path: root/doc/gawk.1

GAWK(1)                                  Utility Commands                                 GAWK(1)

NAME
       gawk - pattern scanning and processing language

SYNOPSIS
       gawk [ POSIX or GNU style options ] -f program-file [ -- ] file ...
       gawk [ POSIX or GNU style options ] [ -- ] program-text file ...

       pgawk [ POSIX or GNU style options ] -f program-file [ -- ] file ...
       pgawk [ POSIX or GNU style options ] [ -- ] program-text file ...

DESCRIPTION
       Gawk  is the GNU Project's implementation of the AWK programming language.  It conforms to
       the definition of the language in the POSIX 1003.2 Command Language  And  Utilities  Stan-
       dard.   This  version in turn is based on the description in The AWK Programming Language,
       by Aho, Kernighan, and Weinberger, with the additional features found in the System V  Re-
       lease  4 version of UNIX awk.  Gawk also provides more recent Bell Laboratories awk exten-
       sions, and a number of GNU-specific extensions.

       Pgawk is the profiling version of gawk.  It is identical in every way to gawk, except that
       programs  run  more slowly, and it automatically produces an execution profile in the file
       awkprof.out when done.  See the --profile option, below.

       The command line consists of options to gawk itself, the AWK program text (if not supplied
       via  the  -f or --file options), and values to be made available in the ARGC and ARGV pre-
       defined AWK variables.

OPTION FORMAT
       Gawk options may be either traditional POSIX one letter options, or  GNU  style  long  op-
       tions.   POSIX  options start with a single "-", while long options start with "--".  Long
       options are provided for both GNU-specific features and for POSIX-mandated features.

       Following the POSIX standard, gawk-specific options are supplied via arguments to  the  -W
       option.   Multiple  -W options may be supplied Each -W option has a corresponding long op-
       tion, as detailed below.  Arguments to long options are either joined with the  option  by
       an  =  sign,  with no intervening spaces, or they may be provided in the next command line
       argument.  Long options may be abbreviated, as long as the abbreviation remains unique.

OPTIONS
       Gawk accepts the following options, listed alphabetically.

       -F fs
       --field-separator fs
              Use fs for the input field separator (the value of the FS predefined variable).

       -v var=val
       --assign var=val
              Assign the value val to the variable var, before execution of the  program  begins.
              Such variable values are available to the BEGIN block of an AWK program.

       -f program-file
       --file program-file
              Read  the  AWK program source from the file program-file, instead of from the first
              command line argument.  Multiple -f (or --file) options may be used.

       -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 Laboratories research version of UNIX awk.  They  are  ig-
              nored by gawk, since gawk has no pre-defined limits.

       -W compat
       -W traditional
       --compat
       --traditional
              Run in compatibility mode.  In compatibility mode, gawk behaves identically to UNIX
              awk; none of the GNU-specific extensions are recognized.  The use of  --traditional
              is  preferred  over the other forms of this option.  See GNU EXTENSIONS, below, for
              more information.

       -W copyleft
       -W copyright
       --copyleft
       --copyright
              Print the short version of the GNU copyright information message  on  the  standard
              output and exit successfully.

       -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 uses 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 pro-
              gram with a lot of functions, and you want to be sure that your functions don't in-
              advertently  use  global variables that you meant to be local.  (This is a particu-
              larly easy mistake to make with simple variable names like i, j, and so on.)

       -W help
       -W usage
       --help
       --usage
              Print a relatively short summary of the available options on the  standard  output.
              (Per the GNU Coding Standards, these options cause an immediate, successful exit.)

       -W lint[=value]
       --lint[=value]
              Provide warnings about constructs that are dubious or non-portable to other AWK im-
              plementations.  With an optional argument of fatal, lint warnings become fatal  er-
              rors.  This may be drastic, but its use will certainly encourage the development of
              cleaner AWK programs.  With an optional argument of invalid,  only  warnings  about
              things that are actually invalid are issued. (This is not fully implemented yet.)

       -W lint-old
       --lint-old
              Provide  warnings about constructs that are not portable to the original version of
              Unix awk.

       -W gen-po
       --gen-po
              Scan and parse the AWK program, and generate a GNU .po format file on standard out-
              put with entries for all localizable strings in the program.  The program itself is
              not executed.  See the GNU gettext distribution for more information on .po files.

       -W non-decimal-data
       --non-decimal-data
              Recognize octal and hexadecimal values in input data.  Use this option  with  great
              caution!

       -W posix
       --posix
              This turns on compatibility mode, with the following additional restrictions:

              +o \x escape sequences are not recognized.

              +o Only space and tab act as field separators when FS is set to a single space, new-
                line does not.

              +o You cannot continue lines after ?  and :.

              +o The synonym func for the keyword function is not recognized.

              +o The operators ** and **= cannot be used in place of ^ and ^=.

              +o The fflush() function is not available.

       -W profile[=prof_file]
       --profile[=prof_file]
              Send profiling data to prof_file.  The default is awkprof.out.  When run with gawk,
              the  profile  is  just  a  "pretty  printed" version of the program.  When run with
              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.

       -W re-interval
       --re-interval
              Enable  the use of interval expressions in regular expression matching (see Regular
              Expressions, below).  Interval expressions were not traditionally available in  the
              AWK language.  The POSIX standard added them, to make awk and egrep consistent with
              each other.  However, their use is likely to break old AWK programs, so  gawk  only
              provides them if they are requested with this option, or when --posix is specified.

       -W source program-text
       --source program-text
              Use program-text as AWK program source code.  This option allows the easy intermix-
              ing of library functions (used via the -f and --file options) with source code  en-
              tered  on  the command line.  It is intended primarily for medium to large AWK pro-
              grams used in shell scripts.

       -W version
       --version
              Print version information for this particular copy of gawk on the standard  output.
              This  is useful mainly for knowing if the current copy of gawk on your system is up
              to date with respect to whatever the  Free  Software  Foundation  is  distributing.
              This  is also useful when reporting bugs.  (Per the GNU Coding Standards, these op-
              tions cause an immediate, successful exit.)

       --     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 the argu-
              ment parsing convention used by most other POSIX programs.
       In compatibility mode, any other options are flagged as invalid,  but  are  otherwise  ig-
       nored.   In  normal  operation, as long as program text has been supplied, unknown options
       are passed on to the AWK program in the ARGV array for processing.  This  is  particularly
       useful for running AWK programs via the "#!" executable interpreter mechanism.
AWK PROGRAM EXECUTION
       An  AWK  program consists of a sequence of pattern-action statements and optional function
       definitions.
              pattern   { action statements }
              function name(parameter list) { statements }
       Gawk first reads the program source from the program-file(s) if specified, from  arguments
       to  --source,  or  from  the  first  non-option  argument on the command line.  The -f and
       --source options may be used multiple times on the command line.  Gawk reads  the  program
       text  as  if all the program-files and command line source texts had been concatenated to-
       gether.  This is useful for building libraries of AWK functions, without having to include
       them  in each new AWK program that uses them.  It also provides the ability to mix library
       functions with command line programs.
       The environment variable AWKPATH specifies a search path to use when finding source  files
       named  with  the  -f  option.   If  this  variable  does  not  exist,  the default path is
       ".:/usr/local/share/awk".  (The actual directory may vary, depending  upon  how  gawk  was
       built  and installed.)  If a file name given to the -f option contains a "/" character, no
       path search is performed.
       Gawk executes AWK programs in the following order.  First, all variable assignments speci-
       fied  via  the  -v option are performed.  Next, gawk compiles the program into an internal
       form.  Then, gawk executes the code in the BEGIN block(s) (if any), and then  proceeds  to
       read  each file named in the ARGV array.  If there are no files named on the command line,
       gawk reads the standard input.
       If a filename on the command line has the form var=val it is treated as a variable assign-
       ment.   The  variable  var  will be assigned the value val.  (This happens after any BEGIN
       block(s) have been run.)  Command line variable assignment is most useful for  dynamically
       assigning  values to the variables AWK uses to control how input is broken into fields and
       records.  It is also useful for controlling state if multiple passes  are  needed  over  a
       single data file.
       If the value of a particular element of ARGV is empty (""), gawk skips over it.
       For  each record in the input, gawk tests to see if it matches any pattern in the AWK pro-
       gram.  For each pattern that the record matches, the associated action is  executed.   The
       patterns are tested in the order they occur in the program.
       Finally,  after all the input is exhausted, gawk executes the code in the END block(s) (if
       any).
VARIABLES, RECORDS AND FIELDS
       AWK variables are dynamic; they come into existence when they are first used.  Their  val-
       ues  are  either  floating-point  numbers or strings, or both, depending upon how they are
       used.  AWK also has one dimensional arrays; arrays with multiple dimensions may  be  simu-
       lated.   Several  pre-defined variables are set as a program runs; these will be described
       as needed and summarized below.
   Records
       Normally, records are separated by newline characters.  You can control  how  records  are
       separated by assigning values to the built-in variable RS.  If RS is any single character,
       that character separates records.  Otherwise, RS is a regular expression.  Text in the in-
       put  that matches this regular expression separates the record.  However, in compatibility
       mode, only the first character of its string value is used for separating records.  If  RS
       is  set  to the null string, then records are separated by blank lines.  When RS is set to
       the null string, the newline character always acts as a field separator,  in  addition  to
       whatever value FS may have.
   Fields
       As  each  input record is read, gawk splits the record 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.  If FS is the null string, then each individual character becomes a sepa-
       rate field.  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 and/or tabs and/or
       newlines.  (But see the discussion of --posix, below).  NOTE: The value of IGNORECASE (see
       below)  also affects how fields are split when FS is a regular expression, and how records
       are separated when RS is a regular expression.
       If the FIELDWIDTHS variable is set to a space separated list of numbers, each field is ex-
       pected to have fixed width, and gawk splits up the record using the specified widths.  The
       value of FS is ignored.  Assigning a new value to FS overrides the use of FIELDWIDTHS, and
       restores the default behavior.
       Each  field  in the input record may be referenced by its position, $1, $2, and so on.  $0
       is the whole record.  Fields need not be referenced by constants:
              n = 5
              print $n
       prints the fifth field in the input record.
       The variable NF is set to the total number of fields in the input record.
       References to non-existent fields (i.e. fields after $NF) produce the  null-string.   How-
       ever,  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.  References
       to negative numbered fields cause a fatal error.  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.
       Assigning a value to an existing field causes the whole record to be rebuilt  when  $0  is
       referenced.   Similarly, assigning a value to $0 causes the record to be resplit, creating
       new values for the fields.
   Built-in Variables
       Gawk's built-in variables are:
       ARGC        The number of command line arguments (does not include options to gawk, or the
                   program source).
       ARGIND      The index in ARGV of the current file being processed.
       ARGV        Array  of  command  line  arguments.  The array is indexed from 0 to ARGC - 1.
                   Dynamically changing the contents of ARGV can control the files used for data.
       BINMODE     On non-POSIX systems, specifies use of "binary" mode for all  file  I/O.   Nu-
                   meric  values  of  1,  2, or 3, specify that input files, output files, or all
                   files, respectively, should use binary I/O.  String  values  of  "r",  or  "w"
                   specify  that  input  files,  or output files, respectively, should use binary
                   I/O.  String values of "rw" or "wr" specify that all files should  use  binary
                   I/O.   Any other string value is treated as "rw", but generates a warning mes-
                   sage.
       CONVFMT     The conversion format for numbers, "%.6g", by default.
       ENVIRON     An array containing the values of the current environment.  The array  is  in-
                   dexed by the environment variables, each element being the value of that vari-
                   able (e.g., ENVIRON["HOME"] might be /home/arnold).  Changing this array  does
                   not  affect the environment seen by programs which gawk spawns via redirection
                   or the system() function.
       ERRNO       If a system error occurs either doing a redirection for getline, during a read
                   for  getline, or during a close(), then ERRNO will contain a string describing
                   the error.  The value is subject to translation in non-English locales.
       FIELDWIDTHS A white-space separated list of fieldwidths.  When set, gawk parses the  input
                   into  fields  of fixed width, instead of using the value of the FS variable as
                   the field separator.
       FILENAME    The name of the current input file.  If no files are specified on the  command
                   line, the value of FILENAME is "-".  However, FILENAME is undefined inside the
                   BEGIN block (unless set by getline).
       FNR         The input record number in the current input file.
       FS          The input field separator, a space by default.  See Fields, above.
       IGNORECASE  Controls the case-sensitivity of all regular expression and string operations.
                   If IGNORECASE has a non-zero value, then string comparisons and pattern match-
                   ing in rules, field splitting with FS, record separating with RS, regular  ex-
                   pression  matching  with ~ and !~, and the gensub(), gsub(), index(), match(),
                   split(), and sub() built-in functions all ignore case when doing  regular  ex-
                   pression  operations.  NOTE: Array subscripting is not affected.  However, the
                   asort() and asorti() functions are affected.
                   Thus, if IGNORECASE is not equal to zero, /aB/  matches  all  of  the  strings
                   "ab",  "aB",  "Ab", and "AB".  As with all AWK variables, the initial value of
                   IGNORECASE is zero, so all regular expression and string operations  are  nor-
                   mally  case-sensitive.   Under Unix, the full ISO 8859-1 Latin-1 character set
                   is used when ignoring case.  As of gawk  3.1.4,  the  case  equivalencies  are
                   fully locale-aware, based on the C <ctype.h> facilities such as isalpha(), and
                   tolupper().
       LINT        Provides dynamic control of the --lint option  from  within  an  AWK  program.
                   When  true, gawk prints lint warnings. When false, it does not.  When assigned
                   the string value "fatal", lint warnings  become  fatal  errors,  exactly  like
                   --lint=fatal.  Any other true value just prints warnings.
       NF          The number of fields in the current input record.
       NR          The total number of input records seen so far.
       OFMT        The output format for numbers, "%.6g", by default.
       OFS         The output field separator, a space by default.
       ORS         The output record separator, by default a newline.
       PROCINFO    The elements of this array provide access to information about the running AWK
                   program.  On some systems, there  may  be  elements  in  the  array,  "group1"
                   through  "groupn" for some n, which is the number of supplementary groups that
                   the process has.  Use the in operator to test for these elements.  The follow-
                   ing elements are guaranteed to be available:
                   PROCINFO["egid"]   the value of the getegid(2) system call.
                   PROCINFO["euid"]   the value of the geteuid(2) system call.
                   PROCINFO["FS"]     "FS"  if  field  splitting with FS is in effect, or "FIELD-
                                      WIDTHS" if field splitting with FIELDWIDTHS is in effect.
                   PROCINFO["gid"]    the value of the getgid(2) 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(2) system call.
                   PROCINFO["version"]
                                      The version of gawk.  This is available from version  3.1.4
                                      and later.
       RS          The input record separator, by default a newline.
       RT          The  record terminator.  Gawk sets RT to the input text that matched the char-
                   acter or regular expression specified by RS.
       RSTART      The index of the first character matched by match(); 0 if no match.  (This im-
                   plies that character indices start at one.)
       RLENGTH     The length of the string matched by match(); -1 if no match.
       SUBSEP      The  character  used to separate multiple subscripts in array elements, by de-
                   fault "\034".
       TEXTDOMAIN  The text domain of the AWK program; used to find  the  localized  translations
                   for the program's strings.
   Arrays
       Arrays  are  subscripted with an expression between square brackets ([ and ]).  If the ex-
       pression is an expression list (expr, expr ...)  then the array subscript is a string con-
       sisting  of  the  concatenation of the (string) value of each expression, separated by the
       value of the SUBSEP variable.  This facility is used to simulate multiply dimensioned  ar-
       rays.  For example:
              i = "A"; j = "B"; k = "C"
              x[i, j, k] = "hello, world\n"
       assigns  the string "hello, world\n" to the element of the array x which is indexed by the
       string "A\034B\034C".  All arrays in AWK are associative, i.e. indexed by string values.
       The special operator in may be used in an if or while statement to see if an array has  an
       index consisting of a particular value.
              if (val in array)
                   print array[val]
       If the array has multiple subscripts, use (i, j) in array.
       The in construct may also be used in a for loop to iterate over all the elements of an ar-
       ray.
       An element may be deleted from an array using the delete statement.  The delete  statement
       may  also  be used to delete the entire contents of an array, just by specifying the array
       name without a subscript.
   Variable Typing And Conversion
       Variables and fields may be (floating point) numbers, or strings, or both.  How the  value
       of  a  variable is interpreted depends upon its context.  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.
       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.
       When  a  string  must  be converted to a number, the conversion is accomplished using str-
       tod(3).  A number is converted to a string by using the  value  of  CONVFMT  as  a  format
       string  for  sprintf(3), with the numeric value of the variable as the argument.  However,
       even though all numbers in AWK are floating-point, integral values are always converted as
       integers.  Thus, given
              CONVFMT = "%2.2f"
              a = 12
              b = a ""
       the variable b has a string value of "12" and not "12.00".
       Gawk  performs comparisons as follows: If two variables are numeric, they are compared nu-
       merically.  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 con-
       verted to a string and a string comparison is performed.  Two  strings  are  compared,  of
       course,  as strings.  Note that the POSIX standard applies the concept of "numeric string"
       everywhere, even to string constants.  However, this is clearly incorrect, and  gawk  does
       not do this.  (Fortunately, this is fixed in the next version of the standard.)
       Note  that  string  constants, such as "57", are not numeric strings, they are string con-
       stants.  The idea of "numeric string" only applies to  fields,  getline  input,  FILENAME,
       ARGV  elements,  ENVIRON elements and the elements of an array created by split() that are
       numeric strings.  The basic idea is that user input, and only user input, that  looks  nu-
       meric, should be treated that way.
       Uninitialized  variables  have  the  numeric value 0 and the string value "" (the null, or
       empty, string).
   Octal and Hexadecimal Constants
       Starting with version 3.1 of gawk , you may use C-style octal and hexadecimal constants in
       your AWK program source code.  For example, the octal value 011 is equal to decimal 9, and
       the hexadecimal value 0x11 is equal to decimal 17.
   String Constants
       String constants in AWK are sequences of characters enclosed between  double  quotes  (").
       Within strings, certain escape sequences are recognized, as in C.  These are:
       \\   A literal backslash.
       \a   The "alert" character; usually the ASCII BEL character.
       \b   backspace.
       \f   form-feed.
       \n   newline.
       \r   carriage return.
       \t   horizontal tab.
       \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  se-
            quence.   (This feature should tell us something about language design by committee.)
            E.g., "\x1B" is the ASCII ESC (escape) character.
       \ddd The character represented by the 1-, 2-, or 3-digit sequence of octal digits.   E.g.,
            "\033" is the ASCII ESC (escape) character.
       \c   The literal character c.
       The  escape  sequences  may  also  be  used  inside  constant  regular  expressions (e.g.,
       /[ \t\f\n\r\v]/ matches whitespace characters).
       In compatibility mode, the characters represented by  octal  and  hexadecimal  escape  se-
       quences are treated literally when used in regular expression constants.  Thus, /a\52b/ is
       equivalent to /a\*b/.
PATTERNS AND ACTIONS
       AWK is a line-oriented language.  The pattern comes first, and then  the  action.   Action
       statements  are enclosed in { and }.  Either the pattern may be missing, or the action may
       be missing, but, 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
              { print }
       which prints the entire record.
       Comments  begin  with  the  "#"  character, and continue until the end of the line.  Blank
       lines may be used to separate statements.  Normally, a statement ends with a newline, how-
       ever, 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
       will be ignored.
       Multiple statements may be put on one line by separating them with a ";".  This applies to
       both  the statements within the action part of a pattern-action pair (the usual case), and
       to the pattern-action statements themselves.
   Patterns
       AWK patterns may be one of the following:
              BEGIN
              END
              /regular expression/
              relational expression
              pattern && pattern
              pattern || pattern
              pattern ? pattern : pattern
              (pattern)
              ! pattern
              pattern1, pattern2
       BEGIN and END are two special kinds of patterns which are not tested  against  the  input.
       The  action parts of all BEGIN patterns are merged as if all the statements had been writ-
       ten in a single BEGIN block.  They are executed before any of the input  is  read.   Simi-
       larly,  all  the  END  blocks are merged, 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 patterns 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 the same as those  in
       egrep(1), and are summarized below.
       A  relational  expression may use any of the operators defined below in the section on ac-
       tions.  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 is true then the
       pattern used for testing is the second pattern, otherwise it is the third.   Only  one  of
       the second and third patterns is evaluated.
       The  pattern1,  pattern2  form of an expression is called a range pattern.  It matches all
       input records starting with a record that matches pattern1, and continuing until a  record
       that  matches pattern2, inclusive.  It does not combine with any other sort of pattern ex-
       pression.
   Regular Expressions
       Regular expressions are the extended kind found in egrep.  They are composed of characters
       as follows:
       c          matches the non-metacharacter c.
       \c         matches the literal character c.
       .          matches any character including newline.
       ^          matches the beginning of a string.
       $          matches the end of a string.
       [abc...]   character list, matches any of the characters abc....
       [^abc...]  negated character list, matches any character except abc....
       r1|r2      alternation: matches either r1 or r2.
       r1r2       concatenation: matches r1, and then r2.
       r+         matches one or more r's.
       r*         matches zero or more r's.
       r?         matches zero or one r's.
       (r)        grouping: matches r.
       r{n}
       r{n,}
       r{n,m}     One  or  two  numbers inside braces denote an interval expression.  If there is
                  one number in the braces, the preceding regular  expression  r  is  repeated  n
                  times.   If  there  are  two numbers separated by a comma, r is repeated n to m
                  times.  If there is one number followed by a comma, then r is repeated at least
                  n times.
                  Interval  expressions  are only available if either --posix or --re-interval is
                  specified on the command line.

       \y         matches the empty string at either the beginning or the end of a word.

       \B         matches the empty string within a word.

       \<         matches the empty string at the beginning of a word.

       \>         matches the empty string at the end of a word.

       \w         matches any word-constituent character (letter, digit, or underscore).

       \W         matches any character that is not word-constituent.

       \`         matches the empty string at the beginning of a buffer (string).

       \'         matches the empty string at the end of a buffer.

       The escape sequences that are valid in string constants (see below) are also valid in reg-
       ular expressions.

       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  charac-
       ter differs in the USA and in France.

       A character class is only valid in a regular expression inside the brackets of a character
       list.  Character classes consist of [:, a keyword denoting the class, and :].  The charac-
       ter classes defined by the POSIX standard are:

       [:alnum:]  Alphanumeric characters.

       [:alpha:]  Alphabetic characters.

       [:blank:]  Space or tab characters.

       [:cntrl:]  Control characters.

       [:digit:]  Numeric characters.

       [:graph:]  Characters that are both printable and 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 charac-
                  ters, 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 would have
       had to write /[A-Za-z0-9]/.  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:]]/,  and this matches 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 repre-
       sented 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 regular expression
              that matches this collating element,  while  [ch]  is  a  regular  expression  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 regular ex-
              pression that matches any of e, e', or e`.

       These features are very valuable in non-English speaking locales.  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.

       The \y, \B, \<, \>, \w, \W, \`, and \' operators are specific to gawk; they are extensions
       based on facilities in the GNU regular expression libraries.

       The various command line options control how gawk interprets characters in regular expres-
       sions.

       No options
              In the default case, gawk provide all the facilities of POSIX  regular  expressions
              and  the  GNU  regular expression operators described above.  However, interval ex-
              pressions are not supported.

       --posix
              Only POSIX regular expressions are supported, the GNU operators  are  not  special.
              (E.g., \w matches a literal w).  Interval expressions are allowed.

       --traditional
              Traditional  Unix  awk  regular expressions are matched.  The GNU operators are not
              special, interval expressions are not available, and neither are the POSIX  charac-
              ter classes ([[:alnum:]] and so on).  Characters described by octal and hexadecimal
              escape sequences are treated literally, even if they represent  regular  expression
              metacharacters.

       --re-interval
              Allow  interval  expressions in regular expressions, even if --traditional has been
              provided.

   Actions
       Action statements are enclosed in braces, { and }.  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 patterned after those in C.

   Operators
       The operators in AWK, in order of decreasing precedence, are

       (...)       Grouping

       $           Field reference.

       ++ --       Increment and decrement, both prefix and postfix.

       ^           Exponentiation (** may also be used, and **= for the assignment operator).

       + - !       Unary plus, unary minus, and logical negation.

       * / %       Multiplication, division, and modulus.

       + -         Addition and subtraction.

       space       String concatenation.

       < >
       <= >=
       != ==       The regular relational operators.

       ~ !~        Regular expression match, negated match.  NOTE: Do not use a constant  regular
                   expression  (/foo/)  on  the left-hand side of a ~ or !~.  Only use one on the
                   right-hand side.  The expression /foo/ ~ exp has the same meaning  as  (($0  ~
                   /foo/) ~ exp).  This is usually not what was intended.

       in          Array membership.

       &&          Logical AND.

       ||          Logical OR.

       ?:          The  C  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.

       = += -=
       *= /= %= ^= Assignment.   Both  absolute  assignment (var = value) and operator-assignment
                   (the other forms) are supported.

   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 }

   I/O Statements
       The input/output statements are as follows:

       close(file [, how])   Close file, pipe or co-process.  The optional  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 "to" or "from".

       getline               Set $0 from next input record; set NF, NR, FNR.

       getline <file         Set $0 from next record of file; set NF.

       getline var           Set var from next input record; set NR, FNR.

       getline var <file     Set var from next record of file.

       command | getline [var]
                             Run command piping the output either into $0 or var, as above.

       command |& getline [var]
                             Run command as a co-process piping the output either into $0 or var,
                             as above.  Co-processes are a gawk extension.

       next                  Stop  processing the current input record.  The next input record is
                             read and processing starts over with the first pattern  in  the  AWK
                             program.  If the end of the input data is reached, the END block(s),
                             if any, are executed.

       nextfile              Stop processing the current input file.  The next input record  read
                             comes  from  the  next input file.  FILENAME and ARGIND are updated,
                             FNR is reset to 1, and processing starts over with the first pattern
                             in the AWK program. If the end of the input data is reached, the END
                             block(s), if any, are executed.

       print                 Prints the current record.  The output record is terminated with the
                             value of the ORS variable.

       print expr-list       Prints  expressions.   Each  expression is separated by the value of
                             the OFS variable.  The output record is terminated with the value of
                             the ORS variable.

       print expr-list >file Prints  expressions  on  file.   Each expression is separated by the
                             value of the OFS variable.  The output record is terminated with the
                             value of the ORS variable.

       printf fmt, expr-list Format and print.

       printf fmt, expr-list >file
                             Format and print on file.

       system(cmd-line)      Execute the command cmd-line, and return the exit status.  (This may
                             not be available on non-POSIX systems.)

       fflush([file])        Flush any buffers associated with the open output file or pipe file.
                             If file is missing, then standard output is flushed.  If file is the
                             null string, then all open output files and pipes have their buffers
                             flushed.

       Additional output redirections are allowed for print and printf.

       print ... >> file
              appends output to the file.

       print ... | command
              writes on a pipe.

       print ... |& command
              sends data to a co-process.

       The  getline  command  returns  0 on end of file and -1 on an error.  Upon an error, ERRNO
       contains a string describing the problem.

       NOTE: If using a pipe or co-process to getline, or from print or printf within a loop, you
       must use close() to create new instances of the command.  AWK does not automatically close
       pipes or co-processes when they return EOF.

   The printf Statement
       The AWK versions of the printf statement and sprintf() function  (see  below)  accept  the
       following conversion specification formats:

       %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.

       %d, %i  A decimal number (the integer part).

       %e ,  %E
               A  floating point number of the form [-]d.dddddde[+-]dd.  The %E format uses E in-
               stead of e.

       %f      A floating point number of the form [-]ddd.dddddd.

       %g ,  %G
               Use %e or %f conversion, whichever is  shorter,  with  nonsignificant  zeros  sup-
               pressed.  The %G format uses %E instead of %e.

       %o      An unsigned octal number (also an integer).

       %u      An unsigned decimal number (again, an integer).

       %s      A character string.

       %x ,  %X
               An unsigned hexadecimal number (an integer).  The %X format uses ABCDEF instead of
               abcdef.

       %%      A single % character; no argument is converted.

       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. If --lint is provided on
       the command line gawk warns about this.  Other versions of awk may print invalid values or
       do something else entirely.

       Optional, additional parameters may lie between the % and the control letter:

       count$ Use  the count'th argument at this point in the formatting.  This is called a posi-
              tional 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 gawk extension.

       -      The expression should be left-justified within its field.

       space  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.

       #      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 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 ze-
              roes 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.

       width  The  field  should be padded to this width.  The field is normally padded with spa-
              ces.  If the 0 flag has been used, it is padded with zeroes.

       .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 sig-
              nificant digits.  For the %d, %o, %i, %u, %x, and %X formats, it specifies the min-
              imum number of digits to print.  For %s, it specifies the maximum number of charac-
              ters from the string that should be printed.

       The  dynamic width and prec capabilities of the ANSI C printf() routines are supported.  A
       * in place of either the width or prec specifications causes their values to be taken from
       the  argument  list  to printf or sprintf().  To use a positional specifier with a dynamic
       width or precision, supply the count$ after the * in  the  format  string.   For  example,
       "%3$*2$.*1$s".

   Special File Names
       When  doing I/O redirection from either print or printf into a file, or via getline from a
       file, gawk recognizes certain special filenames internally.  These filenames allow  access
       to  open file descriptors inherited from 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:

       /dev/stdin  The standard input.

       /dev/stdout The standard output.

       /dev/stderr The standard error output.

       /dev/fd/n   The file associated with the open file descriptor n.

       These are particularly useful for error messages.  For example:

              print "You blew it!" > "/dev/stderr"

       whereas you would otherwise have to use

              print "You blew it!" | "cat 1>&2"

       The following special filenames may be used with the |& co-process operator  for  creating
       TCP/IP network connections.

       /inet/tcp/lport/rhost/rport  File for TCP/IP connection on local port lport to remote host
                                    rhost on remote port rport.  Use a port of 0 to have the sys-
                                    tem pick a port.

       /inet/udp/lport/rhost/rport  Similar, but use UDP/IP instead of TCP/IP.

       /inet/raw/lport/rhost/rport  Reserved for future use.

       Other  special  filenames  provide  access  to information about the running gawk process.
       These filenames are now obsolete.  Use the PROCINFO array to obtain the  information  they
       provide.  The filenames are:

       /dev/pid    Reading  this  file returns the process ID of the current process, in decimal,
                   terminated with a newline.

       /dev/ppid   Reading this file returns the parent process ID of  the  current  process,  in
                   decimal, terminated with a newline.

       /dev/pgrpid Reading this file returns the process group ID of the current process, in dec-
                   imal, terminated with a newline.

       /dev/user   Reading this file returns a single record  terminated  with  a  newline.   The
                   fields  are  separated  with  spaces.  $1 is the value of the getuid(2) system
                   call, $2 is the value of the geteuid(2) system call, $3 is the  value  of  the
                   getgid(2)  system call, and $4 is the value of the getegid(2) system call.  If
                   there are any additional fields, they are  the  group  IDs  returned  by  get-
                   groups(2).  Multiple groups may not be supported on all systems.

   Numeric Functions
       AWK has the following built-in arithmetic functions:

       atan2(y, x)   Returns the arctangent of y/x in radians.

       cos(expr)     Returns the cosine of expr, which is in radians.

       exp(expr)     The exponential function.

       int(expr)     Truncates to integer.

       log(expr)     The natural logarithm function.

       rand()        Returns a random number N, between 0 and 1, such that 0 <= N < 1.

       sin(expr)     Returns the sine of expr, which is in radians.

       sqrt(expr)    The square root function.

       srand([expr]) Uses expr as a new seed for the random number generator.  If no expr is pro-
                     vided, the time of day is used.  The return value is the previous  seed  for
                     the random number generator.

   String Functions
       Gawk has the following built-in string functions:

       asort(s [, d])          Returns  the  number  of elements in the source array s.  The con-
                               tents of s are sorted using gawk's normal rules for comparing val-
                               ues,  and  the indexes of the sorted values of s are replaced with
                               sequential integers starting with 1. If the  optional  destination
                               array  d is specified, then s is first duplicated into d, and then
                               d is sorted, leaving the indexes of the source array s unchanged.

       asorti(s [, d])         Returns the number of elements in the source array s.  The  behav-
                               ior  is the same as that of asort(), except that the array indices
                               are used for sorting, not the array values.  When done, the  array
                               is  indexed  numerically, and the values are those of the original
                               indices.  The original values are lost; thus provide a second  ar-
                               ray if you wish to preserve the original.

       gensub(r, s, h [, t])   Search  the  target string t for matches of the regular expression
                               r.  If h is a string beginning with  g  or  G,  then  replace  all
                               matches  of  r  with s.  Otherwise, h is a number indicating which
                               match of r to replace.  If t is not supplied, $0 is used  instead.
                               Within the replacement text s, the sequence \n, where n is a digit
                               from 1 to 9, may be used to indicate just the  text  that  matched
                               the  n'th parenthesized subexpression.  The sequence \0 represents
                               the entire matched text, as does the character  &.   Unlike  sub()
                               and  gsub(),  the modified string is returned as the result of the
                               function, and the original target string is not changed.

       gsub(r, s [, t])        For each substring matching the regular expression r in the string
                               t,  substitute  the  string  s, and return the number of substitu-
                               tions.  If t is not supplied, use $0.  An  &  in  the  replacement
                               text  is replaced with the text that was actually matched.  Use \&
                               to get a literal &.  (This must be typed as "\\&"; see  GAWK:  Ef-
                               fective  AWK  Programming for a fuller discussion of the rules for
                               &'s and backslashes in the replacement text of sub(), gsub(),  and
                               gensub().)

       index(s, t)             Returns  the  index  of the string t in the string s, or 0 if t is
                               not present.  (This implies that character indices start at one.)

       length([s])             Returns the length of the string s, or the length of $0  if  s  is
                               not supplied.

       match(s, r [, a])       Returns  the  position in s where the regular expression r occurs,
                               or 0 if r is not present,  and  sets  the  values  of  RSTART  and
                               RLENGTH.   Note  that  the argument order is the same as for the ~
                               operator: str ~ re.  If array a is provided, a is cleared and then
                               elements  1 through n are filled with the portions of s that match
                               the corresponding parenthesized subexpression in r.  The 0'th ele-
                               ment  of a contains the portion of s matched by the entire regular
                               expression r.  Subscripts a[n, "start"], and a[n,  "length"]  pro-
                               vide  the starting index in the string and length respectively, of
                               each matching substring.

       split(s, a [, r])       Splits the string s into the array a on the regular expression  r,
                               and returns the number of fields.  If r is omitted, FS is used in-
                               stead.  The array a is cleared first.  Splitting  behaves  identi-
                               cally to field splitting, described above.

       sprintf(fmt, expr-list) Prints  expr-list  according  to  fmt,  and  returns the resulting
                               string.

       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.

       sub(r, s [, t])         Just  like  gsub(),  but  only the first matching substring is re-
                               placed.

       substr(s, i [, n])      Returns the at most n-character substring of s starting at i.   If
                               n is omitted, the rest of s is used.

       tolower(str)            Returns  a copy of the string str, with all the upper-case charac-
                               ters in str translated to their corresponding lower-case  counter-
                               parts.  Non-alphabetic characters are left unchanged.

       toupper(str)            Returns  a copy of the string str, with all the lower-case charac-
                               ters in str translated to their corresponding upper-case  counter-
                               parts.  Non-alphabetic characters are left unchanged.

   Time Functions
       Since  one  of  the primary uses of AWK programs is processing log files that contain time
       stamp information, gawk provides the following functions for  obtaining  time  stamps  and
       formatting them.

       mktime(datespec)
                 Turns datespec into a time stamp of the same form as returned by systime().  The
                 datespec is a string of the form YYYY MM DD HH MM SS[ DST].  The contents of the
                 string  are six or seven numbers representing respectively the full year includ-
                 ing 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 mid-
                 night.  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), mktime() attempts to determine whether  daylight  saving
                 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]])
                 Formats timestamp according to  the  specification  in  format.   The  timestamp
                 should  be  of the same form as returned by systime().  If timestamp is missing,
                 the current time of day is used.  If format is missing, a default format equiva-
                 lent to the output of date(1) is used.  See the specification for the strftime()
                 function in ANSI C for the format conversions that are guaranteed to  be  avail-
                 able.   A  public-domain  version of strftime(3) and a man page for it come with
                 gawk; if that version was used to build gawk, then all of  the  conversions  de-
                 scribed in that man page are available to gawk.

       systime() Returns  the  current  time  of  day  as  the  number of seconds since the Epoch
                 (1970-01-01 00:00:00 UTC on POSIX systems).

   Bit Manipulations Functions
       Starting with version 3.1 of gawk, the following bit manipulation functions are available.
       They  work by converting double-precision floating point values to unsigned long integers,
       doing the operation, and then converting the result back to floating point.  The functions
       are:

       and(v1, v2)         Return the bitwise AND 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.

       or(v1, v2)          Return the bitwise OR of the values provided by v1 and v2.

       rshift(val, count)  Return the value of val, shifted right by count bits.

       xor(v1, v2)         Return the bitwise XOR of the values provided by v1 and v2.

   Internationalization Functions
       Starting  with  version  3.1 of gawk, the following functions may be used from within your
       AWK program for translating strings at run-time.  For full details,  see  GAWK:  Effective
       AWK Programming.

       bindtextdomain(directory [, domain])
              Specifies  the  directory where gawk looks for the .mo files, in case they will not
              or cannot be placed in the ``standard'' locations (e.g., during testing).   It  re-
              turns 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.

       dcgettext(string [, domain [, category]])
              Returns the translation of string in text domain domain for locale  category  cate-
              gory.   The  default  value for domain is the current value of TEXTDOMAIN.  The de-
              fault 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 GAWK: Effective AWK Programming.  You must also sup-
              ply a text domain.  Use TEXTDOMAIN if you want to use the current domain.

       dcngettext(string1 , string2 , number [, domain [, category]])
              Returns the plural form used for number of the translation of string1  and  string2
              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_MES-
              SAGES".
              If  you  supply a value for category, it must be a string equal to one of the known
              locale categories described in GAWK: Effective AWK Programming.  You must also sup-
              ply a text domain.  Use TEXTDOMAIN if you want to use the current domain.

USER-DEFINED FUNCTIONS
       Functions in AWK are defined as follows:

              function name(parameter list) { statements }

       Functions  are executed when they are called from within expressions in either patterns or
       actions.  Actual parameters supplied in the function call are used to instantiate the for-
       mal  parameters declared in the function.  Arrays are passed by reference, other variables
       are passed by value.

       Since functions were not originally part of the AWK  language,  the  provision  for  local
       variables  is  rather clumsy: They are declared as extra parameters in the parameter list.
       The convention is to separate local variables from real parameters by extra spaces in  the
       parameter list.  For example:

              function  f(p, q,     a, b)   # a and b are local
              {
                   ...
              }

              /abc/     { ... ; f(1, 2) ; ... }

       The  left  parenthesis  in  a function call is required to immediately follow the function
       name, without any intervening white space.  This is to avoid a  syntactic  ambiguity  with
       the  concatenation  operator.   This  restriction does not apply to the built-in functions
       listed above.

       Functions may call each other and may be recursive.  Function  parameters  used  as  local
       variables are initialized to the null string and the number zero upon function invocation.

       Use  return  expr  to return a value from a function.  The return value is undefined if no
       value is provided, or if the function returns by "falling off" the end.

       If --lint has been provided, gawk 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.

       The word func may be used in place of function.

DYNAMICALLY LOADING NEW FUNCTIONS
       Beginning  with version 3.1 of gawk, you can dynamically add new built-in functions to the
       running gawk interpreter.  The full details are beyond the scope of this manual page;  see
       GAWK: Effective AWK Programming for the details.

       extension(object, function)
               Dynamically  link  the  shared object file named by object, and invoke function in
               that object, to perform initialization.  These should both be provided as strings.
               Returns the value returned by function.

       This  function  is  provided and documented in GAWK: Effective AWK Programming, but every-
       thing 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.

SIGNALS
       pgawk accepts two signals.  SIGUSR1 causes it to dump a profile and function call stack to
       the profile file, which is either awkprof.out, or whatever file was named with the  --pro-
       file option.  It then continues to run.  SIGHUP causes it to dump the profile and function
       call stack and then exit.

EXAMPLES
       Print and sort the login names of all users:

            BEGIN     { FS = ":" }
                 { print $1 | "sort" }

       Count lines in a file:

                 { nlines++ }
            END  { print nlines }

       Precede each line by its number in the file:

            { print FNR, $0 }

       Concatenate and line number (a variation on a theme):

            { print NR, $0 }
       Run an external command for particular lines of data:

            tail -f access_log |
            awk '/myhome.html/ { system("nmap " $1 ">> logdir/myhome.html") }'

INTERNATIONALIZATION
       String constants are sequences of characters enclosed in double  quotes.   In  non-English
       speaking  environments,  it  is  possible  to mark strings in the AWK program as requiring
       translation to the native natural language. Such strings are marked  in  the  AWK  program
       with a leading underscore ("_").  For example,

              gawk 'BEGIN { print "hello, world" }'

       always prints hello, world.  But,

              gawk 'BEGIN { print _"hello, world" }'

       might print bonjour, monde in France.

       There are several steps involved in producing and running a localizable AWK program.

       1.  Add a BEGIN action to assign a value to the TEXTDOMAIN variable to set the text domain
           to a name associated with your program.

                BEGIN { TEXTDOMAIN = "myprog" }

           This allows gawk to find the .mo file associated  with  your  program.   Without  this
           step,  gawk  uses the messages text domain, which likely does not contain translations
           for your program.

       2.  Mark all strings that should be translated with leading underscores.

       3.  If necessary, use the dcgettext() and/or bindtextdomain() functions in  your  program,
           as appropriate.

       4.  Run gawk --gen-po -f myprog.awk > myprog.po to generate a .po file for your program.

       5.  Provide appropriate translations, and build and install a corresponding .mo file.

       The internationalization features are described in full detail in GAWK: Effective AWK Pro-
       gramming.

POSIX COMPATIBILITY
       A primary goal for gawk is compatibility with the POSIX standard, as well as with the lat-
       est  version  of UNIX awk.  To this end, gawk incorporates the following user visible fea-
       tures which are not described in the AWK book, but are part of the Bell Laboratories  ver-
       sion of awk, and are in the POSIX standard.

       The  book indicates that command line variable assignment happens when awk would otherwise
       open the argument as a file, which is after the BEGIN block is executed.  However, in ear-
       lier  implementations, when such an assignment appeared before any file names, the assign-
       ment would happen before the BEGIN block was run.  Applications came  to  depend  on  this
       "feature."   When  awk was changed to match its documentation, the -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 Bell Laboratories and
       the GNU developers.)

       The -W option for implementation specific features is from the POSIX standard.

       When processing arguments, gawk uses the special option "--" to signal the  end  of  argu-
       ments.  In compatibility mode, it warns about but otherwise ignores undefined options.  In
       normal operation, such arguments are passed on to the AWK program for it to process.

       The AWK book does not define the return value of srand().  The POSIX standard has  it  re-
       turn  the seed it was using, to allow keeping track of random number sequences.  Therefore
       srand() in gawk also returns its current seed.

       Other new features are: The use of multiple -f options (from MKS awk); the ENVIRON  array;
       the  \a, and \v escape sequences (done originally in gawk and fed back into the Bell Labo-
       ratories version); the tolower() and toupper() built-in functions (from the Bell Laborato-
       ries  version); and the ANSI C conversion specifications in printf (done first in the Bell
       Laboratories version).

HISTORICAL FEATURES
       There are two features of historical AWK implementations that gawk supports.  First, it is
       possible  to call the length() built-in function not only with no argument, but even with-
       out parentheses!  Thus,

              a = length     # Holy Algol 60, Batman!

       is the same as either of

              a = length()
              a = length($0)

       This feature is marked as "deprecated" in the POSIX standard, and gawk  issues  a  warning
       about its use if --lint is specified on the command line.

       The  other  feature  is the use of either the continue or the break statements outside the
       body of a while, for, or do loop.  Traditional AWK implementations have treated such usage
       as  equivalent  to the next statement.  Gawk supports this usage if --traditional has been
       specified.

GNU EXTENSIONS
       Gawk has a number of extensions to POSIX awk.  They are described in  this  section.   All
       the  extensions described here can be disabled by invoking gawk with the --traditional op-
       tion.

       The following features of gawk are not available in POSIX awk.

       +o No path search is performed for files named via the -f option.   Therefore  the  AWKPATH
         environment variable is not special.

       +o The \x escape sequence.  (Disabled with --posix.)

       +o The fflush() function.  (Disabled with --posix.)

       +o The ability to continue lines after ?  and :.  (Disabled with --posix.)

       +o Octal and hexadecimal constants in AWK programs.

       +o The ARGIND, BINMODE, ERRNO, LINT, RT and TEXTDOMAIN variables are not special.

       +o The IGNORECASE variable and its side-effects are not available.

       +o The FIELDWIDTHS variable and fixed-width field splitting.

       +o The PROCINFO array is not available.

       +o The use of RS as a regular expression.

       +o The special file names available for I/O redirection are not recognized.

       +o The |& operator for creating co-processes.

       +o The ability to split out individual characters using the null string as the value of FS,
         and as the third argument to split().

       +o The optional second argument to the close() function.

       +o The optional third argument to the match() function.

       +o The ability to use positional specifiers with printf and sprintf().

       +o The use of delete array to delete the entire contents of an array.

       +o The use of nextfile to abandon processing of the current input file.

       +o The and(), asort(), asorti(), bindtextdomain(), compl(), dcgettext(), dcngettext(), gen-
         sub(),  lshift(),  mktime(), or(), rshift(), strftime(), strtonum(), systime() and xor()
         functions.

       +o Localizable strings.

       +o Adding new built-in functions dynamically with the extension() function.

       The AWK book does not define the return value of the close() function.  Gawk's close() re-
       turns the value from fclose(3), or pclose(3), when closing an output file or pipe, respec-
       tively.  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.

       When gawk is invoked with the --traditional option, if the fs argument to the -F option is
       "t", then FS is set to the tab character.  Note that typing gawk -F\t ...   simply  causes
       the  shell  to  quote  the "t,", and does not pass "\t" to the -F option.  Since this is a
       rather ugly special case, it is not the default behavior.  This behavior also does not oc-
       cur  if --posix has been specified.  To really get a tab character as the field separator,
       it is best to use single quotes: gawk -F'\t' ....

       If gawk is configured with the --enable-switch option to the configure  command,  then  it
       accepts an additional control-flow statement:
              switch (expression) {
              case value|regex : statement
              ...
              [ default: statement ]
              }

ENVIRONMENT VARIABLES
       The  AWKPATH  environment  variable can be used to provide a list of directories that gawk
       searches when looking for files named via the -f and --file options.

       If POSIXLY_CORRECT exists in the environment, then gawk behaves exactly as if --posix  had
       been  specified  on the command line.  If --lint has been specified, gawk issues a warning
       message to this effect.

SEE ALSO
       egrep(1), getpid(2), getppid(2), getpgrp(2), getuid(2), geteuid(2), getgid(2), getegid(2),
       getgroups(2)

       The  AWK Programming Language, Alfred V. Aho, Brian W. Kernighan, Peter J. Weinberger, Ad-
       dison-Wesley, 1988.  ISBN 0-201-07981-X.

       GAWK: Effective AWK Programming, Edition 3.0, published by the Free  Software  Foundation,
       2001.

BUGS
       The  -F option is not necessary given the command line variable assignment feature; it re-
       mains only for backwards compatibility.

       Syntactically invalid single character programs tend to overflow the parse stack, generat-
       ing  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.

AUTHORS
       The original version of UNIX awk was designed and implemented by Alfred Aho,  Peter  Wein-
       berger,  and  Brian Kernighan of Bell Laboratories.  Brian Kernighan continues to maintain
       and enhance it.

       Paul Rubin and Jay Fenlason, of the Free Software Foundation, wrote gawk, to be compatible
       with the original version of awk distributed in Seventh Edition UNIX.  John Woods contrib-
       uted a number of bug fixes.  David Trueman, with contributions from Arnold  Robbins,  made
       gawk  compatible  with  the  new version of UNIX awk.  Arnold Robbins is the current main-
       tainer.

       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, Stephen Davies pro-
       vided the Tandem port, and Martin Brown provided the BeOS port.

VERSION INFORMATION
       This man page documents gawk, version 3.1.4.

BUG REPORTS
       If you find a bug in gawk, please send electronic mail to  bug-gawk@gnu.org.   Please  in-
       clude  your  operating system and its revision, the version of gawk (from 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.

       Before sending a bug report, please do two things.  First, verify that you have the latest
       version of gawk.  Many bugs (usually subtle ones) are fixed at each release, and if  yours
       is  out  of  date, the problem may already have been solved.  Second, please read this man
       page and the reference manual carefully to be sure that what you think is a bug really is,
       instead of just a quirk in the language.

       Whatever you do, do NOT post a bug report in comp.lang.awk.  While the gawk developers oc-
       casionally read this newsgroup, posting bug reports there is an unreliable way  to  report
       bugs.  Instead, please use the electronic mail addresses given above.

       If  you're  using a GNU/Linux system or BSD-based system, you may wish to submit a bug re-
       port to the vendor of your distribution.  That's fine, but please send a copy to the offi-
       cial  email  address as well, since there's no guarantee that the bug will be forwarded to
       the gawk maintainer.

ACKNOWLEDGEMENTS
       Brian Kernighan of Bell Laboratories provided valuable assistance during testing  and  de-
       bugging.  We thank him.

COPYING PERMISSIONS
       Copyright  (C)  1989,  1991,  1992,  1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002,
       2003, 2004 Free Software Foundation, Inc.

       Permission is granted to make and distribute verbatim copies of this manual page  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 page 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 page 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.

Free Software Foundation                   July 28 2004                                   GAWK(1)