lines of text have something to be compared to. - -The second rule does the work. The variable @code{equal} will be one or zero -depending upon the results of @code{are_equal}'s comparison. If @code{uniq} -is counting repeated lines, then the @code{count} variable is incremented if -the lines are equal. Otherwise the line is printed and @code{count} is -reset, since the two lines are not equal. +The @code{getgrgid} function is similar, it takes a numeric group-id and +looks up the information associated with that group-id: -If @code{uniq} is not counting, @code{count} is incremented if the lines are -equal. Otherwise, if @code{uniq} is counting repeated lines, and more than -one line has been seen, or if @code{uniq} is counting non-repeated lines, -and only one line has been seen, then the line is printed, and @code{count} -is reset. +@cindex @code{getgrgid} user-defined function +@example +@c file eg/lib/groupawk.in +function getgrgid(gid) +@{ + _gr_init() + if (gid in _gr_bygid) + return _gr_bygid[gid] + return "" +@} +@c endfile +@end example -Finally, similar logic is used in the @code{END} rule to print the final -line of input data. +The @code{getgruser} function does not have a C counterpart. It takes a +username and returns the list of groups that have the user as a member: +@cindex @code{getgruser} user-defined function @example -@c @group -@c file eg/prog/uniq.awk -@group -NR == 1 @{ - last = $0 - next -@} -@end group - +@c file eg/lib/groupawk.in +function getgruser(user) @{ - equal = are_equal() + _gr_init() + if (user in _gr_groupsbyuser) + return _gr_groupsbyuser[user] + return "" +@} +@c endfile +@end example - if (do_count) @{ # overrides -d and -u - if (equal) - count++ - else @{ - printf("%4d %s\n", count, last) > outputfile - last = $0 - count = 1 # reset - @} - next - @} - - if (equal) - count++ - else @{ - if ((repeated_only && count > 1) || - (non_repeated_only && count == 1)) - print last > outputfile - last = $0 - count = 1 - @} -@} +The @code{getgrent} function steps through the database one entry at a time. +It uses @code{_gr_count} to track its position in the list: -@group -END @{ - if (do_count) - printf("%4d %s\n", count, last) > outputfile - else if ((repeated_only && count > 1) || - (non_repeated_only && count == 1)) - print last > outputfile +@cindex @code{getgrent} user-defined function +@example +@c file eg/lib/groupawk.in +function getgrent() +@{ + _gr_init() + if (++_gr_count in _gr_bycount) + return _gr_bycount[_gr_count] + return "" @} -@end group @c endfile -@c @end group @end example -@node Wc Program, , Uniq Program, Clones -@subsection Counting Things - -@cindex @code{wc} utility -The @code{wc} (word count) utility counts lines, words, and characters in -one or more input files. Its usage is: +The @code{endgrent} function resets @code{_gr_count} to zero so that @code{getgrent} can +start over again: +@cindex @code{endgrent} user-defined function @example -wc @r{[}-lwc@r{]} @r{[} @var{files} @dots{} @r{]} +@c file eg/lib/groupawk.in +function endgrent() +@{ + _gr_count = 0 +@} +@c endfile @end example -If no files are specified on the command line, @code{wc} reads its standard -input. If there are multiple files, it will also print total counts for all -the files. The options and their meanings are: +As with the user database routines, each function calls @code{_gr_init} to +initialize the arrays. Doing so only incurs the extra overhead of running +@command{grcat} if these functions are used (as opposed to moving the body of +@code{_gr_init} into a @code{BEGIN} rule). -@table @code -@item -l -Only count lines. +Most of the work is in scanning the database and building the various +associative arrays. The functions that the user calls are themselves very +simple, relying on @command{awk}'s associative arrays to do work. -@item -w -Only count words. -A ``word'' is a contiguous sequence of non-whitespace characters, separated -by spaces and/or tabs. Happily, this is the normal way @code{awk} separates -fields in its input data. +The @command{id} program in @ref{Id Program, ,Printing out User Information}, +uses these functions. -@item -c -Only count characters. -@end table +@node Sample Programs, Language History, Library Functions, Top +@chapter Practical @command{awk} Programs -Implementing @code{wc} in @code{awk} is particularly elegant, since -@code{awk} does a lot of the work for us; it splits lines into words (i.e.@: -fields) and counts them, it counts lines (i.e.@: records) for us, and it can -easily tell us how long a line is. +@ref{Library Functions, ,A Library of @command{awk} Functions}, +presents the idea that reading programs in a language contributes to +learning that language. This @value{CHAPTER} continues that theme, +presenting a potpourri of @command{awk} programs for your reading +enjoyment. +@ifnotinfo +There are three sections. +The first describes how to run the programs presented +in this @value{CHAPTER}. -This version uses the @code{getopt} library function -(@pxref{Getopt Function, ,Processing Command Line Options}), -and the file transition functions -(@pxref{Filetrans Function, ,Noting Data File Boundaries}). +The second presents @command{awk} +versions of several common POSIX utilities. +These are programs that you are hopefully already familiar with, +and therefore, whose problems are understood. +By reimplementing these programs in @command{awk}, +you can focus on the @command{awk}-related aspects of solving +the programming problem. + +The third is a grab bag of interesting programs. +These solve a number of different data-manipulation and management +problems. Many of the programs are short, which emphasizes @command{awk}'s +ability to do a lot in just a few lines of code. +@end ifnotinfo + +Many of these programs use the library functions presented in +@ref{Library Functions, ,A Library of @command{awk} Functions}. + +@menu +* Running Examples:: How to run these examples. +* Clones:: Clones of common utilities. +* Miscellaneous Programs:: Some interesting @command{awk} programs. +@end menu -This version has one major difference from traditional versions of @code{wc}. -Our version always prints the counts in the order lines, words, -and characters. Traditional versions note the order of the @samp{-l}, -@samp{-w}, and @samp{-c} options on the command line, and print the counts -in that order. +@node Running Examples, Clones, Sample Programs, Sample Programs +@section Running the Example Programs -The @code{BEGIN} rule does the argument processing. -The variable @code{print_total} will -be true if more than one file was named on the command line. +To run a given program, you would typically do something like this: -@findex wc.awk @example -@c @group -@c file eg/prog/wc.awk -# wc.awk --- count lines, words, characters -# Arnold Robbins, arnold@@gnu.org, Public Domain -# May 1993 +awk -f @var{program} -- @var{options} @var{files} +@end example -# Options: -# -l only count lines -# -w only count words -# -c only count characters -# -# Default is to count lines, words, characters +@noindent +Here, @var{program} is the name of the @command{awk} program (such as +@file{cut.awk}), @var{options} are any command-line options for the +program that start with a @samp{-}, and @var{files} are the actual @value{DF}s. -BEGIN @{ - # let getopt print a message about - # invalid options. we ignore them - while ((c = getopt(ARGC, ARGV, "lwc")) != -1) @{ - if (c == "l") - do_lines = 1 - else if (c == "w") - do_words = 1 - else if (c == "c") - do_chars = 1 - @} - for (i = 1; i < Optind; i++) - ARGV[i] = "" +If your system supports the @samp{#!} executable interpreter mechanism +(@pxref{Executable Scripts, , Executable @command{awk} Programs}), +you can instead run your program directly: - # if no options, do all - if (! do_lines && ! do_words && ! do_chars) - do_lines = do_words = do_chars = 1 +@example +cut.awk -c1-8 myfiles > results +@end example - print_total = (ARGC - i > 2) -@} -@c endfile -@c @end group +If your @command{awk} is not @command{gawk}, you may instead need to use this: + +@example +cut.awk -- -c1-8 myfiles > results @end example -The @code{beginfile} function is simple; it just resets the counts of lines, -words, and characters to zero, and saves the current file name in -@code{fname}. +@node Clones, Miscellaneous Programs, Running Examples, Sample Programs +@section Reinventing Wheels for Fun and Profit -The @code{endfile} function adds the current file's numbers to the running -totals of lines, words, and characters. It then prints out those numbers -for the file that was just read. It relies on @code{beginfile} to reset the -numbers for the following data file. +This @value{SECTION} presents a number of POSIX utilities that are implemented in +@command{awk}. Reinventing these programs in @command{awk} is often enjoyable, +because the algorithms can be very clearly expressed, and the code is usually +very concise and simple. This is true because @command{awk} does so much for you. -@example -@c left brace on line with `function' because of page breaking -@c file eg/prog/wc.awk -@group -function beginfile(file) @{ - chars = lines = words = 0 - fname = FILENAME -@} -@end group +It should be noted that these programs are not necessarily intended to +replace the installed versions on your system. Instead, their +purpose is to illustrate @command{awk} language programming for ``real world'' +tasks. -function endfile(file) -@{ - tchars += chars - tlines += lines - twords += words - if (do_lines) - printf "\t%d", lines - if (do_words) - printf "\t%d", words - if (do_chars) - printf "\t%d", chars - printf "\t%s\n", fname -@} -@c endfile -@end example +The programs are presented in alphabetical order. -There is one rule that is executed for each line. It adds the length of the -record to @code{chars}. It has to add one, since the newline character -separating records (the value of @code{RS}) is not part of the record -itself. @code{lines} is incremented for each line read, and @code{words} is -incremented by the value of @code{NF}, the number of ``words'' on this -line.@footnote{Examine the code in -@ref{Filetrans Function, ,Noting Data File Boundaries}. -Why must @code{wc} use a separate @code{lines} variable, instead of using -the value of @code{FNR} in @code{endfile}?} +@menu +* Cut Program:: The @command{cut} utility. +* Egrep Program:: The @command{egrep} utility. +* Id Program:: The @command{id} utility. +* Split Program:: The @command{split} utility. +* Tee Program:: The @command{tee} utility. +* Uniq Program:: The @command{uniq} utility. +* Wc Program:: The @command{wc} utility. +@end menu -Finally, the @code{END} rule simply prints the totals for all the files. +@node Cut Program, Egrep Program, Clones, Clones +@subsection Cutting out Fields and Columns -@example -@c @group -@c file eg/prog/wc.awk -# do per line -@{ - chars += length($0) + 1 # get newline - lines++ - words += NF -@} +@cindex @command{cut} utility +The @command{cut} utility selects, or ``cuts,'' characters or fields +from its standard input and sends them to its standard output. +Fields are separated by tabs by default, +but you may supply a command-line option to change the field +@dfn{delimiter} (i.e., the field separator character). @command{cut}'s +definition of fields is less general than @command{awk}'s. -END @{ - if (print_total) @{ - if (do_lines) - printf "\t%d", tlines - if (do_words) - printf "\t%d", twords - if (do_chars) - printf "\t%d", tchars - print "\ttotal" - @} -@} -@c endfile -@c @end group +A common use of @command{cut} might be to pull out just the login name of +logged-on users from the output of @command{who}. For example, the following +pipeline generates a sorted, unique list of the logged-on users: + +@example +who | cut -c1-8 | sort | uniq @end example -@node Miscellaneous Programs, , Clones, Sample Programs -@section A Grab Bag of @code{awk} Programs +The options for @command{cut} are: -This section is a large ``grab bag'' of miscellaneous programs. -We hope you find them both interesting and enjoyable. +@table @code +@item -c @var{list} +Use @var{list} as the list of characters to cut out. Items within the list +may be separated by commas, and ranges of characters can be separated with +dashes. The list @samp{1-8,15,22-35} specifies characters 1 through +8, 15, and 22 through 35. -@menu -* Dupword Program:: Finding duplicated words in a document. -* Alarm Program:: An alarm clock. -* Translate Program:: A program similar to the @code{tr} utility. -* Labels Program:: Printing mailing labels. -* Word Sorting:: A program to produce a word usage count. -* History Sorting:: Eliminating duplicate entries from a history - file. -* Extract Program:: Pulling out programs from Texinfo source - files. -* Simple Sed:: A Simple Stream Editor. -* Igawk Program:: A wrapper for @code{awk} that includes files. -@end menu +@item -f @var{list} +Use @var{list} as the list of fields to cut out. -@node Dupword Program, Alarm Program, Miscellaneous Programs, Miscellaneous Programs -@subsection Finding Duplicated Words in a Document +@item -d @var{delim} +Use @var{delim} as the field separator character instead of the tab +character. -A common error when writing large amounts of prose is to accidentally -duplicate words. Often you will see this in text as something like ``the -the program does the following @dots{}.'' When the text is on-line, often -the duplicated words occur at the end of one line and the beginning of -another, making them very difficult to spot. -@c as here! +@item -s +Suppress printing of lines that do not contain the field delimiter. +@end table -This program, @file{dupword.awk}, scans through a file one line at a time, -and looks for adjacent occurrences of the same word. It also saves the last -word on a line (in the variable @code{prev}) for comparison with the first -word on the next line. +The @command{awk} implementation of @command{cut} uses the @code{getopt} library +function (@pxref{Getopt Function, ,Processing Command-Line Options}) +and the @code{join} library function +(@pxref{Join Function, ,Merging an Array into a String}). -The first two statements make sure that the line is all lower-case, so that, -for example, -``The'' and ``the'' compare equal to each other. The second statement -removes all non-alphanumeric and non-whitespace characters from the line, so -that punctuation does not affect the comparison either. This sometimes -leads to reports of duplicated words that really are different, but this is -unusual. +The program begins with a comment describing the options, the library +functions needed, and a @code{usage} function that prints out a usage +message and exits. @code{usage} is called if invalid arguments are +supplied: -@c FIXME: add check for $i != "" -@findex dupword.awk +@cindex @code{cut.awk} program @example -@group -@c file eg/prog/dupword.awk -# dupword --- find duplicate words in text +@c file eg/prog/cut.awk +# cut.awk --- implement cut in awk +@c endfile +@ignore +@c file eg/prog/cut.awk +# # Arnold Robbins, arnold@@gnu.org, Public Domain -# December 1991 +# May 1993 + +@c endfile +@end ignore +@c file eg/prog/cut.awk +# Options: +# -f list Cut fields +# -d c Field delimiter character +# -c list Cut characters +# +# -s Suppress lines without the delimiter +# +# Requires getopt and join library functions +@group +function usage( e1, e2) @{ - $0 = tolower($0) - gsub(/[^A-Za-z0-9 \t]/, ""); - if ($1 == prev) - printf("%s:%d: duplicate %s\n", - FILENAME, FNR, $1) - for (i = 2; i <= NF; i++) - if ($i == $(i-1)) - printf("%s:%d: duplicate %s\n", - FILENAME, FNR, $i) - prev = $NF + e1 = "usage: cut [-f list] [-d c] [-s] [files...]" + e2 = "usage: cut [-c list] [files...]" + print e1 > "/dev/stderr" + print e2 > "/dev/stderr" + exit 1 @} -@c endfile @end group +@c endfile @end example -@node Alarm Program, Translate Program, Dupword Program, Miscellaneous Programs -@subsection An Alarm Clock Program - -The following program is a simple ``alarm clock'' program. -You give it a time of day, and an optional message. At the given time, -it prints the message on the standard output. In addition, you can give it -the number of times to repeat the message, and also a delay between -repetitions. - -This program uses the @code{gettimeofday} function from -@ref{Gettimeofday Function, ,Managing the Time of Day}. +@noindent +The variables @code{e1} and @code{e2} are used so that the function +fits nicely on the +@ifnotinfo +page. +@end ifnotinfo +@ifnottex +screen. +@end ifnottex -All the work is done in the @code{BEGIN} rule. The first part is argument -checking and setting of defaults; the delay, the count, and the message to -print. If the user supplied a message, but it does not contain the ASCII BEL -character (known as the ``alert'' character, @samp{\a}), then it is added to -the message. (On many systems, printing the ASCII BEL generates some sort -of audible alert. Thus, when the alarm goes off, the system calls attention -to itself, in case the user is not looking at their computer or terminal.) +Next comes a @code{BEGIN} rule that parses the command-line options. +It sets @code{FS} to a single tab character, because that is @command{cut}'s +default field separator. The output field separator is also set to be the +same as the input field separator. Then @code{getopt} is used to step +through the command-line options. One or the other of the variables +@code{by_fields} or @code{by_chars} is set to true, to indicate that +processing should be done by fields or by characters, respectively. +When cutting by characters, the output field separator is set to the null +string. -@findex alarm.awk @example -@c @group -@c file eg/prog/alarm.awk -# alarm --- set an alarm -# Arnold Robbins, arnold@@gnu.org, Public Domain -# May 1993 - -# usage: alarm time [ "message" [ count [ delay ] ] ] - +@c file eg/prog/cut.awk BEGIN \ @{ - # Initial argument sanity checking - usage1 = "usage: alarm time ['message' [count [delay]]]" - usage2 = sprintf("\t(%s) time ::= hh:mm", ARGV[1]) - - if (ARGC < 2) @{ - print usage > "/dev/stderr" - exit 1 - @} else if (ARGC == 5) @{ - delay = ARGV[4] + 0 - count = ARGV[3] + 0 - message = ARGV[2] - @} else if (ARGC == 4) @{ - count = ARGV[3] + 0 - message = ARGV[2] - @} else if (ARGC == 3) @{ - message = ARGV[2] - @} else if (ARGV[1] !~ /[0-9]?[0-9]:[0-9][0-9]/) @{ - print usage1 > "/dev/stderr" - print usage2 > "/dev/stderr" - exit 1 + FS = "\t" # default + OFS = FS + while ((c = getopt(ARGC, ARGV, "sf:c:d:")) != -1) @{ + if (c == "f") @{ + by_fields = 1 + fieldlist = Optarg + @} else if (c == "c") @{ + by_chars = 1 + fieldlist = Optarg + OFS = "" + @} else if (c == "d") @{ + if (length(Optarg) > 1) @{ + printf("Using first character of %s" \ + " for delimiter\n", Optarg) > "/dev/stderr" + Optarg = substr(Optarg, 1, 1) + @} + FS = Optarg + OFS = FS + if (FS == " ") # defeat awk semantics + FS = "[ ]" + @} else if (c == "s") + suppress++ + else + usage() @} - # set defaults for once we reach the desired time - if (delay == 0) - delay = 180 # 3 minutes - if (count == 0) - count = 5 -@group - if (message == "") - message = sprintf("\aIt is now %s!\a", ARGV[1]) - else if (index(message, "\a") == 0) - message = "\a" message "\a" -@end group + for (i = 1; i < Optind; i++) + ARGV[i] = "" @c endfile @end example -The next section of code turns the alarm time into hours and minutes, -and converts it if necessary to a 24-hour clock. Then it turns that -time into a count of the seconds since midnight. Next it turns the current -time into a count of seconds since midnight. The difference between the two -is how long to wait before setting off the alarm. +Special care is taken when the field delimiter is a space. Using +a single space (@code{@w{" "}}) for the value of @code{FS} is +incorrect---@command{awk} would separate fields with runs of spaces, +tabs, and/or newlines, and we want them to be separated with individual +spaces. Also, note that after @code{getopt} is through, we have to +clear out all the elements of @code{ARGV} from 1 to @code{Optind}, +so that @command{awk} does not try to process the command-line options +as @value{FN}s. + +After dealing with the command-line options, the program verifies that the +options make sense. Only one or the other of @option{-c} and @option{-f} +should be used, and both require a field list. Then the program calls +either @code{set_fieldlist} or @code{set_charlist} to pull apart the +list of fields or characters: @example -@c @group -@c file eg/prog/alarm.awk - # split up dest time - split(ARGV[1], atime, ":") - hour = atime[1] + 0 # force numeric - minute = atime[2] + 0 # force numeric +@c file eg/prog/cut.awk + if (by_fields && by_chars) + usage() - # get current broken down time - gettimeofday(now) + if (by_fields == 0 && by_chars == 0) + by_fields = 1 # default - # if time given is 12-hour hours and it's after that - # hour, e.g., `alarm 5:30' at 9 a.m. means 5:30 p.m., - # then add 12 to real hour - if (hour < 12 && now["hour"] > hour) - hour += 12 + if (fieldlist == "") @{ + print "cut: needs list for -c or -f" > "/dev/stderr" + exit 1 + @} - # set target time in seconds since midnight - target = (hour * 60 * 60) + (minute * 60) + if (by_fields) + set_fieldlist() + else + set_charlist() +@} +@c endfile +@end example - # get current time in seconds since midnight - current = (now["hour"] * 60 * 60) + \ - (now["minute"] * 60) + now["second"] +@code{set_fieldlist} is used to split the field list apart at the commas, +and into an array. Then, for each element of the array, it looks to +see if it is actually a range, and if so, splits it apart. The range +is verified to make sure the first number is smaller than the second. +Each number in the list is added to the @code{flist} array, which +simply lists the fields that will be printed. Normal field splitting +is used. The program lets @command{awk} handle the job of doing the +field splitting: - # how long to sleep for - naptime = target - current - if (naptime <= 0) @{ - print "time is in the past!" > "/dev/stderr" - exit 1 +@example +@c file eg/prog/cut.awk +function set_fieldlist( n, m, i, j, k, f, g) +@{ + n = split(fieldlist, f, ",") + j = 1 # index in flist + for (i = 1; i <= n; i++) @{ + if (index(f[i], "-") != 0) @{ # a range + m = split(f[i], g, "-") +@group + if (m != 2 || g[1] >= g[2]) @{ + printf("bad field list: %s\n", + f[i]) > "/dev/stderr" + exit 1 + @} +@end group + for (k = g[1]; k <= g[2]; k++) + flist[j++] = k + @} else + flist[j++] = f[i] @} + nfields = j - 1 +@} @c endfile -@c @end group @end example -Finally, the program uses the @code{system} function -(@pxref{I/O Functions, ,Built-in Functions for Input/Output}) -to call the @code{sleep} utility. The @code{sleep} utility simply pauses -for the given number of seconds. If the exit status is not zero, -the program assumes that @code{sleep} was interrupted, and exits. If -@code{sleep} exited with an OK status (zero), then the program prints the -message in a loop, again using @code{sleep} to delay for however many -seconds are necessary. +The @code{set_charlist} function is more complicated than @code{set_fieldlist}. +The idea here is to use @command{gawk}'s @code{FIELDWIDTHS} variable +(@pxref{Constant Size, ,Reading Fixed-Width Data}), +which describes constant width input. When using a character list, that is +exactly what we have. + +Setting up @code{FIELDWIDTHS} is more complicated than simply listing the +fields that need to be printed. We have to keep track of the fields to +print and also the intervening characters that have to be skipped. +For example, suppose you wanted characters 1 through 8, 15, and +22 through 35. You would use @samp{-c 1-8,15,22-35}. The necessary value +for @code{FIELDWIDTHS} is @code{@w{"8 6 1 6 14"}}. This yields five +fields, and the fields to print +are @code{$1}, @code{$3}, and @code{$5}. +The intermediate fields are @dfn{filler}, +which is stuff in between the desired data. +@code{flist} lists the fields to print, and @code{t} tracks the +complete field list, including filler fields: @example -@c file eg/prog/alarm.awk +@c file eg/prog/cut.awk +function set_charlist( field, i, j, f, g, t, + filler, last, len) +@{ + field = 1 # count total fields + n = split(fieldlist, f, ",") + j = 1 # index in flist + for (i = 1; i <= n; i++) @{ + if (index(f[i], "-") != 0) @{ # range + m = split(f[i], g, "-") + if (m != 2 || g[1] >= g[2]) @{ + printf("bad character list: %s\n", + f[i]) > "/dev/stderr" + exit 1 + @} + len = g[2] - g[1] + 1 + if (g[1] > 1) # compute length of filler + filler = g[1] - last - 1 + else + filler = 0 @group - # zzzzzz..... go away if interrupted - if (system(sprintf("sleep %d", naptime)) != 0) - exit 1 + if (filler) + t[field++] = filler @end group - - # time to notify! - command = sprintf("sleep %d", delay) - for (i = 1; i <= count; i++) @{ - print message - # if sleep command interrupted, go away - if (system(command) != 0) - break + t[field++] = len # length of field + last = g[2] + flist[j++] = field - 1 + @} else @{ + if (f[i] > 1) + filler = f[i] - last - 1 + else + filler = 0 + if (filler) + t[field++] = filler + t[field++] = 1 + last = f[i] + flist[j++] = field - 1 + @} @} - - exit 0 + FIELDWIDTHS = join(t, 1, field - 1) + nfields = j - 1 @} @c endfile @end example -@node Translate Program, Labels Program, Alarm Program, Miscellaneous Programs -@subsection Transliterating Characters +Next is the rule that actually processes the data. If the @option{-s} option +is given, then @code{suppress} is true. The first @code{if} statement +makes sure that the input record does have the field separator. If +@command{cut} is processing fields, @code{suppress} is true, and the field +separator character is not in the record, then the record is skipped. -The system @code{tr} utility transliterates characters. For example, it is -often used to map upper-case letters into lower-case, for further -processing. +If the record is valid, then @command{gawk} has split the data +into fields, either using the character in @code{FS} or using fixed-length +fields and @code{FIELDWIDTHS}. The loop goes through the list of fields +that should be printed. The corresponding field is printed if it contains data. +If the next field also has data, then the separator character is +written out between the fields: @example -@var{generate data} | tr '[A-Z]' '[a-z]' | @var{process data} @dots{} +@c file eg/prog/cut.awk +@{ + if (by_fields && suppress && index($0, FS) != 0) + next + + for (i = 1; i <= nfields; i++) @{ + if ($flist[i] != "") @{ + printf "%s", $flist[i] + if (i < nfields && $flist[i+1] != "") + printf "%s", OFS + @} + @} + print "" +@} +@c endfile @end example -You give @code{tr} two lists of characters enclosed in square brackets. -Usually, the lists are quoted to keep the shell from attempting to do a -filename expansion.@footnote{On older, non-POSIX systems, @code{tr} often -does not require that the lists be enclosed in square brackets and quoted. -This is a feature.} When processing the input, the -first character in the first list is replaced with the first character in the -second list, the second character in the first list is replaced with the -second character in the second list, and so on. -If there are more characters in the ``from'' list than in the ``to'' list, -the last character of the ``to'' list is used for the remaining characters -in the ``from'' list. +This version of @command{cut} relies on @command{gawk}'s @code{FIELDWIDTHS} +variable to do the character-based cutting. While it is possible in +other @command{awk} implementations to use @code{substr} +(@pxref{String Functions, ,String Manipulation Functions}), +it is also extremely painful. +The @code{FIELDWIDTHS} variable supplies an elegant solution to the problem +of picking the input line apart by characters. + +@c Exercise: Rewrite using split with "". -Some time ago, -@c early or mid-1989! -a user proposed to us that we add a transliteration function to @code{gawk}. -Being opposed to ``creeping featurism,'' I wrote the following program to -prove that character transliteration could be done with a user-level -function. This program is not as complete as the system @code{tr} utility, -but it will do most of the job. +@node Egrep Program, Id Program, Cut Program, Clones +@subsection Searching for Regular Expressions in Files -The @code{translate} program demonstrates one of the few weaknesses of -standard -@code{awk}: dealing with individual characters is very painful, requiring -repeated use of the @code{substr}, @code{index}, and @code{gsub} built-in -functions -(@pxref{String Functions, ,Built-in Functions for String Manipulation}).@footnote{This -program was written before @code{gawk} acquired the ability to -split each character in a string into separate array elements. -How might you use this new feature to simplify the program?} +@cindex @command{egrep} utility +The @command{egrep} utility searches files for patterns. It uses regular +expressions that are almost identical to those available in @command{awk} +(@pxref{Regexp, ,Regular Expressions}). +It is used in the following manner: -There are two functions. The first, @code{stranslate}, takes three -arguments. +@example +egrep @r{[} @var{options} @r{]} '@var{pattern}' @var{files} @dots{} +@end example + +The @var{pattern} is a regular expression. In typical usage, the regular +expression is quoted to prevent the shell from expanding any of the +special characters as @value{FN} wildcards. Normally, @command{egrep} +prints the lines that matched. If multiple @value{FN}s are provided on +the command line, each output line is preceded by the name of the file +and a colon. + +The options to @command{egrep} are as follows: @table @code -@item from -A list of characters to translate from. +@item -c +Print out a count of the lines that matched the pattern, instead of the +lines themselves. -@item to -A list of characters to translate to. +@item -s +Be silent. No output is produced and the exit value indicates whether +the pattern was matched. -@item target -The string to do the translation on. -@end table +@item -v +Invert the sense of the test. @command{egrep} prints the lines that do +@emph{not} match the pattern and exits successfully if the pattern is not +matched. -Associative arrays make the translation part fairly easy. @code{t_ar} holds -the ``to'' characters, indexed by the ``from'' characters. Then a simple -loop goes through @code{from}, one character at a time. For each character -in @code{from}, if the character appears in @code{target}, @code{gsub} -is used to change it to the corresponding @code{to} character. +@item -i +Ignore case distinctions in both the pattern and the input data. -The @code{translate} function simply calls @code{stranslate} using @code{$0} -as the target. The main program sets two global variables, @code{FROM} and -@code{TO}, from the command line, and then changes @code{ARGV} so that -@code{awk} will read from the standard input. +@item -l +Only print (list) the names of the files that matched, not the lines that matched. + +@item -e @var{pattern} +Use @var{pattern} as the regexp to match. The purpose of the @option{-e} +option is to allow patterns that start with a @samp{-}. +@end table + +This version uses the @code{getopt} library function +(@pxref{Getopt Function, ,Processing Command-Line Options}) +and the file transition library program +(@pxref{Filetrans Function, ,Noting @value{DDF} Boundaries}). -Finally, the processing rule simply calls @code{translate} for each record. +The program begins with a descriptive comment and then a @code{BEGIN} rule +that processes the command-line arguments with @code{getopt}. The @option{-i} +(ignore case) option is particularly easy with @command{gawk}; we just use the +@code{IGNORECASE} built-in variable +(@pxref{Built-in Variables}): -@findex translate.awk +@cindex @code{egrep.awk} program @example -@c @group -@c file eg/prog/translate.awk -# translate --- do tr like stuff +@c file eg/prog/egrep.awk +# egrep.awk --- simulate egrep in awk +@c endfile +@ignore +@c file eg/prog/egrep.awk +# # Arnold Robbins, arnold@@gnu.org, Public Domain -# August 1989 - -# bugs: does not handle things like: tr A-Z a-z, it has -# to be spelled out. However, if `to' is shorter than `from', -# the last character in `to' is used for the rest of `from'. +# May 1993 -function stranslate(from, to, target, lf, lt, t_ar, i, c) -@{ - lf = length(from) - lt = length(to) - for (i = 1; i <= lt; i++) - t_ar[substr(from, i, 1)] = substr(to, i, 1) - if (lt < lf) - for (; i <= lf; i++) - t_ar[substr(from, i, 1)] = substr(to, lt, 1) - for (i = 1; i <= lf; i++) @{ - c = substr(from, i, 1) - if (index(target, c) > 0) - gsub(c, t_ar[c], target) - @} - return target -@} - -function translate(from, to) -@{ - return $0 = stranslate(from, to, $0) -@} +@c endfile +@end ignore +@c file eg/prog/egrep.awk +# Options: +# -c count of lines +# -s silent - use exit value +# -v invert test, success if no match +# -i ignore case +# -l print filenames only +# -e argument is pattern +# +# Requires getopt and file transition library functions -@group -# main program BEGIN @{ - if (ARGC < 3) @{ - print "usage: translate from to" > "/dev/stderr" - exit + while ((c = getopt(ARGC, ARGV, "ce:svil")) != -1) @{ + if (c == "c") + count_only++ + else if (c == "s") + no_print++ + else if (c == "v") + invert++ + else if (c == "i") + IGNORECASE = 1 + else if (c == "l") + filenames_only++ + else if (c == "e") + pattern = Optarg + else + usage() @} -@end group - FROM = ARGV[1] - TO = ARGV[2] - ARGC = 2 - ARGV[1] = "-" -@} - -@{ - translate(FROM, TO) - print -@} @c endfile -@c @end group @end example -While it is possible to do character transliteration in a user-level -function, it is not necessarily efficient, and we started to consider adding -a built-in function. However, shortly after writing this program, we learned -that the System V Release 4 @code{awk} had added the @code{toupper} and -@code{tolower} functions. These functions handle the vast majority of the -cases where character transliteration is necessary, and so we chose to -simply add those functions to @code{gawk} as well, and then leave well -enough alone. +Next comes the code that handles the @command{egrep}-specific behavior. If no +pattern is supplied with @option{-e}, the first non-option on the +command line is used. The @command{awk} command-line arguments up to @code{ARGV[Optind]} +are cleared, so that @command{awk} won't try to process them as files. If no +files are specified, the standard input is used, and if multiple files are +specified, we make sure to note this so that the @value{FN}s can precede the +matched lines in the output: -An obvious improvement to this program would be to set up the -@code{t_ar} array only once, in a @code{BEGIN} rule. However, this -assumes that the ``from'' and ``to'' lists -will never change throughout the lifetime of the program. +@example +@c file eg/prog/egrep.awk + if (pattern == "") + pattern = ARGV[Optind++] -@node Labels Program, Word Sorting, Translate Program, Miscellaneous Programs -@subsection Printing Mailing Labels + for (i = 1; i < Optind; i++) + ARGV[i] = "" + if (Optind >= ARGC) @{ + ARGV[1] = "-" + ARGC = 2 + @} else if (ARGC - Optind > 1) + do_filenames++ -Here is a ``real world''@footnote{``Real world'' is defined as -``a program actually used to get something done.''} -program. This script reads lists of names and -addresses, and generates mailing labels. Each page of labels has 20 labels -on it, two across and ten down. The addresses are guaranteed to be no more -than five lines of data. Each address is separated from the next by a blank -line. +# if (IGNORECASE) +# pattern = tolower(pattern) +@} +@c endfile +@end example -The basic idea is to read 20 labels worth of data. Each line of each label -is stored in the @code{line} array. The single rule takes care of filling -the @code{line} array and printing the page when 20 labels have been read. +The last two lines are commented out, since they are not needed in +@command{gawk}. They should be uncommented if you have to use another version +of @command{awk}. -The @code{BEGIN} rule simply sets @code{RS} to the empty string, so that -@code{awk} will split records at blank lines -(@pxref{Records, ,How Input is Split into Records}). -It sets @code{MAXLINES} to 100, since @code{MAXLINE} is the maximum number -of lines on the page (20 * 5 = 100). +The next set of lines should be uncommented if you are not using +@command{gawk}. This rule translates all the characters in the input line +into lowercase if the @option{-i} option is specified.@footnote{It +also introduces a subtle bug; +if a match happens, we output the translated line, not the original.} +The rule is +commented out since it is not necessary with @command{gawk}: -Most of the work is done in the @code{printpage} function. -The label lines are stored sequentially in the @code{line} array. But they -have to be printed horizontally; @code{line[1]} next to @code{line[6]}, -@code{line[2]} next to @code{line[7]}, and so on. Two loops are used to -accomplish this. The outer loop, controlled by @code{i}, steps through -every 10 lines of data; this is each row of labels. The inner loop, -controlled by @code{j}, goes through the lines within the row. -As @code{j} goes from zero to four, @samp{i+j} is the @code{j}'th line in -the row, and @samp{i+j+5} is the entry next to it. The output ends up -looking something like this: +@c Exercise: Fix this, w/array and new line as key to original line @example -line 1 line 6 -line 2 line 7 -line 3 line 8 -line 4 line 9 -line 5 line 10 +@c file eg/prog/egrep.awk +#@{ +# if (IGNORECASE) +# $0 = tolower($0) +#@} +@c endfile @end example -As a final note, at lines 21 and 61, an extra blank line is printed, to keep -the output lined up on the labels. This is dependent on the particular -brand of labels in use when the program was written. You will also note -that there are two blank lines at the top and two blank lines at the bottom. +The @code{beginfile} function is called by the rule in @file{ftrans.awk} +when each new file is processed. In this case, it is very simple; all it +does is initialize a variable @code{fcount} to zero. @code{fcount} tracks +how many lines in the current file matched the pattern. +(Naming the parameter @code{junk} shows we know that @code{beginfile} +is called with a parameter, but that we're not interested in its value.): -The @code{END} rule arranges to flush the final page of labels; there may -not have been an even multiple of 20 labels in the data. +@example +@c file eg/prog/egrep.awk +function beginfile(junk) +@{ + fcount = 0 +@} +@c endfile +@end example + +The @code{endfile} function is called after each file has been processed. +It affects the output only when the user wants a count of the number of lines that +matched. @code{no_print} is true only if the exit status is desired. +@code{count_only} is true if line counts are desired. @command{egrep} +therefore only prints line counts if printing and counting are enabled. +The output format must be adjusted depending upon the number of files to +process. Finally, @code{fcount} is added to @code{total}, so that we +know how many lines altogether matched the pattern: -@findex labels.awk @example -@c @group -@c file eg/prog/labels.awk -# labels.awk -# Arnold Robbins, arnold@@gnu.org, Public Domain -# June 1992 +@c file eg/prog/egrep.awk +function endfile(file) +@{ + if (! no_print && count_only) + if (do_filenames) + print file ":" fcount + else + print fcount + + total += fcount +@} +@c endfile +@end example -# Program to print labels. Each label is 5 lines of data -# that may have blank lines. The label sheets have 2 -# blank lines at the top and 2 at the bottom. +The following rule does most of the work of matching lines. The variable +@code{matches} is true if the line matched the pattern. If the user +wants lines that did not match, the sense of @code{matches} is inverted +using the @samp{!} operator. @code{fcount} is incremented with the value of +@code{matches}, which is either one or zero, depending upon a +successful or unsuccessful match. If the line does not match, the +@code{next} statement just moves on to the next record. -BEGIN @{ RS = "" ; MAXLINES = 100 @} +A number of additional tests are made, but they are only done if we +are not counting lines. First, if the user only wants exit status +(@code{no_print} is true), then it is enough to know that @emph{one} +line in this file matched, and we can skip on to the next file with +@code{nextfile}. Similarly, if we are only printing @value{FN}s, we can +print the @value{FN}, and then skip to the next file with @code{nextfile}. +Finally, each line is printed, with a leading @value{FN} and colon +if necessary: -function printpage( i, j) +@cindex @code{!} operator +@example +@c file eg/prog/egrep.awk @{ - if (Nlines <= 0) - return + matches = ($0 ~ pattern) + if (invert) + matches = ! matches - printf "\n\n" # header + fcount += matches # 1 or 0 - for (i = 1; i <= Nlines; i += 10) @{ - if (i == 21 || i == 61) - print "" - for (j = 0; j < 5; j++) @{ - if (i + j > MAXLINES) - break - printf " %-41s %s\n", line[i+j], line[i+j+5] - @} - print "" - @} + if (! matches) + next - printf "\n\n" # footer + if (! count_only) @{ + if (no_print) + nextfile - for (i in line) - line[i] = "" -@} + if (filenames_only) @{ + print FILENAME + nextfile + @} -# main rule -@{ - if (Count >= 20) @{ - printpage() - Count = 0 - Nlines = 0 + if (do_filenames) + print FILENAME ":" $0 + else + print @} - n = split($0, a, "\n") - for (i = 1; i <= n; i++) - line[++Nlines] = a[i] - for (; i <= 5; i++) - line[++Nlines] = "" - Count++ @} +@c endfile +@end example + +The @code{END} rule takes care of producing the correct exit status. If +there are no matches, the exit status is one, otherwise it is zero: +@example +@c file eg/prog/egrep.awk END \ @{ - printpage() + if (total == 0) + exit 1 + exit 0 @} @c endfile -@c @end group @end example -@node Word Sorting, History Sorting, Labels Program, Miscellaneous Programs -@subsection Generating Word Usage Counts - -The following @code{awk} program prints -the number of occurrences of each word in its input. It illustrates the -associative nature of @code{awk} arrays by using strings as subscripts. It -also demonstrates the @samp{for @var{x} in @var{array}} construction. -Finally, it shows how @code{awk} can be used in conjunction with other -utility programs to do a useful task of some complexity with a minimum of -effort. Some explanations follow the program listing. +The @code{usage} function prints a usage message in case of invalid options, +and then exits: @example -awk ' -# Print list of word frequencies +@c file eg/prog/egrep.awk +function usage( e) @{ - for (i = 1; i <= NF; i++) - freq[$i]++ + e = "Usage: egrep [-csvil] [-e pat] [files ...]" + e = e "\n\tegrep [-csvil] pat [files ...]" + print e > "/dev/stderr" + exit 1 @} - -@group -END @{ - for (word in freq) - printf "%s\t%d\n", word, freq[word] -@}' -@end group +@c endfile @end example -The first thing to notice about this program is that it has two rules. The -first rule, because it has an empty pattern, is executed on every line of -the input. It uses @code{awk}'s field-accessing mechanism -(@pxref{Fields, ,Examining Fields}) to pick out the individual words from -the line, and the built-in variable @code{NF} (@pxref{Built-in Variables}) -to know how many fields are available. - -For each input word, an element of the array @code{freq} is incremented to -reflect that the word has been seen an additional time. +The variable @code{e} is used so that the function fits nicely +on the printed page. -The second rule, because it has the pattern @code{END}, is not executed -until the input has been exhausted. It prints out the contents of the -@code{freq} table that has been built up inside the first action. +@cindex backslash continuation +Just a note on programming style: you may have noticed that the @code{END} +rule uses backslash continuation, with the open brace on a line by +itself. This is so that it more closely resembles the way functions +are written. Many of the examples +in this @value{CHAPTER} +use this style. You can decide for yourself if you like writing +your @code{BEGIN} and @code{END} rules this way +or not. -This program has several problems that would prevent it from being -useful by itself on real text files: +@node Id Program, Split Program, Egrep Program, Clones +@subsection Printing out User Information -@itemize @bullet -@item -Words are detected using the @code{awk} convention that fields are -separated by whitespace and that other characters in the input (except -newlines) don't have any special meaning to @code{awk}. This means that -punctuation characters count as part of words. +@cindex @command{id} utility +The @command{id} utility lists a user's real and effective user-id numbers, +real and effective group-id numbers, and the user's group set, if any. +@command{id} only prints the effective user-id and group-id if they are +different from the real ones. If possible, @command{id} also supplies the +corresponding user and group names. The output might look like this: -@item -The @code{awk} language considers upper- and lower-case characters to be -distinct. Therefore, @samp{bartender} and @samp{Bartender} are not treated -as the same word. This is undesirable since, in normal text, words -are capitalized if they begin sentences, and a frequency analyzer should not -be sensitive to capitalization. +@example +$ id +@print{} uid=2076(arnold) gid=10(staff) groups=10(staff),4(tty) +@end example -@item -The output does not come out in any useful order. You're more likely to be -interested in which words occur most frequently, or having an alphabetized -table of how frequently each word occurs. -@end itemize +This information is part of what is provided by @command{gawk}'s +@code{PROCINFO} array (@pxref{Built-in Variables}). +However, the @command{id} utility provides a more palatable output than just +individual numbers. -The way to solve these problems is to use some of the more advanced -features of the @code{awk} language. First, we use @code{tolower} to remove -case distinctions. Next, we use @code{gsub} to remove punctuation -characters. Finally, we use the system @code{sort} utility to process the -output of the @code{awk} script. Here is the new version of -the program: +Here is a simple version of @command{id} written in @command{awk}. +It uses the user database library functions +(@pxref{Passwd Functions, ,Reading the User Database}) +and the group database library functions +(@pxref{Group Functions, ,Reading the Group Database}): + +The program is fairly straightforward. All the work is done in the +@code{BEGIN} rule. The user and group ID numbers are obtained from +@code{PROCINFO}. +The code is repetitive. The entry in the user database for the real user-id +number is split into parts at the @samp{:}. The name is the first field. +Similar code is used for the effective user-id number and the group +numbers. -@findex wordfreq.sh +@cindex @code{id.awk} program @example -@c file eg/prog/wordfreq.awk -# Print list of word frequencies -@{ - $0 = tolower($0) # remove case distinctions - gsub(/[^a-z0-9_ \t]/, "", $0) # remove punctuation - for (i = 1; i <= NF; i++) - freq[$i]++ -@} +@c file eg/prog/id.awk +# id.awk --- implement id in awk +# +# Requires user and group library functions +@c endfile +@ignore +@c file eg/prog/id.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# May 1993 +# Revised February 1996 + @c endfile +@end ignore +@c file eg/prog/id.awk +# output is: +# uid=12(foo) euid=34(bar) gid=3(baz) \ +# egid=5(blat) groups=9(nine),2(two),1(one) @group -END @{ - for (word in freq) - printf "%s\t%d\n", word, freq[word] -@} +BEGIN \ +@{ + uid = PROCINFO["uid"] + euid = PROCINFO["euid"] + gid = PROCINFO["gid"] + egid = PROCINFO["egid"] @end group -@end example - -Assuming we have saved this program in a file named @file{wordfreq.awk}, -and that the data is in @file{file1}, the following pipeline -@example -awk -f wordfreq.awk file1 | sort +1 -nr -@end example + printf("uid=%d", uid) + pw = getpwuid(uid) + if (pw != "") @{ + split(pw, a, ":") + printf("(%s)", a[1]) + @} -@noindent -produces a table of the words appearing in @file{file1} in order of -decreasing frequency. + if (euid != uid) @{ + printf(" euid=%d", euid) + pw = getpwuid(euid) + if (pw != "") @{ + split(pw, a, ":") + printf("(%s)", a[1]) + @} + @} -The @code{awk} program suitably massages the data and produces a word -frequency table, which is not ordered. + printf(" gid=%d", gid) + pw = getgrgid(gid) + if (pw != "") @{ + split(pw, a, ":") + printf("(%s)", a[1]) + @} -The @code{awk} script's output is then sorted by the @code{sort} utility and -printed on the terminal. The options given to @code{sort} in this example -specify to sort using the second field of each input line (skipping one field), -that the sort keys should be treated as numeric quantities (otherwise -@samp{15} would come before @samp{5}), and that the sorting should be done -in descending (reverse) order. + if (egid != gid) @{ + printf(" egid=%d", egid) + pw = getgrgid(egid) + if (pw != "") @{ + split(pw, a, ":") + printf("(%s)", a[1]) + @} + @} -We could have even done the @code{sort} from within the program, by -changing the @code{END} action to: + for (i = 1; ("group" i) in PROCINFO; i++) @{ + if (i == 1) + printf(" groups=") + group = PROCINFO["group" i] + printf("%d", group) + pw = getgrgid(group) + if (pw != "") @{ + split(pw, a, ":") + printf("(%s)", a[1]) + @} + if (("group" (i+1)) in PROCINFO) + printf(",") + @} -@example -@c file eg/prog/wordfreq.awk -END @{ - sort = "sort +1 -nr" - for (word in freq) - printf "%s\t%d\n", word, freq[word] | sort - close(sort) + print "" @} @c endfile @end example -You would have to use this way of sorting on systems that do not -have true pipes. +@cindex @code{in} operator +The test in the @code{for} loop is worth noting. +Any supplementary groups in the @code{PROCINFO} array have the +indices @code{"group1"} through @code{"group@var{N}"} for some +@var{N}; i.e., the total number of supplementary groups. +The problem is, we don't know in advance how many of these groups +there are. + +This loop works by starting at one, concatenating the value with +@code{"group"}, and then using @code{in} to see if that value is +in the array. Eventually, @code{i} is incremented past +the last group in the array and the loop exits. + +The loop is also correct if there are @emph{no} supplementary +groups; then the condition is false the first time it's +tested, and the loop body never executes. -See the general operating system documentation for more information on how -to use the @code{sort} program. +@c exercise!!! +@ignore +The POSIX version of @command{id} takes arguments that control which +information is printed. Modify this version to accept the same +arguments and perform in the same way. +@end ignore -@node History Sorting, Extract Program, Word Sorting, Miscellaneous Programs -@subsection Removing Duplicates from Unsorted Text +@node Split Program, Tee Program, Id Program, Clones +@subsection Splitting a Large File into Pieces -The @code{uniq} program -(@pxref{Uniq Program, ,Printing Non-duplicated Lines of Text}), -removes duplicate lines from @emph{sorted} data. +@cindex @code{split} utility +The @code{split} program splits large text files into smaller pieces. +The usage is as follows: -Suppose, however, you need to remove duplicate lines from a data file, but -that you wish to preserve the order the lines are in? A good example of -this might be a shell history file. The history file keeps a copy of all -the commands you have entered, and it is not unusual to repeat a command -several times in a row. Occasionally you might wish to compact the history -by removing duplicate entries. Yet it is desirable to maintain the order -of the original commands. +@example +split @r{[}-@var{count}@r{]} file @r{[} @var{prefix} @r{]} +@end example -This simple program does the job. It uses two arrays. The @code{data} -array is indexed by the text of each line. -For each line, @code{data[$0]} is incremented. +By default, +the output files are named @file{xaa}, @file{xab}, and so on. Each file has +1000 lines in it, with the likely exception of the last file. To change the +number of lines in each file, supply a number on the command line +preceded with a minus; e.g., @samp{-500} for files with 500 lines in them +instead of 1000. To change the name of the output files to something like +@file{myfileaa}, @file{myfileab}, and so on, supply an additional +argument that specifies the @value{FN} prefix. -If a particular line has not -been seen before, then @code{data[$0]} will be zero. -In that case, the text of the line is stored in @code{lines[count]}. -Each element of @code{lines} is a unique command, and the indices of -@code{lines} indicate the order in which those lines were encountered. -The @code{END} rule simply prints out the lines, in order. +Here is a version of @code{split} in @command{awk}. It uses the @code{ord} and +@code{chr} functions presented in +@ref{Ordinal Functions, ,Translating Between Characters and Numbers}. -@cindex Rakitzis, Byron -@findex histsort.awk +The program first sets its defaults, and then tests to make sure there are +not too many arguments. It then looks at each argument in turn. The +first argument could be a minus followed by a number. If it is, this happens +to look like a negative number, so it is made positive, and that is the +count of lines. The data @value{FN} is skipped over and the final argument +is used as the prefix for the output @value{FN}s: + +@cindex @code{split.awk} program @example -@group -@c file eg/prog/histsort.awk -# histsort.awk --- compact a shell history file +@c file eg/prog/split.awk +# split.awk --- do split in awk +# +# Requires ord and chr library functions +@c endfile +@ignore +@c file eg/prog/split.awk +# # Arnold Robbins, arnold@@gnu.org, Public Domain # May 1993 -# Thanks to Byron Rakitzis for the general idea -@{ - if (data[$0]++ == 0) - lines[++count] = $0 -@} +@c endfile +@end ignore +@c file eg/prog/split.awk +# usage: split [-num] [file] [outname] -END @{ - for (i = 1; i <= count; i++) - print lines[i] +BEGIN @{ + outfile = "x" # default + count = 1000 + if (ARGC > 4) + usage() + + i = 1 + if (ARGV[i] ~ /^-[0-9]+$/) @{ + count = -ARGV[i] + ARGV[i] = "" + i++ + @} + # test argv in case reading from stdin instead of file + if (i in ARGV) + i++ # skip data file name + if (i in ARGV) @{ + outfile = ARGV[i] + ARGV[i] = "" + @} + + s1 = s2 = "a" + out = (outfile s1 s2) @} @c endfile -@end group @end example -This program also provides a foundation for generating other useful -information. For example, using the following @code{print} satement in the -@code{END} rule would indicate how often a particular command was used. +The next rule does most of the work. @code{tcount} (temporary count) tracks +how many lines have been printed to the output file so far. If it is greater +than @code{count}, it is time to close the current file and start a new one. +@code{s1} and @code{s2} track the current suffixes for the @value{FN}. If +they are both @samp{z}, the file is just too big. Otherwise, @code{s1} +moves to the next letter in the alphabet and @code{s2} starts over again at +@samp{a}: +@c else on separate line here for page breaking @example -print data[lines[i]], lines[i] +@c file eg/prog/split.awk +@{ + if (++tcount > count) @{ + close(out) + if (s2 == "z") @{ + if (s1 == "z") @{ + printf("split: %s is too large to split\n", + FILENAME) > "/dev/stderr" + exit 1 + @} + s1 = chr(ord(s1) + 1) + s2 = "a" + @} +@group + else + s2 = chr(ord(s2) + 1) +@end group + out = (outfile s1 s2) + tcount = 1 + @} + print > out +@} +@c endfile @end example -This works because @code{data[$0]} was incremented each time a line was -seen. +@c Exercise: do this with just awk builtin functions, index("abc..."), substr, etc. -@node Extract Program, Simple Sed, History Sorting, Miscellaneous Programs -@subsection Extracting Programs from Texinfo Source Files +@noindent +The @code{usage} function simply prints an error message and exits: -@iftex -Both this chapter and the previous chapter -(@ref{Library Functions, ,A Library of @code{awk} Functions}), -present a large number of @code{awk} programs. -@end iftex -@ifinfo -The nodes -@ref{Library Functions, ,A Library of @code{awk} Functions}, -and @ref{Sample Programs, ,Practical @code{awk} Programs}, -are the top level nodes for a large number of @code{awk} programs. -@end ifinfo -If you wish to experiment with these programs, it is tedious to have to type -them in by hand. Here we present a program that can extract parts of a -Texinfo input file into separate files. +@example +@c file eg/prog/split.awk +function usage( e) +@{ + e = "usage: split [-num] [file] [outname]" + print e > "/dev/stderr" + exit 1 +@} +@c endfile +@end example -This @value{DOCUMENT} is written in Texinfo, the GNU project's document -formatting language. A single Texinfo source file can be used to produce both -printed and on-line documentation. -@iftex -Texinfo is fully documented in @cite{Texinfo---The GNU Documentation Format}, -available from the Free Software Foundation. -@end iftex +@noindent +The variable @code{e} is used so that the function +fits nicely on the @ifinfo -The Texinfo language is described fully, starting with -@ref{Top, , Introduction, texi, Texinfo---The GNU Documentation Format}. +screen. @end ifinfo +@ifnotinfo +page. +@end ifnotinfo -For our purposes, it is enough to know three things about Texinfo input -files. +This program is a bit sloppy; it relies on @command{awk} to close the last file +for it automatically, instead of doing it in an @code{END} rule. +It also assumes that letters are contiguous in the character set, +which isn't true for EBCDIC systems. +@c BFD... -@itemize @bullet -@item -The ``at'' symbol, @samp{@@}, is special in Texinfo, much like @samp{\} in C -or @code{awk}. Literal @samp{@@} symbols are represented in Texinfo source -files as @samp{@@@@}. +@node Tee Program, Uniq Program, Split Program, Clones +@subsection Duplicating Output into Multiple Files -@item -Comments start with either @samp{@@c} or @samp{@@comment}. -The file extraction program will work by using special comments that start -at the beginning of a line. +@cindex @code{tee} utility +The @code{tee} program is known as a ``pipe fitting.'' @code{tee} copies +its standard input to its standard output and also duplicates it to the +files named on the command line. Its usage is as follows: -@item -Example text that should not be split across a page boundary is bracketed -between lines containing @samp{@@group} and @samp{@@end group} commands. -@end itemize +@example +tee @r{[}-a@r{]} file @dots{} +@end example -The following program, @file{extract.awk}, reads through a Texinfo source -file, and does two things, based on the special comments. -Upon seeing @samp{@w{@@c system @dots{}}}, -it runs a command, by extracting the command text from the -control line and passing it on to the @code{system} function -(@pxref{I/O Functions, ,Built-in Functions for Input/Output}). -Upon seeing @samp{@@c file @var{filename}}, each subsequent line is sent to -the file @var{filename}, until @samp{@@c endfile} is encountered. -The rules in @file{extract.awk} will match either @samp{@@c} or -@samp{@@comment} by letting the @samp{omment} part be optional. -Lines containing @samp{@@group} and @samp{@@end group} are simply removed. -@file{extract.awk} uses the @code{join} library function -(@pxref{Join Function, ,Merging an Array Into a String}). - -The example programs in the on-line Texinfo source for @cite{@value{TITLE}} -(@file{gawk.texi}) have all been bracketed inside @samp{file}, -and @samp{endfile} lines. The @code{gawk} distribution uses a copy of -@file{extract.awk} to extract the sample -programs and install many of them in a standard directory, where -@code{gawk} can find them. -The Texinfo file looks something like this: - -@example -@dots{} -This program has a @@code@{BEGIN@} block, -which prints a nice message: - -@@example -@@c file examples/messages.awk -BEGIN @@@{ print "Don't panic!" @@@} -@@c end file -@@end example - -It also prints some final advice: - -@@example -@@c file examples/messages.awk -END @@@{ print "Always avoid bored archeologists!" @@@} -@@c end file -@@end example -@dots{} -@end example +The @option{-a} option tells @code{tee} to append to the named files, instead of +truncating them and starting over. -@file{extract.awk} begins by setting @code{IGNORECASE} to one, so that -mixed upper-case and lower-case letters in the directives won't matter. +The @code{BEGIN} rule first makes a copy of all the command-line arguments +into an array named @code{copy}. +@code{ARGV[0]} is not copied, since it is not needed. +@code{tee} cannot use @code{ARGV} directly, since @command{awk} attempts to +process each @value{FN} in @code{ARGV} as input data. -The first rule handles calling @code{system}, checking that a command was -given (@code{NF} is at least three), and also checking that the command -exited with a zero exit status, signifying OK. +@cindex flag variables +If the first argument is @option{-a}, then the flag variable +@code{append} is set to true, and both @code{ARGV[1]} and +@code{copy[1]} are deleted. If @code{ARGC} is less than two, then no +@value{FN}s were supplied and @code{tee} prints a usage message and exits. +Finally, @command{awk} is forced to read the standard input by setting +@code{ARGV[1]} to @code{"-"} and @code{ARGC} to two: -@findex extract.awk +@c NEXT ED: Add more leading commentary in this program +@cindex @code{tee.awk} program @example -@c @group -@c file eg/prog/extract.awk -# extract.awk --- extract files and run programs -# from texinfo files -# Arnold Robbins, arnold@@gnu.org, Public Domain, May 1993 - -BEGIN @{ IGNORECASE = 1 @} +@c file eg/prog/tee.awk +# tee.awk --- tee in awk +@c endfile +@ignore +@c file eg/prog/tee.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# May 1993 +# Revised December 1995 -@group -/^@@c(omment)?[ \t]+system/ \ +@c endfile +@end ignore +@c file eg/prog/tee.awk +BEGIN \ @{ - if (NF < 3) @{ - e = (FILENAME ":" FNR) - e = (e ": badly formed `system' line") - print e > "/dev/stderr" - next + for (i = 1; i < ARGC; i++) + copy[i] = ARGV[i] + + if (ARGV[1] == "-a") @{ + append = 1 + delete ARGV[1] + delete copy[1] + ARGC-- @} - $1 = "" - $2 = "" - stat = system($0) - if (stat != 0) @{ - e = (FILENAME ":" FNR) - e = (e ": warning: system returned " stat) - print e > "/dev/stderr" + if (ARGC < 2) @{ + print "usage: tee [-a] file ..." > "/dev/stderr" + exit 1 @} + ARGV[1] = "-" + ARGC = 2 @} -@end group @c endfile @end example -@noindent -The variable @code{e} is used so that the function -fits nicely on the -@iftex -page. -@end iftex -@ifinfo -screen. -@end ifinfo - -The second rule handles moving data into files. It verifies that a file -name was given in the directive. If the file named is not the current file, -then the current file is closed. This means that an @samp{@@c endfile} was -not given for that file. (We should probably print a diagnostic in this -case, although at the moment we do not.) - -The @samp{for} loop does the work. It reads lines using @code{getline} -(@pxref{Getline, ,Explicit Input with @code{getline}}). -For an unexpected end of file, it calls the @code{@w{unexpected_eof}} -function. If the line is an ``endfile'' line, then it breaks out of -the loop. -If the line is an @samp{@@group} or @samp{@@end group} line, then it -ignores it, and goes on to the next line. -(These Texinfo control lines keep blocks of code together on one page; -unfortunately, @TeX{} isn't always smart enough to do things exactly right, -and we have to give it some advice.) - -Most of the work is in the following few lines. If the line has no @samp{@@} -symbols, it can be printed directly. Otherwise, each leading @samp{@@} must be -stripped off. - -To remove the @samp{@@} symbols, the line is split into separate elements of -the array @code{a}, using the @code{split} function -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). -Each element of @code{a} that is empty indicates two successive @samp{@@} -symbols in the original line. For each two empty elements (@samp{@@@@} in -the original file), we have to add back in a single @samp{@@} symbol. - -When the processing of the array is finished, @code{join} is called with the -value of @code{SUBSEP}, to rejoin the pieces back into a single -line. That line is then printed to the output file. +The single rule does all the work. Since there is no pattern, it is +executed for each line of input. The body of the rule simply prints the +line into each file on the command line, and then to the standard output: @example -@c @group -@c file eg/prog/extract.awk -@group -/^@@c(omment)?[ \t]+file/ \ +@c file eg/prog/tee.awk @{ - if (NF != 3) @{ - e = (FILENAME ":" FNR ": badly formed `file' line") - print e > "/dev/stderr" - next - @} -@end group - if ($3 != curfile) @{ - if (curfile != "") - close(curfile) - curfile = $3 - @} - - for (;;) @{ - if ((getline line) <= 0) - unexpected_eof() - if (line ~ /^@@c(omment)?[ \t]+endfile/) - break - else if (line ~ /^@@(end[ \t]+)?group/) - continue - if (index(line, "@@") == 0) @{ - print line > curfile - continue - @} - n = split(line, a, "@@") -@group - # if a[1] == "", means leading @@, - # don't add one back in. -@end group - for (i = 2; i <= n; i++) @{ - if (a[i] == "") @{ # was an @@@@ - a[i] = "@@" - if (a[i+1] == "") - i++ - @} - @} - print join(a, 1, n, SUBSEP) > curfile - @} + # moving the if outside the loop makes it run faster + if (append) + for (i in copy) + print >> copy[i] + else + for (i in copy) + print > copy[i] + print @} @c endfile -@c @end group @end example -An important thing to note is the use of the @samp{>} redirection. -Output done with @samp{>} only opens the file once; it stays open and -subsequent output is appended to the file -(@pxref{Redirection, , Redirecting Output of @code{print} and @code{printf}}). -This allows us to easily mix program text and explanatory prose for the same -sample source file (as has been done here!) without any hassle. The file is -only closed when a new data file name is encountered, or at the end of the -input file. +@noindent +It is also possible to write the loop this way: -Finally, the function @code{@w{unexpected_eof}} prints an appropriate -error message and then exits. +@example +for (i in copy) + if (append) + print >> copy[i] + else + print > copy[i] +@end example + +@noindent +This is more concise but it is also less efficient. The @samp{if} is +tested for each record and for each output file. By duplicating the loop +body, the @samp{if} is only tested once for each input record. If there are +@var{N} input records and @var{M} output files, the first method only +executes @var{N} @samp{if} statements, while the second executes +@var{N}@code{*}@var{M} @samp{if} statements. -The @code{END} rule handles the final cleanup, closing the open file. +Finally, the @code{END} rule cleans up by closing all the output files: @example -@c file eg/prog/extract.awk -@group -function unexpected_eof() +@c file eg/prog/tee.awk +END \ @{ - printf("%s:%d: unexpected EOF or error\n", \ - FILENAME, FNR) > "/dev/stderr" - exit 1 -@} -@end group - -END @{ - if (curfile) - close(curfile) + for (i in copy) + close(copy[i]) @} @c endfile @end example -@node Simple Sed, Igawk Program, Extract Program, Miscellaneous Programs -@subsection A Simple Stream Editor - -@cindex @code{sed} utility -The @code{sed} utility is a ``stream editor,'' a program that reads a -stream of data, makes changes to it, and passes the modified data on. -It is often used to make global changes to a large file, or to a stream -of data generated by a pipeline of commands. +@node Uniq Program, Wc Program, Tee Program, Clones +@subsection Printing Non-Duplicated Lines of Text -While @code{sed} is a complicated program in its own right, its most common -use is to perform global substitutions in the middle of a pipeline: +@cindex @command{uniq} utility +The @command{uniq} utility reads sorted lines of data on its standard +input, and by default removes duplicate lines. In other words, it only +prints unique lines---hence the name. @command{uniq} has a number of +options. The usage is as follows: @example -command1 < orig.data | sed 's/old/new/g' | command2 > result +uniq @r{[}-udc @r{[}-@var{n}@r{]]} @r{[}+@var{n}@r{]} @r{[} @var{input file} @r{[} @var{output file} @r{]]} @end example -Here, the @samp{s/old/new/g} tells @code{sed} to look for the regexp -@samp{old} on each input line, and replace it with the text @samp{new}, -globally (i.e.@: all the occurrences on a line). This is similar to -@code{awk}'s @code{gsub} function -(@pxref{String Functions, , Built-in Functions for String Manipulation}). - -The following program, @file{awksed.awk}, accepts at least two command line -arguments; the pattern to look for and the text to replace it with. Any -additional arguments are treated as data file names to process. If none -are provided, the standard input is used. +The option meanings are: -@cindex Brennan, Michael -@cindex @code{awksed} -@cindex simple stream editor -@cindex stream editor, simple -@example -@c @group -@c file eg/prog/awksed.awk -# awksed.awk --- do s/foo/bar/g using just print -# Thanks to Michael Brennan for the idea +@table @code +@item -d +Only print repeated lines. -# Arnold Robbins, arnold@@gnu.org, Public Domain -# August 1995 +@item -u +Only print non-repeated lines. -function usage() -@{ - print "usage: awksed pat repl [files...]" > "/dev/stderr" - exit 1 -@} +@item -c +Count lines. This option overrides @option{-d} and @option{-u}. Both repeated +and non-repeated lines are counted. -@group -BEGIN @{ - # validate arguments - if (ARGC < 3) - usage() -@end group +@item -@var{n} +Skip @var{n} fields before comparing lines. The definition of fields +is similar to @command{awk}'s default: non-whitespace characters separated +by runs of spaces and/or tabs. - RS = ARGV[1] - ORS = ARGV[2] +@item +@var{n} +Skip @var{n} characters before comparing lines. Any fields specified with +@samp{-@var{n}} are skipped first. - # don't use arguments as files - ARGV[1] = ARGV[2] = "" -@} +@item @var{input file} +Data is read from the input file named on the command line, instead of from +the standard input. -# look ma, no hands! -@{ - if (RT == "") - printf "%s", $0 - else - print -@} -@c endfile -@c @end group -@end example +@item @var{output file} +The generated output is sent to the named output file, instead of to the +standard output. +@end table -The program relies on @code{gawk}'s ability to have @code{RS} be a regexp -and on the setting of @code{RT} to the actual text that terminated the -record (@pxref{Records, ,How Input is Split into Records}). +Normally @command{uniq} behaves as if both the @option{-d} and +@option{-u} options are provided. -The idea is to have @code{RS} be the pattern to look for. @code{gawk} -will automatically set @code{$0} to the text between matches of the pattern. -This is text that we wish to keep, unmodified. Then, by setting @code{ORS} -to the replacement text, a simple @code{print} statement will output the -text we wish to keep, followed by the replacement text. +@command{uniq} uses the +@code{getopt} library function +(@pxref{Getopt Function, ,Processing Command-Line Options}) +and the @code{join} library function +(@pxref{Join Function, ,Merging an Array into a String}). -There is one wrinkle to this scheme, which is what to do if the last record -doesn't end with text that matches @code{RS}? Using a @code{print} -statement unconditionally prints the replacement text, which is not correct. - -However, if the file did not end in text that matches @code{RS}, @code{RT} -will be set to the null string. In this case, we can print @code{$0} using -@code{printf} -(@pxref{Printf, ,Using @code{printf} Statements for Fancier Printing}). - -The @code{BEGIN} rule handles the setup, checking for the right number -of arguments, and calling @code{usage} if there is a problem. Then it sets -@code{RS} and @code{ORS} from the command line arguments, and sets -@code{ARGV[1]} and @code{ARGV[2]} to the null string, so that they will -not be treated as file names -(@pxref{ARGC and ARGV, , Using @code{ARGC} and @code{ARGV}}). - -The @code{usage} function prints an error message and exits. +The program begins with a @code{usage} function and then a brief outline of +the options and their meanings in a comment. +The @code{BEGIN} rule deals with the command-line arguments and options. It +uses a trick to get @code{getopt} to handle options of the form @samp{-25}, +treating such an option as the option letter @samp{2} with an argument of +@samp{5}. If indeed two or more digits are supplied (@code{Optarg} looks +like a number), @code{Optarg} is +concatenated with the option digit and then the result is added to zero to make +it into a number. If there is only one digit in the option, then +@code{Optarg} is not needed. @code{Optind} must be decremented so that +@code{getopt} processes it next time. This code is admittedly a bit +tricky. -Finally, the single rule handles the printing scheme outlined above, -using @code{print} or @code{printf} as appropriate, depending upon the -value of @code{RT}. +If no options are supplied, then the default is taken, to print both +repeated and non-repeated lines. The output file, if provided, is assigned +to @code{outputfile}. Early on, @code{outputfile} is initialized to the +standard output, @file{/dev/stdout}: +@cindex @code{uniq.awk} program +@example +@c file eg/prog/uniq.awk +@group +# uniq.awk --- do uniq in awk +# +# Requires getopt and join library functions +@end group +@c endfile @ignore -Exercise, compare the performance of this version with the more -straightforward: +@c file eg/prog/uniq.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# May 1993 -BEGIN { - pat = ARGV[1] - repl = ARGV[2] - ARGV[1] = ARGV[2] = "" -} +@c endfile +@end ignore +@c file eg/prog/uniq.awk +function usage( e) +@{ + e = "Usage: uniq [-udc [-n]] [+n] [ in [ out ]]" + print e > "/dev/stderr" + exit 1 +@} -{ gsub(pat, repl); print } +# -c count lines. overrides -d and -u +# -d only repeated lines +# -u only non-repeated lines +# -n skip n fields +# +n skip n characters, skip fields first -Exercise: what are the advantages and disadvantages of this version vs. sed? - Advantage: egrep regexps - speed (?) - Disadvantage: no & in replacement text +BEGIN \ +@{ + count = 1 + outputfile = "/dev/stdout" + opts = "udc0:1:2:3:4:5:6:7:8:9:" + while ((c = getopt(ARGC, ARGV, opts)) != -1) @{ + if (c == "u") + non_repeated_only++ + else if (c == "d") + repeated_only++ + else if (c == "c") + do_count++ + else if (index("0123456789", c) != 0) @{ + # getopt requires args to options + # this messes us up for things like -5 + if (Optarg ~ /^[0-9]+$/) + fcount = (c Optarg) + 0 + else @{ + fcount = c + 0 + Optind-- + @} + @} else + usage() + @} -Others? -@end ignore + if (ARGV[Optind] ~ /^\+[0-9]+$/) @{ + charcount = substr(ARGV[Optind], 2) + 0 + Optind++ + @} -@node Igawk Program, , Simple Sed, Miscellaneous Programs -@subsection An Easy Way to Use Library Functions + for (i = 1; i < Optind; i++) + ARGV[i] = "" -Using library functions in @code{awk} can be very beneficial. It -encourages code re-use and the writing of general functions. Programs are -smaller, and therefore clearer. -However, using library functions is only easy when writing @code{awk} -programs; it is painful when running them, requiring multiple @samp{-f} -options. If @code{gawk} is unavailable, then so too is the @code{AWKPATH} -environment variable and the ability to put @code{awk} functions into a -library directory (@pxref{Options, ,Command Line Options}). + if (repeated_only == 0 && non_repeated_only == 0) + repeated_only = non_repeated_only = 1 + + if (ARGC - Optind == 2) @{ + outputfile = ARGV[ARGC - 1] + ARGV[ARGC - 1] = "" + @} +@} +@c endfile +@end example -It would be nice to be able to write programs like so: +The following function, @code{are_equal}, compares the current line, +@code{$0}, to the +previous line, @code{last}. It handles skipping fields and characters. +If no field count and no character count are specified, @code{are_equal} +simply returns one or zero depending upon the result of a simple string +comparison of @code{last} and @code{$0}. Otherwise, things get more +complicated. +If fields have to be skipped, each line is broken into an array using +@code{split} +(@pxref{String Functions, ,String Manipulation Functions}); +the desired fields are then joined back into a line using @code{join}. +The joined lines are stored in @code{clast} and @code{cline}. +If no fields are skipped, @code{clast} and @code{cline} are set to +@code{last} and @code{$0}, respectively. +Finally, if characters are skipped, @code{substr} is used to strip off the +leading @code{charcount} characters in @code{clast} and @code{cline}. The +two strings are then compared and @code{are_equal} returns the result: @example -# library functions -@@include getopt.awk -@@include join.awk -@dots{} +@c file eg/prog/uniq.awk +function are_equal( n, m, clast, cline, alast, aline) +@{ + if (fcount == 0 && charcount == 0) + return (last == $0) -# main program -BEGIN @{ - while ((c = getopt(ARGC, ARGV, "a:b:cde")) != -1) - @dots{} - @dots{} + if (fcount > 0) @{ + n = split(last, alast) + m = split($0, aline) + clast = join(alast, fcount+1, n) + cline = join(aline, fcount+1, m) + @} else @{ + clast = last + cline = $0 + @} + if (charcount) @{ + clast = substr(clast, charcount + 1) + cline = substr(cline, charcount + 1) + @} + + return (clast == cline) @} +@c endfile @end example -The following program, @file{igawk.sh}, provides this service. -It simulates @code{gawk}'s searching of the @code{AWKPATH} variable, -and also allows @dfn{nested} includes; i.e.@: a file that has been included -with @samp{@@include} can contain further @samp{@@include} statements. -@code{igawk} will make an effort to only include files once, so that nested -includes don't accidentally include a library function twice. +The following two rules are the body of the program. The first one is +executed only for the very first line of data. It sets @code{last} equal to +@code{$0}, so that subsequent lines of text have something to be compared to. -@code{igawk} should behave externally just like @code{gawk}. This means it -should accept all of @code{gawk}'s command line arguments, including the -ability to have multiple source files specified via @samp{-f}, and the -ability to mix command line and library source files. +The second rule does the work. The variable @code{equal} is one or zero, +depending upon the results of @code{are_equal}'s comparison. If @command{uniq} +is counting repeated lines, and the lines are equal, then it increments the @code{count} variable. +Otherwise it prints the line and resets @code{count}, +since the two lines are not equal. + +If @command{uniq} is not counting, and if the lines are equal, @code{count} is incremented. +Nothing is printed, since the point is to remove duplicates. +Otherwise, if @command{uniq} is counting repeated lines and more than +one line is seen, or if @command{uniq} is counting non-repeated lines +and only one line is seen, then the line is printed, and @code{count} +is reset. -The program is written using the POSIX Shell (@code{sh}) command language. -The way the program works is as follows: +Finally, similar logic is used in the @code{END} rule to print the final +line of input data: -@enumerate -@item -Loop through the arguments, saving anything that doesn't represent -@code{awk} source code for later, when the expanded program is run. +@example +@c file eg/prog/uniq.awk +NR == 1 @{ + last = $0 + next +@} -@item -For any arguments that do represent @code{awk} text, put the arguments into -a temporary file that will be expanded. There are two cases. +@{ + equal = are_equal() -@enumerate a -@item -Literal text, provided with @samp{--source} or @samp{--source=}. This -text is just echoed directly. The @code{echo} program will automatically -supply a trailing newline. + if (do_count) @{ # overrides -d and -u + if (equal) + count++ + else @{ + printf("%4d %s\n", count, last) > outputfile + last = $0 + count = 1 # reset + @} + next + @} -@item -File names provided with @samp{-f}. We use a neat trick, and echo -@samp{@@include @var{filename}} into the temporary file. Since the file -inclusion program will work the way @code{gawk} does, this will get the text -of the file included into the program at the correct point. -@end enumerate + if (equal) + count++ + else @{ + if ((repeated_only && count > 1) || + (non_repeated_only && count == 1)) + print last > outputfile + last = $0 + count = 1 + @} +@} -@item -Run an @code{awk} program (naturally) over the temporary file to expand -@samp{@@include} statements. The expanded program is placed in a second -temporary file. +END @{ + if (do_count) + printf("%4d %s\n", count, last) > outputfile + else if ((repeated_only && count > 1) || + (non_repeated_only && count == 1)) + print last > outputfile +@} +@c endfile +@end example -@item -Run the expanded program with @code{gawk} and any other original command line -arguments that the user supplied (such as the data file names). -@end enumerate +@node Wc Program, , Uniq Program, Clones +@subsection Counting Things -The initial part of the program turns on shell tracing if the first -argument was @samp{debug}. Otherwise, a shell @code{trap} statement -arranges to clean up any temporary files on program exit or upon an -interrupt. +@cindex @command{wc} utility +The @command{wc} (word count) utility counts lines, words, and characters in +one or more input files. Its usage is as follows: -@c 2e: For the temp file handling, go with Darrel's ig=${TMP:-/tmp}/igs.$$ -@c 2e: or something as similar as possible. +@example +wc @r{[}-lwc@r{]} @r{[} @var{files} @dots{} @r{]} +@end example -The next part loops through all the command line arguments. -There are several cases of interest. +If no files are specified on the command line, @command{wc} reads its standard +input. If there are multiple files, it also prints total counts for all +the files. The options and their meanings are shown in the following list: @table @code -@item -- -This ends the arguments to @code{igawk}. Anything else should be passed on -to the user's @code{awk} program without being evaluated. - -@item -W -This indicates that the next option is specific to @code{gawk}. To make -argument processing easier, the @samp{-W} is appended to the front of the -remaining arguments and the loop continues. (This is an @code{sh} -programming trick. Don't worry about it if you are not familiar with -@code{sh}.) - -@item -v -@itemx -F -These are saved and passed on to @code{gawk}. - -@item -f -@itemx --file -@itemx --file= -@itemx -Wfile= -The file name is saved to the temporary file @file{/tmp/ig.s.$$} with an -@samp{@@include} statement. -The @code{sed} utility is used to remove the leading option part of the -argument (e.g., @samp{--file=}). +@item -l +Only count lines. -@item --source -@itemx --source= -@itemx -Wsource= -The source text is echoed into @file{/tmp/ig.s.$$}. +@item -w +Only count words. +A ``word'' is a contiguous sequence of non-whitespace characters, separated +by spaces and/or tabs. Happily, this is the normal way @command{awk} separates +fields in its input data. -@item --version -@itemx -Wversion -@code{igawk} prints its version number, and runs @samp{gawk --version} -to get the @code{gawk} version information, and then exits. +@item -c +Only count characters. @end table -If none of @samp{-f}, @samp{--file}, @samp{-Wfile}, @samp{--source}, -or @samp{-Wsource}, were supplied, then the first non-option argument -should be the @code{awk} program. If there are no command line -arguments left, @code{igawk} prints an error message and exits. -Otherwise, the first argument is echoed into @file{/tmp/ig.s.$$}. +Implementing @command{wc} in @command{awk} is particularly elegant, +since @command{awk} does a lot of the work for us; it splits lines into +words (i.e., fields) and counts them, it counts lines (i.e., records), +and it can easily tell us how long a line is. -In any case, after the arguments have been processed, -@file{/tmp/ig.s.$$} contains the complete text of the original @code{awk} -program. +This uses the @code{getopt} library function +(@pxref{Getopt Function, ,Processing Command-Line Options}) +and the file transition functions +(@pxref{Filetrans Function, ,Noting @value{DDF} Boundaries}). -The @samp{$$} in @code{sh} represents the current process ID number. -It is often used in shell programs to generate unique temporary file -names. This allows multiple users to run @code{igawk} without worrying -that the temporary file names will clash. +This version has one notable difference from traditional versions of +@command{wc}: it always prints the counts in the order lines, words, +and characters. Traditional versions note the order of the @option{-l}, +@option{-w}, and @option{-c} options on the command line, and print the +counts in that order. -@cindex @code{sed} utility -Here's the program: +The @code{BEGIN} rule does the argument processing. The variable +@code{print_total} is true if more than one file is named on the +command line: -@findex igawk.sh +@cindex @code{wc.awk} program @example -@c @group -@c file eg/prog/igawk.sh -#! /bin/sh - -# igawk --- like gawk but do @@include processing +@c file eg/prog/wc.awk +# wc.awk --- count lines, words, characters +@c endfile +@ignore +@c file eg/prog/wc.awk +# # Arnold Robbins, arnold@@gnu.org, Public Domain -# July 1993 +# May 1993 +@c endfile +@end ignore +@c file eg/prog/wc.awk -if [ "$1" = debug ] -then - set -x - shift -else - # cleanup on exit, hangup, interrupt, quit, termination - trap 'rm -f /tmp/ig.[se].$$' 0 1 2 3 15 -fi - -while [ $# -ne 0 ] # loop over arguments -do - case $1 in - --) shift; break;; - - -W) shift - set -- -W"$@@" - continue;; - - -[vF]) opts="$opts $1 '$2'" - shift;; - - -[vF]*) opts="$opts '$1'" ;; - - -f) echo @@include "$2" >> /tmp/ig.s.$$ - shift;; - -@group - -f*) f=`echo "$1" | sed 's/-f//'` - echo @@include "$f" >> /tmp/ig.s.$$ ;; -@end group - - -?file=*) # -Wfile or --file - f=`echo "$1" | sed 's/-.file=//'` - echo @@include "$f" >> /tmp/ig.s.$$ ;; - - -?file) # get arg, $2 - echo @@include "$2" >> /tmp/ig.s.$$ - shift;; - - -?source=*) # -Wsource or --source - t=`echo "$1" | sed 's/-.source=//'` - echo "$t" >> /tmp/ig.s.$$ ;; - - -?source) # get arg, $2 - echo "$2" >> /tmp/ig.s.$$ - shift;; - - -?version) - echo igawk: version 1.0 1>&2 - gawk --version - exit 0 ;; - - -[W-]*) opts="$opts '$1'" ;; +# Options: +# -l only count lines +# -w only count words +# -c only count characters +# +# Default is to count lines, words, characters +# +# Requires getopt and file transition library functions - *) break;; - esac - shift -done +BEGIN @{ + # let getopt print a message about + # invalid options. we ignore them + while ((c = getopt(ARGC, ARGV, "lwc")) != -1) @{ + if (c == "l") + do_lines = 1 + else if (c == "w") + do_words = 1 + else if (c == "c") + do_chars = 1 + @} + for (i = 1; i < Optind; i++) + ARGV[i] = "" -if [ ! -s /tmp/ig.s.$$ ] -then - if [ -z "$1" ] - then - echo igawk: no program! 1>&2 - exit 1 - else - echo "$1" > /tmp/ig.s.$$ - shift - fi -fi + # if no options, do all + if (! do_lines && ! do_words && ! do_chars) + do_lines = do_words = do_chars = 1 -# at this point, /tmp/ig.s.$$ has the program + print_total = (ARGC - i > 2) +@} @c endfile -@c @end group @end example -The @code{awk} program to process @samp{@@include} directives reads through -the program, one line at a time using @code{getline} -(@pxref{Getline, ,Explicit Input with @code{getline}}). -The input file names and @samp{@@include} statements are managed using a -stack. As each @samp{@@include} is encountered, the current file name is -``pushed'' onto the stack, and the file named in the @samp{@@include} -directive becomes -the current file name. As each file is finished, the stack is ``popped,'' -and the previous input file becomes the current input file again. -The process is started by making the original file the first one on the -stack. - -The @code{pathto} function does the work of finding the full path to a -file. It simulates @code{gawk}'s behavior when searching the @code{AWKPATH} -environment variable -(@pxref{AWKPATH Variable, ,The @code{AWKPATH} Environment Variable}). -If a file name has a @samp{/} in it, no path search -is done. Otherwise, the file name is concatenated with the name of each -directory in the path, and an attempt is made to open the generated file -name. The only way in @code{awk} to test if a file can be read is to go -ahead and try to read it with @code{getline}; that is what @code{pathto} -does.@footnote{On some very old versions of @code{awk}, the test -@samp{getline junk < t} can loop forever if the file exists but is empty. -Caveat Emptor.} -If the file can be read, it is closed, and the file name is -returned. -@ignore -An alternative way to test for the file's existence would be to call -@samp{system("test -r " t)}, which uses the @code{test} utility to -see if the file exists and is readable. The disadvantage to this method -is that it requires creating an extra process, and can thus be slightly -slower. -@end ignore +The @code{beginfile} function is simple; it just resets the counts of lines, +words, and characters to zero, and saves the current @value{FN} in +@code{fname}: +@c NEXT ED: make it lines = words = chars = 0 @example -@c file eg/prog/igawk.sh -gawk -- ' -# process @@include directives -@c endfile - -@group -@c file eg/prog/igawk.sh -function pathto(file, i, t, junk) +@c file eg/prog/wc.awk +function beginfile(file) @{ - if (index(file, "/") != 0) - return file - - for (i = 1; i <= ndirs; i++) @{ - t = (pathlist[i] "/" file) - if ((getline junk < t) > 0) @{ - # found it - close(t) - return t - @} - @} - return "" + chars = lines = words = 0 + fname = FILENAME @} @c endfile -@end group @end example -The main program is contained inside one @code{BEGIN} rule. The first thing it -does is set up the @code{pathlist} array that @code{pathto} uses. After -splitting the path on @samp{:}, null elements are replaced with @code{"."}, -which represents the current directory. +The @code{endfile} function adds the current file's numbers to the running +totals of lines, words, and characters. It then prints out those numbers +for the file that was just read. It relies on @code{beginfile} to reset the +numbers for the following @value{DF}: +@c NEXT ED: make order for += be lines, words, chars @example +@c file eg/prog/wc.awk +function endfile(file) +@{ + tchars += chars + tlines += lines + twords += words + if (do_lines) + printf "\t%d", lines @group -@c file eg/prog/igawk.sh -BEGIN @{ - path = ENVIRON["AWKPATH"] - ndirs = split(path, pathlist, ":") - for (i = 1; i <= ndirs; i++) @{ - if (pathlist[i] == "") - pathlist[i] = "." - @} -@c endfile + if (do_words) + printf "\t%d", words @end group + if (do_chars) + printf "\t%d", chars + printf "\t%s\n", fname +@} +@c endfile @end example -The stack is initialized with @code{ARGV[1]}, which will be @file{/tmp/ig.s.$$}. -The main loop comes next. Input lines are read in succession. Lines that -do not start with @samp{@@include} are printed verbatim. - -If the line does start with @samp{@@include}, the file name is in @code{$2}. -@code{pathto} is called to generate the full path. If it could not, then we -print an error message and continue. - -The next thing to check is if the file has been included already. The -@code{processed} array is indexed by the full file name of each included -file, and it tracks this information for us. If the file has been -seen, a warning message is printed. Otherwise, the new file name is -pushed onto the stack and processing continues. - -Finally, when @code{getline} encounters the end of the input file, the file -is closed and the stack is popped. When @code{stackptr} is less than zero, -the program is done. +There is one rule that is executed for each line. It adds the length of +the record, plus one, to @code{chars}. Adding one plus the record length +is needed because the newline character separating records (the value +of @code{RS}) is not part of the record itself, and thus not included +in its length. Next, @code{lines} is incremented for each line read, +and @code{words} is incremented by the value of @code{NF}, which is the +number of ``words'' on this line:@footnote{@command{wc} can't just use +the value of @code{FNR} in @code{endfile}. If you examine the code in +@ref{Filetrans Function, ,Noting @value{DDF} Boundaries}, +you will see that @code{FNR} has already been reset by the time +@code{endfile} is called.} +@c ONE DAY: make the above an exercise, instead of giving away the answer. @example -@c @group -@c file eg/prog/igawk.sh - stackptr = 0 - input[stackptr] = ARGV[1] # ARGV[1] is first file - - for (; stackptr >= 0; stackptr--) @{ - while ((getline < input[stackptr]) > 0) @{ - if (tolower($1) != "@@include") @{ - print - continue - @} - fpath = pathto($2) - if (fpath == "") @{ - printf("igawk:%s:%d: cannot find %s\n", \ - input[stackptr], FNR, $2) > "/dev/stderr" - continue - @} -@group - if (! (fpath in processed)) @{ - processed[fpath] = input[stackptr] - input[++stackptr] = fpath - @} else - print $2, "included in", input[stackptr], \ - "already included in", \ - processed[fpath] > "/dev/stderr" - @} -@end group -@group - close(input[stackptr]) - @} -@}' /tmp/ig.s.$$ > /tmp/ig.e.$$ -@end group +@c file eg/prog/wc.awk +# do per line +@{ + chars += length($0) + 1 # get newline + lines++ + words += NF +@} @c endfile -@c @end group @end example -The last step is to call @code{gawk} with the expanded program and the original -options and command line arguments that the user supplied. @code{gawk}'s -exit status is passed back on to @code{igawk}'s calling program. - -@c this causes more problems than it solves, so leave it out. -@ignore -The special file @file{/dev/null} is passed as a data file to @code{gawk} -to handle an interesting case. Suppose that the user's program only has -a @code{BEGIN} rule, and there are no data files to read. The program should exit without reading any data -files. However, suppose that an included library file defines an @code{END} -rule of its own. In this case, @code{gawk} will hang, reading standard -input. In order to avoid this, @file{/dev/null} is explicitly to the -command line. Reading from @file{/dev/null} always returns an immediate -end of file indication. - -@c Hmm. Add /dev/null if $# is 0? Still messes up ARGV. Sigh. -@end ignore +Finally, the @code{END} rule simply prints the totals for all the files. @example -@c @group -@c file eg/prog/igawk.sh -eval gawk -f /tmp/ig.e.$$ $opts -- "$@@" - -exit $? +@c file eg/prog/wc.awk +END @{ + if (print_total) @{ + if (do_lines) + printf "\t%d", tlines + if (do_words) + printf "\t%d", twords + if (do_chars) + printf "\t%d", tchars + print "\ttotal" + @} +@} @c endfile -@c @end group @end example -This version of @code{igawk} represents my third attempt at this program. -There are three key simplifications that made the program work better. +@node Miscellaneous Programs, , Clones, Sample Programs +@section A Grab Bag of @command{awk} Programs -@enumerate -@item -Using @samp{@@include} even for the files named with @samp{-f} makes building -the initial collected @code{awk} program much simpler; all the -@samp{@@include} processing can be done once. +This @value{SECTION} is a large ``grab bag'' of miscellaneous programs. +We hope you find them both interesting and enjoyable. -@item -The @code{pathto} function doesn't try to save the line read with -@code{getline} when testing for the file's accessibility. Trying to save -this line for use with the main program complicates things considerably. -@c what problem does this engender though - exercise -@c answer, reading from "-" or /dev/stdin +@menu +* Dupword Program:: Finding duplicated words in a document. +* Alarm Program:: An alarm clock. +* Translate Program:: A program similar to the @command{tr} utility. +* Labels Program:: Printing mailing labels. +* Word Sorting:: A program to produce a word usage count. +* History Sorting:: Eliminating duplicate entries from a history + file. +* Extract Program:: Pulling out programs from Texinfo source + files. +* Simple Sed:: A Simple Stream Editor. +* Igawk Program:: A wrapper for @command{awk} that includes + files. +@end menu -@item -Using a @code{getline} loop in the @code{BEGIN} rule does it all in one -place. It is not necessary to call out to a separate loop for processing -nested @samp{@@include} statements. -@end enumerate +@node Dupword Program, Alarm Program, Miscellaneous Programs, Miscellaneous Programs +@subsection Finding Duplicated Words in a Document -Also, this program illustrates that it is often worthwhile to combine -@code{sh} and @code{awk} programming together. You can usually accomplish -quite a lot, without having to resort to low-level programming in C or C++, and it -is frequently easier to do certain kinds of string and argument manipulation -using the shell than it is in @code{awk}. +A common error when writing large amounts of prose is to accidentally +duplicate words. Typically you will see this in text as something like ``the +the program does the following @dots{}.'' When the text is online, often +the duplicated words occur at the end of one line and the beginning of +another, making them very difficult to spot. +@c as here! -Finally, @code{igawk} shows that it is not always necessary to add new -features to a program; they can often be layered on top. With @code{igawk}, -there is no real reason to build @samp{@@include} processing into -@code{gawk} itself. +This program, @file{dupword.awk}, scans through a file one line at a time +and looks for adjacent occurrences of the same word. It also saves the last +word on a line (in the variable @code{prev}) for comparison with the first +word on the next line. -As an additional example of this, consider the idea of having two -files in a directory in the search path. +@cindex Texinfo +The first two statements make sure that the line is all lowercase, +so that, for example, ``The'' and ``the'' compare equal to each other. +The next statement replaces non-alphanumeric and non-whitespace characters +with spaces, so that punctuation does not affect the comparison either. +The characters are replaced with spaces so that formatting controls +don't create nonsense words (e.g., the Texinfo @samp{@@code@{NF@}} +becomes @samp{codeNF} if punctuation is simply deleted). The record is +then re-split into fields, yielding just the actual words on the line, +and insuring that there are no empty fields. -@table @file -@item default.awk -This file would contain a set of default library functions, such -as @code{getopt} and @code{assert}. +If there are no fields left after removing all the punctuation, the +current record is skipped. Otherwise, the program loops through each +word, comparing it to the previous one: -@item site.awk -This file would contain library functions that are specific to a site or -installation, i.e.@: locally developed functions. -Having a separate file allows @file{default.awk} to change with -new @code{gawk} releases, without requiring the system administrator to -update it each time by adding the local functions. -@end table +@cindex @code{dupword.awk} program +@example +@c file eg/prog/dupword.awk +# dupword.awk --- find duplicate words in text +@c endfile +@ignore +@c file eg/prog/dupword.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# December 1991 +# Revised October 2000 -One user -@c Karl Berry, karl@ileaf.com, 10/95 -suggested that @code{gawk} be modified to automatically read these files -upon startup. Instead, it would be very simple to modify @code{igawk} -to do this. Since @code{igawk} can process nested @samp{@@include} -directives, @file{default.awk} could simply contain @samp{@@include} -statements for the desired library functions. +@c endfile +@end ignore +@c file eg/prog/dupword.awk +@{ + $0 = tolower($0) + gsub(/[^[:alnum:][:blank:]]/, " "); + $0 = $0 # re-split + if (NF == 0) + next + if ($1 == prev) + printf("%s:%d: duplicate %s\n", + FILENAME, FNR, $1) + for (i = 2; i <= NF; i++) + if ($i == $(i-1)) + printf("%s:%d: duplicate %s\n", + FILENAME, FNR, $i) + prev = $NF +@} +@c endfile +@end example -@c Exercise: make this change +@node Alarm Program, Translate Program, Dupword Program, Miscellaneous Programs +@subsection An Alarm Clock Program +@cindex insomnia, cure for +@cindex Robbins, Arnold +@quotation +@i{Nothing cures insomnia like a ringing alarm clock.}@* +Arnold Robbins +@end quotation -@node Language History, Gawk Summary, Sample Programs, Top -@chapter The Evolution of the @code{awk} Language +The following program is a simple ``alarm clock'' program. +You give it a time of day and an optional message. At the specified time, +it prints the message on the standard output. In addition, you can give it +the number of times to repeat the message as well as a delay between +repetitions. -This @value{DOCUMENT} describes the GNU implementation of @code{awk}, which follows -the POSIX specification. Many @code{awk} users are only familiar -with the original @code{awk} implementation in Version 7 Unix. -(This implementation was the basis for @code{awk} in Berkeley Unix, -through 4.3--Reno. The 4.4 release of Berkeley Unix uses @code{gawk} 2.15.2 -for its version of @code{awk}.) This chapter briefly describes the -evolution of the @code{awk} language, with cross references to other parts -of the @value{DOCUMENT} where you can find more information. +This program uses the @code{gettimeofday} function from +@ref{Gettimeofday Function, ,Managing the Time of Day}. -@menu -* V7/SVR3.1:: The major changes between V7 and System V - Release 3.1. -* SVR4:: Minor changes between System V Releases 3.1 - and 4. -* POSIX:: New features from the POSIX standard. -* BTL:: New features from the Bell Laboratories - version of @code{awk}. -* POSIX/GNU:: The extensions in @code{gawk} not in POSIX - @code{awk}. -@end menu +All the work is done in the @code{BEGIN} rule. The first part is argument +checking and setting of defaults: the delay, the count, and the message to +print. If the user supplied a message without the ASCII BEL +character (known as the ``alert'' character, @code{"\a"}), then it is added to +the message. (On many systems, printing the ASCII BEL generates some sort +of audible alert. Thus when the alarm goes off, the system calls attention +to itself in case the user is not looking at their computer or terminal.): -@node V7/SVR3.1, SVR4, Language History, Language History -@section Major Changes between V7 and SVR3.1 +@cindex @code{alarm.awk} program +@example +@c file eg/prog/alarm.awk +# alarm.awk --- set an alarm +# +# Requires gettimeofday library function +@c endfile +@ignore +@c file eg/prog/alarm.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# May 1993 -The @code{awk} language evolved considerably between the release of -Version 7 Unix (1978) and the new version first made generally available in -System V Release 3.1 (1987). This section summarizes the changes, with -cross-references to further details. +@c endfile +@end ignore +@c file eg/prog/alarm.awk +# usage: alarm time [ "message" [ count [ delay ] ] ] -@itemize @bullet -@item -The requirement for @samp{;} to separate rules on a line -(@pxref{Statements/Lines, ,@code{awk} Statements Versus Lines}). +BEGIN \ +@{ + # Initial argument sanity checking + usage1 = "usage: alarm time ['message' [count [delay]]]" + usage2 = sprintf("\t(%s) time ::= hh:mm", ARGV[1]) -@item -User-defined functions, and the @code{return} statement -(@pxref{User-defined, ,User-defined Functions}). + if (ARGC < 2) @{ + print usage1 > "/dev/stderr" + print usage2 > "/dev/stderr" + exit 1 + @} else if (ARGC == 5) @{ + delay = ARGV[4] + 0 + count = ARGV[3] + 0 + message = ARGV[2] + @} else if (ARGC == 4) @{ + count = ARGV[3] + 0 + message = ARGV[2] + @} else if (ARGC == 3) @{ + message = ARGV[2] + @} else if (ARGV[1] !~ /[0-9]?[0-9]:[0-9][0-9]/) @{ + print usage1 > "/dev/stderr" + print usage2 > "/dev/stderr" + exit 1 + @} -@item -The @code{delete} statement (@pxref{Delete, ,The @code{delete} Statement}). + # set defaults for once we reach the desired time + if (delay == 0) + delay = 180 # 3 minutes +@group + if (count == 0) + count = 5 +@end group + if (message == "") + message = sprintf("\aIt is now %s!\a", ARGV[1]) + else if (index(message, "\a") == 0) + message = "\a" message "\a" +@c endfile +@end example -@item -The @code{do}-@code{while} statement -(@pxref{Do Statement, ,The @code{do}-@code{while} Statement}). +The next @value{SECTION} of code turns the alarm time into hours and minutes, +converts it (if necessary) to a 24-hour clock, and then turns that +time into a count of the seconds since midnight. Next it turns the current +time into a count of seconds since midnight. The difference between the two +is how long to wait before setting off the alarm: -@item -The built-in functions @code{atan2}, @code{cos}, @code{sin}, @code{rand} and -@code{srand} (@pxref{Numeric Functions, ,Numeric Built-in Functions}). +@example +@c file eg/prog/alarm.awk + # split up alarm time + split(ARGV[1], atime, ":") + hour = atime[1] + 0 # force numeric + minute = atime[2] + 0 # force numeric -@item -The built-in functions @code{gsub}, @code{sub}, and @code{match} -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). + # get current broken down time + gettimeofday(now) -@item -The built-in functions @code{close}, and @code{system} -(@pxref{I/O Functions, ,Built-in Functions for Input/Output}). + # if time given is 12-hour hours and it's after that + # hour, e.g., `alarm 5:30' at 9 a.m. means 5:30 p.m., + # then add 12 to real hour + if (hour < 12 && now["hour"] > hour) + hour += 12 -@item -The @code{ARGC}, @code{ARGV}, @code{FNR}, @code{RLENGTH}, @code{RSTART}, -and @code{SUBSEP} built-in variables (@pxref{Built-in Variables}). + # set target time in seconds since midnight + target = (hour * 60 * 60) + (minute * 60) -@item -The conditional expression using the ternary operator @samp{?:} -(@pxref{Conditional Exp, ,Conditional Expressions}). + # get current time in seconds since midnight + current = (now["hour"] * 60 * 60) + \ + (now["minute"] * 60) + now["second"] -@item -The exponentiation operator @samp{^} -(@pxref{Arithmetic Ops, ,Arithmetic Operators}) and its assignment operator -form @samp{^=} (@pxref{Assignment Ops, ,Assignment Expressions}). + # how long to sleep for + naptime = target - current + if (naptime <= 0) @{ + print "time is in the past!" > "/dev/stderr" + exit 1 + @} +@c endfile +@end example -@item -C-compatible operator precedence, which breaks some old @code{awk} -programs (@pxref{Precedence, ,Operator Precedence (How Operators Nest)}). +@cindex @command{sleep} utility +Finally, the program uses the @code{system} function +(@pxref{I/O Functions, ,Input/Output Functions}) +to call the @command{sleep} utility. The @command{sleep} utility simply pauses +for the given number of seconds. If the exit status is not zero, +the program assumes that @command{sleep} was interrupted and exits. If +@command{sleep} exited with an OK status (zero), then the program prints the +message in a loop, again using @command{sleep} to delay for however many +seconds are necessary: -@item -Regexps as the value of @code{FS} -(@pxref{Field Separators, ,Specifying How Fields are Separated}), and as the -third argument to the @code{split} function -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). +@example +@c file eg/prog/alarm.awk + # zzzzzz..... go away if interrupted + if (system(sprintf("sleep %d", naptime)) != 0) + exit 1 -@item -Dynamic regexps as operands of the @samp{~} and @samp{!~} operators -(@pxref{Regexp Usage, ,How to Use Regular Expressions}). + # time to notify! + command = sprintf("sleep %d", delay) + for (i = 1; i <= count; i++) @{ + print message + # if sleep command interrupted, go away + if (system(command) != 0) + break + @} -@item -The escape sequences @samp{\b}, @samp{\f}, and @samp{\r} -(@pxref{Escape Sequences}). -(Some vendors have updated their old versions of @code{awk} to -recognize @samp{\r}, @samp{\b}, and @samp{\f}, but this is not -something you can rely on.) + exit 0 +@} +@c endfile +@end example -@item -Redirection of input for the @code{getline} function -(@pxref{Getline, ,Explicit Input with @code{getline}}). +@node Translate Program, Labels Program, Alarm Program, Miscellaneous Programs +@subsection Transliterating Characters -@item -Multiple @code{BEGIN} and @code{END} rules -(@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}). +@cindex @command{tr} utility +The system @command{tr} utility transliterates characters. For example, it is +often used to map uppercase letters into lowercase for further processing: -@item -Multi-dimensional arrays -(@pxref{Multi-dimensional, ,Multi-dimensional Arrays}). -@end itemize +@example +@var{generate data} | tr 'A-Z' 'a-z' | @var{process data} @dots{} +@end example -@node SVR4, POSIX, V7/SVR3.1, Language History -@section Changes between SVR3.1 and SVR4 +@command{tr} requires two lists of characters.@footnote{On some older +System V systems, +@command{tr} may require that the lists be written as +range expressions enclosed in square brackets (@samp{[a-z]}) and quoted, +to prevent the shell from attempting a @value{FN} expansion. This is +not a feature.} When processing the input, the first character in the +first list is replaced with the first character in the second list, +the second character in the first list is replaced with the second +character in the second list, and so on. If there are more characters +in the ``from'' list than in the ``to'' list, the last character of the +``to'' list is used for the remaining characters in the ``from'' list. -@cindex @code{awk} language, V.4 version -The System V Release 4 version of Unix @code{awk} added these features -(some of which originated in @code{gawk}): +Some time ago, +@c early or mid-1989! +a user proposed that a transliteration function should +be added to @command{gawk}. +@c Wishing to avoid gratuitous new features, +@c at least theoretically +The following program was written to +prove that character transliteration could be done with a user-level +function. This program is not as complete as the system @command{tr} utility +but it does most of the job. + +The @command{translate} program demonstrates one of the few weaknesses +of standard @command{awk}: dealing with individual characters is very +painful, requiring repeated use of the @code{substr}, @code{index}, +and @code{gsub} built-in functions +(@pxref{String Functions, ,String Manipulation Functions}).@footnote{This +program was written before @command{gawk} acquired the ability to +split each character in a string into separate array elements.} +@c Exercise: How might you use this new feature to simplify the program? -@itemize @bullet -@item -The @code{ENVIRON} variable (@pxref{Built-in Variables}). +There are two functions. The first, @code{stranslate}, takes three +arguments: -@item -Multiple @samp{-f} options on the command line -(@pxref{Options, ,Command Line Options}). +@table @code +@item from +A list of characters to translate from. -@item -The @samp{-v} option for assigning variables before program execution begins -(@pxref{Options, ,Command Line Options}). +@item to +A list of characters to translate to. -@item -The @samp{--} option for terminating command line options. +@item target +The string to do the translation on. +@end table -@item -The @samp{\a}, @samp{\v}, and @samp{\x} escape sequences -(@pxref{Escape Sequences}). +Associative arrays make the translation part fairly easy. @code{t_ar} holds +the ``to'' characters, indexed by the ``from'' characters. Then a simple +loop goes through @code{from}, one character at a time. For each character +in @code{from}, if the character appears in @code{target}, @code{gsub} +is used to change it to the corresponding @code{to} character. -@item -A defined return value for the @code{srand} built-in function -(@pxref{Numeric Functions, ,Numeric Built-in Functions}). +The @code{translate} function simply calls @code{stranslate} using @code{$0} +as the target. The main program sets two global variables, @code{FROM} and +@code{TO}, from the command line, and then changes @code{ARGV} so that +@command{awk} reads from the standard input. -@item -The @code{toupper} and @code{tolower} built-in string functions -for case translation -(@pxref{String Functions, ,Built-in Functions for String Manipulation}). +Finally, the processing rule simply calls @code{translate} for each record: -@item -A cleaner specification for the @samp{%c} format-control letter in the -@code{printf} function -(@pxref{Control Letters, ,Format-Control Letters}). +@cindex @code{translate.awk} program +@example +@c file eg/prog/translate.awk +# translate.awk --- do tr-like stuff +@c endfile +@ignore +@c file eg/prog/translate.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# August 1989 -@item -The ability to dynamically pass the field width and precision (@code{"%*.*d"}) -in the argument list of the @code{printf} function -(@pxref{Control Letters, ,Format-Control Letters}). +@c endfile +@end ignore +@c file eg/prog/translate.awk +# Bugs: does not handle things like: tr A-Z a-z, it has +# to be spelled out. However, if `to' is shorter than `from', +# the last character in `to' is used for the rest of `from'. +function stranslate(from, to, target, lf, lt, t_ar, i, c) +@{ + lf = length(from) + lt = length(to) + for (i = 1; i <= lt; i++) + t_ar[substr(from, i, 1)] = substr(to, i, 1) + if (lt < lf) + for (; i <= lf; i++) + t_ar[substr(from, i, 1)] = substr(to, lt, 1) + for (i = 1; i <= lf; i++) @{ + c = substr(from, i, 1) + if (index(target, c) > 0) + gsub(c, t_ar[c], target) + @} + return target +@} + +function translate(from, to) +@{ + return $0 = stranslate(from, to, $0) +@} + +# main program +BEGIN @{ +@group + if (ARGC < 3) @{ + print "usage: translate from to" > "/dev/stderr" + exit + @} +@end group + FROM = ARGV[1] + TO = ARGV[2] + ARGC = 2 + ARGV[1] = "-" +@} + +@{ + translate(FROM, TO) + print +@} +@c endfile +@end example + +While it is possible to do character transliteration in a user-level +function, it is not necessarily efficient, and we (the @command{gawk} +authors) started to consider adding a built-in function. However, +shortly after writing this program, we learned that the System V Release 4 +@command{awk} had added the @code{toupper} and @code{tolower} functions +(@pxref{String Functions, ,String Manipulation Functions}). +These functions handle the vast majority of the +cases where character transliteration is necessary, and so we chose to +simply add those functions to @command{gawk} as well and then leave well +enough alone. + +An obvious improvement to this program would be to set up the +@code{t_ar} array only once, in a @code{BEGIN} rule. However, this +assumes that the ``from'' and ``to'' lists +will never change throughout the lifetime of the program. + +@node Labels Program, Word Sorting, Translate Program, Miscellaneous Programs +@subsection Printing Mailing Labels + +Here is a ``real world''@footnote{``Real world'' is defined as +``a program actually used to get something done.''} +program. This +script reads lists of names and +addresses and generates mailing labels. Each page of labels has 20 labels +on it, two across and ten down. The addresses are guaranteed to be no more +than five lines of data. Each address is separated from the next by a blank +line. + +The basic idea is to read 20 labels worth of data. Each line of each label +is stored in the @code{line} array. The single rule takes care of filling +the @code{line} array and printing the page when 20 labels have been read. + +The @code{BEGIN} rule simply sets @code{RS} to the empty string, so that +@command{awk} splits records at blank lines +(@pxref{Records, ,How Input Is Split into Records}). +It sets @code{MAXLINES} to 100, since 100 is the maximum number +of lines on the page (20 * 5 = 100). + +Most of the work is done in the @code{printpage} function. +The label lines are stored sequentially in the @code{line} array. But they +have to print horizontally; @code{line[1]} next to @code{line[6]}, +@code{line[2]} next to @code{line[7]}, and so on. Two loops are used to +accomplish this. The outer loop, controlled by @code{i}, steps through +every 10 lines of data; this is each row of labels. The inner loop, +controlled by @code{j}, goes through the lines within the row. +As @code{j} goes from 0 to 4, @samp{i+j} is the @code{j}'th line in +the row, and @samp{i+j+5} is the entry next to it. The output ends up +looking something like this: + +@example +line 1 line 6 +line 2 line 7 +line 3 line 8 +line 4 line 9 +line 5 line 10 +@dots{} +@end example + +As a final note, an extra blank line is printed at lines 21 and 61, to keep +the output lined up on the labels. This is dependent on the particular +brand of labels in use when the program was written. You will also note +that there are two blank lines at the top and two blank lines at the bottom. + +The @code{END} rule arranges to flush the final page of labels; there may +not have been an even multiple of 20 labels in the data: + +@cindex @code{labels.awk} program +@example +@c file eg/prog/labels.awk +# labels.awk --- print mailing labels +@c endfile +@ignore +@c file eg/prog/labels.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# June 1992 +@c endfile +@end ignore +@c file eg/prog/labels.awk + +# Each label is 5 lines of data that may have blank lines. +# The label sheets have 2 blank lines at the top and 2 at +# the bottom. + +BEGIN @{ RS = "" ; MAXLINES = 100 @} + +function printpage( i, j) +@{ + if (Nlines <= 0) + return + + printf "\n\n" # header + + for (i = 1; i <= Nlines; i += 10) @{ + if (i == 21 || i == 61) + print "" + for (j = 0; j < 5; j++) @{ + if (i + j > MAXLINES) + break + printf " %-41s %s\n", line[i+j], line[i+j+5] + @} + print "" + @} + + printf "\n\n" # footer + + for (i in line) + line[i] = "" +@} + +# main rule +@{ + if (Count >= 20) @{ + printpage() + Count = 0 + Nlines = 0 + @} + n = split($0, a, "\n") + for (i = 1; i <= n; i++) + line[++Nlines] = a[i] + for (; i <= 5; i++) + line[++Nlines] = "" + Count++ +@} + +END \ +@{ + printpage() +@} +@c endfile +@end example + +@node Word Sorting, History Sorting, Labels Program, Miscellaneous Programs +@subsection Generating Word Usage Counts + +@c NEXT ED: Rewrite this whole section and example +The following @command{awk} program prints +the number of occurrences of each word in its input. It illustrates the +associative nature of @command{awk} arrays by using strings as subscripts. It +also demonstrates the @samp{for @var{index} in @var{array}} mechanism. +Finally, it shows how @command{awk} is used in conjunction with other +utility programs to do a useful task of some complexity with a minimum of +effort. Some explanations follow the program listing: + +@example +# Print list of word frequencies +@{ + for (i = 1; i <= NF; i++) + freq[$i]++ +@} + +END @{ + for (word in freq) + printf "%s\t%d\n", word, freq[word] +@} +@end example + +@c Exercise: Use asort() here + +This program has two rules. The +first rule, because it has an empty pattern, is executed for every input line. +It uses @command{awk}'s field-accessing mechanism +(@pxref{Fields, ,Examining Fields}) to pick out the individual words from +the line, and the built-in variable @code{NF} (@pxref{Built-in Variables}) +to know how many fields are available. +For each input word, it increments an element of the array @code{freq} to +reflect that the word has been seen an additional time. + +The second rule, because it has the pattern @code{END}, is not executed +until the input has been exhausted. It prints out the contents of the +@code{freq} table that has been built up inside the first action. +This program has several problems that would prevent it from being +useful by itself on real text files: + +@itemize @bullet @item -The use of regexp constants such as @code{/foo/} as expressions, where -they are equivalent to using the matching operator, as in @samp{$0 ~ /foo/} -(@pxref{Using Constant Regexps, ,Using Regular Expression Constants}). +Words are detected using the @command{awk} convention that fields are +separated just by whitespace. Other characters in the input (except +newlines) don't have any special meaning to @command{awk}. This means that +punctuation characters count as part of words. + +@item +The @command{awk} language considers upper- and lowercase characters to be +distinct. Therefore, ``bartender'' and ``Bartender'' are not treated +as the same word. This is undesirable, since in normal text, words +are capitalized if they begin sentences, and a frequency analyzer should not +be sensitive to capitalization. + +@item +The output does not come out in any useful order. You're more likely to be +interested in which words occur most frequently or in having an alphabetized +table of how frequently each word occurs. @end itemize -@node POSIX, BTL, SVR4, Language History -@section Changes between SVR4 and POSIX @code{awk} +@cindex @command{sort} utility +The way to solve these problems is to use some of @command{awk}'s more advanced +features. First, we use @code{tolower} to remove +case distinctions. Next, we use @code{gsub} to remove punctuation +characters. Finally, we use the system @command{sort} utility to process the +output of the @command{awk} script. Here is the new version of +the program: + +@cindex @code{wordfreq.awk} program +@example +@c file eg/prog/wordfreq.awk +# wordfreq.awk --- print list of word frequencies + +@{ + $0 = tolower($0) # remove case distinctions + # remove punctuation + gsub(/[^[:alnum:]_[:blank:]]/, "", $0) + for (i = 1; i <= NF; i++) + freq[$i]++ +@} + +END @{ + for (word in freq) + printf "%s\t%d\n", word, freq[word] +@} +@c endfile +@end example + +Assuming we have saved this program in a file named @file{wordfreq.awk}, +and that the data is in @file{file1}, the following pipeline: + +@example +awk -f wordfreq.awk file1 | sort +1 -nr +@end example + +@noindent +produces a table of the words appearing in @file{file1} in order of +decreasing frequency. The @command{awk} program suitably massages the +data and produces a word frequency table, which is not ordered. + +The @command{awk} script's output is then sorted by the @command{sort} +utility and printed on the terminal. The options given to @command{sort} +specify a sort that uses the second field of each input line (skipping +one field), that the sort keys should be treated as numeric quantities +(otherwise @samp{15} would come before @samp{5}), and that the sorting +should be done in descending (reverse) order. + +The @command{sort} could even be done from within the program, by changing +the @code{END} action to: + +@example +@c file eg/prog/wordfreq.awk +END @{ + sort = "sort +1 -nr" + for (word in freq) + printf "%s\t%d\n", word, freq[word] | sort + close(sort) +@} +@c endfile +@end example + +This way of sorting must be used on systems that do not +have true pipes at the command-line (or batch-file) level. +See the general operating system documentation for more information on how +to use the @command{sort} program. + +@node History Sorting, Extract Program, Word Sorting, Miscellaneous Programs +@subsection Removing Duplicates from Unsorted Text + +The @command{uniq} program +(@pxref{Uniq Program, ,Printing Non-Duplicated Lines of Text}), +removes duplicate lines from @emph{sorted} data. + +Suppose, however, you need to remove duplicate lines from a @value{DF} but +that you want to preserve the order the lines are in. A good example of +this might be a shell history file. The history file keeps a copy of all +the commands you have entered, and it is not unusual to repeat a command +several times in a row. Occasionally you might want to compact the history +by removing duplicate entries. Yet it is desirable to maintain the order +of the original commands. + +This simple program does the job. It uses two arrays. The @code{data} +array is indexed by the text of each line. +For each line, @code{data[$0]} is incremented. +If a particular line has not +been seen before, then @code{data[$0]} is zero. +In this case, the text of the line is stored in @code{lines[count]}. +Each element of @code{lines} is a unique command, and the indices of +@code{lines} indicate the order in which those lines are encountered. +The @code{END} rule simply prints out the lines, in order: + +@cindex Rakitzis, Byron +@cindex @code{histsort.awk} program +@example +@c file eg/prog/histsort.awk +# histsort.awk --- compact a shell history file +# Thanks to Byron Rakitzis for the general idea +@c endfile +@ignore +@c file eg/prog/histsort.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# May 1993 + +@c endfile +@end ignore +@c file eg/prog/histsort.awk +@group +@{ + if (data[$0]++ == 0) + lines[++count] = $0 +@} +@end group + +END @{ + for (i = 1; i <= count; i++) + print lines[i] +@} +@c endfile +@end example + +This program also provides a foundation for generating other useful +information. For example, using the following @code{print} statement in the +@code{END} rule indicates how often a particular command is used: + +@example +print data[lines[i]], lines[i] +@end example + +This works because @code{data[$0]} is incremented each time a line is +seen. + +@node Extract Program, Simple Sed, History Sorting, Miscellaneous Programs +@subsection Extracting Programs from Texinfo Source Files + +@ifnotinfo +Both this chapter and the previous chapter +(@ref{Library Functions, ,A Library of @command{awk} Functions}) +present a large number of @command{awk} programs. +@end ifnotinfo +@ifinfo +The nodes +@ref{Library Functions, ,A Library of @command{awk} Functions}, +and @ref{Sample Programs, ,Practical @command{awk} Programs}, +are the top level nodes for a large number of @command{awk} programs. +@end ifinfo +If you want to experiment with these programs, it is tedious to have to type +them in by hand. Here we present a program that can extract parts of a +Texinfo input file into separate files. + +@cindex Texinfo +This @value{DOCUMENT} is written in Texinfo, the GNU project's document +formatting +language. +A single Texinfo source file can be used to produce both +printed and online documentation. +@ifnotinfo +Texinfo is fully documented in the book +@cite{Texinfo---The GNU Documentation Format}, +available from the Free Software Foundation. +@end ifnotinfo +@ifinfo +The Texinfo language is described fully, starting with +@ref{Top}. +@end ifinfo -The POSIX Command Language and Utilities standard for @code{awk} -introduced the following changes into the language: +For our purposes, it is enough to know three things about Texinfo input +files: @itemize @bullet @item -The use of @samp{-W} for implementation-specific options. - -@item -The use of @code{CONVFMT} for controlling the conversion of numbers -to strings (@pxref{Conversion, ,Conversion of Strings and Numbers}). +The ``at'' symbol (@samp{@@}) is special in Texinfo, much as +the backslash (@samp{\}) is in C +or @command{awk}. Literal @samp{@@} symbols are represented in Texinfo source +files as @samp{@@@@}. @item -The concept of a numeric string, and tighter comparison rules to go -with it (@pxref{Typing and Comparison, ,Variable Typing and Comparison Expressions}). +Comments start with either @samp{@@c} or @samp{@@comment}. +The file extraction program works by using special comments that start +at the beginning of a line. @item -More complete documentation of many of the previously undocumented -features of the language. +Lines containing @samp{@@group} and @samp{@@end group} commands bracket +example text that should not be split across a page boundary. +(Unfortunately, @TeX{} isn't always smart enough to do things exactly right +and we have to give it some help.) @end itemize -The following common extensions are not permitted by the POSIX -standard: +The following program, @file{extract.awk}, reads through a Texinfo source +file and does two things, based on the special comments. +Upon seeing @samp{@w{@@c system @dots{}}}, +it runs a command, by extracting the command text from the +control line and passing it on to the @code{system} function +(@pxref{I/O Functions, ,Input/Output Functions}). +Upon seeing @samp{@@c file @var{filename}}, each subsequent line is sent to +the file @var{filename}, until @samp{@@c endfile} is encountered. +The rules in @file{extract.awk} match either @samp{@@c} or +@samp{@@comment} by letting the @samp{omment} part be optional. +Lines containing @samp{@@group} and @samp{@@end group} are simply removed. +@file{extract.awk} uses the @code{join} library function +(@pxref{Join Function, ,Merging an Array into a String}). -@c IMPORTANT! Keep this list in sync with the one in node Options +The example programs in the online Texinfo source for @cite{@value{TITLE}} +(@file{gawk.texi}) have all been bracketed inside @samp{file} and +@samp{endfile} lines. The @command{gawk} distribution uses a copy of +@file{extract.awk} to extract the sample programs and install many +of them in a standard directory where @command{gawk} can find them. +The Texinfo file looks something like this: -@itemize @bullet -@item -@code{\x} escape sequences are not recognized -(@pxref{Escape Sequences}). +@example +@dots{} +This program has a @@code@{BEGIN@} rule, +that prints a nice message: -@item -Newlines do not act as whitespace to separate fields when @code{FS} is -equal to a single space. +@@example +@@c file examples/messages.awk +BEGIN @@@{ print "Don't panic!" @@@} +@@c end file +@@end example -@item -The synonym @code{func} for the keyword @code{function} is not -recognized (@pxref{Definition Syntax, ,Function Definition Syntax}). +It also prints some final advice: -@item -The operators @samp{**} and @samp{**=} cannot be used in -place of @samp{^} and @samp{^=} (@pxref{Arithmetic Ops, ,Arithmetic Operators}, -and also @pxref{Assignment Ops, ,Assignment Expressions}). +@@example +@@c file examples/messages.awk +END @@@{ print "Always avoid bored archeologists!" @@@} +@@c end file +@@end example +@dots{} +@end example -@item -Specifying @samp{-Ft} on the command line does not set the value -of @code{FS} to be a single tab character -(@pxref{Field Separators, ,Specifying How Fields are Separated}). +@file{extract.awk} begins by setting @code{IGNORECASE} to one, so that +mixed upper- and lowercase letters in the directives won't matter. -@item -The @code{fflush} built-in function is not supported -(@pxref{I/O Functions, , Built-in Functions for Input/Output}). -@end itemize +The first rule handles calling @code{system}, checking that a command is +given (@code{NF} is at least three) and also checking that the command +exits with a zero exit status, signifying OK: -@node BTL, POSIX/GNU, POSIX, Language History -@section Extensions in the Bell Laboratories @code{awk} +@cindex @code{extract.awk} program +@example +@c file eg/prog/extract.awk +# extract.awk --- extract files and run programs +# from texinfo files +@c endfile +@ignore +@c file eg/prog/extract.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# May 1993 +# Revised September 2000 -@cindex Kernighan, Brian -Brian Kernighan, one of the original designers of Unix @code{awk}, -has made his version available via anonymous @code{ftp} -(@pxref{Other Versions, ,Other Freely Available @code{awk} Implementations}). -This section describes extensions in his version of @code{awk} that are -not in POSIX @code{awk}. +@c endfile +@end ignore +@c file eg/prog/extract.awk +BEGIN @{ IGNORECASE = 1 @} -@itemize @bullet -@item -The @samp{-mf @var{NNN}} and @samp{-mr @var{NNN}} command line options -to set the maximum number of fields, and the maximum -record size, respectively -(@pxref{Options, ,Command Line Options}). +/^@@c(omment)?[ \t]+system/ \ +@{ + if (NF < 3) @{ + e = (FILENAME ":" FNR) + e = (e ": badly formed `system' line") + print e > "/dev/stderr" + next + @} + $1 = "" + $2 = "" + stat = system($0) + if (stat != 0) @{ + e = (FILENAME ":" FNR) + e = (e ": warning: system returned " stat) + print e > "/dev/stderr" + @} +@} +@c endfile +@end example -@item -The @code{fflush} built-in function for flushing buffered output -(@pxref{I/O Functions, ,Built-in Functions for Input/Output}). +@noindent +The variable @code{e} is used so that the function +fits nicely on the +@ifnotinfo +page. +@end ifnotinfo +@ifnottex +screen. +@end ifnottex + +The second rule handles moving data into files. It verifies that a +@value{FN} is given in the directive. If the file named is not the +current file, then the current file is closed. Keeping the current file +open until a new file is encountered allows the use of the @samp{>} +redirection for printing the contents, keeping open file management +simple. + +The @samp{for} loop does the work. It reads lines using @code{getline} +(@pxref{Getline, ,Explicit Input with @code{getline}}). +For an unexpected end of file, it calls the @code{@w{unexpected_eof}} +function. If the line is an ``endfile'' line, then it breaks out of +the loop. +If the line is an @samp{@@group} or @samp{@@end group} line, then it +ignores it and goes on to the next line. +Similarly, comments within examples are also ignored. + +Most of the work is in the following few lines. If the line has no @samp{@@} +symbols, the program can print it directly. +Otherwise, each leading @samp{@@} must be stripped off. +To remove the @samp{@@} symbols, the line is split into separate elements of +the array @code{a}, using the @code{split} function +(@pxref{String Functions, ,String Manipulation Functions}). +The @samp{@@} symbol is used as the separator character. +Each element of @code{a} that is empty indicates two successive @samp{@@} +symbols in the original line. For each two empty elements (@samp{@@@@} in +the original file), we have to add a single @samp{@@} symbol back in. + +When the processing of the array is finished, @code{join} is called with the +value of @code{SUBSEP}, to rejoin the pieces back into a single +line. That line is then printed to the output file: + +@example +@c file eg/prog/extract.awk +/^@@c(omment)?[ \t]+file/ \ +@{ + if (NF != 3) @{ + e = (FILENAME ":" FNR ": badly formed `file' line") + print e > "/dev/stderr" + next + @} + if ($3 != curfile) @{ + if (curfile != "") + close(curfile) + curfile = $3 + @} + + for (;;) @{ + if ((getline line) <= 0) + unexpected_eof() + if (line ~ /^@@c(omment)?[ \t]+endfile/) + break + else if (line ~ /^@@(end[ \t]+)?group/) + continue + else if (line ~ /^@@c(omment+)?[ \t]+/) + continue + if (index(line, "@@") == 0) @{ + print line > curfile + continue + @} + n = split(line, a, "@@") + # if a[1] == "", means leading @@, + # don't add one back in. + for (i = 2; i <= n; i++) @{ + if (a[i] == "") @{ # was an @@@@ + a[i] = "@@" + if (a[i+1] == "") + i++ + @} + @} + print join(a, 1, n, SUBSEP) > curfile + @} +@} +@c endfile +@end example + +An important thing to note is the use of the @samp{>} redirection. +Output done with @samp{>} only opens the file once; it stays open and +subsequent output is appended to the file +(@pxref{Redirection, , Redirecting Output of @code{print} and @code{printf}}). +This makes it easy to mix program text and explanatory prose for the same +sample source file (as has been done here!) without any hassle. The file is +only closed when a new data @value{FN} is encountered or at the end of the +input file. + +Finally, the function @code{@w{unexpected_eof}} prints an appropriate +error message and then exits. +The @code{END} rule handles the final cleanup, closing the open file: + +@c function lb put on same line for page breaking. sigh +@example +@c file eg/prog/extract.awk +@group +function unexpected_eof() @{ + printf("%s:%d: unexpected EOF or error\n", + FILENAME, FNR) > "/dev/stderr" + exit 1 +@} +@end group + +END @{ + if (curfile) + close(curfile) +@} +@c endfile +@end example + +@node Simple Sed, Igawk Program, Extract Program, Miscellaneous Programs +@subsection A Simple Stream Editor + +@cindex @command{sed} utility +@cindex stream editor +The @command{sed} utility is a ``stream editor,'' a program that reads a +stream of data, makes changes to it, and passes it on. +It is often used to make global changes to a large file or to a stream +of data generated by a pipeline of commands. +While @command{sed} is a complicated program in its own right, its most common +use is to perform global substitutions in the middle of a pipeline: +@example +command1 < orig.data | sed 's/old/new/g' | command2 > result +@end example + +Here, @samp{s/old/new/g} tells @command{sed} to look for the regexp +@samp{old} on each input line and globally replace it with the text +@samp{new}, (i.e., all the occurrences on a line). This is similar to +@command{awk}'s @code{gsub} function +(@pxref{String Functions, ,String Manipulation Functions}). + +The following program, @file{awksed.awk}, accepts at least two command-line +arguments: the pattern to look for and the text to replace it with. Any +additional arguments are treated as data @value{FN}s to process. If none +are provided, the standard input is used: + +@cindex Brennan, Michael +@cindex @command{awksed.awk} program +@cindex simple stream editor +@cindex stream editor, simple +@example +@c file eg/prog/awksed.awk +# awksed.awk --- do s/foo/bar/g using just print +# Thanks to Michael Brennan for the idea +@c endfile @ignore -@item -The @code{SYMTAB} array, that allows access to the internal symbol -table of @code{awk}. This feature is not documented, largely because -it is somewhat shakily implemented. For instance, you cannot access arrays -or array elements through it. +@c file eg/prog/awksed.awk +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# August 1995 + +@c endfile @end ignore -@end itemize +@c file eg/prog/awksed.awk +function usage() +@{ + print "usage: awksed pat repl [files...]" > "/dev/stderr" + exit 1 +@} + +BEGIN @{ + # validate arguments + if (ARGC < 3) + usage() -@node POSIX/GNU, , BTL, Language History -@section Extensions in @code{gawk} Not in POSIX @code{awk} + RS = ARGV[1] + ORS = ARGV[2] -@cindex compatibility mode -The GNU implementation, @code{gawk}, adds a number of features. -This sections lists them in the order they were added to @code{gawk}. -They can all be disabled with either the @samp{--traditional} or -@samp{--posix} options -(@pxref{Options, ,Command Line Options}). + # don't use arguments as files + ARGV[1] = ARGV[2] = "" +@} + +@group +# look ma, no hands! +@{ + if (RT == "") + printf "%s", $0 + else + print +@} +@end group +@c endfile +@end example -Version 2.10 of @code{gawk} introduced these features: +The program relies on @command{gawk}'s ability to have @code{RS} be a regexp, +as well as on the setting of @code{RT} to the actual text that terminates the +record (@pxref{Records, ,How Input Is Split into Records}). -@itemize @bullet -@item -The @code{AWKPATH} environment variable for specifying a path search for -the @samp{-f} command line option -(@pxref{Options, ,Command Line Options}). +The idea is to have @code{RS} be the pattern to look for. @command{gawk} +automatically sets @code{$0} to the text between matches of the pattern. +This is text that we want to keep, unmodified. Then, by setting @code{ORS} +to the replacement text, a simple @code{print} statement outputs the +text we want to keep, followed by the replacement text. -@item -The @code{IGNORECASE} variable and its effects -(@pxref{Case-sensitivity, ,Case-sensitivity in Matching}). +There is one wrinkle to this scheme, which is what to do if the last record +doesn't end with text that matches @code{RS}. Using a @code{print} +statement unconditionally prints the replacement text, which is not correct. +However, if the file did not end in text that matches @code{RS}, @code{RT} +is set to the null string. In this case, we can print @code{$0} using +@code{printf} +(@pxref{Printf, ,Using @code{printf} Statements for Fancier Printing}). -@item -The @file{/dev/stdin}, @file{/dev/stdout}, @file{/dev/stderr}, and -@file{/dev/fd/@var{n}} file name interpretation -(@pxref{Special Files, ,Special File Names in @code{gawk}}). -@end itemize +The @code{BEGIN} rule handles the setup, checking for the right number +of arguments and calling @code{usage} if there is a problem. Then it sets +@code{RS} and @code{ORS} from the command-line arguments and sets +@code{ARGV[1]} and @code{ARGV[2]} to the null string, so that they are +not treated as @value{FN}s +(@pxref{ARGC and ARGV, , Using @code{ARGC} and @code{ARGV}}). -Version 2.13 of @code{gawk} introduced these features: +The @code{usage} function prints an error message and exits. +Finally, the single rule handles the printing scheme outlined above, +using @code{print} or @code{printf} as appropriate, depending upon the +value of @code{RT}. -@itemize @bullet -@item -The @code{FIELDWIDTHS} variable and its effects -(@pxref{Constant Size, ,Reading Fixed-width Data}). +@ignore +Exercise, compare the performance of this version with the more +straightforward: -@item -The @code{systime} and @code{strftime} built-in functions for obtaining -and printing time stamps -(@pxref{Time Functions, ,Functions for Dealing with Time Stamps}). +BEGIN { + pat = ARGV[1] + repl = ARGV[2] + ARGV[1] = ARGV[2] = "" +} -@item -The @samp{-W lint} option to provide source code and run time error -and portability checking -(@pxref{Options, ,Command Line Options}). +{ gsub(pat, repl); print } -@item -The @samp{-W compat} option to turn off these extensions -(@pxref{Options, ,Command Line Options}). +Exercise: what are the advantages and disadvantages of this version vs. sed? + Advantage: egrep regexps + speed (?) + Disadvantage: no & in replacement text -@item -The @samp{-W posix} option for full POSIX compliance -(@pxref{Options, ,Command Line Options}). -@end itemize +Others? +@end ignore -Version 2.14 of @code{gawk} introduced these features: +@node Igawk Program, , Simple Sed, Miscellaneous Programs +@subsection An Easy Way to Use Library Functions -@itemize @bullet -@item -The @code{next file} statement for skipping to the next data file -(@pxref{Nextfile Statement, ,The @code{nextfile} Statement}). -@end itemize +Using library functions in @command{awk} can be very beneficial. It +encourages code reuse and the writing of general functions. Programs are +smaller and therefore clearer. +However, using library functions is only easy when writing @command{awk} +programs; it is painful when running them, requiring multiple @option{-f} +options. If @command{gawk} is unavailable, then so too is the @env{AWKPATH} +environment variable and the ability to put @command{awk} functions into a +library directory (@pxref{Options, ,Command-Line Options}). +It would be nice to be able to write programs in the following manner: -Version 2.15 of @code{gawk} introduced these features: +@example +# library functions +@@include getopt.awk +@@include join.awk +@dots{} -@itemize @bullet -@item -The @code{ARGIND} variable, that tracks the movement of @code{FILENAME} -through @code{ARGV} (@pxref{Built-in Variables}). +# main program +BEGIN @{ + while ((c = getopt(ARGC, ARGV, "a:b:cde")) != -1) + @dots{} + @dots{} +@} +@end example -@item -The @code{ERRNO} variable, that contains the system error message when -@code{getline} returns @minus{}1, or when @code{close} fails -(@pxref{Built-in Variables}). +The following program, @file{igawk.sh}, provides this service. +It simulates @command{gawk}'s searching of the @env{AWKPATH} variable +and also allows @dfn{nested} includes; i.e., a file that is included +with @samp{@@include} can contain further @samp{@@include} statements. +@command{igawk} makes an effort to only include files once, so that nested +includes don't accidentally include a library function twice. -@item -The ability to use GNU-style long named options that start with @samp{--} -(@pxref{Options, ,Command Line Options}). +@command{igawk} should behave just like @command{gawk} externally. This +means it should accept all of @command{gawk}'s command-line arguments, +including the ability to have multiple source files specified via +@option{-f}, and the ability to mix command-line and library source files. -@item -The @samp{--source} option for mixing command line and library -file source code -(@pxref{Options, ,Command Line Options}). +The program is written using the POSIX Shell (@command{sh}) command language. +The way the program works is as follows: +@enumerate @item -The @file{/dev/pid}, @file{/dev/ppid}, @file{/dev/pgrpid}, and -@file{/dev/user} file name interpretation -(@pxref{Special Files, ,Special File Names in @code{gawk}}). -@end itemize - -Version 3.0 of @code{gawk} introduced these features: +Loop through the arguments, saving anything that doesn't represent +@command{awk} source code for later, when the expanded program is run. -@itemize @bullet @item -The @code{next file} statement became @code{nextfile} -(@pxref{Nextfile Statement, ,The @code{nextfile} Statement}). +For any arguments that do represent @command{awk} text, put the arguments into +a temporary file that will be expanded. There are two cases: +@enumerate a @item -The @samp{--lint-old} option to -warn about constructs that are not available in -the original Version 7 Unix version of @code{awk} -(@pxref{V7/SVR3.1, , Major Changes between V7 and SVR3.1}). +Literal text, provided with @option{--source} or @option{--source=}. This +text is just echoed directly. The @command{echo} program automatically +supplies a trailing newline. @item -The @samp{--traditional} option was added as a better name for -@samp{--compat} (@pxref{Options, ,Command Line Options}). +Source @value{FN}s provided with @option{-f}. We use a neat trick and echo +@samp{@@include @var{filename}} into the temporary file. Since the file +inclusion program works the way @command{gawk} does, this gets the text +of the file included into the program at the correct point. +@end enumerate @item -The ability for @code{FS} to be a null string, and for the third -argument to @code{split} to be the null string -(@pxref{Single Character Fields, , Making Each Character a Separate Field}). +Run an @command{awk} program (naturally) over the temporary file to expand +@samp{@@include} statements. The expanded program is placed in a second +temporary file. @item -The ability for @code{RS} to be a regexp -(@pxref{Records, , How Input is Split into Records}). +Run the expanded program with @command{gawk} and any other original command-line +arguments that the user supplied (such as the data @value{FN}s). +@end enumerate -@item -The @code{RT} variable -(@pxref{Records, , How Input is Split into Records}). +The initial part of the program turns on shell tracing if the first +argument is @samp{debug}. Otherwise, a shell @code{trap} statement +arranges to clean up any temporary files on program exit or upon an +interrupt. -@item -The @code{gensub} function for more powerful text manipulation -(@pxref{String Functions, , Built-in Functions for String Manipulation}). +@c 2e: For the temp file handling, go with Darrel's ig=${TMP:-/tmp}/igs.$$ +@c 2e: or something as similar as possible. -@item -The @code{strftime} function acquired a default time format, -allowing it to be called with no arguments -(@pxref{Time Functions, , Functions for Dealing with Time Stamps}). +The next part loops through all the command-line arguments. +There are several cases of interest: -@item -Full support for both POSIX and GNU regexps -(@pxref{Regexp, , Regular Expressions}). +@table @code +@item -- +This ends the arguments to @command{igawk}. Anything else should be passed on +to the user's @command{awk} program without being evaluated. -@item -The @samp{--re-interval} option to provide interval expressions in regexps -(@pxref{Regexp Operators, , Regular Expression Operators}). +@item -W +This indicates that the next option is specific to @command{gawk}. To make +argument processing easier, the @option{-W} is appended to the front of the +remaining arguments and the loop continues. (This is an @command{sh} +programming trick. Don't worry about it if you are not familiar with +@command{sh}.) -@item -@code{IGNORECASE} changed, now applying to string comparison as well -as regexp operations -(@pxref{Case-sensitivity, ,Case-sensitivity in Matching}). +@item -v@r{,} -F +These are saved and passed on to @command{gawk}. -@item -The @samp{-m} option and the @code{fflush} function from the -Bell Labs research version of @code{awk} -(@pxref{Options, ,Command Line Options}; also -@pxref{I/O Functions, ,Built-in Functions for Input/Output}). +@item -f@r{,} --file@r{,} --file=@r{,} -Wfile= +The @value{FN} is saved to the temporary file @file{/tmp/ig.s.$$} with an +@samp{@@include} statement. +The @command{sed} utility is used to remove the leading option part of the +argument (e.g., @samp{--file=}). -@item -The use of GNU Autoconf to control the configuration process -(@pxref{Quick Installation, , Compiling @code{gawk} for Unix}). +@item --source@r{,} --source=@r{,} -Wsource= +The source text is echoed into @file{/tmp/ig.s.$$}. -@item -Amiga support -(@pxref{Amiga Installation, ,Installing @code{gawk} on an Amiga}). +@item --version@r{,} -Wversion +@command{igawk} prints its version number, runs @samp{gawk --version} +to get the @command{gawk} version information, and then exits. +@end table -@c XXX ADD MORE STUFF HERE +If none of the @option{-f}, @option{--file}, @option{-Wfile}, @option{--source}, +or @option{-Wsource} arguments are supplied, then the first non-option argument +should be the @command{awk} program. If there are no command-line +arguments left, @command{igawk} prints an error message and exits. +Otherwise, the first argument is echoed into @file{/tmp/ig.s.$$}. +In any case, after the arguments have been processed, +@file{/tmp/ig.s.$$} contains the complete text of the original @command{awk} +program. -@end itemize +@cindex @command{sed} utility +@cindex stream editor +The @samp{$$} in @command{sh} represents the current process ID number. +It is often used in shell programs to generate unique temporary @value{FN}s. +This allows multiple users to run @command{igawk} without worrying +that the temporary @value{FN}s will clash. +The program is as follows: -@node Gawk Summary, Installation, Language History, Top -@appendix @code{gawk} Summary +@cindex @code{igawk.sh} program +@example +@c file eg/prog/igawk.sh +#! /bin/sh +# igawk --- like gawk but do @@include processing +@c endfile +@ignore +@c file eg/prog/igawk.sh +# +# Arnold Robbins, arnold@@gnu.org, Public Domain +# July 1993 -This appendix provides a brief summary of the @code{gawk} command line and the -@code{awk} language. It is designed to serve as ``quick reference.'' It is -therefore terse, but complete. +@c endfile +@end ignore +@c file eg/prog/igawk.sh +if [ "$1" = debug ] +then + set -x + shift +else + # cleanup on exit, hangup, interrupt, quit, termination + trap 'rm -f /tmp/ig.[se].$$' 0 1 2 3 15 +fi -@menu -* Command Line Summary:: Recapitulation of the command line. -* Language Summary:: A terse review of the language. -* Variables/Fields:: Variables, fields, and arrays. -* Rules Summary:: Patterns and Actions, and their component - parts. -* Actions Summary:: Quick overview of actions. -* Functions Summary:: Defining and calling functions. -* Historical Features:: Some undocumented but supported ``features''. -@end menu +while [ $# -ne 0 ] # loop over arguments +do + case $1 in + --) shift; break;; -@node Command Line Summary, Language Summary, Gawk Summary, Gawk Summary -@appendixsec Command Line Options Summary + -W) shift + set -- -W"$@@" + continue;; -The command line consists of options to @code{gawk} itself, the -@code{awk} program text (if not supplied via the @samp{-f} option), and -values to be made available in the @code{ARGC} and @code{ARGV} -predefined @code{awk} variables: + -[vF]) opts="$opts $1 '$2'" + shift;; -@example -gawk @r{[@var{POSIX or GNU style options}]} -f @var{source-file} @r{[@code{--}]} @var{file} @dots{} -gawk @r{[@var{POSIX or GNU style options}]} @r{[@code{--}]} '@var{program}' @var{file} @dots{} -@end example + -[vF]*) opts="$opts '$1'" ;; -The options that @code{gawk} accepts are: + -f) echo @@include "$2" >> /tmp/ig.s.$$ + shift;; -@table @code -@item -F @var{fs} -@itemx --field-separator @var{fs} -Use @var{fs} for the input field separator (the value of the @code{FS} -predefined variable). - -@item -f @var{program-file} -@itemx --file @var{program-file} -Read the @code{awk} program source from the file @var{program-file}, instead -of from the first command line argument. - -@item -mf @var{NNN} -@itemx -mr @var{NNN} -The @samp{f} flag sets -the maximum number of fields, and the @samp{r} flag sets the maximum -record size. These options are ignored by @code{gawk}, since @code{gawk} -has no predefined limits; they are only for compatibility with the -Bell Labs research version of Unix @code{awk}. + -f*) f=`echo "$1" | sed 's/-f//'` + echo @@include "$f" >> /tmp/ig.s.$$ ;; -@item -v @var{var}=@var{val} -@itemx --assign @var{var}=@var{val} -Assign the variable @var{var} the value @var{val} before program execution -begins. + -?file=*) # -Wfile or --file + f=`echo "$1" | sed 's/-.file=//'` + echo @@include "$f" >> /tmp/ig.s.$$ ;; -@item -W traditional -@itemx -W compat -@itemx --traditional -@itemx --compat -Use compatibility mode, in which @code{gawk} extensions are turned -off. + -?file) # get arg, $2 + echo @@include "$2" >> /tmp/ig.s.$$ + shift;; -@item -W copyleft -@itemx -W copyright -@itemx --copyleft -@itemx --copyright -Print the short version of the General Public License on the standard -output, and exit. This option may disappear in a future version of @code{gawk}. + -?source=*) # -Wsource or --source + t=`echo "$1" | sed 's/-.source=//'` + echo "$t" >> /tmp/ig.s.$$ ;; -@item -W help -@itemx -W usage -@itemx --help -@itemx --usage -Print a relatively short summary of the available options on the standard -output, and exit. + -?source) # get arg, $2 + echo "$2" >> /tmp/ig.s.$$ + shift;; -@item -W lint -@itemx --lint -Give warnings about dubious or non-portable @code{awk} constructs. + -?version) + echo igawk: version 1.0 1>&2 + gawk --version + exit 0 ;; -@item -W lint-old -@itemx --lint-old -Warn about constructs that are not available in -the original Version 7 Unix version of @code{awk}. + -[W-]*) opts="$opts '$1'" ;; -@item -W posix -@itemx --posix -Use POSIX compatibility mode, in which @code{gawk} extensions -are turned off and additional restrictions apply. + *) break;; + esac + shift +done -@item -W re-interval -@itemx --re-interval -Allow interval expressions -(@pxref{Regexp Operators, , Regular Expression Operators}), -in regexps. +if [ ! -s /tmp/ig.s.$$ ] +then +@group + if [ -z "$1" ] + then + echo igawk: no program! 1>&2 + exit 1 +@end group + else + echo "$1" > /tmp/ig.s.$$ + shift + fi +fi -@item -W source=@var{program-text} -@itemx --source @var{program-text} -Use @var{program-text} as @code{awk} program source code. This option allows -mixing command line source code with source code from files, and is -particularly useful for mixing command line programs with library functions. +# at this point, /tmp/ig.s.$$ has the program +@c endfile +@end example -@item -W version -@itemx --version -Print version information for this particular copy of @code{gawk} on the error -output. +The @command{awk} program to process @samp{@@include} directives +reads through the program, one line at a time, using @code{getline} +(@pxref{Getline, ,Explicit Input with @code{getline}}). The input +@value{FN}s and @samp{@@include} statements are managed using a stack. +As each @samp{@@include} is encountered, the current @value{FN} is +``pushed'' onto the stack and the file named in the @samp{@@include} +directive becomes the current @value{FN}. As each file is finished, +the stack is ``popped,'' and the previous input file becomes the current +input file again. The process is started by making the original file +the first one on the stack. + +The @code{pathto} function does the work of finding the full path to +a file. It simulates @command{gawk}'s behavior when searching the +@env{AWKPATH} environment variable +(@pxref{AWKPATH Variable, ,The @env{AWKPATH} Environment Variable}). +If a @value{FN} has a @samp{/} in it, no path search is done. Otherwise, +the @value{FN} is concatenated with the name of each directory in +the path, and an attempt is made to open the generated @value{FN}. +The only way to test if a file can be read in @command{awk} is to go +ahead and try to read it with @code{getline}; this is what @code{pathto} +does.@footnote{On some very old versions of @command{awk}, the test +@samp{getline junk < t} can loop forever if the file exists but is empty. +Caveat emptor.} If the file can be read, it is closed and the @value{FN} +is returned: -@item -- -Signal the end of options. This is useful to allow further arguments to the -@code{awk} program itself to start with a @samp{-}. This is mainly for -consistency with POSIX argument parsing conventions. -@end table +@ignore +An alternative way to test for the file's existence would be to call +@samp{system("test -r " t)}, which uses the @command{test} utility to +see if the file exists and is readable. The disadvantage to this method +is that it requires creating an extra process and can thus be slightly +slower. +@end ignore -Any other options are flagged as invalid, but are otherwise ignored. -@xref{Options, ,Command Line Options}, for more details. - -@node Language Summary, Variables/Fields, Command Line Summary, Gawk Summary -@appendixsec Language Summary - -An @code{awk} program consists of a sequence of zero or more pattern-action -statements and optional function definitions. One or the other of the -pattern and action may be omitted. - -@example -@var{pattern} @{ @var{action statements} @} -@var{pattern} - @{ @var{action statements} @} - -function @var{name}(@var{parameter list}) @{ @var{action statements} @} -@end example - -@code{gawk} first reads the program source from the -@var{program-file}(s), if specified, or from the first non-option -argument on the command line. The @samp{-f} option may be used multiple -times on the command line. @code{gawk} reads the program text from all -the @var{program-file} files, effectively concatenating them in the -order they are specified. This is useful for building libraries of -@code{awk} functions, without having to include them in each new -@code{awk} program that uses them. To use a library function in a file -from a program typed in on the command line, specify -@samp{--source '@var{program}'}, and type your program in between the single -quotes. -@xref{Options, ,Command Line Options}. - -The environment variable @code{AWKPATH} specifies a search path to use -when finding source files named with the @samp{-f} option. The default -path, which is -@samp{.:/usr/local/share/awk}@footnote{The path may use a directory -other than @file{/usr/local/share/awk}, depending upon how @code{gawk} -was built and installed.} is used if @code{AWKPATH} is not set. -If a file name given to the @samp{-f} option contains a @samp{/} character, -no path search is performed. -@xref{AWKPATH Variable, ,The @code{AWKPATH} Environment Variable}. - -@code{gawk} compiles the program into an internal form, and then proceeds to -read each file named in the @code{ARGV} array. -The initial values of @code{ARGV} come from the command line arguments. -If there are no files named -on the command line, @code{gawk} reads the standard input. - -If a ``file'' named on the command line has the form -@samp{@var{var}=@var{val}}, it is treated as a variable assignment: the -variable @var{var} is assigned the value @var{val}. -If any of the files have a value that is the null string, that -element in the list is skipped. - -For each record in the input, @code{gawk} tests to see if it matches any -@var{pattern} in the @code{awk} program. For each pattern that the record -matches, the associated @var{action} is executed. - -@node Variables/Fields, Rules Summary, Language Summary, Gawk Summary -@appendixsec Variables and Fields - -@code{awk} variables are not declared; they come into existence when they are -first used. Their values are either floating-point numbers or strings. -@code{awk} also has one-dimensional arrays; multiple-dimensional arrays -may be simulated. There are several predefined variables that -@code{awk} sets as a program runs; these are summarized below. +@example +@c file eg/prog/igawk.sh +gawk -- ' +# process @@include directives -@menu -* Fields Summary:: Input field splitting. -* Built-in Summary:: @code{awk}'s built-in variables. -* Arrays Summary:: Using arrays. -* Data Type Summary:: Values in @code{awk} are numbers or strings. -@end menu +function pathto(file, i, t, junk) +@{ + if (index(file, "/") != 0) + return file -@node Fields Summary, Built-in Summary, Variables/Fields, Variables/Fields -@appendixsubsec Fields - -As each input line is read, @code{gawk} splits the line into -@var{fields}, using the value of the @code{FS} variable as the field -separator. If @code{FS} is a single character, fields are separated by -that character. Otherwise, @code{FS} is expected to be a full regular -expression. In the special case that @code{FS} is a single space, -fields are separated by runs of spaces, tabs and/or newlines.@footnote{In -POSIX @code{awk}, newline does not separate fields.} -If @code{FS} is the null string (@code{""}), then each individual -character in the record becomes a separate field. -Note that the value -of @code{IGNORECASE} (@pxref{Case-sensitivity, ,Case-sensitivity in Matching}) -also affects how fields are split when @code{FS} is a regular expression. + for (i = 1; i <= ndirs; i++) @{ + t = (pathlist[i] "/" file) +@group + if ((getline junk < t) > 0) @{ + # found it + close(t) + return t + @} +@end group + @} + return "" +@} +@c endfile +@end example -Each field in the input line may be referenced by its position, @code{$1}, -@code{$2}, and so on. @code{$0} is the whole line. The value of a field may -be assigned to as well. Field numbers need not be constants: +The main program is contained inside one @code{BEGIN} rule. The first thing it +does is set up the @code{pathlist} array that @code{pathto} uses. After +splitting the path on @samp{:}, null elements are replaced with @code{"."}, +which represents the current directory: @example -n = 5 -print $n +@c file eg/prog/igawk.sh +BEGIN @{ + path = ENVIRON["AWKPATH"] + ndirs = split(path, pathlist, ":") + for (i = 1; i <= ndirs; i++) @{ + if (pathlist[i] == "") + pathlist[i] = "." + @} +@c endfile @end example -@noindent -prints the fifth field in the input line. The variable @code{NF} is set to -the total number of fields in the input line. - -References to non-existent fields (i.e.@: fields after @code{$NF}) return -the null string. However, assigning to a non-existent field (e.g., -@code{$(NF+2) = 5}) increases the value of @code{NF}, creates any -intervening fields with the null string as their value, and causes the -value of @code{$0} to be recomputed, with the fields being separated by -the value of @code{OFS}. -Decrementing @code{NF} causes the values of fields past the new value to -be lost, and the value of @code{$0} to be recomputed, with the fields being -separated by the value of @code{OFS}. -@xref{Reading Files, ,Reading Input Files}. - -@node Built-in Summary, Arrays Summary, Fields Summary, Variables/Fields -@appendixsubsec Built-in Variables - -@code{gawk}'s built-in variables are: - -@table @code -@item ARGC -The number of elements in @code{ARGV}. See below for what is actually -included in @code{ARGV}. - -@item ARGIND -The index in @code{ARGV} of the current file being processed. -When @code{gawk} is processing the input data files, -it is always true that @samp{FILENAME == ARGV[ARGIND]}. - -@item ARGV -The array of command line arguments. The array is indexed from zero to -@code{ARGC} @minus{} 1. Dynamically changing @code{ARGC} and -the contents of @code{ARGV} -can control the files used for data. A null-valued element in -@code{ARGV} is ignored. @code{ARGV} does not include the options to -@code{awk} or the text of the @code{awk} program itself. +The stack is initialized with @code{ARGV[1]}, which will be @file{/tmp/ig.s.$$}. +The main loop comes next. Input lines are read in succession. Lines that +do not start with @samp{@@include} are printed verbatim. +If the line does start with @samp{@@include}, the @value{FN} is in @code{$2}. +@code{pathto} is called to generate the full path. If it cannot, then we +print an error message and continue. -@item CONVFMT -The conversion format to use when converting numbers to strings. +The next thing to check is if the file is included already. The +@code{processed} array is indexed by the full @value{FN} of each included +file and it tracks this information for us. If the file is +seen again, a warning message is printed. Otherwise, the new @value{FN} is +pushed onto the stack and processing continues. -@item FIELDWIDTHS -A space separated list of numbers describing the fixed-width input data. +Finally, when @code{getline} encounters the end of the input file, the file +is closed and the stack is popped. When @code{stackptr} is less than zero, +the program is done: -@item ENVIRON -An array of environment variable values. The array -is indexed by variable name, each element being the value of that -variable. Thus, the environment variable @code{HOME} is -@code{ENVIRON["HOME"]}. One possible value might be @file{/home/arnold}. +@example +@c file eg/prog/igawk.sh + stackptr = 0 + input[stackptr] = ARGV[1] # ARGV[1] is first file -Changing this array does not affect the environment seen by programs -which @code{gawk} spawns via redirection or the @code{system} function. -(This may change in a future version of @code{gawk}.) + for (; stackptr >= 0; stackptr--) @{ + while ((getline < input[stackptr]) > 0) @{ + if (tolower($1) != "@@include") @{ + print + continue + @} + fpath = pathto($2) +@group + if (fpath == "") @{ + printf("igawk:%s:%d: cannot find %s\n", + input[stackptr], FNR, $2) > "/dev/stderr" + continue + @} +@end group + if (! (fpath in processed)) @{ + processed[fpath] = input[stackptr] + input[++stackptr] = fpath # push onto stack + @} else + print $2, "included in", input[stackptr], + "already included in", + processed[fpath] > "/dev/stderr" + @} + close(input[stackptr]) + @} +@}' /tmp/ig.s.$$ > /tmp/ig.e.$$ +@c endfile +@end example -Some operating systems do not have environment variables. -The @code{ENVIRON} array is empty when running on these systems. +The last step is to call @command{gawk} with the expanded program, +along with the original +options and command-line arguments that the user supplied. @command{gawk}'s +exit status is passed back on to @command{igawk}'s calling program: -@item ERRNO -The system error message when an error occurs using @code{getline} -or @code{close}. +@c this causes more problems than it solves, so leave it out. +@ignore +The special file @file{/dev/null} is passed as a @value{DF} to @command{gawk} +to handle an interesting case. Suppose that the user's program only has +a @code{BEGIN} rule and there are no @value{DF}s to read. +The program should exit without reading any @value{DF}s. +However, suppose that an included library file defines an @code{END} +rule of its own. In this case, @command{gawk} will hang, reading standard +input. In order to avoid this, @file{/dev/null} is explicitly added to the +command-line. Reading from @file{/dev/null} always returns an immediate +end of file indication. -@item FILENAME -The name of the current input file. If no files are specified on the command -line, the value of @code{FILENAME} is the null string. +@c Hmm. Add /dev/null if $# is 0? Still messes up ARGV. Sigh. +@end ignore -@item FNR -The input record number in the current input file. +@example +@c file eg/prog/igawk.sh +eval gawk -f /tmp/ig.e.$$ $opts -- "$@@" -@item FS -The input field separator, a space by default. - -@item IGNORECASE -The case-sensitivity flag for string comparisons and regular expression -operations. If @code{IGNORECASE} has a non-zero value, then pattern -matching in rules, record separating with @code{RS}, field splitting -with @code{FS}, regular expression matching with @samp{~} and -@samp{!~}, and the @code{gensub}, @code{gsub}, @code{index}, -@code{match}, @code{split} and @code{sub} built-in functions all -ignore case when doing regular expression operations, and all string -comparisons are done ignoring case. -The value of @code{IGNORECASE} does @emph{not} affect array subscripting. +exit $? +@c endfile +@end example -@item NF -The number of fields in the current input record. +This version of @command{igawk} represents my third attempt at this program. +There are three key simplifications that make the program work better: -@item NR -The total number of input records seen so far. +@itemize @bullet +@item +Using @samp{@@include} even for the files named with @option{-f} makes building +the initial collected @command{awk} program much simpler; all the +@samp{@@include} processing can be done once. -@item OFMT -The output format for numbers for the @code{print} statement, -@code{"%.6g"} by default. +@item +The @code{pathto} function doesn't try to save the line read with +@code{getline} when testing for the file's accessibility. Trying to save +this line for use with the main program complicates things considerably. +@c what problem does this engender though - exercise +@c answer, reading from "-" or /dev/stdin -@item OFS -The output field separator, a space by default. +@item +Using a @code{getline} loop in the @code{BEGIN} rule does it all in one +place. It is not necessary to call out to a separate loop for processing +nested @samp{@@include} statements. +@end itemize -@item ORS -The output record separator, by default a newline. +Also, this program illustrates that it is often worthwhile to combine +@command{sh} and @command{awk} programming together. You can usually +accomplish quite a lot, without having to resort to low-level programming +in C or C++, and it is frequently easier to do certain kinds of string +and argument manipulation using the shell than it is in @command{awk}. -@item RS -The input record separator, by default a newline. -If @code{RS} is set to the null string, then records are separated by -blank lines. When @code{RS} is set to the null string, then the newline -character always acts as a field separator, in addition to whatever value -@code{FS} may have. If @code{RS} is set to a multi-character -string, it denotes a regexp; input text matching the regexp -separates records. - -@item RT -The input text that matched the text denoted by @code{RS}, -the record separator. +Finally, @command{igawk} shows that it is not always necessary to add new +features to a program; they can often be layered on top. With @command{igawk}, +there is no real reason to build @samp{@@include} processing into +@command{gawk} itself. -@item RSTART -The index of the first character last matched by @code{match}; zero if no match. +@cindex search path +@cindex directory search +@cindex path, search +@cindex search path, for source files +As an additional example of this, consider the idea of having two +files in a directory in the search path: -@item RLENGTH -The length of the string last matched by @code{match}; @minus{}1 if no match. +@table @file +@item default.awk +This file contains a set of default library functions, such +as @code{getopt} and @code{assert}. -@item SUBSEP -The string used to separate multiple subscripts in array elements, by -default @code{"\034"}. +@item site.awk +This file contains library functions that are specific to a site or +installation; i.e., locally developed functions. +Having a separate file allows @file{default.awk} to change with +new @command{gawk} releases, without requiring the system administrator to +update it each time by adding the local functions. @end table -@xref{Built-in Variables}, for more information. - -@node Arrays Summary, Data Type Summary, Built-in Summary, Variables/Fields -@appendixsubsec Arrays - -Arrays are subscripted with an expression between square brackets -(@samp{[} and @samp{]}). Array subscripts are @emph{always} strings; -numbers are converted to strings as necessary, following the standard -conversion rules -(@pxref{Conversion, ,Conversion of Strings and Numbers}). - -If you use multiple expressions separated by commas inside the square -brackets, then the array subscript is a string consisting of the -concatenation of the individual subscript values, converted to strings, -separated by the subscript separator (the value of @code{SUBSEP}). - -The special operator @code{in} may be used in a conditional context -to see if an array has an index consisting of a particular value. - -@example -if (val in array) - print array[val] -@end example - -If the array has multiple subscripts, use @samp{(i, j, @dots{}) in @var{array}} -to test for existence of an element. - -The @code{in} construct may also be used in a @code{for} loop to iterate -over all the elements of an array. -@xref{Scanning an Array, ,Scanning All Elements of an Array}. - -You can remove an element from an array using the @code{delete} statement. - -You can clear an entire array using @samp{delete @var{array}}. +One user +@c Karl Berry, karl@ileaf.com, 10/95 +suggested that @command{gawk} be modified to automatically read these files +upon startup. Instead, it would be very simple to modify @command{igawk} +to do this. Since @command{igawk} can process nested @samp{@@include} +directives, @file{default.awk} could simply contain @samp{@@include} +statements for the desired library functions. -@xref{Arrays, ,Arrays in @code{awk}}. +@c Exercise: make this change -@node Data Type Summary, , Arrays Summary, Variables/Fields -@appendixsubsec Data Types +@ignore +@c Try this +@iftex +@page +@headings off +@majorheading III@ @ @ Appendixes +Part III provides the appendixes, the Glossary, and two licenses that cover +the @command{gawk} source code and this @value{DOCUMENT}, respectively. +It contains the following appendixes: -The value of an @code{awk} expression is always either a number -or a string. +@itemize @bullet +@item +@ref{Language History, ,The Evolution of the @command{awk} Language}. -Some contexts (such as arithmetic operators) require numeric -values. They convert strings to numbers by interpreting the text -of the string as a number. If the string does not look like a -number, it converts to zero. +@item +@ref{Installation, ,Installing @command{gawk}}. -Other contexts (such as concatenation) require string values. -They convert numbers to strings by effectively printing them -with @code{sprintf}. -@xref{Conversion, ,Conversion of Strings and Numbers}, for the details. +@item +@ref{Notes, ,Implementation Notes}. -To force conversion of a string value to a number, simply add zero -to it. If the value you start with is already a number, this -does not change it. +@item +@ref{Basic Concepts, ,Basic Programming Concepts}. -To force conversion of a numeric value to a string, concatenate it with -the null string. +@item +@ref{Glossary}. -Comparisons are done numerically if both operands are numeric, or if -one is numeric and the other is a numeric string. Otherwise one or -both operands are converted to strings and a string comparison is -performed. Fields, @code{getline} input, @code{FILENAME}, @code{ARGV} -elements, @code{ENVIRON} elements and the elements of an array created -by @code{split} are the only items that can be numeric strings. String -constants, such as @code{"3.1415927"} are not numeric strings, they are -string constants. The full rules for comparisons are described in -@ref{Typing and Comparison, ,Variable Typing and Comparison Expressions}. +@item +@ref{Copying, ,GNU General Public License}. -Uninitialized variables have the string value @code{""} (the null, or -empty, string). In contexts where a number is required, this is -equivalent to zero. +@item +@ref{GNU Free Documentation License}. +@end itemize -@xref{Variables}, for more information on variable naming and initialization; -@pxref{Conversion, ,Conversion of Strings and Numbers}, for more information -on how variable values are interpreted. +@page +@evenheading @thispage@ @ @ @strong{@value{TITLE}} @| @| +@oddheading @| @| @strong{@thischapter}@ @ @ @thispage +@end iftex +@end ignore -@node Rules Summary, Actions Summary, Variables/Fields, Gawk Summary -@appendixsec Patterns +@node Language History, Installation, Sample Programs, Top +@appendix The Evolution of the @command{awk} Language + +This @value{DOCUMENT} describes the GNU implementation of @command{awk}, which follows +the POSIX specification. +Many long-time @command{awk} users learned @command{awk} programming +with the original @command{awk} implementation in Version 7 Unix. +(This implementation was the basis for @command{awk} in Berkeley Unix, +through 4.3--Reno. Subsequent versions of Berkeley Unix, and systems +derived from 4.4BSD--Lite, use various versions of @command{gawk} +for their @command{awk}.) +This @value{CHAPTER} briefly describes the +evolution of the @command{awk} language, with cross references to other parts +of the @value{DOCUMENT} where you can find more information. @menu -* Pattern Summary:: Quick overview of patterns. -* Regexp Summary:: Quick overview of regular expressions. +* V7/SVR3.1:: The major changes between V7 and System V + Release 3.1. +* SVR4:: Minor changes between System V Releases 3.1 + and 4. +* POSIX:: New features from the POSIX standard. +* BTL:: New features from the Bell Laboratories + version of @command{awk}. +* POSIX/GNU:: The extensions in @command{gawk} not in POSIX + @command{awk}. +* Contributors:: The major contributors to @command{gawk}. @end menu -An @code{awk} program is mostly composed of rules, each consisting of a -pattern followed by an action. The action is enclosed in @samp{@{} and -@samp{@}}. Either the pattern may be missing, or the action may be -missing, but not both. If the pattern is missing, the -action is executed for every input record. A missing action is -equivalent to @samp{@w{@{ print @}}}, which prints the entire line. - -@c These paragraphs repeated for both patterns and actions. I don't -@c like this, but I also don't see any way around it. Update both copies -@c if they need fixing. -Comments begin with the @samp{#} character, and continue until the end of the -line. Blank lines may be used to separate statements. Statements normally -end with a newline; however, this is not the case for lines ending in a -@samp{,}, @samp{@{}, @samp{?}, @samp{:}, @samp{&&}, or @samp{||}. Lines -ending in @code{do} or @code{else} also have their statements automatically -continued on the following line. In other cases, a line can be continued by -ending it with a @samp{\}, in which case the newline is ignored. - -Multiple statements may be put on one line by separating each one with -a @samp{;}. -This applies to both the statements within the action part of a rule (the -usual case), and to the rule statements. - -@xref{Comments, ,Comments in @code{awk} Programs}, for information on -@code{awk}'s commenting convention; -@pxref{Statements/Lines, ,@code{awk} Statements Versus Lines}, for a -description of the line continuation mechanism in @code{awk}. - -@node Pattern Summary, Regexp Summary, Rules Summary, Rules Summary -@appendixsubsec Pattern Summary - -@code{awk} patterns may be one of the following: - -@example -/@var{regular expression}/ -@var{relational expression} -@var{pattern} && @var{pattern} -@var{pattern} || @var{pattern} -@var{pattern} ? @var{pattern} : @var{pattern} -(@var{pattern}) -! @var{pattern} -@var{pattern1}, @var{pattern2} -BEGIN -END -@end example - -@code{BEGIN} and @code{END} are two special kinds of patterns that are not -tested against the input. The action parts of all @code{BEGIN} rules are -concatenated as if all the statements had been written in a single @code{BEGIN} -rule. They are executed before any of the input is read. Similarly, all the -@code{END} rules are concatenated, and executed when all the input is exhausted (or -when an @code{exit} statement is executed). @code{BEGIN} and @code{END} -patterns cannot be combined with other patterns in pattern expressions. -@code{BEGIN} and @code{END} rules cannot have missing action parts. - -For @code{/@var{regular-expression}/} patterns, the associated statement is -executed for each input record that matches the regular expression. Regular -expressions are summarized below. - -A @var{relational expression} may use any of the operators defined below in -the section on actions. These generally test whether certain fields match -certain regular expressions. - -The @samp{&&}, @samp{||}, and @samp{!} operators are logical ``and,'' -logical ``or,'' and logical ``not,'' respectively, as in C. They do -short-circuit evaluation, also as in C, and are used for combining more -primitive pattern expressions. As in most languages, parentheses may be -used to change the order of evaluation. - -The @samp{?:} operator is like the same operator in C. If the first -pattern matches, then the second pattern is matched against the input -record; otherwise, the third is matched. Only one of the second and -third patterns is matched. - -The @samp{@var{pattern1}, @var{pattern2}} form of a pattern is called a -range pattern. It matches all input lines starting with a line that -matches @var{pattern1}, and continuing until a line that matches -@var{pattern2}, inclusive. A range pattern cannot be used as an operand -of any of the pattern operators. - -@xref{Pattern Overview, ,Pattern Elements}. - -@node Regexp Summary, , Pattern Summary, Rules Summary -@appendixsubsec Regular Expressions - -Regular expressions are based on POSIX EREs (extended regular expressions). -The escape sequences allowed in string constants are also valid in -regular expressions (@pxref{Escape Sequences}). -Regexps are composed of characters as follows: - -@table @code -@item @var{c} -matches the character @var{c} (assuming @var{c} is none of the characters -listed below). - -@item \@var{c} -matches the literal character @var{c}. - -@item . -matches any character, @emph{including} newline. -In strict POSIX mode, @samp{.} does not match the @sc{nul} -character, which is a character with all bits equal to zero. - -@item ^ -matches the beginning of a string. - -@item $ -matches the end of a string. - -@item [@var{abc}@dots{}] -matches any of the characters @var{abc}@dots{} (character list). +@node V7/SVR3.1, SVR4, Language History, Language History +@appendixsec Major Changes Between V7 and SVR3.1 -@item [[:@var{class}:]] -matches any character in the character class @var{class}. Allowable classes -are @code{alnum}, @code{alpha}, @code{blank}, @code{cntrl}, -@code{digit}, @code{graph}, @code{lower}, @code{print}, @code{punct}, -@code{space}, @code{upper}, and @code{xdigit}. +The @command{awk} language evolved considerably between the release of +Version 7 Unix (1978) and the new version that was first made generally available in +System V Release 3.1 (1987). This @value{SECTION} summarizes the changes, with +cross-references to further details: -@item [[.@var{symbol}.]] -matches the multi-character collating symbol @var{symbol}. -@code{gawk} does not currently support collating symbols. +@itemize @bullet +@item +The requirement for @samp{;} to separate rules on a line +(@pxref{Statements/Lines, ,@command{awk} Statements Versus Lines}). -@item [[=@var{classname}=]] -matches any of the equivalent characters in the current locale named by the -equivalence class @var{classname}. -@code{gawk} does not currently support equivalence classes. +@item +User-defined functions and the @code{return} statement +(@pxref{User-defined, ,User-Defined Functions}). -@item [^@var{abc}@dots{}] -matches any character except @var{abc}@dots{} (negated -character list). +@item +The @code{delete} statement (@pxref{Delete, ,The @code{delete} Statement}). -@item @var{r1}|@var{r2} -matches either @var{r1} or @var{r2} (alternation). +@item +The @code{do}-@code{while} statement +(@pxref{Do Statement, ,The @code{do}-@code{while} Statement}). -@item @var{r1r2} -matches @var{r1}, and then @var{r2} (concatenation). +@item +The built-in functions @code{atan2}, @code{cos}, @code{sin}, @code{rand}, and +@code{srand} (@pxref{Numeric Functions}). -@item @var{r}+ -matches one or more @var{r}'s. +@item +The built-in functions @code{gsub}, @code{sub}, and @code{match} +(@pxref{String Functions, ,String Manipulation Functions}). -@item @var{r}* -matches zero or more @var{r}'s. +@item +The built-in functions @code{close} and @code{system} +(@pxref{I/O Functions, ,Input/Output Functions}). -@item @var{r}? -matches zero or one @var{r}'s. +@item +The @code{ARGC}, @code{ARGV}, @code{FNR}, @code{RLENGTH}, @code{RSTART}, +and @code{SUBSEP} built-in variables (@pxref{Built-in Variables}). -@item (@var{r}) -matches @var{r} (grouping). +@item +The conditional expression using the ternary operator @samp{?:} +(@pxref{Conditional Exp, ,Conditional Expressions}). -@item @var{r}@{@var{n}@} -@itemx @var{r}@{@var{n},@} -@itemx @var{r}@{@var{n},@var{m}@} -matches at least @var{n}, @var{n} to any number, or @var{n} to @var{m} -occurrences of @var{r} (interval expressions). +@item +The exponentiation operator @samp{^} +(@pxref{Arithmetic Ops, ,Arithmetic Operators}) and its assignment operator +form @samp{^=} (@pxref{Assignment Ops, ,Assignment Expressions}). -@item \y -matches the empty string at either the beginning or the -end of a word. +@item +C-compatible operator precedence, which breaks some old @command{awk} +programs (@pxref{Precedence, ,Operator Precedence (How Operators Nest)}). -@item \B -matches the empty string within a word. +@item +Regexps as the value of @code{FS} +(@pxref{Field Separators, ,Specifying How Fields Are Separated}) and as the +third argument to the @code{split} function +(@pxref{String Functions, ,String Manipulation Functions}). -@item \< -matches the empty string at the beginning of a word. +@item +Dynamic regexps as operands of the @samp{~} and @samp{!~} operators +(@pxref{Regexp Usage, ,How to Use Regular Expressions}). -@item \> -matches the empty string at the end of a word. +@item +The escape sequences @samp{\b}, @samp{\f}, and @samp{\r} +(@pxref{Escape Sequences}). +(Some vendors have updated their old versions of @command{awk} to +recognize @samp{\b}, @samp{\f}, and @samp{\r}, but this is not +something you can rely on.) -@item \w -matches any word-constituent character (alphanumeric characters and -the underscore). +@item +Redirection of input for the @code{getline} function +(@pxref{Getline, ,Explicit Input with @code{getline}}). -@item \W -matches any character that is not word-constituent. +@item +Multiple @code{BEGIN} and @code{END} rules +(@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}). -@item \` -matches the empty string at the beginning of a buffer (same as a string -in @code{gawk}). +@item +Multidimensional arrays +(@pxref{Multi-dimensional, ,Multidimensional Arrays}). +@end itemize -@item \' -matches the empty string at the end of a buffer. -@end table +@node SVR4, POSIX, V7/SVR3.1, Language History +@appendixsec Changes Between SVR3.1 and SVR4 -The various command line options -control how @code{gawk} interprets characters in regexps. +@cindex @command{awk} language, V.4 version +The System V Release 4 (1989) version of Unix @command{awk} added these features +(some of which originated in @command{gawk}): -@c NOTE!!! Keep this in sync with the same table in the regexp chapter! -@table @asis -@item No options -In the default case, @code{gawk} provide all the facilities of -POSIX regexps and the GNU regexp operators described above. -However, interval expressions are not supported. +@itemize @bullet +@item +The @code{ENVIRON} variable (@pxref{Built-in Variables}). +@c gawk and MKS awk -@item @code{--posix} -Only POSIX regexps are supported, the GNU operators are not special -(e.g., @samp{\w} matches a literal @samp{w}). Interval expressions -are allowed. +@item +Multiple @option{-f} options on the command line +(@pxref{Options, ,Command-Line Options}). +@c MKS awk -@item @code{--traditional} -Traditional Unix @code{awk} regexps are matched. The GNU operators -are not special, interval expressions are not available, and neither -are the POSIX character classes (@code{[[:alnum:]]} and so on). -Characters described by octal and hexadecimal escape sequences are -treated literally, even if they represent regexp metacharacters. +@item +The @option{-v} option for assigning variables before program execution begins +(@pxref{Options, ,Command-Line Options}). +@c GNU, Bell Laboratories & MKS together -@item @code{--re-interval} -Allow interval expressions in regexps, even if @samp{--traditional} -has been provided. -@end table +@item +The @option{--} option for terminating command-line options. -@xref{Regexp, ,Regular Expressions}. +@item +The @samp{\a}, @samp{\v}, and @samp{\x} escape sequences +(@pxref{Escape Sequences}). +@c GNU, for ANSI C compat -@node Actions Summary, Functions Summary, Rules Summary, Gawk Summary -@appendixsec Actions +@item +A defined return value for the @code{srand} built-in function +(@pxref{Numeric Functions}). -Action statements are enclosed in braces, @samp{@{} and @samp{@}}. -A missing action statement is equivalent to @samp{@w{@{ print @}}}. +@item +The @code{toupper} and @code{tolower} built-in string functions +for case translation +(@pxref{String Functions, ,String Manipulation Functions}). -Action statements consist of the usual assignment, conditional, and looping -statements found in most languages. The operators, control statements, -and Input/Output statements available are similar to those in C. +@item +A cleaner specification for the @samp{%c} format-control letter in the +@code{printf} function +(@pxref{Control Letters, ,Format-Control Letters}). -@c These paragraphs repeated for both patterns and actions. I don't -@c like this, but I also don't see any way around it. Update both copies -@c if they need fixing. -Comments begin with the @samp{#} character, and continue until the end of the -line. Blank lines may be used to separate statements. Statements normally -end with a newline; however, this is not the case for lines ending in a -@samp{,}, @samp{@{}, @samp{?}, @samp{:}, @samp{&&}, or @samp{||}. Lines -ending in @code{do} or @code{else} also have their statements automatically -continued on the following line. In other cases, a line can be continued by -ending it with a @samp{\}, in which case the newline is ignored. +@item +The ability to dynamically pass the field width and precision (@code{"%*.*d"}) +in the argument list of the @code{printf} function +(@pxref{Control Letters, ,Format-Control Letters}). -Multiple statements may be put on one line by separating each one with -a @samp{;}. -This applies to both the statements within the action part of a rule (the -usual case), and to the rule statements. +@item +The use of regexp constants, such as @code{/foo/}, as expressions, where +they are equivalent to using the matching operator, as in @samp{$0 ~ /foo/} +(@pxref{Using Constant Regexps, ,Using Regular Expression Constants}). -@xref{Comments, ,Comments in @code{awk} Programs}, for information on -@code{awk}'s commenting convention; -@pxref{Statements/Lines, ,@code{awk} Statements Versus Lines}, for a -description of the line continuation mechanism in @code{awk}. +@item +Processing of escape sequences inside command-line variable assignments +(@pxref{Assignment Options, ,Assigning Variables on the Command Line}). +@end itemize -@menu -* Operator Summary:: @code{awk} operators. -* Control Flow Summary:: The control statements. -* I/O Summary:: The I/O statements. -* Printf Summary:: A summary of @code{printf}. -* Special File Summary:: Special file names interpreted internally. -* Built-in Functions Summary:: Built-in numeric and string functions. -* Time Functions Summary:: Built-in time functions. -* String Constants Summary:: Escape sequences in strings. -@end menu +@node POSIX, BTL, SVR4, Language History +@appendixsec Changes Between SVR4 and POSIX @command{awk} -@node Operator Summary, Control Flow Summary, Actions Summary, Actions Summary -@appendixsubsec Operators +The POSIX Command Language and Utilities standard for @command{awk} (1992) +introduced the following changes into the language: -The operators in @code{awk}, in order of decreasing precedence, are: +@itemize @bullet +@item +The use of @option{-W} for implementation-specific options +(@pxref{Options, ,Command-Line Options}). -@table @code -@item (@dots{}) -Grouping. +@item +The use of @code{CONVFMT} for controlling the conversion of numbers +to strings (@pxref{Conversion, ,Conversion of Strings and Numbers}). -@item $ -Field reference. +@item +The concept of a numeric string and tighter comparison rules to go +with it (@pxref{Typing and Comparison, ,Variable Typing and Comparison Expressions}). -@item ++ -- -Increment and decrement, both prefix and postfix. +@item +More complete documentation of many of the previously undocumented +features of the language. +@end itemize -@item ^ -Exponentiation (@samp{**} may also be used, and @samp{**=} for the assignment -operator, but they are not specified in the POSIX standard). +The following common extensions are not permitted by the POSIX +standard: -@item + - ! -Unary plus, unary minus, and logical negation. +@c IMPORTANT! Keep this list in sync with the one in node Options -@item * / % -Multiplication, division, and modulus. +@itemize @bullet +@item +@code{\x} escape sequences are not recognized +(@pxref{Escape Sequences}). -@item + - -Addition and subtraction. +@item +Newlines do not act as whitespace to separate fields when @code{FS} is +equal to a single space +(@pxref{Fields, ,Examining Fields}). -@item @var{space} -String concatenation. +@item +Newlines are not allowed after @samp{?} or @samp{:} +(@pxref{Conditional Exp, ,Conditional Expressions}). -@item < <= > >= != == -The usual relational operators. +@item +The synonym @code{func} for the keyword @code{function} is not +recognized (@pxref{Definition Syntax, ,Function Definition Syntax}). -@item ~ !~ -Regular expression match, negated match. +@item +The operators @samp{**} and @samp{**=} cannot be used in +place of @samp{^} and @samp{^=} (@pxref{Arithmetic Ops, ,Arithmetic Operators}, +and @ref{Assignment Ops, ,Assignment Expressions}). -@item in -Array membership. +@item +Specifying @samp{-Ft} on the command line does not set the value +of @code{FS} to be a single tab character +(@pxref{Field Separators, ,Specifying How Fields Are Separated}). -@item && -Logical ``and''. +@item +The @code{fflush} built-in function is not supported +(@pxref{I/O Functions, ,Input/Output Functions}). +@end itemize -@item || -Logical ``or''. +@node BTL, POSIX/GNU, POSIX, Language History +@appendixsec Extensions in the Bell Laboratories @command{awk} -@item ?: -A conditional expression. This has the form @samp{@var{expr1} ? -@var{expr2} : @var{expr3}}. If @var{expr1} is true, the value of the -expression is @var{expr2}; otherwise it is @var{expr3}. Only one of -@var{expr2} and @var{expr3} is evaluated. - -@item = += -= *= /= %= ^= -Assignment. Both absolute assignment (@code{@var{var}=@var{value}}) -and operator assignment (the other forms) are supported. -@end table +@cindex extensions, Bell Laboratories @command{awk} +@cindex Kernighan, Brian +Brian Kernighan, one of the original designers of Unix @command{awk}, +has made his version available via his home page +(@pxref{Other Versions, ,Other Freely Available @command{awk} Implementations}). +This @value{SECTION} describes extensions in his version of @command{awk} that are +not in POSIX @command{awk}. -@xref{Expressions}. +@itemize @bullet +@item +The @samp{-mf @var{N}} and @samp{-mr @var{N}} command-line options +to set the maximum number of fields and the maximum +record size, respectively +(@pxref{Options, ,Command-Line Options}). +As a side note, his @command{awk} no longer needs these options; +it continues to accept them to avoid breaking old programs. -@node Control Flow Summary, I/O Summary, Operator Summary, Actions Summary -@appendixsubsec Control Statements +@item +The @code{fflush} built-in function for flushing buffered output +(@pxref{I/O Functions, ,Input/Output Functions}). -The control statements are as follows: +@item +The @samp{**} and @samp{**=} operators +(@pxref{Arithmetic Ops, ,Arithmetic Operators} +and +@ref{Assignment Ops, ,Assignment Expressions}). -@example -if (@var{condition}) @var{statement} @r{[} else @var{statement} @r{]} -while (@var{condition}) @var{statement} -do @var{statement} while (@var{condition}) -for (@var{expr1}; @var{expr2}; @var{expr3}) @var{statement} -for (@var{var} in @var{array}) @var{statement} -break -continue -delete @var{array}[@var{index}] -delete @var{array} -exit @r{[} @var{expression} @r{]} -@{ @var{statements} @} -@end example +@item +The use of @code{func} as an abbreviation for @code{function} +(@pxref{Definition Syntax, ,Function Definition Syntax}). -@xref{Statements, ,Control Statements in Actions}. +@ignore +@item +The @code{SYMTAB} array, that allows access to @command{awk}'s internal symbol +table. This feature is not documented, largely because +it is somewhat shakily implemented. For instance, you cannot access arrays +or array elements through it. +@end ignore +@end itemize -@node I/O Summary, Printf Summary, Control Flow Summary, Actions Summary -@appendixsubsec I/O Statements +The Bell Laboratories @command{awk} also incorporates the following extensions, +originally developed for @command{gawk}: -The Input/Output statements are as follows: +@itemize @bullet +@item +The @samp{\x} escape sequence +(@pxref{Escape Sequences}). -@table @code -@item getline -Set @code{$0} from next input record; set @code{NF}, @code{NR}, @code{FNR}. -@xref{Getline, ,Explicit Input with @code{getline}}. - -@item getline <@var{file} -Set @code{$0} from next record of @var{file}; set @code{NF}. - -@item getline @var{var} -Set @var{var} from next input record; set @code{NR}, @code{FNR}. - -@item getline @var{var} <@var{file} -Set @var{var} from next record of @var{file}. - -@item @var{command} | getline -Run @var{command}, piping its output into @code{getline}; sets @code{$0}, -@code{NF}, @code{NR}. - -@item @var{command} | getline @code{var} -Run @var{command}, piping its output into @code{getline}; sets @var{var}. - -@item next -Stop processing the current input record. The next input record is read and -processing starts over with the first pattern in the @code{awk} program. -If the end of the input data is reached, the @code{END} rule(s), if any, -are executed. -@xref{Next Statement, ,The @code{next} Statement}. - -@item nextfile -Stop processing the current input file. The next input record read comes -from the next input file. @code{FILENAME} is updated, @code{FNR} is set to one, -@code{ARGIND} is incremented, -and processing starts over with the first pattern in the @code{awk} program. -If the end of the input data is reached, the @code{END} rule(s), if any, -are executed. -Earlier versions of @code{gawk} used @samp{next file}; this usage is still -supported, but is considered to be deprecated. -@xref{Nextfile Statement, ,The @code{nextfile} Statement}. - -@item print -Prints the current record. -@xref{Printing, ,Printing Output}. +@item +The @file{/dev/stdin}, @file{/dev/stdout}, and @file{/dev/stderr} +special files +(@pxref{Special Files, ,Special @value{FFN}s in @command{gawk}}). -@item print @var{expr-list} -Prints expressions. +@item +The ability for @code{FS} and for the third +argument to @code{split} to be null strings +(@pxref{Single Character Fields, , Making Each Character a Separate Field}). -@item print @var{expr-list} > @var{file} -Prints expressions to @var{file}. If @var{file} does not exist, it is -created. If it does exist, its contents are deleted the first time the -@code{print} is executed. +@item +The @code{nextfile} statement +(@pxref{Nextfile Statement, ,Using @command{gawk}'s @code{nextfile} Statement}). -@item print @var{expr-list} >> @var{file} -Prints expressions to @var{file}. The previous contents of @var{file} -are retained, and the output of @code{print} is appended to the file. +@item +The ability to delete all of an array at once with @samp{delete @var{array}} +(@pxref{Delete, ,The @code{delete} Statement}). +@end itemize -@item print @var{expr-list} | @var{command} -Prints expressions, sending the output down a pipe to @var{command}. -The pipeline to the command stays open until the @code{close} function -is called. +@node POSIX/GNU, Contributors, BTL, Language History +@appendixsec Extensions in @command{gawk} Not in POSIX @command{awk} -@item printf @var{fmt}, @var{expr-list} -Format and print. +@ignore +I've tried to follow this general order, esp. for the 3.0 and 3.1 sections: + variables + special files + language changes (e.g., hex constants) + differences in standard awk functions + new gawk functions + new keywords + new command-line options + new ports +Within each category, be alphabetical. +@end ignore -@item printf @var{fmt}, @var{expr-list} > @var{file} -Format and print to @var{file}. If @var{file} does not exist, it is -created. If it does exist, its contents are deleted the first time the -@code{printf} is executed. +@cindex compatibility mode +The GNU implementation, @command{gawk}, adds a large number of features. +This @value{SECTION} lists them in the order they were added to @command{gawk}. +They can all be disabled with either the @option{--traditional} or +@option{--posix} options +(@pxref{Options, ,Command-Line Options}). -@item printf @var{fmt}, @var{expr-list} >> @var{file} -Format and print to @var{file}. The previous contents of @var{file} -are retained, and the output of @code{printf} is appended to the file. +Version 2.10 of @command{gawk} introduced the following features: -@item printf @var{fmt}, @var{expr-list} | @var{command} -Format and print, sending the output down a pipe to @var{command}. -The pipeline to the command stays open until the @code{close} function -is called. -@end table +@itemize @bullet +@item +The @env{AWKPATH} environment variable for specifying a path search for +the @option{-f} command-line option +(@pxref{Options, ,Command-Line Options}). -@code{getline} returns zero on end of file, and @minus{}1 on an error. -In the event of an error, @code{getline} will set @code{ERRNO} to -the value of a system-dependent string that describes the error. +@item +The @code{IGNORECASE} variable and its effects +(@pxref{Case-sensitivity, ,Case Sensitivity in Matching}). -@node Printf Summary, Special File Summary, I/O Summary, Actions Summary -@appendixsubsec @code{printf} Summary +@item +The @file{/dev/stdin}, @file{/dev/stdout}, @file{/dev/stderr} and +@file{/dev/fd/@var{N}} special @value{FN}s +(@pxref{Special Files, ,Special @value{FFN}s in @command{gawk}}). +@end itemize -Conversion specification have the form -@code{%}[@var{flag}][@var{width}][@code{.}@var{prec}]@var{format}. -@c whew! -Items in brackets are optional. +Version 2.13 of @command{gawk} introduced the following features: -The @code{awk} @code{printf} statement and @code{sprintf} function -accept the following conversion specification formats: +@itemize @bullet +@item +The @code{FIELDWIDTHS} variable and its effects +(@pxref{Constant Size, ,Reading Fixed-Width Data}). -@table @code -@item %c -An ASCII character. If the argument used for @samp{%c} is numeric, it is -treated as a character and printed. Otherwise, the argument is assumed to -be a string, and the only first character of that string is printed. +@item +The @code{systime} and @code{strftime} built-in functions for obtaining +and printing timestamps +(@pxref{Time Functions, ,Using @command{gawk}'s Timestamp Functions}). -@item %d -@itemx %i -A decimal number (the integer part). +@item +The @option{-W lint} option to provide error and portability checking +for both the source code and at runtime +(@pxref{Options, ,Command-Line Options}). -@item %e -@itemx %E -A floating point number of the form -@samp{@r{[}-@r{]}d.dddddde@r{[}+-@r{]}dd}. -The @samp{%E} format uses @samp{E} instead of @samp{e}. +@item +The @option{-W compat} option to turn off the GNU extensions +(@pxref{Options, ,Command-Line Options}). -@item %f -A floating point number of the form -@r{[}@code{-}@r{]}@code{ddd.dddddd}. +@item +The @option{-W posix} option for full POSIX compliance +(@pxref{Options, ,Command-Line Options}). +@end itemize -@item %g -@itemx %G -Use either the @samp{%e} or @samp{%f} formats, whichever produces a shorter -string, with non-significant zeros suppressed. -@samp{%G} will use @samp{%E} instead of @samp{%e}. +Version 2.14 of @command{gawk} introduced the following feature: -@item %o -An unsigned octal number (also an integer). +@itemize @bullet +@item +The @code{next file} statement for skipping to the next @value{DF} +(@pxref{Nextfile Statement, ,Using @command{gawk}'s @code{nextfile} Statement}). +@end itemize -@item %u -An unsigned decimal number (again, an integer). +Version 2.15 of @command{gawk} introduced the following features: -@item %s -A character string. +@itemize @bullet +@item +The @code{ARGIND} variable, which tracks the movement of @code{FILENAME} +through @code{ARGV} (@pxref{Built-in Variables}). -@item %x -@itemx %X -An unsigned hexadecimal number (an integer). -The @samp{%X} format uses @samp{A} through @samp{F} instead of -@samp{a} through @samp{f} for decimal 10 through 15. +@item +The @code{ERRNO} variable, which contains the system error message when +@code{getline} returns @minus{}1 or when @code{close} fails +(@pxref{Built-in Variables}). -@item %% -A single @samp{%} character; no argument is converted. -@end table +@item +The @file{/dev/pid}, @file{/dev/ppid}, @file{/dev/pgrpid}, and +@file{/dev/user} @value{FN} interpretation +(@pxref{Special Files, ,Special @value{FFN}s in @command{gawk}}). -There are optional, additional parameters that may lie between the @samp{%} -and the control letter: +@item +The ability to delete all of an array at once with @samp{delete @var{array}} +(@pxref{Delete, ,The @code{delete} Statement}). -@table @code -@item - -The expression should be left-justified within its field. +@item +The ability to use GNU-style long-named options that start with @option{--} +(@pxref{Options, ,Command-Line Options}). -@item @var{space} -For numeric conversions, prefix positive values with a space, and -negative values with a minus sign. +@item +The @option{--source} option for mixing command-line and library +file source code +(@pxref{Options, ,Command-Line Options}). +@end itemize -@item + -The plus sign, used before the width modifier (see below), -says to always supply a sign for numeric conversions, even if the data -to be formatted is positive. The @samp{+} overrides the space modifier. +Version 3.0 of @command{gawk} introduced the following features: -@item # -Use an ``alternate form'' for certain control letters. -For @samp{o}, supply a leading zero. -For @samp{x}, and @samp{X}, supply a leading @samp{0x} or @samp{0X} for -a non-zero result. -For @samp{e}, @samp{E}, and @samp{f}, the result will always contain a -decimal point. -For @samp{g}, and @samp{G}, trailing zeros are not removed from the result. +@itemize @bullet +@item +@code{IGNORECASE} changed, now applying to string comparison as well +as regexp operations +(@pxref{Case-sensitivity, ,Case Sensitivity in Matching}). -@item 0 -A leading @samp{0} (zero) acts as a flag, that indicates output should be -padded with zeros instead of spaces. -This applies even to non-numeric output formats. -This flag only has an effect when the field width is wider than the -value to be printed. +@item +The @code{RT} variable that contains the input text that +matched @code{RS} +(@pxref{Records, ,How Input Is Split into Records}). -@item @var{width} -The field should be padded to this width. The field is normally padded -with spaces. If the @samp{0} flag has been used, it is padded with zeros. +@item +Full support for both POSIX and GNU regexps +(@pxref{Regexp, , Regular Expressions}). -@item .@var{prec} -A number that specifies the precision to use when printing. -For the @samp{e}, @samp{E}, and @samp{f} formats, this specifies the -number of digits you want printed to the right of the decimal point. -For the @samp{g}, and @samp{G} formats, it specifies the maximum number -of significant digits. For the @samp{d}, @samp{o}, @samp{i}, @samp{u}, -@samp{x}, and @samp{X} formats, it specifies the minimum number of -digits to print. For the @samp{s} format, it specifies the maximum number of -characters from the string that should be printed. -@end table +@item +The @code{gensub} function for more powerful text manipulation +(@pxref{String Functions, ,String Manipulation Functions}). -Either or both of the @var{width} and @var{prec} values may be specified -as @samp{*}. In that case, the particular value is taken from the argument -list. +@item +The @code{strftime} function acquired a default time format, +allowing it to be called with no arguments +(@pxref{Time Functions, ,Using @command{gawk}'s Timestamp Functions}). -@xref{Printf, ,Using @code{printf} Statements for Fancier Printing}. +@item +The ability for @code{FS} and for the third +argument to @code{split} to be null strings +(@pxref{Single Character Fields, , Making Each Character a Separate Field}). -@node Special File Summary, Built-in Functions Summary, Printf Summary, Actions Summary -@appendixsubsec Special File Names +@item +The ability for @code{RS} to be a regexp +(@pxref{Records, ,How Input Is Split into Records}). -When doing I/O redirection from either @code{print} or @code{printf} into a -file, or via @code{getline} from a file, @code{gawk} recognizes certain special -file names internally. These file names allow access to open file descriptors -inherited from @code{gawk}'s parent process (usually the shell). The -file names are: +@item +The @code{next file} statement became @code{nextfile} +(@pxref{Nextfile Statement, ,Using @command{gawk}'s @code{nextfile} Statement}). -@table @file -@item /dev/stdin -The standard input. +@item +The @option{--lint-old} option to +warn about constructs that are not available in +the original Version 7 Unix version of @command{awk} +(@pxref{V7/SVR3.1, ,Major Changes Between V7 and SVR3.1}). -@item /dev/stdout -The standard output. +@item +The @option{-m} option and the @code{fflush} function from the +Bell Laboratories research version of @command{awk} +(@pxref{Options, ,Command-Line Options}; also +@pxref{I/O Functions, ,Input/Output Functions}). -@item /dev/stderr -The standard error output. +@item +The @option{--re-interval} option to provide interval expressions in regexps +(@pxref{Regexp Operators, , Regular Expression Operators}). -@item /dev/fd/@var{n} -The file denoted by the open file descriptor @var{n}. -@end table +@item +The @option{--traditional} option was added as a better name for +@option{--compat} (@pxref{Options, ,Command-Line Options}). -In addition, reading the following files provides process related information -about the running @code{gawk} program. All returned records are terminated -with a newline. +@item +The use of GNU Autoconf to control the configuration process +(@pxref{Quick Installation, , Compiling @command{gawk} for Unix}). -@table @file -@item /dev/pid -Returns the process ID of the current process. +@item +Amiga support +(@pxref{Amiga Installation, ,Installing @command{gawk} on an Amiga}). -@item /dev/ppid -Returns the parent process ID of the current process. +@end itemize -@item /dev/pgrpid -Returns the process group ID of the current process. +Version 3.1 of @command{gawk} introduced the following features: -@item /dev/user -At least four space-separated fields, containing the return values of -the @code{getuid}, @code{geteuid}, @code{getgid}, and @code{getegid} -system calls. -If there are any additional fields, they are the group IDs returned by -@code{getgroups} system call. -(Multiple groups may not be supported on all systems.) -@end table +@itemize @bullet +@item +The @code{BINMODE} special variable for non-POSIX systems, +which allows binary I/O for input and/or output files +(@pxref{PC Using, ,Using @command{gawk} on PC Operating Systems}). -@noindent -These file names may also be used on the command line to name data files. -These file names are only recognized internally if you do not -actually have files with these names on your system. +@item +The @code{LINT} special variable, which dynamically controls lint warnings +(@pxref{Built-in Variables}). -@xref{Special Files, ,Special File Names in @code{gawk}}, for a longer description that -provides the motivation for this feature. +@item +The @code{PROCINFO} array for providing process-related information +(@pxref{Built-in Variables}). -@node Built-in Functions Summary, Time Functions Summary, Special File Summary, Actions Summary -@appendixsubsec Built-in Functions +@item +The @code{TEXTDOMAIN} special variable for setting an application's +internationalization text domain +(@pxref{Built-in Variables}, +and +@ref{Internationalization, ,Internationalization with @command{gawk}}). -@code{awk} provides a number of built-in functions for performing -numeric operations, string related operations, and I/O related operations. +@item +The ability to use octal and hexadecimal constants in @command{awk} +program source code +(@pxref{Non-decimal-numbers, ,Octal and Hexadecimal Numbers}). -@c NEEDED -@page -The built-in arithmetic functions are: +@item +The @samp{|&} operator for two-way I/O to a coprocess +(@pxref{Two-way I/O, ,Two-Way Communications with Another Process}). -@table @code -@item atan2(@var{y}, @var{x}) -the arctangent of @var{y/x} in radians. +@item +The @file{/inet} special files for TCP/IP networking using @samp{|&} +(@pxref{TCP/IP Networking, , Using @command{gawk} for Network Programming}). -@item cos(@var{expr}) -the cosine of @var{expr}, which is in radians. +@item +The optional second argument to @code{close} that allows closing one end +of a two-way pipe to a coprocess +(@pxref{Two-way I/O, ,Two-Way Communications with Another Process}). -@item exp(@var{expr}) -the exponential function (@code{e ^ @var{expr}}). +@item +The optional third argument to the @code{match} function +for capturing text-matching subexpressions within a regexp +(@pxref{String Functions, , String Manipulation Functions}). -@item int(@var{expr}) -truncates to integer. +@item +Positional specifiers in @code{printf} formats for +making translations easier +(@pxref{Printf Ordering, , Rearranging @code{printf} Arguments}). -@item log(@var{expr}) -the natural logarithm of @code{expr}. +@item +The @code{asort} function for sorting arrays +(@pxref{Array Sorting, ,Sorting Array Values and Indices with @command{gawk}}). -@item rand() -a random number between zero and one. +@item +The @code{bindtextdomain} and @code{dcgettext} functions +for internationalization +(@pxref{Programmer i18n, ,Internationalizing @command{awk} Programs}). -@item sin(@var{expr}) -the sine of @var{expr}, which is in radians. +@item +The @code{extension} built-in function and the ability to add +new built-in functions dynamically +(@pxref{Dynamic Extensions, , Adding New Built-in Functions to @command{gawk}}). -@item sqrt(@var{expr}) -the square root function. +@item +The @code{mktime} built-in function for creating timestamps +(@pxref{Time Functions, ,Using @command{gawk}'s Timestamp Functions}). -@item srand(@r{[}@var{expr}@r{]}) -use @var{expr} as a new seed for the random number generator. If no @var{expr} -is provided, the time of day is used. The return value is the previous -seed for the random number generator. -@end table +@item +The +@code{and}, +@code{or}, +@code{xor}, +@code{compl}, +@code{lshift}, +@code{rshift}, +and +@code{strtonum} built-in +functions +(@pxref{Bitwise Functions, ,Using @command{gawk}'s Bit Manipulation Functions}). -@code{awk} has the following built-in string functions: +@item +@cindex @code{next file} statement +The support for @samp{next file} as two words was removed completely +(@pxref{Nextfile Statement, ,Using @command{gawk}'s @code{nextfile} Statement}). -@table @code -@item gensub(@var{regex}, @var{subst}, @var{how} @r{[}, @var{target}@r{]}) -If @var{how} is a string beginning with @samp{g} or @samp{G}, then -replace each match of @var{regex} in @var{target} with @var{subst}. -Otherwise, replace the @var{how}'th occurrence. If @var{target} is not -supplied, use @code{$0}. The return value is the changed string; the -original @var{target} is not modified. Within @var{subst}, -@samp{\@var{n}}, where @var{n} is a digit from one to nine, can be used to -indicate the text that matched the @var{n}'th parenthesized -subexpression. -This function is @code{gawk}-specific. - -@item gsub(@var{regex}, @var{subst} @r{[}, @var{target}@r{]}) -for each substring matching the regular expression @var{regex} in the string -@var{target}, substitute the string @var{subst}, and return the number of -substitutions. If @var{target} is not supplied, use @code{$0}. - -@item index(@var{str}, @var{search}) -returns the index of the string @var{search} in the string @var{str}, or -zero if -@var{search} is not present. - -@item length(@r{[}@var{str}@r{]}) -returns the length of the string @var{str}. The length of @code{$0} -is returned if no argument is supplied. - -@item match(@var{str}, @var{regex}) -returns the position in @var{str} where the regular expression @var{regex} -occurs, or zero if @var{regex} is not present, and sets the values of -@code{RSTART} and @code{RLENGTH}. - -@item split(@var{str}, @var{arr} @r{[}, @var{regex}@r{]}) -splits the string @var{str} into the array @var{arr} on the regular expression -@var{regex}, and returns the number of elements. If @var{regex} is omitted, -@code{FS} is used instead. @var{regex} can be the null string, causing -each character to be placed into its own array element. -The array @var{arr} is cleared first. - -@item sprintf(@var{fmt}, @var{expr-list}) -prints @var{expr-list} according to @var{fmt}, and returns the resulting string. - -@item sub(@var{regex}, @var{subst} @r{[}, @var{target}@r{]}) -just like @code{gsub}, but only the first matching substring is replaced. - -@item substr(@var{str}, @var{index} @r{[}, @var{len}@r{]}) -returns the @var{len}-character substring of @var{str} starting at @var{index}. -If @var{len} is omitted, the rest of @var{str} is used. - -@item tolower(@var{str}) -returns a copy of the string @var{str}, with all the upper-case characters in -@var{str} translated to their corresponding lower-case counterparts. -Non-alphabetic characters are left unchanged. - -@item toupper(@var{str}) -returns a copy of the string @var{str}, with all the lower-case characters in -@var{str} translated to their corresponding upper-case counterparts. -Non-alphabetic characters are left unchanged. -@end table +@item +The @option{--dump-variables} option to print a list of all global variables +(@pxref{Options, ,Command-Line Options}). -The I/O related functions are: +@item +The @option{--gen-po} command-line option and the use of a leading +underscore to mark strings that should be translated +(@pxref{String Extraction, ,Extracting Marked Strings}). -@table @code -@item close(@var{expr}) -Close the open file or pipe denoted by @var{expr}. +@item +The @option{--non-decimal-data} option to allow non-decimal +input data +(@pxref{Non-decimal Data, ,Allowing Non-Decimal Input Data}). -@item fflush(@r{[}@var{expr}@r{]}) -Flush any buffered output for the output file or pipe denoted by @var{expr}. -If @var{expr} is omitted, standard output is flushed. -If @var{expr} is the null string (@code{""}), all output buffers are flushed. +@item +The @option{--profile} option and @command{pgawk}, the +profiling version of @command{gawk}, for producing execution +profiles of @command{awk} programs +(@pxref{Profiling, ,Profiling Your @command{awk} Programs}). -@item system(@var{cmd-line}) -Execute the command @var{cmd-line}, and return the exit status. -If your operating system does not support @code{system}, calling it will -generate a fatal error. +@item +The @option{--enable-portals} configuration option to enable special treatment of +pathnames that begin with @file{/p} as BSD portals +(@pxref{Portal Files, , Using @command{gawk} with BSD Portals}). -@samp{system("")} can be used to force @code{awk} to flush any pending -output. This is more portable, but less obvious, than calling @code{fflush}. -@end table +@item +The use of GNU Automake to help in standardizing the configuration process +(@pxref{Quick Installation, , Compiling @command{gawk} for Unix}). -@node Time Functions Summary, String Constants Summary, Built-in Functions Summary, Actions Summary -@appendixsubsec Time Functions +@item +The use of GNU @code{gettext} for @command{gawk}'s own message output +(@pxref{Gawk I18N, ,@command{gawk} Can Speak Your Language}). -The following two functions are available for getting the current -time of day, and for formatting time stamps. -They are specific to @code{gawk}. +@item +BeOS support +(@pxref{BeOS Installation, , Installing @command{gawk} on BeOS}). -@table @code -@item systime() -returns the current time of day as the number of seconds since a particular -epoch (Midnight, January 1, 1970 UTC, on POSIX systems). - -@item strftime(@r{[}@var{format}@r{[}, @var{timestamp}@r{]]}) -formats @var{timestamp} according to the specification in @var{format}. -The current time of day is used if no @var{timestamp} is supplied. -A default format equivalent to the output of the @code{date} utility is used if -no @var{format} is supplied. -@xref{Time Functions, ,Functions for Dealing with Time Stamps}, for the -details on the conversion specifiers that @code{strftime} accepts. -@end table +@item +Tandem support +(@pxref{Tandem Installation, ,Installing @command{gawk} on a Tandem}). -@iftex -@xref{Built-in, ,Built-in Functions}, for a description of all of -@code{awk}'s built-in functions. -@end iftex +@item +The Atari port became officially unsupported +(@pxref{Atari Installation, ,Installing @command{gawk} on the Atari ST}). -@node String Constants Summary, , Time Functions Summary, Actions Summary -@appendixsubsec String Constants +@item +The source code now uses new-style function definitions, with +@command{ansi2knr} to convert the code on systems with old compilers. -String constants in @code{awk} are sequences of characters enclosed -in double quotes (@code{"}). Within strings, certain @dfn{escape sequences} -are recognized, as in C. These are: +@end itemize -@table @code -@item \\ -A literal backslash. +@c XXX ADD MORE STUFF HERE -@item \a -The ``alert'' character; usually the ASCII BEL character. +@node Contributors, , POSIX/GNU, Language History +@appendixsec Major Contributors to @command{gawk} +@cindex contributors to @command{gawk} +@quotation +@i{Always give credit where credit is due.}@* +Anonymous +@end quotation -@item \b -Backspace. +This @value{SECTION} names the major contributors to @command{gawk} +and/or this @value{DOCUMENT}, in approximate chronological order: -@item \f -Formfeed. +@itemize @bullet +@item +@cindex Aho, Alfred +@cindex Weinberger, Peter +@cindex Kernighan, Brian +Dr.@: Alfred V.@: Aho, +Dr.@: Peter J.@: Weinberger, and +Dr.@: Brian W.@: Kernighan, all of Bell Laboratories, +designed and implemented Unix @command{awk}, +from which @command{gawk} gets the majority of its feature set. -@item \n -Newline. +@item +@cindex Rubin, Paul +Paul Rubin +did the initial design and implementation in 1986, and wrote +the first draft (around 40 pages) of this @value{DOCUMENT}. -@item \r -Carriage return. +@item +@cindex Fenlason, Jay +Jay Fenlason +finished the initial implementation. -@item \t -Horizontal tab. +@item +@cindex Close, Diane +Diane Close +revised the first draft of this @value{DOCUMENT}, bringing it +to around 90 pages. -@item \v -Vertical tab. - -@item \x@var{hex digits} -The character represented by the string of hexadecimal digits following -the @samp{\x}. As in ANSI C, all following hexadecimal digits are -considered part of the escape sequence. E.g., @code{"\x1B"} is a -string containing the ASCII ESC (escape) character. (The @samp{\x} -escape sequence is not in POSIX @code{awk}.) - -@item \@var{ddd} -The character represented by the one, two, or three digit sequence of octal -digits. Thus, @code{"\033"} is also a string containing the ASCII ESC -(escape) character. - -@item \@var{c} -The literal character @var{c}, if @var{c} is not one of the above. -@end table +@item +@cindex Stallman, Richard +Richard Stallman +helped finish the implementation and the initial draft of this +@value{DOCUMENT}. +He is also the founder of the FSF and the GNU project. -The escape sequences may also be used inside constant regular expressions -(e.g., the regexp @code{@w{/[@ \t\f\n\r\v]/}} matches whitespace -characters). +@item +@cindex Woods, John +John Woods +contributed parts of the code (mostly fixes) in +the initial version of @command{gawk}. -@xref{Escape Sequences}. +@item +@cindex Trueman, David +In 1988, +David Trueman +took over primary maintenance of @command{gawk}, +making it compatible with ``new'' @command{awk}, and +greatly improving its performance. -@node Functions Summary, Historical Features, Actions Summary, Gawk Summary -@appendixsec User-defined Functions +@item +@cindex Rankin, Pat +Pat Rankin +provided the VMS port and its documentation. -Functions in @code{awk} are defined as follows: +@item +@cindex Kwok, Conrad +@cindex Garfinkle, Scott +@cindex Williams, Kent +Conrad Kwok, +Scott Garfinkle, +and +Kent Williams +did the initial ports to MS-DOS with various versions of MSC. -@example -function @var{name}(@var{parameter list}) @{ @var{statements} @} -@end example +@item +@cindex Peterson, Hal +Hal Peterson +provided help in porting @command{gawk} to Cray systems. -Actual parameters supplied in the function call are used to instantiate -the formal parameters declared in the function. Arrays are passed by -reference, other variables are passed by value. +@item +@cindex Rommel, Kai Uwe +Kai Uwe Rommel +provided the port to OS/2 and its documentation. -If there are fewer arguments passed than there are names in @var{parameter-list}, -the extra names are given the null string as their value. Extra names have the -effect of local variables. +@item +@cindex Jaegermann, Michal +Michal Jaegermann +provided the port to Atari systems and its documentation. +He continues to provide portability checking with DEC Alpha +systems, and has done a lot of work to make sure @command{gawk} +works on non-32-bit systems. -The open-parenthesis in a function call of a user-defined function must -immediately follow the function name, without any intervening white space. -This is to avoid a syntactic ambiguity with the concatenation operator. +@item +@cindex Fish, Fred +Fred Fish +provided the port to Amiga systems and its documentation. -The word @code{func} may be used in place of @code{function} (but not in -POSIX @code{awk}). +@item +@cindex Deifik, Scott +Scott Deifik +currently maintains the MS-DOS port. -Use the @code{return} statement to return a value from a function. +@item +@cindex Grigera, Juan +Juan Grigera +maintains the port to Win32 systems. -@xref{User-defined, ,User-defined Functions}. +@item +@cindex Hankerson, Darrel +Dr.@: Darrel Hankerson +acts as coordinator for the various ports to different PC platforms +and creates binary distributions for various PC operating systems. +He is also instrumental in keeping the documentation up to date for +the various PC platforms. -@node Historical Features, , Functions Summary, Gawk Summary -@appendixsec Historical Features +@item +@cindex Zoulas, Christos +Christos Zoulas +provided the @code{extension} +built-in function for dynamically adding new modules. -@cindex historical features -There are two features of historical @code{awk} implementations that -@code{gawk} supports. +@item +@cindex Kahrs, J@"urgen +J@"urgen Kahrs +contributed the initial version of the TCP/IP networking +code and documentation, and motivated the inclusion of the @samp{|&} operator. -First, it is possible to call the @code{length} built-in function not only -with no arguments, but even without parentheses! +@item +@cindex Davies, Stephen +Stephen Davies +provided the port to Tandem systems and its documentation. -@example -a = length -@end example +@item +@cindex Brown, Martin +Martin Brown +provided the port to BeOS and its documentation. -@noindent -is the same as either of +@item +@cindex Peters, Arno +Arno Peters +did the initial work to convert @command{gawk} to use +GNU Automake and @code{gettext}. -@example -a = length() -a = length($0) -@end example +@item +@cindex Broder, Alan J.@: +Alan J.@: Broder +provided the initial version of the @code{asort} function +as well as the code for the new optional third argument to the @code{match} function. -@noindent -For example: +@item +@cindex Robbins, Arnold +Arnold Robbins +has been working on @command{gawk} since 1988, at first +helping David Trueman, and as the primary maintainer since around 1994. +@end itemize -@example -$ echo abcdef | awk '@{ print length @}' -@print{} 6 -@end example +@node Installation, Notes, Language History, Top +@appendix Installing @command{gawk} -@noindent -This feature is marked as ``deprecated'' in the POSIX standard, and -@code{gawk} will issue a warning about its use if @samp{--lint} is -specified on the command line. -(The ability to use @code{length} this way was actually an accident of the -original Unix @code{awk} implementation. If any built-in function used -@code{$0} as its default argument, it was possible to call that function -without the parentheses. In particular, it was common practice to use -the @code{length} function in this fashion, and this usage was documented -in the @code{awk} manual page.) - -The other historical feature is the use of either the @code{break} statement, -or the @code{continue} statement -outside the body of a @code{while}, @code{for}, or @code{do} loop. Traditional -@code{awk} implementations have treated such usage as equivalent to the -@code{next} statement. More recent versions of Unix @code{awk} do not allow -it. @code{gawk} supports this usage if @samp{--traditional} has been -specified. - -@xref{Options, ,Command Line Options}, for more information about the -@samp{--posix} and @samp{--lint} options. - -@node Installation, Notes, Gawk Summary, Top -@appendix Installing @code{gawk} - -This appendix provides instructions for installing @code{gawk} on the +@cindex Linux +@cindex GNU/Linux +This appendix provides instructions for installing @command{gawk} on the various platforms that are supported by the developers. The primary -developers support Unix (and one day, GNU), while the other ports were -contributed. The file @file{ACKNOWLEDGMENT} in the @code{gawk} -distribution lists the electronic mail addresses of the people who did -the respective ports, and they are also provided in -@ref{Bugs, , Reporting Problems and Bugs}. +developer supports GNU/Linux (and Unix), whereas the other ports are +contributed. +@xref{Bugs, , Reporting Problems and Bugs}, +for the electronic mail addresses of the people who did +the respective ports. @menu -* Gawk Distribution:: What is in the @code{gawk} distribution. -* Unix Installation:: Installing @code{gawk} under various versions - of Unix. -* VMS Installation:: Installing @code{gawk} on VMS. -* PC Installation:: Installing and Compiling @code{gawk} on MS-DOS - and OS/2 -* Atari Installation:: Installing @code{gawk} on the Atari ST. -* Amiga Installation:: Installing @code{gawk} on an Amiga. +* Gawk Distribution:: What is in the @command{gawk} distribution. +* Unix Installation:: Installing @command{gawk} under various + versions of Unix. +* Non-Unix Installation:: Installation on Other Operating Systems. +* Unsupported:: Systems whose ports are no longer supported. * Bugs:: Reporting Problems and Bugs. -* Other Versions:: Other freely available @code{awk} +* Other Versions:: Other freely available @command{awk} implementations. @end menu @node Gawk Distribution, Unix Installation, Installation, Installation -@appendixsec The @code{gawk} Distribution +@appendixsec The @command{gawk} Distribution -This section first describes how to get the @code{gawk} +This @value{SECTION} describes how to get the @command{gawk} distribution, how to extract it, and then what is in the various files and subdirectories. @@ -18647,228 +21545,135 @@ subdirectories. @end menu @node Getting, Extracting, Gawk Distribution, Gawk Distribution -@appendixsubsec Getting the @code{gawk} Distribution -@cindex getting @code{gawk} -@cindex anonymous @code{ftp} -@cindex @code{ftp}, anonymous -@cindex Free Software Foundation -There are three ways you can get GNU software. +@appendixsubsec Getting the @command{gawk} Distribution +@cindex getting @command{gawk} +@cindex anonymous @command{ftp} +@cindex @command{ftp}, anonymous +@cindex source code, @command{gawk} +@cindex @command{gawk}, source code +There are three ways to get GNU software: -@enumerate +@itemize @bullet @item -You can copy it from someone else who already has it. +Copy it from someone else who already has it. +@cindex FSF @cindex Free Software Foundation @item -You can order @code{gawk} directly from the Free Software Foundation. +Order @command{gawk} directly from the Free Software Foundation. Software distributions are available for Unix, MS-DOS, and VMS, on -tape and CD-ROM. The address is: +tape and CD-ROM. Their address is: -@quotation -Free Software Foundation @* -59 Temple Place---Suite 330 @* -Boston, MA 02111-1307 USA @* -Phone: +1-617-542-5942 @* -Fax (including Japan): +1-617-542-2652 @* -Email: @code{gnu@@gnu.org} @* -URL: @code{http://www.gnu.org/} @* -@end quotation +@display +Free Software Foundation +59 Temple Place, Suite 330 +Boston, MA 02111-1307 USA +Phone: +1-617-542-5942 +Fax (including Japan): +1-617-542-2652 +Email: @email{gnu@@gnu.org} +URL: @uref{http://www.gnu.org/} +@end display @noindent Ordering from the FSF directly contributes to the support of the foundation and to the production of more free software. @item -You can get @code{gawk} by using anonymous @code{ftp} to the Internet host +Retrieve @command{gawk} by using anonymous @command{ftp} to the Internet host @code{gnudist.gnu.org}, in the directory @file{/gnu/gawk}. +@end itemize -Here is a list of alternate @code{ftp} sites from which you can obtain GNU -software. When a site is listed as ``@var{site}@code{:}@var{directory}'' the -@var{directory} indicates the directory where GNU software is kept. -You should use a site that is geographically close to you. - -@table @asis -@item Asia: -@table @code -@item cair-archive.kaist.ac.kr:/pub/gnu -@itemx ftp.cs.titech.ac.jp -@itemx ftp.nectec.or.th:/pub/mirrors/gnu -@itemx utsun.s.u-tokyo.ac.jp:/ftpsync/prep -@end table - -@c NEEDED -@page -@item Australia: -@table @code -@item archie.au:/gnu -(@code{archie.oz} or @code{archie.oz.au} for ACSnet) -@end table - -@item Africa: -@table @code -@item ftp.sun.ac.za:/pub/gnu -@end table - -@item Middle East: -@table @code -@item ftp.technion.ac.il:/pub/unsupported/gnu -@end table - -@item Europe: -@table @code -@item archive.eu.net -@itemx ftp.denet.dk -@itemx ftp.eunet.ch -@itemx ftp.funet.fi:/pub/gnu -@itemx ftp.ieunet.ie:pub/gnu -@itemx ftp.informatik.rwth-aachen.de:/pub/gnu -@itemx ftp.informatik.tu-muenchen.de -@itemx ftp.luth.se:/pub/unix/gnu -@itemx ftp.mcc.ac.uk -@itemx ftp.stacken.kth.se -@itemx ftp.sunet.se:/pub/gnu -@itemx ftp.univ-lyon1.fr:pub/gnu -@itemx ftp.win.tue.nl:/pub/gnu -@itemx irisa.irisa.fr:/pub/gnu -@itemx isy.liu.se -@itemx nic.switch.ch:/mirror/gnu -@itemx src.doc.ic.ac.uk:/gnu -@itemx unix.hensa.ac.uk:/pub/uunet/systems/gnu -@end table - -@item South America: -@table @code -@item ftp.inf.utfsm.cl:/pub/gnu -@itemx ftp.unicamp.br:/pub/gnu -@end table - -@item Western Canada: -@table @code -@item ftp.cs.ubc.ca:/mirror2/gnu -@end table - -@item USA: -@table @code -@item col.hp.com:/mirrors/gnu -@itemx f.ms.uky.edu:/pub3/gnu -@itemx ftp.cc.gatech.edu:/pub/gnu -@itemx ftp.cs.columbia.edu:/archives/gnu/prep -@itemx ftp.digex.net:/pub/gnu -@itemx ftp.hawaii.edu:/mirrors/gnu -@itemx ftp.kpc.com:/pub/mirror/gnu -@end table - -@c NEEDED -@page -@item USA (continued): -@table @code -@itemx ftp.uu.net:/systems/gnu -@itemx gatekeeper.dec.com:/pub/GNU -@itemx jaguar.utah.edu:/gnustuff -@itemx labrea.stanford.edu -@itemx mrcnext.cso.uiuc.edu:/pub/gnu -@itemx vixen.cso.uiuc.edu:/gnu -@itemx wuarchive.wustl.edu:/systems/gnu -@end table -@end table -@end enumerate +The GNU software archive is mirrored around the world. +The up-to-date list of mirror sites is available from +@uref{http://www.gnu.org/order/ftp.html, the main FSF web site}. +Try to use one of the mirrors; they +will be less busy, and you can usually find one closer to your site. @node Extracting, Distribution contents, Getting, Gawk Distribution @appendixsubsec Extracting the Distribution -@code{gawk} is distributed as a @code{tar} file compressed with the +@command{gawk} is distributed as a @code{tar} file compressed with the GNU Zip program, @code{gzip}. Once you have the distribution (for example, -@file{gawk-@value{VERSION}.@value{PATCHLEVEL}.tar.gz}), first use @code{gzip} to expand the -file, and then use @code{tar} to extract it. You can use the following -pipeline to produce the @code{gawk} distribution: +@file{gawk-@value{VERSION}.@value{PATCHLEVEL}.tar.gz}), +use @code{gzip} to expand the +file and then use @code{tar} to extract it. You can use the following +pipeline to produce the @command{gawk} distribution: @example -# Under System V, add 'o' to the tar flags +# Under System V, add 'o' to the tar options gzip -d -c gawk-@value{VERSION}.@value{PATCHLEVEL}.tar.gz | tar -xvpf - @end example @noindent -This will create a directory named @file{gawk-@value{VERSION}.@value{PATCHLEVEL}} in the current -directory. +This creates a directory named @file{gawk-@value{VERSION}.@value{PATCHLEVEL}} +in the current directory. -The distribution file name is of the form -@file{gawk-@var{V}.@var{R}.@var{n}.tar.gz}. -The @var{V} represents the major version of @code{gawk}, +The distribution @value{FN} is of the form +@file{gawk-@var{V}.@var{R}.@var{P}.tar.gz}. +The @var{V} represents the major version of @command{gawk}, the @var{R} represents the current release of version @var{V}, and -the @var{n} represents a @dfn{patch level}, meaning that minor bugs have +the @var{P} represents a @dfn{patch level}, meaning that minor bugs have been fixed in the release. The current patch level is @value{PATCHLEVEL}, -but when -retrieving distributions, you should get the version with the highest -version, release, and patch level. (Note that release levels greater than -or equal to 90 denote ``beta,'' or non-production software; you may not wish +but when retrieving distributions, you should get the version with the highest +version, release, and patch level. (Note, however, that patch levels greater than +or equal to 80 denote ``beta'' or non-production software; you might not want to retrieve such a version unless you don't mind experimenting.) - -If you are not on a Unix system, you will need to make other arrangements -for getting and extracting the @code{gawk} distribution. You should consult +If you are not on a Unix system, you need to make other arrangements +for getting and extracting the @command{gawk} distribution. You should consult a local expert. -@node Distribution contents, , Extracting, Gawk Distribution -@appendixsubsec Contents of the @code{gawk} Distribution +@node Distribution contents, , Extracting, Gawk Distribution +@appendixsubsec Contents of the @command{gawk} Distribution -The @code{gawk} distribution has a number of C source files, +The @command{gawk} distribution has a number of C source files, documentation files, -subdirectories and files related to the configuration process -(@pxref{Unix Installation, ,Compiling and Installing @code{gawk} on Unix}), -and several subdirectories related to different, non-Unix, -operating systems. +subdirectories, and files related to the configuration process +(@pxref{Unix Installation, ,Compiling and Installing @command{gawk} on Unix}), +as well as several subdirectories related to different non-Unix +operating systems: @table @asis -@item various @samp{.c}, @samp{.y}, and @samp{.h} files -These files are the actual @code{gawk} source code. +@item Various @samp{.c}, @samp{.y}, and @samp{.h} files: +These files are the actual @command{gawk} source code. @end table @table @file @item README @itemx README_d/README.* -Descriptive files: @file{README} for @code{gawk} under Unix, and the +Descriptive files: @file{README} for @command{gawk} under Unix and the rest for the various hardware and software combinations. @item INSTALL A file providing an overview of the configuration and installation process. -@item PORTS -A list of systems to which @code{gawk} has been ported, and which -have successfully run the test suite. - -@item ACKNOWLEDGMENT -A list of the people who contributed major parts of the code or documentation. - @item ChangeLog A detailed list of source code changes as bugs are fixed or improvements made. @item NEWS -A list of changes to @code{gawk} since the last release or patch. +A list of changes to @command{gawk} since the last release or patch. @item COPYING The GNU General Public License. @item FUTURES -A brief list of features and/or changes being contemplated for future +A brief list of features and changes being contemplated for future releases, with some indication of the time frame for the feature, based on its difficulty. @item LIMITATIONS -A list of those factors that limit @code{gawk}'s performance. +A list of those factors that limit @command{gawk}'s performance. Most of these depend on the hardware or operating system software, and -are not limits in @code{gawk} itself. +are not limits in @command{gawk} itself. @item POSIX.STD -A description of one area where the POSIX standard for @code{awk} is -incorrect, and how @code{gawk} handles the problem. - -@item PROBLEMS -A file describing known problems with the current release. +A description of one area where the POSIX standard for @command{awk} is +incorrect as well as how @command{gawk} handles the problem. -@cindex artificial intelligence, using @code{gawk} -@cindex AI programming, using @code{gawk} +@cindex artificial intelligence, using @command{gawk} +@cindex AI programming, using @command{gawk} @item doc/awkforai.txt -A short article describing why @code{gawk} is a good language for +A short article describing why @command{gawk} is a good language for AI (Artificial Intelligence) programming. @item doc/README.card @@ -18879,25 +21684,41 @@ AI (Artificial Intelligence) programming. @itemx doc/macros @itemx doc/no.colors @itemx doc/setter.outline -The @code{troff} source for a five-color @code{awk} reference card. -A modern version of @code{troff}, such as GNU Troff (@code{groff}) is +The @command{troff} source for a five-color @command{awk} reference card. +A modern version of @command{troff} such as GNU @command{troff} (@command{groff}) is needed to produce the color version. See the file @file{README.card} -for instructions if you have an older @code{troff}. +for instructions if you have an older @command{troff}. @item doc/gawk.1 -The @code{troff} source for a manual page describing @code{gawk}. +The @command{troff} source for a manual page describing @command{gawk}. This is distributed for the convenience of Unix users. +@cindex Texinfo @item doc/gawk.texi The Texinfo source file for this @value{DOCUMENT}. It should be processed with @TeX{} to produce a printed document, and -with @code{makeinfo} to produce an Info file. +with @command{makeinfo} to produce an Info or HTML file. @item doc/gawk.info The generated Info file for this @value{DOCUMENT}. +@item doc/gawkinet.texi +The Texinfo source file for +@ifinfo +@xref{Top}. +@end ifinfo +@ifnotinfo +@cite{TCP/IP Internetworking with @command{gawk}}. +@end ifnotinfo +It should be processed with @TeX{} to produce a printed document and +with @command{makeinfo} to produce an Info or HTML file. + +@item doc/gawkinet.info +The generated Info file for +@cite{TCP/IP Internetworking with @command{gawk}}. + @item doc/igawk.1 -The @code{troff} source for a manual page describing the @code{igawk} +The @command{troff} source for a manual page describing the @command{igawk} program presented in @ref{Igawk Program, ,An Easy Way to Use Library Functions}. @@ -18905,86 +21726,113 @@ program presented in The input file used during the configuration process to generate the actual @file{Makefile} for creating the documentation. +@item Makefile.am +@itemx */Makefile.am +Files used by the GNU @command{automake} software for generating +the @file{Makefile.in} files used by @command{autoconf} and +@command{configure}. + @item Makefile.in @itemx acconfig.h +@itemx acinclude.m4 @itemx aclocal.m4 @itemx configh.in @itemx configure.in @itemx configure @itemx custom.h -@itemx missing/* -These files and subdirectory are used when configuring @code{gawk} -for various Unix systems. They are explained in detail in -@ref{Unix Installation, ,Compiling and Installing @code{gawk} on Unix}. +@itemx missing_d/* +@itemx m4/* +These files and subdirectories are used when configuring @command{gawk} +for various Unix systems. They are explained in +@ref{Unix Installation, ,Compiling and Installing @command{gawk} on Unix}. + +@item intl/* +@itemx po/* +The @file{intl} directory provides the GNU @code{gettext} library, which implements +@command{gawk}'s internationalization features, while the @file{po} library +contains message translations. @item awklib/extract.awk +@itemx awklib/Makefile.am @itemx awklib/Makefile.in +@itemx awklib/eg/* The @file{awklib} directory contains a copy of @file{extract.awk} (@pxref{Extract Program, ,Extracting Programs from Texinfo Source Files}), which can be used to extract the sample programs from the Texinfo -source file for this @value{DOCUMENT}, and a @file{Makefile.in} file, which -@code{configure} uses to generate a @file{Makefile}. -As part of the process of building @code{gawk}, the library functions from -@ref{Library Functions, , A Library of @code{awk} Functions}, -and the @code{igawk} program from +source file for this @value{DOCUMENT}. It also contains a @file{Makefile.in} file, which +@command{configure} uses to generate a @file{Makefile}. +@file{Makefile.am} is used by GNU Automake to create @file{Makefile.in}. +The library functions from +@ref{Library Functions, , A Library of @command{awk} Functions}, +and the @command{igawk} program from @ref{Igawk Program, , An Easy Way to Use Library Functions}, -are extracted into ready to use files. +are included as ready-to-use files in the @command{gawk} distribution. They are installed as part of the installation process. +The rest of the programs in this @value{DOCUMENT} are available in appropriate +subdirectories of @file{awklib/eg}. + +@item unsupported/atari/* +Files needed for building @command{gawk} on an Atari ST +(@pxref{Atari Installation, ,Installing @command{gawk} on the Atari ST}, for details). -@item atari/* -Files needed for building @code{gawk} on an Atari ST. -@xref{Atari Installation, ,Installing @code{gawk} on the Atari ST}, for details. +@item unsupported/tandem/* +Files needed for building @command{gawk} on a Tandem +(@pxref{Tandem Installation, ,Installing @command{gawk} on a Tandem}, for details). + +@item posix/* +Files needed for building @command{gawk} on POSIX-compliant systems. @item pc/* -Files needed for building @code{gawk} under MS-DOS and OS/2. -@xref{PC Installation, ,MS-DOS and OS/2 Installation and Compilation}, for details. +Files needed for building @command{gawk} under MS-DOS, MS Windows and OS/2 +(@pxref{PC Installation, ,Installation on PC Operating Systems}, for details). @item vms/* -Files needed for building @code{gawk} under VMS. -@xref{VMS Installation, ,How to Compile and Install @code{gawk} on VMS}, for details. +Files needed for building @command{gawk} under VMS +(@pxref{VMS Installation, ,How to Compile and Install @command{gawk} on VMS}, for details). @item test/* A test suite for -@code{gawk}. You can use @samp{make check} from the top level @code{gawk} -directory to run your version of @code{gawk} against the test suite. -If @code{gawk} successfully passes @samp{make check} then you can +@command{gawk}. You can use @samp{make check} from the top-level @command{gawk} +directory to run your version of @command{gawk} against the test suite. +If @command{gawk} successfully passes @samp{make check}, then you can be confident of a successful port. @end table -@node Unix Installation, VMS Installation, Gawk Distribution, Installation -@appendixsec Compiling and Installing @code{gawk} on Unix +@node Unix Installation, Non-Unix Installation, Gawk Distribution, Installation +@appendixsec Compiling and Installing @command{gawk} on Unix -Usually, you can compile and install @code{gawk} by typing only two -commands. However, if you do use an unusual system, you may need -to configure @code{gawk} for your system yourself. +Usually, you can compile and install @command{gawk} by typing only two +commands. However, if you use an unusual system, you may need +to configure @command{gawk} for your system yourself. @menu -* Quick Installation:: Compiling @code{gawk} under Unix. -* Configuration Philosophy:: How it's all supposed to work. +* Quick Installation:: Compiling @command{gawk} under Unix. +* Additional Configuration Options:: Other compile-time options. +* Configuration Philosophy:: How it's all supposed to work. @end menu -@node Quick Installation, Configuration Philosophy, Unix Installation, Unix Installation -@appendixsubsec Compiling @code{gawk} for Unix +@node Quick Installation, Additional Configuration Options, Unix Installation, Unix Installation +@appendixsubsec Compiling @command{gawk} for Unix @cindex installation, unix -After you have extracted the @code{gawk} distribution, @code{cd} +After you have extracted the @command{gawk} distribution, @command{cd} to @file{gawk-@value{VERSION}.@value{PATCHLEVEL}}. Like most GNU software, -@code{gawk} is configured -automatically for your Unix system by running the @code{configure} program. -This program is a Bourne shell script that was generated automatically using -GNU @code{autoconf}. -@iftex -(The @code{autoconf} software is +@command{gawk} is configured +automatically for your Unix system by running the @command{configure} program. +This program is a Bourne shell script that is generated automatically using +GNU @command{autoconf}. +@ifnotinfo +(The @command{autoconf} software is described fully in @cite{Autoconf---Generating Automatic Configuration Scripts}, which is available from the Free Software Foundation.) -@end iftex +@end ifnotinfo @ifinfo -(The @code{autoconf} software is described fully starting with -@ref{Top, , Introduction, autoconf, Autoconf---Generating Automatic Configuration Scripts}.) +(The @command{autoconf} software is described fully starting with +@ref{Top}.) @end ifinfo -To configure @code{gawk}, simply run @code{configure}: +To configure @command{gawk}, simply run @command{configure}: @example sh ./configure @@ -18992,24 +21840,24 @@ sh ./configure This produces a @file{Makefile} and @file{config.h} tailored to your system. The @file{config.h} file describes various facts about your system. -You may wish to edit the @file{Makefile} to +You might want to edit the @file{Makefile} to change the @code{CFLAGS} variable, which controls -the command line options that are passed to the C compiler (such as -optimization levels, or compiling for debugging). +the command-line options that are passed to the C compiler (such as +optimization levels or compiling for debugging). -Alternatively, you can add your own values for most @code{make} -variables, such as @code{CC} and @code{CFLAGS}, on the command line when -running @code{configure}: +Alternatively, you can add your own values for most @command{make} +variables on the command line, such as @code{CC} and @code{CFLAGS}, when +running @command{configure}: @example CC=cc CFLAGS=-g sh ./configure @end example @noindent -See the file @file{INSTALL} in the @code{gawk} distribution for +See the file @file{INSTALL} in the @command{gawk} distribution for all the details. -After you have run @code{configure}, and possibly edited the @file{Makefile}, +After you have run @command{configure} and possibly edited the @file{Makefile}, type: @example @@ -19017,91 +21865,406 @@ make @end example @noindent -and shortly thereafter, you should have an executable version of @code{gawk}. +Shortly thereafter, you should have an executable version of @command{gawk}. That's all there is to it! -(If these steps do not work, please send in a bug report; -@pxref{Bugs, ,Reporting Problems and Bugs}.) +To verify that @command{gawk} is working properly, +run @samp{make check}. All of the tests should succeed. +If these steps do not work, or if any of the tests fail, +check the files in the @file{README_d} directory to see if you've +found a known problem. If the failure is not described there, +please send in a bug report +(@pxref{Bugs, ,Reporting Problems and Bugs}.) + +@node Additional Configuration Options, Configuration Philosophy, Quick Installation, Unix Installation +@appendixsubsec Additional Configuration Options + +There are several additional options you may use on the @command{configure} +command line when compiling @command{gawk} from scratch. + +@table @code +@cindex @code{--enable-portals} configuration option +@cindex configuration option, @code{--enable-portals} +@item --enable-portals +This option causes @command{gawk} to treat pathnames that begin +with @file{/p} as BSD portal files when doing two-way I/O with +the @samp{|&} operator +(@pxref{Portal Files, , Using @command{gawk} with BSD Portals}). + +@cindex Linux +@cindex GNU/Linux +@cindex @code{--with-included-gettext} configuration option +@cindex configuration option, @code{--with-included-gettext} +@item --with-included-gettext +Use the version of the @code{gettext} library that comes with @command{gawk}. +This option should be used on systems that do @emph{not} use @value{PVERSION} 2 (or later) +of the GNU C library. +All known modern GNU/Linux systems use Glibc 2. Use this option on any other system. + +@cindex @code{--disable-nls} configuration option +@cindex configuration option, @code{--disable-nls} +@item --disable-nls +Disable all message translation facilities. +This is usually not desirable, but it may bring you some slight performance +improvement. +You should also use this option if @option{--with-included-gettext} +doesn't work on your system. +@end table -@node Configuration Philosophy, , Quick Installation, Unix Installation +@node Configuration Philosophy, , Additional Configuration Options, Unix Installation @appendixsubsec The Configuration Process -@cindex configuring @code{gawk} -(This section is of interest only if you know something about using the -C language and the Unix operating system.) +@cindex configuring @command{gawk} +This @value{SECTION} is of interest only if you know something about using the +C language and the Unix operating system. -The source code for @code{gawk} generally attempts to adhere to formal -standards wherever possible. This means that @code{gawk} uses library -routines that are specified by the ANSI C standard and by the POSIX -operating system interface standard. When using an ANSI C compiler, +The source code for @command{gawk} generally attempts to adhere to formal +standards wherever possible. This means that @command{gawk} uses library +routines that are specified by the ISO C standard and by the POSIX +operating system interface standard. When using an ISO C compiler, function prototypes are used to help improve the compile-time checking. -Many Unix systems do not support all of either the ANSI or the -POSIX standards. The @file{missing} subdirectory in the @code{gawk} -distribution contains replacement versions of those subroutines that are +Many Unix systems do not support all of either the ISO or the +POSIX standards. The @file{missing_d} subdirectory in the @command{gawk} +distribution contains replacement versions of those functions that are most likely to be missing. -The @file{config.h} file that is created by the @code{configure} program -contains definitions that describe features of the particular operating -system where you are attempting to compile @code{gawk}. The three things -described by this file are what header files are available, so that -they can be correctly included, -what (supposedly) standard functions are actually available in your C -libraries, and -other miscellaneous facts about your -variant of Unix. For example, there may not be an @code{st_blksize} -element in the @code{stat} structure. In this case @samp{HAVE_ST_BLKSIZE} -would be undefined. +The @file{config.h} file that @command{configure} creates contains +definitions that describe features of the particular operating system +where you are attempting to compile @command{gawk}. The three things +described by this file are: what header files are available, so that +they can be correctly included, what (supposedly) standard functions +are actually available in your C libraries, and various miscellaneous +facts about your variant of Unix. For example, there may not be an +@code{st_blksize} element in the @code{stat} structure. In this case, +@samp{HAVE_ST_BLKSIZE} is undefined. @cindex @code{custom.h} configuration file -It is possible for your C compiler to lie to @code{configure}. It may +It is possible for your C compiler to lie to @command{configure}. It may do so by not exiting with an error when a library function is not -available. To get around this, you can edit the file @file{custom.h}. +available. To get around this, edit the file @file{custom.h}. Use an @samp{#ifdef} that is appropriate for your system, and either -@code{#define} any constants that @code{configure} should have defined but -didn't, or @code{#undef} any constants that @code{configure} defined and +@code{#define} any constants that @command{configure} should have defined but +didn't, or @code{#undef} any constants that @command{configure} defined and should not have. @file{custom.h} is automatically included by @file{config.h}. -It is also possible that the @code{configure} program generated by -@code{autoconf} -will not work on your system in some other fashion. If you do have a problem, -the file -@file{configure.in} is the input for @code{autoconf}. You may be able to -change this file, and generate a new version of @code{configure} that will -work on your system. @xref{Bugs, ,Reporting Problems and Bugs}, for -information on how to report problems in configuring @code{gawk}. The same -mechanism may be used to send in updates to @file{configure.in} and/or -@file{custom.h}. +It is also possible that the @command{configure} program generated by +@command{autoconf} will not work on your system in some other fashion. +If you do have a problem, the file @file{configure.in} is the input for +@command{autoconf}. You may be able to change this file and generate a +new version of @command{configure} that works on your system +(@pxref{Bugs, ,Reporting Problems and Bugs}, +for information on how to report problems in configuring @command{gawk}). +The same mechanism may be used to send in updates to @file{configure.in} +and/or @file{custom.h}. + +@node Non-Unix Installation, Unsupported, Unix Installation, Installation +@appendixsec Installation on Other Operating Systems + +This @value{SECTION} describes how to install @command{gawk} on +various non-Unix systems. + +@menu +* Amiga Installation:: Installing @command{gawk} on an Amiga. +* BeOS Installation:: Installing @command{gawk} on BeOS. +* PC Installation:: Installing and Compiling @command{gawk} on + MS-DOS and OS/2. +* VMS Installation:: Installing @command{gawk} on VMS. +@end menu + +@node Amiga Installation, BeOS Installation, Non-Unix Installation, Non-Unix Installation +@appendixsubsec Installing @command{gawk} on an Amiga + +@cindex amiga +@cindex installation, amiga +You can install @command{gawk} on an Amiga system using a Unix emulation +environment, available via anonymous @command{ftp} from +@code{ftp.ninemoons.com} in the directory @file{pub/ade/current}. +This includes a shell based on @command{pdksh}. The primary component of +this environment is a Unix emulation library, @file{ixemul.lib}. +@c could really use more background here, who wrote this, etc. + +A more complete distribution for the Amiga is available on +the Geek Gadgets CD-ROM, available from: + +@display +CRONUS +1840 E. Warner Road #105-265 +Tempe, AZ 85284 USA +US Toll Free: (800) 804-0833 +Phone: +1-602-491-0442 +FAX: +1-602-491-0048 +Email: @email{info@@ninemoons.com} +WWW: @uref{http://www.ninemoons.com} +Anonymous @command{ftp} site: @code{ftp.ninemoons.com} +@end display + +Once you have the distribution, you can configure @command{gawk} simply by +running @command{configure}: + +@example +configure -v m68k-amigaos +@end example + +Then run @command{make} and you should be all set! +If these steps do not work, please send in a bug report +(@pxref{Bugs, ,Reporting Problems and Bugs}). + +@node BeOS Installation, PC Installation, Amiga Installation, Non-Unix Installation +@appendixsubsec Installing @command{gawk} on BeOS +@cindex BeOS +@cindex installation, beos + +@c From email contributed by Martin Brown, mc@whoever.com +Since BeOS DR9, all the tools that you should need to build @code{gawk} are +included with BeOS. The process is basically identical to the Unix process +of running @command{configure} and then @command{make}. Full instructions are given below. + +You can compile @command{gawk} under BeOS by extracting the standard sources +and running @command{configure}. You @emph{must} specify the location +prefix for the installation directory. For BeOS DR9 and beyond, the best directory to +use is @file{/boot/home/config}, so the @command{configure} command is: + +@example +configure --prefix=/boot/home/config +@end example + +This installs the compiled application into @file{/boot/home/config/bin}, +which is already specified in the standard @env{PATH}. + +Once the configuration process is completed, you can run @command{make}, +and then @samp{make install}: + +@example +$ make +@dots{} +$ make install +@end example + +BeOS uses @command{bash} as its shell; thus, you use @command{gawk} the same way you would +under Unix. +If these steps do not work, please send in a bug report +(@pxref{Bugs, ,Reporting Problems and Bugs}). + +@c Rewritten by Scott Deifik +@c and Darrel Hankerson + +@node PC Installation, VMS Installation, BeOS Installation, Non-Unix Installation +@appendixsubsec Installation on PC Operating Systems + +@cindex installation, pc operating systems +This @value{SECTION} covers installation and usage of @command{gawk} on x86 machines +running DOS, any version of Windows, or OS/2. +In this @value{SECTION}, the term ``Win32'' +refers to any of Windows-95/98/ME/NT/2000. + +The limitations of DOS (and DOS shells under Windows or OS/2) has meant +that various ``DOS extenders'' are often used with programs such as +@command{gawk}. The varying capabilities of Microsoft Windows 3.1 +and Win32 can add to the confusion. For an overview of the +considerations, please refer to @file{README_d/README.pc} in the +distribution. + +@menu +* PC Binary Installation:: Installing a prepared distribution. +* PC Compiling:: Compiling @command{gawk} for MS-DOS, Win32, + and OS/2. +* PC Using:: Running @command{gawk} on MS-DOS, Win32 and + OS/2. +@end menu + +@node PC Binary Installation, PC Compiling, PC Installation, PC Installation +@appendixsubsubsec Installing a Prepared Distribution for PC Systems + +If you have received a binary distribution prepared by the DOS +maintainers, then @command{gawk} and the necessary support files appear +under the @file{gnu} directory, with executables in @file{gnu/bin}, +libraries in @file{gnu/lib/awk}, and manual pages under @file{gnu/man}. +This is designed for easy installation to a @file{/gnu} directory on your +drive---however, the files can be installed anywhere provided @env{AWKPATH} is +set properly. Regardless of the installation directory, the first line of +@file{igawk.cmd} and @file{igawk.bat} (in @file{gnu/bin}) may need to be +edited. + +The binary distribution contains a separate file describing the +contents. In particular, it may include more than one version of the +@command{gawk} executable. OS/2 binary distributions may have a +different arrangement, but installation is similar. + +@node PC Compiling, PC Using, PC Binary Installation, PC Installation +@appendixsubsubsec Compiling @command{gawk} for PC Operating Systems + +@command{gawk} can be compiled for MS-DOS, Win32, and OS/2 using the GNU +development tools from DJ Delorie (DJGPP; MS-DOS only) or Eberhard +Mattes (EMX; MS-DOS, Win32 and OS/2). Microsoft Visual C/C++ can be used +to build a Win32 version, and Microsoft C/C++ can be +used to build 16-bit versions for MS-DOS and OS/2. The file +@file{README_d/README.pc} in the @command{gawk} distribution contains +additional notes, and @file{pc/Makefile} contains important information on +compilation options. + +To build @command{gawk}, copy the files in the @file{pc} directory +(@emph{except} for @file{ChangeLog}) to the directory with the rest of +the @command{gawk} sources. The @file{Makefile} contains a configuration +section with comments and may need to be edited in order to work with +your @command{make} utility. + +The @file{Makefile} contains a number of targets for building various MS-DOS, +Win32, and OS/2 versions. A list of targets is printed if the @command{make} +command is given without a target. As an example, to build @command{gawk} +using the DJGPP tools, enter @samp{make djgpp}. + +Using @command{make} to run the standard tests and to install @command{gawk} +requires additional Unix-like tools, including @command{sh}, @command{sed}, and +@command{cp}. In order to run the tests, the @file{test/*.ok} files may need to +be converted so that they have the usual DOS-style end-of-line markers. Most +of the tests work properly with Stewartson's shell along with the +companion utilities or appropriate GNU utilities. However, some editing of +@file{test/Makefile} is required. It is recommended that you copy the file +@file{pc/Makefile.tst} over the file @file{test/Makefile} as a +replacement. Details can be found in @file{README_d/README.pc} +and in the file @file{pc/Makefile.tst}. + +@node PC Using, , PC Compiling, PC Installation +@appendixsubsubsec Using @command{gawk} on PC Operating Systems + +@cindex search path +@cindex directory search +@cindex path, search +@cindex search path, for source files +The OS/2 and MS-DOS versions of @command{gawk} search for program files as +described in @ref{AWKPATH Variable, ,The @env{AWKPATH} Environment Variable}. +However, semicolons (rather than colons) separate elements +in the @env{AWKPATH} variable. If @env{AWKPATH} is not set or is empty, +then the default search path is @code{@w{".;c:/lib/awk;c:/gnu/lib/awk"}}. + +An @command{sh}-like shell (as opposed to @command{command.com} under MS-DOS +or @command{cmd.exe} under OS/2) may be useful for @command{awk} programming. +Ian Stewartson has written an excellent shell for MS-DOS and OS/2, +Daisuke Aoyama has ported GNU @command{bash} to MS-DOS using the DJGPP tools, +and several shells are available for OS/2, including @command{ksh}. The file +@file{README_d/README.pc} in the @command{gawk} distribution contains +information on these shells. Users of Stewartson's shell on DOS should +examine its documentation for handling command lines; in particular, +the setting for @command{gawk} in the shell configuration may need to be +changed and the @code{ignoretype} option may also be of interest. + +@cindex @code{BINMODE} variable +Under OS/2 and DOS, @command{gawk} (and many other text programs) silently +translate end-of-line @code{"\r\n"} to @code{"\n"} on input and @code{"\n"} +to @code{"\r\n"} on output. A special @code{BINMODE} variable allows +control over these translations and is interpreted as follows. + +@itemize @bullet +@item +If @code{BINMODE} is @samp{"r"}, or +@code{(BINMODE & 1)} is nonzero, then +binary mode is set on read (i.e., no translations on reads). + +@item +If @code{BINMODE} is @code{"w"}, or +@code{(BINMODE & 2)} is nonzero, then +binary mode is set on write (i.e., no translations on writes). + +@item +If @code{BINMODE} is @code{"rw"} or @code{"wr"}, +binary mode is set for both read and write +(same as @code{(BINMODE & 3)}). + +@item +@code{BINMODE=@var{non-null-string}} is +the same as @samp{BINMODE=3} (i.e., no translations on +reads or writes). However, @command{gawk} issues a warning +message if the string is not one of @code{"rw"} or @code{"wr"}. +@end itemize + +@noindent +The modes for standard input and standard output are set one time +only (after the +command line is read, but before processing any of the @command{awk} program). +Setting @code{BINMODE} for standard input or +standard output is accomplished by using an +appropriate @samp{-v BINMODE=@var{N}} option on the command line. +@code{BINMODE} is set at the time a file or pipe is opened and cannot be +changed mid-stream. + +The name @code{BINMODE} was chosen to match @command{mawk} +(@pxref{Other Versions, , Other Freely Available @command{awk} Implementations}). +Both @command{mawk} and @command{gawk} handle @code{BINMODE} similarly; however, +@command{mawk} adds a @samp{-W BINMODE=@var{N}} option and an environment +variable that can set @code{BINMODE}, @code{RS}, and @code{ORS}. The +files @file{binmode[1-3].awk} (under @file{gnu/lib/awk} in some of the +prepared distributions) have been chosen to match @command{mawk}'s @samp{-W +BINMODE=@var{N}} option. These can be changed or discarded; in particular, +the setting of @code{RS} giving the fewest ``surprises'' is open to debate. +@command{mawk} uses @samp{RS = "\r\n"} if binary mode is set on read, which is +appropriate for files with the DOS-style end-of-line. + +To Illustrate, the following examples set binary mode on writes for standard +output and other files, and set @code{ORS} as the ``usual'' DOS-style +end-of-line: + +@example +gawk -v BINMODE=2 -v ORS="\r\n" @dots{} +@end example + +@noindent +or: + +@example +gawk -v BINMODE=w -f binmode2.awk @dots{} +@end example + +@noindent +These give the same result as the @samp{-W BINMODE=2} option in +@command{mawk}. +The following changes the record separator to @code{"\r\n"} and sets binary +mode on reads, but does not affect the mode on standard input: + +@example +gawk -v RS="\r\n" --source "BEGIN @{ BINMODE = 1 @}" @dots{} +@end example + +@noindent +or: + +@example +gawk -f binmode1.awk @dots{} +@end example + +@noindent +With proper quoting, in the first example the setting of @code{RS} can be +moved into the @code{BEGIN} rule. -@node VMS Installation, PC Installation, Unix Installation, Installation -@appendixsec How to Compile and Install @code{gawk} on VMS +@node VMS Installation, , PC Installation, Non-Unix Installation +@appendixsubsec How to Compile and Install @command{gawk} on VMS @c based on material from Pat Rankin @cindex installation, vms -This section describes how to compile and install @code{gawk} under VMS. +This @value{SUBSECTION} describes how to compile and install @command{gawk} under VMS. @menu -* VMS Compilation:: How to compile @code{gawk} under VMS. -* VMS Installation Details:: How to install @code{gawk} under VMS. -* VMS Running:: How to run @code{gawk} under VMS. +* VMS Compilation:: How to compile @command{gawk} under VMS. +* VMS Installation Details:: How to install @command{gawk} under VMS. +* VMS Running:: How to run @command{gawk} under VMS. * VMS POSIX:: Alternate instructions for VMS POSIX. @end menu @node VMS Compilation, VMS Installation Details, VMS Installation, VMS Installation -@appendixsubsec Compiling @code{gawk} on VMS +@appendixsubsubsec Compiling @command{gawk} on VMS -To compile @code{gawk} under VMS, there is a @code{DCL} command procedure that -will issue all the necessary @code{CC} and @code{LINK} commands, and there is +To compile @command{gawk} under VMS, there is a @code{DCL} command procedure that +issues all the necessary @code{CC} and @code{LINK} commands. There is also a @file{Makefile} for use with the @code{MMS} utility. From the source -directory, use either +directory, use either: @example $ @@[.VMS]VMSBUILD.COM @end example @noindent -or +or: @example $ MMS/DESCRIPTION=[.VMS]DESCRIP.MMS GAWK @@ -19125,21 +22288,21 @@ and comment out or delete the two lines @samp{#define __STDC__ 0} and @item GNU C Edit @file{vmsbuild.com} or @file{descrip.mms}; the changes are different -from those for VAX C V2.x, but equally straightforward. No changes to -@file{config.h} should be needed. +from those for VAX C V2.x but equally straightforward. No changes to +@file{config.h} are needed. @item DEC C Edit @file{vmsbuild.com} or @file{descrip.mms} according to their comments. -No changes to @file{config.h} should be needed. +No changes to @file{config.h} are needed. @end table -@code{gawk} has been tested under VAX/VMS 5.5-1 using VAX C V3.2, +@command{gawk} has been tested under VAX/VMS 5.5-1 using VAX C V3.2, and GNU C 1.40 and 2.3. It should work without modifications for VMS V4.6 and up. @node VMS Installation Details, VMS Running, VMS Compilation, VMS Installation -@appendixsubsec Installing @code{gawk} on VMS +@appendixsubsubsec Installing @command{gawk} on VMS -To install @code{gawk}, all you need is a ``foreign'' command, which is +To install @command{gawk}, all you need is a ``foreign'' command, which is a @code{DCL} symbol whose value begins with a dollar sign. For example: @example @@ -19147,13 +22310,13 @@ $ GAWK :== $disk1:[gnubin]GAWK @end example @noindent -(Substitute the actual location of @code{gawk.exe} for -@samp{$disk1:[gnubin]}.) The symbol should be placed in the -@file{login.com} of any user who wishes to run @code{gawk}, -so that it will be defined every time the user logs on. +Substitute the actual location of @command{gawk.exe} for +@samp{$disk1:[gnubin]}. The symbol should be placed in the +@file{login.com} of any user who wants to run @command{gawk}, +so that it is defined every time the user logs on. Alternatively, the symbol may be placed in the system-wide -@file{sylogin.com} procedure, which will allow all users -to run @code{gawk}. +@file{sylogin.com} procedure, which allows all users +to run @command{gawk}. Optionally, the help entry can be loaded into a VMS help library: @@ -19164,31 +22327,32 @@ $ LIBRARY/HELP SYS$HELP:HELPLIB [.VMS]GAWK.HLP @noindent (You may want to substitute a site-specific help library rather than the standard VMS library @samp{HELPLIB}.) After loading the help text, +the command: @example $ HELP GAWK @end example @noindent -will provide information about both the @code{gawk} implementation and the -@code{awk} programming language. +provides information about both the @command{gawk} implementation and the +@command{awk} programming language. The logical name @samp{AWK_LIBRARY} can designate a default location -for @code{awk} program files. For the @samp{-f} option, if the specified -filename has no device or directory path information in it, @code{gawk} -will look in the current directory first, then in the directory specified -by the translation of @samp{AWK_LIBRARY} if the file was not found. -If after searching in both directories, the file still is not found, -then @code{gawk} appends the suffix @samp{.awk} to the filename and the -file search will be re-tried. If @samp{AWK_LIBRARY} is not defined, that -portion of the file search will fail benignly. +for @command{awk} program files. For the @option{-f} option, if the specified +@value{FN} has no device or directory path information in it, @command{gawk} +looks in the current directory first, then in the directory specified +by the translation of @samp{AWK_LIBRARY} if the file is not found. +If, after searching in both directories, the file still is not found, +@command{gawk} appends the suffix @samp{.awk} to the filename and retries +the file search. If @samp{AWK_LIBRARY} is not defined, that +portion of the file search fails benignly. @node VMS Running, VMS POSIX, VMS Installation Details, VMS Installation -@appendixsubsec Running @code{gawk} on VMS +@appendixsubsubsec Running @command{gawk} on VMS -Command line parsing and quoting conventions are significantly different +Command-line parsing and quoting conventions are significantly different on VMS, so examples in this @value{DOCUMENT} or from other sources often need minor -changes. They @emph{are} minor though, and all @code{awk} programs +changes. They @emph{are} minor though, and all @command{awk} programs should run correctly. Here are a couple of trivial tests: @@ -19200,284 +22364,246 @@ $ gawk -"W" version @end example @noindent -Note that upper-case and mixed-case text must be quoted. +Note that uppercase and mixed-case text must be quoted. -The VMS port of @code{gawk} includes a @code{DCL}-style interface in addition +The VMS port of @command{gawk} includes a @code{DCL}-style interface in addition to the original shell-style interface (see the help entry for details). -One side-effect of dual command line parsing is that if there is only a +One side effect of dual command-line parsing is that if there is only a single parameter (as in the quoted string program above), the command -becomes ambiguous. To work around this, the normally optional @samp{--} +becomes ambiguous. To work around this, the normally optional @option{--} flag is required to force Unix style rather than @code{DCL} parsing. If any -other dash-type options (or multiple parameters such as data files to be -processed) are present, there is no ambiguity and @samp{--} can be omitted. +other dash-type options (or multiple parameters such as @value{DF}s to +process) are present, there is no ambiguity and @option{--} can be omitted. -The default search path when looking for @code{awk} program files specified -by the @samp{-f} option is @code{"SYS$DISK:[],AWK_LIBRARY:"}. The logical +@cindex search path +@cindex directory search +@cindex path, search +@cindex search path, for source files +The default search path, when looking for @command{awk} program files specified +by the @option{-f} option, is @code{"SYS$DISK:[],AWK_LIBRARY:"}. The logical name @samp{AWKPATH} can be used to override this default. The format of @samp{AWKPATH} is a comma-separated list of directory specifications. When defining it, the value should be quoted so that it retains a single -translation, and not a multi-translation @code{RMS} searchlist. +translation and not a multitranslation @code{RMS} searchlist. -@node VMS POSIX, , VMS Running, VMS Installation -@appendixsubsec Building and Using @code{gawk} on VMS POSIX +@node VMS POSIX, , VMS Running, VMS Installation +@appendixsubsubsec Building and Using @command{gawk} on VMS POSIX Ignore the instructions above, although @file{vms/gawk.hlp} should still be made available in a help library. The source tree should be unpacked -into a container file subsystem rather than into the ordinary VMS file -system. Make sure that the two scripts, @file{configure} and +into a container file subsystem rather than into the ordinary VMS filesystem. +Make sure that the two scripts, @file{configure} and @file{vms/posix-cc.sh}, are executable; use @samp{chmod +x} on them if necessary. Then execute the following two commands: @example -@group psx> CC=vms/posix-cc.sh configure psx> make CC=c89 gawk -@end group @end example @noindent -The first command will construct files @file{config.h} and @file{Makefile} out -of templates, using a script to make the C compiler fit @code{configure}'s -expectations. The second command will compile and link @code{gawk} using -the C compiler directly; ignore any warnings from @code{make} about being -unable to redefine @code{CC}. @code{configure} will take a very long -time to execute, but at least it provides incremental feedback as it -runs. +The first command constructs files @file{config.h} and @file{Makefile} out +of templates, using a script to make the C compiler fit @command{configure}'s +expectations. The second command compiles and links @command{gawk} using +the C compiler directly; ignore any warnings from @command{make} about being +unable to redefine @code{CC}. @command{configure} takes a very long +time to execute, but at least it provides incremental feedback as it runs. This has been tested with VAX/VMS V6.2, VMS POSIX V2.0, and DEC C V5.2. -Once built, @code{gawk} will work like any other shell utility. Unlike -the normal VMS port of @code{gawk}, no special command line manipulation is +Once built, @command{gawk} works like any other shell utility. Unlike +the normal VMS port of @command{gawk}, no special command-line manipulation is needed in the VMS POSIX environment. -@c Rewritten by Scott Deifik -@c and Darrel Hankerson -@node PC Installation, Atari Installation, VMS Installation, Installation -@appendixsec MS-DOS and OS/2 Installation and Compilation - -@cindex installation, MS-DOS and OS/2 -If you have received a binary distribution prepared by the DOS -maintainers, then @code{gawk} and the necessary support files will appear -under the @file{gnu} directory, with executables in @file{gnu/bin}, -libraries in @file{gnu/lib/awk}, and manual pages under @file{gnu/man}. -This is designed for easy installation to a @file{/gnu} directory on your -drive, but the files can be installed anywhere provided @code{AWKPATH} is -set properly. Regardless of the installation directory, the first line of -@file{igawk.cmd} and @file{igawk.bat} (in @file{gnu/bin}) may need to be -edited. - -The binary distribution will contain a separate file describing the -contents. In particular, it may include more than one version of the -@code{gawk} executable. OS/2 binary distributions may have a -different arrangement, but installation is similar. +@node Unsupported, Bugs, Non-Unix Installation, Installation +@appendixsec Unsupported Operating System Ports -The OS/2 and MS-DOS versions of @code{gawk} search for program files as -described in @ref{AWKPATH Variable, ,The @code{AWKPATH} Environment Variable}. -However, semicolons (rather than colons) separate elements -in the @code{AWKPATH} variable. If @code{AWKPATH} is not set or is empty, -then the default search path is @code{@w{".;c:/lib/awk;c:/gnu/lib/awk"}}. +This sections describes systems for which +the @command{gawk} port is no longer supported. -An @code{sh}-like shell (as opposed to @code{command.com} under MS-DOS -or @code{cmd.exe} under OS/2) may be useful for @code{awk} programming. -Ian Stewartson has written an excellent shell for MS-DOS and OS/2, and a -@code{ksh} clone and GNU Bash are available for OS/2. The file -@file{README_d/README.pc} in the @code{gawk} distribution contains -information on these shells. Users of Stewartson's shell on DOS should -examine its documentation on handling of command-lines. In particular, -the setting for @code{gawk} in the shell configuration may need to be -changed, and the @code{ignoretype} option may also be of interest. - -@code{gawk} can be compiled for MS-DOS and OS/2 using the GNU development tools -from DJ Delorie (DJGPP, MS-DOS-only) or Eberhard Mattes (EMX, MS-DOS and OS/2). -Microsoft C can be used to build 16-bit versions for MS-DOS and OS/2. The file -@file{README_d/README.pc} in the @code{gawk} distribution contains additional -notes, and @file{pc/Makefile} contains important notes on compilation options. - -To build @code{gawk}, copy the files in the @file{pc} directory (@emph{except} -for @file{ChangeLog}) to the -directory with the rest of the @code{gawk} sources. The @file{Makefile} -contains a configuration section with comments, and may need to be -edited in order to work with your @code{make} utility. - -The @file{Makefile} contains a number of targets for building various MS-DOS -and OS/2 versions. A list of targets will be printed if the @code{make} -command is given without a target. As an example, to build @code{gawk} -using the DJGPP tools, enter @samp{make djgpp}. +@menu +* Atari Installation:: Installing @command{gawk} on the Atari ST. +* Tandem Installation:: Installing @command{gawk} on a Tandem. +@end menu -Using @code{make} to run the standard tests and to install @code{gawk} -requires additional Unix-like tools, including @code{sh}, @code{sed}, and -@code{cp}. In order to run the tests, the @file{test/*.ok} files may need to -be converted so that they have the usual DOS-style end-of-line markers. Most -of the tests will work properly with Stewartson's shell along with the -companion utilities or appropriate GNU utilities. However, some editing of -@file{test/Makefile} is required. It is recommended that the file -@file{pc/Makefile.tst} be copied to @file{test/Makefile} as a -replacement. Details can be found in @file{README_d/README.pc}. +@node Atari Installation, Tandem Installation, Unsupported, Unsupported +@appendixsubsec Installing @command{gawk} on the Atari ST -@node Atari Installation, Amiga Installation, PC Installation, Installation -@appendixsec Installing @code{gawk} on the Atari ST +The Atari port is no longer supported. It is +included for those who might want to use it but it is no longer being +actively maintained. @c based on material from Michal Jaegermann - @cindex atari @cindex installation, atari -There are no substantial differences when installing @code{gawk} on -various Atari models. Compiled @code{gawk} executables do not require -a large amount of memory with most @code{awk} programs and should run on all -Motorola processor based models (called further ST, even if that is not +There are no substantial differences when installing @command{gawk} on +various Atari models. Compiled @command{gawk} executables do not require +a large amount of memory with most @command{awk} programs, and should run on all +Motorola processor-based models (called further ST, even if that is not exactly right). -In order to use @code{gawk}, you need to have a shell, either text or +In order to use @command{gawk}, you need to have a shell, either text or graphics, that does not map all the characters of a command line to -upper-case. Maintaining case distinction in option flags is very -important (@pxref{Options, ,Command Line Options}). -These days this is the default, and it may only be a problem for some +uppercase. Maintaining case distinction in option flags is very +important (@pxref{Options, ,Command-Line Options}). +These days this is the default and it may only be a problem for some very old machines. If your system does not preserve the case of option -flags, you will need to upgrade your tools. Support for I/O -redirection is necessary to make it easy to import @code{awk} programs -from other environments. Pipes are nice to have, but not vital. +flags, you need to upgrade your tools. Support for I/O +redirection is necessary to make it easy to import @command{awk} programs +from other environments. Pipes are nice to have but not vital. @menu -* Atari Compiling:: Compiling @code{gawk} on Atari -* Atari Using:: Running @code{gawk} on Atari +* Atari Compiling:: Compiling @command{gawk} on Atari. +* Atari Using:: Running @command{gawk} on Atari. @end menu @node Atari Compiling, Atari Using, Atari Installation, Atari Installation -@appendixsubsec Compiling @code{gawk} on the Atari ST +@appendixsubsubsec Compiling @command{gawk} on the Atari ST -A proper compilation of @code{gawk} sources when @code{sizeof(int)} -differs from @code{sizeof(void *)} requires an ANSI C compiler. An initial -port was done with @code{gcc}. You may actually prefer executables -where @code{int}s are four bytes wide, but the other variant works as well. +A proper compilation of @command{gawk} sources when @code{sizeof(int)} +differs from @code{sizeof(void *)} requires an ISO C compiler. An initial +port was done with @command{gcc}. You may actually prefer executables +where @code{int}s are four bytes wide but the other variant works as well. -You may need quite a bit of memory when trying to recompile the @code{gawk} +You may need quite a bit of memory when trying to recompile the @command{gawk} sources, as some source files (@file{regex.c} in particular) are quite big. If you run out of memory compiling such a file, try reducing the -optimization level for this particular file; this may help. +optimization level for this particular file, which may help. @cindex Linux -With a reasonable shell (Bash will do), and in particular if you run -Linux, MiNT or a similar operating system, you have a pretty good -chance that the @code{configure} utility will succeed. Otherwise +@cindex GNU/Linux +With a reasonable shell (@command{bash} will do), you have a pretty good chance +that the @command{configure} utility will succeed, and in particular if +you run GNU/Linux, MiNT or a similar operating system. Otherwise sample versions of @file{config.h} and @file{Makefile.st} are given in the @file{atari} subdirectory and can be edited and copied to the corresponding files in the main source directory. Even if -@code{configure} produced something, it might be advisable to compare +@command{configure} produces something, it might be advisable to compare its results with the sample versions and possibly make adjustments. -Some @code{gawk} source code fragments depend on a preprocessor define -@samp{atarist}. This basically assumes the TOS environment with @code{gcc}. +Some @command{gawk} source code fragments depend on a preprocessor define +@samp{atarist}. This basically assumes the TOS environment with @command{gcc}. Modify these sections as appropriate if they are not right for your -environment. Also see the remarks about @code{AWKPATH} and @code{envsep} in -@ref{Atari Using, ,Running @code{gawk} on the Atari ST}. +environment. Also see the remarks about @env{AWKPATH} and @code{envsep} in +@ref{Atari Using, ,Running @command{gawk} on the Atari ST}. As shipped, the sample @file{config.h} claims that the @code{system} function is missing from the libraries, which is not true, and an alternative implementation of this function is provided in -@file{atari/system.c}. Depending upon your particular combination of -shell and operating system, you may wish to change the file to indicate +@file{unsupported/atari/system.c}. +Depending upon your particular combination of +shell and operating system, you might want to change the file to indicate that @code{system} is available. @node Atari Using, , Atari Compiling, Atari Installation -@appendixsubsec Running @code{gawk} on the Atari ST +@appendixsubsubsec Running @command{gawk} on the Atari ST -An executable version of @code{gawk} should be placed, as usual, -anywhere in your @code{PATH} where your shell can find it. +An executable version of @command{gawk} should be placed, as usual, +anywhere in your @env{PATH} where your shell can find it. -While executing, @code{gawk} creates a number of temporary files. When -using @code{gcc} libraries for TOS, @code{gawk} looks for either of -the environment variables @code{TEMP} or @code{TMPDIR}, in that order. +While executing, the Atari version of @command{gawk} creates a number of temporary files. When +using @command{gcc} libraries for TOS, @command{gawk} looks for either of +the environment variables, @env{TEMP} or @env{TMPDIR}, in that order. If either one is found, its value is assumed to be a directory for temporary files. This directory must exist, and if you can spare the memory, it is a good idea to put it on a RAM drive. If neither -@code{TEMP} nor @code{TMPDIR} are found, then @code{gawk} uses the +@env{TEMP} nor @env{TMPDIR} are found, then @command{gawk} uses the current directory for its temporary files. -The ST version of @code{gawk} searches for its program files as described in -@ref{AWKPATH Variable, ,The @code{AWKPATH} Environment Variable}. -The default value for the @code{AWKPATH} variable is taken from -@code{DEFPATH} defined in @file{Makefile}. The sample @code{gcc}/TOS +The ST version of @command{gawk} searches for its program files, as described in +@ref{AWKPATH Variable, ,The @env{AWKPATH} Environment Variable}. +The default value for the @env{AWKPATH} variable is taken from +@code{DEFPATH} defined in @file{Makefile}. The sample @command{gcc}/TOS @file{Makefile} for the ST in the distribution sets @code{DEFPATH} to @code{@w{".,c:\lib\awk,c:\gnu\lib\awk"}}. The search path can be -modified by explicitly setting @code{AWKPATH} to whatever you wish. +modified by explicitly setting @env{AWKPATH} to whatever you want. Note that colons cannot be used on the ST to separate elements in the -@code{AWKPATH} variable, since they have another, reserved, meaning. +@env{AWKPATH} variable, since they have another reserved meaning. Instead, you must use a comma to separate elements in the path. When recompiling, the separating character can be modified by initializing -the @code{envsep} variable in @file{atari/gawkmisc.atr} to another +the @code{envsep} variable in @file{unsupported/atari/gawkmisc.atr} to another value. -Although @code{awk} allows great flexibility in doing I/O redirections +Although @command{awk} allows great flexibility in doing I/O redirections from within a program, this facility should be used with care on the ST -running under TOS. In some circumstances the OS routines for file -handle pool processing lose track of certain events, causing the -computer to crash, and requiring a reboot. Often a warm reboot is -sufficient. Fortunately, this happens infrequently, and in rather +running under TOS. In some circumstances, the OS routines for file-handle +pool processing lose track of certain events, causing the +computer to crash and requiring a reboot. Often a warm reboot is +sufficient. Fortunately, this happens infrequently and in rather esoteric situations. In particular, avoid having one part of an -@code{awk} program using @code{print} statements explicitly redirected -to @code{"/dev/stdout"}, while other @code{print} statements use the +@command{awk} program using @code{print} statements explicitly redirected +to @file{/dev/stdout}, while other @code{print} statements use the default standard output, and a calling shell has redirected standard output to a file. +@c 10/2000: Is this still true, now that gawk does /dev/stdout internally? -When @code{gawk} is compiled with the ST version of @code{gcc} and its -usual libraries, it will accept both @samp{/} and @samp{\} as path separators. -While this is convenient, it should be remembered that this removes one, -technically valid, character (@samp{/}) from your file names, and that -it may create problems for external programs, called via the @code{system} +When @command{gawk} is compiled with the ST version of @command{gcc} and its +usual libraries, it accepts both @samp{/} and @samp{\} as path separators. +While this is convenient, it should be remembered that this removes one +technically valid character (@samp{/}) from your @value{FN}. +It may also create problems for external programs called via the @code{system} function, which may not support this convention. Whenever it is possible -that a file created by @code{gawk} will be used by some other program, -use only backslashes. Also remember that in @code{awk}, backslashes in +that a file created by @command{gawk} will be used by some other program, +use only backslashes. Also remember that in @command{awk}, backslashes in strings have to be doubled in order to get literal backslashes (@pxref{Escape Sequences}). -@node Amiga Installation, Bugs, Atari Installation, Installation -@appendixsec Installing @code{gawk} on an Amiga - -@cindex amiga -@cindex installation, amiga -You can install @code{gawk} on an Amiga system using a Unix emulation -environment available via anonymous @code{ftp} from -@code{ftp.ninemoons.com} in the directory @file{pub/ade/current}. -This includes a shell based on @code{pdksh}. The primary component of -this environment is a Unix emulation library, @file{ixemul.lib}. -@c could really use more background here, who wrote this, etc. - -A more complete distribution for the Amiga is available on -the Geek Gadgets CD-ROM from: - -@quotation -CRONUS @* -1840 E. Warner Road #105-265 @* -Tempe, AZ 85284 USA @* -US Toll Free: (800) 804-0833 @* -Phone: +1-602-491-0442 @* -FAX: +1-602-491-0048 @* -Email: @code{info@@ninemoons.com} @* -WWW: @code{http://www.ninemoons.com} @* -Anonymous @code{ftp} site: @code{ftp.ninemoons.com} @* -@end quotation - -Once you have the distribution, you can configure @code{gawk} simply by -running @code{configure}: - -@example -configure -v m68k-amigaos -@end example +@node Tandem Installation, , Atari Installation, Unsupported +@appendixsubsec Installing @command{gawk} on a Tandem +@cindex tandem +@cindex installation, tandem -Then run @code{make}, and you should be all set! -(If these steps do not work, please send in a bug report; -@pxref{Bugs, ,Reporting Problems and Bugs}.) +The Tandem port is only minimally supported. +The port's contributor no longer has access to a Tandem system. -@node Bugs, Other Versions, Amiga Installation, Installation +@c This section based on README.Tandem by Stephen Davies (scldad@sdc.com.au) +The Tandem port was done on a Cyclone machine running D20. +The port is pretty clean and all facilities seem to work except for +the I/O piping facilities +(@pxref{Getline/Pipe, , Using @code{getline} from a Pipe}, +@ref{Getline/Variable/Pipe, ,Using @code{getline} into a Variable from a Pipe}, +and +@ref{Redirection, ,Redirecting Output of @code{print} and @code{printf}}), +which is just too foreign a concept for Tandem. + +To build a Tandem executable from source, download all of the files so +that the @value{FN}s on the Tandem box conform to the restrictions of D20. +For example, @file{array.c} becomes @file{ARRAYC}, and @file{awk.h} +becomes @file{AWKH}. The totally Tandem-specific files are in the +@file{tandem} ``subvolume'' (@file{unsupported/tandem} in the @command{gawk} +distribution) and should be copied to the main source directory before +building @command{gawk}. + +The file @file{compit} can then be used to compile and bind an executable. +Alas, there is no @command{configure} or @command{make}. + +Usage is the same as for Unix, except that D20 requires all @samp{@{} and +@samp{@}} characters to be escaped with @samp{~} on the command line +(but @emph{not} in script files). Also, the standard Tandem syntax for +@samp{/in filename,out filename/} must be used instead of the usual +Unix @samp{<} and @samp{>} for file redirection. (Redirection options +on @code{getline}, @code{print} etc., are supported.) + +The @samp{-mr @var{val}} option +(@pxref{Options, ,Command-Line Options}) +has been ``stolen'' to enable Tandem users to process fixed-length +records with no ``end-of-line'' character. That is, @samp{-mr 74} tells +@command{gawk} to read the input file as fixed 74-byte records. + +@node Bugs, Other Versions, Unsupported, Installation @appendixsec Reporting Problems and Bugs -@display -@i{There is nothing more dangerous than a bored archeologist.} +@cindex archeologists +@quotation +@i{There is nothing more dangerous than a bored archeologist.}@* The Hitchhiker's Guide to the Galaxy +@end quotation @c the radio show, not the book. :-) -@end display -@sp 1 -If you have problems with @code{gawk} or think that you have found a bug, +@cindex bug reports +@cindex problem reports +@cindex reporting bugs +@cindex reporting problems +If you have problems with @command{gawk} or think that you have found a bug, please report it to the developers; we cannot promise to do anything but we might well want to fix it. @@ -19487,74 +22613,114 @@ what you're trying to do. If it's not clear whether you should be able to do something or not, report that too; it's a bug in the documentation! Before reporting a bug or trying to fix it yourself, try to isolate it -to the smallest possible @code{awk} program and input data file that -reproduces the problem. Then send us the program and data file, -some idea of what kind of Unix system you're using, and the exact results -@code{gawk} gave you. Also say what you expected to occur; this will help -us decide whether the problem was really in the documentation. - +to the smallest possible @command{awk} program and input @value{DF} that +reproduces the problem. Then send us the program and @value{DF}, +some idea of what kind of Unix system you're using, +the compiler you used to compile @command{gawk}, and the exact results +@command{gawk} gave you. Also say what you expected to occur; this helps +us decide whether the problem is really in the documentation. + +@cindex @code{bug-gawk@@gnu.org} bug reporting address +@cindex emaill address for bug reports, @code{bug-gawk@@gnu.org} +@cindex bug reports, email address, @code{bug-gawk@@gnu.org} Once you have a precise problem, send email to @email{bug-gawk@@gnu.org}. -Please include the version number of @code{gawk} you are using. +@cindex Robbins, Arnold +Please include the version number of @command{gawk} you are using. You can get this information with the command @samp{gawk --version}. -Using this address will automatically send a carbon copy of your -mail to Arnold Robbins. If necessary, he can be reached directly at -@email{arnold@@gnu.org}. - -@cindex @code{comp.lang.awk} -@strong{Important!} Do @emph{not} try to report bugs in @code{gawk} by +Using this address automatically sends a carbon copy of your +mail to me. If necessary, I can be reached directly at +@email{arnold@@gnu.org}. The bug reporting address is preferred since the +email list is archived at the GNU Project. +@emph{All email should be in English, since that is my native language.} + +@cindex @code{comp.lang.awk} Usenet news group +@strong{Caution:} Do @emph{not} try to report bugs in @command{gawk} by posting to the Usenet/Internet newsgroup @code{comp.lang.awk}. -While the @code{gawk} developers do occasionally read this newsgroup, +While the @command{gawk} developers do occasionally read this newsgroup, there is no guarantee that we will see your posting. The steps described -above are the official, recognized ways for reporting bugs. +above are the official recognized ways for reporting bugs. Non-bug suggestions are always welcome as well. If you have questions about things that are unclear in the documentation or are just obscure -features, ask Arnold Robbins; he will try to help you out, although he -may not have the time to fix the problem. You can send him electronic -mail at the Internet address above. +features, ask me; I will try to help you out, although I +may not have the time to fix the problem. You can send me electronic +mail at the Internet address noted previously. -If you find bugs in one of the non-Unix ports of @code{gawk}, please send +If you find bugs in one of the non-Unix ports of @command{gawk}, please send an electronic mail message to the person who maintains that port. They -are listed below, and also in the @file{README} file in the @code{gawk} +are named in the following list, as well as in the @file{README} file in the @command{gawk} distribution. Information in the @file{README} file should be considered authoritative if it conflicts with this @value{DOCUMENT}. -@c NEEDED for looks -@page -The people maintaining the non-Unix ports of @code{gawk} are: +The people maintaining the non-Unix ports of @command{gawk} are +as follows: -@cindex Deifik, Scott +@ignore +@table @asis @cindex Fish, Fred +@item Amiga +Fred Fish, @email{fnf@@ninemoons.com}. + +@cindex Brown, Martin +@item BeOS +Martin Brown, @email{mc@@whoever.com}. + +@cindex Deifik, Scott @cindex Hankerson, Darrel -@cindex Jaegermann, Michal -@cindex Rankin, Pat -@cindex Rommel, Kai Uwe -@table @asis @item MS-DOS -Scott Deifik, @samp{scottd@@amgen.com}, and -Darrel Hankerson, @samp{hankedr@@mail.auburn.edu}. +Scott Deifik, @email{scottd@@amgen.com} and +Darrel Hankerson, @email{hankedr@@mail.auburn.edu}. + +@cindex Grigera, Juan +@item MS-Windows +Juan Grigera, @email{juan@@biophnet.unlp.edu.ar}. +@cindex Rommel, Kai Uwe @item OS/2 -Kai Uwe Rommel, @samp{rommel@@ars.de}. +Kai Uwe Rommel, @email{rommel@@ars.de}. + +@cindex Davies, Stephen +@item Tandem +Stephen Davies, @email{scldad@@sdc.com.au}. +@cindex Rankin, Pat @item VMS -Pat Rankin, @samp{rankin@@eql.caltech.edu}. +Pat Rankin, @email{rankin@@eql.caltech.edu}. +@end table +@end ignore -@item Atari ST -Michal Jaegermann, @samp{michal@@gortel.phys.ualberta.ca}. +@multitable {MS-Windows} {123456789012345678901234567890123456789001234567890} +@cindex Fish, Fred +@item Amiga @tab Fred Fish, @email{fnf@@ninemoons.com}. -@item Amiga -Fred Fish, @samp{fnf@@ninemoons.com}. -@end table +@cindex Brown, Martin +@item BeOS @tab Martin Brown, @email{mc@@whoever.com}. -If your bug is also reproducible under Unix, please send copies of your -report to the general GNU bug list, as well as to Arnold Robbins, at the -addresses listed above. +@cindex Deifik, Scott +@cindex Hankerson, Darrel +@item MS-DOS @tab Scott Deifik, @email{scottd@@amgen.com} and +Darrel Hankerson, @email{hankedr@@mail.auburn.edu}. + +@cindex Grigera, Juan +@item MS-Windows @tab Juan Grigera, @email{juan@@biophnet.unlp.edu.ar}. + +@cindex Rommel, Kai Uwe +@item OS/2 @tab Kai Uwe Rommel, @email{rommel@@ars.de}. + +@cindex Davies, Stephen +@item Tandem @tab Stephen Davies, @email{scldad@@sdc.com.au}. + +@cindex Rankin, Pat +@item VMS @tab Pat Rankin, @email{rankin@@eql.caltech.edu}. +@end multitable + +If your bug is also reproducible under Unix, please send a copy of your +report to the @email{bug-gawk@@gnu.org} email list as well. @node Other Versions, , Bugs, Installation -@appendixsec Other Freely Available @code{awk} Implementations -@cindex Brennan, Michael +@appendixsec Other Freely Available @command{awk} Implementations +@cindex other @command{awk} implementations @ignore From: emory!amc.com!brennan (Michael Brennan) Subject: C++ comments in awk programs @@ -19562,77 +22728,168 @@ To: arnold@gnu.ai.mit.edu (Arnold Robbins) Date: Wed, 4 Sep 1996 08:11:48 -0700 (PDT) @end ignore -@display -@i{It's kind of fun to put comments like this in your awk code.} - @code{// Do C++ comments work? answer: yes! of course} +@cindex Brennan, Michael +@quotation +@i{It's kind of fun to put comments like this in your awk code.}@* +@ @ @ @ @ @ @code{// Do C++ comments work? answer: yes! of course}@* Michael Brennan -@end display -@sp 1 +@end quotation -There are two other freely available @code{awk} implementations. -This section briefly describes where to get them. +There are three other freely available @command{awk} implementations. +This @value{SECTION} briefly describes where to get them: @table @asis @cindex Kernighan, Brian -@cindex anonymous @code{ftp} -@cindex @code{ftp}, anonymous -@item Unix @code{awk} -Brian Kernighan has been able to make his implementation of -@code{awk} freely available. You can get it via anonymous @code{ftp} -to the host @code{@w{netlib.bell-labs.com}}. Change directory to -@file{/netlib/research}. Use ``binary'' or ``image'' mode, and -retrieve @file{awk.bundle.gz}. - -This is a shell archive that has been compressed with the GNU @code{gzip} -utility. It can be uncompressed with the @code{gunzip} utility. - -You can also retrieve this version via the World Wide Web from his -@uref{http://cm.bell-labs.com/who/bwk, home page}. - -This version requires an ANSI C compiler; GCC (the GNU C compiler) +@cindex Unix @command{awk}, source code +@cindex source code, Unix @command{awk} +@item Unix @command{awk} +Brian Kernighan has made his implementation of +@command{awk} freely available. +You can retrieve this version via the World Wide Web from +his home page.@footnote{@uref{http://cm.bell-labs.com/who/bwk}} +It is available in several archive formats: + +@table @asis +@item Shell archive +@uref{http://cm.bell-labs.com/who/bwk/awk.shar} + +@item Compressed @command{tar} file +@uref{http://cm.bell-labs.com/who/bwk/awk.tar.gz} + +@item Zip file +@uref{http://cm.bell-labs.com/who/bwk/awk.zip} +@end table + +This version requires an ISO C (1990 standard) compiler; +the C compiler from +GCC (the GNU Compiler Collection) works quite nicely. +@xref{BTL, ,Extensions in the Bell Laboratories @command{awk}}, +for a list of extensions in this @command{awk} that are not in POSIX @command{awk}. + +@cindex GPL +@cindex General Public License +@cindex GNU General Public License @cindex Brennan, Michael -@cindex @code{mawk} -@item @code{mawk} -Michael Brennan has written an independent implementation of @code{awk}, -called @code{mawk}. It is available under the GPL -(@pxref{Copying, ,GNU GENERAL PUBLIC LICENSE}), -just as @code{gawk} is. - -You can get it via anonymous @code{ftp} to the host +@cindex @command{mawk}, source code +@cindex source code, @command{mawk} +@item @command{mawk} +Michael Brennan has written an independent implementation of @command{awk}, +called @command{mawk}. It is available under the GPL +(@pxref{Copying, ,GNU General Public License}), +just as @command{gawk} is. + +You can get it via anonymous @command{ftp} to the host @code{@w{ftp.whidbey.net}}. Change directory to @file{/pub/brennan}. Use ``binary'' or ``image'' mode, and retrieve @file{mawk1.3.3.tar.gz} (or the latest version that is there). -@code{gunzip} may be used to decompress this file. Installation -is similar to @code{gawk}'s -(@pxref{Unix Installation, , Compiling and Installing @code{gawk} on Unix}). +@command{gunzip} may be used to decompress this file. Installation +is similar to @command{gawk}'s +(@pxref{Unix Installation, , Compiling and Installing @command{gawk} on Unix}). + +@cindex extensions, @command{mawk} +@command{mawk} has the following extensions that are not in POSIX @command{awk}: + +@itemize @bullet +@item +The @code{fflush} built-in function for flushing buffered output +(@pxref{I/O Functions, ,Input/Output Functions}). + +@item +The @samp{**} and @samp{**=} operators +(@pxref{Arithmetic Ops, ,Arithmetic Operators} +and also see +@ref{Assignment Ops, ,Assignment Expressions}). + +@item +The use of @code{func} as an abbreviation for @code{function} +(@pxref{Definition Syntax, ,Function Definition Syntax}). + +@item +The @samp{\x} escape sequence +(@pxref{Escape Sequences}). + +@item +The @file{/dev/stdout}, and @file{/dev/stderr} +special files +(@pxref{Special Files, ,Special @value{FFN}s in @command{gawk}}). +Use @code{"-"} instead of @code{"/dev/stdin"} with @command{mawk}. + +@item +The ability for @code{FS} and for the third +argument to @code{split} to be null strings +(@pxref{Single Character Fields, , Making Each Character a Separate Field}). + +@item +The ability to delete all of an array at once with @samp{delete @var{array}} +(@pxref{Delete, ,The @code{delete} Statement}). + +@item +The ability for @code{RS} to be a regexp +(@pxref{Records, ,How Input Is Split into Records}). + +@item +The @code{BINMODE} special variable for non-Unix operating systems +(@pxref{PC Using, ,Using @command{gawk} on PC Operating Systems}). +@end itemize + +The next version of @command{mawk} will support @code{nextfile}. + +@cindex Sumner, Andrew +@cindex @command{awka} compiler for @command{awk} programs +@cindex @command{awka}, source code +@cindex source code, @command{awka} +@item @command{awka} +Written by Andrew Sumner, +@command{awka} translates @command{awk} programs into C, compiles them, +and links them with a library of functions that provides the core +@command{awk} functionality. +It also has a number of extensions. + +@cindex GPL +@cindex General Public License +@cindex GNU General Public License +@cindex LGPL +@cindex Lesser General Public License +@cindex GNU Lesser General Public License +The @command{awk} translator is released under the GPL, and the library +is under the LGPL. + +@ignore +To get @command{awka}, go to its home page at +Go to @uref{http://awka.sourceforge.net}. +@end ignore +To get @command{awka}, go to @uref{http://awka.sourceforge.net}. +You can reach Andrew Sumner at @email{andrew_sumner@@bigfoot.com}. @end table -@node Notes, Glossary, Installation, Top +@node Notes, Basic Concepts, Installation, Top @appendix Implementation Notes This appendix contains information mainly of interest to implementors and -maintainers of @code{gawk}. Everything in it applies specifically to -@code{gawk}, and not to other implementations. +maintainers of @command{gawk}. Everything in it applies specifically to +@command{gawk} and not to other implementations. @menu -* Compatibility Mode:: How to disable certain @code{gawk} extensions. -* Additions:: Making Additions To @code{gawk}. +* Compatibility Mode:: How to disable certain @command{gawk} + extensions. +* Additions:: Making Additions To @command{gawk}. +* Dynamic Extensions:: Adding new built-in functions to + @command{gawk}. * Future Extensions:: New features that may be implemented one day. -* Improvements:: Suggestions for improvements by volunteers. @end menu @node Compatibility Mode, Additions, Notes, Notes @appendixsec Downward Compatibility and Debugging -@xref{POSIX/GNU, ,Extensions in @code{gawk} Not in POSIX @code{awk}}, -for a summary of the GNU extensions to the @code{awk} language and program. -All of these features can be turned off by invoking @code{gawk} with the -@samp{--traditional} option, or with the @samp{--posix} option. +@xref{POSIX/GNU, ,Extensions in @command{gawk} Not in POSIX @command{awk}}, +for a summary of the GNU extensions to the @command{awk} language and program. +All of these features can be turned off by invoking @command{gawk} with the +@option{--traditional} option or with the @option{--posix} option. -If @code{gawk} is compiled for debugging with @samp{-DDEBUG}, then there +If @command{gawk} is compiled for debugging with @samp{-DDEBUG}, then there is one more option available on the command line: @table @code @@ -19641,70 +22898,82 @@ is one more option available on the command line: Print out the parse stack information as the program is being parsed. @end table -This option is intended only for serious @code{gawk} developers, +This option is intended only for serious @command{gawk} developers and not for the casual user. It probably has not even been compiled into -your version of @code{gawk}, since it slows down execution. +your version of @command{gawk}, since it slows down execution. -@node Additions, Future Extensions, Compatibility Mode, Notes -@appendixsec Making Additions to @code{gawk} +@node Additions, Dynamic Extensions, Compatibility Mode, Notes +@appendixsec Making Additions to @command{gawk} -If you should find that you wish to enhance @code{gawk} in a significant +If you find that you want to enhance @command{gawk} in a significant fashion, you are perfectly free to do so. That is the point of having -free software; the source code is available, and you are free to change -it as you wish (@pxref{Copying, ,GNU GENERAL PUBLIC LICENSE}). +free software; the source code is available and you are free to change +it as you want (@pxref{Copying, ,GNU General Public License}). -This section discusses the ways you might wish to change @code{gawk}, -and any considerations you should bear in mind. +This @value{SECTION} discusses the ways you might want to change @command{gawk} +as well as any considerations you should bear in mind. @menu -* Adding Code:: Adding code to the main body of @code{gawk}. -* New Ports:: Porting @code{gawk} to a new operating system. +* Adding Code:: Adding code to the main body of + @command{gawk}. +* New Ports:: Porting @command{gawk} to a new operating + system. @end menu @node Adding Code, New Ports, Additions, Additions @appendixsubsec Adding New Features @cindex adding new features -@cindex features, adding -You are free to add any new features you like to @code{gawk}. -However, if you want your changes to be incorporated into the @code{gawk} +@cindex features, adding to @command{gawk} +You are free to add any new features you like to @command{gawk}. +However, if you want your changes to be incorporated into the @command{gawk} distribution, there are several steps that you need to take in order to -make it possible for me to include your changes. +make it possible for me to include your changes: @enumerate 1 +@item +Before building the new feature into @command{gawk} itself, +consider writing it as an extension module +(@pxref{Dynamic Extensions, ,Adding New Built-in Functions to @command{gawk}}). +If that's not possible, continue with the rest of the steps in this list. + @item Get the latest version. It is much easier for me to integrate changes if they are relative to -the most recent distributed version of @code{gawk}. If your version of -@code{gawk} is very old, I may not be able to integrate them at all. -@xref{Getting, ,Getting the @code{gawk} Distribution}, -for information on getting the latest version of @code{gawk}. +the most recent distributed version of @command{gawk}. If your version of +@command{gawk} is very old, I may not be able to integrate them at all. +(@xref{Getting, ,Getting the @command{gawk} Distribution}, +for information on getting the latest version of @command{gawk}.) @item -@iftex +@ifnotinfo Follow the @cite{GNU Coding Standards}. -@end iftex +@end ifnotinfo @ifinfo See @inforef{Top, , Version, standards, GNU Coding Standards}. @end ifinfo This document describes how GNU software should be written. If you haven't -read it, please do so, preferably @emph{before} starting to modify @code{gawk}. -(The @cite{GNU Coding Standards} are available as part of the Autoconf -distribution, from the FSF.) - -@cindex @code{gawk} coding style -@cindex coding style used in @code{gawk} +read it, please do so, preferably @emph{before} starting to modify @command{gawk}. +(The @cite{GNU Coding Standards} are available from +the GNU Project's +@command{ftp} +site, at +@uref{ftp://gnudist.gnu.org/gnu/GNUInfo/standards.text}. +Texinfo, Info, and DVI versions are also available.) + +@cindex @command{gawk}, coding style +@cindex coding style used in @command{gawk} @item -Use the @code{gawk} coding style. -The C code for @code{gawk} follows the instructions in the +Use the @command{gawk} coding style. +The C code for @command{gawk} follows the instructions in the @cite{GNU Coding Standards}, with minor exceptions. The code is formatted -using the traditional ``K&R'' style, particularly as regards the placement -of braces and the use of tabs. In brief, the coding rules for @code{gawk} -are: +using the traditional ``K&R'' style, particularly as regards to the placement +of braces and the use of tabs. In brief, the coding rules for @command{gawk} +are as follows: @itemize @bullet @item -Use old style (non-prototype) function headers when defining functions. +Use ANSI/ISO style (prototype) function headers when defining functions. @item Put the name of the function at the beginning of its own line. @@ -19713,22 +22982,19 @@ Put the name of the function at the beginning of its own line. Put the return type of the function, even if it is @code{int}, on the line above the line with the name and arguments of the function. -@item -The declarations for the function arguments should not be indented. - @item Put spaces around parentheses used in control structures -(@code{if}, @code{while}, @code{for}, @code{do}, @code{switch} +(@code{if}, @code{while}, @code{for}, @code{do}, @code{switch}, and @code{return}). @item Do not put spaces in front of parentheses used in function calls. @item -Put spaces around all C operators, and after commas in function calls. +Put spaces around all C operators and after commas in function calls. @item -Do not use the comma operator to produce multiple side-effects, except +Do not use the comma operator to produce multiple side effects, except in @code{for} loop initialization and increment parts, and in macro bodies. @item @@ -19739,15 +23005,20 @@ Use the ``K&R'' brace layout style. @item Use comparisons against @code{NULL} and @code{'\0'} in the conditions of -@code{if}, @code{while} and @code{for} statements, and in the @code{case}s +@code{if}, @code{while}, and @code{for} statements, as well as in the @code{case}s of @code{switch} statements, instead of just the plain pointer or character value. @item -Use the @code{TRUE}, @code{FALSE}, and @code{NULL} symbolic constants, +Use the @code{TRUE}, @code{FALSE} and @code{NULL} symbolic constants and the character constant @code{'\0'} where appropriate, instead of @code{1} and @code{0}. +@item +Use the @code{ISALPHA}, @code{ISDIGIT}, etc.@: macros, instead of the +traditional lowercase versions; these macros are better behaved for +non-ASCII character sets. + @item Provide one-line descriptive comments for each function. @@ -19756,104 +23027,113 @@ Do not use @samp{#elif}. Many older Unix C compilers cannot handle it. @item Do not use the @code{alloca} function for allocating memory off the stack. -Its use causes more portability trouble than the minor benefit of not having +Its use causes more portability trouble than is worth the minor benefit of not having to free the storage. Instead, use @code{malloc} and @code{free}. @end itemize +@strong{Note:} If I have to reformat your code to follow the coding style used in -@code{gawk}, I may not bother. +@command{gawk}, I may not bother to integrate your changes at all. @item Be prepared to sign the appropriate paperwork. In order for the FSF to distribute your changes, you must either place -those changes in the public domain, and submit a signed statement to that +those changes in the public domain and submit a signed statement to that effect, or assign the copyright in your changes to the FSF. -Both of these actions are easy to do, and @emph{many} people have done so +Both of these actions are easy to do and @emph{many} people have done so already. If you have questions, please contact me (@pxref{Bugs, , Reporting Problems and Bugs}), -or @code{gnu@@gnu.org}. +or @email{gnu@@gnu.org}. +@cindex Texinfo @item Update the documentation. -Along with your new code, please supply new sections and or chapters +Along with your new code, please supply new sections and/or chapters for this @value{DOCUMENT}. If at all possible, please use real Texinfo, instead of just supplying unformatted ASCII text (although even that is better than no documentation at all). Conventions to be followed in @cite{@value{TITLE}} are provided -after the @samp{@@bye} at the end of the Texinfo source file. -If possible, please update the man page as well. +after the @samp{@@bye} at the end of the Texinfo source file. +If possible, please update the @command{man} page as well. You will also have to sign paperwork for your documentation changes. @item Submit changes as context diffs or unified diffs. Use @samp{diff -c -r -N} or @samp{diff -u -r -N} to compare -the original @code{gawk} source tree with your version. -(I find context diffs to be more readable, but unified diffs are +the original @command{gawk} source tree with your version. +(I find context diffs to be more readable but unified diffs are more compact.) -I recommend using the GNU version of @code{diff}. -Send the output produced by either run of @code{diff} to me when you +I recommend using the GNU version of @command{diff}. +Send the output produced by either run of @command{diff} to me when you submit your changes. -@xref{Bugs, , Reporting Problems and Bugs}, for the electronic mail -information. +(@xref{Bugs, , Reporting Problems and Bugs}, for the electronic mail +information.) Using this format makes it easy for me to apply your changes to the -master version of the @code{gawk} source code (using @code{patch}). +master version of the @command{gawk} source code (using @code{patch}). If I have to apply the changes manually, using a text editor, I may not do so, particularly if there are lots of changes. @item Include an entry for the @file{ChangeLog} file with your submission. -This further helps minimize the amount of work I have to do, +This helps further minimize the amount of work I have to do, making it easier for me to accept patches. @end enumerate Although this sounds like a lot of work, please remember that while you -may write the new code, I have to maintain it and support it, and if it +may write the new code, I have to maintain it and support it. If it isn't possible for me to do that with a minimum of extra work, then I probably will not. - @node New Ports, , Adding Code, Additions -@appendixsubsec Porting @code{gawk} to a New Operating System +@appendixsubsec Porting @command{gawk} to a New Operating System -@cindex porting @code{gawk} -If you wish to port @code{gawk} to a new operating system, there are -several steps to follow. +@cindex porting @command{gawk} +If you want to port @command{gawk} to a new operating system, there are +several steps to follow: @enumerate 1 @item Follow the guidelines in +@ifinfo @ref{Adding Code, ,Adding New Features}, +@end ifinfo +@ifnotinfo +the previous @value{SECTION} +@end ifnotinfo concerning coding style, submission of diffs, and so on. @item When doing a port, bear in mind that your code must co-exist peacefully -with the rest of @code{gawk}, and the other ports. Avoid gratuitous +with the rest of @command{gawk} and the other ports. Avoid gratuitous changes to the system-independent parts of the code. If at all possible, avoid sprinkling @samp{#ifdef}s just for your port throughout the code. +@cindex GPL +@cindex General Public License +@cindex GNU General Public License If the changes needed for a particular system affect too much of the -code, I probably will not accept them. In such a case, you will, of course, -be able to distribute your changes on your own, as long as you comply +code, I probably will not accept them. In such a case, you can, of course, +distribute your changes on your own, as long as you comply with the GPL -(@pxref{Copying, ,GNU GENERAL PUBLIC LICENSE}). +(@pxref{Copying, ,GNU General Public License}). @item -A number of the files that come with @code{gawk} are maintained by other +A number of the files that come with @command{gawk} are maintained by other people at the Free Software Foundation. Thus, you should not change them -unless it is for a very good reason. I.e.@: changes are not out of the -question, but changes to these files will be scrutinized extra carefully. -The files are @file{alloca.c}, @file{getopt.h}, @file{getopt.c}, +unless it is for a very good reason; i.e., changes are not out of the +question, but changes to these files are scrutinized extra carefully. +The files are @file{getopt.h}, @file{getopt.c}, @file{getopt1.c}, @file{regex.h}, @file{regex.c}, @file{dfa.h}, @file{dfa.c}, @file{install-sh}, and @file{mkinstalldirs}. @item Be willing to continue to maintain the port. Non-Unix operating systems are supported by volunteers who maintain -the code needed to compile and run @code{gawk} on their systems. If no-one -volunteers to maintain a port, that port becomes unsupported, and it may +the code needed to compile and run @command{gawk} on their systems. If noone +volunteers to maintain a port, it becomes unsupported and it may be necessary to remove it from the distribution. @item @@ -19866,15 +23146,15 @@ the main source directory includes the appropriate Be sure to update it as well. Each port's @file{gawkmisc.???} file has a suffix reminiscent of the machine -or operating system for the port. For example, @file{pc/gawkmisc.pc} and +or operating system for the port---for example, @file{pc/gawkmisc.pc} and @file{vms/gawkmisc.vms}. The use of separate suffixes, instead of plain @file{gawkmisc.c}, makes it possible to move files from a port's subdirectory into the main subdirectory, without accidentally destroying the real -@file{gawkmisc.c} file. (Currently, this is only an issue for the MS-DOS -and OS/2 ports.) +@file{gawkmisc.c} file. (Currently, this is only an issue for the +PC operating system ports.) @item -Supply a @file{Makefile} and any other C source and header files that are +Supply a @file{Makefile} as well as any other C source and header files that are necessary for your operating system. All your code should be in a separate subdirectory, with a name that is the same as, or reminiscent of, either your operating system or the computer system. If possible, @@ -19886,38 +23166,705 @@ duplicate the names of files in the main source directory. @item Update the documentation. Please write a section (or sections) for this @value{DOCUMENT} describing the -installation and compilation steps needed to install and/or compile -@code{gawk} for your system. +installation and compilation steps needed to compile and/or install +@command{gawk} for your system. + +@item +Be prepared to sign the appropriate paperwork. +In order for the FSF to distribute your code, you must either place +your code in the public domain and submit a signed statement to that +effect, or assign the copyright in your code to the FSF. +@ifinfo +Both of these actions are easy to do and @emph{many} people have done so +already. If you have questions, please contact me, or +@email{gnu@@gnu.org}. +@end ifinfo +@end enumerate + +Following these steps makes it much easier to integrate your changes +into @command{gawk} and have them co-exist happily with other +operating systems' code that is already there. + +In the code that you supply and maintain, feel free to use a +coding style and brace layout that suits your taste. + +@node Dynamic Extensions, Future Extensions, Additions, Notes +@appendixsec Adding New Built-in Functions to @command{gawk} +@cindex Robinson, Will +@cindex robot, the +@cindex Lost In Space +@quotation +@i{Danger Will Robinson! Danger!!@* +Warning! Warning!}@* +The Robot +@end quotation + +@cindex Linux +@cindex GNU/Linux +Beginning with @command{gawk} 3.1, it is possible to add new built-in +functions to @command{gawk} using dynamically loaded libraries. This +facility is available on systems (such as GNU/Linux) that support +the @code{dlopen} and @code{dlsym} functions. +This @value{SECTION} describes how to write and use dynamically +loaded extentions for @command{gawk}. +Experience with programming in +C or C++ is necessary when reading this @value{SECTION}. + +@strong{Caution:} The facilities described in this @value{SECTION} +are very much subject to change in the next @command{gawk} release. +Be aware that you may have to re-do everything, perhaps from scratch, +upon the next release. + +@menu +* Internals:: A brief look at some @command{gawk} internals. +* Sample Library:: A example of new functions. +@end menu + +@node Internals, Sample Library, Dynamic Extensions, Dynamic Extensions +@appendixsubsec A Minimal Introduction to @command{gawk} Internals + +The truth is that @command{gawk} was not designed for simple extensibility. +The facilities for adding functions using shared libraries work, but +are something of a ``bag on the side.'' Thus, this tour is +brief and simplistic; would-be @command{gawk} hackers are encouraged to +spend some time reading the source code before trying to write +extensions based on the material presented here. Of particular note +are the files @file{awk.h}, @file{builtin.c}, and @file{eval.c}. +Reading @file{awk.y} in order to see how the parse tree is built +would also be of use. + +With the disclaimers out of the way, the following types, structure +members, functions, and macros are declared in @file{awk.h} and are of +use when writing extensions. The next @value{SECTION} +shows how they are used: + +@table @code +@cindex @code{AWKNUM} internal type +@cindex internal type, @code{AWKNUM} +@item AWKNUM +An @code{AWKNUM} is the internal type of @command{awk} +floating-point numbers. Typically, it is a C @code{double}. + +@cindex @code{NODE} internal type +@cindex internal type, @code{NODE} +@item NODE +Just about everything is done using objects of type @code{NODE}. +These contain both strings and numbers, as well as variables and arrays. + +@cindex @code{force_number} internal function +@cindex internal function, @code{force_number} +@item AWKNUM force_number(NODE *n) +This macro forces a value to be numeric. It returns the actual +numeric value contained in the node. +It may end up calling an internal @command{gawk} function. + +@cindex @code{force_string} internal function +@cindex internal function, @code{force_string} +@item void force_string(NODE *n) +This macro guarantees that a @code{NODE}'s string value is current. +It may end up calling an internal @command{gawk} function. +It also guarantees that the string is zero-terminated. + +@cindex @code{param_cnt} internal variable +@cindex internal variable, @code{param_cnt} +@item n->param_cnt +The number of parameters actually passed in a function call at runtime. + +@cindex @code{stptr} internal variable +@cindex @code{stlen} internal variable +@cindex internal variable, @code{stptr} +@cindex internal variable, @code{stlen} +@item n->stptr +@itemx n->stlen +The data and length of a @code{NODE}'s string value, respectively. +The string is @emph{not} guaranteed to be zero-terminated. +If you need to pass the string value to a C library function, save +the value in @code{n->stptr[n->stlen]}, assign @code{'\0'} to it, +call the routine, and then restore the value. + +@cindex @code{type} internal variable +@cindex internal variable, @code{type} +@item n->type +The type of the @code{NODE}. This is a C @code{enum}. Values should +be either @code{Node_var} or @code{Node_var_array} for function +parameters. + +@cindex @code{vname} internal variable +@cindex internal variable, @code{vname} +@item n->vname +The ``variable name'' of a node. This is not of much use inside +externally written extensions. + +@cindex @code{assoc_clear} internal function +@cindex internal function, @code{assoc_clear} +@item void assoc_clear(NODE *n) +Clears the associative array pointed to by @code{n}. +Make sure that @samp{n->type == Node_var_array} first. + +@cindex @code{assoc_lookup} internal function +@cindex internal function, @code{assoc_lookup} +@item NODE **assoc_lookup(NODE *symbol, NODE *subs, int reference) +Finds, and installs if necessary, array elements. +@code{symbol} is the array, @code{subs} is the subscript. +This is usually a value created with @code{tmp_string} (see below). +@code{reference} should be @code{TRUE} if it is an error to use the +value before it is created. Typically, @code{FALSE} is the +correct value to use from extension functions. + +@cindex @code{make_string} internal function +@cindex internal function, @code{make_string} +@item NODE *make_string(char *s, size_t len) +Take a C string and turn it into a pointer to a @code{NODE} that +can be stored appropriately. This is permanent storage; understanding +of @command{gawk} memory management is helpful. + +@cindex @code{make_number} internal function +@cindex internal function, @code{make_number} +@item NODE *make_number(AWKNUM val) +Take an @code{AWKNUM} and turn it into a pointer to a @code{NODE} that +can be stored appropriately. This is permanent storage; understanding +of @command{gawk} memory management is helpful. + +@cindex @code{tmp_string} internal function +@item NODE *tmp_string(char *s, size_t len); +@cindex internal function, @code{tmp_string} +Take a C string and turn it into a pointer to a @code{NODE} that +can be stored appropriately. This is temporary storage; understanding +of @command{gawk} memory management is helpful. + +@cindex @code{tmp_number} internal function +@item NODE *tmp_number(AWKNUM val) +@cindex internal function, @code{tmp_number} +Take an @code{AWKNUM} and turn it into a pointer to a @code{NODE} that +can be stored appropriately. This is temporary storage; +understanding of @command{gawk} memory management is helpful. + +@cindex @code{dupnode} internal function +@cindex internal function, @code{dupnode} +@item NODE *dupnode(NODE *n) +Duplicate a node. In most cases, this increments an internal +reference count instead of actually duplicating the entire @code{NODE}; +understanding of @command{gawk} memory management is helpful. + +@cindex @code{free_temp} internal macro +@cindex internal macro, @code{free_temp} +@item void free_temp(NODE *n) +This macro releases the memory associated with a @code{NODE} +allocated with @code{tmp_string} or @code{tmp_number}. +Understanding of @command{gawk} memory management is helpful. + +@cindex @code{make_builtin} internal function +@cindex internal function, @code{make_builtin} +@item void make_builtin(char *name, NODE *(*func)(NODE *), int count) +Register a C function pointed to by @code{func} as new built-in +function @code{name}. @code{name} is a regular C string. @code{count} +is the maximum number of arguments that the function takes. +The function should be written in the following manner: + +@example +/* do_xxx --- do xxx function for gawk */ + +NODE * +do_xxx(NODE *tree) +@{ + @dots{} +@} +@end example + +@cindex @code{get_argument} internal function +@cindex internal function, @code{get_argument} +@item NODE *get_argument(NODE *tree, int i) +This function is called from within a C extension function to get +the @code{i}'th argument from the function call. +The first argument is argument zero. + +@cindex @code{set_value} internal function +@item void set_value(NODE *tree) +@cindex internal function, @code{set_value} +This function is called from within a C extension function to set +the return value from the extension function. This value is +what the @command{awk} program sees as the return value from the +new @command{awk} function. + +@cindex @code{update_ERRNO} internal function +@item void update_ERRNO(void) +@cindex internal function, @code{update_ERRNO} +This function is called from within a C extension function to set +the value of @command{gawk}'s @code{ERRNO} variable, based on the current +value of the C @code{errno} variable. +It is provided as a convenience. +@end table + +An argument that is supposed to be an array needs to be handled with +some extra code, in case the array being passed in is actually +from a function parameter. +The following ``boiler plate'' code shows how to do this: + +@smallexample +NODE *the_arg; + +the_arg = get_argument(tree, 2); /* assume need 3rd arg, 0-based */ + +/* if a parameter, get it off the stack */ +if (the_arg->type == Node_param_list) + the_arg = stack_ptr[the_arg->param_cnt]; + +/* parameter referenced an array, get it */ +if (the_arg->type == Node_array_ref) + the_arg = the_arg->orig_array; + +/* check type */ +if (the_arg->type != Node_var && the_arg->type != Node_var_array) + fatal("newfunc: third argument is not an array"); + +/* force it to be an array, if necessary, clear it */ +the_arg->type = Node_var_array; +assoc_clear(the_arg); +@end smallexample + +Again, you should spend time studying the @command{gawk} internals; +don't just blindly copy this code. + +@node Sample Library, , Internals, Dynamic Extensions +@appendixsubsec Directory and File Operation Built-ins + +Two useful functions that are not in @command{awk} are @code{chdir} +(so that an @command{awk} program can change its directory) and +@code{stat} (so that an @command{awk} program can gather information about +a file). +This @value{SECTION} implements these functions for @command{gawk} in an +external extension library. + +@menu +* Internal File Description:: What the new functions will do. +* Internal File Ops:: The code for internal file operations. +* Using Internal File Ops:: How to use an external extension. +@end menu + +@node Internal File Description, Internal File Ops, Sample Library, Sample Library +@appendixsubsubsec Using @code{chdir} and @code{stat} + +This @value{SECTION} shows how to use the new functions at the @command{awk} +level once they've been integrated into the running @command{gawk} +interpreter. +Using @code{chdir} is very straightforward. It takes one argument, +the new directory to change to: + +@example +@dots{} +newdir = "/home/arnold/funstuff" +ret = chdir(newdir) +if (ret < 0) @{ + printf("could not change to %s: %s\n", + newdir, ERRNO) > "/dev/stderr" + exit 1 +@} +@dots{} +@end example + +The return value is negative if the @code{chdir} failed, +and @code{ERRNO} +(@pxref{Built-in Variables}) +is set to a string indicating the error. + +Using @code{stat} is a bit more complicated. +The C @code{stat} function fills in a structure that has a fair +amount of information. +The right way to model this in @command{awk} is to fill in an associative +array with the appropriate information: + +@c broke printf for page breaking +@example +file = "/home/arnold/.profile" +fdata[1] = "x" # force `fdata' to be an array +ret = stat(file, fdata) +if (ret < 0) @{ + printf("could not stat %s: %s\n", + file, ERRNO) > "/dev/stderr" + exit 1 +@} +printf("size of %s is %d bytes\n", file, fdata["size"]) +@end example + +The @code{stat} function always clears the data array, even if +the @code{stat} fails. It fills in the following elements: + +@table @code +@item "name" +The name of the file that was @code{stat}'ed. + +@item "dev" +@itemx "ino" +The file's device and inode numbers, respectively. + +@item "mode" +The file's mode, as a numeric value. This includes both the file's +type and its permissions. + +@item "nlink" +The number of hard links (directory entries) the file has. + +@item "uid" +@itemx "gid" +The numeric user and group ID numbers of the file's owner. + +@item "size" +The size in bytes of the file. + +@item "blocks" +The number of disk blocks the file actually occupies. This may not +be a function of the file's size if the file has holes. + +@item "atime" +@itemx "mtime" +@itemx "ctime" +The file's last access, modification, and inode update times, +respectively. These are numeric timestamps, suitable for formatting +with @code{strftime} +(@pxref{Built-in, ,Built-in Functions}). + +@item "pmode" +The file's ``printable mode.'' This is a string representation of +the file's type and permissions, such as what is produced by +@samp{ls -l}---for example, @code{"drwxr-xr-x"}. + +@item "type" +A printable string representation of the file's type. The value +is one of the following: + +@table @code +@item "blockdev" +@itemx "chardev" +The file is a block or character device (``special file''). + +@ignore +@item "door" +The file is a Solaris ``door'' (special file used for +interprocess communications). +@end ignore + +@item "directory" +The file is a directory. + +@item "fifo" +The file is a named-pipe (also known as a FIFO). + +@item "file" +The file is just a regular file. + +@item "socket" +The file is an @code{AF_UNIX} (``Unix domain'') socket in the +filesystem. + +@item "symlink" +The file is a symbolic link. +@end table +@end table + +Several additional elements may be present depending upon the operating +system and the type of the file. You can test for them in your @command{awk} +program by using the @code{in} operator +(@pxref{Reference to Elements, ,Referring to an Array Element}): + +@table @code +@item "blksize" +The preferred block size for I/O to the file. This field is not +present on all POSIX-like systems in the C @code{stat} structure. + +@item "linkval" +If the file is a symbolic link, this element is the name of the +file the link points to (i.e., the value of the link). + +@item "rdev" +@itemx "major" +@itemx "minor" +If the file is a block or character device file, then these values +represent the numeric device number and the major and minor components +of that number, respectively. +@end table + +@node Internal File Ops, Using Internal File Ops, Internal File Description, Sample Library +@appendixsubsubsec C Code for @code{chdir} and @code{stat} + +@cindex Linux +@cindex GNU/Linux +Here is the C code for these extensions. They were written for +GNU/Linux. The code needs some more work for complete portability +to other POSIX-compliant systems:@footnote{This version is edited +slightly for presentation. The complete version can be found in +@file{extension/filefuncs.c} in the @command{gawk} distribution.} + +@c break line for page breaking +@example +#include "awk.h" + +#include + +/* do_chdir --- provide dynamically loaded + chdir() builtin for gawk */ + +static NODE * +do_chdir(tree) +NODE *tree; +@{ + NODE *newdir; + int ret = -1; + + newdir = get_argument(tree, 0); +@end example + +The file includes the @code{"awk.h"} header file for definitions +for the @command{gawk} internals. It includes @code{} +for access to the @code{major} and @code{minor} macros. + +@cindex conventions, programming +@cindex programming conventions +By convention, for an @command{awk} function @code{foo}, the function that +implements it is called @samp{do_foo}. The function should take +a @samp{NODE *} argument, usually called @code{tree}, that +represents the argument list to the function. The @code{newdir} +variable represents the new directory to change to, retrieved +with @code{get_argument}. Note that the first argument is +numbered zero. + +This code actually accomplishes the @code{chdir}. It first forces +the argument to be a string and passes the string value to the +@code{chdir} system call. If the @code{chdir} fails, @code{ERRNO} +is updated. +The result of @code{force_string} has to be freed with @code{free_temp}: + +@example + if (newdir != NULL) @{ + (void) force_string(newdir); + ret = chdir(newdir->stptr); + if (ret < 0) + update_ERRNO(); + + free_temp(newdir); + @} +@end example + +Finally, the function returns the return value to the @command{awk} level, +using @code{set_value}. Then it must return a value from the call to +the new built-in (this value ignored by the interpreter): + +@example + /* Set the return value */ + set_value(tmp_number((AWKNUM) ret)); + + /* Just to make the interpreter happy */ + return tmp_number((AWKNUM) 0); +@} +@end example + +The @code{stat} built-in is more involved. First comes a function +that turns a numeric mode into a printable representation +(e.g., 644 becomes @samp{-rw-r--r--}). This is omitted here for brevity: + +@c break line for page breaking +@example +/* format_mode --- turn a stat mode field + into something readable */ + +static char * +format_mode(fmode) +unsigned long fmode; +@{ + @dots{} +@} +@end example + +Next comes the actual @code{do_stat} function itself. First come the +variable declarations and argument checking: + +@ignore +Changed message for page breaking. Used to be: + "stat: called with incorrect number of arguments (%d), should be 2", +@end ignore +@example +/* do_stat --- provide a stat() function for gawk */ + +static NODE * +do_stat(tree) +NODE *tree; +@{ + NODE *file, *array; + struct stat sbuf; + int ret; + char *msg; + NODE **aptr; + char *pmode; /* printable mode */ + char *type = "unknown"; + + /* check arg count */ + if (tree->param_cnt != 2) + fatal( + "stat: called with %d arguments, should be 2", + tree->param_cnt); +@end example + +Then comes the actual work. First, we get the arguments. +Then, we always clear the array. To get the file information, +we use @code{lstat}, in case the file is a symbolic link. +If there's an error, we set @code{ERRNO} and return: + +@c comment made multiline for page breaking +@example + /* + * directory is first arg, + * array to hold results is second + */ + file = get_argument(tree, 0); + array = get_argument(tree, 1); + + /* empty out the array */ + assoc_clear(array); + + /* lstat the file, if error, set ERRNO and return */ + (void) force_string(file); + ret = lstat(file->stptr, & sbuf); + if (ret < 0) @{ + update_ERRNO(); + + set_value(tmp_number((AWKNUM) ret)); + + free_temp(file); + return tmp_number((AWKNUM) 0); + @} +@end example + +Now comes the tedious part: filling in the array. Only a few of the +calls are shown here, since they all follow the same pattern: + +@example + /* fill in the array */ + aptr = assoc_lookup(array, tmp_string("name", 4), FALSE); + *aptr = dupnode(file); + + aptr = assoc_lookup(array, tmp_string("mode", 4), FALSE); + *aptr = make_number((AWKNUM) sbuf.st_mode); + + aptr = assoc_lookup(array, tmp_string("pmode", 5), FALSE); + pmode = format_mode(sbuf.st_mode); + *aptr = make_string(pmode, strlen(pmode)); +@end example + +When done, we free the temporary value containing the @value{FN}, +set the return value, and return: + +@example + free_temp(file); + + /* Set the return value */ + set_value(tmp_number((AWKNUM) ret)); + + /* Just to make the interpreter happy */ + return tmp_number((AWKNUM) 0); +@} +@end example + +@cindex conventions, programming +@cindex programming conventions +Finally, it's necessary to provide the ``glue'' that loads the +new function(s) into @command{gawk}. By convention, each library has +a routine named @code{dlload} that does the job: + +@example +/* dlload --- load new builtins in this library */ + +NODE * +dlload(tree, dl) +NODE *tree; +void *dl; +@{ + make_builtin("chdir", do_chdir, 1); + make_builtin("stat", do_stat, 2); + return tmp_number((AWKNUM) 0); +@} +@end example + +And that's it! As an exercise, consider adding functions to +implement system calls such as @code{chown}, @code{chmod}, and @code{umask}. + +@node Using Internal File Ops, , Internal File Ops, Sample Library +@appendixsubsubsec Integrating the Extensions + +@cindex Linux +@cindex GNU/Linux +Now that the code is written, it must be possible to add it at +runtime to the running @command{gawk} interpreter. First, the +code must be compiled. Assuming that the functions are in +a file named @file{filefuncs.c}, and @var{idir} is the location +of the @command{gawk} include files, +the following steps create +a GNU/Linux shared library: + +@example +$ gcc -shared -DHAVE_CONFIG_H -c -O -g -I@var{idir} filefuncs.c +$ ld -o filefuncs.so -shared filefuncs.o +@end example -@item -Be prepared to sign the appropriate paperwork. -In order for the FSF to distribute your code, you must either place -your code in the public domain, and submit a signed statement to that -effect, or assign the copyright in your code to the FSF. -@ifinfo -Both of these actions are easy to do, and @emph{many} people have done so -already. If you have questions, please contact me, or -@code{gnu@@gnu.org}. -@end ifinfo -@end enumerate +@cindex @code{extension} built-in function +Once the library exists, it is loaded by calling the @code{extension} +built-in function. +This function takes two arguments: the name of the +library to load and the name of a function to call when the library +is first loaded. This function adds the new functions to @command{gawk}. +It returns the value returned by the initialization function +within the shared library: + +@example +# file testff.awk +BEGIN @{ + extension("./filefuncs.so", "dlload") + + chdir(".") # no-op + + data[1] = 1 # force `data' to be an array + print "Info for testff.awk" + ret = stat("testff.awk", data) + print "ret =", ret + for (i in data) + printf "data[\"%s\"] = %s\n", i, data[i] + print "testff.awk modified:", + strftime("%m %d %y %H:%M:%S", data["mtime"]) +@} +@end example -Following these steps will make it much easier to integrate your changes -into @code{gawk}, and have them co-exist happily with the code for other -operating systems that is already there. +Here are the results of running the program: -In the code that you supply, and that you maintain, feel free to use a -coding style and brace layout that suits your taste. +@example +$ gawk -f testff.awk +@print{} Info for testff.awk +@print{} ret = 0 +@print{} data["blksize"] = 4096 +@print{} data["mtime"] = 932361936 +@print{} data["mode"] = 33188 +@print{} data["type"] = file +@print{} data["dev"] = 2065 +@print{} data["gid"] = 10 +@print{} data["ino"] = 878597 +@print{} data["ctime"] = 971431797 +@print{} data["blocks"] = 2 +@print{} data["nlink"] = 1 +@print{} data["name"] = testff.awk +@print{} data["atime"] = 971608519 +@print{} data["pmode"] = -rw-r--r-- +@print{} data["size"] = 607 +@print{} data["uid"] = 2076 +@print{} testff.awk modified: 07 19 99 08:25:36 +@end example -@node Future Extensions, Improvements, Additions, Notes +@node Future Extensions, , Dynamic Extensions, Notes @appendixsec Probable Future Extensions @ignore From emory!scalpel.netlabs.com!lwall Tue Oct 31 12:43:17 1995 Return-Path: Message-Id: <9510311732.AA28472@scalpel.netlabs.com> To: arnold@skeeve.atl.ga.us (Arnold D. Robbins) -Subject: Re: May I quote you? +Subject: Re: May I quote you? In-Reply-To: Your message of "Tue, 31 Oct 95 09:11:00 EST." - + Date: Tue, 31 Oct 95 09:32:46 -0800 From: Larry Wall @@ -19925,7 +23872,7 @@ From: Larry Wall : thoroughly updated manual. One of the sections deals with planned future : extensions and enhancements. I have the following at the beginning : of it: -: +: : @cindex PERL : @cindex Wall, Larry : @display @@ -19935,7 +23882,7 @@ From: Larry Wall : @i{Hey!} @* : Larry Wall : @end display -: +: : Before I actually release this for publication, I wanted to get your : permission to quote you. (Hopefully, in the spirit of much of GNU, the : implied humor is visible... :-) @@ -19946,213 +23893,790 @@ Larry @end ignore @cindex PERL @cindex Wall, Larry -@display -@i{AWK is a language similar to PERL, only considerably more elegant.} +@cindex Robbins, Arnold +@quotation +@i{AWK is a language similar to PERL, only considerably more elegant.}@* Arnold Robbins -@i{Hey!} +@i{Hey!}@* Larry Wall -@end display -@sp 1 +@end quotation -This section briefly lists extensions and possible improvements +This @value{SECTION} briefly lists extensions and possible improvements that indicate the directions we are -currently considering for @code{gawk}. The file @file{FUTURES} in the -@code{gawk} distributions lists these extensions as well. +currently considering for @command{gawk}. The file @file{FUTURES} in the +@command{gawk} distribution lists these extensions as well. -This is a list of probable future changes that will be usable by the -@code{awk} language programmer. +Following is a list of probable future changes visible at the +@command{awk} language level: @c these are ordered by likelihood @table @asis -@item Localization -The GNU project is starting to support multiple languages. -It will at least be possible to make @code{gawk} print its warnings and -error messages in languages other than English. -It may be possible for @code{awk} programs to also use the multiple -language facilities, separate from @code{gawk} itself. +@item Loadable Module Interface +It is not clear that the @command{awk}-level interface to the +modules facility is as good as it should be. The interface needs to be +redesigned, particularly taking namespace issues into account, as +well as possibly including issues such as library search path order +and versioning. + +@item @code{RECLEN} variable for fixed length records +Along with @code{FIELDWIDTHS}, this would speed up the processing of +fixed-length records. +@code{PROCINFO["RS"]} would be @code{"RS"} or @code{"RECLEN"}, +depending upon which kind of record processing is in effect. + +@item Additional @code{printf} specifiers +The 1999 ISO C standard added a number of additional @code{printf} +format specifiers. These should be evaluated for possible inclusion +in @command{gawk}. + +@ignore +@item A @samp{%'d} flag +Add @samp{%'d} for putting in commas in formatting numeric values. +@end ignore @item Databases -It may be possible to map a GDBM/NDBM/SDBM file into an @code{awk} array. +It may be possible to map a GDBM/NDBM/SDBM file into an @command{awk} array. -@item A @code{PROCINFO} Array -The special files that provide process-related information -(@pxref{Special Files, ,Special File Names in @code{gawk}}) -will be superseded by a @code{PROCINFO} array that would provide the same -information, in an easier to access fashion. +@item Large Character Sets +It would be nice if @command{gawk} could handle UTF-8 and other +character sets that are larger than eight bits. @item More @code{lint} warnings There are more things that could be checked for portability. +@end table -@item Control of subprocess environment -Changes made in @code{gawk} to the array @code{ENVIRON} may be -propagated to subprocesses run by @code{gawk}. - -@ignore -@item @code{RECLEN} variable for fixed length records -Along with @code{FIELDWIDTHS}, this would speed up the processing of -fixed-length records. +Following is a list of probable improvements that will make @command{gawk}'s +source code easier to work with: -@item A @code{restart} keyword -After modifying @code{$0}, @code{restart} would restart the pattern -matching loop, without reading a new record from the input. - -@item A @samp{|&} redirection -The @samp{|&} redirection, in place of @samp{|}, would open a two-way -pipeline for communication with a sub-process (via @code{getline} and -@code{print} and @code{printf}). - -@item Function valued variables -It would be possible to assign the name of a user-defined or built-in -function to a regular @code{awk} variable, and then call the function -indirectly, by using the regular variable. This would make it possible -to write general purpose sorting and comparing routines, for example, -by simply passing the name of one function into another. - -@item A built-in @code{stat} function -The @code{stat} function would provide an easy-to-use hook to the -@code{stat} system call so that @code{awk} programs could determine information -about files. - -@item A built-in @code{ftw} function -Combined with function valued variables and the @code{stat} function, -@code{ftw} (file tree walk) would make it easy for an @code{awk} program -to walk an entire file tree. -@end ignore +@table @asis +@item Loadable Module Mechanics +The current extension mechanism works +(@pxref{Dynamic Extensions, ,Adding New Built-in Functions to @command{gawk}}), +but is rather primitive. It requires a fair amount of manual work +to create and integrate a loadable module. +Nor is the current mechanism as portable as might be desired. +The GNU @command{libtool} package provides a number of features that +would make using loadable modules much easier. +@command{gawk} should be changed to use @command{libtool}. + +@item Loadable Module Internals +The API to its internals that @command{gawk} ``exports'' should be revised. +Too many things are needlessly exposed. A new API should be designed +and implemented to make module writing easier. + +@item Better Array Subscript Management +@command{gawk}'s management of array subscript storage could use revamping, +so that using the same value to index multiple arrays only +stores one copy of the index value. + +@item Integrating the DBUG Library +Integrating Fred Fish's DBUG library would be helpful during development, +but it's a lot of work to do. @end table -This is a list of probable improvements that will make @code{gawk} -perform better. +Following is a list of probable improvements that will make @command{gawk} +perform better: @table @asis @item An Improved Version of @code{dfa} -The @code{dfa} pattern matcher from GNU @code{grep} has some +The @code{dfa} pattern matcher from GNU @command{grep} has some problems. Either a new version or a fixed one will deal with some important regexp matching issues. -@item Use of GNU @code{malloc} -The GNU version of @code{malloc} could potentially speed up @code{gawk}, -since it relies heavily on the use of dynamic memory allocation. - -@end table - -@node Improvements, , Future Extensions, Notes -@appendixsec Suggestions for Improvements - -Here are some projects that would-be @code{gawk} hackers might like to take -on. They vary in size from a few days to a few weeks of programming, -depending on which one you choose and how fast a programmer you are. Please -send any improvements you write to the maintainers at the GNU project. -@xref{Adding Code, , Adding New Features}, -for guidelines to follow when adding new features to @code{gawk}. -@xref{Bugs, ,Reporting Problems and Bugs}, for information on -contacting the maintainers. - -@enumerate -@item -Compilation of @code{awk} programs: @code{gawk} uses a Bison (YACC-like) +@c NEXT ED: remove this item. awka and mawk do these respectively +@item Compilation of @command{awk} programs +@command{gawk} uses a Bison (YACC-like) parser to convert the script given it into a syntax tree; the syntax tree is then executed by a simple recursive evaluator. This method incurs a lot of overhead, since the recursive evaluator performs many procedure calls to do even the simplest things. -It should be possible for @code{gawk} to convert the script's parse tree +It should be possible for @command{gawk} to convert the script's parse tree into a C program which the user would then compile, using the normal -C compiler and a special @code{gawk} library to provide all the needed -functions (regexps, fields, associative arrays, type coercion, and so -on). +C compiler and a special @command{gawk} library to provide all the needed +functions (regexps, fields, associative arrays, type coercion, and so on). -An easier possibility might be for an intermediate phase of @code{awk} to +An easier possibility might be for an intermediate phase of @command{gawk} to convert the parse tree into a linear byte code form like the one used in GNU Emacs Lisp. The recursive evaluator would then be replaced by a straight line byte code interpreter that would be intermediate in speed -between running a compiled program and doing what @code{gawk} does +between running a compiled program and doing what @command{gawk} does now. +@end table -@item -The programs in the test suite could use documenting in this @value{DOCUMENT}. +Finally, +the programs in the test suite could use documenting in this @value{DOCUMENT}. -@item -See the @file{FUTURES} file for more ideas. Contact us if you would -seriously like to tackle any of the items listed there. -@end enumerate +@xref{Additions, ,Making Additions to @command{gawk}}, +if you are interested in tackling any of these projects. + +@node Basic Concepts, Glossary, Notes, Top +@appendix Basic Programming Concepts +@cindex basic programming concepts +@cindex programming concepts, basic + +This @value{APPENDIX} attempts to define some of the basic concepts +and terms that are used throughout the rest of this @value{DOCUMENT}. +As this @value{DOCUMENT} is specifically about @command{awk}, +and not about computer programming in general, the coverage here +is by necessity fairly cursory and simplistic. +(If you need more background, there are many +other introductory texts that you should refer to instead.) + +@menu +* Basic High Level:: The high level view. +* Basic Data Typing:: A very quick intro to data types. +* Floating Point Issues:: Stuff to know about floating-point numbers. +@end menu + +@node Basic High Level, Basic Data Typing, Basic Concepts, Basic Concepts +@appendixsec What a Program Does + +@cindex processing data +At the most basic level, the job of a program is to process +some input data and produce results. + +@c NEXT ED: Use real images here +@iftex +@tex +\expandafter\ifx\csname graph\endcsname\relax \csname newbox\endcsname\graph\fi +\expandafter\ifx\csname graphtemp\endcsname\relax \csname newdimen\endcsname\graphtemp\fi +\setbox\graph=\vtop{\vskip 0pt\hbox{% + \special{pn 20}% + \special{pa 2425 200}% + \special{pa 2850 200}% + \special{fp}% + \special{sh 1.000}% + \special{pn 20}% + \special{pa 2750 175}% + \special{pa 2850 200}% + \special{pa 2750 225}% + \special{pa 2750 175}% + \special{fp}% + \special{pn 20}% + \special{pa 850 200}% + \special{pa 1250 200}% + \special{fp}% + \special{sh 1.000}% + \special{pn 20}% + \special{pa 1150 175}% + \special{pa 1250 200}% + \special{pa 1150 225}% + \special{pa 1150 175}% + \special{fp}% + \special{pn 20}% + \special{pa 2950 400}% + \special{pa 3650 400}% + \special{pa 3650 0}% + \special{pa 2950 0}% + \special{pa 2950 400}% + \special{fp}% + \special{pn 10}% + \special{ar 1800 200 450 200 0 6.28319}% + \graphtemp=.5ex\advance\graphtemp by 0.200in + \rlap{\kern 3.300in\lower\graphtemp\hbox to 0pt{\hss Results\hss}}% + \graphtemp=.5ex\advance\graphtemp by 0.200in + \rlap{\kern 1.800in\lower\graphtemp\hbox to 0pt{\hss Program\hss}}% + \special{pn 10}% + \special{pa 0 400}% + \special{pa 700 400}% + \special{pa 700 0}% + \special{pa 0 0}% + \special{pa 0 400}% + \special{fp}% + \graphtemp=.5ex\advance\graphtemp by 0.200in + \rlap{\kern 0.350in\lower\graphtemp\hbox to 0pt{\hss Data\hss}}% + \hbox{\vrule depth0.400in width0pt height 0pt}% + \kern 3.650in + }% +}% +\centerline{\box\graph} +@end tex +@end iftex +@ifnottex +@example + _______ ++------+ / \ +---------+ +| Data | -----> < Program > -----> | Results | ++------+ \_______/ +---------+ +@end example +@end ifnottex + +@cindex compiled programs +@cindex programs, compiled +@cindex interpreted programs +@cindex programs, interpreted +The ``program'' in the figure can be either a compiled +program@footnote{Compiled programs are typically written +in lower-level languages such as C, C++, Fortran, or Ada, +and then translated, or @dfn{compiled}, into a form that +the computer can execute directly.} +(such as @command{ls}), +or it may be @dfn{interpreted}. In the latter case, a machine-executable +program such as @command{awk} reads your program, and then uses the +instructions in your program to process the data. + +@cindex programming, basic steps +When you write a program, it usually consists +of the following, very basic set of steps: + +@c NEXT ED: Use real images here +@iftex +@tex +\expandafter\ifx\csname graph\endcsname\relax \csname newbox\endcsname\graph\fi +\expandafter\ifx\csname graphtemp\endcsname\relax \csname newdimen\endcsname\graphtemp\fi +\setbox\graph=\vtop{\vskip 0pt\hbox{% + \graphtemp=.5ex\advance\graphtemp by 0.600in + \rlap{\kern 2.800in\lower\graphtemp\hbox to 0pt{\hss Yes\hss}}% + \graphtemp=.5ex\advance\graphtemp by 0.100in + \rlap{\kern 3.300in\lower\graphtemp\hbox to 0pt{\hss No\hss}}% + \special{pn 8}% + \special{pa 2100 1000}% + \special{pa 1600 1000}% + \special{pa 1600 1000}% + \special{pa 1600 300}% + \special{fp}% + \special{sh 1.000}% + \special{pn 8}% + \special{pa 1575 400}% + \special{pa 1600 300}% + \special{pa 1625 400}% + \special{pa 1575 400}% + \special{fp}% + \special{pn 8}% + \special{pa 2600 500}% + \special{pa 2600 900}% + \special{fp}% + \special{sh 1.000}% + \special{pn 8}% + \special{pa 2625 800}% + \special{pa 2600 900}% + \special{pa 2575 800}% + \special{pa 2625 800}% + \special{fp}% + \special{pn 8}% + \special{pa 3200 200}% + \special{pa 4000 200}% + \special{fp}% + \special{sh 1.000}% + \special{pn 8}% + \special{pa 3900 175}% + \special{pa 4000 200}% + \special{pa 3900 225}% + \special{pa 3900 175}% + \special{fp}% + \special{pn 8}% + \special{pa 1400 200}% + \special{pa 2100 200}% + \special{fp}% + \special{sh 1.000}% + \special{pn 8}% + \special{pa 2000 175}% + \special{pa 2100 200}% + \special{pa 2000 225}% + \special{pa 2000 175}% + \special{fp}% + \special{pn 8}% + \special{ar 2600 1000 400 100 0 6.28319}% + \graphtemp=.5ex\advance\graphtemp by 1.000in + \rlap{\kern 2.600in\lower\graphtemp\hbox to 0pt{\hss Process\hss}}% + \special{pn 8}% + \special{pa 2200 400}% + \special{pa 3100 400}% + \special{pa 3100 0}% + \special{pa 2200 0}% + \special{pa 2200 400}% + \special{fp}% + \graphtemp=.5ex\advance\graphtemp by 0.200in + \rlap{\kern 2.688in\lower\graphtemp\hbox to 0pt{\hss More Data?\hss}}% + \special{pn 8}% + \special{ar 650 200 650 200 0 6.28319}% + \graphtemp=.5ex\advance\graphtemp by 0.200in + \rlap{\kern 0.613in\lower\graphtemp\hbox to 0pt{\hss Initialization\hss}}% + \special{pn 8}% + \special{ar 0 200 0 0 0 6.28319}% + \special{pn 8}% + \special{ar 4550 200 450 100 0 6.28319}% + \graphtemp=.5ex\advance\graphtemp by 0.200in + \rlap{\kern 4.600in\lower\graphtemp\hbox to 0pt{\hss Clean Up\hss}}% + \hbox{\vrule depth1.100in width0pt height 0pt}% + \kern 5.000in + }% +}% +\centerline{\box\graph} +@end tex +@end iftex +@ifnottex +@example + ______ ++----------------+ / More \ No +----------+ +| Initialization | -------> < Data > -------> | Clean Up | ++----------------+ ^ \ ? / +----------+ + | +--+-+ + | | Yes + | | + | V + | +---------+ + +-----+ Process | + +---------+ +@end example +@end ifnottex + +@table @asis +@item Initialization +These are the things you do before actually starting to process +data, such as checking arguments, initializing any data you need +to work with, and so on. +This step corresponds to @command{awk}'s @code{BEGIN} rule +(@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}). + +If you were baking a cake, this might consist of laying out all the +mixing bowls and the baking pan, and making sure you have all the +ingredients that you need. + +@item Processing +This is where the actual work is done. Your program reads data, +one logical chunk at a time, and processes it as appropriate. + +In most programming languages, you have to manually manage the reading +of data, checking to see if there is more each time you read a chunk. +@command{awk}'s pattern-action paradigm +(@pxref{Getting Started, ,Getting Started with @command{awk}}) +handles the mechanics of this for you. + +In baking a cake, the processing corresponds to the actual labor: +breaking eggs, mixing the flour, water, and other ingredients, and then putting the cake +into the oven. + +@item Clean Up +Once you've processed all the data, you may have things you need to +do before exiting. +This step corresponds to @command{awk}'s @code{END} rule +(@pxref{BEGIN/END, ,The @code{BEGIN} and @code{END} Special Patterns}). + +After the cake comes out of the oven, you still have to wrap it in +plastic wrap to keep anyone from tasting it, as well as wash +the mixing bowls and other utensils. +@end table + +@cindex algorithm, definition of +An @dfn{algorithm} is a detailed set of instructions necessary to accomplish +a task, or process data. It is much the same as a recipe for baking +a cake. Programs implement algorithms. Often, it is up to you to design +the algorithm and implement it, simultaneously. + +@cindex record, definition of +@cindex fields, definition of +The ``logical chunks'' we talked about previously are called @dfn{records}, +similar to the records a company keeps on employees, a school keeps for +students, or a doctor keeps for patients. +Each record has many component parts, such as first and last names, +date of birth, address, and so on. The component parts are referred +to as the @dfn{fields} of the record. + +The act of reading data is termed @dfn{input}, and that of +generating results, not too surprisingly, is termed @dfn{output}. +They are often referred to together as ``Input/Output,'' +and even more often, as ``I/O'' for short. +(You will also see ``input'' and ``output'' used as verbs.) + +@cindex data-driven languages +@cindex language, data-driven +@command{awk} manages the reading of data for you, as well as the +breaking it up into records and fields. Your program's job is to +tell @command{awk} what to with the data. You do this by describing +@dfn{patterns} in the data to look for, and @dfn{actions} to execute +when those patterns are seen. This @dfn{data-driven} nature of +@command{awk} programs usually makes them both easier to write +and easier to read. + +@node Basic Data Typing, Floating Point Issues, Basic High Level, Basic Concepts +@appendixsec Data Values in a Computer + +@cindex variable, definition of +In a program, +you keep track of information and values in things called @dfn{variables}. +A variable is just a name for a given value, such as @code{first_name}, +@code{last_name}, @code{address}, and so on. +@command{awk} has several pre-defined variables, and it has +special names to refer to the current input record +and the fields of the record. +You may also group multiple +associated values under one name, as an array. + +@cindex values, numeric +@cindex values, string +@cindex scalar, definition of +Data, particularly in @command{awk}, consists of either numeric +values, such as 42 or 3.1415927, or string values. +String values are essentially anything that's not a number, such as a name. +Strings are sometimes referred to as @dfn{character data}, since they +store the individual characters that comprise them. +Individual variables, as well as numeric and string variables, are +referred to as @dfn{scalar} values. +Groups of values, such as arrays, are not scalars. + +@cindex integer, definition of +@cindex floating-point, definition of +Within computers, there are two kinds of numeric values: @dfn{integers}, +and @dfn{floating-point}. +In school, integer values were referred to as ``whole'' numbers---that is, +numbers without any fractional part, such as 1, 42, or @minus{}17. +The advantage to integer numbers is that they represent values exactly. +The disadvantage is that their range is limited. On most modern systems, +this range is @minus{}2,147,483,648 to 2,147,483,647. + +@cindex unsigned integers +@cindex integer, unsigned +Integer values come in two flavors: @dfn{signed} and @dfn{unsigned}. +Signed values may be negative or positive, with the range of values just +described. +Unsigned values are always positive. On most modern systems, +the range is from 0 to 4,294,967,295. + +@cindex double-precision floating-point, definition of +@cindex single-precision floating-point, definition of +Floating-point numbers represent what are called ``real'' numbers; i.e., +those that do have a fractional part, such as 3.1415927. +The advantage to floating-point numbers is that they +can represent a much larger range of values. +The disadvantage is that there are numbers that they cannot represent +exactly. +@command{awk} uses @dfn{double-precision} floating-point numbers, which +can hold more digits than @dfn{single-precision} +floating-point numbers. +Floating-point issues are discussed more fully in +@ref{Floating Point Issues, ,Floating-Point Number Caveats}. + +At the very lowest level, computers store values as groups of binary digits, +or @dfn{bits}. Modern computers group bits into groups of eight, called @dfn{bytes}. +Advanced applications sometimes have to manipulate bits directly, +and @command{gawk} provides functions for doing so. + +@cindex null string, definition of +@cindex empty string, definition of +While you are probably used to the idea of a number without a value (i.e., zero), +it takes a bit more getting used to the idea of zero-length character data. +Nevertheless, such a thing exists. +It is called the @dfn{null string}. +The null string is character data that has no value. +In other words, it is empty. It is written in @command{awk} programs +like this: @code{""}. + +Humans are used to working in decimal; i.e., base 10. In base 10, +numbers go from 0 to 9, and then ``roll over'' into the next +column. (Remember grade school? 42 is 4 times 10 plus 2.) + +There are other number bases though. Computers commonly use base 2 +or @dfn{binary}, base 8 or @dfn{octal}, and base 16 or @dfn{hexadecimal}. +In binary, each column represents two times the value in the column to +its right. Each column may contain either a 0 or a 1. +Thus, binary 1010 represents 1 times 8, plus 0 times 4, plus 1 times 2, +plus 0 times 1, or decimal 10. +Octal and hexadecimal are discussed more in +@ref{Non-decimal-numbers, ,Octal and Hexadecimal Numbers}. + +Programs are written in programming languages. +Hundreds, if not thousands, of programming languages exist. +One of the most popular is the C programming language. +The C language had a very strong influence on the design of +the @command{awk} language. + +@cindex Kernighan, Brian +@cindex Ritchie, Dennis +There have been several versions of C. The first is often referred to +as ``K&R'' C, after the initials of Brian Kernighan and Dennis Ritchie, +the authors of the first book on C. (Dennis Ritchie created the language, +and Brian Kernighan was one of the creators of @command{awk}.) + +In the mid-1980's, an effort began to produce an international standard +for C. This work culminated in 1989, with the production of the ANSI +standard for C. This standard became an ISO standard in 1990. +Where it makes sense, POSIX @command{awk} is compatible with 1990 ISO C. + +In 1999, a revised ISO C standard was approved and released. +Future versions of @command{gawk} will be as compatible as possible +with this standard. + +@node Floating Point Issues, , Basic Data Typing, Basic Concepts +@appendixsec Floating-Point Number Caveats + +As mentioned earlier, floating-point numbers represent what are called +``real'' numbers; i.e., those that have a fractional part. @command{awk} +uses double-precision floating-point numbers to represent all +numeric values. This @value{SECTION} describes some of the issues +involved in using floating-point numbers. + +There is a very nice paper on floating-point arithmetic by +David Goldberg, @cite{What Every +Computer Scientist Should Know About Floating-point Arithmetic}, +@cite{ACM Computing Surveys} @strong{23}, 1 (1991-03), +5-48.@footnote{@uref{http://www.validgh.com/goldberg/paper.ps}} +This is worth reading if you are interested in the details, +but it does require a background in Computer Science. + +Internally, @command{awk} keeps both the numeric value +(double-precision floating-point) and the string value for a variable. +Separately, @command{awk} keeps +track of what type the variable has +(@pxref{Typing and Comparison, ,Variable Typing and Comparison Expressions}), +which plays a role in how variables are used in comparisons. + +It is important to note that the string value for a number may not +reflect the full value (all the digits) that the numeric value +actually contains. +The following program (@file{values.awk}) illustrates this: + +@example +@{ + $1 = $2 + $3 + # see it for what it is + printf("$1 = %.12g\n", $1) + # use CONVFMT + a = "<" $1 ">" + print "a =", a +@group + # use OFMT + print "$1 =", $1 +@end group +@} +@end example + +@noindent +This program shows the full value of the sum of @code{$2} and @code{$3} +using @code{printf}, and then prints the string values obtained +from both automatic conversion (via @code{CONVFMT}) and +from printing (via @code{OFMT}). + +Here is what happens when the program is run: + +@example +$ echo 2 3.654321 1.2345678 | awk -f values.awk +@print{} $1 = 4.8888888 +@print{} a = <4.88889> +@print{} $1 = 4.88889 +@end example + +This makes it clear that the full numeric value is different from +what the default string representations show. + +@code{CONVFMT}'s default value is @code{"%.6g"}, which yields a value with +at least six significant digits. For some applications, you might want to +change it to specify more precision. +On most modern machines, most of the time, +17 digits is enough to capture a floating-point number's +value exactly.@footnote{Pathological cases can require up to +752 digits (!), but we doubt that you need to worry about this.} + +@cindex floating-point, precision issues +Unlike numbers in the abstract sense (such as what you studied in high school +or college math), numbers stored in computers are limited in certain ways. +They cannot represent an infinite number of digits, nor can they always +represent things exactly. +In particular, +floating-point numbers cannot +always represent values exactly. Here is an example: + +@example +$ awk '@{ printf("%010d\n", $1 * 100) @}' +515.79 +@print{} 0000051579 +515.80 +@print{} 0000051579 +515.81 +@print{} 0000051580 +515.82 +@print{} 0000051582 +@kbd{Ctrl-d} +@end example -@node Glossary, Copying, Notes, Top -@appendix Glossary +@noindent +This shows that some values can be represented exactly, +whereas others are only approximated. This is not a ``bug'' +in @command{awk}, but simply an artifact of how computers +represent numbers. + +@cindex negative zero +@cindex positive zero +@cindex zero, negative vs.@: positive +@cindex floating-point, positive and negative values for zero +Another peculiarity of floating-point numbers on modern systems +is that they often have more than one representation for the number zero! +In particular, it is possible to represent ``minus zero'' as well as +regular, or ``positive'' zero. + +This example shows that negative and positive zero are distinct values +when stored internally, but that they are in fact equal to each other, +as well as to ``regular'' zero: + +@smallexample +$ gawk 'BEGIN @{ mz = -0 ; pz = 0 +> printf "-0 = %g, +0 = %g, (-0 == +0) -> %d\n", mz, pz, mz == pz +> printf "mz == 0 -> %d, pz == 0 -> %d\n", mz == 0, pz == 0 +> @}' +@print{} -0 = -0, +0 = 0, (-0 == +0) -> 1 +@print{} mz == 0 -> 1, pz == 0 -> 1 +@end smallexample + +It helps to keep this in mind should you process numeric data +that contains negative zero values; the fact that the zero is negative +is noted and can affect comparisons. + +@node Glossary, Copying, Basic Concepts, Top +@unnumbered Glossary @table @asis @item Action -A series of @code{awk} statements attached to a rule. If the rule's -pattern matches an input record, @code{awk} executes the +A series of @command{awk} statements attached to a rule. If the rule's +pattern matches an input record, @command{awk} executes the rule's action. Actions are always enclosed in curly braces. -@xref{Action Overview, ,Overview of Actions}. +(@xref{Action Overview, ,Actions}.) -@item Amazing @code{awk} Assembler +@cindex Spencer, Henry +@cindex @command{sed} utility +@cindex amazing @command{awk} assembler (@command{aaa}) +@item Amazing @command{awk} Assembler Henry Spencer at the University of Toronto wrote a retargetable assembler -completely as @code{awk} scripts. It is thousands of lines long, including -machine descriptions for several eight-bit microcomputers. -It is a good example of a -program that would have been better written in another language. - -@item Amazingly Workable Formatter (@code{awf}) +completely as @command{sed} and @command{awk} scripts. It is thousands +of lines long, including machine descriptions for several eight-bit +microcomputers. It is a good example of a program that would have been +better written in another language. +You can get it from @uref{ftp://ftp.freefriends.org/arnold/Awkstuff/aaa.tgz}. + +@cindex amazingly workable formatter (@command{awf}) +@cindex @command{awf} (amazingly workable formatter) program +@item Amazingly Workable Formatter (@command{awf}) Henry Spencer at the University of Toronto wrote a formatter that accepts a large subset of the @samp{nroff -ms} and @samp{nroff -man} formatting -commands, using @code{awk} and @code{sh}. +commands, using @command{awk} and @command{sh}. +It is available over the Internet +from @uref{ftp://ftp.freefriends.org/arnold/Awkstuff/awf.tgz}. +@item Anchor +The regexp metacharacters @samp{^} and @samp{$}, which force the match +to the beginning or end of the string, respectively. + +@cindex ANSI @item ANSI The American National Standards Institute. This organization produces many standards, among them the standards for the C and C++ programming languages. +These standards often become international standards as well. See also +``ISO.'' + +@item Array +A grouping of multiple values under the same name. +Most languages just provide sequential arrays. +@command{awk} provides associative arrays. + +@item Assertion +A statement in a program that a condition is true at this point in the program. +Useful for reasoning about how a program is supposed to behave. @item Assignment -An @code{awk} expression that changes the value of some @code{awk} +An @command{awk} expression that changes the value of some @command{awk} variable or data object. An object that you can assign to is called an @dfn{lvalue}. The assigned values are called @dfn{rvalues}. @xref{Assignment Ops, ,Assignment Expressions}. -@item @code{awk} Language -The language in which @code{awk} programs are written. +@item Associative Array +Arrays in which the indices may be numbers or strings, not just +sequential integers in a fixed range. + +@item @command{awk} Language +The language in which @command{awk} programs are written. -@item @code{awk} Program -An @code{awk} program consists of a series of @dfn{patterns} and +@item @command{awk} Program +An @command{awk} program consists of a series of @dfn{patterns} and @dfn{actions}, collectively known as @dfn{rules}. For each input record given to the program, the program's rules are all processed in turn. -@code{awk} programs may also contain function definitions. +@command{awk} programs may also contain function definitions. -@item @code{awk} Script -Another name for an @code{awk} program. +@item @command{awk} Script +Another name for an @command{awk} program. @item Bash -The GNU version of the standard shell (the Bourne-Again shell). -See ``Bourne Shell.'' +The GNU version of the standard shell +@iftex +(the @b{B}ourne-@b{A}gain @b{SH}ell). +@end iftex +@ifnottex +(the Bourne-Again SHell). +@end ifnottex +See also ``Bourne Shell.'' @item BBS See ``Bulletin Board System.'' +@item Bit +Short for ``Binary Digit.'' +All values in computer memory ultimately reduce to binary digits: values +that are either zero or one. +Groups of bits may be interpreted differently---as integers, +floating-point numbers, character data, addresses of other +memory objects, or other data. +@command{awk} lets you work with floating-point numbers and strings. +@command{gawk} lets you manipulate bit values with the built-in +functions described in +@ref{Bitwise Functions, ,Using @command{gawk}'s Bit Manipulation Functions}. + +Computers are often defined by how many bits they use to represent integer +values. Typical systems are 32-bit systems, but 64-bit systems are +becoming increasingly popular, and 16-bit systems are waning in +popularity. + @item Boolean Expression -Named after the English mathematician Boole. See ``Logical Expression.'' +Named after the English mathematician Boole. See also ``Logical Expression.'' @item Bourne Shell The standard shell (@file{/bin/sh}) on Unix and Unix-like systems, originally written by Steven R.@: Bourne. -Many shells (Bash, @code{ksh}, @code{pdksh}, @code{zsh}) are +Many shells (@command{bash}, @command{ksh}, @command{pdksh}, @command{zsh}) are generally upwardly compatible with the Bourne shell. @item Built-in Function -The @code{awk} language provides built-in functions that perform various -numerical, time stamp related, and string computations. Examples are +The @command{awk} language provides built-in functions that perform various +numerical, I/O-related, and string computations. Examples are @code{sqrt} (for the square root of a number) and @code{substr} (for a -substring of a string). @xref{Built-in, ,Built-in Functions}. +substring of a string). +@command{gawk} provides functions for timestamp management, bit manipulation, +and runtime string translation. +(@xref{Built-in, ,Built-in Functions}.) @item Built-in Variable -@code{ARGC}, @code{ARGIND}, @code{ARGV}, @code{CONVFMT}, @code{ENVIRON}, -@code{ERRNO}, @code{FIELDWIDTHS}, @code{FILENAME}, @code{FNR}, @code{FS}, -@code{IGNORECASE}, @code{NF}, @code{NR}, @code{OFMT}, @code{OFS}, @code{ORS}, -@code{RLENGTH}, @code{RSTART}, @code{RS}, @code{RT}, and @code{SUBSEP}, -are the variables that have special meaning to @code{awk}. -Changing some of them affects @code{awk}'s running environment. -Several of these variables are specific to @code{gawk}. -@xref{Built-in Variables}. +@code{ARGC}, +@code{ARGV}, +@code{CONVFMT}, +@code{ENVIRON}, +@code{FILENAME}, +@code{FNR}, +@code{FS}, +@code{NF}, +@code{NR}, +@code{OFMT}, +@code{OFS}, +@code{ORS}, +@code{RLENGTH}, +@code{RSTART}, +@code{RS}, +and +@code{SUBSEP} +are the variables that have special meaning to @command{awk}. +In addition, +@code{ARGIND}, +@code{BINMODE}, +@code{ERRNO}, +@code{FIELDWIDTHS}, +@code{IGNORECASE}, +@code{LINT}, +@code{PROCINFO}, +@code{RT}, +and +@code{TEXTDOMAIN} +are the variables that have special meaning to @command{gawk}. +Changing some of them affects @command{awk}'s running environment. +(@xref{Built-in Variables}.) @item Braces See ``Curly Braces.'' @@ -20164,11 +24688,19 @@ board. @item C The system programming language that most GNU software is written in. The -@code{awk} programming language has C-like syntax, and this @value{DOCUMENT} -points out similarities between @code{awk} and C when appropriate. +@command{awk} programming language has C-like syntax, and this @value{DOCUMENT} +points out similarities between @command{awk} and C when appropriate. + +In general, @command{gawk} attempts to be as similar to the 1990 version +of ISO C as makes sense. Future versions of @command{gawk} may adopt features +from the newer 1999 standard, as appropriate. + +@item C++ +A popular object-oriented programming language derived from C. @cindex ISO 8859-1 @cindex ISO Latin-1 +@cindex character sets (machine character encodings) @item Character Set The set of numeric codes used by a computer system to represent the characters (letters, numbers, punctuation, etc.) of a particular country @@ -20176,156 +24708,255 @@ or place. The most common character set in use today is ASCII (American Standard Code for Information Interchange). Many European countries use an extension of ASCII known as ISO-8859-1 (ISO Latin-1). +@cindex @command{chem} utility @item CHEM -A preprocessor for @code{pic} that reads descriptions of molecules -and produces @code{pic} input for drawing them. It was written in @code{awk} +A preprocessor for @command{pic} that reads descriptions of molecules +and produces @command{pic} input for drawing them. +It was written in @command{awk} by Brian Kernighan and Jon Bentley, and is available from -@email{@w{netlib@@research.bell-labs.com}}. +@uref{http://cm.bell-labs.com/netlib/typesetting/chem.gz}. + +@item Coprocess +A subordinate program with which two-way communications is possible. + +@cindex compiled programs +@item Compiler +A program that translates human-readable source code into +machine-executable object code. The object code is then executed +directly by the computer. +See also ``Interpreter.'' @item Compound Statement -A series of @code{awk} statements, enclosed in curly braces. Compound +A series of @command{awk} statements, enclosed in curly braces. Compound statements may be nested. -@xref{Statements, ,Control Statements in Actions}. +(@xref{Statements, ,Control Statements in Actions}.) @item Concatenation Concatenating two strings means sticking them together, one after another, -giving a new string. For example, the string @samp{foo} concatenated with +producing a new string. For example, the string @samp{foo} concatenated with the string @samp{bar} gives the string @samp{foobar}. -@xref{Concatenation, ,String Concatenation}. +(@xref{Concatenation, ,String Concatenation}.) @item Conditional Expression An expression using the @samp{?:} ternary operator, such as @samp{@var{expr1} ? @var{expr2} : @var{expr3}}. The expression @var{expr1} is evaluated; if the result is true, the value of the whole -expression is the value of @var{expr2}, otherwise the value is +expression is the value of @var{expr2}; otherwise the value is @var{expr3}. In either case, only one of @var{expr2} and @var{expr3} -is evaluated. @xref{Conditional Exp, ,Conditional Expressions}. +is evaluated. (@xref{Conditional Exp, ,Conditional Expressions}.) @item Comparison Expression A relation that is either true or false, such as @samp{(a < b)}. Comparison expressions are used in @code{if}, @code{while}, @code{do}, and @code{for} statements, and in patterns to select which input records to process. -@xref{Typing and Comparison, ,Variable Typing and Comparison Expressions}. +(@xref{Typing and Comparison, ,Variable Typing and Comparison Expressions}.) @item Curly Braces The characters @samp{@{} and @samp{@}}. Curly braces are used in -@code{awk} for delimiting actions, compound statements, and function +@command{awk} for delimiting actions, compound statements, and function bodies. +@cindex dark corner @item Dark Corner An area in the language where specifications often were (or still are) not clear, leading to unexpected or undesirable behavior. -Such areas are marked in this @value{DOCUMENT} with ``(d.c.)'' in the -text, and are indexed under the heading ``dark corner.'' +Such areas are marked in this @value{DOCUMENT} with +@iftex +the picture of a flashlight in the margin +@end iftex +@ifnottex +``(d.c.)'' in the text +@end ifnottex +and are indexed under the heading ``dark corner.'' + +@item Data Driven +A description of @command{awk} programs, where you specify the data you +are interested in processing, and what to do when that data is seen. @item Data Objects These are numbers and strings of characters. Numbers are converted into strings and vice versa, as needed. -@xref{Conversion, ,Conversion of Strings and Numbers}. +(@xref{Conversion, ,Conversion of Strings and Numbers}.) -@item Double Precision +@item Deadlock +The situation in which two communicating processes are each waiting +for the other to perform an action. + +@item Double-Precision An internal representation of numbers that can have fractional parts. -Double precision numbers keep track of more digits than do single precision -numbers, but operations on them are more expensive. This is the way -@code{awk} stores numeric values. It is the C type @code{double}. +Double-precision numbers keep track of more digits than do single-precision +numbers, but operations on them are sometimes more expensive. This is the way +@command{awk} stores numeric values. It is the C type @code{double}. @item Dynamic Regular Expression A dynamic regular expression is a regular expression written as an ordinary expression. It could be a string constant, such as @code{"foo"}, but it may also be an expression whose value can vary. -@xref{Computed Regexps, , Using Dynamic Regexps}. +(@xref{Computed Regexps, , Using Dynamic Regexps}.) @item Environment A collection of strings, of the form @var{name@code{=}val}, that each program has available to it. Users generally place values into the environment in order to provide information to various programs. Typical -examples are the environment variables @code{HOME} and @code{PATH}. +examples are the environment variables @env{HOME} and @env{PATH}. @item Empty String See ``Null String.'' +@cindex epoch, definition of +@item Epoch +The date used as the ``beginning of time'' for timestamps. +Time values in Unix systems are represented as seconds since the epoch, +with library functions available for converting these values into +standard date and time formats. + +The epoch on Unix and POSIX systems is 1970-01-01 00:00:00 UTC. +See also ``GMT'' and ``UTC.'' + @item Escape Sequences A special sequence of characters used for describing non-printing -characters, such as @samp{\n} for newline, or @samp{\033} for the ASCII -ESC (escape) character. @xref{Escape Sequences}. +characters, such as @samp{\n} for newline or @samp{\033} for the ASCII +ESC (Escape) character. (@xref{Escape Sequences}.) + +@item FDL +See ``Free Documentation License.'' @item Field -When @code{awk} reads an input record, it splits the record into pieces -separated by whitespace (or by a separator regexp which you can +When @command{awk} reads an input record, it splits the record into pieces +separated by whitespace (or by a separator regexp that you can change by setting the built-in variable @code{FS}). Such pieces are called fields. If the pieces are of fixed length, you can use the built-in variable @code{FIELDWIDTHS} to describe their lengths. -@xref{Field Separators, ,Specifying How Fields are Separated}, -and also see -@xref{Constant Size, , Reading Fixed-width Data}. +(@xref{Field Separators, ,Specifying How Fields Are Separated}, +and +@ref{Constant Size, ,Reading Fixed-Width Data}.) -@item Floating Point Number -Often referred to in mathematical terms as a ``rational'' number, this is -just a number that can have a fractional part. -See ``Double Precision'' and ``Single Precision.'' +@item Flag +A variable whose truth value indicates the existence or non-existence +of some condition. + +@item Floating-Point Number +Often referred to in mathematical terms as a ``rational'' or real number, +this is just a number that can have a fractional part. +See also ``Double-Precision'' and ``Single-Precision.'' @item Format Format strings are used to control the appearance of output in the -@code{printf} statement. Also, data conversions from numbers to strings +@code{strftime} and @code{sprintf} functions, and are used in the +@code{printf} statement as well. Also, data conversions from numbers to strings are controlled by the format string contained in the built-in variable -@code{CONVFMT}. @xref{Control Letters, ,Format-Control Letters}. +@code{CONVFMT}. (@xref{Control Letters, ,Format-Control Letters}.) + +@item Free Documentation License +This document describes the terms under which this @value{DOCUMENT} +is published and may be copied. (@xref{GNU Free Documentation License}.) @item Function A specialized group of statements used to encapsulate general -or program-specific tasks. @code{awk} has a number of built-in +or program-specific tasks. @command{awk} has a number of built-in functions, and also allows you to define your own. -@xref{Built-in, ,Built-in Functions}, -and @ref{User-defined, ,User-defined Functions}. +(@xref{Functions}.) @item FSF See ``Free Software Foundation.'' +@cindex FSF +@cindex Free Software Foundation +@cindex Stallman, Richard @item Free Software Foundation A non-profit organization dedicated to the production and distribution of freely distributable software. It was founded by Richard M.@: Stallman, the author of the original Emacs editor. GNU Emacs is the most widely used version of Emacs today. -@item @code{gawk} -The GNU implementation of @code{awk}. +@item @command{gawk} +The GNU implementation of @command{awk}. +@cindex GPL +@cindex General Public License +@cindex GNU General Public License @item General Public License -This document describes the terms under which @code{gawk} and its source -code may be distributed. (@pxref{Copying, ,GNU GENERAL PUBLIC LICENSE}) +This document describes the terms under which @command{gawk} and its source +code may be distributed. (@xref{Copying, ,GNU General Public License}.) +@item GMT +``Greenwich Mean Time.'' +This is the old term for UTC. +It is the time of day used as the epoch for Unix and POSIX systems. +See also ``Epoch'' and ``UTC.'' + +@cindex FSF +@cindex Free Software Foundation +@cindex GNU Project @item GNU ``GNU's not Unix''. An on-going project of the Free Software Foundation to create a complete, freely distributable, POSIX-compliant computing environment. +@item GNU/Linux +A variant of the GNU system using the Linux kernel, instead of the +Free Software Foundation's Hurd kernel. +Linux is a stable, efficient, full-featured clone of Unix that has +been ported to a variety of architectures. +It is most popular on PC-class systems, but runs well on a variety of +other systems too. +The Linux kernel source code is available under the terms of the GNU General +Public License, which is perhaps its most important aspect. + @item GPL See ``General Public License.'' @item Hexadecimal -Base 16 notation, where the digits are @code{0}-@code{9} and -@code{A}-@code{F}, with @samp{A} -representing 10, @samp{B} representing 11, and so on up to @samp{F} for 15. +Base 16 notation, where the digits are @code{0}--@code{9} and +@code{A}--@code{F}, with @samp{A} +representing 10, @samp{B} representing 11, and so on, up to @samp{F} for 15. Hexadecimal numbers are written in C using a leading @samp{0x}, -to indicate their base. Thus, @code{0x12} is 18 (one times 16 plus 2). +to indicate their base. Thus, @code{0x12} is 18 (1 times 16 plus 2). @item I/O Abbreviation for ``Input/Output,'' the act of moving data into and/or out of a running program. @item Input Record -A single chunk of data read in by @code{awk}. Usually, an @code{awk} input +A single chunk of data that is read in by @command{awk}. Usually, an @command{awk} input record consists of one line of text. -@xref{Records, ,How Input is Split into Records}. +(@xref{Records, ,How Input Is Split into Records}.) @item Integer -A whole number, i.e.@: a number that does not have a fractional part. +A whole number, i.e., a number that does not have a fractional part. + +@item Internationalization +The process of writing or modifying a program so +that it can use multiple languages without requiring +further source code changes. + +@cindex interpreted programs +@item Interpreter +A program that reads human-readable source code directly, and uses +the instructions in it to process data and produce results. +@command{awk} is typically (but not always) implemented as an interpreter. +See also ``Compiler.'' + +@item Interval Expression +A component of a regular expression that lets you specify repeated matches of +some part of the regexp. Interval expressions were not traditionally available +in @command{awk} programs. + +@cindex ISO +@item ISO +The International Standards Organization. +This organization produces international standards for many things, including +programming languages, such as C and C++. +In the computer arena, important standards like those for C, C++, and POSIX +become both American national and ISO international standards simultaneously. +This @value{DOCUMENT} refers to Standard C as ``ISO C'' throughout. @item Keyword -In the @code{awk} language, a keyword is a word that has special +In the @command{awk} language, a keyword is a word that has special meaning. Keywords are reserved and may not be used as variable names. -@code{gawk}'s keywords are: +@command{gawk}'s keywords are: @code{BEGIN}, @code{END}, @code{if}, @@ -20341,88 +24972,124 @@ meaning. Keywords are reserved and may not be used as variable names. @code{nextfile}, @code{function}, @code{func}, -and @code{exit}. +and +@code{exit}. + +@cindex LGPL +@cindex Lesser General Public License +@cindex GNU Lesser General Public License +@item Lesser General Public License +This document describes the terms under which binary library archives +or shared objects, +and their source code may be distributed. + +@item Linux +See ``GNU/Linux.'' + +@item LGPL +See ``Lesser General Public License.'' + +@item Localization +The process of providing the data necessary for an +internationalized program to work in a particular language. @item Logical Expression An expression using the operators for logic, AND, OR, and NOT, written -@samp{&&}, @samp{||}, and @samp{!} in @code{awk}. Often called Boolean +@samp{&&}, @samp{||}, and @samp{!} in @command{awk}. Often called Boolean expressions, after the mathematician who pioneered this kind of mathematical logic. @item Lvalue An expression that can appear on the left side of an assignment operator. In most languages, lvalues can be variables or array -elements. In @code{awk}, a field designator can also be used as an +elements. In @command{awk}, a field designator can also be used as an lvalue. +@item Matching +The act of testing a string against a regular expression. If the +regexp describes the contents of the string, it is said to @dfn{match} it. + +@item Metacharacters +Characters used within a regexp that do not stand for themselves. +Instead, they denote regular expression operations, such as repetition, +grouping, or alternation. + @item Null String A string with no characters in it. It is represented explicitly in -@code{awk} programs by placing two double-quote characters next to +@command{awk} programs by placing two double quote characters next to each other (@code{""}). It can appear in input data by having two successive occurrences of the field separator appear next to each other. @item Number -A numeric valued data object. The @code{gawk} implementation uses double -precision floating point to represent numbers. -Very old @code{awk} implementations use single precision floating -point. +A numeric-valued data object. Modern @command{awk} implementations use +double-precision floating-point to represent numbers. +Very old @command{awk} implementations use single-precision floating-point. @item Octal -Base-eight notation, where the digits are @code{0}-@code{7}. +Base-eight notation, where the digits are @code{0}--@code{7}. Octal numbers are written in C using a leading @samp{0}, to indicate their base. Thus, @code{013} is 11 (one times 8 plus 3). +@cindex P1003.2 POSIX standard +@item P1003.2 +See ``POSIX.'' + @item Pattern -Patterns tell @code{awk} which input records are interesting to which +Patterns tell @command{awk} which input records are interesting to which rules. A pattern is an arbitrary conditional expression against which input is tested. If the condition is satisfied, the pattern is said to @dfn{match} the input record. A typical pattern might compare the input record against -a regular expression. @xref{Pattern Overview, ,Pattern Elements}. +a regular expression. (@xref{Pattern Overview, ,Pattern Elements}.) @item POSIX -The name for a series of standards being developed by the IEEE +The name for a series of standards +@c being developed by the IEEE that specify a Portable Operating System interface. The ``IX'' denotes the Unix heritage of these standards. The main standard of interest for -@code{awk} users is +@command{awk} users is @cite{IEEE Standard for Information Technology, Standard 1003.2-1992, Portable Operating System Interface (POSIX) Part 2: Shell and Utilities}. Informally, this standard is often referred to as simply ``P1003.2.'' +@item Precedence +The order in which operations are performed when operators are used +without explicit parentheses. + @item Private Variables and/or functions that are meant for use exclusively by library -functions, and not for the main @code{awk} program. Special care must be +functions and not for the main @command{awk} program. Special care must be taken when naming such variables and functions. -@xref{Library Names, , Naming Library Function Global Variables}. +(@xref{Library Names, , Naming Library Function Global Variables}.) @item Range (of input lines) -A sequence of consecutive lines from the input file. A pattern -can specify ranges of input lines for @code{awk} to process, or it can -specify single lines. @xref{Pattern Overview, ,Pattern Elements}. +A sequence of consecutive lines from the input file(s). A pattern +can specify ranges of input lines for @command{awk} to process or it can +specify single lines. (@xref{Pattern Overview, ,Pattern Elements}.) @item Recursion When a function calls itself, either directly or indirectly. If this isn't clear, refer to the entry for ``recursion.'' @item Redirection -Redirection means performing input from other than the standard input -stream, or output to other than the standard output stream. +Redirection means performing input from something other than the standard input +stream, or performing output to something other than the standard output stream. You can redirect the output of the @code{print} and @code{printf} statements -to a file or a system command, using the @samp{>}, @samp{>>}, and @samp{|} +to a file or a system command, using the @samp{>}, @samp{>>}, @samp{|}, and @samp{|&} operators. You can redirect input to the @code{getline} statement using -the @samp{<} and @samp{|} operators. -@xref{Redirection, ,Redirecting Output of @code{print} and @code{printf}}, -and @ref{Getline, ,Explicit Input with @code{getline}}. +the @samp{<}, @samp{|}, and @samp{|&} operators. +(@xref{Redirection, ,Redirecting Output of @code{print} and @code{printf}}, +and @ref{Getline, ,Explicit Input with @code{getline}}.) @item Regexp Short for @dfn{regular expression}. A regexp is a pattern that denotes a set of strings, possibly an infinite set. For example, the regexp @samp{R.*xp} matches any string starting with the letter @samp{R} -and ending with the letters @samp{xp}. In @code{awk}, regexps are +and ending with the letters @samp{xp}. In @command{awk}, regexps are used in patterns and in conditional expressions. Regexps may contain -escape sequences. @xref{Regexp, ,Regular Expressions}. +escape sequences. (@xref{Regexp, ,Regular Expressions}.) @item Regular Expression See ``regexp.'' @@ -20430,89 +25097,129 @@ See ``regexp.'' @item Regular Expression Constant A regular expression constant is a regular expression written within slashes, such as @code{/foo/}. This regular expression is chosen -when you write the @code{awk} program, and cannot be changed doing -its execution. @xref{Regexp Usage, ,How to Use Regular Expressions}. +when you write the @command{awk} program and cannot be changed during +its execution. (@xref{Regexp Usage, ,How to Use Regular Expressions}.) @item Rule -A segment of an @code{awk} program that specifies how to process single +A segment of an @command{awk} program that specifies how to process single input records. A rule consists of a @dfn{pattern} and an @dfn{action}. -@code{awk} reads an input record; then, for each rule, if the input record -satisfies the rule's pattern, @code{awk} executes the rule's action. +@command{awk} reads an input record; then, for each rule, if the input record +satisfies the rule's pattern, @command{awk} executes the rule's action. Otherwise, the rule does nothing for that input record. @item Rvalue A value that can appear on the right side of an assignment operator. -In @code{awk}, essentially every expression has a value. These values +In @command{awk}, essentially every expression has a value. These values are rvalues. -@item @code{sed} +@item Scalar +A single value, be it a number or a string. +Regular variables are scalars; arrays and functions are not. + +@item Search Path +In @command{gawk}, a list of directories to search for @command{awk} program source files. +In the shell, a list of directories to search for executable programs. + +@item Seed +The initial value, or starting point, for a sequence of random numbers. + +@item @command{sed} See ``Stream Editor.'' +@item Shell +The command interpreter for Unix and POSIX-compliant systems. +The shell works both interactively, and as a programming language +for batch files, or shell scripts. + @item Short-Circuit -The nature of the @code{awk} logical operators @samp{&&} and @samp{||}. -If the value of the entire expression can be deduced from evaluating just -the left-hand side of these operators, the right-hand side will not -be evaluated -(@pxref{Boolean Ops, ,Boolean Expressions}). +The nature of the @command{awk} logical operators @samp{&&} and @samp{||}. +If the value of the entire expression is determinable from evaluating just +the lefthand side of these operators, the righthand side is not +evaluated. +(@xref{Boolean Ops, ,Boolean Expressions}.) @item Side Effect A side effect occurs when an expression has an effect aside from merely producing a value. Assignment expressions, increment and decrement -expressions and function calls have side effects. -@xref{Assignment Ops, ,Assignment Expressions}. +expressions, and function calls have side effects. +(@xref{Assignment Ops, ,Assignment Expressions}.) -@item Single Precision +@item Single-Precision An internal representation of numbers that can have fractional parts. -Single precision numbers keep track of fewer digits than do double precision -numbers, but operations on them are less expensive in terms of CPU time. -This is the type used by some very old versions of @code{awk} to store +Single-precision numbers keep track of fewer digits than do double-precision +numbers, but operations on them are sometimes less expensive in terms of CPU time. +This is the type used by some very old versions of @command{awk} to store numeric values. It is the C type @code{float}. @item Space The character generated by hitting the space bar on the keyboard. @item Special File -A file name interpreted internally by @code{gawk}, instead of being handed -directly to the underlying operating system. For example, @file{/dev/stderr}. -@xref{Special Files, ,Special File Names in @code{gawk}}. +A @value{FN} interpreted internally by @command{gawk}, instead of being handed +directly to the underlying operating system---for example, @file{/dev/stderr}. +(@xref{Special Files, ,Special @value{FFN}s in @command{gawk}}.) @item Stream Editor A program that reads records from an input stream and processes them one or more at a time. This is in contrast with batch programs, which may expect to read their input files in entirety before starting to do -anything, and with interactive programs, which require input from the +anything, as well as with interactive programs which require input from the user. @item String A datum consisting of a sequence of characters, such as @samp{I am a -string}. Constant strings are written with double-quotes in the -@code{awk} language, and may contain escape sequences. -@xref{Escape Sequences}. +string}. Constant strings are written with double quotes in the +@command{awk} language and may contain escape sequences. +(@xref{Escape Sequences}.) @item Tab The character generated by hitting the @kbd{TAB} key on the keyboard. It usually expands to up to eight spaces upon output. +@item Text Domain +A unique name that identifies an application. +Used for grouping messages that are translated at runtime +into the local language. + +@item Timestamp +A value in the ``seconds since the epoch'' format used by Unix +and POSIX systems. Used for the @command{gawk} functions +@code{mktime}, @code{strftime}, and @code{systime}. +See also ``Epoch'' and ``UTC.'' + +@cindex Linux +@cindex GNU/Linux +@cindex Unix +@cindex BSD-based operating systems +@cindex NetBSD +@cindex FreeBSD +@cindex OpenBSD @item Unix A computer operating system originally developed in the early 1970's at AT&T Bell Laboratories. It initially became popular in universities around -the world, and later moved into commercial evnironments as a software +the world and later moved into commercial environments as a software development system and network server system. There are many commercial versions of Unix, as well as several work-alike systems whose source code -is freely available (such as Linux, NetBSD, and FreeBSD). +is freely available (such as GNU/Linux, NetBSD, FreeBSD, and OpenBSD). + +@item UTC +The accepted abbreviation for ``Universal Coordinated Time.'' +This is standard time in Greenwich, England, which is used as a +reference time for day and date calculations. +See also ``Epoch'' and ``GMT.'' @item Whitespace A sequence of space, tab, or newline characters occurring inside an input record or a string. @end table -@node Copying, Index, Glossary, Top -@unnumbered GNU GENERAL PUBLIC LICENSE +@node Copying, GNU Free Documentation License, Glossary, Top +@unnumbered GNU General Public License @center Version 2, June 1991 @display Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc. -59 Temple Place --- Suite 330, Boston, MA 02111-1307, USA +59 Temple Place, Suite 330, Boston, MA 02111, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. @@ -20569,10 +25276,10 @@ patent must be licensed for everyone's free use or not licensed at all. The precise terms and conditions for copying, distribution and modification follow. -@iftex +@ifnotinfo @c fakenode --- for prepinfo -@unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION -@end iftex +@unnumberedsec Terms and Conditions for Copying, Distribution and Modification +@end ifnotinfo @ifinfo @center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION @end ifinfo @@ -20680,7 +25387,7 @@ customarily used for software interchange; or, @item Accompany it with the information you received as to the offer to distribute corresponding source code. (This alternative is -allowed only for non-commercial distribution and only if you +allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.) @end enumerate @@ -20795,10 +25502,10 @@ make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally. -@iftex +@ifnotinfo @c fakenode --- for prepinfo @heading NO WARRANTY -@end iftex +@end ifnotinfo @ifinfo @center NO WARRANTY @end ifinfo @@ -20826,10 +25533,10 @@ PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. @end enumerate -@iftex +@ifnotinfo @c fakenode --- for prepinfo @heading END OF TERMS AND CONDITIONS -@end iftex +@end ifnotinfo @ifinfo @center END OF TERMS AND CONDITIONS @end ifinfo @@ -20863,7 +25570,7 @@ GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software -Foundation, Inc., 59 Temple Place --- Suite 330, Boston, MA 02111-1307, USA. +Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA. @end smallexample Also add information on how to contact you by electronic and paper mail. @@ -20875,7 +25582,7 @@ when it starts in an interactive mode: Gnomovision version 69, Copyright (C) @var{year} @var{name of author} Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome -to redistribute it under certain conditions; type `show c' +to redistribute it under certain conditions; type `show c' for details. @end smallexample @@ -20893,7 +25600,7 @@ necessary. Here is a sample; alter the names: @group Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' -(which makes passes at compilers) written +(which makes passes at compilers) written by James Hacker. @var{signature of Ty Coon}, 1 April 1989 @@ -20904,15 +25611,413 @@ Ty Coon, President of Vice This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the -library. If this is what you want to do, use the GNU Library General +library. If this is what you want to do, use the GNU Lesser General Public License instead of this License. -@node Index, , Copying, Top +@node GNU Free Documentation License, Index, Copying, Top +@unnumbered GNU Free Documentation License +@center Version 1.1, March 2000 +@cindex FDL +@cindex Free Documentation License +@cindex GNU Free Documentation License + +@display +Copyright (C) 2000 Free Software Foundation, Inc. +59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + +Everyone is permitted to copy and distribute verbatim copies +of this license document, but changing it is not allowed. +@end display +@sp 1 +@enumerate 0 +@item +PREAMBLE + +The purpose of this License is to make a manual, textbook, or other +written document ``free'' in the sense of freedom: to assure everyone +the effective freedom to copy and redistribute it, with or without +modifying it, either commercially or noncommercially. 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We recommend this License +principally for works whose purpose is instruction or reference. + +@sp 1 +@item +APPLICABILITY AND DEFINITIONS + +This License applies to any manual or other work that contains a +notice placed by the copyright holder saying it can be distributed +under the terms of this License. The ``Document'', below, refers to any +such manual or work. Any member of the public is a licensee, and is +addressed as ``you''. + +A ``Modified Version'' of the Document means any work containing the +Document or a portion of it, either copied verbatim, or with +modifications and/or translated into another language. + +A ``Secondary Section'' is a named appendix or a front-matter section of +the Document that deals exclusively with the relationship of the +publishers or authors of the Document to the Document's overall subject +(or to related matters) and contains nothing that could fall directly +within that overall subject. 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Such a compilation is called an ``aggregate'', and this +License does not apply to the other self-contained works thus compiled +with the Document, on account of their being thus compiled, if they +are not themselves derivative works of the Document. + +If the Cover Text requirement of section 3 is applicable to these +copies of the Document, then if the Document is less than one quarter +of the entire aggregate, the Document's Cover Texts may be placed on +covers that surround only the Document within the aggregate. +Otherwise they must appear on covers around the whole aggregate. +@sp 1 +@item +TRANSLATION + +Translation is considered a kind of modification, so you may +distribute translations of the Document under the terms of section 4. +Replacing Invariant Sections with translations requires special +permission from their copyright holders, but you may include +translations of some or all Invariant Sections in addition to the +original versions of these Invariant Sections. You may include a +translation of this License provided that you also include the +original English version of this License. In case of a disagreement +between the translation and the original English version of this +License, the original English version will prevail. +@sp 1 +@item +TERMINATION + +You may not copy, modify, sublicense, or distribute the Document except +as expressly provided for under this License. Any other attempt to +copy, modify, sublicense or distribute the Document is void, and will +automatically terminate your rights under this License. However, +parties who have received copies, or rights, from you under this +License will not have their licenses terminated so long as such +parties remain in full compliance. +@sp 1 +@item +FUTURE REVISIONS OF THIS LICENSE + +The Free Software Foundation may publish new, revised versions +of the GNU Free Documentation License from time to time. Such new +versions will be similar in spirit to the present version, but may +differ in detail to address new problems or concerns. See +@uref{http://www.gnu.org/copyleft/}. + +Each version of the License is given a distinguishing version number. +If the Document specifies that a particular numbered version of this +License ``or any later version'' applies to it, you have the option of +following the terms and conditions either of that specified version or +of any later version that has been published (not as a draft) by the +Free Software Foundation. If the Document does not specify a version +number of this License, you may choose any version ever published (not +as a draft) by the Free Software Foundation. + +@end enumerate + +@c fakenode --- for prepinfo +@unnumberedsec ADDENDUM: How to use this License for your documents + +To use this License in a document you have written, include a copy of +the License in the document and put the following copyright and +license notices just after the title page: + +@smallexample +@group + + Copyright (C) @var{year} @var{your name}. + Permission is granted to copy, distribute and/or modify this document + under the terms of the GNU Free Documentation License, Version 1.1 + or any later version published by the Free Software Foundation; + with the Invariant Sections being @var{list their titles}, with the + Front-Cover Texts being @var{list}, and with the Back-Cover Texts being @var{list}. + A copy of the license is included in the section entitled ``GNU + Free Documentation License''. +@end group +@end smallexample +If you have no Invariant Sections, write ``with no Invariant Sections'' +instead of saying which ones are invariant. If you have no +Front-Cover Texts, write ``no Front-Cover Texts'' instead of +``Front-Cover Texts being @var{list}''; likewise for Back-Cover Texts. + +If your document contains nontrivial examples of program code, we +recommend releasing these examples in parallel under your choice of +free software license, such as the GNU General Public License, +to permit their use in free software. + +@node Index, , GNU Free Documentation License, Top @unnumbered Index @printindex cp -@summarycontents -@contents @bye Unresolved Issues: @@ -20936,19 +26041,30 @@ Consistency issues: Use ESC and not ESCAPE Use space and not blank to describe the space bar's character The term "blank" is thus basically reserved for "blank lines" etc. - The `(d.c.)' should appear inside the closing `.' of a sentence - It should come before (pxref{...}) + To make dark corners work, the @value{DARKCORNER} has to be outside + closing `.' of a sentence and after (pxref{...}). This is + a change from earlier versions. " " should have an @w{} around it Use "non-" everywhere - Use @code{ftp} when talking about anonymous ftp - Use upper-case and lower-case, not "upper case" and "lower case" + Use @command{ftp} when talking about anonymous ftp + Use uppercase and lowercase, not "upper-case" and "lower-case" + or "upper case" and "lower case" + Use "single precision" and "double precision", not "single-precision" or "double-precision" Use alphanumeric, not alpha-numeric + Use POSIX-compliant, not POSIX compliant Use --foo, not -Wfoo when describing long options - Use findex for all programs and functions in the example chapters Use "Bell Laboratories", but not "Bell Labs". Use "behavior" instead of "behaviour". Use "zeros" instead of "zeroes". + Use "nonzero" not "non-zero". + Use "runtime" not "run time" or "run-time". + Use "command-line" not "command line". + Use "online" not "on-line". + Use "whitespace" not "white space". Use "Input/Output", not "input/output". Also "I/O", not "i/o". + Use "lefthand"/"righthand", not "left-hand"/"right-hand". + Use "workaround", not "work-around". + Use "startup"/"cleanup", not "start-up"/"clean-up" Use @code{do}, and not @code{do}-@code{while}, except where actually discussing the do-while. The words "a", "and", "as", "between", "for", "from", "in", "of", @@ -20957,20 +26073,39 @@ Consistency issues: "Into" and "How" should. Search for @dfn; make sure important items are also indexed. "e.g." should always be followed by a comma. - "i.e." should never be followed by a comma, and should be followed - by `@:'. + "i.e." should always be followed by a comma. The numbers zero through ten should be spelled out, except when talking about file descriptor numbers. > 10 and < 0, it's ok to use numbers. - In tables, put command line options in @code, while in the text, - put them in @samp. + In tables, put command-line options in @code, while in the text, + put them in @option. When using @strong, use "Note:" or "Caution:" with colons and not exclamation points. Do not surround the paragraphs with @quotation ... @end quotation. + For most cases, do NOT put a comma before "and", "or" or "but". + But exercise taste with this rule. + Don't show the awk command with a program in quotes when it's + just the program. I.e. + + { + .... + } + + not + awk '{ + ... + }' + + Do show it when showing command-line arguments, data files, etc, even + if there is no output shown. + + Use numbered lists only to show a sequential series of steps. + + Use @code{xxx} for the xxx operator in indexing statements, not @samp. Date: Wed, 13 Apr 94 15:20:52 -0400 -From: rsm@gnu.ai.mit.edu (Richard Stallman) -To: gnu-prog@gnu.ai.mit.edu +From: rms@gnu.org (Richard Stallman) +To: gnu-prog@gnu.org Subject: A reminder: no pathnames in GNU It's a GNU convention to use the term "file name" for the name of a @@ -20984,6 +26119,9 @@ have used "pathname". Note that "file name" should be two words when it appears as ordinary text. It's ok as one word when it's a metasyntactic variable, though. +------------------------ +ORA uses filename, thus the macro. + Suggestions: ------------ Enhance FIELDWIDTHS with some way to indicate "the rest of the record". @@ -20991,4 +26129,41 @@ E.g., a length of 0 or -1 or something. May be "n"? Make FIELDWIDTHS be an array? -What if FIELDWIDTHS has invalid values in it? +% Next edition: +% 1. Talk about common extensions, those in nawk, gawk, mawk +% 2. Use @code{foo} for variables and @code{foo()} for functions +% 3. Standardize the error messages from the functions and programs +% in Chapters 12 and 13. +% 4. Nuke the BBS stuff and use something that won't be obsolete +% 5. Reorg chapters 5 & 7 like so: +%Chapter 5: +% - Constants, Variables, and Conversions +% + Constant Expressions +% + Using Regular Expression Constants +% + Variables +% + Conversion of Strings and Numbers +% - Operators +% + Arithmetic Operators +% + String Concatenation +% + Assignment Expressions +% + Increment and Decrement Operators +% - Truth Values and Conditions +% + True and False in Awk +% + Boolean Expressions +% + Conditional Expressions +% - Function Calls +% - Operator Precedence +% +%Chapter 7: +% - Array Basics +% + Introduction to Arrays +% + Referring to an Array Element +% + Assigning Array Elements +% + Basic Array Example +% + Scanning All Elements of an Array +% - The delete Statement +% - Using Numbers to Subscript Arrays +% - Using Uninitialized Variables as Subscripts +% - Multidimensional Arrays +% + Scanning Multidimensional Arrays +% - Sorting Array Values and Indices with gawk diff --git a/doc/gawkinet.info b/doc/gawkinet.info new file mode 100644 index 00000000..3d5e5d3f --- /dev/null +++ b/doc/gawkinet.info @@ -0,0 +1,4246 @@ +This is gawkinet.info, produced by makeinfo version 4.0 from +gawkinet.texi. + +INFO-DIR-SECTION GNU Packages +START-INFO-DIR-ENTRY +* Gawkinet: (gawkinet). TCP/IP Internetworking With `gawk'. +END-INFO-DIR-ENTRY + + This file documents the networking features in GNU `awk'. + + This is Edition 1.1 of `TCP/IP Internetworking With `gawk'', for the +3.1.0 (or later) version of the GNU implementation of AWK. + + Copyright (C) 2000, 2001 Free Software Foundation, Inc. + + Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "GNU General Public License", the Front-Cover +texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +"GNU Free Documentation License". + + a. "A GNU Manual" + + b. "You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development." + + +File: gawkinet.info, Node: Top, Next: Preface, Prev: (dir), Up: (dir) + +General Introduction +******************** + + This file documents the networking features in GNU Awk (`gawk') +version 3.1 and later. + +* Menu: + +* Preface:: About this document. +* Introduction:: About networkiing. +* Using Networking:: Some examples. +* Some Applications and Techniques:: More extended examples. +* Links:: Where to find the stuff mentioned in this + document. +* GNU Free Documentation License:: The license for this document. +* Index:: The index. + +* Stream Communications:: Sending data streams. +* Datagram Communications:: Sending self-contained messages. +* The TCP/IP Protocols:: How these models work in the Internet. +* Basic Protocols:: The basic protocols. +* Ports:: The idea behind ports. +* Making Connections:: Making TCP/IP connections. +* Gawk Special Files:: How to do `gawk' networking. +* Special File Fields:: The fields in the special file name. +* Comparing Protocols:: Differences between the protocols. +* File /inet/tcp:: The TCP special file. +* File /inet/udp:: The UDB special file. +* File /inet/raw:: The RAW special file. +* TCP Connecting:: Making a TCP connection. +* Troubleshooting:: Troubleshooting TCP/IP connections. +* Interacting:: Interacting with a service. +* Setting Up:: Setting up a service. +* Email:: Reading email. +* Web page:: Reading a Web page. +* Primitive Service:: A primitive Web service. +* Interacting Service:: A Web service with interaction. +* CGI Lib:: A simple CGI library. +* Simple Server:: A simple Web server. +* Caveats:: Network programming caveats. +* Challenges:: Where to go from here. +* PANIC:: An Emergency Web Server. +* GETURL:: Retrieving Web Pages. +* REMCONF:: Remote Configuration Of Embedded Systems. +* URLCHK:: Look For Changed Web Pages. +* WEBGRAB:: Extract Links From A Page. +* STATIST:: Graphing A Statistical Distribution. +* MAZE:: Walking Through A Maze In Virtual Reality. +* MOBAGWHO:: A Simple Mobile Agent. +* STOXPRED:: Stock Market Prediction As A Service. +* PROTBASE:: Searching Through A Protein Database. + + +File: gawkinet.info, Node: Preface, Next: Introduction, Prev: Top, Up: Top + +Preface +******* + + In May of 1997, Ju"rgen Kahrs felt the need for network access from +`awk', and, with a little help from me, set about adding features to do +this for `gawk'. At that time, he wrote the bulk of this Info file. + + The code and documentation were added to the `gawk' 3.1 development +tree, and languished somewhat until I could finally get down to some +serious work on that version of `gawk'. This finally happened in the +middle of 2000. + + Meantime, Ju"rgen wrote an article about the Internet special files +and `|&' operator for `Linux Journal', and made a networking patch for +the production versions of `gawk' available from his home page. In +August of 2000 (for `gawk' 3.0.6), this patch also made it to the main +GNU `ftp' distribution site. + + For release with `gawk', I edited Ju"rgen's prose for English +grammar and style, as he is not a native English speaker. I also +rearranged the material somewhat for what I felt was a better order of +presentation, and (re)wrote some of the introductory material. + + The majority of this document and the code are his work, and the +high quality and interesting ideas speak for themselves. It is my hope +that these features will be of significant value to the `awk' community. + + +Arnold Robbins +Nof Ayalon, ISRAEL +March, 2001 + + +File: gawkinet.info, Node: Introduction, Next: Using Networking, Prev: Preface, Up: Top + +Networking Concepts +******************* + + This major node provides a (necessarily) brief intoduction to +computer networking concepts. For many applications of `gawk' to +TCP/IP networking, we hope that this is enough. For more advanced +tasks, you will need deeper background, and it may be necessary to +switch to lower-level programming in C or C++. + + There are two real-life models for the way computers send messages +to each other over a network. While the analogies are not perfect, +they are close enough to convey the major concepts. These two models +are the phone system (reliable byte-stream communications), and the +postal system (best-effort datagrams). + +* Menu: + +* Stream Communications:: Sending data streams. +* Datagram Communications:: Sending self-contained messages. +* The TCP/IP Protocols:: How these models work in the Internet. +* Making Connections:: Making TCP/IP connections. + + +File: gawkinet.info, Node: Stream Communications, Next: Datagram Communications, Prev: Introduction, Up: Introduction + +Reliable Byte-streams (Phone Calls) +=================================== + + When you make a phone call, the following steps occur: + + 1. You dial a number. + + 2. The phone system connects to the called party, telling them there + is an incoming call. (Their phone rings.) + + 3. The other party answers the call, or, in the case of a computer + network, refuses to answer the call. + + 4. Assuming the other party answers, the connection between you is + now a "duplex" (two-way), "reliable" (no data lost), sequenced + (data comes out in the order sent) data stream. + + 5. You and your friend may now talk freely, with the phone system + moving the data (your voices) from one end to the other. From + your point of view, you have a direct end-to-end connection with + the person on the other end. + + The same steps occur in a duplex reliable computer networking +connection. There is considerably more overhead in setting up the +communications, but once it's done, data moves in both directions, +reliably, in sequence. + + +File: gawkinet.info, Node: Datagram Communications, Next: The TCP/IP Protocols, Prev: Stream Communications, Up: Introduction + +Best-effort Datagrams (Mailed Letters) +====================================== + + Suppose you mail three different documents to your office on the +other side of the country on two different days. Doing so entails the +following. + + 1. Each document travels in its own envelope. + + 2. Each envelope contains both the sender and the recipient address. + + 3. Each envelope may travel a different route to its destination. + + 4. The envelopes may arrive in a different order from the one in + which they were sent. + + 5. One or more may get lost in the mail. (Although, fortunately, + this does not occur very often.) + + 6. In a computer network, one or more "packets" may also arrive + multiple times. (This doesn't happen with the postal system!) + + + The important characteristics of datagram communications, like those +of the postal system are thus: + + * Delivery is "best effort;" the data may never get there. + + * Each message is self-contained, including the source and + destination addresses. + + * Delivery is _not_ sequenced; packets may arrive out of order, + and/or multiple times. + + * Unlike the phone system, overhead is considerably lower. It is + not necessary to set up the call first. + + The price the user pays for the lower overhead of datagram +communications is exactly the lower reliability; it is often necessary +for user-level protocols that use datagram communications to add their +own reliabilty features on top of the basic communications. + + +File: gawkinet.info, Node: The TCP/IP Protocols, Next: Making Connections, Prev: Datagram Communications, Up: Introduction + +The Internet Protocols +====================== + + The Internet Protocol Suite (usually referred as just TCP/IP)(1) +consists of a number of different protocols at different levels or +"layers." For our purposes, three protocols provide the fundamental +communications mechanisms. All other defined protocols are referred to +as user-level protocols (e.g., HTTP, used later in this Info file). + +* Menu: + +* Basic Protocols:: The basic protocols. +* Ports:: The idea behind ports. + + ---------- Footnotes ---------- + + (1) It should be noted that although the Internet seems to have +conquered the world, there are other networking protocol suites in +existence and in use. + + +File: gawkinet.info, Node: Basic Protocols, Next: Ports, Prev: The TCP/IP Protocols, Up: The TCP/IP Protocols + +The Basic Internet Protocols +---------------------------- + +IP + The Internet Protocol. This protocol is almost never used + directly by applications. It provides the basic packet delivery + and routing infrastructure of the Internet. Much like the phone + company's switching centers or the Post Office's trucks, it is not + of much day-to-day interest to the regular user (or programmer). + It happens to be a best effort datagram protocol. + +UDP + The User Datagram Protocol. This is a best effort datagram + protocol. It provides a small amount of extra reliability over + IP, and adds the notion of "ports", described in *Note TCP and UDP + Ports: Ports. + +TCP + The Transmission Control Protocol. This is a duplex, reliable, + sequenced byte-stream protocol, again layered on top of IP, and + also providing the notion of ports. This is the protocol that you + will most likely use when using `gawk' for network programming. + + All other user-level protocols use either TCP or UDP to do their +basic communications. Examples are SMTP (Simple Mail Transfer +Protocol), FTP (File Transfer Protocol) and HTTP (HyperText Transfer +Protocol). + + +File: gawkinet.info, Node: Ports, Prev: Basic Protocols, Up: The TCP/IP Protocols + +TCP and UDP Ports +----------------- + + In the postal system, the address on an envelope indicates a physical +location, such as a residence or office building. But there may be +more than one person at the location; thus you have to further quantify +the recipient by putting a person or company name on the envelope. + + In the phone system, one phone number may represent an entire +company, in which case you need a person's extension number in order to +reach that individual directly. Or, when you call a home, you have to +say, "May I please speak to ..." before talking to the person directly. + + IP networking provides the concept of addressing. An IP address +represents a particular computer, but no more. In order to reach the +mail service on a system, or the FTP or WWW service on a system, you +have to have some way to further specify which service you want. In +the Internet Protocol suite, this is done with "port numbers", which +represent the services, much like an extension number used with a phone +number. + + Port numbers are 16-bit integers. Unix and Unix-like systems +reserve ports below 1024 for "well known" services, such as SMTP, FTP, +and HTTP. Numbers above 1024 may be used by any application, although +there is no promise made that a particular port number is always +available. + + +File: gawkinet.info, Node: Making Connections, Prev: The TCP/IP Protocols, Up: Introduction + +Making TCP/IP Connections (And Some Terminology) +================================================ + + Two terms come up repeatedly when discussing networking: "client" +and "server". For now, we'll discuss these terms at the "connection +level", when first establishing connections between two processes on +different systems over a network. (Once the connection is established, +the higher level, or "application level" protocols, such as HTTP or +FTP, determine who is the client and who is the server. Often, it +turns out that the client and server are the same in both roles.) + + The "server" is the system providing the service, such as the web +server or email server. It is the "host" (system) which is _connected +to_ in a transaction. For this to work though, the server must be +expecting connections. Much as there has to be someone at the office +building to answer the phone(1), the server process (usually) has to be +started first and waiting for a connection. + + The "client" is the system requesting the service. It is the system +_initiating the connection_ in a transaction. (Just as when you pick +up the phone to call an office or store.) + + In the TCP/IP framework, each end of a connection is represented by +a pair of (ADDRESS, PORT) pairs. For the duration of the connection, +the ports in use at each end are unique, and cannot be used +simultaneously by other processes on the same system. (Only after +closing a connection can a new one be built up on the same port. This +is contrary to the usual behavior of fully developed web servers which +have to avoid situations in which they are not reachable. We have to +pay this price in order to enjoy the benefits of a simple communication +paradigm in `gawk'.) + + Furthermore, once the connection is established, communications are +"synchronous". I.e., each end waits on the other to finish +transmitting, before replying. This is much like two people in a phone +conversation. While both could talk simultaneously, doing so usually +doesn't work too well. + + In the case of TCP, the synchronicity is enforced by the protocol +when sending data. Data writes "block" until the data have been +received on the other end. For both TCP and UDP, data reads block +until there is incoming data waiting to be read. This is summarized in +the following table, where an "X" indicates that the given action +blocks. + +TCP X X +UDP X +RAW X + + ---------- Footnotes ---------- + + (1) In the days before voice mail systems! + + +File: gawkinet.info, Node: Using Networking, Next: Some Applications and Techniques, Prev: Introduction, Up: Top + +Networking With `gawk' +********************** + + The `awk' programming language was originally developed as a +pattern-matching language for writing short programs to perform data +manipulation tasks. `awk''s strength is the manipulation of textual +data that is stored in files. It was never meant to be used for +networking purposes. To exploit its features in a networking context, +it's necessary to use an access mode for network connections that +resembles the access of files as closely as possible. + + `awk' is also meant to be a prototyping language. It is used to +demonstrate feasibility and to play with features and user interfaces. +This can be done with file-like handling of network connections. +`gawk' trades the lack of many of the advanced features of the TCP/IP +family of protocols for the convenience of simple connection handling. +The advanced features are available when programming in C or Perl. In +fact, the network programming in this major node is very similar to +what is described in books like `Internet Programming with Python', +`Advanced Perl Programming', or `Web Client Programming with Perl'. +But it's done here without first having to learn object-oriented +ideology, underlying languages such as Tcl/Tk, Perl, Python, or all of +the libraries necessary to extend these languages before they are ready +for the Internet. + + This major node demonstrates how to use the TCP protocol. The other +protocols are much less important for most users (UDP) or even +untractable (RAW). + +* Menu: + +* Gawk Special Files:: How to do `gawk' networking. +* TCP Connecting:: Making a TCP connection. +* Troubleshooting:: Troubleshooting TCP/IP connections. +* Interacting:: Interacting with a service. +* Setting Up:: Setting up a service. +* Email:: Reading email. +* Web page:: Reading a Web page. +* Primitive Service:: A primitive Web service. +* Interacting Service:: A Web service with interaction. +* Simple Server:: A simple Web server. +* Caveats:: Network programming caveats. +* Challenges:: Where to go from here. + + +File: gawkinet.info, Node: Gawk Special Files, Next: TCP Connecting, Prev: Using Networking, Up: Using Networking + +`gawk' Networking Mechanisms +============================ + + The `|&' operator introduced in `gawk' 3.1 for use in communicating +with a "co-process" is described in *Note Two-way Communications With +Another Process: (gawk)Two-way I/O. It shows how to do two-way I/O to a +separate process, sending it data with `print' or `printf' and reading +data with `getline'. If you haven't read it already, you should detour +there to do so. + + `gawk' transparently extends the two-way I/O mechanism to simple +networking through the use of special file names. When a "co-process" +is started that matches the special files we are about to describe, +`gawk' creates the appropriate network connection, and then two-way I/O +proceeds as usual. + + At the C, C++ (and basic Perl) level, networking is accomplished via +"sockets", an Application Programming Interface (API) originally +developed at the University of California at Berkeley that is now used +almost universally for TCP/IP networking. Socket level programming, +while fairly straightforward, requires paying attention to a number of +details, as well as using binary data. It is not well-suited for use +from a high-level language like `awk'. The special files provided in +`gawk' hide the details from the programmer, making things much simpler +and easier to use. + + The special file name for network access is made up of several +fields, all of them mandatory, none of them optional: + + /inet/PROTOCOL/LOCALPORT/HOSTNAME/REMOTEPORT + + The `/inet/' field is, of course, constant when accessing the +network. The LOCALPORT and REMOTEPORT fields do not have a meaning +when used with `/inet/raw' because "ports" only apply to TCP and UDP. +So, when using `/inet/raw', the port fields always have to be `0'. + +* Menu: + +* Special File Fields:: The fields in the special file name. +* Comparing Protocols:: Differences between the protocols. + + +File: gawkinet.info, Node: Special File Fields, Next: Comparing Protocols, Prev: Gawk Special Files, Up: Gawk Special Files + +The Fields of the Special File Name +----------------------------------- + + This node explains the meaning of all the other fields, as well as +the range of values and the defaults. All of the fields are mandatory. +To let the system pick a value, or if the field doesn't apply to the +protocol, specify it as `0'. + +PROTOCOL + Determines which member of the TCP/IP family of protocols is + selected to transport the data across the network. There are three + possible values (always written in lowercase): `tcp', `udp', and + `raw'. The exact meaning of each is explained later in this node. + +LOCALPORT + Determines which port on the local machine is used to communicate + across the network. It has no meaning with `/inet/raw' and must + therefore be `0'. Application level clients usually use `0' to + indicate they do not care which local port is used--instead they + specify a remote port to connect to. It is vital for application + level servers to use a number different from `0' here because + their service has to be available at a specific publicly-known + port number. It is possible to use a name from `/etc/services' + here. + +HOSTNAME + Determines which remote host is to be at the other end of the + connection. Application level servers must fill this field with a + `0' to indicate their being open for all other hosts to connect to + them and enforce connection level server behavior this way. It is + not possible for an application level server to restrict its + availability to one remote host by entering a host name here. + Application level clients must enter a name different from `0'. + The name can be either symbolic (e.g., `jpl-devvax.jpl.nasa.gov') + or numeric (e.g., `128.149.1.143'). + +REMOTEPORT + Determines which port on the remote machine is used to communicate + across the network. It has no meaning with `/inet/raw' and must + therefore be 0. For `/inet/tcp' and `/inet/udp', application + level clients _must_ use a number other than `0' to indicate which + port on the remote machine they want to connect to. Application + level servers must not fill this field with a `0'. Instead they + specify a local port for clients to connect to. It is possible to + use a name from `/etc/services' here. + + Experts in network programming will notice that the usual +client/server asymmetry found at the level of the socket API is not +visible here. This is for the sake of simplicity of the high-level +concept. If this asymmetry is necessary for your application, use +another language. For `gawk', it is more important to enable users to +write a client program with a minimum of code. What happens when first +accessing a network connection is seen in the following pseudo-code: + + if ((name of remote host given) && (other side accepts connection)) { + rendez-vous successful; transmit with getline or print + } else { + if ((other side did not accept) && (localport == 0)) + exit unsuccessful + if (TCP) { + set up a server accepting connections + this means waiting for the client on the other side to connect + } else + ready + } + + The exact behavior of this algorithm depends on the values of the +fields of the special file name. When in doubt, the following table +gives you the combinations of values and their meaning. If this table +is too complicated, focus on the three lines printed in *bold*. All the +examples in *Note Networking With `gawk': Using Networking, use only the +patterns printed in bold letters. + +PROTOCOL LOCAL HOST REMOTE RESULTING CONNECTION LEVEL + PORT NAME PORT BEHAVIOR +*tcp* *0* *x* *x* *Dedicated client, fails + if immediately connecting + to a server + on the other side fails* +udp 0 x x Dedicated client +raw 0 x 0 Dedicated client, works + only as `root' +*tcp, udp* *x* *x* *x* *Client, switches to + dedicated server if + necessary* +*tcp, udp* *x* *0* *0* *Dedicated server* +raw 0 0 0 Dedicated server, works + only as `root' +tcp, udp, raw x x 0 Invalid +tcp, udp, raw 0 0 x Invalid +tcp, udp, raw x 0 x Invalid +tcp, udp 0 0 0 Invalid +tcp, udp 0 x 0 Invalid +raw x 0 0 Invalid +raw 0 x x Invalid +raw x x x Invalid + + In general, TCP is the preferred mechanism to use. It is the +simplest protocol to understand and to use. Use the others only if +circumstances demand low-overhead. + + +File: gawkinet.info, Node: Comparing Protocols, Prev: Special File Fields, Up: Gawk Special Files + +Comparing Protocols +------------------- + + This node develops a pair of programs (sender and receiver) that do +nothing but send a timestamp from one machine to another. The sender +and the receiver are implemented with each of the three protocols +available and demonstrate the differences between them. + +* Menu: + +* File /inet/tcp:: The TCP special file. +* File /inet/udp:: The UDB special file. +* File /inet/raw:: The RAW special file. + + +File: gawkinet.info, Node: File /inet/tcp, Next: File /inet/udp, Prev: Comparing Protocols, Up: Comparing Protocols + +`/inet/tcp' +........... + + Once again, always use TCP. (Use UDP when low-overhead is a +necessity, and use RAW for network experimentation.) The first example +is the sender program: + + # Server + BEGIN { + print strftime() |& "/inet/tcp/8888/0/0" + close("/inet/tcp/8888/0/0") + } + + The receiver is very simple: + + # Client + BEGIN { + "/inet/tcp/0/localhost/8888" |& getline + print $0 + close("/inet/tcp/0/localhost/8888") + } + + TCP guarantees that the bytes arrive at the receiving end in exactly +the same order that they were sent. No byte is lost (except for broken +connections), doubled, or out of order. Some overhead is necessary to +accomplish this, but this is the price to pay for a reliable service. +It does matter which side starts first. The sender/server has to be +started first, and it waits for the receiver to read a line. + + +File: gawkinet.info, Node: File /inet/udp, Next: File /inet/raw, Prev: File /inet/tcp, Up: Comparing Protocols + +`/inet/udp' +........... + + The server and client programs that use UDP are almost identical to +their TCP counterparts; only the PROTOCOL has changed. As before, it +does matter which side starts first. The receiving side blocks and +waits for the sender. In this case, the receiver/client has to be +started first: + + # Server + BEGIN { + print strftime() |& "/inet/udp/8888/0/0" + close("/inet/udp/8888/0/0") + } + + The receiver is almost identical to the TCP receiver: + + # Client + BEGIN { + "/inet/udp/0/localhost/8888" |& getline + print $0 + close("/inet/udp/0/localhost/8888") + } + + UDP cannot guarantee that the datagrams at the receiving end will +arrive in exactly the same order they were sent. Some datagrams could be +lost, some doubled, and some out of order. But no overhead is necessary +to accomplish this. This unreliable behavior is good enough for tasks +such as data acquisition, logging, and even stateless services like NFS. + + +File: gawkinet.info, Node: File /inet/raw, Prev: File /inet/udp, Up: Comparing Protocols + +`/inet/raw' +........... + + This is an IP-level protocol. Only `root' is allowed to access this +special file. It is meant to be the basis for implementing and +experimenting with transport level protocols.(1) In the most general +case, the sender has to supply the encapsulating header bytes in front +of the packet and the receiver has to strip the additional bytes from +the message. + + RAW receivers cannot receive packets sent with TCP or UDP because the +operating system does not deliver the packets to a RAW receiver. The +operating system knows about some of the protocols on top of IP and +decides on its own which packet to deliver to which process. (d.c.) +Therefore, the UDP receiver must be used for receiving UDP datagrams +sent with the RAW sender. This is a dark corner, not only of `gawk', +but also of TCP/IP. + + For extended experimentation with protocols, look into the approach +implemented in a tool called SPAK. This tool reflects the hierarchical +layering of protocols (encapsulation) in the way data streams are piped +out of one program into the next one. It shows which protocol is based +on which other (lower-level) protocol by looking at the command-line +ordering of the program calls. Cleverly thought out, SPAK is much +better than `gawk''s `/inet' for learning the meaning of each and every +bit in the protocol headers. + + The next example uses the RAW protocol to emulate the behavior of +UDP. The sender program is the same as above, but with some additional +bytes that fill the places of the UDP fields: + + BEGIN { + Message = "Hello world\n" + SourcePort = 0 + DestinationPort = 8888 + MessageLength = length(Message)+8 + RawService = "/inet/raw/0/localhost/0" + printf("%c%c%c%c%c%c%c%c%s", + SourcePort/256, SourcePort%256, + DestinationPort/256, DestinationPort%256, + MessageLength/256, MessageLength%256, + 0, 0, Message) |& RawService + fflush(RawService) + close(RawService) + } + + Since this program tries to emulate the behavior of UDP, it checks if +the RAW sender is understood by the UDP receiver but not if the RAW +receiver can understand the UDP sender. In a real network, the RAW +receiver is hardly of any use because it gets every IP packet that +comes across the network. There are usually so many packets that `gawk' +would be too slow for processing them. Only on a network with little +traffic can the IP-level receiver program be tested. Programs for +analyzing IP traffic on modem or ISDN channels should be possible. + + Port numbers do not have a meaning when using `/inet/raw'. Their +fields have to be `0'. Only TCP and UDP use ports. Receiving data from +`/inet/raw' is difficult, not only because of processing speed but also +because data is usually binary and not restricted to ASCII. This +implies that line separation with `RS' does not work as usual. + + ---------- Footnotes ---------- + + (1) This special file is reserved, but not otherwise currently +implemented. + + +File: gawkinet.info, Node: TCP Connecting, Next: Troubleshooting, Prev: Gawk Special Files, Up: Using Networking + +Establishing a TCP Connection +============================= + + Let's observe a network connection at work. Type in the following +program and watch the output. Within a second, it connects via TCP +(`/inet/tcp') to the machine it is running on (`localhost'), and asks +the service `daytime' on the machine what time it is: + + BEGIN { + "/inet/tcp/0/localhost/daytime" |& getline + print $0 + close("/inet/tcp/0/localhost/daytime") + } + + Even experienced `awk' users will find the second line strange in two +respects: + + * A special file is used as a shell command that pipes its output + into `getline'. One would rather expect to see the special file + being read like any other file (`getline < + "/inet/tcp/0/localhost/daytime")'. + + * The operator `|&' has not been part of any `awk' implementation + (until now). It is actually the only extension of the `awk' + language needed (apart from the special files) to introduce + network access. + + The `|&' operator was introduced in `gawk' 3.1 in order to overcome +the crucial restriction that access to files and pipes in `awk' is +always unidirectional. It was formerly impossible to use both access +modes on the same file or pipe. Instead of changing the whole concept +of file access, the `|&' operator behaves exactly like the usual pipe +operator except for two additions: + + * Normal shell commands connected to their `gawk' program with a `|&' + pipe can be accessed bidirectionally. The `|&' turns out to be a + quite general, useful, and natural extension of `awk'. + + * Pipes that consist of a special file name for network connections + are not executed as shell commands. Instead, they can be read and + written to, just like a full-duplex network connection. + + In the earlier example, the `|&' operator tells `getline' to read a +line from the special file `/inet/tcp/0/localhost/daytime'. We could +also have printed a line into the special file. But instead we just +read a line with the time, printed it, and closed the connection. +(While we could just let `gawk' close the connection by finishing the +program, in this Info file we are pedantic, and always explicitly close +the connections.) + + +File: gawkinet.info, Node: Troubleshooting, Next: Interacting, Prev: TCP Connecting, Up: Using Networking + +Troubleshooting Connection Problems +=================================== + + It may well be that for some reason the above program does not run +on your machine. When looking at possible reasons for this, you will +learn much about typical problems that arise in network programming. +First of all, your implementation of `gawk' may not support network +access because it is a pre-3.1 version or you do not have a network +interface in your machine. Perhaps your machine uses some other +protocol like DECnet or Novell's IPX. For the rest of this major node, +we will assume you work on a Unix machine that supports TCP/IP. If the +above program does not run on such a machine, it may help to replace +the name `localhost' with the name of your machine or its IP address. +If it does, you could replace `localhost' with the name of another +machine in your vicinity. This way, the program connects to another +machine. Now you should see the date and time being printed by the +program. Otherwise your machine may not support the `daytime' service. +Try changing the service to `chargen' or `ftp'. This way, the program +connects to other services that should give you some response. If you +are curious, you should have a look at your file `/etc/services'. It +could look like this: + + # /etc/services: + # + # Network services, Internet style + # + # Name Number/Protcol Alternate name # Comments + + echo 7/tcp + echo 7/udp + discard 9/tcp sink null + discard 9/udp sink null + daytime 13/tcp + daytime 13/udp + chargen 19/tcp ttytst source + chargen 19/udp ttytst source + ftp 21/tcp + telnet 23/tcp + smtp 25/tcp mail + finger 79/tcp + www 80/tcp http # WorldWideWeb HTTP + www 80/udp # HyperText Transfer Protocol + pop-2 109/tcp postoffice # POP version 2 + pop-2 109/udp + pop-3 110/tcp # POP version 3 + pop-3 110/udp + nntp 119/tcp readnews untp # USENET News + irc 194/tcp # Internet Relay Chat + irc 194/udp + ... + + Here, you find a list of services that traditional Unix machines +usually support. If your GNU/Linux machine does not do so, it may be +that these services are switched off in some startup script. Systems +running some flavor of Microsoft Windows usually do _not_ support such +services. Nevertheless, it _is_ possible to do networking with `gawk' +on Microsoft Windows.(1) The first column of the file gives the name of +the service, the second a unique number, and the protocol that one can +use to connect to this service. The rest of the line is treated as a +comment. You see that some services (`echo') support TCP as well as +UDP. + + ---------- Footnotes ---------- + + (1) Microsoft prefered to ignore the TCP/IP family of protocols +until 1995. Then came the rise of the Netscape browser as a landmark +"killer application." Microsoft added TCP/IP support and their own +browser to Microsoft Windows 95 at the last minute. They even +back-ported their TCP/IP implementation to Microsoft Windows for +Workgroups 3.11, but it was a rather rudimentary and half-hearted +implementation. Nevertheless, the equivalent of `/etc/services' resides +under `c:\windows\services' on Microsoft Windows. + + +File: gawkinet.info, Node: Interacting, Next: Setting Up, Prev: Troubleshooting, Up: Using Networking + +Interacting with a Network Service +================================== + + The next program makes use of the possibility to really interact +with a network service by printing something into the special file. It +asks the so-called `finger' service if a user of the machine is logged +in. When testing this program, try to change `localhost' to some other +machine name in your local network: + + BEGIN { + NetService = "/inet/tcp/0/localhost/finger" + print "NAME" |& NetService + while ((NetService |& getline) > 0) + print $0 + close(NetService) + } + + After telling the service on the machine which user to look for, the +program repeatedly reads lines that come as a reply. When no more lines +are coming (because the service has closed the connection), the program +also closes the connection. Try replacing `"NAME"' with your login name +(or the name of someone else logged in). For a list of all users +currently logged in, replace NAME with an empty string `""'. + + The final `close' command could be safely deleted from the above +script, because the operating system closes any open connection by +default when a script reaches the end of execution. In order to avoid +portability problems, it is best to always close connections explicitly. +With the Linux kernel, for example, proper closing results in flushing +of buffers. Letting the close happen by default may result in +discarding buffers. + + When looking at `/etc/services' you may have noticed that the +`daytime' service is also available with `udp'. In the earlier example, +change `tcp' to `udp', and change `finger' to `daytime'. After +starting the modified program, you see the expected day and time +message. The program then hangs, because it waits for more lines +coming from the service. However, they never come. This behavior is a +consequence of the differences between TCP and UDP. When using UDP, +neither party is automatically informed about the other closing the +connection. Continuing to experiment this way reveals many other subtle +differences between TCP and UDP. To avoid such trouble, one should +always remember the advice Douglas E. Comer and David Stevens give in +Volume III of their series `Internetworking With TCP' (page 14): + + When designing client-server applications, beginners are strongly + advised to use TCP because it provides reliable, + connection-oriented communication. Programs only use UDP if the + application protocol handles reliability, the application requires + hardware broadcast or multicast, or the application cannot + tolerate virtual circuit overhead. + + +File: gawkinet.info, Node: Setting Up, Next: Email, Prev: Interacting, Up: Using Networking + +Setting Up a Service +==================== + + The preceding programs behaved as clients that connect to a server +somewhere on the Internet and request a particular service. Now we set +up such a service to mimic the behavior of the `daytime' service. Such +a server does not know in advance who is going to connect to it over +the network. Therefore we cannot insert a name for the host to connect +to in our special file name. + + Start the following program in one window. Notice that the service +does not have the name `daytime', but the number `8888'. From looking +at `/etc/services', you know that names like `daytime' are just +mnemonics for predetermined 16-bit integers. Only the system +administrator (`root') could enter our new service into `/etc/services' +with an appropriate name. Also notice that the service name has to be +entered into a different field of the special file name because we are +setting up a server, not a client: + + BEGIN { + print strftime() |& "/inet/tcp/8888/0/0" + close("/inet/tcp/8888/0/0") + } + + Now open another window on the same machine. Copy the client +program given as the first example (*note Establishing a TCP +Connection: TCP Connecting.) to a new file and edit it, changing the +name `daytime' to `8888'. Then start the modified client. You should +get a reply like this: + + Sat Sep 27 19:08:16 CEST 1997 + +Both programs explicitly close the connection. + + Now we will intentionally make a mistake to see what happens when +the name `8888' (the so-called port) is already used by another service. +Start the server program in both windows. The first one works, but the +second one complains that it could not open the connection. Each port +on a single machine can only be used by one server program at a time. +Now terminate the server program and change the name `8888' to `echo'. +After restarting it, the server program does not run any more and you +know why: there already is an `echo' service running on your machine. +But even if this isn't true, you would not get your own `echo' server +running on a Unix machine, because the ports with numbers smaller than +1024 (`echo' is at port 7) are reserved for `root'. On machines +running some flavor of Microsoft Windows, there is no restriction that +reserves ports 1 to 1024 for a privileged user; hence you can start an +`echo' server there. + + Turning this short server program into something really useful is +simple. Imagine a server that first reads a file name from the client +through the network connection, then does something with the file and +sends a result back to the client. The server-side processing could be: + + BEGIN { + NetService = "/inet/tcp/8888/0/0" + NetService |& getline + CatPipe = ("cat " $1) # sets $0 and the fields + while ((CatPipe | getline) > 0) + print $0 |& NetService + close(NetService) + } + +and we would have a remote copying facility. Such a server reads the +name of a file from any client that connects to it and transmits the +contents of the named file across the net. The server-side processing +could also be the execution of a command that is transmitted across the +network. From this example, you can see how simple it is to open up a +security hole on your machine. If you allow clients to connect to your +machine and execute arbitrary commands, anyone would be free to do `rm +-rf *'. + + +File: gawkinet.info, Node: Email, Next: Web page, Prev: Setting Up, Up: Using Networking + +Reading Email +============= + + The distribution of email is usually done by dedicated email servers +that communicate with your machine using special protocols. To receive +email, we will use the Post Office Protocol (POP). Sending can be done +with the much older Simple Mail Transfer Protocol (SMTP). + + When you type in the following program, replace the EMAILHOST by the +name of your local email server. Ask your administrator if the server +has a POP service, and then use its name or number in the program below. +Now the program is ready to connect to your email server, but it will +not succeed in retrieving your mail because it does not yet know your +login name or password. Replace them in the program and it shows you +the first email the server has in store: + + BEGIN { + POPService = "/inet/tcp/0/EMAILHOST/pop3" + RS = ORS = "\r\n" + print "user NAME" |& POPService + POPService |& getline + print "pass PASSWORD" |& POPService + POPService |& getline + print "retr 1" |& POPService + POPService |& getline + if ($1 != "+OK") exit + print "quit" |& POPService + RS = "\r\n\\.\r\n" + POPService |& getline + print $0 + close(POPService) + } + + The record separators `RS' and `ORS' are redefined because the +protocol (POP) requires CR-LF to separate lines. After identifying +yourself to the email service, the command `retr 1' instructs the +service to send the first of all your email messages in line. If the +service replies with something other than `+OK', the program exits; +maybe there is no email. Otherwise, the program first announces that it +intends to finish reading email, and then redefines `RS' in order to +read the entire email as multiline input in one record. From the POP +RFC, we know that the body of the email always ends with a single line +containing a single dot. The program looks for this using `RS = +"\r\n\\.\r\n"'. When it finds this sequence in the mail message, it +quits. You can invoke this program as often as you like; it does not +delete the message it reads, but instead leaves it on the server. + + +File: gawkinet.info, Node: Web page, Next: Primitive Service, Prev: Email, Up: Using Networking + +Reading a Web Page +================== + + Retrieving a web page from a web server is as simple as retrieving +email from an email server. We only have to use a similar, but not +identical, protocol and a different port. The name of the protocol is +HyperText Transfer Protocol (HTTP) and the port number is usually 80. +As in the preceding node, ask your administrator about the name of your +local web server or proxy web server and its port number for HTTP +requests. + + The following program employs a rather crude approach toward +retrieving a web page. It uses the prehistoric syntax of HTTP 0.9, +which almost all web servers still support. The most noticeable thing +about it is that the program directs the request to the local proxy +server whose name you insert in the special file name (which in turn +calls `www.yahoo.com'): + + BEGIN { + RS = ORS = "\r\n" + HttpService = "/inet/tcp/0/PROXY/80" + print "GET http://www.yahoo.com" |& HttpService + while ((HttpService |& getline) > 0) + print $0 + close(HttpService) + } + + Again, lines are separated by a redefined `RS' and `ORS'. The `GET' +request that we send to the server is the only kind of HTTP request +that existed when the web was created in the early 1990s. HTTP calls +this `GET' request a "method," which tells the service to transmit a +web page (here the home page of the Yahoo! search engine). Version 1.0 +added the request methods `HEAD' and `POST'. The current version of +HTTP is 1.1,(1) and knows the additional request methods `OPTIONS', +`PUT', `DELETE', and `TRACE'. You can fill in any valid web address, +and the program prints the HTML code of that page to your screen. + + Notice the similarity between the responses of the POP and HTTP +services. First, you get a header that is terminated by an empty line, +and then you get the body of the page in HTML. The lines of the +headers also have the same form as in POP. There is the name of a +parameter, then a colon, and finally the value of that parameter. + + Images (`.png' or `.gif' files) can also be retrieved this way, but +then you get binary data that should be redirected into a file. Another +application is calling a CGI (Common Gateway Interface) script on some +server. CGI scripts are used when the contents of a web page are not +constant, but generated instantly at the moment you send a request for +the page. For example, to get a detailed report about the current +quotes of Motorola stock shares, call a CGI script at Yahoo! with the +following: + + get = "GET http://quote.yahoo.com/q?s=MOT&d=t" + print get |& HttpService + + You can also request weather reports this way. + + ---------- Footnotes ---------- + + (1) Version 1.0 of HTTP was defined in RFC 1945. HTTP 1.1 was +initially specified in RFC 2068. In June 1999, RFC 2068 was made +obsolete by RFC 2616. It is an update without any substantial changes. + + +File: gawkinet.info, Node: Primitive Service, Next: Interacting Service, Prev: Web page, Up: Using Networking + +A Primitive Web Service +======================= + + Now we know enough about HTTP to set up a primitive web service that +just says `"Hello, world"' when someone connects to it with a browser. +Compared to the situation in the preceding node, our program changes +the role. It tries to behave just like the server we have observed. +Since we are setting up a server here, we have to insert the port +number in the `localport' field of the special file name. The other two +fields (HOSTNAME and REMOTEPORT) have to contain a `0' because we do +not know in advance which host will connect to our service. + + In the early 1990s, all a server had to do was send an HTML document +and close the connection. Here, we adhere to the modern syntax of HTTP. +The steps are as follows: + + 1. Send a status line telling the web browser that everything is OK. + + 2. Send a line to tell the browser how many bytes follow in the body + of the message. This was not necessary earlier because both + parties knew that the document ended when the connection closed. + Nowadays it is possible to stay connected after the transmission + of one web page. This is to avoid the network traffic necessary + for repeatedly establishing TCP connections for requesting several + images. Thus, there is the need to tell the receiving party how + many bytes will be sent. The header is terminated as usual with an + empty line. + + 3. Send the `"Hello, world"' body in HTML. The useless `while' loop + swallows the request of the browser. We could actually omit the + loop, and on most machines the program would still work. First, + start the following program: + + BEGIN { + RS = ORS = "\r\n" + HttpService = "/inet/tcp/8080/0/0" + Hello = "" \ + "A Famous Greeting" \ + "

Hello, world

" + Len = length(Hello) + length(ORS) + print "HTTP/1.0 200 OK" |& HttpService + print "Content-Length: " Len ORS |& HttpService + print Hello |& HttpService + while ((HttpService |& getline) > 0) + continue; + close(HttpService) + } + + Now, on the same machine, start your favorite browser and let it +point to `http://localhost:8080' (the browser needs to know on which +port our server is listening for requests). If this does not work, the +browser probably tries to connect to a proxy server that does not know +your machine. If so, change the browser's configuration so that the +browser does not try to use a proxy to connect to your machine. + + +File: gawkinet.info, Node: Interacting Service, Next: Simple Server, Prev: Primitive Service, Up: Using Networking + +A Web Service with Interaction +============================== + + This node shows how to set up a simple web server. The subnode is a +library file that we will use with all the examples in *Note Some +Applications and Techniques::. + +* Menu: + +* CGI Lib:: A simple CGI library. + + Setting up a web service that allows user interaction is more +difficult and shows us the limits of network access in `gawk'. In this +node, we develop a main program (a `BEGIN' pattern and its action) +that will become the core of event-driven execution controlled by a +graphical user interface (GUI). Each HTTP event that the user triggers +by some action within the browser is received in this central +procedure. Parameters and menu choices are extracted from this request +and an appropriate measure is taken according to the user's choice. +For example: + + BEGIN { + if (MyHost == "") { + "uname -n" | getline MyHost + close("uname -n") + } + if (MyPort == 0) MyPort = 8080 + HttpService = "/inet/tcp/" MyPort "/0/0" + MyPrefix = "http://" MyHost ":" MyPort + SetUpServer() + while ("awk" != "complex") { + # header lines are terminated this way + RS = ORS = "\r\n" + Status = 200 # this means OK + Reason = "OK" + Header = TopHeader + Document = TopDoc + Footer = TopFooter + if (GETARG["Method"] == "GET") { + HandleGET() + } else if (GETARG["Method"] == "HEAD") { + # not yet implemented + } else if (GETARG["Method"] != "") { + print "bad method", GETARG["Method"] + } + Prompt = Header Document Footer + print "HTTP/1.0", Status, Reason |& HttpService + print "Connection: Close" |& HttpService + print "Pragma: no-cache" |& HttpService + len = length(Prompt) + length(ORS) + print "Content-length:", len |& HttpService + print ORS Prompt |& HttpService + # ignore all the header lines + while ((HttpService |& getline) > 0) + ; + # stop talking to this client + close(HttpService) + # wait for new client request + HttpService |& getline + # do some logging + print systime(), strftime(), $0 + # read request parameters + CGI_setup($1, $2, $3) + } + } + + This web server presents menu choices in the form of HTML links. +Therefore, it has to tell the browser the name of the host it is +residing on. When starting the server, the user may supply the name of +the host from the command line with `gawk -v MyHost="Rumpelstilzchen"'. +If the user does not do this, the server looks up the name of the host +it is running on for later use as a web address in HTML documents. The +same applies to the port number. These values are inserted later into +the HTML content of the web pages to refer to the home system. + + Each server that is built around this core has to initialize some +application-dependent variables (such as the default home page) in a +procedure `SetUpServer', which is called immediately before entering the +infinite loop of the server. For now, we will write an instance that +initiates a trivial interaction. With this home page, the client user +can click on two possible choices, and receive the current date either +in human-readable format or in seconds since 1970: + + function SetUpServer() { + TopHeader = "" + TopHeader = TopHeader \ + "My name is GAWK, GNU AWK" + TopDoc = "

\ + Do you prefer your date human or \ + POSIXed?

" ORS ORS + TopFooter = "" + } + + On the first run through the main loop, the default line terminators +are set and the default home page is copied to the actual home page. +Since this is the first run, `GETARG["Method"]' is not initialized yet, +hence the case selection over the method does nothing. Now that the +home page is initialized, the server can start communicating to a +client browser. + + It does so by printing the HTTP header into the network connection +(`print ... |& HttpService'). This command blocks execution of the +server script until a client connects. If this server script is +compared with the primitive one we wrote before, you will notice two +additional lines in the header. The first instructs the browser to +close the connection after each request. The second tells the browser +that it should never try to _remember_ earlier requests that had +identical web addresses (no caching). Otherwise, it could happen that +the browser retrieves the time of day in the previous example just once, +and later it takes the web page from the cache, always displaying the +same time of day although time advances each second. + + Having supplied the initial home page to the browser with a valid +document stored in the parameter `Prompt', it closes the connection and +waits for the next request. When the request comes, a log line is +printed that allows us to see which request the server receives. The +final step in the loop is to call the function `CGI_setup', which reads +all the lines of the request (coming from the browser), processes them, +and stores the transmitted parameters in the array `PARAM'. The complete +text of these application-independent functions can be found in *Note A +Simple CGI Library: CGI Lib. For now, we use a simplified version of +`CGI_setup': + + function CGI_setup( method, uri, version, i) { + delete GETARG; delete MENU; delete PARAM + GETARG["Method"] = $1 + GETARG["URI"] = $2 + GETARG["Version"] = $3 + i = index($2, "?") + # is there a "?" indicating a CGI request? + if (i > 0) { + split(substr($2, 1, i-1), MENU, "[/:]") + split(substr($2, i+1), PARAM, "&") + for (i in PARAM) { + j = index(PARAM[i], "=") + GETARG[substr(PARAM[i], 1, j-1)] = \ + substr(PARAM[i], j+1) + } + } else { # there is no "?", no need for splitting PARAMs + split($2, MENU, "[/:]") + } + } + + At first, the function clears all variables used for global storage +of request parameters. The rest of the function serves the purpose of +filling the global parameters with the extracted new values. To +accomplish this, the name of the requested resource is split into parts +and stored for later evaluation. If the request contains a `?', then +the request has CGI variables seamlessly appended to the web address. +Everything in front of the `?' is split up into menu items, and +everything behind the `?' is a list of `VARIABLE=VALUE' pairs +(separated by `&') that also need splitting. This way, CGI variables are +isolated and stored. This procedure lacks recognition of special +characters that are transmitted in coded form(1). Here, any optional +request header and body parts are ignored. We do not need header +parameters and the request body. However, when refining our approach or +working with the `POST' and `PUT' methods, reading the header and body +becomes inevitable. Header parameters should then be stored in a global +array as well as the body. + + On each subsequent run through the main loop, one request from a +browser is received, evaluated, and answered according to the user's +choice. This can be done by letting the value of the HTTP method guide +the main loop into execution of the procedure `HandleGET', which +evaluates the user's choice. In this case, we have only one +hierarchical level of menus, but in the general case, menus are nested. +The menu choices at each level are separated by `/', just as in file +names. Notice how simple it is to construct menus of arbitrary depth: + + function HandleGET() { + if ( MENU[2] == "human") { + Footer = strftime() TopFooter + } else if (MENU[2] == "POSIX") { + Footer = systime() TopFooter + } + } + + The disadvantage of this approach is that our server is slow and can +handle only one request at a time. Its main advantage, however, is that +the server consists of just one `gawk' program. No need for installing +an `httpd', and no need for static separate HTML files, CGI scripts, or +`root' privileges. This is rapid prototyping. This program can be +started on the same host that runs your browser. Then let your browser +point to `http://localhost:8080'. + + It is also possible to include images into the HTML pages. Most +browsers support the not very well-known `.xbm' format, which may +contain only monochrome pictures but is an ASCII format. Binary images +are possible but not so easy to handle. Another way of including images +is to generate them with a tool such as GNUPlot, by calling the tool +with the `system' function or through a pipe. + + ---------- Footnotes ---------- + + (1) As defined in RFC 2068. + + +File: gawkinet.info, Node: CGI Lib, Prev: Interacting Service, Up: Interacting Service + +A Simple CGI Library +-------------------- + + HTTP is like being married: you have to be able to handle whatever + you're given, while being very careful what you send back. + Phil Smith III, + `http://www.netfunny.com/rhf/jokes/99/Mar/http.html' + + In *Note A Web Service with Interaction: Interacting Service, we saw +the function `CGI_setup' as part of the web server "core logic" +framework. The code presented there handles almost everything necessary +for CGI requests. One thing it doesn't do is handle encoded characters +in the requests. For example, an `&' is encoded as a percent sign +followed by the hexadecimal value--`%26'. These encoded values should +be decoded. Following is a simple library to perform these tasks. +This code is used for all web server examples used throughout the rest +of this Info file. If you want to use it for your own web server, +store the source code into a file named `inetlib.awk'. Then you can +include these functions into your code by placing the following +statement into your program: + + @include inetlib.awk + +on the first line of your script. But beware, this mechanism is only +possible if you invoke your web server script with `igawk' instead of +the usual `awk' or `gawk'. Here is the code: + + # CGI Library and core of a web server + # Global arrays + # GETARG --- arguments to CGI GET command + # MENU --- menu items (path names) + # PARAM --- parameters of form x=y + + # Optional variable MyHost contains host address + # Optional variable MyPort contains port number + # Needs TopHeader, TopDoc, TopFooter + # Sets MyPrefix, HttpService, Status, Reason + + BEGIN { + if (MyHost == "") { + "uname -n" | getline MyHost + close("uname -n") + } + if (MyPort == 0) MyPort = 8080 + HttpService = "/inet/tcp/" MyPort "/0/0" + MyPrefix = "http://" MyHost ":" MyPort + SetUpServer() + while ("awk" != "complex") { + # header lines are terminated this way + RS = ORS = "\r\n" + Status = 200 # this means OK + Reason = "OK" + Header = TopHeader + Document = TopDoc + Footer = TopFooter + if (GETARG["Method"] == "GET") { + HandleGET() + } else if (GETARG["Method"] == "HEAD") { + # not yet implemented + } else if (GETARG["Method"] != "") { + print "bad method", GETARG["Method"] + } + Prompt = Header Document Footer + print "HTTP/1.0", Status, Reason |& HttpService + print "Connection: Close" |& HttpService + print "Pragma: no-cache" |& HttpService + len = length(Prompt) + length(ORS) + print "Content-length:", len |& HttpService + print ORS Prompt |& HttpService + # ignore all the header lines + while ((HttpService |& getline) > 0) + continue + # stop talking to this client + close(HttpService) + # wait for new client request + HttpService |& getline + # do some logging + print systime(), strftime(), $0 + CGI_setup($1, $2, $3) + } + } + + function CGI_setup( method, uri, version, i) + { + delete GETARG + delete MENU + delete PARAM + GETARG["Method"] = method + GETARG["URI"] = uri + GETARG["Version"] = version + + i = index(uri, "?") + if (i > 0) { # is there a "?" indicating a CGI request? + split(substr(uri, 1, i-1), MENU, "[/:]") + split(substr(uri, i+1), PARAM, "&") + for (i in PARAM) { + PARAM[i] = _CGI_decode(PARAM[i]) + j = index(PARAM[i], "=") + GETARG[substr(PARAM[i], 1, j-1)] = \ + substr(PARAM[i], j+1) + } + } else { # there is no "?", no need for splitting PARAMs + split(uri, MENU, "[/:]") + } + for (i in MENU) # decode characters in path + if (i > 4) # but not those in host name + MENU[i] = _CGI_decode(MENU[i]) + } + + This isolates details in a single function, `CGI_setup'. Decoding +of encoded characters is pushed off to a helper function, +`_CGI_decode'. The use of the leading underscore (`_') in the function +name is intended to indicate that it is an "internal" function, +although there is nothing to enforce this: + + function _CGI_decode(str, hexdigs, i, pre, code1, code2, + val, result) + { + hexdigs = "123456789abcdef" + + i = index(str, "%") + if (i == 0) # no work to do + return str + + do { + pre = substr(str, 1, i-1) # part before %xx + code1 = substr(str, i+1, 1) # first hex digit + code2 = substr(str, i+2, 1) # second hex digit + str = substr(str, i+3) # rest of string + + code1 = tolower(code1) + code2 = tolower(code2) + val = index(hexdigs, code1) * 16 \ + + index(hexdigs, code2) + + result = result pre sprintf("%c", val) + i = index(str, "%") + } while (i != 0) + if (length(str) > 0) + result = result str + return result + } + + This works by splitting the string apart around an encoded character. +The two digits are converted to lowercase and looked up in a string of +hex digits. Note that `0' is not in the string on purpose; `index' +returns zero when it's not found, automatically giving the correct +value! Once the hexadecimal value is converted from characters in a +string into a numerical value, `sprintf' converts the value back into a +real character. The following is a simple test harness for the above +functions: + + BEGIN { + CGI_setup("GET", + "http://www.gnu.org/cgi-bin/foo?p1=stuff&p2=stuff%26junk" \ + "&percent=a %25 sign", + "1.0") + for (i in MENU) + printf "MENU[\"%s\"] = %s\n", i, MENU[i] + for (i in PARAM) + printf "PARAM[\"%s\"] = %s\n", i, PARAM[i] + for (i in GETARG) + printf "GETARG[\"%s\"] = %s\n", i, GETARG[i] + } + + And this is the result when we run it: + + $ gawk -f testserv.awk + -| MENU["4"] = www.gnu.org + -| MENU["5"] = cgi-bin + -| MENU["6"] = foo + -| MENU["1"] = http + -| MENU["2"] = + -| MENU["3"] = + -| PARAM["1"] = p1=stuff + -| PARAM["2"] = p2=stuff&junk + -| PARAM["3"] = percent=a % sign + -| GETARG["p1"] = stuff + -| GETARG["percent"] = a % sign + -| GETARG["p2"] = stuff&junk + -| GETARG["Method"] = GET + -| GETARG["Version"] = 1.0 + -| GETARG["URI"] = http://www.gnu.org/cgi-bin/foo?p1=stuff& + p2=stuff%26junk&percent=a %25 sign + + +File: gawkinet.info, Node: Simple Server, Next: Caveats, Prev: Interacting Service, Up: Using Networking + +A Simple Web Server +=================== + + In the preceding node, we built the core logic for event driven GUIs. +In this node, we finally extend the core to a real application. No one +would actually write a commercial web server in `gawk', but it is +instructive to see that it is feasible in principle. + + The application is ELIZA, the famous program by Joseph Weizenbaum +that mimics the behavior of a professional psychotherapist when talking +to you. Weizenbaum would certainly object to this description, but +this is part of the legend around ELIZA. Take the site-independent +core logic and append the following code: + + function SetUpServer() { + SetUpEliza() + TopHeader = \ + "An HTTP-based System with GAWK\ + \ + " + TopDoc = "\ +

Please choose one of the following actions:

\ + " + TopFooter = "" + } + + `SetUpServer' is similar to the previous example, except for calling +another function, `SetUpEliza'. This approach can be used to implement +other kinds of servers. The only changes needed to do so are hidden in +the functions `SetUpServer' and `HandleGET'. Perhaps it might be +necessary to implement other HTTP methods. The `igawk' program that +comes with `gawk' may be useful for this process. + + When extending this example to a complete application, the first +thing to do is to implement the function `SetUpServer' to initialize +the HTML pages and some variables. These initializations determine the +way your HTML pages look (colors, titles, menu items, etc.). + + The function `HandleGET' is a nested case selection that decides +which page the user wants to see next. Each nesting level refers to a +menu level of the GUI. Each case implements a certain action of the +menu. On the deepest level of case selection, the handler essentially +knows what the user wants and stores the answer into the variable that +holds the HTML page contents: + + function HandleGET() { + # A real HTTP server would treat some parts of the URI as a file name. + # We take parts of the URI as menu choices and go on accordingly. + if(MENU[2] == "AboutServer") { + Document = "This is not a CGI script.\ + This is an httpd, an HTML file, and a CGI script all \ + in one GAWK script. It needs no separate www-server, \ + no installation, and no root privileges.\ +

To run it, do this:

    \ +
  • start this script with \"gawk -f httpserver.awk\",
    • \ +
  • and on the same host let your www browser open location\ + \"http://localhost:8080\"
    • \ +
\

\ Details of HTTP come from:

    \ +
  • Hethmon: Illustrated Guide to HTTP

    \ +
  • RFC 2068

JK 14.9.1997

" + } else if (MENU[2] == "AboutELIZA") { + Document = "This is an implementation of the famous ELIZA\ + program by Joseph Weizenbaum. It is written in GAWK and\ + /bin/sh: expad: command not found + } else if (MENU[2] == "StartELIZA") { + gsub(/\+/, " ", GETARG["YouSay"]) + # Here we also have to substitute coded special characters + Document = "
" \ + "

" ElizaSays(GETARG["YouSay"]) "

\ +

\ +

" + } + } + + Now we are down to the heart of ELIZA, so you can see how it works. +Initially the user does not say anything; then ELIZA resets its money +counter and asks the user to tell what comes to mind open heartedly. +The subsequent answers are converted to uppercase and stored for later +comparison. ELIZA presents the bill when being confronted with a +sentence that contains the phrase "shut up." Otherwise, it looks for +keywords in the sentence, conjugates the rest of the sentence, remembers +the keyword for later use, and finally selects an answer from the set of +possible answers: + + function ElizaSays(YouSay) { + if (YouSay == "") { + cost = 0 + answer = "HI, IM ELIZA, TELL ME YOUR PROBLEM" + } else { + q = toupper(YouSay) + gsub("'", "", q) + if(q == qold) { + answer = "PLEASE DONT REPEAT YOURSELF !" + } else { + if (index(q, "SHUT UP") > 0) { + answer = "WELL, PLEASE PAY YOUR BILL. ITS EXACTLY ... $"\ + int(100*rand()+30+cost/100) + } else { + qold = q + w = "-" # no keyword recognized yet + for (i in k) { # search for keywords + if (index(q, i) > 0) { + w = i + break + } + } + if (w == "-") { # no keyword, take old subject + w = wold + subj = subjold + } else { # find subject + subj = substr(q, index(q, w) + length(w)+1) + wold = w + subjold = subj # remember keyword and subject + } + for (i in conj) + gsub(i, conj[i], q) # conjugation + # from all answers to this keyword, select one randomly + answer = r[indices[int(split(k[w], indices) * rand()) + 1]] + # insert subject into answer + gsub("_", subj, answer) + } + } + } + cost += length(answer) # for later payment : 1 cent per character + return answer + } + + In the long but simple function `SetUpEliza', you can see tables for +conjugation, keywords, and answers.(1) The associative array `k' +contains indices into the array of answers `r'. To choose an answer, +ELIZA just picks an index randomly: + + function SetUpEliza() { + srand() + wold = "-" + subjold = " " + + # table for conjugation + conj[" ARE " ] = " AM " + conj["WERE " ] = "WAS " + conj[" YOU " ] = " I " + conj["YOUR " ] = "MY " + conj[" IVE " ] =\ + conj[" I HAVE " ] = " YOU HAVE " + conj[" YOUVE " ] =\ + conj[" YOU HAVE "] = " I HAVE " + conj[" IM " ] =\ + conj[" I AM " ] = " YOU ARE " + conj[" YOURE " ] =\ + conj[" YOU ARE " ] = " I AM " + + # table of all answers + r[1] = "DONT YOU BELIEVE THAT I CAN _" + r[2] = "PERHAPS YOU WOULD LIKE TO BE ABLE TO _ ?" + ... + + # table for looking up answers that + # fit to a certain keyword + k["CAN YOU"] = "1 2 3" + k["CAN I"] = "4 5" + k["YOU ARE"] =\ + k["YOURE"] = "6 7 8 9" + ... + + } + + Some interesting remarks and details (including the original source +code of ELIZA) are found on Mark Humphrys' home page. Yahoo! also has +a page with a collection of ELIZA-like programs. Many of them are +written in Java, some of them disclosing the Java source code, and a +few even explain how to modify the Java source code. + + ---------- Footnotes ---------- + + (1) The version shown here is abbreviated. The full version comes +with the `gawk' distribution. + + +File: gawkinet.info, Node: Caveats, Next: Challenges, Prev: Simple Server, Up: Using Networking + +Network Programming Caveats +=========================== + + By now it should be clear that debugging a networked application is +more complicated than debugging a single-process single-hosted +application. The behavior of a networked application sometimes looks +non-causal because it is not reproducible in a strong sense. Whether a +network application works or not sometimes depends on the following: + + * How crowded the underlying network is. + + * If the party at the other end is running or not. + + * The state of the party at the other end. + + The most difficult problems for a beginner arise from the hidden +states of the underlying network. After closing a TCP connection, it's +often necessary to wait a short while before reopening the connection. +Even more difficult is the establishment of a connection that +previously ended with a "broken pipe." Those connections have to "time +out" for a minute or so before they can reopen. Check this with the +command `netstat -a', which provides a list of still "active" +connections. + + +File: gawkinet.info, Node: Challenges, Prev: Caveats, Up: Using Networking + +Where To Go From Here +===================== + + Now, you have learned enough to build your own application. You +could, for example, take part in the Loebner Contest to win $100,000. +The Loebner Prize is the first formal instantiation of a Turing Test. +Hugh Loebner agreed with The Cambridge Center for Behavioral Studies to +underwrite a contest designed to implement the Turing Test. Dr. +Loebner pledged a Grand Prize of $100,000 for the first computer whose +responses were indistinguishable from a human's. Each year an annual +prize of $2000 and a bronze medal is awarded to the _most_ human +computer. The winner of the annual contest is the best entry relative +to other entries that year, irrespective of how good it is in an +absolute sense. Here is an example of a conversation with the winning +program of 1997: + + (c)1997 Cambridge Center For Behavioral Studies all rights reserved [CONVERSE] + [Intelligent Research Ltd.] Start at: [1997/04/29 08:59:40] + PROGRAM[10:39:20]Hi, my name is Catherine, what's yours? + JUDGE02[10:39:36]My name is Nathan. + PROGRAM[10:39:37]Well, it's nice to meet you, Nathan. + PROGRAM[10:39:45]Did you see that story on CNN last night about the lesbian + PROGRAM[10:40:03]couple who came out at a White House party on Sunday? + JUDGE02[10:40:45]No. I'm sorry I missed that. How did the Prez take it? + PROGRAM[10:40:47]Ellen Degeneres was one of them - she was kissing her lover + PROGRAM[10:41:08]in front of Bill Clinton. Do you think he was very + PROGRAM[10:41:21]embarrassed? + JUDGE02[10:41:37]You tell me. I didn't see it. + PROGRAM[10:41:38]Are you still a Friend of Bill Clinton? + JUDGE02[10:42:22]Yes. I would like to talk about something else. Do you know anything about sculpture. + PROGRAM[10:42:24]Well, I suppose he's doing his best like most of us, but he + PROGRAM[10:42:35]does seem to attract an UNUSUAL amount of bad publicity, + PROGRAM[10:42:51]wouldnt you say--can it all be bad luck? + JUDGE02[10:43:20]I asked you if you knew anything about sculpture. + PROGRAM[10:43:21]OK, but what happens now--does it all drift on, with + PROGRAM[10:43:36]everyone waiting to see how much his friends have said about + PROGRAM[10:43:47]him under threat of lots and lots of jail-or will something + PROGRAM[10:44:01]dramatic actually happen? + JUDGE02[10:44:19]Do you know what sculpture is? + PROGRAM[10:44:20]Well, youre more a fan of his than I am I guess---though I + PROGRAM[10:44:34]cant SWEAR what Id have done in that locked hotel room, I + PROGRAM[10:44:51]must say. + JUDGE02[10:45:26]Have you ever been to the Salmagundi Club? + PROGRAM[10:45:29]Never. to go back to the original discussion Time to get + PROGRAM[10:45:43]off this one I think and onto something more down to earth! + JUDGE02[10:46:20]What is more down to earth than art? + PROGRAM[10:46:21]I don't know what -- to be honest. - + PROGRAM[10:46:30]I suppose it depends on where you're coming from, but as the + PROGRAM[10:46:46]song goes in My Fair Lady, "Why can't a woman be more like a + PROGRAM[10:47:03]man? " + JUDGE02[10:47:52]I liked that song but I prefer "Why can't children be more like we are" + JUDGE02[10:48:10]from another play the name of which I cannot remember. + PROGRAM[10:48:12]What, if anything, do you enjoy about being a man? + JUDGE02[10:49:01]I would enjoy all aspects of life no matter what my gender. + PROGRAM[10:49:02]Do you think of yourself as being attractive? + + This program insists on always speaking about the same story around +Bill Clinton. You see, even a program with a rather narrow mind can +behave so much like a human being that it can win this prize. It is +quite common to let these programs talk to each other via network +connections. But during the competition itself, the program and its +computer have to be present at the place the competition is held. We +all would love to see a `gawk' program win in such an event. Maybe it +is up to you to accomplish this? + + Some other ideas for useful networked applications: + * Read the file `doc/awkforai.txt' in the `gawk' distribution. It + was written by Ronald P. Loui (Associate Professor of Computer + Science, at Washington University in St. Louis, + ) and summarizes why he teaches `gawk' to + students of Artificial Intelligence. Here are some passages from + the text: + + The GAWK manual can be consumed in a single lab session and + the language can be mastered by the next morning by the + average student. GAWK's automatic initialization, implicit + coercion, I/O support and lack of pointers forgive many of + the mistakes that young programmers are likely to make. + Those who have seen C but not mastered it are happy to see + that GAWK retains some of the same sensibilities while adding + what must be regarded as spoonsful of syntactic sugar. + ... + There are further simple answers. Probably the best is the + fact that increasingly, undergraduate AI programming is + involving the Web. Oren Etzioni (University of Washington, + Seattle) has for a while been arguing that the "softbot" is + replacing the mechanical engineers' robot as the most + glamorous AI testbed. If the artifact whose behavior needs + to be controlled in an intelligent way is the software agent, + then a language that is well-suited to controlling the + software environment is the appropriate language. That would + imply a scripting language. If the robot is KAREL, then the + right language is "turn left; turn right." If the robot is + Netscape, then the right language is something that can + generate `netscape -remote + 'openURL(http://cs.wustl.edu/~loui)'' with elan. + ... + AI programming requires high-level thinking. There have + always been a few gifted programmers who can write high-level + programs in assembly language. Most however need the ambient + abstraction to have a higher floor. + ... + Second, inference is merely the expansion of notation. No + matter whether the logic that underlies an AI program is + fuzzy, probabilistic, deontic, defeasible, or deductive, the + logic merely defines how strings can be transformed into + other strings. A language that provides the best support for + string processing in the end provides the best support for + logic, for the exploration of various logics, and for most + forms of symbolic processing that AI might choose to call + "reasoning" instead of "logic." The implication is that + PROLOG, which saves the AI programmer from having to write a + unifier, saves perhaps two dozen lines of GAWK code at the + expense of strongly biasing the logic and representational + expressiveness of any approach. + + Now that `gawk' itself can connect to the Internet, it should be + obvious that it is suitable for writing intelligent web agents. + + * `awk' is strong at pattern recognition and string processing. So, + it is well suited to the classic problem of language translation. + A first try could be a program that knows the 100 most frequent + English words and their counterparts in German or French. The + service could be implemented by regularly reading email with the + program above, replacing each word by its translation and sending + the translation back via SMTP. Users would send English email to + their translation service and get back a translated email message + in return. As soon as this works, more effort can be spent on a + real translation program. + + * Another dialogue-oriented application (on the verge of ridicule) + is the email "support service." Troubled customers write an email + to an automatic `gawk' service that reads the email. It looks for + keywords in the mail and assembles a reply email accordingly. By + carefully investigating the email header, and repeating these + keywords through the reply email, it is rather simple to give the + customer a feeling that someone cares. Ideally, such a service + would search a database of previous cases for solutions. If none + exists, the database could, for example, consist of all the + newsgroups, mailing lists and FAQs on the Internet. + + +File: gawkinet.info, Node: Some Applications and Techniques, Next: Links, Prev: Using Networking, Up: Top + +Some Applications and Techniques +******************************** + + In this major node, we look at a number of self-contained scripts, +with an emphasis on concise networking. Along the way, we work towards +creating building blocks that encapsulate often needed functions of the +networking world, show new techniques that broaden the scope of +problems that can be solved with `gawk', and explore leading edge +technology that may shape the future of networking. + + We often refer to the site-independent core of the server that we +built in *Note A Simple Web Server: Simple Server. When building new +and non-trivial servers, we always copy this building block and append +new instances of the two functions `SetUpServer' and `HandleGET'. + + This makes a lot of sense, since this scheme of event-driven +execution provides `gawk' with an interface to the most widely accepted +standard for GUIs: the web browser. Now, `gawk' can even rival Tcl/Tk. + + Tcl and `gawk' have much in common. Both are simple scripting +languages that allow us to quickly solve problems with short programs. +But Tcl has Tk on top of it and `gawk' had nothing comparable up to +now. While Tcl needs a large and ever changing library (Tk, which was +bound to the X Window System until recently), `gawk' needs just the +networking interface and some kind of browser on the client's side. +Besides better portability, the most important advantage of this +approach (embracing well-established standards such HTTP and HTML) is +that _we do not need to change the language_. We let others do the work +of fighting over protocols and standards. We can use HTML, JavaScript, +VRML, or whatever else comes along to do our work. + +* Menu: + +* PANIC:: An Emergency Web Server. +* GETURL:: Retrieving Web Pages. +* REMCONF:: Remote Configuration Of Embedded Systems. +* URLCHK:: Look For Changed Web Pages. +* WEBGRAB:: Extract Links From A Page. +* STATIST:: Graphing A Statistical Distribution. +* MAZE:: Walking Through A Maze In Virtual Reality. +* MOBAGWHO:: A Simple Mobile Agent. +* STOXPRED:: Stock Market Prediction As A Service. +* PROTBASE:: Searching Through A Protein Database. + + +File: gawkinet.info, Node: PANIC, Next: GETURL, Prev: Some Applications and Techniques, Up: Some Applications and Techniques + +PANIC: an Emergency Web Server +============================== + + At first glance, the `"Hello, world"' example in *Note A Primitive +Web Service: Primitive Service, seems useless. By adding just a few +lines, we can turn it into something useful. + + The PANIC program tells everyone who connects that the local site is +not working. When a web server breaks down, it makes a difference if +customers get a strange "network unreachable" message, or a short +message telling them that the server has a problem. In such an +emergency, the hard disk and everything on it (including the regular +web service) may be unavailable. Rebooting the web server off a +diskette makes sense in this setting. + + To use the PANIC program as an emergency web server, all you need +are the `gawk' executable and the program below on a diskette. By +default, it connects to port 8080. A different value may be supplied on +the command line: + + BEGIN { + RS = ORS = "\r\n" + if (MyPort == 0) MyPort = 8080 + HttpService = "/inet/tcp/" MyPort "/0/0" + Hello = "Out Of Service" \ + "

" \ + "This site is temporarily out of service." \ + "

" + Len = length(Hello) + length(ORS) + while ("awk" != "complex") { + print "HTTP/1.0 200 OK" |& HttpService + print "Content-Length: " Len ORS |& HttpService + print Hello |& HttpService + while ((HttpService |& getline) > 0) + continue; + close(HttpService) + } + } + + +File: gawkinet.info, Node: GETURL, Next: REMCONF, Prev: PANIC, Up: Some Applications and Techniques + +GETURL: Retrieving Web Pages +============================ + + GETURL is a versatile building block for shell scripts that need to +retrieve files from the Internet. It takes a web address as a +command-line parameter and tries to retrieve the contents of this +address. The contents are printed to standard output, while the header +is printed to `/dev/stderr'. A surrounding shell script could analyze +the contents and extract the text or the links. An ASCII browser could +be written around GETURL. But more interestingly, web robots are +straightforward to write on top of GETURL. On the Internet, you can find +several programs of the same name that do the same job. They are usually +much more complex internally and at least 10 times longer. + + At first, GETURL checks if it was called with exactly one web +address. Then, it checks if the user chose to use a special proxy +server whose name is handed over in a variable. By default, it is +assumed that the local machine serves as proxy. GETURL uses the `GET' +method by default to access the web page. By handing over the name of a +different method (such as `HEAD'), it is possible to choose a different +behavior. With the `HEAD' method, the user does not receive the body of +the page content, but does receive the header: + + BEGIN { + if (ARGC != 2) { + print "GETURL - retrieve Web page via HTTP 1.0" + print "IN:\n the URL as a command-line parameter" + print "PARAM(S):\n -v Proxy=MyProxy" + print "OUT:\n the page content on stdout" + print " the page header on stderr" + print "JK 16.05.1997" + print "ADR 13.08.2000" + exit + } + URL = ARGV[1]; ARGV[1] = "" + if (Proxy == "") Proxy = "127.0.0.1" + if (ProxyPort == 0) ProxyPort = 80 + if (Method == "") Method = "GET" + HttpService = "/inet/tcp/0/" Proxy "/" ProxyPort + ORS = RS = "\r\n\r\n" + print Method " " URL " HTTP/1.0" |& HttpService + HttpService |& getline Header + print Header > "/dev/stderr" + while ((HttpService |& getline) > 0) + printf "%s", $0 + close(HttpService) + } + + This program can be changed as needed, but be careful with the last +lines. Make sure transmission of binary data is not corrupted by +additional line breaks. Even as it is now, the byte sequence +`"\r\n\r\n"' would disappear if it were contained in binary data. Don't +get caught in a trap when trying a quick fix on this one. + + +File: gawkinet.info, Node: REMCONF, Next: URLCHK, Prev: GETURL, Up: Some Applications and Techniques + +REMCONF: Remote Configuration of Embedded Systems +================================================= + + Today, you often find powerful processors in embedded systems. +Dedicated network routers and controllers for all kinds of machinery +are examples of embedded systems. Processors like the Intel 80x86 or +the AMD Elan are able to run multitasking operating systems, such as +XINU or GNU/Linux in embedded PCs. These systems are small and usually +do not have a keyboard or a display. Therefore it is difficult to set +up their configuration. There are several widespread ways to set them +up: + + * DIP switches + + * Read Only Memories such as EPROMs + + * Serial lines or some kind of keyboard + + * Network connections via `telnet' or SNMP + + * HTTP connections with HTML GUIs + + In this node, we look at a solution that uses HTTP connections to +control variables of an embedded system that are stored in a file. +Since embedded systems have tight limits on resources like memory, it +is difficult to employ advanced techniques such as SNMP and HTTP +servers. `gawk' fits in quite nicely with its single executable which +needs just a short script to start working. The following program +stores the variables in a file, and a concurrent process in the +embedded system may read the file. The program uses the +site-independent part of the simple web server that we developed in +*Note A Web Service with Interaction: Interacting Service. As +mentioned there, all we have to do is to write two new procedures +`SetUpServer' and `HandleGET': + + function SetUpServer() { + TopHeader = "Remote Configuration" + TopDoc = "\ +

Please choose one of the following actions:

\ + " + TopFooter = "" + if (ConfigFile == "") ConfigFile = "config.asc" + } + + The function `SetUpServer' initializes the top level HTML texts as +usual. It also initializes the name of the file that contains the +configuration parameters and their values. In case the user supplies a +name from the command line, that name is used. The file is expected to +contain one parameter per line, with the name of the parameter in +column one and the value in column two. + + The function `HandleGET' reflects the structure of the menu tree as +usual. The first menu choice tells the user what this is all about. The +second choice reads the configuration file line by line and stores the +parameters and their values. Notice that the record separator for this +file is `"\n"', in contrast to the record separator for HTTP. The third +menu choice builds an HTML table to show the contents of the +configuration file just read. The fourth choice does the real work of +changing parameters, and the last one just saves the configuration into +a file: + + function HandleGET() { + if(MENU[2] == "AboutServer") { + Document = "This is a GUI for remote configuration of an\ + embedded system. It is is implemented as one GAWK script." + } else if (MENU[2] == "ReadConfig") { + RS = "\n" + while ((getline < ConfigFile) > 0) + config[$1] = $2; + close(ConfigFile) + RS = "\r\n" + Document = "Configuration has been read." + } else if (MENU[2] == "CheckConfig") { + Document = "" + for (i in config) + Document = Document "" \ + "" + Document = Document "
" i "" config[i] "
" + } else if (MENU[2] == "ChangeConfig") { + if ("Param" in GETARG) { # any parameter to set? + if (GETARG["Param"] in config) { # is parameter valid? + config[GETARG["Param"]] = GETARG["Value"] + Document = (GETARG["Param"] " = " GETARG["Value"] ".") + } else { + Document = "Parameter " GETARG["Param"] " is invalid." + } + } else { + Document = "

Change one parameter

\ + \ + \ + \ + \ +
ParameterValue
" + } + } else if (MENU[2] == "SaveConfig") { + for (i in config) + printf("%s %s\n", i, config[i]) > ConfigFile + close(ConfigFile) + Document = "Configuration has been saved." + } + } + + We could also view the configuration file as a database. From this +point of view, the previous program acts like a primitive database +server. Real SQL database systems also make a service available by +providing a TCP port that clients can connect to. But the application +level protocols they use are usually proprietary and also change from +time to time. This is also true for the protocol that MiniSQL uses. + + +File: gawkinet.info, Node: URLCHK, Next: WEBGRAB, Prev: REMCONF, Up: Some Applications and Techniques + +URLCHK: Look for Changed Web Pages +================================== + + Most people who make heavy use of Internet resources have a large +bookmark file with pointers to interesting web sites. It is impossible +to regularly check by hand if any of these sites have changed. A program +is needed to automatically look at the headers of web pages and tell +which ones have changed. URLCHK does the comparison after using GETURL +with the `HEAD' method to retrieve the header. + + Like GETURL, this program first checks that it is called with exactly +one command-line parameter. URLCHK also takes the same command-line +variables `Proxy' and `ProxyPort' as GETURL, because these variables +are handed over to GETURL for each URL that gets checked. The one and +only parameter is the name of a file that contains one line for each +URL. In the first column, we find the URL, and the second and third +columns hold the length of the URL's body when checked for the two last +times. Now, we follow this plan: + + 1. Read the URLs from the file and remember their most recent lengths + + 2. Delete the contents of the file + + 3. For each URL, check its new length and write it into the file + + 4. If the most recent and the new length differ, tell the user + + It may seem a bit peculiar to read the URLs from a file together +with their two most recent lengths, but this approach has several +advantages. You can call the program again and again with the same +file. After running the program, you can regenerate the changed URLs by +extracting those lines that differ in their second and third columns: + + BEGIN { + if (ARGC != 2) { + print "URLCHK - check if URLs have changed" + print "IN:\n the file with URLs as a command-line parameter" + print " file contains URL, old length, new length" + print "PARAMS:\n -v Proxy=MyProxy -v ProxyPort=8080" + print "OUT:\n same as file with URLs" + print "JK 02.03.1998" + exit + } + URLfile = ARGV[1]; ARGV[1] = "" + if (Proxy != "") Proxy = " -v Proxy=" Proxy + if (ProxyPort != "") ProxyPort = " -v ProxyPort=" ProxyPort + while ((getline < URLfile) > 0) + Length[$1] = $3 + 0 + close(URLfile) # now, URLfile is read in and can be updated + GetHeader = "gawk " Proxy ProxyPort " -v Method=\"HEAD\" -f geturl.awk " + for (i in Length) { + GetThisHeader = GetHeader i " 2>&1" + while ((GetThisHeader | getline) > 0) + if (toupper($0) ~ /CONTENT-LENGTH/) NewLength = $2 + 0 + close(GetThisHeader) + print i, Length[i], NewLength > URLfile + if (Length[i] != NewLength) # report only changed URLs + print i, Length[i], NewLength + } + close(URLfile) + } + + Another thing that may look strange is the way GETURL is called. +Before calling GETURL, we have to check if the proxy variables need to +be passed on. If so, we prepare strings that will become part of the +command line later. In `GetHeader', we store these strings together +with the longest part of the command line. Later, in the loop over the +URLs, `GetHeader' is appended with the URL and a redirection operator +to form the command that reads the URL's header over the Internet. +GETURL always produces the headers over `/dev/stderr'. That is the +reason why we need the redirection operator to have the header piped in. + + This program is not perfect because it assumes that changing URLs +results in changed lengths, which is not necessarily true. A more +advanced approach is to look at some other header line that holds time +information. But, as always when things get a bit more complicated, +this is left as an exercise to the reader. + + +File: gawkinet.info, Node: WEBGRAB, Next: STATIST, Prev: URLCHK, Up: Some Applications and Techniques + +WEBGRAB: Extract Links from a Page +================================== + + Sometimes it is necessary to extract links from web pages. Browsers +do it, web robots do it, and sometimes even humans do it. Since we +have a tool like GETURL at hand, we can solve this problem with some +help from the Bourne shell: + + BEGIN { RS = "http://[#%&\\+\\-\\./0-9\\:;\\?A-Z_a-z\\~]*" } + RT != "" { + command = ("gawk -v Proxy=MyProxy -f geturl.awk " RT \ + " > doc" NR ".html") + print command + } + + Notice that the regular expression for URLs is rather crude. A +precise regular expression is much more complex. But this one works +rather well. One problem is that it is unable to find internal links of +an HTML document. Another problem is that `ftp', `telnet', `news', +`mailto', and other kinds of links are missing in the regular +expression. However, it is straightforward to add them, if doing so is +necessary for other tasks. + + This program reads an HTML file and prints all the HTTP links that +it finds. It relies on `gawk''s ability to use regular expressions as +record separators. With `RS' set to a regular expression that matches +links, the second action is executed each time a non-empty link is +found. We can find the matching link itself in `RT'. + + The action could use the `system' function to let another GETURL +retrieve the page, but here we use a different approach. This simple +program prints shell commands that can be piped into `sh' for +execution. This way it is possible to first extract the links, wrap +shell commands around them, and pipe all the shell commands into a +file. After editing the file, execution of the file retrieves exactly +those files that we really need. In case we do not want to edit, we can +retrieve all the pages like this: + + gawk -f geturl.awk http://www.suse.de | gawk -f webgrab.awk | sh + + After this, you will find the contents of all referenced documents in +files named `doc*.html' even if they do not contain HTML code. The +most annoying thing is that we always have to pass the proxy to GETURL. +If you do not like to see the headers of the web pages appear on the +screen, you can redirect them to `/dev/null'. Watching the headers +appear can be quite interesting, because it reveals interesting details +such as which web server the companies use. Now, it is clear how the +clever marketing people use web robots to determine the market shares +of Microsoft and Netscape in the web server market. + + Port 80 of any web server is like a small hole in a repellent +firewall. After attaching a browser to port 80, we usually catch a +glimpse of the bright side of the server (its home page). With a tool +like GETURL at hand, we are able to discover some of the more concealed +or even "indecent" services (i.e., lacking conformity to standards of +quality). It can be exciting to see the fancy CGI scripts that lie +there, revealing the inner workings of the server, ready to be called: + + * With a command such as: + + gawk -f geturl.awk http://any.host.on.the.net/cgi-bin/ + + some servers give you a directory listing of the CGI files. + Knowing the names, you can try to call some of them and watch for + useful results. Sometimes there are executables in such directories + (such as Perl interpreters) that you may call remotely. If there + are subdirectories with configuration data of the web server, this + can also be quite interesting to read. + + * The well-known Apache web server usually has its CGI files in the + directory `/cgi-bin'. There you can often find the scripts + `test-cgi' and `printenv'. Both tell you some things about the + current connection and the installation of the web server. Just + call: + + gawk -f geturl.awk http://any.host.on.the.net/cgi-bin/test-cgi + gawk -f geturl.awk http://any.host.on.the.net/cgi-bin/printenv + + * Sometimes it is even possible to retrieve system files like the web + server's log file--possibly containing customer data--or even the + file `/etc/passwd'. (We don't recommend this!) + + *Caution:* Although this may sound funny or simply irrelevant, we +are talking about severe security holes. Try to explore your own system +this way and make sure that none of the above reveals too much +information about your system. + + +File: gawkinet.info, Node: STATIST, Next: MAZE, Prev: WEBGRAB, Up: Some Applications and Techniques + +STATIST: Graphing a Statistical Distribution +============================================ + + In the HTTP server examples we've shown thus far, we never present +an image to the browser and its user. Presenting images is one task. +Generating images that reflect some user input and presenting these +dynamically generated images is another. In this node, we use GNUPlot +for generating `.png', `.ps', or `.gif' files.(1) + + The program we develop takes the statistical parameters of two +samples and computes the t-test statistics. As a result, we get the +probabilities that the means and the variances of both samples are the +same. In order to let the user check plausibility, the program presents +an image of the distributions. The statistical computation follows +`Numerical Recipes in C: The Art of Scientific Computing' by William H. +Press, Saul A. Teukolsky, William T. Vetterling, and Brian P. Flannery. +Since `gawk' does not have a built-in function for the computation of +the beta function, we use the `ibeta' function of GNUPlot. As a side +effect, we learn how to use GNUPlot as a sophisticated calculator. The +comparison of means is done as in `tutest', paragraph 14.2, page 613, +and the comparison of variances is done as in `ftest', page 611 in +`Numerical Recipes'. + + As usual, we take the site-independent code for servers and append +our own functions `SetUpServer' and `HandleGET': + + function SetUpServer() { + TopHeader = "Statistics with GAWK" + TopDoc = "\ +

Please choose one of the following actions:

\ + " + TopFooter = "" + GnuPlot = "gnuplot 2>&1" + m1=m2=0; v1=v2=1; n1=n2=10 + } + + Here, you see the menu structure that the user sees. Later, we will +see how the program structure of the `HandleGET' function reflects the +menu structure. What is missing here is the link for the image we +generate. In an event-driven environment, request, generation, and +delivery of images are separated. + + Notice the way we initialize the `GnuPlot' command string for the +pipe. By default, GNUPlot outputs the generated image via standard +output, as well as the results of `print'(ed) calculations via standard +error. The redirection causes standard error to be mixed into standard +output, enabling us to read results of calculations with `getline'. By +initializing the statistical parameters with some meaningful defaults, +we make sure the user gets an image the first time he uses the program. + + Following is the rather long function `HandleGET', which implements +the contents of this service by reacting to the different kinds of +requests from the browser. Before you start playing with this script, +make sure that your browser supports JavaScript and that it also has +this option switched on. The script uses a short snippet of JavaScript +code for delayed opening of a window with an image. A more detailed +explanation follows: + + function HandleGET() { + if(MENU[2] == "AboutServer") { + Document = "This is a GUI for a statistical computation.\ + It compares means and variances of two distributions.\ + It is implemented as one GAWK script and uses GNUPLOT." + } else if (MENU[2] == "EnterParameters") { + Document = "" + if ("m1" in GETARG) { # are there parameters to compare? + Document = Document "" + m1 = GETARG["m1"]; v1 = GETARG["v1"]; n1 = GETARG["n1"] + m2 = GETARG["m2"]; v2 = GETARG["v2"]; n2 = GETARG["n2"] + t = (m1-m2)/sqrt(v1/n1+v2/n2) + df = (v1/n1+v2/n2)*(v1/n1+v2/n2)/((v1/n1)*(v1/n1)/(n1-1) \ + + (v2/n2)*(v2/n2) /(n2-1)) + if (v1>v2) { + f = v1/v2 + df1 = n1 - 1 + df2 = n2 - 1 + } else { + f = v2/v1 + df1 = n2 - 1 + df2 = n1 - 1 + } + print "pt=ibeta(" df/2 ",0.5," df/(df+t*t) ")" |& GnuPlot + print "pF=2.0*ibeta(" df2/2 "," df1/2 "," \ + df2/(df2+df1*f) ")" |& GnuPlot + print "print pt, pF" |& GnuPlot + RS="\n"; GnuPlot |& getline; RS="\r\n" # $1 is pt, $2 is pF + print "invsqrt2pi=1.0/sqrt(2.0*pi)" |& GnuPlot + print "nd(x)=invsqrt2pi/sd*exp(-0.5*((x-mu)/sd)**2)" |& GnuPlot + print "set term png small color" |& GnuPlot + #print "set term postscript color" |& GnuPlot + #print "set term gif medium size 320,240" |& GnuPlot + print "set yrange[-0.3:]" |& GnuPlot + print "set label 'p(m1=m2) =" $1 "' at 0,-0.1 left" |& GnuPlot + print "set label 'p(v1=v2) =" $2 "' at 0,-0.2 left" |& GnuPlot + print "plot mu=" m1 ",sd=" sqrt(v1) ", nd(x) title 'sample 1',\ + mu=" m2 ",sd=" sqrt(v2) ", nd(x) title 'sample 2'" |& GnuPlot + print "quit" |& GnuPlot + GnuPlot |& getline Image + while ((GnuPlot |& getline) > 0) + Image = Image RS $0 + close(GnuPlot) + } + Document = Document "\ +

Do these samples have the same Gaussian distribution?

\ +
\ + \ + + \ + + \ + + \ + \ + + \ + + \ + + \ + \ +
1. Mean 1. Variance1. Count
2. Mean 2. Variance2. Count

" + } else if (MENU[2] ~ "Image") { + Reason = "OK" ORS "Content-type: image/png" + #Reason = "OK" ORS "Content-type: application/x-postscript" + #Reason = "OK" ORS "Content-type: image/gif" + Header = Footer = "" + Document = Image + } + } + + As usual, we give a short description of the service in the first +menu choice. The third menu choice shows us that generation and +presentation of an image are two separate actions. While the latter +takes place quite instantly in the third menu choice, the former takes +place in the much longer second choice. Image data passes from the +generating action to the presenting action via the variable `Image' +that contains a complete `.png' image, which is otherwise stored in a +file. If you prefer `.ps' or `.gif' images over the default `.png' +images, you may select these options by uncommenting the appropriate +lines. But remember to do so in two places: when telling GNUPlot which +kind of images to generate, and when transmitting the image at the end +of the program. + + Looking at the end of the program, the way we pass the +`Content-type' to the browser is a bit unusual. It is appended to the +`OK' of the first header line to make sure the type information becomes +part of the header. The other variables that get transmitted across +the network are made empty, because in this case we do not have an HTML +document to transmit, but rather raw image data to contain in the body. + + Most of the work is done in the second menu choice. It starts with a +strange JavaScript code snippet. When first implementing this server, +we used a short `""' here. But then +browsers got smarter and tried to improve on speed by requesting the +image and the HTML code at the same time. When doing this, the browser +tries to build up a connection for the image request while the request +for the HTML text is not yet completed. The browser tries to connect to +the `gawk' server on port 8080 while port 8080 is still in use for +transmission of the HTML text. The connection for the image cannot be +built up, so the image appears as "broken" in the browser window. We +solved this problem by telling the browser to open a separate window +for the image, but only after a delay of 1000 milliseconds. By this +time, the server should be ready for serving the next request. + + But there is one more subtlety in the JavaScript code. Each time +the JavaScript code opens a window for the image, the name of the image +is appended with a timestamp (`systime'). Why this constant change of +name for the image? Initially, we always named the image `Image', but +then the Netscape browser noticed the name had _not_ changed since the +previous request and displayed the previous image (caching behavior). +The server core is implemented so that browsers are told _not_ to cache +anything. Obviously HTTP requests do not always work as expected. One +way to circumvent the cache of such overly smart browsers is to change +the name of the image with each request. These three lines of JavaScript +caused us a lot of trouble. + + The rest can be broken down into two phases. At first, we check if +there are statistical parameters. When the program is first started, +there usually are no parameters because it enters the page coming from +the top menu. Then, we only have to present the user a form that he +can use to change statistical parameters and submit them. Subsequently, +the submission of the form causes the execution of the first phase +because _now_ there _are_ parameters to handle. + + Now that we have parameters, we know there will be an image +available. Therefore we insert the JavaScript code here to initiate +the opening of the image in a separate window. Then, we prepare some +variables that will be passed to GNUPlot for calculation of the +probabilities. Prior to reading the results, we must temporarily change +`RS' because GNUPlot separates lines with newlines. After instructing +GNUPlot to generate a `.png' (or `.ps' or `.gif') image, we initiate +the insertion of some text, explaining the resulting probabilities. The +final `plot' command actually generates the image data. This raw binary +has to be read in carefully without adding, changing, or deleting a +single byte. Hence the unusual initialization of `Image' and completion +with a `while' loop. + + When using this server, it soon becomes clear that it is far from +being perfect. It mixes source code of six scripting languages or +protocols: + + * GNU `awk' implements a server for the protocol: + + * HTTP which transmits: + + * HTML text which contains a short piece of: + + * JavaScript code opening a separate window. + + * A Bourne shell script is used for piping commands into: + + * GNUPlot to generate the image to be opened. + + After all this work, the GNUPlot image opens in the JavaScript window +where it can be viewed by the user. + + It is probably better not to mix up so many different languages. +The result is not very readable. Furthermore, the statistical part of +the server does not take care of invalid input. Among others, using +negative variances will cause invalid results. + + ---------- Footnotes ---------- + + (1) Due to licensing problems, the default installation of GNUPlot +disables the generation of `.gif' files. If your installed version +does not accept `set term gif', just download and install the most +recent version of GNUPlot and the GD library +(http://www.boutell.com/gd/) by Thomas Boutell. Otherwise you still +have the chance to generate some ASCII-art style images with GNUPlot by +using `set term dumb'. (We tried it and it worked.) + + +File: gawkinet.info, Node: MAZE, Next: MOBAGWHO, Prev: STATIST, Up: Some Applications and Techniques + +MAZE: Walking Through a Maze In Virtual Reality +=============================================== + + In the long run, every program becomes rococo, and then rubble. + Alan Perlis + + By now, we know how to present arbitrary `Content-type's to a +browser. In this node, our server will present a 3D world to our +browser. The 3D world is described in a scene description language +(VRML, Virtual Reality Modeling Language) that allows us to travel +through a perspective view of a 2D maze with our browser. Browsers with +a VRML plugin enable exploration of this technology. We could do one of +those boring `Hello world' examples here, that are usually presented +when introducing novices to VRML. If you have never written any VRML +code, have a look at the VRML FAQ. Presenting a static VRML scene is a +bit trivial; in order to expose `gawk''s new capabilities, we will +present a dynamically generated VRML scene. The function `SetUpServer' +is very simple because it only sets the default HTML page and +initializes the random number generator. As usual, the surrounding +server lets you browse the maze. + + function SetUpServer() { + TopHeader = "Walk through a maze" + TopDoc = "\ +

Please choose one of the following actions:

\ + " + TopFooter = "" + srand() + } + + The function `HandleGET' is a bit longer because it first computes +the maze and afterwards generates the VRML code that is sent across the +network. As shown in the STATIST example (*note STATIST::), we set the +type of the content to VRML and then store the VRML representation of +the maze as the page content. We assume that the maze is stored in a 2D +array. Initially, the maze consists of walls only. Then, we add an +entry and an exit to the maze and let the rest of the work be done by +the function `MakeMaze'. Now, only the wall fields are left in the +maze. By iterating over the these fields, we generate one line of VRML +code for each wall field. + + function HandleGET() { + if (MENU[2] == "AboutServer") { + Document = "If your browser has a VRML 2 plugin,\ + this server shows you a simple VRML scene." + } else if (MENU[2] == "VRMLtest") { + XSIZE = YSIZE = 11 # initially, everything is wall + for (y = 0; y < YSIZE; y++) + for (x = 0; x < XSIZE; x++) + Maze[x, y] = "#" + delete Maze[0, 1] # entry is not wall + delete Maze[XSIZE-1, YSIZE-2] # exit is not wall + MakeMaze(1, 1) + Document = "\ + #VRML V2.0 utf8\n\ + Group {\n\ + children [\n\ + PointLight {\n\ + ambientIntensity 0.2\n\ + color 0.7 0.7 0.7\n\ + location 0.0 8.0 10.0\n\ + }\n\ + DEF B1 Background {\n\ + skyColor [0 0 0, 1.0 1.0 1.0 ]\n\ + skyAngle 1.6\n\ + groundColor [1 1 1, 0.8 0.8 0.8, 0.2 0.2 0.2 ]\n\ + groundAngle [ 1.2 1.57 ]\n\ + }\n\ + DEF Wall Shape {\n\ + geometry Box {size 1 1 1}\n\ + appearance Appearance { material Material { diffuseColor 0 0 1 } }\n\ + }\n\ + DEF Entry Viewpoint {\n\ + position 0.5 1.0 5.0\n\ + orientation 0.0 0.0 -1.0 0.52\n\ + }\n" + for (i in Maze) { + split(i, t, SUBSEP) + Document = Document " Transform { translation " + Document = Document t[1] " 0 -" t[2] " children USE Wall }\n" + } + Document = Document " ] # end of group for world\n}" + Reason = "OK" ORS "Content-type: model/vrml" + Header = Footer = "" + } + } + + Finally, we have a look at `MakeMaze', the function that generates +the `Maze' array. When entered, this function assumes that the array +has been initialized so that each element represents a wall element and +the maze is initially full of wall elements. Only the entrance and the +exit of the maze should have been left free. The parameters of the +function tell us which element must be marked as not being a wall. +After this, we take a look at the four neighbouring elements and +remember which we have already treated. Of all the neighbouring +elements, we take one at random and walk in that direction. Therefore, +the wall element in that direction has to be removed and then, we call +the function recursively for that element. The maze is only completed +if we iterate the above procedure for _all_ neighbouring elements (in +random order) and for our present element by recursively calling the +function for the present element. This last iteration could have been +done in a loop, but it is done much simpler recursively. + + Notice that elements with coordinates that are both odd are assumed +to be on our way through the maze and the generating process cannot +terminate as long as there is such an element not being `delete'd. All +other elements are potentially part of the wall. + + function MakeMaze(x, y) { + delete Maze[x, y] # here we are, we have no wall here + p = 0 # count unvisited fields in all directions + if (x-2 SUBSEP y in Maze) d[p++] = "-x" + if (x SUBSEP y-2 in Maze) d[p++] = "-y" + if (x+2 SUBSEP y in Maze) d[p++] = "+x" + if (x SUBSEP y+2 in Maze) d[p++] = "+y" + if (p>0) { # if there are univisited fields, go there + p = int(p*rand()) # choose one unvisited field at random + if (d[p] == "-x") { delete Maze[x - 1, y]; MakeMaze(x - 2, y) + } else if (d[p] == "-y") { delete Maze[x, y - 1]; MakeMaze(x, y - 2) + } else if (d[p] == "+x") { delete Maze[x + 1, y]; MakeMaze(x + 2, y) + } else if (d[p] == "+y") { delete Maze[x, y + 1]; MakeMaze(x, y + 2) + } # we are back from recursion + MakeMaze(x, y); # try again while there are unvisited fields + } + } + + +File: gawkinet.info, Node: MOBAGWHO, Next: STOXPRED, Prev: MAZE, Up: Some Applications and Techniques + +MOBAGWHO: a Simple Mobile Agent +=============================== + + There are two ways of constructing a software design: One way is to + make it so simple that there are obviously no deficiencies, and the + other way is to make it so complicated that there are no obvious + deficiencies. + C. A. R. Hoare + + A "mobile agent" is a program that can be dispatched from a computer +and transported to a remote server for execution. This is called +"migration", which means that a process on another system is started +that is independent from its originator. Ideally, it wanders through a +network while working for its creator or owner. In places like the UMBC +Agent Web, people are quite confident that (mobile) agents are a +software engineering paradigm that enables us to significantly increase +the efficiency of our work. Mobile agents could become the mediators +between users and the networking world. For an unbiased view at this +technology, see the remarkable paper `Mobile Agents: Are they a good +idea?'.(1) + + When trying to migrate a process from one system to another, a +server process is needed on the receiving side. Depending on the kind +of server process, several ways of implementation come to mind. How +the process is implemented depends upon the kind of server process: + + * HTTP can be used as the protocol for delivery of the migrating + process. In this case, we use a common web server as the receiving + server process. A universal CGI script mediates between migrating + process and web server. Each server willing to accept migrating + agents makes this universal service available. HTTP supplies the + `POST' method to transfer some data to a file on the web server. + When a CGI script is called remotely with the `POST' method + instead of the usual `GET' method, data is transmitted from the + client process to the standard input of the server's CGI script. + So, to implement a mobile agent, we must not only write the agent + program to start on the client side, but also the CGI script to + receive the agent on the server side. + + * The `PUT' method can also be used for migration. HTTP does not + require a CGI script for migration via `PUT'. However, with common + web servers there is no advantage to this solution, because web + servers such as Apache require explicit activation of a special + `PUT' script. + + * `Agent Tcl' pursues a different course; it relies on a dedicated + server process with a dedicated protocol specialized for receiving + mobile agents. + + Our agent example abuses a common web server as a migration tool. +So, it needs a universal CGI script on the receiving side (the web +server). The receiving script is activated with a `POST' request when +placed into a location like `/httpd/cgi-bin/PostAgent.sh'. Make sure +that the server system uses a version of `gawk' that supports network +access (Version 3.1 or later; verify with `gawk --version'). + + #!/bin/sh + MobAg=/tmp/MobileAgent.$$ + # direct script to mobile agent file + cat > $MobAg + # execute agent concurrently + gawk -f $MobAg $MobAg > /dev/null & + # HTTP header, terminator and body + gawk 'BEGIN { print "\r\nAgent started" }' + rm $MobAg # delete script file of agent + + By making its process id (`$$') part of the unique file name, the +script avoids conflicts between concurrent instances of the script. +First, all lines from standard input (the mobile agent's source code) +are copied into this unique file. Then, the agent is started as a +concurrent process and a short message reporting this fact is sent to +the submitting client. Finally, the script file of the mobile agent is +removed because it is no longer needed. Although it is a short script, +there are several noteworthy points: + +Security + _There is none_. In fact, the CGI script should never be made + available on a server that is part of the Internet because everyone + would be allowed to execute arbitrary commands with it. This + behavior is acceptable only when performing rapid prototyping. + +Self-Reference + Each migrating instance of an agent is started in a way that + enables it to read its own source code from standard input and use + the code for subsequent migrations. This is necessary because it + needs to treat the agent's code as data to transmit. `gawk' is not + the ideal language for such a job. Lisp and Tcl are more suitable + because they do not make a distinction between program code and + data. + +Independence + After migration, the agent is not linked to its former home in any + way. By reporting `Agent started', it waves "Goodbye" to its + origin. The originator may choose to terminate or not. + + The originating agent itself is started just like any other +command-line script, and reports the results on standard output. By +letting the name of the original host migrate with the agent, the agent +that migrates to a host far away from its origin can report the result +back home. Having arrived at the end of the journey, the agent +establishes a connection and reports the results. This is the reason +for determining the name of the host with `uname -n' and storing it in +`MyOrigin' for later use. We may also set variables with the `-v' +option from the command line. This interactivity is only of importance +in the context of starting a mobile agent; therefore this `BEGIN' +pattern and its action do not take part in migration: + + BEGIN { + if (ARGC != 2) { + print "MOBAG - a simple mobile agent" + print "CALL:\n gawk -f mobag.awk mobag.awk" + print "IN:\n the name of this script as a command-line parameter" + print "PARAM:\n -v MyOrigin=myhost.com" + print "OUT:\n the result on stdout" + print "JK 29.03.1998 01.04.1998" + exit + } + if (MyOrigin == "") { + "uname -n" | getline MyOrigin + close("uname -n") + } + } + + Since `gawk' cannot manipulate and transmit parts of the program +directly, the source code is read and stored in strings. Therefore, +the program scans itself for the beginning and the ending of functions. +Each line in between is appended to the code string until the end of +the function has been reached. A special case is this part of the +program itself. It is not a function. Placing a similar framework +around it causes it to be treated like a function. Notice that this +mechanism works for all the functions of the source code, but it cannot +guarantee that the order of the functions is preserved during migration: + + #ReadMySelf + /^function / { FUNC = $2 } + /^END/ || /^#ReadMySelf/ { FUNC = $1 } + FUNC != "" { MOBFUN[FUNC] = MOBFUN[FUNC] RS $0 } + (FUNC != "") && (/^}/ || /^#EndOfMySelf/) \ + { FUNC = "" } + #EndOfMySelf + + The web server code in *Note A Web Service with Interaction: +Interacting Service, was first developed as a site-independent core. +Likewise, the `gawk'-based mobile agent starts with an +agent-independent core, to which can be appended application-dependent +functions. What follows is the only application-independent function +needed for the mobile agent: + + function migrate(Destination, MobCode, Label) { + MOBVAR["Label"] = Label + MOBVAR["Destination"] = Destination + RS = ORS = "\r\n" + HttpService = "/inet/tcp/0/" Destination + for (i in MOBFUN) + MobCode = (MobCode "\n" MOBFUN[i]) + MobCode = MobCode "\n\nBEGIN {" + for (i in MOBVAR) + MobCode = (MobCode "\n MOBVAR[\"" i "\"] = \"" MOBVAR[i] "\"") + MobCode = MobCode "\n}\n" + print "POST /cgi-bin/PostAgent.sh HTTP/1.0" |& HttpService + print "Content-length:", length(MobCode) ORS |& HttpService + printf "%s", MobCode |& HttpService + while ((HttpService |& getline) > 0) + print $0 + close(HttpService) + } + + The `migrate' function prepares the aforementioned strings +containing the program code and transmits them to a server. A +consequence of this modular approach is that the `migrate' function +takes some parameters that aren't needed in this application, but that +will be in future ones. Its mandatory parameter `Destination' holds the +name (or IP address) of the server that the agent wants as a host for +its code. The optional parameter `MobCode' may contain some `gawk' code +that is inserted during migration in front of all other code. The +optional parameter `Label' may contain a string that tells the agent +what to do in program execution after arrival at its new home site. One +of the serious obstacles in implementing a framework for mobile agents +is that it does not suffice to migrate the code. It is also necessary +to migrate the state of execution of the agent. In contrast to `Agent +Tcl', this program does not try to migrate the complete set of +variables. The following conventions are used: + + * Each variable in an agent program is local to the current host and + does _not_ migrate. + + * The array `MOBFUN' shown above is an exception. It is handled by + the function `migrate' and does migrate with the application. + + * The other exception is the array `MOBVAR'. Each variable that + takes part in migration has to be an element of this array. + `migrate' also takes care of this. + + Now it's clear what happens to the `Label' parameter of the function +`migrate'. It is copied into `MOBVAR["Label"]' and travels alongside +the other data. Since travelling takes place via HTTP, records must be +separated with `"\r\n"' in `RS' and `ORS' as usual. The code assembly +for migration takes place in three steps: + + * Iterate over `MOBFUN' to collect all functions verbatim. + + * Prepare a `BEGIN' pattern and put assignments to mobile variables + into the action part. + + * Transmission itself resembles GETURL: the header with the request + and the `Content-length' is followed by the body. In case there is + any reply over the network, it is read completely and echoed to + standard output to avoid irritating the server. + + The application-independent framework is now almost complete. What +follows is the `END' pattern that is executed when the mobile agent has +finished reading its own code. First, it checks whether it is already +running on a remote host or not. In case initialization has not yet +taken place, it starts `MyInit'. Otherwise (later, on a remote host), it +starts `MyJob': + + END { + if (ARGC != 2) exit # stop when called with wrong parameters + if (MyOrigin != "") # is this the originating host? + MyInit() # if so, initialize the application + else # we are on a host with migrated data + MyJob() # so we do our job + } + + All that's left to extend the framework into a complete application +is to write two application-specific functions: `MyInit' and `MyJob'. +Keep in mind that the former is executed once on the originating host, +while the latter is executed after each migration: + + function MyInit() { + MOBVAR["MyOrigin"] = MyOrigin + MOBVAR["Machines"] = "localhost/80 max/80 moritz/80 castor/80" + split(MOBVAR["Machines"], Machines) # which host is the first? + migrate(Machines[1], "", "") # go to the first host + while (("/inet/tcp/8080/0/0" |& getline) > 0) # wait for result + print $0 # print result + close("/inet/tcp/8080/0/0") + } + + As mentioned earlier, this agent takes the name of its origin +(`MyOrigin') with it. Then, it takes the name of its first destination +and goes there for further work. Notice that this name has the port +number of the web server appended to the name of the server, because +the function `migrate' needs it this way to create the `HttpService' +variable. Finally, it waits for the result to arrive. The `MyJob' +function runs on the remote host: + + function MyJob() { + # forget this host + sub(MOBVAR["Destination"], "", MOBVAR["Machines"]) + MOBVAR["Result"]=MOBVAR["Result"] SUBSEP SUBSEP MOBVAR["Destination"] ":" + while (("who" | getline) > 0) # who is logged in? + MOBVAR["Result"] = MOBVAR["Result"] SUBSEP $0 + close("who") + if (index(MOBVAR["Machines"], "/") > 0) { # any more machines to visit? + split(MOBVAR["Machines"], Machines) # which host is next? + migrate(Machines[1], "", "") # go there + } else { # no more machines + gsub(SUBSEP, "\n", MOBVAR["Result"]) # send result to origin + print MOBVAR["Result"] |& "/inet/tcp/0/" MOBVAR["MyOrigin"] "/8080" + close("/inet/tcp/0/" MOBVAR["MyOrigin"] "/8080") + } + } + + After migrating, the first thing to do in `MyJob' is to delete the +name of the current host from the list of hosts to visit. Now, it is +time to start the real work by appending the host's name to the result +string, and reading line by line who is logged in on this host. A very +annoying circumstance is the fact that the elements of `MOBVAR' cannot +hold the newline character (`"\n"'). If they did, migration of this +string did not work because the string didn't obey the syntax rule for +a string in `gawk'. `SUBSEP' is used as a temporary replacement. If +the list of hosts to visit holds at least one more entry, the agent +migrates to that place to go on working there. Otherwise, we replace +the `SUBSEP's with a newline character in the resulting string, and +report it to the originating host, whose name is stored in +`MOBVAR["MyOrigin"]'. + + ---------- Footnotes ---------- + + (1) `http://www.research.ibm.com/massive/mobag.ps' + + +File: gawkinet.info, Node: STOXPRED, Next: PROTBASE, Prev: MOBAGWHO, Up: Some Applications and Techniques + +STOXPRED: Stock Market Prediction As A Service +============================================== + + Far out in the uncharted backwaters of the unfashionable end of + the Western Spiral arm of the Galaxy lies a small unregarded + yellow sun. + + Orbiting this at a distance of roughly ninety-two million miles is + an utterly insignificant little blue-green planet whose + ape-descendent life forms are so amazingly primitive that they + still think digital watches are a pretty neat idea. + + This planet has -- or rather had -- a problem, which was this: + most of the people living on it were unhappy for pretty much of + the time. Many solutions were suggested for this problem, but + most of these were largely concerned with the movements of small + green pieces of paper, which is odd because it wasn't the small + green pieces of paper that were unhappy. + Douglas Adams, `The Hitch Hiker's Guide to the Galaxy' + + Valuable services on the Internet are usually _not_ implemented as +mobile agents. There are much simpler ways of implementing services. +All Unix systems provide, for example, the `cron' service. Unix system +users can write a list of tasks to be done each day, each week, twice a +day, or just once. The list is entered into a file named `crontab'. +For example, to distribute a newsletter on a daily basis this way, use +`cron' for calling a script each day early in the morning. + + # run at 8 am on weekdays, distribute the newsletter + 0 8 * * 1-5 $HOME/bin/daily.job >> $HOME/log/newsletter 2>&1 + + The script first looks for interesting information on the Internet, +assembles it in a nice form and sends the results via email to the +customers. + + The following is an example of a primitive newsletter on stock +market prediction. It is a report which first tries to predict the +change of each share in the Dow Jones Industrial Index for the +particular day. Then it mentions some especially promising shares as +well as some shares which look remarkably bad on that day. The report +ends with the usual disclaimer which tells every child _not_ to try +this at home and hurt anybody. + + Good morning Uncle Scrooge, + + This is your daily stock market report for Monday, October 16, 2000. + Here are the predictions for today: + + AA neutral + GE up + JNJ down + MSFT neutral + ... + UTX up + DD down + IBM up + MO down + WMT up + DIS up + INTC up + MRK down + XOM down + EK down + IP down + + The most promising shares for today are these: + + INTC http://biz.yahoo.com/n/i/intc.html + + The stock shares to avoid today are these: + + EK http://biz.yahoo.com/n/e/ek.html + IP http://biz.yahoo.com/n/i/ip.html + DD http://biz.yahoo.com/n/d/dd.html + ... + + The script as a whole is rather long. In order to ease the pain of +studying other people's source code, we have broken the script up into +meaningful parts which are invoked one after the other. The basic +structure of the script is as follows: + + BEGIN { + Init() + ReadQuotes() + CleanUp() + Prediction() + Report() + SendMail() + } + + The earlier parts store data into variables and arrays which are +subsequently used by later parts of the script. The `Init' function +first checks if the script is invoked correctly (without any +parameters). If not, it informs the user of the correct usage. What +follows are preparations for the retrieval of the historical quote +data. The names of the 30 stock shares are stored in an array `name' +along with the current date in `day', `month', and `year'. + + All users who are separated from the Internet by a firewall and have +to direct their Internet accesses to a proxy must supply the name of +the proxy to this script with the `-v Proxy=NAME' option. For most +users, the default proxy and port number should suffice. + + function Init() { + if (ARGC != 1) { + print "STOXPRED - daily stock share prediction" + print "IN:\n no parameters, nothing on stdin" + print "PARAM:\n -v Proxy=MyProxy -v ProxyPort=80" + print "OUT:\n commented predictions as email" + print "JK 09.10.2000" + exit + } + # Remember ticker symbols from Dow Jones Industrial Index + StockCount = split("AA GE JNJ MSFT AXP GM JPM PG BA HD KO \ + SBC C HON MCD T CAT HWP MMM UTX DD IBM MO WMT DIS INTC \ + MRK XOM EK IP", name); + # Remember the current date as the end of the time series + day = strftime("%d") + month = strftime("%m") + year = strftime("%Y") + if (Proxy == "") Proxy = "chart.yahoo.com" + if (ProxyPort == 0) ProxyPort = 80 + YahooData = "/inet/tcp/0/" Proxy "/" ProxyPort + } + + There are two really interesting parts in the script. One is the +function which reads the historical stock quotes from an Internet +server. The other is the one that does the actual prediction. In the +following function we see how the quotes are read from the Yahoo +server. The data which comes from the server is in CSV format +(comma-separated values): + + Date,Open,High,Low,Close,Volume + 9-Oct-00,22.75,22.75,21.375,22.375,7888500 + 6-Oct-00,23.8125,24.9375,21.5625,22,10701100 + 5-Oct-00,24.4375,24.625,23.125,23.50,5810300 + + Lines contain values of the same time instant, whereas columns are +separated by commas and contain the kind of data that is described in +the header (first) line. At first, `gawk' is instructed to separate +columns by commas (`FS = ","'). In the loop that follows, a connection +to the Yahoo server is first opened, then a download takes place, and +finally the connection is closed. All this happens once for each ticker +symbol. In the body of this loop, an Internet address is built up as a +string according to the rules of the Yahoo server. The starting and +ending date are chosen to be exactly the same, but one year apart in +the past. All the action is initiated within the `printf' command which +transmits the request for data to the Yahoo server. + + In the inner loop, the server's data is first read and then scanned +line by line. Only lines which have six columns and the name of a month +in the first column contain relevant data. This data is stored in the +two-dimensional array `quote'; one dimension being time, the other +being the ticker symbol. During retrieval of the first stock's data, +the calendar names of the time instances are stored in the array `day' +because we need them later. + + function ReadQuotes() { + # Retrieve historical data for each ticker symbol + FS = "," + for (stock = 1; stock <= StockCount; stock++) { + URL = "http://chart.yahoo.com/table.csv?s=" name[stock] \ + "&a=" month "&b=" day "&c=" year-1 \ + "&d=" month "&e=" day "&f=" year \ + "g=d&q=q&y=0&z=" name[stock] "&x=.csv" + printf("GET " URL " HTTP/1.0\r\n\r\n") |& YahooData + while ((YahooData |& getline) > 0) { + if (NF == 6 && $1 ~ /Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec/) { + if (stock == 1) + days[++daycount] = $1; + quote[$1, stock] = $5 + } + } + close(YahooData) + } + FS = " " + } + + Now that we _have_ the data, it can be checked once again to make +sure that no individual stock is missing or invalid, and that all the +stock quotes are aligned correctly. Furthermore, we renumber the time +instances. The most recent day gets day number 1 and all other days get +consecutive numbers. All quotes are rounded toward the nearest whole +number in US Dollars. + + function CleanUp() { + # clean up time series; eliminate incomplete data sets + for (d = 1; d <= daycount; d++) { + for (stock = 1; stock <= StockCount; stock++) + if (! ((days[d], stock) in quote)) + stock = StockCount + 10 + if (stock > StockCount + 1) + continue + datacount++ + for (stock = 1; stock <= StockCount; stock++) + data[datacount, stock] = int(0.5 + quote[days[d], stock]) + } + delete quote + delete days + } + + Now we have arrived at the second really interesting part of the +whole affair. What we present here is a very primitive prediction +algorithm: _If a stock fell yesterday, assume it will also fall today; +if it rose yesterday, assume it will rise today_. (Feel free to +replace this algorithm with a smarter one.) If a stock changed in the +same direction on two consecutive days, this is an indication which +should be highlighted. Two-day advances are stored in `hot' and +two-day declines in `avoid'. + + The rest of the function is a sanity check. It counts the number of +correct predictions in relation to the total number of predictions one +could have made in the year before. + + function Prediction() { + # Predict each ticker symbol by prolonging yesterday's trend + for (stock = 1; stock <= StockCount; stock++) { + if (data[1, stock] > data[2, stock]) { + predict[stock] = "up" + } else if (data[1, stock] < data[2, stock]) { + predict[stock] = "down" + } else { + predict[stock] = "neutral" + } + if ((data[1, stock] > data[2, stock]) && (data[2, stock] > data[3, stock])) + hot[stock] = 1 + if ((data[1, stock] < data[2, stock]) && (data[2, stock] < data[3, stock])) + avoid[stock] = 1 + } + # Do a plausibility check: how many predictions proved correct? + for (s = 1; s <= StockCount; s++) { + for (d = 1; d <= datacount-2; d++) { + if (data[d+1, s] > data[d+2, s]) { + UpCount++ + } else if (data[d+1, s] < data[d+2, s]) { + DownCount++ + } else { + NeutralCount++ + } + if (((data[d, s] > data[d+1, s]) && (data[d+1, s] > data[d+2, s])) || + ((data[d, s] < data[d+1, s]) && (data[d+1, s] < data[d+2, s])) || + ((data[d, s] == data[d+1, s]) && (data[d+1, s] == data[d+2, s]))) + CorrectCount++ + } + } + } + + At this point the hard work has been done: the array `predict' +contains the predictions for all the ticker symbols. It is up to the +function `Report' to find some nice words to introduce the desired +information. + + function Report() { + # Generate report + report = "\nThis is your daily " + report = report "stock market report for "strftime("%A, %B %d, %Y")".\n" + report = report "Here are the predictions for today:\n\n" + for (stock = 1; stock <= StockCount; stock++) + report = report "\t" name[stock] "\t" predict[stock] "\n" + for (stock in hot) { + if (HotCount++ == 0) + report = report "\nThe most promising shares for today are these:\n\n" + report = report "\t" name[stock] "\t\thttp://biz.yahoo.com/n/" \ + tolower(substr(name[stock], 1, 1)) "/" tolower(name[stock]) ".html\n" + } + for (stock in avoid) { + if (AvoidCount++ == 0) + report = report "\nThe stock shares to avoid today are these:\n\n" + report = report "\t" name[stock] "\t\thttp://biz.yahoo.com/n/" \ + tolower(substr(name[stock], 1, 1)) "/" tolower(name[stock]) ".html\n" + } + report = report "\nThis sums up to " HotCount+0 " winners and " AvoidCount+0 + report = report " losers. When using this kind\nof prediction scheme for" + report = report " the 12 months which lie behind us,\nwe get " UpCount + report = report " 'ups' and " DownCount " 'downs' and " NeutralCount + report = report " 'neutrals'. Of all\nthese " UpCount+DownCount+NeutralCount + report = report " predictions " CorrectCount " proved correct next day.\n" + report = report "A success rate of "\ + int(100*CorrectCount/(UpCount+DownCount+NeutralCount)) "%.\n" + report = report "Random choice would have produced a 33% success rate.\n" + report = report "Disclaimer: Like every other prediction of the stock\n" + report = report "market, this report is, of course, complete nonsense.\n" + report = report "If you are stupid enough to believe these predictions\n" + report = report "you should visit a doctor who can treat your ailment." + } + + The function `SendMail' goes through the list of customers and opens +a pipe to the `mail' command for each of them. Each one receives an +email message with a proper subject heading and is addressed with his +full name. + + function SendMail() { + # send report to customers + customer["uncle.scrooge@ducktown.gov"] = "Uncle Scrooge" + customer["more@utopia.org" ] = "Sir Thomas More" + customer["spinoza@denhaag.nl" ] = "Baruch de Spinoza" + customer["marx@highgate.uk" ] = "Karl Marx" + customer["keynes@the.long.run" ] = "John Maynard Keynes" + customer["bierce@devil.hell.org" ] = "Ambrose Bierce" + customer["laplace@paris.fr" ] = "Pierre Simon de Laplace" + for (c in customer) { + MailPipe = "mail -s 'Daily Stock Prediction Newsletter'" c + print "Good morning " customer[c] "," | MailPipe + print report "\n.\n" | MailPipe + close(MailPipe) + } + } + + Be patient when running the script by hand. Retrieving the data for +all the ticker symbols and sending the emails may take several minutes +to complete, depending upon network traffic and the speed of the +available Internet link. The quality of the prediction algorithm is +likely to be disappointing. Try to find a better one. Should you find +one with a success rate of more than 50%, please tell us about it! It +is only for the sake of curiosity, of course. `:-)' + + +File: gawkinet.info, Node: PROTBASE, Prev: STOXPRED, Up: Some Applications and Techniques + +PROTBASE: Searching Through A Protein Database +============================================== + + Hoare's Law of Large Problems: Inside every large problem is a + small problem struggling to get out. + + Yahoo's database of stock market data is just one among the many +large databases on the Internet. Another one is located at NCBI +(National Center for Biotechnology Information). Established in 1988 as +a national resource for molecular biology information, NCBI creates +public databases, conducts research in computational biology, develops +software tools for analyzing genome data, and disseminates biomedical +information. In this section, we look at one of NCBI's public services, +which is called BLAST (Basic Local Alignment Search Tool). + + You probably know that the information necessary for reproducing +living cells is encoded in the genetic material of the cells. The +genetic material is a very long chain of four base nucleotides. It is +the order of appearance (the sequence) of nucleotides which contains +the information about the substance to be produced. Scientists in +biotechnology often find a specific fragment, determine the nucleotide +sequence, and need to know where the sequence at hand comes from. This +is where the large databases enter the game. At NCBI, databases store +the knowledge about which sequences have ever been found and where they +have been found. When the scientist sends his sequence to the BLAST +service, the server looks for regions of genetic material in its +database which look the most similar to the delivered nucleotide +sequence. After a search time of some seconds or minutes the server +sends an answer to the scientist. In order to make access simple, NCBI +chose to offer their database service through popular Internet +protocols. There are four basic ways to use the so-called BLAST +services: + + * The easiest way to use BLAST is through the web. Users may simply + point their browsers at the NCBI home page and link to the BLAST + pages. NCBI provides a stable URL that may be used to perform + BLAST searches without interactive use of a web browser. This is + what we will do later in this section. A demonstration client and + a `README' file demonstrate how to access this URL. + + * Currently, `blastcl3' is the standard network BLAST client. You + can download `blastcl3' from the anonymous FTP location. + + * BLAST 2.0 can be run locally as a full executable and can be used + to run BLAST searches against private local databases, or + downloaded copies of the NCBI databases. BLAST 2.0 executables may + be found on the NCBI anonymous FTP server. + + * The NCBI BLAST Email server is the best option for people without + convenient access to the web. A similarity search can be performed + by sending a properly formatted mail message containing the + nucleotide or protein query sequence to . + The query sequence is compared against the specified database + using the BLAST algorithm and the results are returned in an email + message. For more information on formulating email BLAST searches, + you can send a message consisting of the word "HELP" to the same + address, . + + Our starting point is the demonstration client mentioned in the +first option. The `README' file that comes along with the client +explains the whole process in a nutshell. In the rest of this section, +we first show what such requests look like. Then we show how to use +`gawk' to implement a client in about 10 lines of code. Finally, we +show how to interpret the result returned from the service. + + Sequences are expected to be represented in the standard IUB/IUPAC +amino acid and nucleic acid codes, with these exceptions: lower-case +letters are accepted and are mapped into upper-case; a single hyphen or +dash can be used to represent a gap of indeterminate length; and in +amino acid sequences, `U' and `*' are acceptable letters (see below). +Before submitting a request, any numerical digits in the query sequence +should either be removed or replaced by appropriate letter codes (e.g., +`N' for unknown nucleic acid residue or `X' for unknown amino acid +residue). The nucleic acid codes supported are: + + A --> adenosine M --> A C (amino) + C --> cytidine S --> G C (strong) + G --> guanine W --> A T (weak) + T --> thymidine B --> G T C + U --> uridine D --> G A T + R --> G A (purine) H --> A C T + Y --> T C (pyrimidine) V --> G C A + K --> G T (keto) N --> A G C T (any) + - gap of indeterminate length + + Now you know the alphabet of nucleotide sequences. The last two lines +of the following example query show you such a sequence, which is +obviously made up only of elements of the alphabet just described. +Store this example query into a file named `protbase.request'. You are +now ready to send it to the server with the demonstration client. + + PROGRAM blastn + DATALIB month + EXPECT 0.75 + BEGIN + >GAWK310 the gawking gene GNU AWK + tgcttggctgaggagccataggacgagagcttcctggtgaagtgtgtttcttgaaatcat + caccaccatggacagcaaa + + The actual search request begins with the mandatory parameter +`PROGRAM' in the first column followed by the value `blastn' (the name +of the program) for searching nucleic acids. The next line contains +the mandatory search parameter `DATALIB' with the value `month' for the +newest nucleic acid sequences. The third line contains an optional +`EXPECT' parameter and the value desired for it. The fourth line +contains the mandatory `BEGIN' directive, followed by the query +sequence in FASTA/Pearson format. Each line of information must be +less than 80 characters in length. + + The "month" database contains all new or revised sequences released +in the last 30 days and is useful for searching against new sequences. +There are five different blast programs, `blastn' being the one that +compares a nucleotide query sequence against a nucleotide sequence +database. + + The last server directive that must appear in every request is the +`BEGIN' directive. The query sequence should immediately follow the +`BEGIN' directive and must appear in FASTA/Pearson format. A sequence +in FASTA/Pearson format begins with a single-line description. The +description line, which is required, is distinguished from the lines of +sequence data that follow it by having a greater-than (`>') symbol in +the first column. For the purposes of the BLAST server, the text of +the description is arbitrary. + + If you prefer to use a client written in `gawk', just store the +following 10 lines of code into a file named `protbase.awk' and use +this client instead. Invoke it with `gawk -f protbase.awk +protbase.request'. Then wait a minute and watch the result coming in. +In order to replicate the demonstration client's behaviour as closely +as possible, this client does not use a proxy server. We could also +have extended the client program in *Note Retrieving Web Pages: GETURL, +to implement the client request from `protbase.awk' as a special case. + + { request = request "\n" $0 } + + END { + BLASTService = "/inet/tcp/0/www.ncbi.nlm.nih.gov/80" + printf "POST /cgi-bin/BLAST/nph-blast_report HTTP/1.0\n" |& BLASTService + printf "Content-Length: " length(request) "\n\n" |& BLASTService + printf request |& BLASTService + while ((BLASTService |& getline) > 0) + print $0 + close(BLASTService) + } + + The demonstration client from NCBI is 214 lines long (written in C) +and it is not immediately obvious what it does. Our client is so short +that it _is_ obvious what it does. First it loops over all lines of the +query and stores the whole query into a variable. Then the script +establishes an Internet connection to the NCBI server and transmits the +query by framing it with a proper HTTP request. Finally it receives and +prints the complete result coming from the server. + + Now, let us look at the result. It begins with an HTTP header, which +you can ignore. Then there are some comments about the query having been +filtered to avoid spuriously high scores. After this, there is a +reference to the paper that describes the software being used for +searching the data base. After a repitition of the original query's +description we find the list of significant alignments: + + Sequences producing significant alignments: (bits) Value + + gb|AC021182.14|AC021182 Homo sapiens chromosome 7 clone RP11-733... 38 0.20 + gb|AC021056.12|AC021056 Homo sapiens chromosome 3 clone RP11-115... 38 0.20 + emb|AL160278.10|AL160278 Homo sapiens chromosome 9 clone RP11-57... 38 0.20 + emb|AL391139.11|AL391139 Homo sapiens chromosome X clone RP11-35... 38 0.20 + emb|AL365192.6|AL365192 Homo sapiens chromosome 6 clone RP3-421H... 38 0.20 + emb|AL138812.9|AL138812 Homo sapiens chromosome 11 clone RP1-276... 38 0.20 + gb|AC073881.3|AC073881 Homo sapiens chromosome 15 clone CTD-2169... 38 0.20 + + This means that the query sequence was found in seven human +chromosomes. But the value 0.20 (20%) means that the probability of an +accidental match is rather high (20%) in all cases and should be taken +into account. You may wonder what the first column means. It is a key +to the specific database in which this occurence was found. The unique +sequence identifiers reported in the search results can be used as +sequence retrieval keys via the NCBI server. The syntax of sequence +header lines used by the NCBI BLAST server depends on the database from +which each sequence was obtained. The table below lists the +identifiers for the databases from which the sequences were derived. + + Database Name Identifier Syntax + ============================ ======================== + GenBank gb|accession|locus + EMBL Data Library emb|accession|locus + DDBJ, DNA Database of Japan dbj|accession|locus + NBRF PIR pir||entry + Protein Research Foundation prf||name + SWISS-PROT sp|accession|entry name + Brookhaven Protein Data Bank pdb|entry|chain + Kabat's Sequences of Immuno... gnl|kabat|identifier + Patents pat|country|number + GenInfo Backbone Id bbs|number + + For example, an identifier might be `gb|AC021182.14|AC021182', where +the `gb' tag indicates that the identifier refers to a GenBank sequence, +`AC021182.14' is its GenBank ACCESSION, and `AC021182' is the GenBank +LOCUS. The identifier contains no spaces, so that a space indicates +the end of the identifier. + + Let us continue in the result listing. Each of the seven alignments +mentioned above is subsequently described in detail. We will have a +closer look at the first of them. + + >gb|AC021182.14|AC021182 Homo sapiens chromosome 7 clone RP11-733N23, WORKING DRAFT SEQUENCE, 4 + unordered pieces + Length = 176383 + + Score = 38.2 bits (19), Expect = 0.20 + Identities = 19/19 (100%) + Strand = Plus / Plus + + Query: 35 tggtgaagtgtgtttcttg 53 + ||||||||||||||||||| + Sbjct: 69786 tggtgaagtgtgtttcttg 69804 + + This alignment was located on the human chromosome 7. The fragment +on which part of the query was found had a total length of 176383. Only +19 of the nucleotides matched and the matching sequence ran from +character 35 to 53 in the query sequence and from 69786 to 69804 in the +fragment on chromosome 7. If you are still reading at this point, you +are probably interested in finding out more about Computational Biology +and you might appreciate the following hints. + + 1. There is a book called `Introduction to Computational Biology' by + Michael S. Waterman, which is worth reading if you are seriously + interested. You can find a good book review on the Internet. + + 2. While Waterman's book can explain to you the algorithms employed + internally in the database search engines, most practicioners + prefer to approach the subject differently. The applied side of + Computational Biology is called Bioinformatics, and emphasizes the + tools available for day-to-day work as well as how to actually + _use_ them. One of the very few affordable books on Bioinformatics + is `Developing Bioinformatics Computer Skills'. + + 3. The sequences _gawk_ and _gnuawk_ are in widespread use in the + genetic material of virtually every earthly living being. Let us + take this as a clear indication that the divine creator has + intended `gawk' to prevail over other scripting languages such as + `perl', `tcl', or `python' which are not even proper sequences. + (:-) + + +File: gawkinet.info, Node: Links, Next: GNU Free Documentation License, Prev: Some Applications and Techniques, Up: Top + +Related Links +************* + + This section lists the URLs for various items discussed in this +major node. They are presented in the order in which they appear. + +`Internet Programming with Python' + `http://www.fsbassociates.com/books/python.htm' + +`Advanced Perl Programming' + `http://www.oreilly.com/catalog/advperl' + +`Web Client Programming with Perl' + `http://www.oreilly.com/catalog/webclient' + +Richard Stevens's home page and book + `http://www.kohala.com/~rstevens' + +The SPAK home page + `http://www.userfriendly.net/linux/RPM/contrib/libc6/i386/spak-0.6b-1.i386.html' + +Volume III of `Internetworking with TCP/IP', by Comer and Stevens + `http://www.cs.purdue.edu/homes/dec/tcpip3s.cont.html' + +XBM Graphics File Format + `http://www.wotsit.org/download.asp?f=xbm' + +GNUPlot + `http://www.cs.dartmouth.edu/gnuplot_info.html' + +Mark Humphrys' Eliza page + `http://www.compapp.dcu.ie/~humphrys/eliza.html' + +Yahoo! Eliza Information + `http://dir.yahoo.com/Recreation/Games/Computer_Games/Internet_Games/Web_Games/Artificial_Intelligence' + +Java versions of Eliza + `http://www.tjhsst.edu/Psych/ch1/eliza.html' + +Java versions of Eliza with source code + `http://home.adelphia.net/~lifeisgood/eliza/eliza.htm' + +Eliza Programs with Explanations + `http://chayden.net/chayden/eliza/Eliza.shtml' + +Loebner Contest + `http://acm.org/~loebner/loebner-prize.htmlx' + +Tck/Tk Information + `http://www.scriptics.com/' + +Intel 80x86 Processors + `http://developer.intel.com/design/platform/embedpc/what_is.htm' + +AMD Elan Processors + `http://www.amd.com/products/epd/processors/4.32bitcont/32bitcont/index.html' + +XINU + `http://willow.canberra.edu.au/~chrisc/xinu.html' + +GNU/Linux + `http://uclinux.lineo.com/' + +Embedded PCs + `http://dir.yahoo.com/Business_and_Economy/Business_to_Business/Computers/Hardware/Embedded_Control/' + +MiniSQL + `http://www.hughes.com.au/library/' + +Market Share Surveys + `http://www.netcraft.com/survey' + +`Numerical Recipes in C: The Art of Scientific Computing' + `http://www.nr.com' + +VRML + `http://www.vrml.org' + +The VRML FAQ + `http://www.vrml.org/technicalinfo/specifications/specifications.htm#FAQ' + +The UMBC Agent Web + `http://www.cs.umbc.edu/agents' + +Apache Web Server + `http://www.apache.org' + +National Center for Biotechnology Information (NCBI) + `http://www.ncbi.nlm.nih.gov' + +Basic Local Alignment Search Tool (BLAST) + `http://www.ncbi.nlm.nih.gov/BLAST/blast_overview.html' + +NCBI Home Page + `http://www.ncbi.nlm.nih.gov' + +BLAST Pages + `http://www.ncbi.nlm.nih.gov/BLAST' + +BLAST Demonstration Client + `ftp://ncbi.nlm.nih.gov/blast/blasturl/' + +BLAST anonymous FTP location + `ftp://ncbi.nlm.nih.gov/blast/network/netblast/' + +BLAST 2.0 Executables + `ftp://ncbi.nlm.nih.gov/blast/executables/' + +IUB/IUPAC Amino Acid and Nucleic Acid Codes + `http://www.uthscsa.edu/geninfo/blastmail.html#item6' + +FASTA/Pearson Format + `http://www.ncbi.nlm.nih.gov/BLAST/fasta.html' + +Fasta/Pearson Sequence in Java + `http://www.kazusa.or.jp/java/codon_table_java/' + +Book Review of `Introduction to Computational Biology' + `http://www.acm.org/crossroads/xrds5-1/introcb.html' + +`Developing Bioinformatics Computer Skills' + `http://www.oreilly.com/catalog/bioskills/' + + +File: gawkinet.info, Node: GNU Free Documentation License, Next: Index, Prev: Links, Up: Top + +GNU Free Documentation License +****************************** + + Version 1.1, March 2000 + + Copyright (C) 2000 Free Software Foundation, Inc. + 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + + + 0. 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If + the Document does not specify a version number of this License, + you may choose any version ever published (not as a draft) by the + Free Software Foundation. + + +ADDENDUM: How to use this License for your documents +==================================================== + + To use this License in a document you have written, include a copy of +the License in the document and put the following copyright and license +notices just after the title page: + + + Copyright (C) YEAR YOUR NAME. + Permission is granted to copy, distribute and/or modify this document + under the terms of the GNU Free Documentation License, Version 1.1 + or any later version published by the Free Software Foundation; + with the Invariant Sections being LIST THEIR TITLES, with the + Front-Cover Texts being LIST, and with the Back-Cover Texts being LIST. + A copy of the license is included in the section entitled ``GNU + Free Documentation License''. +If you have no Invariant Sections, write "with no Invariant +Sections" instead of saying which ones are invariant. If you have no +Front-Cover Texts, write "no Front-Cover Texts" instead of "Front-Cover +Texts being LIST"; likewise for Back-Cover Texts. + + If your document contains nontrivial examples of program code, we +recommend releasing these examples in parallel under your choice of +free software license, such as the GNU General Public License, to +permit their use in free software. + + +File: gawkinet.info, Node: Index, Prev: GNU Free Documentation License, Up: Top + +Index +***** + +* Menu: + +* /inet/raw special files: File /inet/raw. +* /inet/tcp special files: File /inet/tcp. +* /inet/udp special files: File /inet/udp. +* agent <1>: MOBAGWHO. +* agent: Challenges. +* AI: Challenges. +* apache <1>: MOBAGWHO. +* apache: WEBGRAB. +* Bioinformatics: PROTBASE. +* BLAST, Basic Local Alignment Search Tool: PROTBASE. +* blocking: Making Connections. +* Boutell, Thomas: STATIST. +* CGI <1>: MOBAGWHO. +* CGI <2>: Interacting Service. +* CGI: Web page. +* client: Making Connections. +* Clinton, Bill: Challenges. +* Computational Biology: PROTBASE. +* Contest: Challenges. +* cron: STOXPRED. +* CSV format: STOXPRED. +* dark corner: File /inet/raw. +* Dow Jones Industrial Index: STOXPRED. +* ELIZA program: Simple Server. +* FASTA/Pearson format: PROTBASE. +* finger utility: Setting Up. +* FTP: Basic Protocols. +* getline built-in function: TCP Connecting. +* GETURL program: GETURL. +* gif image format <1>: STATIST. +* gif image format: Web page. +* GNU/Linux <1>: REMCONF. +* GNU/Linux <2>: Interacting. +* GNU/Linux: Troubleshooting. +* GNUPlot utility <1>: STATIST. +* GNUPlot utility: Interacting Service. +* GUI <1>: Simple Server. +* GUI: Interacting Service. +* Hoare, C.A.R. <1>: PROTBASE. +* Hoare, C.A.R.: MOBAGWHO. +* HTML: Web page. +* HTTP <1>: Web page. +* HTTP: Basic Protocols. +* HTTP server, core logic: Interacting Service. +* Humphrys, Mark: Simple Server. +* image format <1>: STATIST. +* image format: Interacting Service. +* JavaScript <1>: STATIST. +* JavaScript: Some Applications and Techniques. +* Linux <1>: REMCONF. +* Linux <2>: Interacting. +* Linux: Troubleshooting. +* Lisp: MOBAGWHO. +* Loebner, Hugh: Challenges. +* Loui, Ronald P.: Challenges. +* MAZE: MAZE. +* Microsoft Windows <1>: WEBGRAB. +* Microsoft Windows <2>: Setting Up. +* Microsoft Windows: Troubleshooting. +* MiniSQL: REMCONF. +* MOBAGWHO program: MOBAGWHO. +* NCBI, National Center for Biotechnology Information: PROTBASE. +* network <1>: Caveats. +* network <2>: Gawk Special Files. +* network: Using Networking. +* Numerical Recipes: STATIST. +* PANIC program: PANIC. +* Perl: Using Networking. +* Perlis, Alan: MAZE. +* png image format <1>: STATIST. +* png image format: Web page. +* POP: Email. +* PostScript: STATIST. +* PROLOG: Challenges. +* PROTBASE: PROTBASE. +* ps image format: STATIST. +* Python: Using Networking. +* RAW: File /inet/raw. +* REMCONF program: REMCONF. +* reserved ports: Setting Up. +* RFC 1939: Email. +* RFC 1945: Web page. +* RFC 2068 <1>: Interacting Service. +* RFC 2068: Web page. +* RFC 2616: Web page. +* RFC 821: Email. +* robot <1>: WEBGRAB. +* robot <2>: GETURL. +* robot: Challenges. +* server <1>: Setting Up. +* server: Making Connections. +* SMTP <1>: Email. +* SMTP: Basic Protocols. +* SPAK utility: File /inet/raw. +* STATIST program: STATIST. +* STOXPRED program: STOXPRED. +* synchronous communications: Making Connections. +* Tcl/Tk <1>: Some Applications and Techniques. +* Tcl/Tk: Using Networking. +* TCP <1>: Interacting. +* TCP: File /inet/tcp. +* UDP <1>: Interacting. +* UDP: File /inet/udp. +* URLCHK program: URLCHK. +* VRML: MAZE. +* WEBGRAB program: WEBGRAB. +* Weizenbaum, Joseph: Simple Server. +* xbm image format: Interacting Service. +* Yahoo: STOXPRED. +* Yahoo! <1>: REMCONF. +* Yahoo! <2>: Simple Server. +* Yahoo!: Web page. +* |& I/O operator: TCP Connecting. + + + +Tag Table: +Node: Top1119 +Node: Preface3953 +Node: Introduction5331 +Node: Stream Communications6355 +Node: Datagram Communications7523 +Node: The TCP/IP Protocols9148 +Ref: The TCP/IP Protocols-Footnote-19824 +Node: Basic Protocols9981 +Node: Ports11288 +Node: Making Connections12685 +Ref: Making Connections-Footnote-115256 +Node: Using Networking15303 +Node: Gawk Special Files17627 +Node: Special File Fields19649 +Node: Comparing Protocols24957 +Node: File /inet/tcp25537 +Node: File /inet/udp26550 +Node: File /inet/raw27658 +Ref: File /inet/raw-Footnote-130678 +Node: TCP Connecting30758 +Node: Troubleshooting33093 +Ref: Troubleshooting-Footnote-136090 +Node: Interacting36609 +Node: Setting Up39332 +Node: Email42818 +Node: Web page45139 +Ref: Web page-Footnote-147939 +Node: Primitive Service48142 +Node: Interacting Service50869 +Ref: Interacting Service-Footnote-159992 +Node: CGI Lib60024 +Node: Simple Server66994 +Ref: Simple Server-Footnote-174716 +Node: Caveats74817 +Node: Challenges75958 +Node: Some Applications and Techniques84617 +Node: PANIC87073 +Node: GETURL88786 +Node: REMCONF91404 +Node: URLCHK96875 +Node: WEBGRAB100705 +Node: STATIST105150 +Ref: STATIST-Footnote-1116851 +Node: MAZE117296 +Node: MOBAGWHO123476 +Ref: MOBAGWHO-Footnote-1137412 +Node: STOXPRED137467 +Node: PROTBASE151742 +Node: Links164833 +Node: GNU Free Documentation License168265 +Node: Index188159 + +End Tag Table diff --git a/doc/gawkinet.texi b/doc/gawkinet.texi new file mode 100644 index 00000000..2ffb5814 --- /dev/null +++ b/doc/gawkinet.texi @@ -0,0 +1,5075 @@ +\input texinfo @c -*-texinfo-*- +@c %**start of header (This is for running Texinfo on a region.) +@setfilename gawkinet.info +@settitle TCP/IP Internetworking With @command{gawk} +@c %**end of header (This is for running Texinfo on a region.) + +@c inside ifinfo for older versions of texinfo.tex +@ifinfo +@dircategory GNU Packages +@direntry +* Gawkinet: (gawkinet). TCP/IP Internetworking With @command{gawk}. +@end direntry +@end ifinfo + +@iftex +@set DOCUMENT book +@set CHAPTER chapter +@set SECTION section +@set DARKCORNER @inmargin{@image{lflashlight,1cm}, @image{rflashlight,1cm}} +@end iftex +@ifinfo +@set DOCUMENT Info file +@set CHAPTER major node +@set SECTION node +@set DARKCORNER (d.c.) +@end ifinfo +@ifhtml +@set DOCUMENT web page +@set CHAPTER chapter +@set SECTION section +@set DARKCORNER (d.c.) +@end ifhtml + +@set FSF + +@set FN file name +@set FFN File Name + +@c merge the function and variable indexes into the concept index +@ifinfo +@synindex fn cp +@synindex vr cp +@end ifinfo +@iftex +@syncodeindex fn cp +@syncodeindex vr cp +@end iftex + +@c If "finalout" is commented out, the printed output will show +@c black boxes that mark lines that are too long. Thus, it is +@c unwise to comment it out when running a master in case there are +@c overfulls which are deemed okay. + +@iftex +@finalout +@end iftex + +@smallbook + +@c Special files are described in chapter 6 Printing Output under +@c 6.7 Special File Names in gawk. I think the networking does not +@c fit into that chapter, thus this separate document. At over 50 +@c pages, I think this is the right decision. ADR. + +@set TITLE TCP/IP Internetworking With @command{gawk} +@set EDITION 1.1 +@set UPDATE-MONTH March, 2001 +@c gawk versions: +@set VERSION 3.1 +@set PATCHLEVEL 0 + +@ifinfo +This file documents the networking features in GNU @command{awk}. + +This is Edition @value{EDITION} of @cite{@value{TITLE}}, +for the @value{VERSION}.@value{PATCHLEVEL} (or later) version of the GNU +implementation of AWK. + +Copyright (C) 2000, 2001 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'', the Front-Cover +texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +``GNU Free Documentation License''. + +@enumerate a +@item +``A GNU Manual'' + +@item +``You have freedom to copy and modify this GNU Manual, like GNU +software. Copies published by the Free Software Foundation raise +funds for GNU development.'' +@end enumerate +@end ifinfo + +@setchapternewpage odd + +@titlepage +@title @value{TITLE} +@subtitle Edition @value{EDITION} +@subtitle @value{UPDATE-MONTH} +@author J@"urgen Kahrs +@author with Arnold D. Robbins + +@c Include the Distribution inside the titlepage environment so +@c that headings are turned off. Headings on and off do not work. + +@page +@vskip 0pt plus 1filll +Copyright @copyright{} 2000, 2001 Free Software Foundation, Inc. +@sp 1 +@b{User Friendly} Copyright @copyright{} 2000 J.D.@: ``Iliad'' Frazier. +Reprinted by permission. +@sp 2 + +This is Edition @value{EDITION} of @cite{@value{TITLE}}, +for the @value{VERSION}.@value{PATCHLEVEL} (or later) version of the GNU +implementation of AWK. + +@sp 2 +Published by: +@sp 1 + +Free Software Foundation @* +59 Temple Place --- Suite 330 @* +Boston, MA 02111-1307 USA @* +Phone: +1-617-542-5942 @* +Fax: +1-617-542-2652 @* +Email: @email{gnu@@gnu.org} @* +URL: @uref{http://www.gnu.org/} @* + +ISBN 1-882114-93-0 @* + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.1 or +any later version published by the Free Software Foundation; with the +Invariant Sections being ``GNU General Public License'', the Front-Cover +texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +``GNU Free Documentation License''. + +@enumerate a +@item +``A GNU Manual'' + +@item +``You have freedom to copy and modify this GNU Manual, like GNU +software. Copies published by the Free Software Foundation raise +funds for GNU development.'' +@end enumerate +@c @sp 2 +@c Cover art by ?????. +@end titlepage + +@iftex +@headings off +@evenheading @thispage@ @ @ @strong{@value{TITLE}} @| @| +@oddheading @| @| @strong{@thischapter}@ @ @ @thispage +@end iftex + +@ifinfo +@node Top, Preface, (dir), (dir) +@top General Introduction +@comment node-name, next, previous, up + +This file documents the networking features in GNU Awk (@command{gawk}) +version 3.1 and later. +@end ifinfo + +@menu +* Preface:: About this document. +* Introduction:: About networkiing. +* Using Networking:: Some examples. +* Some Applications and Techniques:: More extended examples. +* Links:: Where to find the stuff mentioned in this + document. +* GNU Free Documentation License:: The license for this document. +* Index:: The index. + +@detailmenu +* Stream Communications:: Sending data streams. +* Datagram Communications:: Sending self-contained messages. +* The TCP/IP Protocols:: How these models work in the Internet. +* Basic Protocols:: The basic protocols. +* Ports:: The idea behind ports. +* Making Connections:: Making TCP/IP connections. +* Gawk Special Files:: How to do @command{gawk} networking. +* Special File Fields:: The fields in the special file name. +* Comparing Protocols:: Differences between the protocols. +* File /inet/tcp:: The TCP special file. +* File /inet/udp:: The UDB special file. +* File /inet/raw:: The RAW special file. +* TCP Connecting:: Making a TCP connection. +* Troubleshooting:: Troubleshooting TCP/IP connections. +* Interacting:: Interacting with a service. +* Setting Up:: Setting up a service. +* Email:: Reading email. +* Web page:: Reading a Web page. +* Primitive Service:: A primitive Web service. +* Interacting Service:: A Web service with interaction. +* CGI Lib:: A simple CGI library. +* Simple Server:: A simple Web server. +* Caveats:: Network programming caveats. +* Challenges:: Where to go from here. +* PANIC:: An Emergency Web Server. +* GETURL:: Retrieving Web Pages. +* REMCONF:: Remote Configuration Of Embedded Systems. +* URLCHK:: Look For Changed Web Pages. +* WEBGRAB:: Extract Links From A Page. +* STATIST:: Graphing A Statistical Distribution. +* MAZE:: Walking Through A Maze In Virtual Reality. +* MOBAGWHO:: A Simple Mobile Agent. +* STOXPRED:: Stock Market Prediction As A Service. +* PROTBASE:: Searching Through A Protein Database. +@end detailmenu +@end menu + +@contents + +@node Preface, Introduction, Top, Top +@unnumbered Preface + +In May of 1997, J@"urgen Kahrs felt the need for network access +from @command{awk}, and, with a little help from me, set about adding +features to do this for @command{gawk}. At that time, he +wrote the bulk of this @value{DOCUMENT}. + +The code and documentation were added to the @command{gawk} 3.1 development +tree, and languished somewhat until I could finally get +down to some serious work on that version of @command{gawk}. +This finally happened in the middle of 2000. + +Meantime, J@"urgen wrote an article about the Internet special +files and @samp{|&} operator for @cite{Linux Journal}, and made a +networking patch for the production versions of @command{gawk} +available from his home page. +In August of 2000 (for @command{gawk} 3.0.6), this patch +also made it to the main GNU @command{ftp} distribution site. + +For release with @command{gawk}, I edited J@"urgen's prose +for English grammar and style, as he is not a native English +speaker. I also +rearranged the material somewhat for what I felt was a better order of +presentation, and (re)wrote some of the introductory material. + +The majority of this document and the code are his work, and the +high quality and interesting ideas speak for themselves. It is my +hope that these features will be of significant value to the @command{awk} +community. + +@sp 1 +@noindent +Arnold Robbins @* +Nof Ayalon, ISRAEL @* +March, 2001 + +@node Introduction, Using Networking, Preface, Top +@chapter Networking Concepts + +This @value{CHAPTER} provides a (necessarily) brief intoduction to +computer networking concepts. For many applications of @command{gawk} +to TCP/IP networking, we hope that this is enough. For more +advanced tasks, you will need deeper background, and it may be necessary +to switch to lower-level programming in C or C++. + +There are two real-life models for the way computers send messages +to each other over a network. While the analogies are not perfect, +they are close enough to convey the major concepts. +These two models are the phone system (reliable byte-stream communications), +and the postal system (best-effort datagrams). + +@menu +* Stream Communications:: Sending data streams. +* Datagram Communications:: Sending self-contained messages. +* The TCP/IP Protocols:: How these models work in the Internet. +* Making Connections:: Making TCP/IP connections. +@end menu + +@node Stream Communications, Datagram Communications, Introduction, Introduction +@section Reliable Byte-streams (Phone Calls) + +When you make a phone call, the following steps occur: + +@enumerate +@item +You dial a number. + +@item +The phone system connects to the called party, telling +them there is an incoming call. (Their phone rings.) + +@item +The other party answers the call, or, in the case of a +computer network, refuses to answer the call. + +@item +Assuming the other party answers, the connection between +you is now a @dfn{duplex} (two-way), @dfn{reliable} (no data lost), +sequenced (data comes out in the order sent) data stream. + +@item +You and your friend may now talk freely, with the phone system +moving the data (your voices) from one end to the other. +From your point of view, you have a direct end-to-end +connection with the person on the other end. +@end enumerate + +The same steps occur in a duplex reliable computer networking connection. +There is considerably more overhead in setting up the communications, +but once it's done, data moves in both directions, reliably, in sequence. + +@node Datagram Communications, The TCP/IP Protocols, Stream Communications, Introduction +@section Best-effort Datagrams (Mailed Letters) + +Suppose you mail three different documents to your office on the +other side of the country on two different days. Doing so +entails the following. + +@enumerate +@item +Each document travels in its own envelope. + +@item +Each envelope contains both the sender and the +recipient address. + +@item +Each envelope may travel a different route to its destination. + +@item +The envelopes may arrive in a different order from the one +in which they were sent. + +@item +One or more may get lost in the mail. +(Although, fortunately, this does not occur very often.) + +@item +In a computer network, one or more @dfn{packets} +may also arrive multiple times. (This doesn't happen +with the postal system!) + +@end enumerate + +The important characteristics of datagram communications, like +those of the postal system are thus: + +@itemize @bullet +@item +Delivery is ``best effort;'' the data may never get there. + +@item +Each message is self-contained, including the source and +destination addresses. + +@item +Delivery is @emph{not} sequenced; packets may arrive out +of order, and/or multiple times. + +@item +Unlike the phone system, overhead is considerably lower. +It is not necessary to set up the call first. +@end itemize + +The price the user pays for the lower overhead of datagram communications +is exactly the lower reliability; it is often necessary for user-level +protocols that use datagram communications to add their own reliabilty +features on top of the basic communications. + +@node The TCP/IP Protocols, Making Connections, Datagram Communications, Introduction +@section The Internet Protocols + +The Internet Protocol Suite (usually referred as just TCP/IP)@footnote{ +It should be noted that although the Internet seems to have conquered the +world, there are other networking protocol suites in existence and in use.} +consists of a number of different protocols at different levels or ``layers.'' +For our purposes, three protocols provide the fundamental communications +mechanisms. All other defined protocols are referred to as user-level +protocols (e.g., HTTP, used later in this @value{DOCUMENT}). + +@menu +* Basic Protocols:: The basic protocols. +* Ports:: The idea behind ports. +@end menu + +@node Basic Protocols, Ports, The TCP/IP Protocols, The TCP/IP Protocols +@subsection The Basic Internet Protocols + +@table @asis +@item IP +The Internet Protocol. This protocol is almost never used directly by +applications. It provides the basic packet delivery and routing infrastructure +of the Internet. Much like the phone company's switching centers or the Post +Office's trucks, it is not of much day-to-day interest to the regular user +(or programmer). +It happens to be a best effort datagram protocol. + +@item UDP +The User Datagram Protocol. This is a best effort datagram protocol. +It provides a small amount of extra reliability over IP, and adds +the notion of @dfn{ports}, described in @ref{Ports, ,TCP and UDP Ports}. + +@item TCP +The Transmission Control Protocol. This is a duplex, reliable, sequenced +byte-stream protocol, again layered on top of IP, and also providing the +notion of ports. This is the protocol that you will most likely use +when using @command{gawk} for network programming. +@end table + +All other user-level protocols use either TCP or UDP to do their basic +communications. Examples are SMTP (Simple Mail Transfer Protocol), +FTP (File Transfer Protocol) and HTTP (HyperText Transfer Protocol). +@cindex SMTP +@cindex FTP +@cindex HTTP + +@node Ports, , Basic Protocols, The TCP/IP Protocols +@subsection TCP and UDP Ports + +In the postal system, the address on an envelope indicates a physical +location, such as a residence or office building. But there may be +more than one person at the location; thus you have to further quantify +the recipient by putting a person or company name on the envelope. + +In the phone system, one phone number may represent an entire company, +in which case you need a person's extension number in order to +reach that individual directly. Or, when you call a home, you have to +say, ``May I please speak to ...'' before talking to the person directly. + +IP networking provides the concept of addressing. An IP address represents +a particular computer, but no more. In order to reach the mail service +on a system, or the FTP or WWW service on a system, you have to have some +way to further specify which service you want. In the Internet Protocol suite, +this is done with @dfn{port numbers}, which represent the services, much +like an extension number used with a phone number. + +Port numbers are 16-bit integers. Unix and Unix-like systems reserve ports +below 1024 for ``well known'' services, such as SMTP, FTP, and HTTP. +Numbers above 1024 may be used by any application, although there is no +promise made that a particular port number is always available. + +@node Making Connections, , The TCP/IP Protocols, Introduction +@section Making TCP/IP Connections (And Some Terminology) + +Two terms come up repeatedly when discussing networking: +@dfn{client} and @dfn{server}. For now, we'll discuss these terms +at the @dfn{connection level}, when first establishing connections +between two processes on different systems over a network. +(Once the connection is established, the higher level, or +@dfn{application level} protocols, +such as HTTP or FTP, determine who is the client and who is the +server. Often, it turns out that the client and server are the +same in both roles.) + +@cindex server +The @dfn{server} is the system providing the service, such as the +web server or email server. It is the @dfn{host} (system) which +is @emph{connected to} in a transaction. +For this to work though, the server must be expecting connections. +Much as there has to be someone at the office building to answer +the phone@footnote{In the days before voice mail systems!}, the +server process (usually) has to be started first and waiting +for a connection. + +@cindex client +The @dfn{client} is the system requesting the service. +It is the system @emph{initiating the connection} in a transaction. +(Just as when you pick up the phone to call an office or store.) + +In the TCP/IP framework, each end of a connection is represented by a pair +of (@var{address}, @var{port}) pairs. For the duration of the connection, +the ports in use at each end are unique, and cannot be used simultaneously +by other processes on the same system. (Only after closing a connection +can a new one be built up on the same port. This is contrary to the usual +behavior of fully developed web servers which have to avoid situations +in which they are not reachable. We have to pay this price in order to +enjoy the benefits of a simple communication paradigm in @command{gawk}.) + +@cindex blocking +@cindex synchronous communications +Furthermore, once the connection is established, communications +are @dfn{synchronous}. I.e., each end waits on the other to finish +transmitting, before replying. This is much like two people in a phone +conversation. While both could talk simultaneously, doing so usually +doesn't work too well. + +In the case of TCP, the synchronicity is enforced by the protocol when +sending data. Data writes @dfn{block} until the data have been received on the +other end. For both TCP and UDP, data reads block until there is incoming +data waiting to be read. This is summarized in the following table, +where an ``X'' indicates that the given action blocks. + +@ifnottex +@multitable {Protocol} {Reads} {Writes} +@item TCP @tab X @tab X +@item UDP @tab X @tab +@item RAW @tab X @tab +@end multitable +@end ifnottex +@tex +\centerline{ +\vbox{\bigskip % space above the table (about 1 linespace) +% Because we have vertical rules, we can't let TeX insert interline space +% in its usual way. +\offinterlineskip +\halign{\hfil\strut# &\vrule #& \hfil#\hfil& \hfil#\hfil\cr +Protocol&&\quad Reads\quad &Writes\cr +\noalign{\hrule} +\omit&height 2pt\cr +\noalign{\hrule height0pt}% without this the rule does not extend; why? +TCP&&X&X\cr +UDP&&X&\cr +RAW&&X&\cr +}}} +@end tex + +@node Using Networking, Some Applications and Techniques, Introduction, Top +@comment node-name, next, previous, up +@chapter Networking With @command{gawk} + +@cindex network +The @command{awk} programming language was originally developed as a +pattern-matching language for writing short programs to perform +data manipulation tasks. +@command{awk}'s strength is the manipulation of textual data +that is stored in files. +It was never meant to be used for networking purposes. +To exploit its features in a +networking context, it's necessary to use an access mode for network connections +that resembles the access of files as closely as possible. + +@cindex Perl +@cindex Python +@cindex Tcl/Tk +@command{awk} is also meant to be a prototyping language. It is used +to demonstrate feasibility and to play with features and user interfaces. +This can be done with file-like handling of network +connections. +@command{gawk} trades the lack +of many of the advanced features of the TCP/IP family of protocols +for the convenience of simple connection handling. +The advanced +features are available when programming in C or Perl. In fact, the +network programming +in this @value{CHAPTER} +is very similar to what is described in books like +@cite{Internet Programming with Python}, +@cite{Advanced Perl Programming}, +or +@cite{Web Client Programming with Perl}. +But it's done here without first having to learn object-oriented ideology, underlying +languages such as Tcl/Tk, Perl, Python, or all of the libraries necessary to +extend these languages before they are ready for the Internet. + +This @value{CHAPTER} demonstrates how to use the TCP protocol. The +other protocols are much less important for most users (UDP) or even +untractable (RAW). + +@menu +* Gawk Special Files:: How to do @command{gawk} networking. +* TCP Connecting:: Making a TCP connection. +* Troubleshooting:: Troubleshooting TCP/IP connections. +* Interacting:: Interacting with a service. +* Setting Up:: Setting up a service. +* Email:: Reading email. +* Web page:: Reading a Web page. +* Primitive Service:: A primitive Web service. +* Interacting Service:: A Web service with interaction. +* Simple Server:: A simple Web server. +* Caveats:: Network programming caveats. +* Challenges:: Where to go from here. +@end menu + +@node Gawk Special Files, TCP Connecting, Using Networking, Using Networking +@comment node-name, next, previous, up +@section @command{gawk} Networking Mechanisms +@cindex network + +The @samp{|&} operator introduced in @command{gawk} 3.1 for use in +communicating with a @dfn{co-process} is described in +@ref{Two-way I/O, ,Two-way Communications With Another Process, gawk, GAWK: Effective AWK Programming}. +It shows how to do two-way I/O to a +separate process, sending it data with @code{print} or @code{printf} and +reading data with @code{getline}. If you haven't read it already, you should +detour there to do so. + +@command{gawk} transparently extends the two-way I/O mechanism to simple networking through +the use of special @value{FN}s. When a ``co-process'' is started that matches +the special files we are about to describe, @command{gawk} creates the appropriate network +connection, and then two-way I/O proceeds as usual. + +At the C, C++ (and basic Perl) level, networking is accomplished +via @dfn{sockets}, an Application Programming Interface (API) originally +developed at the University of California at Berkeley that is now used +almost universally for TCP/IP networking. +Socket level programming, while fairly straightforward, requires paying +attention to a number of details, as well as using binary data. It is not +well-suited for use from a high-level language like @command{awk}. +The special files provided in @command{gawk} hide the details from +the programmer, making things much simpler and easier to use. +@c Who sez we can't toot our own horn occasionally? + +The special @value{FN} for network access is made up of several fields, all +of them mandatory, none of them optional: + +@example +/inet/@var{protocol}/@var{localport}/@var{hostname}/@var{remoteport} +@end example + +The @file{/inet/} field is, of course, constant when accessing the network. +The @var{localport} and @var{remoteport} fields do not have a meaning +when used with @file{/inet/raw} because ``ports'' only apply to +TCP and UDP. So, when using @file{/inet/raw}, the port fields always have +to be @samp{0}. + +@menu +* Special File Fields:: The fields in the special file name. +* Comparing Protocols:: Differences between the protocols. +@end menu + +@node Special File Fields, Comparing Protocols, Gawk Special Files, Gawk Special Files +@subsection The Fields of the Special @value{FFN} +This @value{SECTION} explains the meaning of all the other fields, +as well as the range of values and the defaults. +All of the fields are mandatory. To let the system pick a value, +or if the field doesn't apply to the protocol, specify it as @samp{0}. + +@table @var +@item protocol +Determines which member of the TCP/IP +family of protocols is selected to transport the data across the +network. There are three possible values (always written in lowercase): +@samp{tcp}, @samp{udp}, and @samp{raw}. The exact meaning of each is +explained later in this @value{SECTION}. + +@item localport +Determines which port on the local +machine is used to communicate across the network. It has no meaning +with @file{/inet/raw} and must therefore be @samp{0}. Application level clients +usually use @samp{0} to indicate they do not care which local port is +used---instead they specify a remote port to connect to. It is vital for +application level servers to use a number different from @samp{0} here +because their service has to be available at a specific publicly-known +port number. It is possible to use a name from @file{/etc/services} here. + +@item hostname +Determines which remote host is to +be at the other end of the connection. Application level servers must fill +this field with a @samp{0} to indicate their being open for all other hosts +to connect to them and enforce connection level server behavior this way. +It is not possible for an application level server to restrict its +availability to one remote host by entering a host name here. +Application level clients must enter a name different from @samp{0}. +The name can be either symbolic +(e.g., @samp{jpl-devvax.jpl.nasa.gov}) or numeric (e.g., @samp{128.149.1.143}). + +@item remoteport +Determines which port on the remote +machine is used to communicate across the network. It has no meaning +with @file{/inet/raw} and must therefore be 0. +For @file{/inet/tcp} and @file{/inet/udp}, +application level clients @emph{must} use a number +other than @samp{0} to indicate which port on the remote machine +they want to connect to. Application level servers must not fill this field with +a @samp{0}. Instead they specify a local port for clients to connect to. +It is possible to use a name from @file{/etc/services} here. +@end table + +Experts in network programming will notice that the usual +client/server asymmetry found at the level of the socket API is not visible +here. This is for the sake of simplicity of the high-level concept. If this +asymmetry is necessary for your application, +use another language. +For @command{gawk}, it is +more important to enable users to write a client program with a minimum +of code. What happens when first accessing a network connection is seen +in the following pseudo-code: + +@smallexample +if ((name of remote host given) && (other side accepts connection)) @{ + rendez-vous successful; transmit with getline or print +@} else @{ + if ((other side did not accept) && (localport == 0)) + exit unsuccessful + if (TCP) @{ + set up a server accepting connections + this means waiting for the client on the other side to connect + @} else + ready +@} +@end smallexample + +The exact behavior of this algorithm depends on the values of the +fields of the special @value{FN}. When in doubt, the following table +gives you the combinations of values and their meaning. If this +table is too complicated, focus on the three lines printed in +@strong{bold}. All the examples in +@ref{Using Networking, ,Networking With @command{gawk}}, +use only the +patterns printed in bold letters. + +@multitable {12345678901234} {123456} {123456} {1234567} {1234567890123456789012345} +@item @sc{protocol} @tab @sc{local port} @tab @sc{host name} +@tab @sc{remote port} @tab @sc{Resulting connection level behavior} +@item @strong{tcp} @tab @strong{0} @tab @strong{x} @tab @strong{x} @tab + @strong{Dedicated client, fails if immediately connecting to a + server on the other side fails} +@item udp @tab 0 @tab x @tab x @tab Dedicated client +@item raw @tab 0 @tab x @tab 0 @tab Dedicated client, works only as @code{root} +@item @strong{tcp, udp} @tab @strong{x} @tab @strong{x} @tab @strong{x} @tab + @strong{Client, switches to dedicated server if necessary} +@item @strong{tcp, udp} @tab @strong{x} @tab @strong{0} @tab @strong{0} @tab + @strong{Dedicated server} +@item raw @tab 0 @tab 0 @tab 0 @tab Dedicated server, works only as @code{root} +@item tcp, udp, raw @tab x @tab x @tab 0 @tab Invalid +@item tcp, udp, raw @tab 0 @tab 0 @tab x @tab Invalid +@item tcp, udp, raw @tab x @tab 0 @tab x @tab Invalid +@item tcp, udp @tab 0 @tab 0 @tab 0 @tab Invalid +@item tcp, udp @tab 0 @tab x @tab 0 @tab Invalid +@item raw @tab x @tab 0 @tab 0 @tab Invalid +@item raw @tab 0 @tab x @tab x @tab Invalid +@item raw @tab x @tab x @tab x @tab Invalid +@end multitable + +In general, TCP is the preferred mechanism to use. It is the simplest +protocol to understand and to use. Use the others only if circumstances +demand low-overhead. + +@node Comparing Protocols, , Special File Fields, Gawk Special Files +@subsection Comparing Protocols + +This @value{SECTION} develops a pair of programs (sender and receiver) +that do nothing but send a timestamp from one machine to another. The +sender and the receiver are implemented with each of the three protocols +available and demonstrate the differences between them. + +@menu +* File /inet/tcp:: The TCP special file. +* File /inet/udp:: The UDB special file. +* File /inet/raw:: The RAW special file. +@end menu + +@node File /inet/tcp, File /inet/udp, Comparing Protocols, Comparing Protocols +@subsubsection @file{/inet/tcp} +@cindex @file{/inet/tcp} special files +@cindex TCP +Once again, always use TCP. +(Use UDP when low-overhead is a necessity, and use RAW for +network experimentation.) +The first example is the sender +program: + +@example +# Server +BEGIN @{ + print strftime() |& "/inet/tcp/8888/0/0" + close("/inet/tcp/8888/0/0") +@} +@end example + +The receiver is very simple: + +@example +# Client +BEGIN @{ + "/inet/tcp/0/localhost/8888" |& getline + print $0 + close("/inet/tcp/0/localhost/8888") +@} +@end example + +TCP guarantees that the bytes arrive at the receiving end in exactly +the same order that they were sent. No byte is lost +(except for broken connections), doubled, or out of order. Some +overhead is necessary to accomplish this, but this is the price to pay for +a reliable service. +It does matter which side starts first. The sender/server has to be started +first, and it waits for the receiver to read a line. + +@node File /inet/udp, File /inet/raw, File /inet/tcp, Comparing Protocols +@subsubsection @file{/inet/udp} +@cindex @file{/inet/udp} special files +@cindex UDP +The server and client programs that use UDP are almost identical to their TCP counterparts; +only the @var{protocol} has changed. As before, it does matter which side +starts first. The receiving side blocks and waits for the sender. +In this case, the receiver/client has to be started first: + +@page +@example +# Server +BEGIN @{ + print strftime() |& "/inet/udp/8888/0/0" + close("/inet/udp/8888/0/0") +@} +@end example + +The receiver is almost identical to the TCP receiver: + +@example +# Client +BEGIN @{ + "/inet/udp/0/localhost/8888" |& getline + print $0 + close("/inet/udp/0/localhost/8888") +@} +@end example + +UDP cannot guarantee that the datagrams at the receiving end will arrive in exactly +the same order they were sent. Some datagrams could be +lost, some doubled, and some out of order. But no overhead is necessary to +accomplish this. This unreliable behavior is good enough for tasks +such as data acquisition, logging, and even stateless services like NFS. + +@node File /inet/raw, , File /inet/udp, Comparing Protocols +@subsubsection @file{/inet/raw} +@cindex @file{/inet/raw} special files +@cindex RAW + +This is an IP-level protocol. Only @code{root} is allowed to access this +special file. It is meant to be the basis for implementing +and experimenting with transport level protocols.@footnote{This special file +is reserved, but not otherwise currently implemented.} +In the most general case, +the sender has to supply the encapsulating header bytes in front of the +packet and the receiver has to strip the additional bytes from the message. + +@cindex dark corner +RAW receivers cannot receive packets sent with TCP or UDP because the +operating system does not deliver the packets to a RAW receiver. The +operating system knows about some of the protocols on top of IP +and decides on its own which packet to deliver to which process. +@value{DARKCORNER} +Therefore, the UDP receiver must be used for receiving UDP +datagrams sent with the RAW sender. This is a dark corner, not only of +@command{gawk}, but also of TCP/IP. + +@cindex SPAK utility +For extended experimentation with protocols, look into +the approach implemented in a tool called SPAK. +This tool reflects the hierarchical layering of protocols (encapsulation) +in the way data streams are piped out of one program into the next one. +It shows which protocol is based on which other (lower-level) protocol +by looking at the command-line ordering of the program calls. +Cleverly thought out, SPAK is much better than @command{gawk}'s +@file{/inet} for learning the meaning of each and every bit in the +protocol headers. + +The next example uses the RAW protocol to emulate +the behavior of UDP. The sender program is the same as above, but with some +additional bytes that fill the places of the UDP fields: + +@example +@group +BEGIN @{ + Message = "Hello world\n" + SourcePort = 0 + DestinationPort = 8888 + MessageLength = length(Message)+8 + RawService = "/inet/raw/0/localhost/0" + printf("%c%c%c%c%c%c%c%c%s", + SourcePort/256, SourcePort%256, + DestinationPort/256, DestinationPort%256, + MessageLength/256, MessageLength%256, + 0, 0, Message) |& RawService + fflush(RawService) + close(RawService) +@} +@end group +@end example + +Since this program tries +to emulate the behavior of UDP, it checks if +the RAW sender is understood by the UDP receiver but not if the RAW receiver +can understand the UDP sender. In a real network, the +RAW receiver is hardly +of any use because it gets every IP packet that +comes across the network. There are usually so many packets that +@command{gawk} would be too slow for processing them. +Only on a network with little +traffic can the IP-level receiver program be tested. Programs for analyzing +IP traffic on modem or ISDN channels should be possible. + +Port numbers do not have a meaning when using @file{/inet/raw}. Their fields +have to be @samp{0}. Only TCP and UDP use ports. Receiving data from +@file{/inet/raw} is difficult, not only because of processing speed but also +because data is usually binary and not restricted to ASCII. This +implies that line separation with @code{RS} does not work as usual. + +@node TCP Connecting, Troubleshooting, Gawk Special Files, Using Networking +@section Establishing a TCP Connection + +Let's observe a network connection at work. Type in the following program +and watch the output. Within a second, it connects via TCP (@file{/inet/tcp}) +to the machine it is running on (@samp{localhost}), and asks the service +@samp{daytime} on the machine what time it is: + +@cindex @code{|&} I/O operator +@cindex @code{getline} built-in function +@example +BEGIN @{ + "/inet/tcp/0/localhost/daytime" |& getline + print $0 + close("/inet/tcp/0/localhost/daytime") +@} +@end example + +Even experienced @command{awk} users will find the second line strange in two +respects: + +@itemize @bullet +@item +A special file is used as a shell command that pipes its output +into @code{getline}. One would rather expect to see the special file +being read like any other file (@samp{getline < +"/inet/tcp/0/localhost/daytime")}. + +@item +The operator @samp{|&} has not been part of any @command{awk} +implementation (until now). +It is actually the only extension of the @command{awk} +language needed (apart from the special files) to introduce network access. +@end itemize + +The @samp{|&} operator was introduced in @command{gawk} 3.1 in order to +overcome the crucial restriction that access to files and pipes in +@command{awk} is always unidirectional. It was formerly impossible to use +both access modes on the same file or pipe. Instead of changing the whole +concept of file access, the @samp{|&} operator +behaves exactly like the usual pipe operator except for two additions: + +@itemize @bullet +@item +Normal shell commands connected to their @command{gawk} program with a @samp{|&} +pipe can be accessed bidirectionally. The @samp{|&} turns out to be a quite +general, useful, and natural extension of @command{awk}. + +@item +Pipes that consist of a special @value{FN} for network connections are not +executed as shell commands. Instead, they can be read and written to, just +like a full-duplex network connection. +@end itemize + +In the earlier example, the @samp{|&} operator tells @code{getline} +to read a line from the special file @file{/inet/tcp/0/localhost/daytime}. +We could also have printed a line into the special file. But instead we just +read a line with the time, printed it, and closed the connection. +(While we could just let @command{gawk} close the connection by finishing +the program, in this @value{DOCUMENT} +we are pedantic, and always explicitly close the connections.) + +@node Troubleshooting, Interacting, TCP Connecting, Using Networking +@section Troubleshooting Connection Problems +It may well be that for some reason the above program does not run on your +machine. When looking at possible reasons for this, you will learn much +about typical problems that arise in network programming. First of all, +your implementation of @command{gawk} may not support network access +because it is +a pre-3.1 version or you do not have a network interface in your machine. +Perhaps your machine uses some other protocol +like DECnet or Novell's IPX. For the rest of this @value{CHAPTER}, +we will assume +you work on a Unix machine that supports TCP/IP. If the above program does +not run on such a machine, it may help to replace the name +@samp{localhost} with the name of your machine or its IP address. If it +does, you could replace @samp{localhost} with the name of another machine +in your vicinity. This way, the program connects to another machine. +Now you should see the date and time being printed by the program. +Otherwise your machine may not support the @samp{daytime} service. +Try changing the service to @samp{chargen} or @samp{ftp}. This way, the program +connects to other services that should give you some response. If you are +curious, you should have a look at your file @file{/etc/services}. It could +look like this: + +@ignore +@multitable {1234567890123} {1234567890123} {123456789012345678901234567890123456789012} +@item Service @strong{name} @tab Service @strong{number} +@item echo @tab 7/tcp @tab echo sends back each line it receivces +@item echo @tab 7/udp @tab echo is good for testing purposes +@item discard @tab 9/tcp @tab discard behaves like @file{/dev/null} +@item discard @tab 9/udp @tab discard just throws away each line +@item daytime @tab 13/tcp @tab daytime sends date & time once per connection +@item daytime @tab 13/udp +@item chargen @tab 19/tcp @tab chargen infinitely produces character sets +@item chargen @tab 19/udp @tab chargen is good for testing purposes +@item ftp @tab 21/tcp @tab ftp is the usual file transfer protocol +@item telnet @tab 23/tcp @tab telnet is the usual login facility +@item smtp @tab 25/tcp @tab smtp is the Simple Mail Transfer Protocol +@item finger @tab 79/tcp @tab finger tells you who is logged in +@item www @tab 80/tcp @tab www is the HyperText Transfer Protocol +@item pop2 @tab 109/tcp @tab pop2 is an older version of pop3 +@item pop2 @tab 109/udp +@item pop3 @tab 110/tcp @tab pop3 is the Post Office Protocol +@item pop3 @tab 110/udp @tab pop3 is used for receiving email +@item nntp @tab 119/tcp @tab nntp is the USENET News Transfer Protocol +@item irc @tab 194/tcp @tab irc is the Internet Relay Chat +@item irc @tab 194/udp +@end multitable +@end ignore + +@smallexample +# /etc/services: +# +# Network services, Internet style +# +# Name Number/Protcol Alternate name # Comments + +echo 7/tcp +echo 7/udp +discard 9/tcp sink null +discard 9/udp sink null +daytime 13/tcp +daytime 13/udp +chargen 19/tcp ttytst source +chargen 19/udp ttytst source +ftp 21/tcp +telnet 23/tcp +smtp 25/tcp mail +finger 79/tcp +www 80/tcp http # WorldWideWeb HTTP +www 80/udp # HyperText Transfer Protocol +pop-2 109/tcp postoffice # POP version 2 +pop-2 109/udp +pop-3 110/tcp # POP version 3 +pop-3 110/udp +nntp 119/tcp readnews untp # USENET News +irc 194/tcp # Internet Relay Chat +irc 194/udp +@dots{} +@end smallexample + +@cindex Linux +@cindex GNU/Linux +@cindex Microsoft Windows +Here, you find a list of services that traditional Unix machines usually +support. If your GNU/Linux machine does not do so, it may be that these +services are switched off in some startup script. Systems running some +flavor of Microsoft Windows usually do @emph{not} support such services. +Nevertheless, it @emph{is} possible to do networking with @command{gawk} on +Microsoft +Windows.@footnote{Microsoft prefered to ignore the TCP/IP +family of protocols until 1995. Then came the rise of the Netscape browser +as a landmark ``killer application.'' Microsoft added TCP/IP support and +their own browser to Microsoft Windows 95 at the last minute. They even back-ported +their TCP/IP implementation to Microsoft Windows for Workgroups 3.11, but it was +a rather rudimentary and half-hearted implementation. Nevertheless, +the equivalent of @file{/etc/services} resides under +@file{c:\windows\services} on Microsoft Windows.} +The first column of the file gives the name of the service, +the second a unique number, and the protocol that one can use to connect to +this service. +The rest of the line is treated as a comment. +You see that some services (@samp{echo}) support TCP as +well as UDP. + +@node Interacting, Setting Up, Troubleshooting, Using Networking +@section Interacting with a Network Service + +The next program makes use of the possibility to really interact with a +network service by printing something into the special file. It asks the +so-called @command{finger} service if a user of the machine is logged in. When +testing this program, try to change @samp{localhost} to +some other machine name in your local network: + +@c system if test ! -d eg ; then mkdir eg ; fi +@c system if test ! -d eg/network ; then mkdir eg/network ; fi +@example +@c file eg/network/fingerclient.awk +BEGIN @{ + NetService = "/inet/tcp/0/localhost/finger" + print "@var{name}" |& NetService + while ((NetService |& getline) > 0) + print $0 + close(NetService) +@} +@c endfile +@end example + +After telling the service on the machine which user to look for, +the program repeatedly reads lines that come as a reply. When no more +lines are coming (because the service has closed the connection), the +program also closes the connection. Try replacing @code{"@var{name}"} with your +login name (or the name of someone else logged in). For a list +of all users currently logged in, replace @var{name} with an empty string +@code{""}. + +@cindex Linux +@cindex GNU/Linux +The final @code{close} command could be safely deleted from +the above script, because the operating system closes any open connection +by default when a script reaches the end of execution. In order to avoid +portability problems, it is best to always close connections explicitly. +With the Linux kernel, +for example, proper closing results in flushing of buffers. Letting +the close happen by default may result in discarding buffers. + +@ignore +@c Chuck comments that this seems out of place. He's right. I dunno +@c where to put it though. +@cindex @command{finger} utility +@cindex RFC 1288 +In the early days of the Internet (up until about 1992), you could use +such a program to check if some user in another country was logged in on +a specific machine. +RFC 1288@footnote{@uref{http://www.cis.ohio-state.edu/htbin/rfc/rfc1288.html}} +provides the exact definition of the @command{finger} protocol. +Every contemporary Unix system also has a command named @command{finger}, +which functions as a client for the protocol of the same name. +Still today, some people maintain simple information systems +with this ancient protocol. For example, by typing +@samp{finger quake@@seismo.unr.edu} +you get the latest @dfn{Earthquake Bulletin} for the state of Nevada. + +@cindex Earthquake Bulletin +@smallexample +$ finger quake@@seismo.unr.edu + +[@dots{}] + +DATE-(UTC)-TIME LAT LON DEP MAG COMMENTS +yy/mm/dd hh:mm:ss deg. deg. km + +98/12/14 21:09:22 37.47N 116.30W 0.0 2.3Md 76.4 km S of WARM SPRINGS, NEVA +98/12/14 22:05:09 39.69N 120.41W 11.9 2.1Md 53.8 km WNW of RENO, NEVADA +98/12/15 14:14:19 38.04N 118.60W 2.0 2.3Md 51.0 km S of HAWTHORNE, NEVADA +98/12/17 01:49:02 36.06N 117.58W 13.9 3.0Md 74.9 km SE of LONE PINE, CALIFOR +98/12/17 05:39:26 39.95N 120.87W 6.2 2.6Md 101.6 km WNW of RENO, NEVADA +98/12/22 06:07:42 38.68N 119.82W 5.2 2.3Md 50.7 km S of CARSON CITY, NEVAD +@end smallexample + +@noindent +This output from @command{finger} contains the time, location, depth, +magnitude, and a short comment about +the earthquakes registered in that region during the last 10 days. +In many places today the use of such services is restricted +because most networks have firewalls and proxy servers between them +and the Internet. Most firewalls are programmed to not let +@command{finger} requests go beyond the local network. + +@cindex Coke machine +Another (ab)use of the @command{finger} protocol are several Coke machines +that are connected to the Internet. There is a short list of such +Coke machines.@footnote{@uref{http://ca.yahoo.com/Computers_and_Internet/Internet/Devices_Connected_to_the_Internet/Soda_Machines/}} +You can access them either from the command-line or with a simple +@command{gawk} script. They usually tell you about the different +flavors of Coke and beer available there. If you have an account there, +you can even order some drink this way. +@end ignore + +When looking at @file{/etc/services} you may have noticed that the +@samp{daytime} service is also available with @samp{udp}. In the earlier +example, change @samp{tcp} to @samp{udp}, +and change @samp{finger} to @samp{daytime}. +After starting the modified program, you see the expected day and time message. +The program then hangs, because it waits for more lines coming from the +service. However, they never come. This behavior is a consequence of the +differences between TCP and UDP. When using UDP, neither party is +automatically informed about the other closing the connection. +Continuing to experiment this way reveals many other subtle +differences between TCP and UDP. To avoid such trouble, one should always +remember the advice Douglas E.@: Comer and David Stevens give in +Volume III of their series @cite{Internetworking With TCP} +(page 14): + +@cindex TCP +@cindex UDP +@quotation +When designing client-server applications, beginners are strongly +advised to use TCP because it provides reliable, connection-oriented +communication. Programs only use UDP if the application protocol handles +reliability, the application requires hardware broadcast or multicast, +or the application cannot tolerate virtual circuit overhead. +@end quotation + +@node Setting Up, Email, Interacting, Using Networking +@section Setting Up a Service +The preceding programs behaved as clients that connect to a server somewhere +on the Internet and request a particular service. Now we set up such a +service to mimic the behavior of the @samp{daytime} service. +Such a server does not know in advance who is going to connect to it over +the network. Therefore we cannot insert a name for the host to connect to +in our special @value{FN}. + +Start the following program in one window. Notice that the service does +not have the name @samp{daytime}, but the number @samp{8888}. +From looking at @file{/etc/services}, you know that names like @samp{daytime} +are just mnemonics for predetermined 16-bit integers. +Only the system administrator (@code{root}) could enter +our new service into @file{/etc/services} with an appropriate name. +Also notice that the service name has to be entered into a different field +of the special @value{FN} because we are setting up a server, not a client: + +@cindex @command{finger} utility +@cindex server +@example +BEGIN @{ + print strftime() |& "/inet/tcp/8888/0/0" + close("/inet/tcp/8888/0/0") +@} +@end example + +Now open another window on the same machine. +Copy the client program given as the first example +(@pxref{TCP Connecting, ,Establishing a TCP Connection}) +to a new file and edit it, changing the name @samp{daytime} to +@samp{8888}. Then start the modified client. You should get a reply +like this: + +@example +Sat Sep 27 19:08:16 CEST 1997 +@end example + +@noindent +Both programs explicitly close the connection. + +@cindex Microsoft Windows +@cindex reserved ports +Now we will intentionally make a mistake to see what happens when the name +@samp{8888} (the so-called port) is already used by another service. +Start the server +program in both windows. The first one works, but the second one +complains that it could not open the connection. Each port on a single +machine can only be used by one server program at a time. Now terminate the +server program and change the name @samp{8888} to @samp{echo}. After restarting it, +the server program does not run any more and you know why: there already is +an @samp{echo} service running on your machine. But even if this isn't true, +you would not get +your own @samp{echo} server running on a Unix machine, +because the ports with numbers smaller +than 1024 (@samp{echo} is at port 7) are reserved for @code{root}. +On machines running some flavor of Microsoft Windows, there is no restriction +that reserves ports 1 to 1024 for a privileged user; hence you can start +an @samp{echo} server there. + +Turning this short server program into something really useful is simple. +Imagine a server that first reads a @value{FN} from the client through the +network connection, then does something with the file and +sends a result back to the client. The server-side processing +could be: + +@example +BEGIN @{ + NetService = "/inet/tcp/8888/0/0" + NetService |& getline + CatPipe = ("cat " $1) # sets $0 and the fields + while ((CatPipe | getline) > 0) + print $0 |& NetService + close(NetService) +@} +@end example + +@noindent +and we would +have a remote copying facility. Such a server reads the name of a file +from any client that connects to it and transmits the contents of the +named file across the net. The server-side processing could also be +the execution of a command that is transmitted across the network. From this +example, you can see how simple it is to open up a security hole on your +machine. If you allow clients to connect to your machine and +execute arbitrary commands, anyone would be free to do @samp{rm -rf *}. + +@node Email, Web page, Setting Up, Using Networking +@section Reading Email +@cindex POP +@cindex SMTP +@cindex RFC 1939 +@cindex RFC 821 +The distribution of email is usually done by dedicated email servers that +communicate with your machine using special protocols. To receive email, we +will use the Post Office Protocol (POP). Sending can be done with the much +older Simple Mail Transfer Protocol (SMTP). +@ignore +@footnote{RFC 1939 defines POP. +RFC 821 defines SMTP. See +@uref{http://rfc.fh-koeln.de/doc/rfc/html/rfc.html, RFCs in HTML}.} +@end ignore + +When you type in the following program, replace the @var{emailhost} by the +name of your local email server. Ask your administrator if the server has a +POP service, and then use its name or number in the program below. +Now the program is ready to connect to your email server, but it will not +succeed in retrieving your mail because it does not yet know your login +name or password. Replace them in the program and it +shows you the first email the server has in store: + +@example +BEGIN @{ + POPService = "/inet/tcp/0/@var{emailhost}/pop3" + RS = ORS = "\r\n" + print "user @var{name}" |& POPService + POPService |& getline + print "pass @var{password}" |& POPService + POPService |& getline + print "retr 1" |& POPService + POPService |& getline + if ($1 != "+OK") exit + print "quit" |& POPService + RS = "\r\n\\.\r\n" + POPService |& getline + print $0 + close(POPService) +@} +@end example + +@cindex RFC 1939 +The record separators @code{RS} and @code{ORS} are redefined because the +protocol (POP) requires CR-LF to separate lines. After identifying +yourself to the email service, the command @samp{retr 1} instructs the +service to send the first of all your email messages in line. If the service +replies with something other than @samp{+OK}, the program exits; maybe there +is no email. Otherwise, the program first announces that it intends to finish +reading email, and then redefines @code{RS} in order to read the entire +email as multiline input in one record. From the POP RFC, we know that the body +of the email always ends with a single line containing a single dot. +The program looks for this using @samp{RS = "\r\n\\.\r\n"}. +When it finds this sequence in the mail message, it quits. +You can invoke this program as often as you like; it does not delete the +message it reads, but instead leaves it on the server. + +@node Web page, Primitive Service, Email, Using Networking +@section Reading a Web Page +@cindex HTTP +@cindex RFC 2068 +@cindex RFC 2616 + +Retrieving a web page from a web server is as simple as +retrieving email from an email server. We only have to use a +similar, but not identical, protocol and a different port. The name of the +protocol is HyperText Transfer Protocol (HTTP) and the port number is usually +80. As in the preceding @value{SECTION}, ask your administrator about the +name of your local web server or proxy web server and its port number +for HTTP requests. + +@ignore +@c Chuck says this stuff isn't necessary +More detailed information about HTTP can be found at +the home of the web protocols,@footnote{@uref{http://www.w3.org/pub/WWW/Protocols}} +including the specification of HTTP in RFC 2068. The protocol specification +in RFC 2068 is concise and you can get it for free. If you need more +explanation and you are willing to pay for a book, you might be +interested in one of these books: + +@enumerate + +@item +When we started writing web clients and servers with @command{gawk}, +the only book available with details about HTTP was the one by Paul Hethmon +called +@cite{Illustrated Guide to HTTP}.@footnote{@uref{http://www.browsebooks.com/Hethmon/?882}} +Hethmon not only describes HTTP, +he also implements a simple web server in C++. + +@item +Since July 2000, O'Reilly offers the book by Clinton Wong called +@cite{HTTP Pocket Reference}.@footnote{@uref{http://www.oreilly.com/catalog/httppr}} +It only has 75 pages but its +focus definitely is HTTP. This pocket reference is not a replacement +for the RFC, but I wish I had had it back in 1997 when I started writing +scripts to handle HTTP. + +@item +Another small booklet about HTTP is the one by Toexcell Incorporated Staff, +ISBN 1-58348-270-9, called +@cite{Hypertext Transfer Protocol Http 1.0 Specifications} + +@end enumerate +@end ignore + +The following program employs a rather crude approach toward retrieving a +web page. It uses the prehistoric syntax of HTTP 0.9, which almost all +web servers still support. The most noticeable thing about it is that the +program directs the request to the local proxy server whose name you insert +in the special @value{FN} (which in turn calls @samp{www.yahoo.com}): + +@example +BEGIN @{ + RS = ORS = "\r\n" + HttpService = "/inet/tcp/0/@var{proxy}/80" + print "GET http://www.yahoo.com" |& HttpService + while ((HttpService |& getline) > 0) + print $0 + close(HttpService) +@} +@end example + +@cindex RFC 1945 +@cindex HTML +@cindex Yahoo! +Again, lines are separated by a redefined @code{RS} and @code{ORS}. +The @code{GET} request that we send to the server is the only kind of +HTTP request that existed when the web was created in the early 1990s. +HTTP calls this @code{GET} request a ``method,'' which tells the +service to transmit a web page (here the home page of the Yahoo! search +engine). Version 1.0 added the request methods @code{HEAD} and +@code{POST}. The current version of HTTP is 1.1,@footnote{Version 1.0 of +HTTP was defined in RFC 1945. HTTP 1.1 was initially specified in RFC +2068. In June 1999, RFC 2068 was made obsolete by RFC 2616. It is an update +without any substantial changes.} and knows the additional request +methods @code{OPTIONS}, @code{PUT}, @code{DELETE}, and @code{TRACE}. +You can fill in any valid web address, and the program prints the +HTML code of that page to your screen. + +Notice the similarity between the responses of the POP and HTTP +services. First, you get a header that is terminated by an empty line, and +then you get the body of the page in HTML. The lines of the headers also +have the same form as in POP. There is the name of a parameter, +then a colon, and finally the value of that parameter. + +@cindex CGI +@cindex @file{gif} image format +@cindex @file{png} image format +Images (@file{.png} or @file{.gif} files) can also be retrieved this way, +but then you +get binary data that should be redirected into a file. Another +application is calling a CGI (Common Gateway Interface) script on some +server. CGI scripts are used when the contents of a web page are not +constant, but generated instantly at the moment you send a request +for the page. For example, to get a detailed report about the current +quotes of Motorola stock shares, call a CGI script at Yahoo! with +the following: + +@example +get = "GET http://quote.yahoo.com/q?s=MOT&d=t" +print get |& HttpService +@end example + +You can also request weather reports this way. +@ignore +@cindex Boutell, Thomas +A good book to go on with is +the +@cite{HTML Source Book}.@footnote{@uref{http://www.utoronto.ca/webdocs/HTMLdocs/NewHTML/book.html}} +There are also some books on CGI programming +like @cite{CGI Programming in C & Perl}, +by Thomas Boutell@footnote{@uref{http://cseng.aw.com/bookdetail.qry?ISBN=0-201-42219-0&ptype=0}}, +and @cite{The CGI Book}.@footnote{@uref{http://www.cgibook.com}} +Another good source is @cite{The CGI Resource Index}}.@footnote{@uref{http://www.cgi-resources.com}} +@end ignore + +@node Primitive Service, Interacting Service, Web page, Using Networking +@section A Primitive Web Service +Now we know enough about HTTP to set up a primitive web service that just +says @code{"Hello, world"} when someone connects to it with a browser. +Compared +to the situation in the preceding @value{SECTION}, our program changes the role. It +tries to behave just like the server we have observed. Since we are setting +up a server here, we have to insert the port number in the @samp{localport} +field of the special @value{FN}. The other two fields (@var{hostname} and +@var{remoteport}) have to contain a @samp{0} because we do not know in +advance which host will connect to our service. + +In the early 1990s, all a server had to do was send an HTML document and +close the connection. Here, we adhere to the modern syntax of HTTP. +The steps are as follows: + +@enumerate 1 +@item +Send a status line telling the web browser that everything +is OK. + +@item +Send a line to tell the browser how many bytes follow in the +body of the message. This was not necessary earlier because both +parties knew that the document ended when the connection closed. Nowadays +it is possible to stay connected after the transmission of one web page. +This is to avoid the network traffic necessary for repeatedly establishing +TCP connections for requesting several images. Thus, there is the need to tell +the receiving party how many bytes will be sent. The header is terminated +as usual with an empty line. + +@item +Send the @code{"Hello, world"} body +in HTML. +The useless @code{while} loop swallows the request of the browser. +We could actually omit the loop, and on most machines the program would still +work. +First, start the following program: +@end enumerate + +@example +@c file eg/network/hello-serv.awk +BEGIN @{ + RS = ORS = "\r\n" + HttpService = "/inet/tcp/8080/0/0" + Hello = "" \ + "A Famous Greeting" \ + "

Hello, world

" + Len = length(Hello) + length(ORS) + print "HTTP/1.0 200 OK" |& HttpService + print "Content-Length: " Len ORS |& HttpService + print Hello |& HttpService + while ((HttpService |& getline) > 0) + continue; + close(HttpService) +@} +@c endfile +@end example + +Now, on the same machine, start your favorite browser and let it point to +@uref{http://localhost:8080} (the browser needs to know on which port +our server is listening for requests). If this does not work, the browser +probably tries to connect to a proxy server that does not know your machine. +If so, change the browser's configuration so that the browser does not try to +use a proxy to connect to your machine. + +@node Interacting Service, Simple Server, Primitive Service, Using Networking +@section A Web Service with Interaction +@cindex GUI +@ifinfo +This node shows how to set up a simple web server. +The subnode is a library file that we will use with all the examples in +@ref{Some Applications and Techniques}. +@end ifinfo + +@menu +* CGI Lib:: A simple CGI library. +@end menu + +Setting up a web service that allows user interaction is more difficult and +shows us the limits of network access in @command{gawk}. In this @value{SECTION}, +we develop a main program (a @code{BEGIN} pattern and its action) +that will become the core of event-driven execution controlled by a +graphical user interface (GUI). +Each HTTP event that the user triggers by some action within the browser +is received in this central procedure. Parameters and menu choices are +extracted from this request and an appropriate measure is taken according to +the user's choice. +For example: + +@cindex HTTP server, core logic +@example +BEGIN @{ + if (MyHost == "") @{ + "uname -n" | getline MyHost + close("uname -n") + @} + if (MyPort == 0) MyPort = 8080 + HttpService = "/inet/tcp/" MyPort "/0/0" + MyPrefix = "http://" MyHost ":" MyPort + SetUpServer() + while ("awk" != "complex") @{ + # header lines are terminated this way + RS = ORS = "\r\n" + Status = 200 # this means OK + Reason = "OK" + Header = TopHeader + Document = TopDoc + Footer = TopFooter + if (GETARG["Method"] == "GET") @{ + HandleGET() + @} else if (GETARG["Method"] == "HEAD") @{ + # not yet implemented + @} else if (GETARG["Method"] != "") @{ + print "bad method", GETARG["Method"] + @} + Prompt = Header Document Footer + print "HTTP/1.0", Status, Reason |& HttpService + print "Connection: Close" |& HttpService + print "Pragma: no-cache" |& HttpService + len = length(Prompt) + length(ORS) + print "Content-length:", len |& HttpService + print ORS Prompt |& HttpService + # ignore all the header lines + while ((HttpService |& getline) > 0) + ; + # stop talking to this client + close(HttpService) + # wait for new client request + HttpService |& getline + # do some logging + print systime(), strftime(), $0 + # read request parameters + CGI_setup($1, $2, $3) + @} +@} +@end example + +This web server presents menu choices in the form of HTML links. +Therefore, it has to tell the browser the name of the host it is +residing on. When starting the server, the user may supply the name +of the host from the command line with @samp{gawk -v MyHost="Rumpelstilzchen"}. +If the user does not do this, the server looks up the name of the host it is +running on for later use as a web address in HTML documents. The same +applies to the port number. These values are inserted later into the +HTML content of the web pages to refer to the home system. + +Each server that is built around this core has to initialize some +application-dependent variables (such as the default home page) in a procedure +@code{SetUpServer}, which is called immediately before entering the +infinite loop of the server. For now, we will write an instance that +initiates a trivial interaction. With this home page, the client user +can click on two possible choices, and receive the current date either +in human-readable format or in seconds since 1970: + +@example +function SetUpServer() @{ + TopHeader = "" + TopHeader = TopHeader \ + "My name is GAWK, GNU AWK" + TopDoc = "

\ + Do you prefer your date human or \ + POSIXed?

" ORS ORS + TopFooter = "" +@} +@end example + +On the first run through the main loop, the default line terminators are +set and the default home page is copied to the actual home page. Since this +is the first run, @code{GETARG["Method"]} is not initialized yet, hence the +case selection over the method does nothing. Now that the home page is +initialized, the server can start communicating to a client browser. + +@cindex RFC 2068 +@cindex CGI +It does so by printing the HTTP header into the network connection +(@samp{print @dots{} |& HttpService}). This command blocks execution of +the server script until a client connects. If this server +script is compared with the primitive one we wrote before, you will notice +two additional lines in the header. The first instructs the browser +to close the connection after each request. The second tells the +browser that it should never try to @emph{remember} earlier requests +that had identical web addresses (no caching). Otherwise, it could happen +that the browser retrieves the time of day in the previous example just once, +and later it takes the web page from the cache, always displaying the same +time of day although time advances each second. + +Having supplied the initial home page to the browser with a valid document +stored in the parameter @code{Prompt}, it closes the connection and waits +for the next request. When the request comes, a log line is printed that +allows us to see which request the server receives. The final step in the +loop is to call the function @code{CGI_setup}, which reads all the lines +of the request (coming from the browser), processes them, and stores the +transmitted parameters in the array @code{PARAM}. The complete +text of these application-independent functions can be found in +@ref{CGI Lib, ,A Simple CGI Library}. +For now, we use a simplified version of @code{CGI_setup}: + +@example +function CGI_setup( method, uri, version, i) @{ + delete GETARG; delete MENU; delete PARAM + GETARG["Method"] = $1 + GETARG["URI"] = $2 + GETARG["Version"] = $3 + i = index($2, "?") + # is there a "?" indicating a CGI request? +@group + if (i > 0) @{ + split(substr($2, 1, i-1), MENU, "[/:]") + split(substr($2, i+1), PARAM, "&") + for (i in PARAM) @{ + j = index(PARAM[i], "=") + GETARG[substr(PARAM[i], 1, j-1)] = \ + substr(PARAM[i], j+1) + @} + @} else @{ # there is no "?", no need for splitting PARAMs + split($2, MENU, "[/:]") + @} +@end group +@} +@end example + +At first, the function clears all variables used for +global storage of request parameters. The rest of the function serves +the purpose of filling the global parameters with the extracted new values. +To accomplish this, the name of the requested resource is split into +parts and stored for later evaluation. If the request contains a @samp{?}, +then the request has CGI variables seamlessly appended to the web address. +Everything in front of the @samp{?} is split up into menu items, and +everything behind the @samp{?} is a list of @samp{@var{variable}=@var{value}} pairs +(separated by @samp{&}) that also need splitting. This way, CGI variables are +isolated and stored. This procedure lacks recognition of special characters +that are transmitted in coded form@footnote{As defined in RFC 2068.}. Here, any +optional request header and body parts are ignored. We do not need +header parameters and the request body. However, when refining our approach or +working with the @code{POST} and @code{PUT} methods, reading the header +and body +becomes inevitable. Header parameters should then be stored in a global +array as well as the body. + +On each subsequent run through the main loop, one request from a browser is +received, evaluated, and answered according to the user's choice. This can be +done by letting the value of the HTTP method guide the main loop into +execution of the procedure @code{HandleGET}, which evaluates the user's +choice. In this case, we have only one hierarchical level of menus, +but in the general case, +menus are nested. +The menu choices at each level are +separated by @samp{/}, just as in @value{FN}s. Notice how simple it is to +construct menus of arbitrary depth: + +@example +function HandleGET() @{ + if ( MENU[2] == "human") @{ + Footer = strftime() TopFooter + @} else if (MENU[2] == "POSIX") @{ + Footer = systime() TopFooter + @} +@} +@end example + +@cindex CGI +The disadvantage of this approach is that our server is slow and can +handle only one request at a time. Its main advantage, however, is that +the server +consists of just one @command{gawk} program. No need for installing an +@command{httpd}, and no need for static separate HTML files, CGI scripts, or +@code{root} privileges. This is rapid prototyping. +This program can be started on the same host that runs your browser. +Then let your browser point to @uref{http://localhost:8080}. + +@cindex @file{xbm} image format +@cindex image format +@cindex GNUPlot utility +It is also possible to include images into the HTML pages. +Most browsers support the not very well-known +@file{.xbm} format, +which may contain only +monochrome pictures but is an ASCII format. Binary images are possible but +not so easy to handle. Another way of including images is to generate them +with a tool such as GNUPlot, +by calling the tool with the @code{system} function or through a pipe. + +@node CGI Lib, , Interacting Service, Interacting Service +@subsection A Simple CGI Library +@quotation +@i{HTTP is like being married: you have to be able to handle whatever +you're given, while being very careful what you send back.}@* +Phil Smith III,@* +@uref{http://www.netfunny.com/rhf/jokes/99/Mar/http.html} +@end quotation + +In @ref{Interacting Service, ,A Web Service with Interaction}, +we saw the function @code{CGI_setup} as part of the web server +``core logic'' framework. The code presented there handles almost +everything necessary for CGI requests. +One thing it doesn't do is handle encoded characters in the requests. +For example, an @samp{&} is encoded as a percent sign followed by +the hexadecimal value---@samp{%26}. These encoded values should be +decoded. +Following is a simple library to perform these tasks. +This code is used for all web server examples +used throughout the rest of this @value{DOCUMENT}. +If you want to use it for your own web server, store the source code +into a file named @file{inetlib.awk}. Then you can include +these functions into your code by placing the following statement +into your program: + +@example +@@include inetlib.awk +@end example + +@noindent +on the first line of your script. But beware, this mechanism is +only possible if you invoke your web server script with @command{igawk} +instead of the usual @command{awk} or @command{gawk}. +Here is the code: + +@example +@c file eg/network/coreserv.awk +# CGI Library and core of a web server +@c endfile +@ignore +@c file eg/network/coreserv.awk +# +# Juergen Kahrs, Juergen.Kahrs@@vr-web.de +# with Arnold Robbins, arnold@@gnu.org +# September 2000 + +@c endfile +@end ignore +@c file eg/network/coreserv.awk +# Global arrays +# GETARG --- arguments to CGI GET command +# MENU --- menu items (path names) +# PARAM --- parameters of form x=y + +# Optional variable MyHost contains host address +# Optional variable MyPort contains port number +# Needs TopHeader, TopDoc, TopFooter +# Sets MyPrefix, HttpService, Status, Reason + +BEGIN @{ + if (MyHost == "") @{ + "uname -n" | getline MyHost + close("uname -n") + @} + if (MyPort == 0) MyPort = 8080 + HttpService = "/inet/tcp/" MyPort "/0/0" + MyPrefix = "http://" MyHost ":" MyPort + SetUpServer() + while ("awk" != "complex") @{ + # header lines are terminated this way + RS = ORS = "\r\n" + Status = 200 # this means OK + Reason = "OK" + Header = TopHeader + Document = TopDoc + Footer = TopFooter + if (GETARG["Method"] == "GET") @{ + HandleGET() + @} else if (GETARG["Method"] == "HEAD") @{ + # not yet implemented + @} else if (GETARG["Method"] != "") @{ + print "bad method", GETARG["Method"] + @} + Prompt = Header Document Footer + print "HTTP/1.0", Status, Reason |& HttpService + print "Connection: Close" |& HttpService + print "Pragma: no-cache" |& HttpService + len = length(Prompt) + length(ORS) + print "Content-length:", len |& HttpService + print ORS Prompt |& HttpService + # ignore all the header lines + while ((HttpService |& getline) > 0) + continue + # stop talking to this client + close(HttpService) + # wait for new client request + HttpService |& getline + # do some logging + print systime(), strftime(), $0 + CGI_setup($1, $2, $3) + @} +@} + +function CGI_setup( method, uri, version, i) +@{ + delete GETARG + delete MENU + delete PARAM + GETARG["Method"] = method + GETARG["URI"] = uri + GETARG["Version"] = version + + i = index(uri, "?") + if (i > 0) @{ # is there a "?" indicating a CGI request? + split(substr(uri, 1, i-1), MENU, "[/:]") + split(substr(uri, i+1), PARAM, "&") + for (i in PARAM) @{ + PARAM[i] = _CGI_decode(PARAM[i]) + j = index(PARAM[i], "=") + GETARG[substr(PARAM[i], 1, j-1)] = \ + substr(PARAM[i], j+1) + @} + @} else @{ # there is no "?", no need for splitting PARAMs + split(uri, MENU, "[/:]") + @} + for (i in MENU) # decode characters in path + if (i > 4) # but not those in host name + MENU[i] = _CGI_decode(MENU[i]) +@} +@c endfile +@end example + +This isolates details in a single function, @code{CGI_setup}. +Decoding of encoded characters is pushed off to a helper function, +@code{_CGI_decode}. The use of the leading underscore (@samp{_}) in +the function name is intended to indicate that it is an ``internal'' +function, although there is nothing to enforce this: + +@example +@c file eg/network/coreserv.awk +function _CGI_decode(str, hexdigs, i, pre, code1, code2, + val, result) +@{ + hexdigs = "123456789abcdef" + + i = index(str, "%") + if (i == 0) # no work to do + return str + + do @{ + pre = substr(str, 1, i-1) # part before %xx + code1 = substr(str, i+1, 1) # first hex digit + code2 = substr(str, i+2, 1) # second hex digit + str = substr(str, i+3) # rest of string + + code1 = tolower(code1) + code2 = tolower(code2) + val = index(hexdigs, code1) * 16 \ + + index(hexdigs, code2) + + result = result pre sprintf("%c", val) + i = index(str, "%") + @} while (i != 0) + if (length(str) > 0) + result = result str + return result +@} +@c endfile +@end example + +This works by splitting the string apart around an encoded character. +The two digits are converted to lowercase and looked up in a string +of hex digits. Note that @code{0} is not in the string on purpose; +@code{index} returns zero when it's not found, automatically giving +the correct value! Once the hexadecimal value is converted from +characters in a string into a numerical value, @code{sprintf} +converts the value back into a real character. +The following is a simple test harness for the above functions: + +@example +@c file eg/network/testserv.awk +BEGIN @{ + CGI_setup("GET", + "http://www.gnu.org/cgi-bin/foo?p1=stuff&p2=stuff%26junk" \ + "&percent=a %25 sign", + "1.0") + for (i in MENU) + printf "MENU[\"%s\"] = %s\n", i, MENU[i] + for (i in PARAM) + printf "PARAM[\"%s\"] = %s\n", i, PARAM[i] + for (i in GETARG) + printf "GETARG[\"%s\"] = %s\n", i, GETARG[i] +@} +@c endfile +@end example + +And this is the result when we run it: + +@c artificial line wrap in last output line +@example +$ gawk -f testserv.awk +@print{} MENU["4"] = www.gnu.org +@print{} MENU["5"] = cgi-bin +@print{} MENU["6"] = foo +@print{} MENU["1"] = http +@print{} MENU["2"] = +@print{} MENU["3"] = +@print{} PARAM["1"] = p1=stuff +@print{} PARAM["2"] = p2=stuff&junk +@print{} PARAM["3"] = percent=a % sign +@print{} GETARG["p1"] = stuff +@print{} GETARG["percent"] = a % sign +@print{} GETARG["p2"] = stuff&junk +@print{} GETARG["Method"] = GET +@print{} GETARG["Version"] = 1.0 +@print{} GETARG["URI"] = http://www.gnu.org/cgi-bin/foo?p1=stuff& +p2=stuff%26junk&percent=a %25 sign +@end example + +@node Simple Server, Caveats, Interacting Service, Using Networking +@section A Simple Web Server +@cindex GUI +In the preceding @value{SECTION}, we built the core logic for event driven GUIs. +In this @value{SECTION}, we finally extend the core to a real application. +No one would actually write a commercial web server in @command{gawk}, but +it is instructive to see that it is feasible in principle. + +@iftex +@image{uf002331,4in} +@end iftex + +@cindex ELIZA program +@cindex Weizenbaum, Joseph +The application is ELIZA, the famous program by Joseph Weizenbaum that +mimics the behavior of a professional psychotherapist when talking to you. +Weizenbaum would certainly object to this description, but this is part of +the legend around ELIZA. +Take the site-independent core logic and append the following code: + +@example +@c file eg/network/eliza.awk +function SetUpServer() @{ + SetUpEliza() + TopHeader = \ + "An HTTP-based System with GAWK\ + \ + " + TopDoc = "\ +

Please choose one of the following actions:

\ + " + TopFooter = "" +@} +@c endfile +@end example + +@code{SetUpServer} is similar to the previous example, +except for calling another function, @code{SetUpEliza}. +This approach can be used to implement other kinds of servers. +The only changes needed to do so are hidden in the functions +@code{SetUpServer} and @code{HandleGET}. Perhaps it might be necessary to +implement other HTTP methods. +The @command{igawk} program that comes with @command{gawk} +may be useful for this process. + +When extending this example to a complete application, the first +thing to do is to implement the function @code{SetUpServer} to +initialize the HTML pages and some variables. These initializations +determine the way your HTML pages look (colors, titles, menu +items, etc.). + +@cindex GUI +The function @code{HandleGET} is a nested case selection that decides +which page the user wants to see next. Each nesting level refers to a menu +level of the GUI. Each case implements a certain action of the menu. On the +deepest level of case selection, the handler essentially knows what the +user wants and stores the answer into the variable that holds the HTML +page contents: + +@smallexample +@c file eg/network/eliza.awk +function HandleGET() @{ + # A real HTTP server would treat some parts of the URI as a file name. + # We take parts of the URI as menu choices and go on accordingly. + if(MENU[2] == "AboutServer") @{ + Document = "This is not a CGI script.\ + This is an httpd, an HTML file, and a CGI script all \ + in one GAWK script. It needs no separate www-server, \ + no installation, and no root privileges.\ +

To run it, do this:

    \ +
  • start this script with \"gawk -f httpserver.awk\",
    • \ +
  • and on the same host let your www browser open location\ + \"http://localhost:8080\"
    • \ +
\

\ Details of HTTP come from:

    \ +
  • Hethmon: Illustrated Guide to HTTP

    \ +
  • RFC 2068

JK 14.9.1997

" + @} else if (MENU[2] == "AboutELIZA") @{ + Document = "This is an implementation of the famous ELIZA\ + program by Joseph Weizenbaum. It is written in GAWK and\ +/bin/sh: expad: command not found + @} else if (MENU[2] == "StartELIZA") @{ + gsub(/\+/, " ", GETARG["YouSay"]) + # Here we also have to substitute coded special characters + Document = "
" \ + "

" ElizaSays(GETARG["YouSay"]) "

\ +

\ +

" + @} +@} +@c endfile +@end smallexample + +Now we are down to the heart of ELIZA, so you can see how it works. +Initially the user does not say anything; then ELIZA resets its money +counter and asks the user to tell what comes to mind open heartedly. +The subsequent answers are converted to uppercase and stored for +later comparison. ELIZA presents the bill when being confronted with +a sentence that contains the phrase ``shut up.'' Otherwise, it looks for +keywords in the sentence, conjugates the rest of the sentence, remembers +the keyword for later use, and finally selects an answer from the set of +possible answers: + +@smallexample +@c file eg/network/eliza.awk +function ElizaSays(YouSay) @{ + if (YouSay == "") @{ + cost = 0 + answer = "HI, IM ELIZA, TELL ME YOUR PROBLEM" + @} else @{ + q = toupper(YouSay) + gsub("'", "", q) + if(q == qold) @{ + answer = "PLEASE DONT REPEAT YOURSELF !" + @} else @{ + if (index(q, "SHUT UP") > 0) @{ + answer = "WELL, PLEASE PAY YOUR BILL. ITS EXACTLY ... $"\ + int(100*rand()+30+cost/100) + @} else @{ + qold = q + w = "-" # no keyword recognized yet + for (i in k) @{ # search for keywords + if (index(q, i) > 0) @{ + w = i + break + @} + @} + if (w == "-") @{ # no keyword, take old subject + w = wold + subj = subjold + @} else @{ # find subject + subj = substr(q, index(q, w) + length(w)+1) + wold = w + subjold = subj # remember keyword and subject + @} + for (i in conj) + gsub(i, conj[i], q) # conjugation + # from all answers to this keyword, select one randomly + answer = r[indices[int(split(k[w], indices) * rand()) + 1]] + # insert subject into answer + gsub("_", subj, answer) + @} + @} + @} + cost += length(answer) # for later payment : 1 cent per character + return answer +@} +@c endfile +@end smallexample + +In the long but simple function @code{SetUpEliza}, you can see tables +for conjugation, keywords, and answers.@footnote{The version shown +here is abbreviated. The full version comes with the @command{gawk} +distribution.} The associative array @code{k} +contains indices into the array of answers @code{r}. To choose an +answer, ELIZA just picks an index randomly: + +@example +@c file eg/network/eliza.awk +function SetUpEliza() @{ + srand() + wold = "-" + subjold = " " + + # table for conjugation + conj[" ARE " ] = " AM " + conj["WERE " ] = "WAS " + conj[" YOU " ] = " I " + conj["YOUR " ] = "MY " + conj[" IVE " ] =\ + conj[" I HAVE " ] = " YOU HAVE " + conj[" YOUVE " ] =\ + conj[" YOU HAVE "] = " I HAVE " + conj[" IM " ] =\ + conj[" I AM " ] = " YOU ARE " + conj[" YOURE " ] =\ + conj[" YOU ARE " ] = " I AM " + + # table of all answers + r[1] = "DONT YOU BELIEVE THAT I CAN _" + r[2] = "PERHAPS YOU WOULD LIKE TO BE ABLE TO _ ?" +@c endfile + @dots{} +@end example +@ignore +@c file eg/network/eliza.awk + r[3] = "YOU WANT ME TO BE ABLE TO _ ?" + r[4] = "PERHAPS YOU DONT WANT TO _ " + r[5] = "DO YOU WANT TO BE ABLE TO _ ?" + r[6] = "WHAT MAKES YOU THINK I AM _ ?" + r[7] = "DOES IT PLEASE YOU TO BELIEVE I AM _ ?" + r[8] = "PERHAPS YOU WOULD LIKE TO BE _ ?" + r[9] = "DO YOU SOMETIMES WISH YOU WERE _ ?" + r[10] = "DONT YOU REALLY _ ?" + r[11] = "WHY DONT YOU _ ?" + r[12] = "DO YOU WISH TO BE ABLE TO _ ?" + r[13] = "DOES THAT TROUBLE YOU ?" + r[14] = "TELL ME MORE ABOUT SUCH FEELINGS" + r[15] = "DO YOU OFTEN FEEL _ ?" + r[16] = "DO YOU ENJOY FEELING _ ?" + r[17] = "DO YOU REALLY BELIEVE I DONT _ ?" + r[18] = "PERHAPS IN GOOD TIME I WILL _ " + r[19] = "DO YOU WANT ME TO _ ?" + r[20] = "DO YOU THINK YOU SHOULD BE ABLE TO _ ?" + r[21] = "WHY CANT YOU _ ?" + r[22] = "WHY ARE YOU INTERESTED IN WHETHER OR NOT I AM _ ?" + r[23] = "WOULD YOU PREFER IF I WERE NOT _ ?" + r[24] = "PERHAPS IN YOUR FANTASIES I AM _ " + r[25] = "HOW DO YOU KNOW YOU CANT _ ?" + r[26] = "HAVE YOU TRIED ?" + r[27] = "PERHAPS YOU CAN NOW _ " + r[28] = "DID YOU COME TO ME BECAUSE YOU ARE _ ?" + r[29] = "HOW LONG HAVE YOU BEEN _ ?" + r[30] = "DO YOU BELIEVE ITS NORMAL TO BE _ ?" + r[31] = "DO YOU ENJOY BEING _ ?" + r[32] = "WE WERE DISCUSSING YOU -- NOT ME" + r[33] = "Oh, I _" + r[34] = "YOU'RE NOT REALLY TALKING ABOUT ME, ARE YOU ?" + r[35] = "WHAT WOULD IT MEAN TO YOU, IF YOU GOT _ ?" + r[36] = "WHY DO YOU WANT _ ?" + r[37] = "SUPPOSE YOU SOON GOT _" + r[38] = "WHAT IF YOU NEVER GOT _ ?" + r[39] = "I SOMETIMES ALSO WANT _" + r[40] = "WHY DO YOU ASK ?" + r[41] = "DOES THAT QUESTION INTEREST YOU ?" + r[42] = "WHAT ANSWER WOULD PLEASE YOU THE MOST ?" + r[43] = "WHAT DO YOU THINK ?" + r[44] = "ARE SUCH QUESTIONS IN YOUR MIND OFTEN ?" + r[45] = "WHAT IS IT THAT YOU REALLY WANT TO KNOW ?" + r[46] = "HAVE YOU ASKED ANYONE ELSE ?" + r[47] = "HAVE YOU ASKED SUCH QUESTIONS BEFORE ?" + r[48] = "WHAT ELSE COMES TO MIND WHEN YOU ASK THAT ?" + r[49] = "NAMES DON'T INTEREST ME" + r[50] = "I DONT CARE ABOUT NAMES -- PLEASE GO ON" + r[51] = "IS THAT THE REAL REASON ?" + r[52] = "DONT ANY OTHER REASONS COME TO MIND ?" + r[53] = "DOES THAT REASON EXPLAIN ANYTHING ELSE ?" + r[54] = "WHAT OTHER REASONS MIGHT THERE BE ?" + r[55] = "PLEASE DON'T APOLOGIZE !" + r[56] = "APOLOGIES ARE NOT NECESSARY" + r[57] = "WHAT FEELINGS DO YOU HAVE WHEN YOU APOLOGIZE ?" + r[58] = "DON'T BE SO DEFENSIVE" + r[59] = "WHAT DOES THAT DREAM SUGGEST TO YOU ?" + r[60] = "DO YOU DREAM OFTEN ?" + r[61] = "WHAT PERSONS APPEAR IN YOUR DREAMS ?" + r[62] = "ARE YOU DISTURBED BY YOUR DREAMS ?" + r[63] = "HOW DO YOU DO ... PLEASE STATE YOUR PROBLEM" + r[64] = "YOU DON'T SEEM QUITE CERTAIN" + r[65] = "WHY THE UNCERTAIN TONE ?" + r[66] = "CAN'T YOU BE MORE POSITIVE ?" + r[67] = "YOU AREN'T SURE ?" + r[68] = "DON'T YOU KNOW ?" + r[69] = "WHY NO _ ?" + r[70] = "DON'T SAY NO, IT'S ALWAYS SO NEGATIVE" + r[71] = "WHY NOT ?" + r[72] = "ARE YOU SURE ?" + r[73] = "WHY NO ?" + r[74] = "WHY ARE YOU CONCERNED ABOUT MY _ ?" + r[75] = "WHAT ABOUT YOUR OWN _ ?" + r[76] = "CAN'T YOU THINK ABOUT A SPECIFIC EXAMPLE ?" + r[77] = "WHEN ?" + r[78] = "WHAT ARE YOU THINKING OF ?" + r[79] = "REALLY, ALWAYS ?" + r[80] = "DO YOU REALLY THINK SO ?" + r[81] = "BUT YOU ARE NOT SURE YOU _ " + r[82] = "DO YOU DOUBT YOU _ ?" + r[83] = "IN WHAT WAY ?" + r[84] = "WHAT RESEMBLANCE DO YOU SEE ?" + r[85] = "WHAT DOES THE SIMILARITY SUGGEST TO YOU ?" + r[86] = "WHAT OTHER CONNECTION DO YOU SEE ?" + r[87] = "COULD THERE REALLY BE SOME CONNECTIONS ?" + r[88] = "HOW ?" + r[89] = "YOU SEEM QUITE POSITIVE" + r[90] = "ARE YOU SURE ?" + r[91] = "I SEE" + r[92] = "I UNDERSTAND" + r[93] = "WHY DO YOU BRING UP THE TOPIC OF FRIENDS ?" + r[94] = "DO YOUR FRIENDS WORRY YOU ?" + r[95] = "DO YOUR FRIENDS PICK ON YOU ?" + r[96] = "ARE YOU SURE YOU HAVE ANY FRIENDS ?" + r[97] = "DO YOU IMPOSE ON YOUR FRIENDS ?" + r[98] = "PERHAPS YOUR LOVE FOR FRIENDS WORRIES YOU" + r[99] = "DO COMPUTERS WORRY YOU ?" + r[100] = "ARE YOU TALKING ABOUT ME IN PARTICULAR ?" + r[101] = "ARE YOU FRIGHTENED BY MACHINES ?" + r[102] = "WHY DO YOU MENTION COMPUTERS ?" + r[103] = "WHAT DO YOU THINK MACHINES HAVE TO DO WITH YOUR PROBLEMS ?" + r[104] = "DON'T YOU THINK COMPUTERS CAN HELP PEOPLE ?" + r[105] = "WHAT IS IT ABOUT MACHINES THAT WORRIES YOU ?" + r[106] = "SAY, DO YOU HAVE ANY PSYCHOLOGICAL PROBLEMS ?" + r[107] = "WHAT DOES THAT SUGGEST TO YOU ?" + r[108] = "I SEE" + r[109] = "IM NOT SURE I UNDERSTAND YOU FULLY" + r[110] = "COME COME ELUCIDATE YOUR THOUGHTS" + r[111] = "CAN YOU ELABORATE ON THAT ?" + r[112] = "THAT IS QUITE INTERESTING" + r[113] = "WHY DO YOU HAVE PROBLEMS WITH MONEY ?" + r[114] = "DO YOU THINK MONEY IS EVERYTHING ?" + r[115] = "ARE YOU SURE THAT MONEY IS THE PROBLEM ?" + r[116] = "I THINK WE WANT TO TALK ABOUT YOU, NOT ABOUT ME" + r[117] = "WHAT'S ABOUT ME ?" + r[118] = "WHY DO YOU ALWAYS BRING UP MY NAME ?" +@c endfile +@end ignore + +@example +@c file eg/network/eliza.awk + # table for looking up answers that + # fit to a certain keyword + k["CAN YOU"] = "1 2 3" + k["CAN I"] = "4 5" + k["YOU ARE"] =\ + k["YOURE"] = "6 7 8 9" +@c endfile + @dots{} +@end example +@ignore +@c file eg/network/eliza.awk + k["I DONT"] = "10 11 12 13" + k["I FEEL"] = "14 15 16" + k["WHY DONT YOU"] = "17 18 19" + k["WHY CANT I"] = "20 21" + k["ARE YOU"] = "22 23 24" + k["I CANT"] = "25 26 27" + k["I AM"] =\ + k["IM "] = "28 29 30 31" + k["YOU "] = "32 33 34" + k["I WANT"] = "35 36 37 38 39" + k["WHAT"] =\ + k["HOW"] =\ + k["WHO"] =\ + k["WHERE"] =\ + k["WHEN"] =\ + k["WHY"] = "40 41 42 43 44 45 46 47 48" + k["NAME"] = "49 50" + k["CAUSE"] = "51 52 53 54" + k["SORRY"] = "55 56 57 58" + k["DREAM"] = "59 60 61 62" + k["HELLO"] =\ + k["HI "] = "63" + k["MAYBE"] = "64 65 66 67 68" + k[" NO "] = "69 70 71 72 73" + k["YOUR"] = "74 75" + k["ALWAYS"] = "76 77 78 79" + k["THINK"] = "80 81 82" + k["LIKE"] = "83 84 85 86 87 88 89" + k["YES"] = "90 91 92" + k["FRIEND"] = "93 94 95 96 97 98" + k["COMPUTER"] = "99 100 101 102 103 104 105" + k["-"] = "106 107 108 109 110 111 112" + k["MONEY"] = "113 114 115" + k["ELIZA"] = "116 117 118" +@c endfile +@end ignore +@example +@c file eg/network/eliza.awk +@} +@c endfile +@end example + +@cindex Humphrys, Mark +@cindex ELIZA program +@cindex Yahoo! +Some interesting remarks and details (including the original source code +of ELIZA) are found on Mark Humphrys' home page. Yahoo! also has a +page with a collection of ELIZA-like programs. Many of them are written +in Java, some of them disclosing the Java source code, and a few even +explain how to modify the Java source code. + +@node Caveats, Challenges, Simple Server, Using Networking +@section Network Programming Caveats + +By now it should be clear +that debugging a networked application is more +complicated than debugging a single-process single-hosted application. +The behavior of a networked application sometimes looks non-causal because +it is not reproducible in a strong sense. Whether a network application +works or not sometimes depends on the following: + +@itemize @bullet +@item +How crowded the underlying network is. + +@item +If the party at the other end is running or not. + +@item +The state of the party at the other end. +@end itemize + +@cindex network +The most difficult problems for a beginner arise from the hidden states of the +underlying network. After closing a TCP connection, it's often necessary to wait +a short while before reopening the connection. Even more difficult is the +establishment of a connection that previously ended with a ``broken pipe.'' +Those connections have to ``time out'' for a minute or so +before they can reopen. +Check this with the command @samp{netstat -a}, which +provides a list of still ``active'' connections. + +@node Challenges, , Caveats, Using Networking +@section Where To Go From Here + +@cindex Loebner, Hugh +@cindex Contest +Now, you have learned enough to build your own application. You could, +for example, take part in the +Loebner Contest +to win $100,000. The Loebner Prize is the first formal instantiation of +a Turing Test. Hugh Loebner agreed with The Cambridge Center for Behavioral +Studies to underwrite a contest designed to implement the Turing Test. +Dr.@: Loebner pledged a Grand Prize of $100,000 for the first computer whose +responses were indistinguishable from a human's. Each year an annual prize +of $2000 and a bronze medal is awarded to the @emph{most} human computer. +The winner of the annual contest is the best entry relative to other entries +that year, irrespective of how good it is in an absolute sense. Here is +an example of a conversation with the winning program of 1997: + +@smallexample +(c)1997 Cambridge Center For Behavioral Studies all rights reserved [CONVERSE] +[Intelligent Research Ltd.] Start at: [1997/04/29 08:59:40] +PROGRAM[10:39:20]Hi, my name is Catherine, what's yours? +JUDGE02[10:39:36]My name is Nathan. +PROGRAM[10:39:37]Well, it's nice to meet you, Nathan. +PROGRAM[10:39:45]Did you see that story on CNN last night about the lesbian +PROGRAM[10:40:03]couple who came out at a White House party on Sunday? +JUDGE02[10:40:45]No. I'm sorry I missed that. How did the Prez take it? +PROGRAM[10:40:47]Ellen Degeneres was one of them - she was kissing her lover +PROGRAM[10:41:08]in front of Bill Clinton. Do you think he was very +PROGRAM[10:41:21]embarrassed? +JUDGE02[10:41:37]You tell me. I didn't see it. +PROGRAM[10:41:38]Are you still a Friend of Bill Clinton? +JUDGE02[10:42:22]Yes. I would like to talk about something else. Do you know anything about sculpture. +PROGRAM[10:42:24]Well, I suppose he's doing his best like most of us, but he +PROGRAM[10:42:35]does seem to attract an UNUSUAL amount of bad publicity, +PROGRAM[10:42:51]wouldnt you say--can it all be bad luck? +JUDGE02[10:43:20]I asked you if you knew anything about sculpture. +PROGRAM[10:43:21]OK, but what happens now--does it all drift on, with +PROGRAM[10:43:36]everyone waiting to see how much his friends have said about +PROGRAM[10:43:47]him under threat of lots and lots of jail-or will something +PROGRAM[10:44:01]dramatic actually happen? +JUDGE02[10:44:19]Do you know what sculpture is? +PROGRAM[10:44:20]Well, youre more a fan of his than I am I guess---though I +PROGRAM[10:44:34]cant SWEAR what Id have done in that locked hotel room, I +PROGRAM[10:44:51]must say. +JUDGE02[10:45:26]Have you ever been to the Salmagundi Club? +PROGRAM[10:45:29]Never. to go back to the original discussion Time to get +PROGRAM[10:45:43]off this one I think and onto something more down to earth! +JUDGE02[10:46:20]What is more down to earth than art? +PROGRAM[10:46:21]I don't know what -- to be honest. - +PROGRAM[10:46:30]I suppose it depends on where you're coming from, but as the +PROGRAM[10:46:46]song goes in My Fair Lady, "Why can't a woman be more like a +PROGRAM[10:47:03]man? " +JUDGE02[10:47:52]I liked that song but I prefer "Why can't children be more like we are" +JUDGE02[10:48:10]from another play the name of which I cannot remember. +PROGRAM[10:48:12]What, if anything, do you enjoy about being a man? +JUDGE02[10:49:01]I would enjoy all aspects of life no matter what my gender. +PROGRAM[10:49:02]Do you think of yourself as being attractive? +@end smallexample + +@cindex Clinton, Bill +This program insists on always speaking about the same story around Bill +Clinton. You see, even a program with a rather narrow mind can behave so +much like a human being that it can win this prize. It is quite common to +let these programs talk to each other via network connections. But during the +competition itself, the program and its computer have to be present at the +place the competition is held. We all would love to see a @command{gawk} +program win in such an event. Maybe it is up to you to accomplish this? + +Some other ideas for useful networked applications: +@itemize @bullet +@item +Read the file @file{doc/awkforai.txt} in the @command{gawk} distribution. +It was written by Ronald P.@: Loui (Associate Professor of +Computer Science, at Washington University in St. Louis, +@email{loui@@ai.wustl.edu}) and summarizes why +he teaches @command{gawk} to students of Artificial Intelligence. Here are +some passages from the text: + +@cindex AI +@cindex PROLOG +@cindex Loui, Ronald P. +@cindex agent +@quotation +The GAWK manual can +be consumed in a single lab session and the language can be mastered by +the next morning by the average student. GAWK's automatic +initialization, implicit coercion, I/O support and lack of pointers +forgive many of the mistakes that young programmers are likely to make. +Those who have seen C but not mastered it are happy to see that GAWK +retains some of the same sensibilities while adding what must be +regarded as spoonsful of syntactic sugar.@* +@dots{}@* +@cindex robot +There are further simple answers. Probably the best is the fact that +increasingly, undergraduate AI programming is involving the Web. Oren +Etzioni (University of Washington, Seattle) has for a while been arguing +that the ``softbot'' is replacing the mechanical engineers' robot as the +most glamorous AI testbed. If the artifact whose behavior needs to be +controlled in an intelligent way is the software agent, then a language +that is well-suited to controlling the software environment is the +appropriate language. That would imply a scripting language. If the +robot is KAREL, then the right language is ``turn left; turn right.'' If +the robot is Netscape, then the right language is something that can +generate @samp{netscape -remote 'openURL(http://cs.wustl.edu/~loui)'} with +elan.@* +@dots{}@* +AI programming requires high-level thinking. There have always been a few +gifted programmers who can write high-level programs in assembly language. +Most however need the ambient abstraction to have a higher floor.@* +@dots{}@* +Second, inference is merely the expansion of notation. No matter whether +the logic that underlies an AI program is fuzzy, probabilistic, deontic, +defeasible, or deductive, the logic merely defines how strings can be +transformed into other strings. A language that provides the best +support for string processing in the end provides the best support for +logic, for the exploration of various logics, and for most forms of +symbolic processing that AI might choose to call ``reasoning'' instead of +``logic.'' The implication is that PROLOG, which saves the AI programmer +from having to write a unifier, saves perhaps two dozen lines of GAWK +code at the expense of strongly biasing the logic and representational +expressiveness of any approach. +@end quotation + +Now that @command{gawk} itself can connect to the Internet, it should be obvious +that it is suitable for writing intelligent web agents. + +@item +@command{awk} is strong at pattern recognition and string processing. +So, it is well suited to the classic problem of language translation. +A first try could be a program that knows the 100 most frequent English +words and their counterparts in German or French. The service could be +implemented by regularly reading email with the program above, replacing +each word by its translation and sending the translation back via SMTP. +Users would send English email to their translation service and get +back a translated email message in return. As soon as this works, +more effort can be spent on a real translation program. + +@item +Another dialogue-oriented application (on the verge +of ridicule) is the email ``support service.'' Troubled customers write an +email to an automatic @command{gawk} service that reads the email. It looks +for keywords in the mail and assembles a reply email accordingly. By carefully +investigating the email header, and repeating these keywords through the +reply email, it is rather simple to give the customer a feeling that +someone cares. Ideally, such a service would search a database of previous +cases for solutions. If none exists, the database could, for example, consist +of all the newsgroups, mailing lists and FAQs on the Internet. +@end itemize + +@node Some Applications and Techniques, Links, Using Networking, Top +@comment node-name, next, previous, up + +@chapter Some Applications and Techniques +In this @value{CHAPTER}, we look at a number of self-contained +scripts, with an emphasis on concise networking. Along the way, we +work towards creating building blocks that encapsulate often needed +functions of the networking world, show new techniques that +broaden the scope of problems that can be solved with @command{gawk}, and +explore leading edge technology that may shape the future of networking. + +We often refer to the site-independent core of the server that +we built in +@ref{Simple Server, ,A Simple Web Server}. +When building new and non-trivial servers, we +always copy this building block and append new instances of the two +functions @code{SetUpServer} and @code{HandleGET}. + +This makes a lot of sense, since +this scheme of event-driven +execution provides @command{gawk} with an interface to the most widely +accepted standard for GUIs: the web browser. Now, @command{gawk} can even rival +Tcl/Tk. + +@cindex Tcl/Tk +@cindex JavaScript +Tcl and @command{gawk} have much in common. Both are simple scripting languages +that allow us to quickly solve problems with short programs. But Tcl has Tk +on top of it and @command{gawk} had nothing comparable up to now. While Tcl +needs a large and ever changing library (Tk, which was bound to the X Window +System until recently), @command{gawk} needs just the networking interface +and some kind of browser on the client's side. Besides better portability, +the most important advantage of this approach (embracing well-established +standards such HTTP and HTML) is that @emph{we do not need to change the +language}. We let others do the work of fighting over protocols and standards. +We can use HTML, JavaScript, VRML, or whatever else comes along to do our work. + +@menu +* PANIC:: An Emergency Web Server. +* GETURL:: Retrieving Web Pages. +* REMCONF:: Remote Configuration Of Embedded Systems. +* URLCHK:: Look For Changed Web Pages. +* WEBGRAB:: Extract Links From A Page. +* STATIST:: Graphing A Statistical Distribution. +* MAZE:: Walking Through A Maze In Virtual Reality. +* MOBAGWHO:: A Simple Mobile Agent. +* STOXPRED:: Stock Market Prediction As A Service. +* PROTBASE:: Searching Through A Protein Database. +@end menu + +@node PANIC, GETURL, Some Applications and Techniques, Some Applications and Techniques +@section PANIC: an Emergency Web Server +@cindex PANIC program +At first glance, the @code{"Hello, world"} example in +@ref{Primitive Service, ,A Primitive Web Service}, +seems useless. By adding just a few lines, we can turn it into something useful. + +The PANIC program tells everyone who connects that the local +site is not working. When a web server breaks down, it makes a difference +if customers get a strange ``network unreachable'' message, or a short message +telling them that the server has a problem. In such an emergency, +the hard disk and everything on it (including the regular web service) may +be unavailable. Rebooting the web server off a diskette makes sense in this +setting. + +To use the PANIC program as an emergency web server, all you need are the +@command{gawk} executable and the program below on a diskette. By default, +it connects to port 8080. A different value may be supplied on the +command line: + +@example +@c file eg/network/panic.awk +BEGIN @{ + RS = ORS = "\r\n" + if (MyPort == 0) MyPort = 8080 + HttpService = "/inet/tcp/" MyPort "/0/0" + Hello = "Out Of Service" \ + "

" \ + "This site is temporarily out of service." \ + "

" + Len = length(Hello) + length(ORS) + while ("awk" != "complex") @{ + print "HTTP/1.0 200 OK" |& HttpService + print "Content-Length: " Len ORS |& HttpService + print Hello |& HttpService + while ((HttpService |& getline) > 0) + continue; + close(HttpService) + @} +@} +@c endfile +@end example + +@node GETURL, REMCONF, PANIC, Some Applications and Techniques +@section GETURL: Retrieving Web Pages +@cindex GETURL program +@cindex robot +GETURL is a versatile building block for shell scripts that need to retrieve +files from the Internet. It takes a web address as a command-line parameter and +tries to retrieve the contents of this address. The contents are printed +to standard output, while the header is printed to @file{/dev/stderr}. +A surrounding shell script +could analyze the contents and extract the text or the links. An ASCII +browser could be written around GETURL. But more interestingly, web robots are +straightforward to write on top of GETURL. On the Internet, you can find +several programs of the same name that do the same job. They are usually +much more complex internally and at least 10 times longer. + +At first, GETURL checks if it was called with exactly one web address. +Then, it checks if the user chose to use a special proxy server whose name +is handed over in a variable. By default, it is assumed that the local +machine serves as proxy. GETURL uses the @code{GET} method by default +to access the web page. By handing over the name of a different method +(such as @code{HEAD}), it is possible to choose a different behavior. With +the @code{HEAD} method, the user does not receive the body of the page +content, but does receive the header: + +@example +@c file eg/network/geturl.awk +BEGIN @{ + if (ARGC != 2) @{ + print "GETURL - retrieve Web page via HTTP 1.0" + print "IN:\n the URL as a command-line parameter" + print "PARAM(S):\n -v Proxy=MyProxy" + print "OUT:\n the page content on stdout" + print " the page header on stderr" + print "JK 16.05.1997" + print "ADR 13.08.2000" + exit + @} + URL = ARGV[1]; ARGV[1] = "" + if (Proxy == "") Proxy = "127.0.0.1" + if (ProxyPort == 0) ProxyPort = 80 + if (Method == "") Method = "GET" + HttpService = "/inet/tcp/0/" Proxy "/" ProxyPort + ORS = RS = "\r\n\r\n" + print Method " " URL " HTTP/1.0" |& HttpService + HttpService |& getline Header + print Header > "/dev/stderr" + while ((HttpService |& getline) > 0) + printf "%s", $0 + close(HttpService) +@} +@c endfile +@end example + +This program can be changed as needed, but be careful with the last lines. +Make sure transmission of binary data is not corrupted by additional line +breaks. Even as it is now, the byte sequence @code{"\r\n\r\n"} would +disappear if it were contained in binary data. Don't get caught in a +trap when trying a quick fix on this one. + +@node REMCONF, URLCHK, GETURL, Some Applications and Techniques +@section REMCONF: Remote Configuration of Embedded Systems +@cindex REMCONF program +@cindex Linux +@cindex GNU/Linux +@cindex Yahoo! +Today, you often find powerful processors in embedded systems. Dedicated +network routers and controllers for all kinds of machinery are examples +of embedded systems. Processors like the Intel 80x86 or the AMD Elan are +able to run multitasking operating systems, such as XINU or GNU/Linux +in embedded PCs. These systems are small and usually do not have +a keyboard or a display. Therefore it is difficult to set up their +configuration. There are several widespread ways to set them up: + +@itemize @bullet +@item +DIP switches + +@item +Read Only Memories such as EPROMs + +@item +Serial lines or some kind of keyboard + +@item +Network connections via @command{telnet} or SNMP + +@item +HTTP connections with HTML GUIs +@end itemize + +In this @value{SECTION}, we look at a solution that uses HTTP connections +to control variables of an embedded system that are stored in a file. +Since embedded systems have tight limits on resources like memory, +it is difficult to employ advanced techniques such as SNMP and HTTP +servers. @command{gawk} fits in quite nicely with its single executable +which needs just a short script to start working. +The following program stores the variables in a file, and a concurrent +process in the embedded system may read the file. The program uses the +site-independent part of the simple web server that we developed in +@ref{Interacting Service, ,A Web Service with Interaction}. +As mentioned there, all we have to do is to write two new procedures +@code{SetUpServer} and @code{HandleGET}: + +@smallexample +@c file eg/network/remconf.awk +function SetUpServer() @{ + TopHeader = "Remote Configuration" + TopDoc = "\ +

Please choose one of the following actions:

\ + " + TopFooter = "" + if (ConfigFile == "") ConfigFile = "config.asc" +@} +@c endfile +@end smallexample + +The function @code{SetUpServer} initializes the top level HTML texts +as usual. It also initializes the name of the file that contains the +configuration parameters and their values. In case the user supplies +a name from the command line, that name is used. The file is expected to +contain one parameter per line, with the name of the parameter in +column one and the value in column two. + +The function @code{HandleGET} reflects the structure of the menu +tree as usual. The first menu choice tells the user what this is all +about. The second choice reads the configuration file line by line +and stores the parameters and their values. Notice that the record +separator for this file is @code{"\n"}, in contrast to the record separator +for HTTP. The third menu choice builds an HTML table to show +the contents of the configuration file just read. The fourth choice +does the real work of changing parameters, and the last one just saves +the configuration into a file: + +@smallexample +@c file eg/network/remconf.awk +function HandleGET() @{ + if(MENU[2] == "AboutServer") @{ + Document = "This is a GUI for remote configuration of an\ + embedded system. It is is implemented as one GAWK script." + @} else if (MENU[2] == "ReadConfig") @{ + RS = "\n" + while ((getline < ConfigFile) > 0) + config[$1] = $2; + close(ConfigFile) + RS = "\r\n" + Document = "Configuration has been read." + @} else if (MENU[2] == "CheckConfig") @{ + Document = "" + for (i in config) + Document = Document "" \ + "" + Document = Document "
" i "" config[i] "
" + @} else if (MENU[2] == "ChangeConfig") @{ + if ("Param" in GETARG) @{ # any parameter to set? + if (GETARG["Param"] in config) @{ # is parameter valid? + config[GETARG["Param"]] = GETARG["Value"] + Document = (GETARG["Param"] " = " GETARG["Value"] ".") + @} else @{ + Document = "Parameter " GETARG["Param"] " is invalid." + @} + @} else @{ + Document = "

Change one parameter

\ + \ + \ + \ + \ +
ParameterValue
" + @} + @} else if (MENU[2] == "SaveConfig") @{ + for (i in config) + printf("%s %s\n", i, config[i]) > ConfigFile + close(ConfigFile) + Document = "Configuration has been saved." + @} +@} +@c endfile +@end smallexample + +@cindex MiniSQL +We could also view the configuration file as a database. From this +point of view, the previous program acts like a primitive database server. +Real SQL database systems also make a service available by providing +a TCP port that clients can connect to. But the application level protocols +they use are usually proprietary and also change from time to time. +This is also true for the protocol that +MiniSQL uses. + +@node URLCHK, WEBGRAB, REMCONF, Some Applications and Techniques +@section URLCHK: Look for Changed Web Pages +@cindex URLCHK program +Most people who make heavy use of Internet resources have a large +bookmark file with pointers to interesting web sites. It is impossible +to regularly check by hand if any of these sites have changed. A program +is needed to automatically look at the headers of web pages and tell +which ones have changed. URLCHK does the comparison after using GETURL +with the @code{HEAD} method to retrieve the header. + +Like GETURL, this program first checks that it is called with exactly +one command-line parameter. URLCHK also takes the same command-line variables +@code{Proxy} and @code{ProxyPort} as GETURL, +because these variables are handed over to GETURL for each URL +that gets checked. The one and only parameter is the name of a file that +contains one line for each URL. In the first column, we find the URL, and +the second and third columns hold the length of the URL's body when checked +for the two last times. Now, we follow this plan: + +@enumerate +@item +Read the URLs from the file and remember their most recent lengths + +@item +Delete the contents of the file + +@item +For each URL, check its new length and write it into the file + +@item +If the most recent and the new length differ, tell the user +@end enumerate + +It may seem a bit peculiar to read the URLs from a file together +with their two most recent lengths, but this approach has several +advantages. You can call the program again and again with the same +file. After running the program, you can regenerate the changed URLs +by extracting those lines that differ in their second and third columns: + +@c inspired by URLCHK in iX 5/97 166. +@smallexample +@c file eg/network/urlchk.awk +BEGIN @{ + if (ARGC != 2) @{ + print "URLCHK - check if URLs have changed" + print "IN:\n the file with URLs as a command-line parameter" + print " file contains URL, old length, new length" + print "PARAMS:\n -v Proxy=MyProxy -v ProxyPort=8080" + print "OUT:\n same as file with URLs" + print "JK 02.03.1998" + exit + @} + URLfile = ARGV[1]; ARGV[1] = "" + if (Proxy != "") Proxy = " -v Proxy=" Proxy + if (ProxyPort != "") ProxyPort = " -v ProxyPort=" ProxyPort + while ((getline < URLfile) > 0) + Length[$1] = $3 + 0 + close(URLfile) # now, URLfile is read in and can be updated + GetHeader = "gawk " Proxy ProxyPort " -v Method=\"HEAD\" -f geturl.awk " + for (i in Length) @{ + GetThisHeader = GetHeader i " 2>&1" + while ((GetThisHeader | getline) > 0) + if (toupper($0) ~ /CONTENT-LENGTH/) NewLength = $2 + 0 + close(GetThisHeader) + print i, Length[i], NewLength > URLfile + if (Length[i] != NewLength) # report only changed URLs + print i, Length[i], NewLength + @} + close(URLfile) +@} +@c endfile +@end smallexample + +Another thing that may look strange is the way GETURL is called. +Before calling GETURL, we have to check if the proxy variables need +to be passed on. If so, we prepare strings that will become part +of the command line later. In @code{GetHeader}, we store these strings +together with the longest part of the command line. Later, in the loop +over the URLs, @code{GetHeader} is appended with the URL and a redirection +operator to form the command that reads the URL's header over the Internet. +GETURL always produces the headers over @file{/dev/stderr}. That is +the reason why we need the redirection operator to have the header +piped in. + +This program is not perfect because it assumes that changing URLs +results in changed lengths, which is not necessarily true. A more +advanced approach is to look at some other header line that +holds time information. But, as always when things get a bit more +complicated, this is left as an exercise to the reader. + +@node WEBGRAB, STATIST, URLCHK, Some Applications and Techniques +@section WEBGRAB: Extract Links from a Page +@cindex WEBGRAB program +@c Inspired by iX 1/98 157. +@cindex robot +Sometimes it is necessary to extract links from web pages. +Browsers do it, web robots do it, and sometimes even humans do it. +Since we have a tool like GETURL at hand, we can solve this problem with +some help from the Bourne shell: + +@example +@c file eg/network/webgrab.awk +BEGIN @{ RS = "http://[#%&\\+\\-\\./0-9\\:;\\?A-Z_a-z\\~]*" @} +RT != "" @{ + command = ("gawk -v Proxy=MyProxy -f geturl.awk " RT \ + " > doc" NR ".html") + print command +@} +@c endfile +@end example + +Notice that the regular expression for URLs is rather crude. A precise +regular expression is much more complex. But this one works +rather well. One problem is that it is unable to find internal links of +an HTML document. Another problem is that +@samp{ftp}, @samp{telnet}, @samp{news}, @samp{mailto}, and other kinds +of links are missing in the regular expression. +However, it is straightforward to add them, if doing so is necessary for other tasks. + +This program reads an HTML file and prints all the HTTP links that it finds. +It relies on @command{gawk}'s ability to use regular expressions as record +separators. With @code{RS} set to a regular expression that matches links, +the second action is executed each time a non-empty link is found. +We can find the matching link itself in @code{RT}. + +The action could use the @code{system} function to let another GETURL +retrieve the page, but here we use a different approach. +This simple program prints shell commands that can be piped into @command{sh} +for execution. This way it is possible to first extract +the links, wrap shell commands around them, and pipe all the shell commands +into a file. After editing the file, execution of the file retrieves +exactly those files that we really need. In case we do not want to edit, +we can retrieve all the pages like this: + +@smallexample +gawk -f geturl.awk http://www.suse.de | gawk -f webgrab.awk | sh +@end smallexample + +@cindex Microsoft Windows +After this, you will find the contents of all referenced documents in +files named @file{doc*.html} even if they do not contain HTML code. +The most annoying thing is that we always have to pass the proxy to +GETURL. If you do not like to see the headers of the web pages +appear on the screen, you can redirect them to @file{/dev/null}. +Watching the headers appear can be quite interesting, because +it reveals +interesting details such as which web server the companies use. +Now, it is clear how the clever marketing people +use web robots to determine the +market shares +of Microsoft and Netscape in the web server market. + +Port 80 of any web server is like a small hole in a repellent firewall. +After attaching a browser to port 80, we usually catch a glimpse +of the bright side of the server (its home page). With a tool like GETURL +at hand, we are able to discover some of the more concealed +or even ``indecent'' services (i.e., lacking conformity to standards of quality). +It can be exciting to see the fancy CGI scripts that lie +there, revealing the inner workings of the server, ready to be called: + +@itemize @bullet +@item +With a command such as: + +@example +gawk -f geturl.awk http://any.host.on.the.net/cgi-bin/ +@end example + +some servers give you a directory listing of the CGI files. +Knowing the names, you can try to call some of them and watch +for useful results. Sometimes there are executables in such directories +(such as Perl interpreters) that you may call remotely. If there are +subdirectories with configuration data of the web server, this can also +be quite interesting to read. + +@item +@cindex apache +The well-known Apache web server usually has its CGI files in the +directory @file{/cgi-bin}. There you can often find the scripts +@file{test-cgi} and @file{printenv}. Both tell you some things +about the current connection and the installation of the web server. +Just call: + +@smallexample +gawk -f geturl.awk http://any.host.on.the.net/cgi-bin/test-cgi +gawk -f geturl.awk http://any.host.on.the.net/cgi-bin/printenv +@end smallexample + +@item +Sometimes it is even possible to retrieve system files like the web +server's log file---possibly containing customer data---or even the file +@file{/etc/passwd}. +(We don't recommend this!) +@end itemize + +@strong{Caution:} +Although this may sound funny or simply irrelevant, we are talking about +severe security holes. Try to explore your own system this way and make +sure that none of the above reveals too much information about your system. + +@node STATIST, MAZE, WEBGRAB, Some Applications and Techniques +@section STATIST: Graphing a Statistical Distribution +@cindex STATIST program + +@cindex GNUPlot utility +@cindex image format +@cindex @file{gif} image format +@cindex @file{png} image format +@cindex @file{ps} image format +@cindex Boutell, Thomas +@iftex +@image{statist,3in} +@end iftex +In the HTTP server examples we've shown thus far, we never present an image +to the browser and its user. Presenting images is one task. Generating +images that reflect some user input and presenting these dynamically +generated images is another. In this @value{SECTION}, we use GNUPlot +for generating @file{.png}, @file{.ps}, or @file{.gif} +files.@footnote{Due to licensing problems, the default +installation of GNUPlot disables the generation of @file{.gif} files. +If your installed version does not accept @samp{set term gif}, +just download and install the most recent version of GNUPlot and the +@uref{http://www.boutell.com/gd/, GD library} +by Thomas Boutell. +Otherwise you still have the chance to generate some +ASCII-art style images with GNUPlot by using @samp{set term dumb}. +(We tried it and it worked.)} + +The program we develop takes the statistical parameters of two samples +and computes the t-test statistics. As a result, we get the probabilities +that the means and the variances of both samples are the same. In order to +let the user check plausibility, the program presents an image of the +distributions. The statistical computation follows +@cite{Numerical Recipes in C: The Art of Scientific Computing} +by William H.@: Press, Saul A.@: Teukolsky, William T.@: Vetterling, and Brian P. Flannery. +Since @command{gawk} does not have a built-in function +for the computation of the beta function, we use the @code{ibeta} function +of GNUPlot. As a side effect, we learn how to use GNUPlot as a +sophisticated calculator. The comparison of means is done as in @code{tutest}, +paragraph 14.2, page 613, and the comparison of variances is done as in @code{ftest}, +page 611 in @cite{Numerical Recipes}. +@cindex Numerical Recipes + +As usual, we take the site-independent code for servers and append +our own functions @code{SetUpServer} and @code{HandleGET}: + +@smallexample +@c file eg/network/statist.awk +function SetUpServer() @{ + TopHeader = "Statistics with GAWK" + TopDoc = "\ +

Please choose one of the following actions:

\ + " + TopFooter = "" + GnuPlot = "gnuplot 2>&1" + m1=m2=0; v1=v2=1; n1=n2=10 +@} +@c endfile +@end smallexample + +Here, you see the menu structure that the user sees. Later, we +will see how the program structure of the @code{HandleGET} function +reflects the menu structure. What is missing here is the link for the +image we generate. In an event-driven environment, request, +generation, and delivery of images are separated. + +Notice the way we initialize the @code{GnuPlot} command string for +the pipe. By default, +GNUPlot outputs the generated image via standard output, as well as +the results of @code{print}(ed) calculations via standard error. +The redirection causes standard error to be mixed into standard +output, enabling us to read results of calculations with @code{getline}. +By initializing the statistical parameters with some meaningful +defaults, we make sure the user gets an image the first time +he uses the program. + +@cindex JavaScript +Following is the rather long function @code{HandleGET}, which +implements the contents of this service by reacting to the different +kinds of requests from the browser. Before you start playing with +this script, make sure that your browser supports JavaScript and that it also +has this option switched on. The script uses a short snippet of +JavaScript code for delayed opening of a window with an image. +A more detailed explanation follows: + +@smallexample +@c file eg/network/statist.awk +function HandleGET() @{ + if(MENU[2] == "AboutServer") @{ + Document = "This is a GUI for a statistical computation.\ + It compares means and variances of two distributions.\ + It is implemented as one GAWK script and uses GNUPLOT." + @} else if (MENU[2] == "EnterParameters") @{ + Document = "" + if ("m1" in GETARG) @{ # are there parameters to compare? + Document = Document "" + m1 = GETARG["m1"]; v1 = GETARG["v1"]; n1 = GETARG["n1"] + m2 = GETARG["m2"]; v2 = GETARG["v2"]; n2 = GETARG["n2"] + t = (m1-m2)/sqrt(v1/n1+v2/n2) + df = (v1/n1+v2/n2)*(v1/n1+v2/n2)/((v1/n1)*(v1/n1)/(n1-1) \ + + (v2/n2)*(v2/n2) /(n2-1)) + if (v1>v2) @{ + f = v1/v2 + df1 = n1 - 1 + df2 = n2 - 1 + @} else @{ + f = v2/v1 + df1 = n2 - 1 + df2 = n1 - 1 + @} + print "pt=ibeta(" df/2 ",0.5," df/(df+t*t) ")" |& GnuPlot + print "pF=2.0*ibeta(" df2/2 "," df1/2 "," \ + df2/(df2+df1*f) ")" |& GnuPlot + print "print pt, pF" |& GnuPlot + RS="\n"; GnuPlot |& getline; RS="\r\n" # $1 is pt, $2 is pF + print "invsqrt2pi=1.0/sqrt(2.0*pi)" |& GnuPlot + print "nd(x)=invsqrt2pi/sd*exp(-0.5*((x-mu)/sd)**2)" |& GnuPlot + print "set term png small color" |& GnuPlot + #print "set term postscript color" |& GnuPlot + #print "set term gif medium size 320,240" |& GnuPlot + print "set yrange[-0.3:]" |& GnuPlot + print "set label 'p(m1=m2) =" $1 "' at 0,-0.1 left" |& GnuPlot + print "set label 'p(v1=v2) =" $2 "' at 0,-0.2 left" |& GnuPlot + print "plot mu=" m1 ",sd=" sqrt(v1) ", nd(x) title 'sample 1',\ + mu=" m2 ",sd=" sqrt(v2) ", nd(x) title 'sample 2'" |& GnuPlot + print "quit" |& GnuPlot + GnuPlot |& getline Image + while ((GnuPlot |& getline) > 0) + Image = Image RS $0 + close(GnuPlot) + @} + Document = Document "\ +

Do these samples have the same Gaussian distribution?

\ +
\ + \ + + \ + + \ + + \ + \ + + \ + + \ + + \ + \ +
1. Mean 1. Variance1. Count
2. Mean 2. Variance2. Count

" + @} else if (MENU[2] ~ "Image") @{ + Reason = "OK" ORS "Content-type: image/png" + #Reason = "OK" ORS "Content-type: application/x-postscript" + #Reason = "OK" ORS "Content-type: image/gif" + Header = Footer = "" + Document = Image + @} +@} +@c endfile +@end smallexample + +@cindex PostScript +As usual, we give a short description of the service in the first +menu choice. The third menu choice shows us that generation and +presentation of an image are two separate actions. While the latter +takes place quite instantly in the third menu choice, the former +takes place in the much longer second choice. Image data passes from the +generating action to the presenting action via the variable @code{Image} +that contains a complete @file{.png} image, which is otherwise stored +in a file. If you prefer @file{.ps} or @file{.gif} images over the +default @file{.png} images, you may select these options by uncommenting +the appropriate lines. But remember to do so in two places: when +telling GNUPlot which kind of images to generate, and when transmitting the +image at the end of the program. + +Looking at the end of the program, +the way we pass the @samp{Content-type} to the browser is a bit unusual. +It is appended to the @samp{OK} of the first header line +to make sure the type information becomes part of the header. +The other variables that get transmitted across the network are +made empty, because in this case we do not have an HTML document to +transmit, but rather raw image data to contain in the body. + +Most of the work is done in the second menu choice. It starts with a +strange JavaScript code snippet. When first implementing this server, +we used a short @code{@w{""} here. But then +browsers got smarter and tried to improve on speed by requesting the +image and the HTML code at the same time. When doing this, the browser +tries to build up a connection for the image request while the request for +the HTML text is not yet completed. The browser tries to connect +to the @command{gawk} server on port 8080 while port 8080 is still in use for +transmission of the HTML text. The connection for the image cannot be +built up, so the image appears as ``broken'' in the browser window. +We solved this problem by telling the browser to open a separate window +for the image, but only after a delay of 1000 milliseconds. +By this time, the server should be ready for serving the next request. + +But there is one more subtlety in the JavaScript code. +Each time the JavaScript code opens a window for the image, the +name of the image is appended with a timestamp (@code{systime}). +Why this constant change of name for the image? Initially, we always named +the image @code{Image}, but then the Netscape browser noticed the name +had @emph{not} changed since the previous request and displayed the +previous image (caching behavior). The server core +is implemented so that browsers are told @emph{not} to cache anything. +Obviously HTTP requests do not always work as expected. One way to +circumvent the cache of such overly smart browsers is to change the +name of the image with each request. These three lines of JavaScript +caused us a lot of trouble. + +The rest can be broken +down into two phases. At first, we check if there are statistical +parameters. When the program is first started, there usually are no +parameters because it enters the page coming from the top menu. +Then, we only have to present the user a form that he can use to change +statistical parameters and submit them. Subsequently, the submission of +the form causes the execution of the first phase because @emph{now} +there @emph{are} parameters to handle. + +Now that we have parameters, we know there will be an image available. +Therefore we insert the JavaScript code here to initiate the opening +of the image in a separate window. Then, +we prepare some variables that will be passed to GNUPlot for calculation +of the probabilities. Prior to reading the results, we must temporarily +change @code{RS} because GNUPlot separates lines with newlines. +After instructing GNUPlot to generate a @file{.png} (or @file{.ps} or +@file{.gif}) image, we initiate the insertion of some text, +explaining the resulting probabilities. The final @samp{plot} command +actually generates the image data. This raw binary has to be read in carefully +without adding, changing, or deleting a single byte. Hence the unusual +initialization of @code{Image} and completion with a @code{while} loop. + +When using this server, it soon becomes clear that it is far from being +perfect. It mixes source code of six scripting languages or protocols: + +@itemize @bullet +@item GNU @command{awk} implements a server for the protocol: +@item HTTP which transmits: +@item HTML text which contains a short piece of: +@item JavaScript code opening a separate window. +@item A Bourne shell script is used for piping commands into: +@item GNUPlot to generate the image to be opened. +@end itemize + +After all this work, the GNUPlot image opens in the JavaScript window +where it can be viewed by the user. + +It is probably better not to mix up so many different languages. +The result is not very readable. Furthermore, the +statistical part of the server does not take care of invalid input. +Among others, using negative variances will cause invalid results. + +@node MAZE, MOBAGWHO, STATIST, Some Applications and Techniques +@section MAZE: Walking Through a Maze In Virtual Reality +@cindex MAZE +@cindex VRML +@c VRML in iX 11/96 134. +@quotation +@cindex Perlis, Alan +@i{In the long run, every program becomes rococo, and then rubble.}@* +Alan Perlis +@end quotation + +By now, we know how to present arbitrary @samp{Content-type}s to a browser. +In this @value{SECTION}, our server will present a 3D world to our browser. +The 3D world is described in a scene description language (VRML, +Virtual Reality Modeling Language) that allows us to travel through a +perspective view of a 2D maze with our browser. Browsers with a +VRML plugin enable exploration of this technology. We could do +one of those boring @samp{Hello world} examples here, that are usually +presented when introducing novices to +VRML. If you have never written +any VRML code, have a look at +the VRML FAQ. +Presenting a static VRML scene is a bit trivial; in order to expose +@command{gawk}'s new capabilities, we will present a dynamically generated +VRML scene. The function @code{SetUpServer} is very simple because it +only sets the default HTML page and initializes the random number +generator. As usual, the surrounding server lets you browse the maze. + +@smallexample +@c file eg/network/maze.awk +function SetUpServer() @{ + TopHeader = "Walk through a maze" + TopDoc = "\ +

Please choose one of the following actions:

\ + " + TopFooter = "" + srand() +@} +@c endfile +@end smallexample + +The function @code{HandleGET} is a bit longer because it first computes +the maze and afterwards generates the VRML code that is sent across +the network. As shown in the STATIST example +(@pxref{STATIST}), +we set the type of the +content to VRML and then store the VRML representation of the maze as the +page content. We assume that the maze is stored in a 2D array. Initially, +the maze consists of walls only. Then, we add an entry and an exit to the +maze and let the rest of the work be done by the function @code{MakeMaze}. +Now, only the wall fields are left in the maze. By iterating over the these +fields, we generate one line of VRML code for each wall field. + +@smallexample +@c file eg/network/maze.awk +function HandleGET() @{ + if (MENU[2] == "AboutServer") @{ + Document = "If your browser has a VRML 2 plugin,\ + this server shows you a simple VRML scene." + @} else if (MENU[2] == "VRMLtest") @{ + XSIZE = YSIZE = 11 # initially, everything is wall + for (y = 0; y < YSIZE; y++) + for (x = 0; x < XSIZE; x++) + Maze[x, y] = "#" + delete Maze[0, 1] # entry is not wall + delete Maze[XSIZE-1, YSIZE-2] # exit is not wall + MakeMaze(1, 1) + Document = "\ +#VRML V2.0 utf8\n\ +Group @{\n\ + children [\n\ + PointLight @{\n\ + ambientIntensity 0.2\n\ + color 0.7 0.7 0.7\n\ + location 0.0 8.0 10.0\n\ + @}\n\ + DEF B1 Background @{\n\ + skyColor [0 0 0, 1.0 1.0 1.0 ]\n\ + skyAngle 1.6\n\ + groundColor [1 1 1, 0.8 0.8 0.8, 0.2 0.2 0.2 ]\n\ + groundAngle [ 1.2 1.57 ]\n\ + @}\n\ + DEF Wall Shape @{\n\ + geometry Box @{size 1 1 1@}\n\ + appearance Appearance @{ material Material @{ diffuseColor 0 0 1 @} @}\n\ + @}\n\ + DEF Entry Viewpoint @{\n\ + position 0.5 1.0 5.0\n\ + orientation 0.0 0.0 -1.0 0.52\n\ + @}\n" + for (i in Maze) @{ + split(i, t, SUBSEP) + Document = Document " Transform @{ translation " + Document = Document t[1] " 0 -" t[2] " children USE Wall @}\n" + @} + Document = Document " ] # end of group for world\n@}" + Reason = "OK" ORS "Content-type: model/vrml" + Header = Footer = "" + @} +@} +@c endfile +@end smallexample + +Finally, we have a look at @code{MakeMaze}, the function that generates +the @code{Maze} array. When entered, this function assumes that the array +has been initialized so that each element represents a wall element and +the maze is initially full of wall elements. Only the entrance and the exit +of the maze should have been left free. The parameters of the function tell +us which element must be marked as not being a wall. After this, we take +a look at the four neighbouring elements and remember which we have already +treated. Of all the neighbouring elements, we take one at random and +walk in that direction. Therefore, the wall element in that direction has +to be removed and then, we call the function recursively for that element. +The maze is only completed if we iterate the above procedure for +@emph{all} neighbouring elements (in random order) and for our present +element by recursively calling the function for the present element. This +last iteration could have been done in a loop, +but it is done much simpler recursively. + +Notice that elements with coordinates that are both odd are assumed to be +on our way through the maze and the generating process cannot terminate +as long as there is such an element not being @code{delete}d. All other +elements are potentially part of the wall. + +@smallexample +@c file eg/network/maze.awk +function MakeMaze(x, y) @{ + delete Maze[x, y] # here we are, we have no wall here + p = 0 # count unvisited fields in all directions + if (x-2 SUBSEP y in Maze) d[p++] = "-x" + if (x SUBSEP y-2 in Maze) d[p++] = "-y" + if (x+2 SUBSEP y in Maze) d[p++] = "+x" + if (x SUBSEP y+2 in Maze) d[p++] = "+y" + if (p>0) @{ # if there are univisited fields, go there + p = int(p*rand()) # choose one unvisited field at random + if (d[p] == "-x") @{ delete Maze[x - 1, y]; MakeMaze(x - 2, y) + @} else if (d[p] == "-y") @{ delete Maze[x, y - 1]; MakeMaze(x, y - 2) + @} else if (d[p] == "+x") @{ delete Maze[x + 1, y]; MakeMaze(x + 2, y) + @} else if (d[p] == "+y") @{ delete Maze[x, y + 1]; MakeMaze(x, y + 2) + @} # we are back from recursion + MakeMaze(x, y); # try again while there are unvisited fields + @} +@} +@c endfile +@end smallexample + +@node MOBAGWHO, STOXPRED, MAZE, Some Applications and Techniques +@section MOBAGWHO: a Simple Mobile Agent +@cindex MOBAGWHO program +@cindex agent +@quotation +@cindex Hoare, C.A.R. +@i{There are two ways of constructing a software design: One way is to +make it so simple that there are obviously no deficiencies, and the +other way is to make it so complicated that there are no obvious +deficiencies.} @* +C. A. R. Hoare +@end quotation + +A @dfn{mobile agent} is a program that can be dispatched from a computer and +transported to a remote server for execution. This is called @dfn{migration}, +which means that a process on another system is started that is independent +from its originator. Ideally, it wanders through +a network while working for its creator or owner. In places like +the UMBC Agent Web, +people are quite confident that (mobile) agents are a software engineering +paradigm that enables us to significantly increase the efficiency +of our work. Mobile agents could become the mediators between users and +the networking world. For an unbiased view at this technology, +see the remarkable paper @cite{Mobile Agents: Are they a good +idea?}.@footnote{@uref{http://www.research.ibm.com/massive/mobag.ps}} + +@ignore +@c Chuck says to take all of this out. +@cindex Tcl/Tk +A good instance of this paradigm is +@cite{Agent Tcl},@footnote{@uref{http://agent.cs.dartmouth.edu/software/agent2.0/}} +an extension of the Tcl language. After introducing a typical +development environment, the aforementioned paper shows a nice little +example application that we will try to rebuild in @command{gawk}. The +@command{who} agent takes a list of servers and wanders from one server +to the next one, always looking to see who is logged in. +Having reached the last +one, it sends back a message with a list of all users it found on each +machine. + +But before implementing something that might or might not be a mobile +agent, let us clarify the concept and some important terms. The agent +paradigm in general is such a young scientific discipline that it has +not yet developed a widely-accepted terminology. Some authors try to +give precise definitions, but their scope is often not wide enough +to be generally accepted. Franklin and Graesser ask +@cite{Is it an Agent or just a Program: A Taxonomy for Autonomous +Agents}@footnote{@uref{http://www.msci.memphis.edu/~franklin/AgentProg.html}} +and give even better answers than Caglayan and Harrison in their +@cite{Agent Sourcebook}.@footnote{@uref{http://www.aminda.com/mazzu/sourcebook/}} + +@itemize @minus +@item +@i{An autonomous agent is a system situated within and a part of +an environment that senses that environment and acts on it, over time, in +pursuit of its own agenda and so as to effect what it senses in the future.} +(Quoted from Franklin and Graesser.) +@item +A mobile agent is able to transport itself from one machine to another. +@item +The term @dfn{migration} often denotes this process of moving. +But neither of the two sources above even mentions this term, while others +use it regularly. +@end itemize + +Before delving into the (rather demanding) details of +implementation, let us give just one more quotation as a final +motivation. Steven Farley published an excellent paper called +@cite{Mobile Agent System Architecture},@footnote{This often +cited text originally appeared as a conference paper here: +@uref{http://www.sigs.com/publications/docs/java/9705/farley.html} +Many bibliographies on the Internet point to this dead link. Meanwhile, +the paper appeared as a contribution to a book called More Java Gems here: +@uref{http://uk.cambridge.org/computerscience/object/catalogue/0521774772/default.htm}} +in which he asks ``Why use an agent architecture?'' + +@quotation +If client-server systems are the currently established norm and distributed +object systems such as CORBA are defining the future standards, why bother +with agents? Agent architectures have certain advantages over these other +types. Three of the most important advantages are: +@cindex CORBA + +@enumerate +@item +An agent performs much processing at the server where local bandwidth +is high, thus reducing the amount of network bandwidth consumed and increasing +overall performance. In contrast, a CORBA client object with the equivalent +functionality of a given agent must make repeated remote method calls to +the server object because CORBA objects cannot move across the network +at runtime. + +@item +An agent operates independently of the application from which the +agent was invoked. The agent operates asynchronously, meaning that the +client application does not need to wait for the results. This is especially +important for mobile users who are not always connected to the network. + +@item +The use of agents allows for the injection of new functionality into +a system at run time. An agent system essentially contains its own automatic +software distribution mechanism. Since CORBA has no built-in support for +mobile code, new functionality generally has to be installed manually. + +@end enumerate + +Of course a non-agent system can exhibit these same features with some +work. But the mobile code paradigm supports the transfer of executable +code to a remote location for asynchronous execution from the start. An +agent architecture should be considered for systems where the above features +are primary requirements. +@end quotation +@end ignore + +When trying to migrate a process from one system to another, +a server process is needed on the receiving side. Depending on the kind +of server process, several ways of implementation come to mind. +How the process is implemented depends upon the kind of server process: + +@itemize @bullet +@item +HTTP can be used as the protocol for delivery of the migrating +process. In this case, we use a common web +server as the receiving server process. A universal CGI script +mediates between migrating process and web server. +Each server willing to accept migrating agents makes this universal +service available. HTTP supplies the @code{POST} method to transfer +some data to a file on the web server. When a CGI script is called +remotely with the @code{POST} method instead of the usual @code{GET} method, +data is transmitted from the client process to the standard input +of the server's CGI script. So, to implement a mobile agent, +we must not only write the agent program to start on the client +side, but also the CGI script to receive the agent on the server side. + +@cindex CGI +@cindex apache +@item +The @code{PUT} method can also be used for migration. HTTP does not +require a CGI script for migration via @code{PUT}. However, with common web +servers there is no advantage to this solution, because web servers such as +Apache +require explicit activation of a special @code{PUT} script. + +@item +@cite{Agent Tcl} pursues a different course; it relies on a dedicated server +process with a dedicated protocol specialized for receiving mobile agents. +@end itemize + +Our agent example abuses a common web server as a migration tool. So, it needs a +universal CGI script on the receiving side (the web server). The receiving script is +activated with a @code{POST} request when placed into a location like +@file{/httpd/cgi-bin/PostAgent.sh}. Make sure that the server system uses a +version of @command{gawk} that supports network access (Version 3.1 or later; +verify with @samp{gawk --version}). + +@example +@c file eg/network/PostAgent.sh +#!/bin/sh +MobAg=/tmp/MobileAgent.$$ +# direct script to mobile agent file +cat > $MobAg +# execute agent concurrently +gawk -f $MobAg $MobAg > /dev/null & +# HTTP header, terminator and body +gawk 'BEGIN @{ print "\r\nAgent started" @}' +rm $MobAg # delete script file of agent +@c endfile +@end example + +By making its process id (@code{$$}) part of the unique @value{FN}, the +script avoids conflicts between concurrent instances of the script. +First, all lines +from standard input (the mobile agent's source code) are copied into +this unique file. Then, the agent is started as a concurrent process +and a short message reporting this fact is sent to the submitting client. +Finally, the script file of the mobile agent is removed because it is +no longer needed. Although it is a short script, there are several noteworthy +points: + +@table @asis +@item Security +@emph{There is none}. In fact, the CGI script should never +be made available on a server that is part of the Internet because everyone +would be allowed to execute arbitrary commands with it. This behavior is +acceptable only when performing rapid prototyping. + +@item Self-Reference +Each migrating instance of an agent is started +in a way that enables it to read its own source code from standard input +and use the code for subsequent +migrations. This is necessary because it needs to treat the agent's code +as data to transmit. @command{gawk} is not the ideal language for such +a job. Lisp and Tcl are more suitable because they do not make a distinction +between program code and data. + +@item Independence +After migration, the agent is not linked to its +former home in any way. By reporting @samp{Agent started}, it waves +``Goodbye'' to its origin. The originator may choose to terminate or not. +@end table + +@cindex Lisp +The originating agent itself is started just like any other command-line +script, and reports the results on standard output. By letting the name +of the original host migrate with the agent, the agent that migrates +to a host far away from its origin can report the result back home. +Having arrived at the end of the journey, the agent establishes +a connection and reports the results. This is the reason for +determining the name of the host with @samp{uname -n} and storing it +in @code{MyOrigin} for later use. We may also set variables with the +@option{-v} option from the command line. This interactivity is only +of importance in the context of starting a mobile agent; therefore this +@code{BEGIN} pattern and its action do not take part in migration: + +@smallexample +@c file eg/network/mobag.awk +BEGIN @{ + if (ARGC != 2) @{ + print "MOBAG - a simple mobile agent" + print "CALL:\n gawk -f mobag.awk mobag.awk" + print "IN:\n the name of this script as a command-line parameter" + print "PARAM:\n -v MyOrigin=myhost.com" + print "OUT:\n the result on stdout" + print "JK 29.03.1998 01.04.1998" + exit + @} + if (MyOrigin == "") @{ + "uname -n" | getline MyOrigin + close("uname -n") + @} +@} +@c endfile +@end smallexample + +Since @command{gawk} cannot manipulate and transmit parts of the program +directly, the source code is read and stored in strings. +Therefore, the program scans itself for +the beginning and the ending of functions. +Each line in between is appended to the code string until the end of +the function has been reached. A special case is this part of the program +itself. It is not a function. +Placing a similar framework around it causes it to be treated +like a function. Notice that this mechanism works for all the +functions of the source code, but it cannot guarantee that the order +of the functions is preserved during migration: + +@smallexample +@c file eg/network/mobag.awk +#ReadMySelf +/^function / @{ FUNC = $2 @} +/^END/ || /^#ReadMySelf/ @{ FUNC = $1 @} +FUNC != "" @{ MOBFUN[FUNC] = MOBFUN[FUNC] RS $0 @} +(FUNC != "") && (/^@}/ || /^#EndOfMySelf/) \ + @{ FUNC = "" @} +#EndOfMySelf +@c endfile +@end smallexample + +The web server code in +@ref{Interacting Service, ,A Web Service with Interaction}, +was first developed as a site-independent core. Likewise, the +@command{gawk}-based mobile agent +starts with an agent-independent core, to which can be appended +application-dependent functions. What follows is the only +application-independent function needed for the mobile agent: + +@smallexample +@c file eg/network/mobag.awk +function migrate(Destination, MobCode, Label) @{ + MOBVAR["Label"] = Label + MOBVAR["Destination"] = Destination + RS = ORS = "\r\n" + HttpService = "/inet/tcp/0/" Destination + for (i in MOBFUN) + MobCode = (MobCode "\n" MOBFUN[i]) + MobCode = MobCode "\n\nBEGIN @{" + for (i in MOBVAR) + MobCode = (MobCode "\n MOBVAR[\"" i "\"] = \"" MOBVAR[i] "\"") + MobCode = MobCode "\n@}\n" + print "POST /cgi-bin/PostAgent.sh HTTP/1.0" |& HttpService + print "Content-length:", length(MobCode) ORS |& HttpService + printf "%s", MobCode |& HttpService + while ((HttpService |& getline) > 0) + print $0 + close(HttpService) +@} +@c endfile +@end smallexample + +The @code{migrate} function prepares the +aforementioned strings containing the program code and transmits them to a +server. A consequence of this modular approach is that the @code{migrate} +function takes some parameters that aren't needed in this application, +but that will be in future ones. Its mandatory parameter @code{Destination} holds the +name (or IP address) of the server that the agent wants as a host for its +code. The optional parameter @code{MobCode} may contain some @command{gawk} +code that is inserted during migration in front of all other code. +The optional parameter @code{Label} may contain +a string that tells the agent what to do in program execution after +arrival at its new home site. One of the serious obstacles in implementing +a framework for mobile agents is that it does not suffice to migrate the +code. It is also necessary to migrate the state of execution of the agent. In +contrast to @cite{Agent Tcl}, this program does not try to migrate the complete set +of variables. The following conventions are used: + +@itemize @bullet +@item +Each variable in an agent program is local to the current host and does +@emph{not} migrate. + +@item +The array @code{MOBFUN} shown above is an exception. It is handled +by the function @code{migrate} and does migrate with the application. + +@item +The other exception is the array @code{MOBVAR}. Each variable that +takes part in migration has to be an element of this array. +@code{migrate} also takes care of this. +@end itemize + +Now it's clear what happens to the @code{Label} parameter of the +function @code{migrate}. It is copied into @code{MOBVAR["Label"]} and +travels alongside the other data. Since travelling takes place via HTTP, +records must be separated with @code{"\r\n"} in @code{RS} and +@code{ORS} as usual. The code assembly for migration takes place in +three steps: + +@itemize @bullet +@item +Iterate over @code{MOBFUN} to collect all functions verbatim. + +@item +Prepare a @code{BEGIN} pattern and put assignments to mobile +variables into the action part. + +@item +Transmission itself resembles GETURL: the header with the request +and the @code{Content-length} is followed by the body. In case there is +any reply over the network, it is read completely and echoed to +standard output to avoid irritating the server. +@end itemize + +The application-independent framework is now almost complete. What follows +is the @code{END} pattern that is executed when the mobile agent has +finished reading its own code. First, it checks whether it is already +running on a remote host or not. In case initialization has not yet taken +place, it starts @code{MyInit}. Otherwise (later, on a remote host), it +starts @code{MyJob}: + +@smallexample +@c file eg/network/mobag.awk +END @{ + if (ARGC != 2) exit # stop when called with wrong parameters + if (MyOrigin != "") # is this the originating host? + MyInit() # if so, initialize the application + else # we are on a host with migrated data + MyJob() # so we do our job +@} +@c endfile +@end smallexample + +All that's left to extend the framework into a complete application +is to write two application-specific functions: @code{MyInit} and +@code{MyJob}. Keep in mind that the former is executed once on the +originating host, while the latter is executed after each migration: + +@smallexample +@c file eg/network/mobag.awk +function MyInit() @{ + MOBVAR["MyOrigin"] = MyOrigin + MOBVAR["Machines"] = "localhost/80 max/80 moritz/80 castor/80" + split(MOBVAR["Machines"], Machines) # which host is the first? + migrate(Machines[1], "", "") # go to the first host + while (("/inet/tcp/8080/0/0" |& getline) > 0) # wait for result + print $0 # print result + close("/inet/tcp/8080/0/0") +@} +@c endfile +@end smallexample + +As mentioned earlier, this agent takes the name of its origin +(@code{MyOrigin}) with it. Then, it takes the name of its first +destination and goes there for further work. Notice that this name has +the port number of the web server appended to the name of the server, +because the function @code{migrate} needs it this way to create +the @code{HttpService} variable. Finally, it waits for the result to arrive. +The @code{MyJob} function runs on the remote host: + +@smallexample +@c file eg/network/mobag.awk +function MyJob() @{ + # forget this host + sub(MOBVAR["Destination"], "", MOBVAR["Machines"]) + MOBVAR["Result"]=MOBVAR["Result"] SUBSEP SUBSEP MOBVAR["Destination"] ":" + while (("who" | getline) > 0) # who is logged in? + MOBVAR["Result"] = MOBVAR["Result"] SUBSEP $0 + close("who") + if (index(MOBVAR["Machines"], "/") > 0) @{ # any more machines to visit? + split(MOBVAR["Machines"], Machines) # which host is next? + migrate(Machines[1], "", "") # go there + @} else @{ # no more machines + gsub(SUBSEP, "\n", MOBVAR["Result"]) # send result to origin + print MOBVAR["Result"] |& "/inet/tcp/0/" MOBVAR["MyOrigin"] "/8080" + close("/inet/tcp/0/" MOBVAR["MyOrigin"] "/8080") + @} +@} +@c endfile +@end smallexample + +After migrating, the first thing to do in @code{MyJob} is to delete +the name of the current host from the list of hosts to visit. Now, it +is time to start the real work by appending the host's name to the +result string, and reading line by line who is logged in on this host. +A very annoying circumstance is the fact that the elements of +@code{MOBVAR} cannot hold the newline character (@code{"\n"}). If they +did, migration of this string did not work because the string didn't +obey the syntax rule for a string in @command{gawk}. +@code{SUBSEP} is used as a temporary replacement. +If the list of hosts to visit holds +at least one more entry, the agent migrates to that place to go on +working there. Otherwise, we replace the @code{SUBSEP}s +with a newline character in the resulting string, and report it to +the originating host, whose name is stored in @code{MOBVAR["MyOrigin"]}. + +@node STOXPRED, PROTBASE, MOBAGWHO, Some Applications and Techniques +@section STOXPRED: Stock Market Prediction As A Service +@cindex STOXPRED program +@cindex Yahoo +@quotation +@i{Far out in the uncharted backwaters of the unfashionable end of +the Western Spiral arm of the Galaxy lies a small unregarded yellow sun.} + +@i{Orbiting this at a distance of roughly ninety-two million miles is an +utterly insignificant little blue-green planet whose ape-descendent life +forms are so amazingly primitive that they still think digital watches are +a pretty neat idea.} + +@i{This planet has --- or rather had --- a problem, which was this: +most of the people living on it were unhappy for pretty much of the time. +Many solutions were suggested for this problem, but most of these were +largely concerned with the movements of small green pieces of paper, +which is odd because it wasn't the small green pieces of paper that +were unhappy.} @* +Douglas Adams, @cite{The Hitch Hiker's Guide to the Galaxy} +@end quotation + +@cindex @command{cron} +Valuable services on the Internet are usually @emph{not} implemented +as mobile agents. There are much simpler ways of implementing services. +All Unix systems provide, for example, the @command{cron} service. +Unix system users can write a list of tasks to be done each day, each +week, twice a day, or just once. The list is entered into a file named +@file{crontab}. For example, to distribute a newsletter on a daily +basis this way, use @command{cron} for calling a script each day early +in the morning. + +@example +# run at 8 am on weekdays, distribute the newsletter +0 8 * * 1-5 $HOME/bin/daily.job >> $HOME/log/newsletter 2>&1 +@end example + +The script first looks for interesting information on the Internet, +assembles it in a nice form and sends the results via email to +the customers. + +The following is an example of a primitive +newsletter on stock market prediction. It is a report which first +tries to predict the change of each share in the Dow Jones Industrial +Index for the particular day. Then it mentions some especially +promising shares as well as some shares which look remarkably bad +on that day. The report ends with the usual disclaimer which tells +every child @emph{not} to try this at home and hurt anybody. +@cindex Dow Jones Industrial Index + +@smallexample +Good morning Uncle Scrooge, + +This is your daily stock market report for Monday, October 16, 2000. +Here are the predictions for today: + + AA neutral + GE up + JNJ down + MSFT neutral + @dots{} + UTX up + DD down + IBM up + MO down + WMT up + DIS up + INTC up + MRK down + XOM down + EK down + IP down + +The most promising shares for today are these: + + INTC http://biz.yahoo.com/n/i/intc.html + +The stock shares to avoid today are these: + + EK http://biz.yahoo.com/n/e/ek.html + IP http://biz.yahoo.com/n/i/ip.html + DD http://biz.yahoo.com/n/d/dd.html + @dots{} +@end smallexample + +@ignore +@c Chuck suggests removing this paragraph +If you are not into stock market prediction but want to earn money +with a more humane service, you might prefer to send out horoscopes +to your customers. Or, once every refrigerator in every household on this side +of the Chinese Wall is connected to the Internet, such a service could +inspect the contents of your customer's refrigerators each day and +advise them on nutrition. Big Brother is watching them. +@end ignore + +The script as a whole is rather long. In order to ease the pain of +studying other people's source code, we have broken the script +up into meaningful parts which are invoked one after the other. +The basic structure of the script is as follows: + +@example +@c file eg/network/stoxpred.awk +BEGIN @{ + Init() + ReadQuotes() + CleanUp() + Prediction() + Report() + SendMail() +@} +@c endfile +@end example + +The earlier parts store data into variables and arrays which are +subsequently used by later parts of the script. The @code{Init} function +first checks if the script is invoked correctly (without any parameters). +If not, it informs the user of the correct usage. What follows are preparations +for the retrieval of the historical quote data. The names of the 30 stock +shares are stored in an array @code{name} along with the current date +in @code{day}, @code{month}, and @code{year}. + +All users who are separated +from the Internet by a firewall and have to direct their Internet accesses +to a proxy must supply the name of the proxy to this script with the +@samp{-v Proxy=@var{name}} option. For most users, the default proxy and +port number should suffice. + +@example +@c file eg/network/stoxpred.awk +function Init() @{ + if (ARGC != 1) @{ + print "STOXPRED - daily stock share prediction" + print "IN:\n no parameters, nothing on stdin" + print "PARAM:\n -v Proxy=MyProxy -v ProxyPort=80" + print "OUT:\n commented predictions as email" + print "JK 09.10.2000" + exit + @} + # Remember ticker symbols from Dow Jones Industrial Index + StockCount = split("AA GE JNJ MSFT AXP GM JPM PG BA HD KO \ + SBC C HON MCD T CAT HWP MMM UTX DD IBM MO WMT DIS INTC \ + MRK XOM EK IP", name); + # Remember the current date as the end of the time series + day = strftime("%d") + month = strftime("%m") + year = strftime("%Y") + if (Proxy == "") Proxy = "chart.yahoo.com" + if (ProxyPort == 0) ProxyPort = 80 + YahooData = "/inet/tcp/0/" Proxy "/" ProxyPort +@} +@c endfile +@end example + +@cindex CSV format +There are two really interesting parts in the script. One is the +function which reads the historical stock quotes from an Internet +server. The other is the one that does the actual prediction. In +the following function we see how the quotes are read from the +Yahoo server. The data which comes from the server is in +CSV format (comma-separated values): + +@example +@c file eg/network/stoxdata.txt +Date,Open,High,Low,Close,Volume +9-Oct-00,22.75,22.75,21.375,22.375,7888500 +6-Oct-00,23.8125,24.9375,21.5625,22,10701100 +5-Oct-00,24.4375,24.625,23.125,23.50,5810300 +@c endfile +@end example + +Lines contain values of the same time instant, whereas columns are +separated by commas and contain the kind of data that is described +in the header (first) line. At first, @command{gawk} is instructed to +separate columns by commas (@samp{FS = ","}). In the loop that follows, +a connection to the Yahoo server is first opened, then a download takes +place, and finally the connection is closed. All this happens once for +each ticker symbol. In the body of this loop, an Internet address is +built up as a string according to the rules of the Yahoo server. The +starting and ending date are chosen to be exactly the same, but one year +apart in the past. All the action is initiated within the @code{printf} +command which transmits the request for data to the Yahoo server. + +In the inner loop, the server's data is first read and then scanned +line by line. Only lines which have six columns and the name of a month +in the first column contain relevant data. This data is stored +in the two-dimensional array @code{quote}; one dimension +being time, the other being the ticker symbol. During retrieval of the +first stock's data, the calendar names of the time instances are stored +in the array @code{day} because we need them later. + +@smallexample +@c file eg/network/stoxpred.awk +function ReadQuotes() @{ + # Retrieve historical data for each ticker symbol + FS = "," + for (stock = 1; stock <= StockCount; stock++) @{ + URL = "http://chart.yahoo.com/table.csv?s=" name[stock] \ + "&a=" month "&b=" day "&c=" year-1 \ + "&d=" month "&e=" day "&f=" year \ + "g=d&q=q&y=0&z=" name[stock] "&x=.csv" + printf("GET " URL " HTTP/1.0\r\n\r\n") |& YahooData + while ((YahooData |& getline) > 0) @{ + if (NF == 6 && $1 ~ /Jan|Feb|Mar|Apr|May|Jun|Jul|Aug|Sep|Oct|Nov|Dec/) @{ + if (stock == 1) + days[++daycount] = $1; + quote[$1, stock] = $5 + @} + @} + close(YahooData) + @} + FS = " " +@} +@c endfile +@end smallexample + +Now that we @emph{have} the data, it can be checked once again to make sure +that no individual stock is missing or invalid, and that all the stock quotes are +aligned correctly. Furthermore, we renumber the time instances. The +most recent day gets day number 1 and all other days get consecutive +numbers. All quotes are rounded toward the nearest whole number in US Dollars. + +@smallexample +@c file eg/network/stoxpred.awk +function CleanUp() @{ + # clean up time series; eliminate incomplete data sets + for (d = 1; d <= daycount; d++) @{ + for (stock = 1; stock <= StockCount; stock++) + if (! ((days[d], stock) in quote)) + stock = StockCount + 10 + if (stock > StockCount + 1) + continue + datacount++ + for (stock = 1; stock <= StockCount; stock++) + data[datacount, stock] = int(0.5 + quote[days[d], stock]) + @} + delete quote + delete days +@} +@c endfile +@end smallexample + +Now we have arrived at the second really interesting part of the whole affair. +What we present here is a very primitive prediction algorithm: +@emph{If a stock fell yesterday, assume it will also fall today; if +it rose yesterday, assume it will rise today}. (Feel free to replace this +algorithm with a smarter one.) If a stock changed in the same direction +on two consecutive days, this is an indication which should be highlighted. +Two-day advances are stored in @code{hot} and two-day declines in +@code{avoid}. + +The rest of the function is a sanity check. It counts the number of +correct predictions in relation to the total number of predictions +one could have made in the year before. + +@smallexample +@c file eg/network/stoxpred.awk +function Prediction() @{ + # Predict each ticker symbol by prolonging yesterday's trend + for (stock = 1; stock <= StockCount; stock++) @{ + if (data[1, stock] > data[2, stock]) @{ + predict[stock] = "up" + @} else if (data[1, stock] < data[2, stock]) @{ + predict[stock] = "down" + @} else @{ + predict[stock] = "neutral" + @} + if ((data[1, stock] > data[2, stock]) && (data[2, stock] > data[3, stock])) + hot[stock] = 1 + if ((data[1, stock] < data[2, stock]) && (data[2, stock] < data[3, stock])) + avoid[stock] = 1 + @} + # Do a plausibility check: how many predictions proved correct? + for (s = 1; s <= StockCount; s++) @{ + for (d = 1; d <= datacount-2; d++) @{ + if (data[d+1, s] > data[d+2, s]) @{ + UpCount++ + @} else if (data[d+1, s] < data[d+2, s]) @{ + DownCount++ + @} else @{ + NeutralCount++ + @} + if (((data[d, s] > data[d+1, s]) && (data[d+1, s] > data[d+2, s])) || + ((data[d, s] < data[d+1, s]) && (data[d+1, s] < data[d+2, s])) || + ((data[d, s] == data[d+1, s]) && (data[d+1, s] == data[d+2, s]))) + CorrectCount++ + @} + @} +@} +@c endfile +@end smallexample + +At this point the hard work has been done: the array @code{predict} +contains the predictions for all the ticker symbols. It is up to the +function @code{Report} to find some nice words to introduce the +desired information. + +@smallexample +@c file eg/network/stoxpred.awk +function Report() @{ + # Generate report + report = "\nThis is your daily " + report = report "stock market report for "strftime("%A, %B %d, %Y")".\n" + report = report "Here are the predictions for today:\n\n" + for (stock = 1; stock <= StockCount; stock++) + report = report "\t" name[stock] "\t" predict[stock] "\n" + for (stock in hot) @{ + if (HotCount++ == 0) + report = report "\nThe most promising shares for today are these:\n\n" + report = report "\t" name[stock] "\t\thttp://biz.yahoo.com/n/" \ + tolower(substr(name[stock], 1, 1)) "/" tolower(name[stock]) ".html\n" + @} + for (stock in avoid) @{ + if (AvoidCount++ == 0) + report = report "\nThe stock shares to avoid today are these:\n\n" + report = report "\t" name[stock] "\t\thttp://biz.yahoo.com/n/" \ + tolower(substr(name[stock], 1, 1)) "/" tolower(name[stock]) ".html\n" + @} + report = report "\nThis sums up to " HotCount+0 " winners and " AvoidCount+0 + report = report " losers. When using this kind\nof prediction scheme for" + report = report " the 12 months which lie behind us,\nwe get " UpCount + report = report " 'ups' and " DownCount " 'downs' and " NeutralCount + report = report " 'neutrals'. Of all\nthese " UpCount+DownCount+NeutralCount + report = report " predictions " CorrectCount " proved correct next day.\n" + report = report "A success rate of "\ + int(100*CorrectCount/(UpCount+DownCount+NeutralCount)) "%.\n" + report = report "Random choice would have produced a 33% success rate.\n" + report = report "Disclaimer: Like every other prediction of the stock\n" + report = report "market, this report is, of course, complete nonsense.\n" + report = report "If you are stupid enough to believe these predictions\n" + report = report "you should visit a doctor who can treat your ailment." +@} +@c endfile +@end smallexample + +The function @code{SendMail} goes through the list of customers and opens +a pipe to the @code{mail} command for each of them. Each one receives an +email message with a proper subject heading and is addressed with his full name. + +@smallexample +@c file eg/network/stoxpred.awk +function SendMail() @{ + # send report to customers + customer["uncle.scrooge@@ducktown.gov"] = "Uncle Scrooge" + customer["more@@utopia.org" ] = "Sir Thomas More" + customer["spinoza@@denhaag.nl" ] = "Baruch de Spinoza" + customer["marx@@highgate.uk" ] = "Karl Marx" + customer["keynes@@the.long.run" ] = "John Maynard Keynes" + customer["bierce@@devil.hell.org" ] = "Ambrose Bierce" + customer["laplace@@paris.fr" ] = "Pierre Simon de Laplace" + for (c in customer) @{ + MailPipe = "mail -s 'Daily Stock Prediction Newsletter'" c + print "Good morning " customer[c] "," | MailPipe + print report "\n.\n" | MailPipe + close(MailPipe) + @} +@} +@c endfile +@end smallexample + +Be patient when running the script by hand. +Retrieving the data for all the ticker symbols and sending the emails +may take several minutes to complete, depending upon network traffic +and the speed of the available Internet link. +The quality of the prediction algorithm is likely to be disappointing. +Try to find a better one. +Should you find one with a success rate of more than 50%, please tell +us about it! It is only for the sake of curiosity, of course. @code{:-)} + +@ignore +@c chuck says to remove this +Let us give you one final indication as to what one can expect from +a prediction of stock data, which is sometimes said to contain much +randomness. One theory says that all relevant information to be taken +into account when estimating the price of a stock is contained in the +stock quotes. Every bit of useful information has influenced the +fair price. Therefore (the theory says) temporary changes (i.e., fluctuations +within a minute) have to be purely random. But what is the cause of +short-term changes in stock prices? + +Stock prices are fixed when supply and demand meet each other. +What people are willing to pay reflects human expectations. +Human expectations are not necessarily random. On the Internet, +you can find an elucidating paper about predictability and human +expectations: +@uref{http://it.ucsd.edu/IT/Newsletter/archives/meir/05meir.html, +@cite{Reflections on ``Universal Prediction of Individual Sequences''}} +The authors (Feder, Merhav, Gutman) introduce the reader to the subject +by telling a thrilling anecdote. +@cindex Shannon, Claude +@quotation +In the early 50's, at Bell Laboratories, David Hagelbarger built a +simple ``mind reading'' machine, whose purpose was to play the ``penny +matching'' game. In this game, a player chooses head or tail, while a +``mind reading'' machine tries to predict and match his choice. +Surprisingly, as Robert Lucky tells in his book ``Silicon Dreams'', +Hagelbarger's simple, 8-state machine, was able to match the ``pennies'' +of its human opponent 5,218 times over the course of 9,795 plays. +Random guessing would lead to such a high success rate with a probability +less than one out of 10 billion! Shannon, who was interested in prediction, +information, and thinking machines, closely followed Hagelbarger's +machine, and eventually built his own stripped-down version of the machine, +having the same states, but one that used a simpler strategy at each state. +As the legend goes, in a duel between the two machines, Shannon's machine +won by a slight margin! No one knows if this was due to a superior algorithm +or just a chance happening associated with the specific sequence at that game. +In any event, the success of both these machines against ``untrained'' human +opponents was explained by the fact that the human opponents cannot draw +completely random +bits. +@end quotation +@end ignore + +@node PROTBASE, , STOXPRED, Some Applications and Techniques +@section PROTBASE: Searching Through A Protein Database +@cindex PROTBASE +@cindex NCBI, National Center for Biotechnology Information +@cindex BLAST, Basic Local Alignment Search Tool +@cindex Hoare, C.A.R. +@quotation +@i{Hoare's Law of Large Problems: Inside every large problem is a small + problem struggling to get out.} +@end quotation + +Yahoo's database of stock market data is just one among the many large +databases on the Internet. Another one is located at NCBI +(National Center for Biotechnology +Information). Established in 1988 as a national resource for molecular +biology information, NCBI creates public databases, conducts research +in computational biology, develops software tools for analyzing genome +data, and disseminates biomedical information. In this section, we +look at one of NCBI's public services, which is called BLAST +(Basic Local Alignment Search Tool). + +You probably know that the information necessary for reproducing living +cells is encoded in the genetic material of the cells. The genetic material +is a very long chain of four base nucleotides. It is the order of +appearance (the sequence) of nucleotides which contains the information +about the substance to be produced. Scientists in biotechnology often +find a specific fragment, determine the nucleotide sequence, and need +to know where the sequence at hand comes from. This is where the large +databases enter the game. At NCBI, databases store the knowledge +about which sequences have ever been found and where they have been found. +When the scientist sends his sequence to the BLAST service, the server +looks for regions of genetic material in its database which +look the most similar to the delivered nucleotide sequence. After a +search time of some seconds or minutes the server sends an answer to +the scientist. In order to make access simple, NCBI chose to offer +their database service through popular Internet protocols. There are +four basic ways to use the so-called BLAST services: + +@itemize @bullet +@item +The easiest way to use BLAST is through the web. Users may simply point +their browsers at the NCBI home page +and link to the BLAST pages. +NCBI provides a stable URL that may be used to perform BLAST searches +without interactive use of a web browser. This is what we will do later +in this section. +A demonstration client +and a @file{README} file demonstrate how to access this URL. + +@item +Currently, +@command{blastcl3} is the standard network BLAST client. +You can download @command{blastcl3} from the +anonymous FTP location. + +@item +BLAST 2.0 can be run locally as a full executable and can be used to run +BLAST searches against private local databases, or downloaded copies of the +NCBI databases. BLAST 2.0 executables may be found on the NCBI +anonymous FTP server. + +@item +The NCBI BLAST Email server is the best option for people without convenient +access to the web. A similarity search can be performed by sending a properly +formatted mail message containing the nucleotide or protein query sequence to +@email{blast@@ncbi.nlm.nih.gov}. The query sequence is compared against the +specified database using the BLAST algorithm and the results are returned in +an email message. For more information on formulating email BLAST searches, +you can send a message consisting of the word ``HELP'' to the same address, +@email{blast@@ncbi.nlm.nih.gov}. +@end itemize + +Our starting point is the demonstration client mentioned in the first option. +The @file{README} file that comes along with the client explains the whole +process in a nutshell. In the rest of this section, we first show +what such requests look like. Then we show how to use @command{gawk} to +implement a client in about 10 lines of code. Finally, we show how to +interpret the result returned from the service. + +Sequences are expected to be represented in the standard +IUB/IUPAC amino acid and nucleic acid codes, +with these exceptions: lower-case letters are accepted and are mapped +into upper-case; a single hyphen or dash can be used to represent a gap +of indeterminate length; and in amino acid sequences, @samp{U} and @samp{*} +are acceptable letters (see below). Before submitting a request, any numerical +digits in the query sequence should either be removed or replaced by +appropriate letter codes (e.g., @samp{N} for unknown nucleic acid residue +or @samp{X} for unknown amino acid residue). +The nucleic acid codes supported are: + +@example +A --> adenosine M --> A C (amino) +C --> cytidine S --> G C (strong) +G --> guanine W --> A T (weak) +T --> thymidine B --> G T C +U --> uridine D --> G A T +R --> G A (purine) H --> A C T +Y --> T C (pyrimidine) V --> G C A +K --> G T (keto) N --> A G C T (any) + - gap of indeterminate length +@end example + +Now you know the alphabet of nucleotide sequences. The last two lines +of the following example query show you such a sequence, which is obviously +made up only of elements of the alphabet just described. Store this example +query into a file named @file{protbase.request}. You are now ready to send +it to the server with the demonstration client. + +@example +@c file eg/network/protbase.request +PROGRAM blastn +DATALIB month +EXPECT 0.75 +BEGIN +>GAWK310 the gawking gene GNU AWK +tgcttggctgaggagccataggacgagagcttcctggtgaagtgtgtttcttgaaatcat +caccaccatggacagcaaa +@c endfile +@end example + +@cindex FASTA/Pearson format +The actual search request begins with the mandatory parameter @samp{PROGRAM} +in the first column followed by the value @samp{blastn} (the name of the +program) for searching nucleic acids. The next line contains the mandatory +search parameter @samp{DATALIB} with the value @samp{month} for the newest +nucleic acid sequences. The third line contains an optional @samp{EXPECT} +parameter and the value desired for it. The fourth line contains the +mandatory @samp{BEGIN} directive, followed by the query sequence in +FASTA/Pearson format. +Each line of information must be less than 80 characters in length. + +The ``month'' database contains all new or revised sequences released in the +last 30 days and is useful for searching against new sequences. +There are five different blast programs, @command{blastn} being the one that +compares a nucleotide query sequence against a nucleotide sequence database. + +The last server directive that must appear in every request is the +@samp{BEGIN} directive. The query sequence should immediately follow the +@samp{BEGIN} directive and must appear in FASTA/Pearson format. +A sequence in +FASTA/Pearson format begins with a single-line description. +The description line, which is required, is distinguished from the lines of +sequence data that follow it by having a greater-than (@samp{>}) symbol +in the first column. For the purposes of the BLAST server, the text of +the description is arbitrary. + +If you prefer to use a client written in @command{gawk}, just store the following +10 lines of code into a file named @file{protbase.awk} and use this client +instead. Invoke it with @samp{gawk -f protbase.awk protbase.request}. +Then wait a minute and watch the result coming in. In order to replicate +the demonstration client's behaviour as closely as possible, this client +does not use a proxy server. We could also have extended the client program +in @ref{GETURL, ,Retrieving Web Pages}, to implement the client request from +@file{protbase.awk} as a special case. + +@smallexample +@c file eg/network/protbase.awk +@{ request = request "\n" $0 @} + +END @{ + BLASTService = "/inet/tcp/0/www.ncbi.nlm.nih.gov/80" + printf "POST /cgi-bin/BLAST/nph-blast_report HTTP/1.0\n" |& BLASTService + printf "Content-Length: " length(request) "\n\n" |& BLASTService + printf request |& BLASTService + while ((BLASTService |& getline) > 0) + print $0 + close(BLASTService) +@} +@c endfile +@end smallexample + +The demonstration client from NCBI is 214 lines long (written in C) and +it is not immediately obvious what it does. Our client is so short that +it @emph{is} obvious what it does. First it loops over all lines of the +query and stores the whole query into a variable. Then the script +establishes an Internet connection to the NCBI server and transmits the +query by framing it with a proper HTTP request. Finally it receives +and prints the complete result coming from the server. + +Now, let us look at the result. It begins with an HTTP header, which you +can ignore. Then there are some comments about the query having been +filtered to avoid spuriously high scores. After this, there is a reference +to the paper that describes the software being used for searching the data +base. After a repitition of the original query's description we find the +list of significant alignments: + +@smallexample +@c file eg/network/protbase.result +Sequences producing significant alignments: (bits) Value + +gb|AC021182.14|AC021182 Homo sapiens chromosome 7 clone RP11-733... 38 0.20 +gb|AC021056.12|AC021056 Homo sapiens chromosome 3 clone RP11-115... 38 0.20 +emb|AL160278.10|AL160278 Homo sapiens chromosome 9 clone RP11-57... 38 0.20 +emb|AL391139.11|AL391139 Homo sapiens chromosome X clone RP11-35... 38 0.20 +emb|AL365192.6|AL365192 Homo sapiens chromosome 6 clone RP3-421H... 38 0.20 +emb|AL138812.9|AL138812 Homo sapiens chromosome 11 clone RP1-276... 38 0.20 +gb|AC073881.3|AC073881 Homo sapiens chromosome 15 clone CTD-2169... 38 0.20 +@c endfile +@end smallexample + +This means that the query sequence was found in seven human chromosomes. +But the value 0.20 (20%) means that the probability of an accidental match +is rather high (20%) in all cases and should be taken into account. +You may wonder what the first column means. It is a key to the specific +database in which this occurence was found. The unique sequence identifiers +reported in the search results can be used as sequence retrieval keys +via the NCBI server. The syntax of sequence header lines used by the NCBI +BLAST server depends on the database from which each sequence was obtained. +The table below lists the identifiers for the databases from which the +sequences were derived. + +@ifinfo +@example +Database Name Identifier Syntax +============================ ======================== +GenBank gb|accession|locus +EMBL Data Library emb|accession|locus +DDBJ, DNA Database of Japan dbj|accession|locus +NBRF PIR pir||entry +Protein Research Foundation prf||name +SWISS-PROT sp|accession|entry name +Brookhaven Protein Data Bank pdb|entry|chain +Kabat's Sequences of Immuno@dots{} gnl|kabat|identifier +Patents pat|country|number +GenInfo Backbone Id bbs|number +@end example +@end ifinfo + +@ifnotinfo +@multitable {Kabat's Sequences of Immuno@dots{}} {@code{@w{sp|accession|entry name}}} +@item GenBank @tab @code{gb|accession|locus} +@item EMBL Data Library @tab @code{emb|accession|locus} +@item DDBJ, DNA Database of Japan @tab @code{dbj|accession|locus} +@item NBRF PIR @tab @code{pir||entry} +@item Protein Research Foundation @tab @code{prf||name} +@item SWISS-PROT @tab @code{@w{sp|accession|entry name}} +@item Brookhaven Protein Data Bank @tab @code{pdb|entry|chain} +@item Kabat's Sequences of Immuno@dots{} @tab @code{gnl|kabat|identifier} +@item Patents @tab @code{pat|country|number} +@item GenInfo Backbone Id @tab @code{bbs|number} +@end multitable +@end ifnotinfo + + +For example, an identifier might be @samp{gb|AC021182.14|AC021182}, where the +@samp{gb} tag indicates that the identifier refers to a GenBank sequence, +@samp{AC021182.14} is its GenBank ACCESSION, and @samp{AC021182} is the GenBank LOCUS. +The identifier contains no spaces, so that a space indicates the end of the +identifier. + +Let us continue in the result listing. Each of the seven alignments mentioned +above is subsequently described in detail. We will have a closer look at +the first of them. + +@smallexample +>gb|AC021182.14|AC021182 Homo sapiens chromosome 7 clone RP11-733N23, WORKING DRAFT SEQUENCE, 4 + unordered pieces + Length = 176383 + + Score = 38.2 bits (19), Expect = 0.20 + Identities = 19/19 (100%) + Strand = Plus / Plus + +Query: 35 tggtgaagtgtgtttcttg 53 + ||||||||||||||||||| +Sbjct: 69786 tggtgaagtgtgtttcttg 69804 +@end smallexample + +This alignment was located on the human chromosome 7. The fragment on which +part of the query was found had a total length of 176383. Only 19 of the +nucleotides matched and the matching sequence ran from character 35 to 53 +in the query sequence and from 69786 to 69804 in the fragment on chromosome 7. +If you are still reading at this point, you are probably interested in finding +out more about Computational Biology and you might appreciate the following +hints. + +@cindex Computational Biology +@cindex Bioinformatics +@enumerate +@item +There is a book called @cite{Introduction to Computational Biology} +by Michael S. Waterman, which is worth reading if you are seriously +interested. You can find a good +book review +on the Internet. + +@item +While Waterman's book can explain to you the algorithms employed internally +in the database search engines, most practicioners prefer to approach +the subject differently. The applied side of Computational Biology is +called Bioinformatics, and emphasizes the tools available for day-to-day +work as well as how to actually @emph{use} them. One of the very few affordable +books on Bioinformatics is +@cite{Developing Bioinformatics Computer Skills}. + +@item +The sequences @emph{gawk} and @emph{gnuawk} are in widespread use in +the genetic material of virtually every earthly living being. Let us +take this as a clear indication that the divine creator has intended +@code{gawk} to prevail over other scripting languages such as @code{perl}, +@code{tcl}, or @code{python} which are not even proper sequences. (:-) +@end enumerate + +@node Links, GNU Free Documentation License, Some Applications and Techniques, Top +@chapter Related Links + +This section lists the URLs for various items discussed in this @value{CHAPTER}. +They are presented in the order in which they appear. + +@table @asis + +@item @cite{Internet Programming with Python} +@uref{http://www.fsbassociates.com/books/python.htm} + +@item @cite{Advanced Perl Programming} +@uref{http://www.oreilly.com/catalog/advperl} + +@item @cite{Web Client Programming with Perl} +@uref{http://www.oreilly.com/catalog/webclient} + +@item Richard Stevens's home page and book +@uref{http://www.kohala.com/~rstevens} + +@item The SPAK home page +@uref{http://www.userfriendly.net/linux/RPM/contrib/libc6/i386/spak-0.6b-1.i386.html} + +@item Volume III of @cite{Internetworking with TCP/IP}, by Comer and Stevens +@uref{http://www.cs.purdue.edu/homes/dec/tcpip3s.cont.html} + +@item XBM Graphics File Format +@uref{http://www.wotsit.org/download.asp?f=xbm} + +@item GNUPlot +@uref{http://www.cs.dartmouth.edu/gnuplot_info.html} + +@item Mark Humphrys' Eliza page +@uref{http://www.compapp.dcu.ie/~humphrys/eliza.html} + +@item Yahoo! Eliza Information +@uref{http://dir.yahoo.com/Recreation/Games/Computer_Games/Internet_Games/Web_Games/Artificial_Intelligence} + +@item Java versions of Eliza +@uref{http://www.tjhsst.edu/Psych/ch1/eliza.html} + +@item Java versions of Eliza with source code +@uref{http://home.adelphia.net/~lifeisgood/eliza/eliza.htm} + +@item Eliza Programs with Explanations +@uref{http://chayden.net/chayden/eliza/Eliza.shtml} + +@item Loebner Contest +@uref{http://acm.org/~loebner/loebner-prize.htmlx} + +@item Tck/Tk Information +@uref{http://www.scriptics.com/} + +@item Intel 80x86 Processors +@uref{http://developer.intel.com/design/platform/embedpc/what_is.htm} + +@item AMD Elan Processors +@uref{http://www.amd.com/products/epd/processors/4.32bitcont/32bitcont/index.html} + +@item XINU +@uref{http://willow.canberra.edu.au/~chrisc/xinu.html } + +@item GNU/Linux +@uref{http://uclinux.lineo.com/} + +@item Embedded PCs +@uref{http://dir.yahoo.com/Business_and_Economy/Business_to_Business/Computers/Hardware/Embedded_Control/} + +@item MiniSQL +@uref{http://www.hughes.com.au/library/} + +@item Market Share Surveys +@uref{http://www.netcraft.com/survey} + +@item @cite{Numerical Recipes in C: The Art of Scientific Computing} +@uref{http://www.nr.com} + +@item VRML +@uref{http://www.vrml.org} + +@item The VRML FAQ +@uref{http://www.vrml.org/technicalinfo/specifications/specifications.htm#FAQ} + +@item The UMBC Agent Web +@uref{http://www.cs.umbc.edu/agents } + +@item Apache Web Server +@uref{http://www.apache.org} + +@item National Center for Biotechnology Information (NCBI) +@uref{http://www.ncbi.nlm.nih.gov} + +@item Basic Local Alignment Search Tool (BLAST) +@uref{http://www.ncbi.nlm.nih.gov/BLAST/blast_overview.html} + +@item NCBI Home Page +@uref{http://www.ncbi.nlm.nih.gov} + +@item BLAST Pages +@uref{http://www.ncbi.nlm.nih.gov/BLAST} + +@item BLAST Demonstration Client +@uref{ftp://ncbi.nlm.nih.gov/blast/blasturl/} + +@item BLAST anonymous FTP location +@uref{ftp://ncbi.nlm.nih.gov/blast/network/netblast/} + +@item BLAST 2.0 Executables +@uref{ftp://ncbi.nlm.nih.gov/blast/executables/} + +@item IUB/IUPAC Amino Acid and Nucleic Acid Codes +@uref{http://www.uthscsa.edu/geninfo/blastmail.html#item6} + +@item FASTA/Pearson Format +@uref{http://www.ncbi.nlm.nih.gov/BLAST/fasta.html} + +@item Fasta/Pearson Sequence in Java +@uref{http://www.kazusa.or.jp/java/codon_table_java/} + +@item Book Review of @cite{Introduction to Computational Biology} +@uref{http://www.acm.org/crossroads/xrds5-1/introcb.html} + +@item @cite{Developing Bioinformatics Computer Skills} +@uref{http://www.oreilly.com/catalog/bioskills/} + +@end table + +@node GNU Free Documentation License, Index, Links, Top +@unnumbered GNU Free Documentation License +@center Version 1.1, March 2000 + +@display +Copyright (C) 2000 Free Software Foundation, Inc. +59 Temple Place, Suite 330, Boston, MA 02111-1307 USA + +Everyone is permitted to copy and distribute verbatim copies +of this license document, but changing it is not allowed. +@end display +@sp 1 +@enumerate 0 +@item +PREAMBLE + +The purpose of this License is to make a manual, textbook, or other +written document ``free'' in the sense of freedom: to assure everyone +the effective freedom to copy and redistribute it, with or without +modifying it, either commercially or noncommercially. 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If the Document does not specify a version +number of this License, you may choose any version ever published (not +as a draft) by the Free Software Foundation. + +@end enumerate + +@c fakenode --- for prepinfo +@unnumberedsec ADDENDUM: How to use this License for your documents + +To use this License in a document you have written, include a copy of +the License in the document and put the following copyright and +license notices just after the title page: + +@smallexample +@group + + Copyright (C) @var{year} @var{your name}. + Permission is granted to copy, distribute and/or modify this document + under the terms of the GNU Free Documentation License, Version 1.1 + or any later version published by the Free Software Foundation; + with the Invariant Sections being @var{list their titles}, with the + Front-Cover Texts being @var{list}, and with the Back-Cover Texts being @var{list}. + A copy of the license is included in the section entitled ``GNU + Free Documentation License''. +@end group +@end smallexample +If you have no Invariant Sections, write ``with no Invariant Sections'' +instead of saying which ones are invariant. If you have no +Front-Cover Texts, write ``no Front-Cover Texts'' instead of +``Front-Cover Texts being @var{list}''; likewise for Back-Cover Texts. + +If your document contains nontrivial examples of program code, we +recommend releasing these examples in parallel under your choice of +free software license, such as the GNU General Public License, +to permit their use in free software. + +@node Index, , GNU Free Documentation License, Top +@comment node-name, next, previous, up + +@unnumbered Index +@printindex cp +@bye + +Conventions: +1. Functions, built-in or otherwise, do NOT have () after them. +2. Gawk built-in vars and functions are in @code. Also program vars and + functions. +3. HTTP method names are in @code. +4. Protocols such as echo, ftp, etc are in @samp. +5. URLs are in @url. +6. All RFC's in the index. Put a space between `RFC' and the number. diff --git a/doc/lflashlight.eps b/doc/lflashlight.eps new file mode 100644 index 00000000..fdb8cf31 --- /dev/null +++ b/doc/lflashlight.eps @@ -0,0 +1,135 @@ +%! +%%Creator: arnold@skeeve (Aharon Robbins) +%%Title: rflashlight.small.xpic (xpic) +%%CreationDate: Tue Dec 12 09:51:27 2000 +%%Pages: 1 +%%BoundingBox: 0 0 72 28.8 +% (in inches) at 0 0, width 1, height 0.4 +%%EndComments +% Prolog for xpic to PostScript converter +% Author: Mark Moraes +% $Header: x2ps.pro,v 1.2 88/03/19 16:50:09 moraes Exp +% %d D - change style SOLID, DOTTED, SHORT-DASH, LONG-DASH, DOT-DASH +% %s F - change font to fontname +% %d S - change size (font size in points) +% (%s) rj %d t - text right just. (%d is TOPLINE, MIDLINE, BOTLINE) +% (%s) lj %d t - text left just. (%d is TOPLINE, MIDLINE, BOTLINE) +% (%s) ce %d t - text centered (%d is TOPLINE, MIDLINE, BOTLINE) +% %d %d l - lineto +% %d %d m - moveto +% %d %d s - spline segment +% x - flush line, spline +% b - box +% e - ellipse +% %d ss - setscale +% %d W - change linewidth +% getpagesize - gets the values of PAGEHEIGHT and PAGEWIDTH +% %d %d flip - translate by %d, PAGEHEIGHT - %d (this +% transforms to X windows coordinates) +save 50 dict begin /xpic exch def +/StartXpic {newpath 0 0 moveto [] 0 setdash 0 setgray 1 setlinecap} def +% Set defaults +/fontname /Times-Roman def +/ptsize 12 def +% halign has the values for MIDLINE, TOPLINE, BOTLINE +/halign 3 array def +/s {rcurveto} def +/x {stroke} def +/l {lineto} def +/m {moveto} def +/b { + /ury exch def /urx exch def /lly exch def /llx exch def + llx lly moveto urx lly lineto urx ury lineto + llx ury lineto llx lly lineto stroke +} def +/mtrx matrix def +/e { + /yc exch def /xc exch def /yrad exch def /xrad exch def + xc xrad add yc moveto + /savematrix mtrx currentmatrix def + xc yc translate + xrad yrad scale + 0 0 1 0 360 arc + savematrix setmatrix stroke +} def +% The next three take the text string, and moveto the right horiz. position +% leaving the string on the stack. +/lj {} def +/rj {dup stringwidth pop neg 0 rmoveto} def +/ce {dup stringwidth pop 2 div neg 0 rmoveto} def +% And this is invoked after one of the three above, and +% computes the vert. pos, and then displays the string. +/t {halign exch get 0 exch rmoveto show newpath} def +% Store an array of patterns in /styles - a pattern is an array consisting +% of an array and an offset. Corresp to xpic patterns +% solid, dotted, short-dashed, long-dashed, dot-dashed +/styles [ [] 0 ] [ [1 3] 0 ] [ [4 4] 0 ] [ [8 4] 0 ] [ [1 4 4 4] 0 ] + 5 array astore def +% change style to arg. +/D {stroke styles exch get aload pop setdash newpath} def +/W {stroke 0.5 mul setlinewidth newpath} def +% fontbox takes a fontname off the stack, and returns an array +% containing the values of the bottom line of the bounding box, the +% mid line of the bounding box, and the top line of the bounding box +% of that font, taken from the baseline, scaled to a font of size 1 +/fontbox { + findfont dup /FontMatrix get /fm exch def /FontBBox get aload pop + /ytop exch def pop /ybot exch def pop + /ymid ytop ybot sub 2 div def + 0 ybot fm dtransform exch pop % botline + dup neg exch % midline - this works better than (ytop-ybot)/2! + 0 ytop fm dtransform exch pop exch %topline + % now in the order midline, topline, botline. + 3 array astore +} def +% select font +/F { + dup /fontname exch def fontbox + /thisfontbox exch def SF +} def +% set point size +/S {/ptsize exch def SF} def +% actually set font +/SF { + fontname findfont ptsize curscale div scalefont setfont + thisfontbox aload pop + 1 1 3 { + pop ptsize mul curscale div neg 3 1 roll + } for + halign astore pop +} def +% sets the scale to 72 / n, where n is on the stack, and stores the value +% in curscale for font scaling +/curscale 1 def +/getpagesize{newpath clippath pathbbox /pageheight exch def + /pagewidth exch def pop pop newpath} def +/flip{pageheight exch sub translate} def +/ss {/curscale exch 72 exch div dup dup scale def} def +/land {90 rotate} def +StartXpic +%%EndProlog +80 ss +0.5 W +0 D +80 32 m +64 24 l +x +32 24 m +56 32 l +x +32 8 m +56 0 l +x +8 16 56 16 e +0 24 32 8 b +64 16 m +80 16 l +x +64 8 m +80 0 l +x +%%Trailer +showpage +% Trailer for xpic to PostScript converter +% $Header: x2ps.tra,v 1.2 89/07/02 15:59:53 moraes Exp $ +xpic end restore diff --git a/doc/no.colors b/doc/no.colors index 974f985b..d5fb0380 100644 --- a/doc/no.colors +++ b/doc/no.colors @@ -1,6 +1,6 @@ .\" AWK Reference Card --- Arnold Robbins, arnold@gnu.org .\" This file is for troff which does not know what to do -.\" with a literal Poscript and cannot use macros from 'colors'. +.\" with literal Poscript and cannot use the macros from 'colors'. .\" .\" Copyright (C) 1996 Free Software Foundation, Inc. .\" diff --git a/doc/rflashlight.eps b/doc/rflashlight.eps new file mode 100644 index 00000000..28cb7e25 --- /dev/null +++ b/doc/rflashlight.eps @@ -0,0 +1,141 @@ +%! +%%Creator: arnold@skeeve (Aharon Robbins) +%%Title: flashlight.small.xpic (xpic) +%%CreationDate: Tue Oct 24 14:41:28 2000 +%%Pages: 1 +%%BoundingBox: 0 0 72 28.8 +% (in inches) at 0 0, width 1, height 0.4 +%%EndComments +% Prolog for xpic to PostScript converter +% Author: Mark Moraes +% $Header: x2ps.pro,v 1.2 88/03/19 16:50:09 moraes Exp +% %d D - change style SOLID, DOTTED, SHORT-DASH, LONG-DASH, DOT-DASH +% %s F - change font to fontname +% %d S - change size (font size in points) +% (%s) rj %d t - text right just. (%d is TOPLINE, MIDLINE, BOTLINE) +% (%s) lj %d t - text left just. (%d is TOPLINE, MIDLINE, BOTLINE) +% (%s) ce %d t - text centered (%d is TOPLINE, MIDLINE, BOTLINE) +% %d %d l - lineto +% %d %d m - moveto +% %d %d s - spline segment +% x - flush line, spline +% b - box +% e - ellipse +% %d ss - setscale +% %d W - change linewidth +% getpagesize - gets the values of PAGEHEIGHT and PAGEWIDTH +% %d %d flip - translate by %d, PAGEHEIGHT - %d (this +% transforms to X windows coordinates) +save 50 dict begin /xpic exch def +/StartXpic {newpath 0 0 moveto [] 0 setdash 0 setgray 1 setlinecap} def +% Set defaults +/fontname /Times-Roman def +/ptsize 12 def +% halign has the values for MIDLINE, TOPLINE, BOTLINE +/halign 3 array def +/s {rcurveto} def +/x {stroke} def +/l {lineto} def +/m {moveto} def +/b { + /ury exch def /urx exch def /lly exch def /llx exch def + llx lly moveto urx lly lineto urx ury lineto + llx ury lineto llx lly lineto stroke +} def +/mtrx matrix def +/e { + /yc exch def /xc exch def /yrad exch def /xrad exch def + xc xrad add yc moveto + /savematrix mtrx currentmatrix def + xc yc translate + xrad yrad scale + 0 0 1 0 360 arc + savematrix setmatrix stroke +} def +% The next three take the text string, and moveto the right horiz. position +% leaving the string on the stack. +/lj {} def +/rj {dup stringwidth pop neg 0 rmoveto} def +/ce {dup stringwidth pop 2 div neg 0 rmoveto} def +% And this is invoked after one of the three above, and +% computes the vert. pos, and then displays the string. +/t {halign exch get 0 exch rmoveto show newpath} def +% Store an array of patterns in /styles - a pattern is an array consisting +% of an array and an offset. Corresp to xpic patterns +% solid, dotted, short-dashed, long-dashed, dot-dashed +/styles [ [] 0 ] [ [1 3] 0 ] [ [4 4] 0 ] [ [8 4] 0 ] [ [1 4 4 4] 0 ] + 5 array astore def +% change style to arg. +/D {stroke styles exch get aload pop setdash newpath} def +/W {stroke 0.5 mul setlinewidth newpath} def +% fontbox takes a fontname off the stack, and returns an array +% containing the values of the bottom line of the bounding box, the +% mid line of the bounding box, and the top line of the bounding box +% of that font, taken from the baseline, scaled to a font of size 1 +/fontbox { + findfont dup /FontMatrix get /fm exch def /FontBBox get aload pop + /ytop exch def pop /ybot exch def pop + /ymid ytop ybot sub 2 div def + 0 ybot fm dtransform exch pop % botline + dup neg exch % midline - this works better than (ytop-ybot)/2! + 0 ytop fm dtransform exch pop exch %topline + % now in the order midline, topline, botline. + 3 array astore +} def +% select font +/F { + dup /fontname exch def fontbox + /thisfontbox exch def SF +} def +% set point size +/S {/ptsize exch def SF} def +% actually set font +/SF { + fontname findfont ptsize curscale div scalefont setfont + thisfontbox aload pop + 1 1 3 { + pop ptsize mul curscale div neg 3 1 roll + } for + halign astore pop +} def +% sets the scale to 72 / n, where n is on the stack, and stores the value +% in curscale for font scaling +/curscale 1 def +/getpagesize{newpath clippath pathbbox /pageheight exch def + /pagewidth exch def pop pop newpath} def +/flip{pageheight exch sub translate} def +/ss {/curscale exch 72 exch div dup dup scale def} def +/land {90 rotate} def +StartXpic +%%EndProlog +80 ss +0.5 W +0 D +8 16 24 16 e +24 32 m +48 24 l +x +24 0 m +48 8 l +x +48 24 m +0 0 0 -5.33333 0 -16 s +x +48 24 80 8 b +0 8 m +0 8 l +x +0 0 m +16 8 l +x +0 16 m +16 16 l +x +16 24 m +0 32 l +x +%%Trailer +showpage +% Trailer for xpic to PostScript converter +% $Header: x2ps.tra,v 1.2 89/07/02 15:59:53 moraes Exp $ +xpic end restore diff --git a/doc/statist.eps b/doc/statist.eps new file mode 100644 index 00000000..1e1f09fa --- /dev/null +++ b/doc/statist.eps @@ -0,0 +1,557 @@ +%!PS-Adobe-2.0 +%%Creator: gnuplot 3.7 patchlevel 0.1 +%%CreationDate: Sun Jan 7 14:23:12 2001 +%%DocumentFonts: (atend) +%%BoundingBox: 50 50 554 770 +%%Orientation: Portrait +%%Pages: (atend) +%%EndComments +/gnudict 256 dict def +gnudict begin +/Color true def +/Solid false def +/gnulinewidth 5.000 def +/userlinewidth gnulinewidth def +/vshift -46 def +/dl {10 mul} def +/hpt_ 31.5 def +/vpt_ 31.5 def +/hpt hpt_ def +/vpt vpt_ def +/M {moveto} bind def +/L {lineto} bind def +/R {rmoveto} bind def +/V {rlineto} bind def +/vpt2 vpt 2 mul def +/hpt2 hpt 2 mul def +/Lshow { currentpoint stroke M + 0 vshift R show } def +/Rshow { currentpoint stroke M + dup stringwidth pop neg vshift R show } def +/Cshow { currentpoint stroke M + dup stringwidth pop -2 div vshift R show } def +/UP { dup vpt_ mul /vpt exch def hpt_ mul /hpt exch def + /hpt2 hpt 2 mul def /vpt2 vpt 2 mul def } def +/DL { Color {setrgbcolor Solid {pop []} if 0 setdash } + {pop pop pop Solid {pop []} if 0 setdash} ifelse } def +/BL { stroke gnulinewidth 2 mul setlinewidth } def +/AL { stroke gnulinewidth 2 div setlinewidth } def +/UL { gnulinewidth mul /userlinewidth exch def } def +/PL { stroke userlinewidth setlinewidth } def +/LTb { BL [] 0 0 0 DL } def +/LTa { AL [1 dl 2 dl] 0 setdash 0 0 0 setrgbcolor } def +/LT0 { PL [] 1 0 0 DL } def +/LT1 { PL [4 dl 2 dl] 0 1 0 DL } def +/LT2 { PL [2 dl 3 dl] 0 0 1 DL } def +/LT3 { PL [1 dl 1.5 dl] 1 0 1 DL } def +/LT4 { PL [5 dl 2 dl 1 dl 2 dl] 0 1 1 DL } def +/LT5 { PL [4 dl 3 dl 1 dl 3 dl] 1 1 0 DL } def +/LT6 { PL [2 dl 2 dl 2 dl 4 dl] 0 0 0 DL } def +/LT7 { PL [2 dl 2 dl 2 dl 2 dl 2 dl 4 dl] 1 0.3 0 DL } def +/LT8 { PL [2 dl 2 dl 2 dl 2 dl 2 dl 2 dl 2 dl 4 dl] 0.5 0.5 0.5 DL } def +/Pnt { stroke [] 0 setdash + gsave 1 setlinecap M 0 0 V stroke grestore } def +/Dia { stroke [] 0 setdash 2 copy vpt add M + hpt neg vpt neg V hpt vpt neg V + hpt vpt V hpt neg vpt V closepath stroke + Pnt } def +/Pls { stroke [] 0 setdash vpt sub M 0 vpt2 V + currentpoint stroke M + hpt neg vpt neg R hpt2 0 V stroke + } def +/Box { stroke [] 0 setdash 2 copy exch hpt sub exch vpt add M + 0 vpt2 neg V hpt2 0 V 0 vpt2 V + hpt2 neg 0 V closepath stroke + Pnt } def +/Crs { stroke [] 0 setdash exch hpt sub exch vpt add M + hpt2 vpt2 neg V currentpoint stroke M + hpt2 neg 0 R hpt2 vpt2 V stroke } def +/TriU { stroke [] 0 setdash 2 copy vpt 1.12 mul add M + hpt neg vpt -1.62 mul V + hpt 2 mul 0 V + hpt neg vpt 1.62 mul V closepath stroke + Pnt } def +/Star { 2 copy Pls Crs } def +/BoxF { stroke [] 0 setdash exch hpt sub exch vpt add M + 0 vpt2 neg V hpt2 0 V 0 vpt2 V + hpt2 neg 0 V closepath fill } def +/TriUF { stroke [] 0 setdash vpt 1.12 mul add M + hpt neg vpt -1.62 mul V + hpt 2 mul 0 V + hpt neg vpt 1.62 mul V closepath fill } def +/TriD { stroke [] 0 setdash 2 copy vpt 1.12 mul sub M + hpt neg vpt 1.62 mul V + hpt 2 mul 0 V + hpt neg vpt -1.62 mul V closepath stroke + Pnt } def +/TriDF { stroke [] 0 setdash vpt 1.12 mul sub M + hpt neg vpt 1.62 mul V + hpt 2 mul 0 V + hpt neg vpt -1.62 mul V closepath fill} def +/DiaF { stroke [] 0 setdash vpt add M + hpt neg vpt neg V hpt vpt neg V + hpt vpt V hpt neg vpt V closepath fill } def +/Pent { stroke [] 0 setdash 2 copy gsave + translate 0 hpt M 4 {72 rotate 0 hpt L} repeat + closepath stroke grestore Pnt } def +/PentF { stroke [] 0 setdash gsave + translate 0 hpt M 4 {72 rotate 0 hpt L} repeat + closepath fill grestore } def +/Circle { stroke [] 0 setdash 2 copy + hpt 0 360 arc stroke Pnt } def +/CircleF { stroke [] 0 setdash hpt 0 360 arc fill } def +/C0 { BL [] 0 setdash 2 copy moveto vpt 90 450 arc } bind def +/C1 { BL [] 0 setdash 2 copy moveto + 2 copy vpt 0 90 arc closepath fill + vpt 0 360 arc closepath } bind def +/C2 { BL [] 0 setdash 2 copy moveto + 2 copy vpt 90 180 arc closepath fill + vpt 0 360 arc closepath } bind def +/C3 { BL [] 0 setdash 2 copy moveto + 2 copy vpt 0 180 arc closepath fill + vpt 0 360 arc closepath } bind def +/C4 { BL [] 0 setdash 2 copy moveto + 2 copy vpt 180 270 arc closepath fill + vpt 0 360 arc closepath } bind def +/C5 { BL [] 0 setdash 2 copy moveto + 2 copy vpt 0 90 arc + 2 copy moveto + 2 copy vpt 180 270 arc closepath fill + vpt 0 360 arc } bind def +/C6 { BL [] 0 setdash 2 copy moveto + 2 copy vpt 90 270 arc closepath fill + vpt 0 360 arc closepath } bind def +/C7 { BL [] 0 setdash 2 copy moveto + 2 copy vpt 0 270 arc closepath fill + vpt 0 360 arc closepath } bind def +/C8 { BL [] 0 setdash 2 copy moveto + 2 copy vpt 270 360 arc closepath fill + vpt 0 360 arc closepath } bind def +/C9 { BL [] 0 setdash 2 copy moveto + 2 copy vpt 270 450 arc closepath fill + vpt 0 360 arc closepath } bind def +/C10 { BL [] 0 setdash 2 copy 2 copy moveto vpt 270 360 arc closepath fill + 2 copy moveto + 2 copy vpt 90 180 arc closepath fill + vpt 0 360 arc closepath } bind def +/C11 { BL [] 0 setdash 2 copy moveto + 2 copy vpt 0 180 arc closepath fill + 2 copy moveto + 2 copy vpt 270 360 arc closepath fill + vpt 0 360 arc closepath } bind def +/C12 { BL [] 0 setdash 2 copy moveto + 2 copy vpt 180 360 arc closepath fill + vpt 0 360 arc closepath } bind def +/C13 { BL [] 0 setdash 2 copy moveto + 2 copy vpt 0 90 arc closepath fill + 2 copy moveto + 2 copy vpt 180 360 arc closepath fill + vpt 0 360 arc closepath } bind def +/C14 { BL [] 0 setdash 2 copy moveto + 2 copy vpt 90 360 arc closepath fill + vpt 0 360 arc } bind def +/C15 { BL [] 0 setdash 2 copy vpt 0 360 arc closepath fill + vpt 0 360 arc closepath } bind def +/Rec { newpath 4 2 roll moveto 1 index 0 rlineto 0 exch rlineto + neg 0 rlineto closepath } bind def +/Square { dup Rec } bind def +/Bsquare { vpt sub exch vpt sub exch vpt2 Square } bind def +/S0 { BL [] 0 setdash 2 copy moveto 0 vpt rlineto BL Bsquare } bind def +/S1 { BL [] 0 setdash 2 copy vpt Square fill Bsquare } bind def +/S2 { BL [] 0 setdash 2 copy exch vpt sub exch vpt Square fill Bsquare } bind def +/S3 { BL [] 0 setdash 2 copy exch vpt sub exch vpt2 vpt Rec fill Bsquare } bind def +/S4 { BL [] 0 setdash 2 copy exch vpt sub exch vpt sub vpt Square fill Bsquare } bind def +/S5 { BL [] 0 setdash 2 copy 2 copy vpt Square fill + exch vpt sub exch vpt sub vpt Square fill Bsquare } bind def +/S6 { BL [] 0 setdash 2 copy exch vpt sub exch vpt sub vpt vpt2 Rec fill Bsquare } bind def +/S7 { BL [] 0 setdash 2 copy exch vpt sub exch vpt sub vpt vpt2 Rec fill + 2 copy vpt Square fill + Bsquare } bind def +/S8 { BL [] 0 setdash 2 copy vpt sub vpt Square fill Bsquare } bind def +/S9 { BL [] 0 setdash 2 copy vpt sub vpt vpt2 Rec fill Bsquare } bind def +/S10 { BL [] 0 setdash 2 copy vpt sub vpt Square fill 2 copy exch vpt sub exch vpt Square fill + Bsquare } bind def +/S11 { BL [] 0 setdash 2 copy vpt sub vpt Square fill 2 copy exch vpt sub exch vpt2 vpt Rec fill + Bsquare } bind def +/S12 { BL [] 0 setdash 2 copy exch vpt sub exch vpt sub vpt2 vpt Rec fill Bsquare } bind def +/S13 { BL [] 0 setdash 2 copy exch vpt sub exch vpt sub vpt2 vpt Rec fill + 2 copy vpt Square fill Bsquare } bind def +/S14 { BL [] 0 setdash 2 copy exch vpt sub exch vpt sub vpt2 vpt Rec fill + 2 copy exch vpt sub exch vpt Square fill Bsquare } bind def +/S15 { BL [] 0 setdash 2 copy Bsquare fill Bsquare } bind def +/D0 { gsave translate 45 rotate 0 0 S0 stroke grestore } bind def +/D1 { gsave translate 45 rotate 0 0 S1 stroke grestore } bind def +/D2 { gsave translate 45 rotate 0 0 S2 stroke grestore } bind def +/D3 { gsave translate 45 rotate 0 0 S3 stroke grestore } bind def +/D4 { gsave translate 45 rotate 0 0 S4 stroke grestore } bind def +/D5 { gsave translate 45 rotate 0 0 S5 stroke grestore } bind def +/D6 { gsave translate 45 rotate 0 0 S6 stroke grestore } bind def +/D7 { gsave translate 45 rotate 0 0 S7 stroke grestore } bind def +/D8 { gsave translate 45 rotate 0 0 S8 stroke grestore } bind def +/D9 { gsave translate 45 rotate 0 0 S9 stroke grestore } bind def +/D10 { gsave translate 45 rotate 0 0 S10 stroke grestore } bind def +/D11 { gsave translate 45 rotate 0 0 S11 stroke grestore } bind def +/D12 { gsave translate 45 rotate 0 0 S12 stroke grestore } bind def +/D13 { gsave translate 45 rotate 0 0 S13 stroke grestore } bind def +/D14 { gsave translate 45 rotate 0 0 S14 stroke grestore } bind def +/D15 { gsave translate 45 rotate 0 0 S15 stroke grestore } bind def +/DiaE { stroke [] 0 setdash vpt add M + hpt neg vpt neg V hpt vpt neg V + hpt vpt V hpt neg vpt V closepath stroke } def +/BoxE { stroke [] 0 setdash exch hpt sub exch vpt add M + 0 vpt2 neg V hpt2 0 V 0 vpt2 V + hpt2 neg 0 V closepath stroke } def +/TriUE { stroke [] 0 setdash vpt 1.12 mul add M + hpt neg vpt -1.62 mul V + hpt 2 mul 0 V + hpt neg vpt 1.62 mul V closepath stroke } def +/TriDE { stroke [] 0 setdash vpt 1.12 mul sub M + hpt neg vpt 1.62 mul V + hpt 2 mul 0 V + hpt neg vpt -1.62 mul V closepath stroke } def +/PentE { stroke [] 0 setdash gsave + translate 0 hpt M 4 {72 rotate 0 hpt L} repeat + closepath stroke grestore } def +/CircE { stroke [] 0 setdash + hpt 0 360 arc stroke } def +/Opaque { gsave closepath 1 setgray fill grestore 0 setgray closepath } def +/DiaW { stroke [] 0 setdash vpt add M + hpt neg vpt neg V hpt vpt neg V + hpt vpt V hpt neg vpt V Opaque stroke } def +/BoxW { stroke [] 0 setdash exch hpt sub exch vpt add M + 0 vpt2 neg V hpt2 0 V 0 vpt2 V + hpt2 neg 0 V Opaque stroke } def +/TriUW { stroke [] 0 setdash vpt 1.12 mul add M + hpt neg vpt -1.62 mul V + hpt 2 mul 0 V + hpt neg vpt 1.62 mul V Opaque stroke } def +/TriDW { stroke [] 0 setdash vpt 1.12 mul sub M + hpt neg vpt 1.62 mul V + hpt 2 mul 0 V + hpt neg vpt -1.62 mul V Opaque stroke } def +/PentW { stroke [] 0 setdash gsave + translate 0 hpt M 4 {72 rotate 0 hpt L} repeat + Opaque stroke grestore } def +/CircW { stroke [] 0 setdash + hpt 0 360 arc Opaque stroke } def +/BoxFill { gsave Rec 1 setgray fill grestore } def +end +%%EndProlog +%%Page: 1 1 +gnudict begin +gsave +50 50 translate +0.100 0.100 scale +0 setgray +newpath +(Helvetica) findfont 140 scalefont setfont +1.000 UL +LTb +574 280 M +63 0 V +4165 0 R +-63 0 V +490 280 M +(-0.3) Rshow +574 1245 M +63 0 V +4165 0 R +-63 0 V +-4249 0 R +(-0.2) Rshow +574 2209 M +63 0 V +4165 0 R +-63 0 V +-4249 0 R +(-0.1) Rshow +574 3174 M +63 0 V +4165 0 R +-63 0 V +-4249 0 R +(0) Rshow +574 4138 M +63 0 V +4165 0 R +-63 0 V +-4249 0 R +(0.1) Rshow +574 5103 M +63 0 V +4165 0 R +-63 0 V +-4249 0 R +(0.2) Rshow +574 6067 M +63 0 V +4165 0 R +-63 0 V +-4249 0 R +(0.3) Rshow +574 7032 M +63 0 V +4165 0 R +-63 0 V +-4249 0 R +(0.4) Rshow +574 280 M +0 63 V +0 6689 R +0 -63 V +574 140 M +(-10) Cshow +1631 280 M +0 63 V +0 6689 R +0 -63 V +0 -6829 R +(-5) Cshow +2688 280 M +0 63 V +0 6689 R +0 -63 V +0 -6829 R +(0) Cshow +3745 280 M +0 63 V +0 6689 R +0 -63 V +0 -6829 R +(5) Cshow +4802 280 M +0 63 V +0 6689 R +0 -63 V +0 -6829 R +(10) Cshow +1.000 UL +LTb +574 280 M +4228 0 V +0 6752 V +-4228 0 V +574 280 L +2688 2209 M +(p\(m1=m2\) =0.0863798346775753) Lshow +2688 1245 M +(p\(v1=v2\) =0.31647637745891) Lshow +1.000 UL +LT0 +4151 6899 M +(sample 1) Rshow +4235 6899 M +399 0 V +574 3174 M +43 0 V +42 0 V +43 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +43 0 V +42 1 V +43 2 V +43 4 V +42 8 V +43 13 V +43 24 V +42 41 V +43 65 V +43 101 V +43 146 V +42 205 V +43 271 V +43 340 V +42 404 V +43 450 V +43 470 V +43 452 V +42 390 V +43 288 V +43 153 V +42 0 V +43 -153 V +43 -288 V +42 -390 V +43 -452 V +43 -470 V +43 -450 V +42 -404 V +43 -340 V +43 -271 V +42 -205 V +43 -146 V +43 -101 V +43 -65 V +42 -41 V +43 -24 V +43 -13 V +42 -8 V +43 -4 V +43 -2 V +42 -1 V +43 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +43 0 V +42 0 V +43 0 V +1.000 UL +LT1 +4151 6759 M +(sample 2) Rshow +4235 6759 M +399 0 V +574 3174 M +43 0 V +42 0 V +43 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +42 0 V +43 1 V +43 1 V +43 1 V +42 3 V +43 4 V +43 6 V +42 9 V +43 13 V +43 19 V +42 27 V +43 37 V +43 51 V +43 66 V +42 85 V +43 106 V +43 130 V +42 155 V +43 179 V +43 201 V +43 219 V +42 231 V +43 236 V +43 229 V +42 214 V +43 187 V +43 149 V +42 104 V +43 52 V +43 -3 V +43 -57 V +42 -109 V +43 -154 V +43 -189 V +42 -216 V +43 -231 V +43 -235 V +43 -231 V +42 -217 V +43 -199 V +43 -177 V +42 -152 V +43 -127 V +43 -104 V +42 -83 V +43 -65 V +43 -49 V +43 -36 V +42 -26 V +43 -19 V +43 -12 V +42 -9 V +43 -6 V +43 -3 V +43 -3 V +42 -1 V +43 -1 V +43 -1 V +42 0 V +43 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +42 0 V +43 0 V +43 0 V +43 0 V +42 0 V +43 0 V +stroke +grestore +end +showpage +%%Trailer +%%DocumentFonts: Helvetica +%%Pages: 1 diff --git a/doc/statist.jpg b/doc/statist.jpg new file mode 100644 index 00000000..92428f25 Binary files /dev/null and b/doc/statist.jpg differ diff --git a/doc/texinfo.tex b/doc/texinfo.tex index ebf58d8e..0b5b9033 100644 --- a/doc/texinfo.tex +++ b/doc/texinfo.tex @@ -3,10 +3,10 @@ % Load plain if necessary, i.e., if running under initex. \expandafter\ifx\csname fmtname\endcsname\relax\input plain\fi % -\def\texinfoversion{1999-10-01.07} +\def\texinfoversion{2001-03-28.08} % -% Copyright (C) 1985, 86, 88, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 -% Free Software Foundation, Inc. +% Copyright (C) 1985, 86, 88, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, +% 2000, 01 Free Software Foundation, Inc. % % This texinfo.tex file is free software; you can redistribute it and/or % modify it under the terms of the GNU General Public License as @@ -214,6 +214,9 @@ \normalturnoffactive % \ in index entries must not stay \, e.g., if % the page break happens to be in the middle of an example. \shipout\vbox{% + % Do this early so pdf references go to the beginning of the page. + \ifpdfmakepagedest \pdfmkdest{\the\pageno} \fi + % \ifcropmarks \vbox to \outervsize\bgroup \hsize = \outerhsize \vskip-\topandbottommargin @@ -243,8 +246,6 @@ \unvbox\footlinebox \fi % - \ifpdfmakepagedest \pdfmkdest{\the\pageno} \fi - % \ifcropmarks \egroup % end of \vbox\bgroup \hfil\egroup % end of (centering) \line\bgroup @@ -687,16 +688,54 @@ where each line of input produces a line of output.} \def\nofillexdentyyy #1{{\advance \leftskip by -\exdentamount \leftline{\hskip\leftskip{\rm#1}}}} -% @inmargin{TEXT} puts TEXT in the margin next to the current paragraph. - -\def\inmargin#1{% -\strut\vadjust{\nobreak\kern-\strutdepth - \vtop to \strutdepth{\baselineskip\strutdepth\vss - \llap{\rightskip=\inmarginspacing \vbox{\noindent #1}}\null}}} +% @inmargin{WHICH}{TEXT} puts TEXT in the WHICH margin next to the current +% paragraph. For more general purposes, use the \margin insertion +% class. WHICH is `l' or `r'. +% \newskip\inmarginspacing \inmarginspacing=1cm \def\strutdepth{\dp\strutbox} - -%\hbox{{\rm#1}}\hfil\break}} +% +\def\doinmargin#1#2{\strut\vadjust{% + \nobreak + \kern-\strutdepth + \vtop to \strutdepth{% + \baselineskip=\strutdepth + \vss + % if you have multiple lines of stuff to put here, you'll need to + % make the vbox yourself of the appropriate size. + \ifx#1l% + \llap{\ignorespaces #2\hskip\inmarginspacing}% + \else + \rlap{\hskip\hsize \hskip\inmarginspacing \ignorespaces #2}% + \fi + \null + }% +}} +\def\inleftmargin{\doinmargin l} +\def\inrightmargin{\doinmargin r} +% +% @inmargin{TEXT [, RIGHT-TEXT]} +% (if RIGHT-TEXT is given, use TEXT for left page, RIGHT-TEXT for right; +% else use TEXT for both). +% +\def\inmargin#1{\parseinmargin #1,,\finish} +\def\parseinmargin#1,#2,#3\finish{% not perfect, but better than nothing. + \setbox0 = \hbox{\ignorespaces #2}% + \ifdim\wd0 > 0pt + \def\lefttext{#1}% have both texts + \def\righttext{#2}% + \else + \def\lefttext{#1}% have only one text + \def\righttext{#1}% + \fi + % + \ifodd\pageno + \def\temp{\inrightmargin\righttext}% odd page -> outside is right margin + \else + \def\temp{\inleftmargin\lefttext}% + \fi + \temp +} % @include file insert text of that file as input. % Allow normal characters that we make active in the argument (a file name). @@ -885,13 +924,17 @@ where each line of input produces a line of output.} \fi \ifx\empty\imagewidth\else width \imagewidth \fi \ifx\empty\imageheight\else height \imageheight \fi - {#1.pdf}% + \ifnum\pdftexversion<13 + #1.pdf% + \else + {#1.pdf}% + \fi \ifnum\pdftexversion < 14 \else \pdfrefximage \pdflastximage \fi} - \def\pdfmkdest#1{\pdfdest name{#1@} xyz} + \def\pdfmkdest#1{\pdfdest name{#1} xyz} \def\pdfmkpgn#1{#1@} - \let\linkcolor = \Cyan + \let\linkcolor = \Blue % was Cyan, but that seems light? \def\endlink{\Black\pdfendlink} % Adding outlines to PDF; macros for calculating structure of outlines % come from Petr Olsak @@ -906,7 +949,8 @@ where each line of input produces a line of output.} \closein 1 \indexnofonts \def\tt{} - % thanh's hack / proper braces in bookmarks + \let\_ = \normalunderscore + % Thanh's hack / proper braces in bookmarks \edef\mylbrace{\iftrue \string{\else}\fi}\let\{=\mylbrace \edef\myrbrace{\iffalse{\else\string}\fi}\let\}=\myrbrace % @@ -1670,7 +1714,10 @@ where each line of input produces a line of output.} } % Subroutines used in generating headings -% Produces Day Month Year style of output. +% This produces Day Month Year style of output. +% Only define if not already defined, in case a txi-??.tex file has set +% up a different format (e.g., txi-cs.tex does this). +\ifx\today\undefined \def\today{% \number\day\space \ifcase\month @@ -1679,6 +1726,7 @@ where each line of input produces a line of output.} \or\putwordMSep\or\putwordMOct\or\putwordMNov\or\putwordMDec \fi \space\number\year} +\fi % @settitle line... specifies the title of the document, for headings. % It generates no output of its own. @@ -2587,42 +2635,48 @@ width0pt\relax} \fi } % @defindex foo == \newindex{foo} - +% \def\defindex{\parsearg\newindex} % Define @defcodeindex, like @defindex except put all entries in @code. - +% +\def\defcodeindex{\parsearg\newcodeindex} +% \def\newcodeindex#1{% \iflinks \expandafter\newwrite \csname#1indfile\endcsname \openout \csname#1indfile\endcsname \jobname.#1 \fi \expandafter\xdef\csname#1index\endcsname{% - \noexpand\docodeindex{#1}} + \noexpand\docodeindex{#1}}% } -\def\defcodeindex{\parsearg\newcodeindex} % @synindex foo bar makes index foo feed into index bar. % Do this instead of @defindex foo if you don't want it as a separate index. -% The \closeout helps reduce unnecessary open files; the limit on the -% Acorn RISC OS is a mere 16 files. -\def\synindex#1 #2 {% - \expandafter\let\expandafter\synindexfoo\expandafter=\csname#2indfile\endcsname - \expandafter\closeout\csname#1indfile\endcsname - \expandafter\let\csname#1indfile\endcsname=\synindexfoo - \expandafter\xdef\csname#1index\endcsname{% define \xxxindex - \noexpand\doindex{#2}}% -} - +% % @syncodeindex foo bar similar, but put all entries made for index foo % inside @code. -\def\syncodeindex#1 #2 {% - \expandafter\let\expandafter\synindexfoo\expandafter=\csname#2indfile\endcsname - \expandafter\closeout\csname#1indfile\endcsname - \expandafter\let\csname#1indfile\endcsname=\synindexfoo - \expandafter\xdef\csname#1index\endcsname{% define \xxxindex - \noexpand\docodeindex{#2}}% +% +\def\synindex#1 #2 {\dosynindex\doindex{#1}{#2}} +\def\syncodeindex#1 #2 {\dosynindex\docodeindex{#1}{#2}} + +% #1 is \doindex or \docodeindex, #2 the index getting redefined (foo), +% #3 the target index (bar). +\def\dosynindex#1#2#3{% + % Only do \closeout if we haven't already done it, else we'll end up + % closing the target index. + \expandafter \ifx\csname donesynindex#2\endcsname \undefined + % The \closeout helps reduce unnecessary open files; the limit on the + % Acorn RISC OS is a mere 16 files. + \expandafter\closeout\csname#2indfile\endcsname + \expandafter\let\csname\donesynindex#2\endcsname = 1 + \fi + % redefine \fooindfile: + \expandafter\let\expandafter\temp\expandafter=\csname#3indfile\endcsname + \expandafter\let\csname#2indfile\endcsname=\temp + % redefine \fooindex: + \expandafter\xdef\csname#2index\endcsname{\noexpand#1{#3}}% } % Define \doindex, the driver for all \fooindex macros. @@ -2854,16 +2908,17 @@ width0pt\relax} \fi % Now the real index entry with the fonts. \toks0 = {#2}% % - % If third (subentry) arg is present, add it to the index - % string. And include a space. + % If the third (subentry) arg is present, add it to the index + % line to write. \ifx\thirdarg\emptymacro \else - \toks0 = \expandafter{\the\toks0 \space #3}% + \toks0 = \expandafter{\the\toks0{#3}}% \fi % - % Set up the complete index entry, with both the sort key - % and the original text, including any font commands. We write - % three arguments to \entry to the .?? file, texindex reduces to - % two when writing the .??s sorted result. + % Set up the complete index entry, with both the sort key and + % the original text, including any font commands. We write + % three arguments to \entry to the .?? file (four in the + % subentry case), texindex reduces to two when writing the .??s + % sorted result. \edef\temp{% \write\csname#1indfile\endcsname{% \realbackslash entry{\indexsorttmp}{\folio}{\the\toks0}}% @@ -3085,11 +3140,18 @@ width0pt\relax} \fi \def\primary #1{\line{#1\hfil}} \newskip\secondaryindent \secondaryindent=0.5cm - -\def\secondary #1#2{ -{\parfillskip=0in \parskip=0in -\hangindent =1in \hangafter=1 -\noindent\hskip\secondaryindent\hbox{#1}\indexdotfill #2\par +\def\secondary#1#2{{% + \parfillskip=0in + \parskip=0in + \hangindent=1in + \hangafter=1 + \noindent\hskip\secondaryindent\hbox{#1}\indexdotfill + \ifpdf + \pdfgettoks#2.\ \the\toksA % The page number ends the paragraph. + \else + #2 + \fi + \par }} % Define two-column mode, which we use to typeset indexes. @@ -3149,7 +3211,6 @@ width0pt\relax} \fi % % Double the \vsize as well. (We don't need a separate register here, % since nobody clobbers \vsize.) - \advance\vsize by -\ht\partialpage \vsize = 2\vsize } @@ -3163,6 +3224,7 @@ width0pt\relax} \fi % previous page. \dimen@ = \vsize \divide\dimen@ by 2 + \advance\dimen@ by -\ht\partialpage % % box0 will be the left-hand column, box2 the right. \setbox0=\vsplit255 to\dimen@ \setbox2=\vsplit255 to\dimen@ @@ -3170,15 +3232,18 @@ width0pt\relax} \fi \unvbox255 \penalty\outputpenalty } +% +% Re-output the contents of the output page -- any previous material, +% followed by the two boxes we just split, in box0 and box2. \def\pagesofar{% - % Re-output the contents of the output page -- any previous material, - % followed by the two boxes we just split, in box0 and box2. \unvbox\partialpage % \hsize = \doublecolumnhsize \wd0=\hsize \wd2=\hsize \hbox to\pagewidth{\box0\hfil\box2}% } +% +% All done with double columns. \def\enddoublecolumns{% \output = {% % Split the last of the double-column material. Leave it on the @@ -3203,8 +3268,9 @@ width0pt\relax} \fi % \endgroup where \vsize got restored). \pagegoal = \vsize } +% +% Called at the end of the double column material. \def\balancecolumns{% - % Called at the end of the double column material. \setbox0 = \vbox{\unvbox255}% like \box255 but more efficient, see p.120. \dimen@ = \ht0 \advance\dimen@ by \topskip @@ -4265,6 +4331,7 @@ width0pt\relax} \fi \gobble } + % @quotation does normal linebreaking (hence we can't use \nonfillstart) % and narrows the margins. % @@ -4287,6 +4354,158 @@ width0pt\relax} \fi } +% LaTeX-like @verbatim...@end verbatim and @verb{...} +% If we want to allow any as delimiter, +% we need the curly braces so that makeinfo sees the @verb command, eg: +% `@verbx...x' would look like the '@verbx' command. --janneke@gnu.org +% +% [Knuth]: Donald Ervin Knuth, 1996. The TeXbook. +% +% [Knuth] p. 344; only we need to do '@' too +\def\dospecials{% + \do\ \do\\\do\@\do\{\do\}\do\$\do\&% + \do\#\do\^\do\^^K\do\_\do\^^A\do\%\do\~} +% +% [Knuth] p. 380 +\def\uncatcodespecials{% + \def\do##1{\catcode`##1=12}\dospecials} +% +% [Knuth] pp. 380,381,391 +% Disable Spanish ligatures ?` and !` of \tt font +\begingroup + \catcode`\`=\active\gdef`{\relax\lq} +\endgroup +% +% Setup for the @verb command. +% +% Eight spaces for a tab +\begingroup + \catcode`\^^I=\active + \gdef\tabeightspaces{\catcode`\^^I=\active\def^^I{\ \ \ \ \ \ \ \ }} +\endgroup +% +\def\setupverb{% + \tt % easiest (and conventionally used) font for verbatim + \def\par{\leavevmode\endgraf}% + \catcode`\`=\active + \tabeightspaces + % Respect line breaks, + % print special symbols as themselves, and + % make each space count + % must do in this order: + \obeylines \uncatcodespecials \sepspaces +} + +% Setup for the @verbatim environment +% +% Real tab expansion +\newdimen\tabw \setbox0=\hbox{\tt\space} \tabw=8\wd0 % tab amount +% +\def\starttabbox{\setbox0=\hbox\bgroup} +\begingroup + \catcode`\^^I=\active + \gdef\tabexpand{% + \catcode`\^^I=\active + \def^^I{\leavevmode\egroup + \dimen0=\wd0 % the width so far, or since the previous tab + \divide\dimen0 by\tabw + \multiply\dimen0 by\tabw % compute previous multiple of \tabw + \advance\dimen0 by\tabw % advance to next multiple of \tabw + \wd0=\dimen0 \box0 \starttabbox + }% + } +\endgroup +\def\setupverbatim{% + % Easiest (and conventionally used) font for verbatim + \tt + \def\par{\leavevmode\egroup\box0\endgraf}% + \catcode`\`=\active + \tabexpand + % Respect line breaks, + % print special symbols as themselves, and + % make each space count + % must do in this order: + \obeylines \uncatcodespecials \sepspaces + \everypar{\starttabbox}% +} + +% Do the @verb magic: verbatim text is quoted by unique +% delimiter characters. Before first delimiter expect a +% right brace, after last delimiter expect closing brace: +% +% \def\doverb'{'#1'}'{#1} +% +% [Knuth] p. 382; only eat outer {} +\begingroup + \catcode`[=1\catcode`]=2\catcode`\{=12\catcode`\}=12 + \gdef\doverb{#1[\def\next##1#1}[##1\endgroup]\next] +\endgroup +% +\def\verb{\begingroup\setupverb\doverb} +% +% +% Do the @verbatim magic: define the macro \doverbatim so that +% the (first) argument ends when '@end verbatim' is reached, ie: +% +% \def\doverbatim#1@end verbatim{#1} +% +% For Texinfo it's a lot easier than for LaTeX, +% because texinfo's \verbatim doesn't stop at '\end{verbatim}': +% we need not redefine '\', '{' and '}' +% +% Inspired by LaTeX's verbatim command set [latex.ltx] +%% Include LaTeX hack for completeness -- never know +%% \begingroup +%% \catcode`|=0 \catcode`[=1 +%% \catcode`]=2\catcode`\{=12\catcode`\}=12\catcode`\ =\active +%% \catcode`\\=12|gdef|doverbatim#1@end verbatim[ +%% #1|endgroup|def|Everbatim[]|end[verbatim]] +%% |endgroup +\begingroup + \catcode`\ =\active + \gdef\doverbatim#1@end verbatim{#1\end{verbatim}} +\endgroup +% +\def\verbatim{% + \def\Everbatim{\nonfillfinish\endgroup}% + \begingroup + \nonfillstart + \advance\leftskip by -\defbodyindent + \begingroup\setupverbatim\doverbatim +} + +% @verbatiminclude FILE - insert text of file in verbatim environment. +% +% Allow normal characters that we make active in the argument (a file name). +\def\verbatiminclude{% + \begingroup + \catcode`\\=12 + \catcode`~=12 + \catcode`^=12 + \catcode`_=12 + \catcode`|=12 + \catcode`<=12 + \catcode`>=12 + \catcode`+=12 + \parsearg\doverbatiminclude +} +\def\setupverbatiminclude{% + \begingroup + \nonfillstart + \advance\leftskip by -\defbodyindent + \begingroup\setupverbatim +} +% +\def\doverbatiminclude#1{% + % Restore active chars for included file. + \endgroup + \begingroup + \def\thisfile{#1}% + \expandafter\expandafter\setupverbatiminclude\input\thisfile + \endgroup\nonfillfinish\endgroup +} + + \message{defuns,} % @defun etc. @@ -4710,7 +4929,8 @@ width0pt\relax} \fi \def\deftypeivarheader#1#2#3{% \dosubind{vr}{\code{#3}}{\putwordof\ \code{#1}}% entry in variable index \begingroup - \defname{#3}{\putwordInstanceVariableof\ \code{#1}}% + \defname{\defheaderxcond#2\relax$$$#3} + {\putwordInstanceVariableof\ \code{#1}}% \defvarargs{#3}% \endgroup } @@ -5628,7 +5848,8 @@ width0pt\relax} \fi \setbox0 = \hbox{\ignorespaces #2}\ifdim\wd0 > 0pt \epsfxsize=#2\relax \fi \setbox0 = \hbox{\ignorespaces #3}\ifdim\wd0 > 0pt \epsfysize=#3\relax \fi \begingroup - \catcode`\^^M = 5 % in case we're inside an example + \catcode`\^^M = 5 % in case we're inside an example + \normalturnoffactive % allow _ et al. in names % If the image is by itself, center it. \ifvmode \nobreak\bigskip @@ -5740,6 +5961,15 @@ should work if nowhere else does.} \setemergencystretch } +% Use `small' versions. +% +\def\smallenvironments{% + \let\smalldisplay = \smalldisplayx + \let\smallexample = \smalllispx + \let\smallformat = \smallformatx + \let\smalllisp = \smalllispx +} + % @letterpaper (the default). \def\letterpaper{{\globaldefs = 1 \parskip = 3pt plus 2pt minus 1pt @@ -5762,11 +5992,7 @@ should work if nowhere else does.} \contentsrightmargin = 0pt \deftypemargin = 0pt \defbodyindent = .5cm - % - \let\smalldisplay = \smalldisplayx - \let\smallexample = \smalllispx - \let\smallformat = \smallformatx - \let\smalllisp = \smalllispx + \smallenvironments }} % Use @afourpaper to print on European A4 paper. @@ -5780,6 +6006,26 @@ should work if nowhere else does.} \hfuzz = 1pt }} +% Use @afivepaper to print on European A5 paper. +% From romildo@urano.iceb.ufop.br, 2 July 2000. +% He also recommends making @example and @lisp be small. +\def\afivepaper{{\globaldefs = 1 + \setleading{12.5pt}% + \parskip = 2pt plus 1pt minus 0.1pt + % + \internalpagesizes{166mm}{120mm}{\voffset}{-8mm}{\bindingoffset}{8pt}% + % + \lispnarrowing = 0.2in + \tolerance = 800 + \hfuzz = 1.2pt + \contentsrightmargin = 0mm + \deftypemargin = 0pt + \defbodyindent = 2mm + \tableindent = 12mm + % + \smallenvironments +}} + % A specific text layout, 24x15cm overall, intended for A4 paper. 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