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 1003.1 Standard.   This  version  in  turn  is
       based  on  the  description  in The AWK Programming Language, by Aho, Kernighan, and Wein-
       berger, with the additional features found in the System V Release 4 version of UNIX  awk.
       Gawk  also provides more recent Bell Laboratories awk extensions, and a number of GNU-spe-
       cific 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.

       Additionally, each long option has a corresponding short  option,  so  that  the  option's
       functionality may be used from within #!  executable scripts.

OPTIONS
       Gawk  accepts  the  following options.  Standard options are listed first, followed by op-
       tions for gawk extensions, listed alphabetically by short option.

       -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.

       -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.

       -b
       --characters-as-bytes
              Treat all input data as single-byte characters. In other words, don't pay  any  at-
              tention  to  the locale information when attempting to process strings as multibyte
              characters.  The --posix option overrides this one.

       -c
       --compat
       --traditional
              Run in compatibility mode.  In compatibility mode, gawk behaves identically to UNIX
              awk;  none  of the GNU-specific extensions are recognized.  See GNU EXTENSIONS, be-
              low, for more information.

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

       -d [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.)

       -e 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.

       -E file
       --exec file
              Similar  to  -f, however, this is option is the last one processed.  This should be
              used with #!  scripts, particularly for CGI applications, to avoid passing  in  op-
              tions or source code (!) on the command line from a URL.  This option disables com-
              mand-line variable assignments.

       -g
       --gen-pot
              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.

       -h
       --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.)

       -l [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.)

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

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

       -N
       --use-lc-numeric
              This  forces  gawk  to  use the locale's decimal point character when parsing input
              data.  Although the POSIX standard requires this behavior, and gawk  does  so  when
              --posix  is  in effect, the default is to follow traditional behavior and use a pe-
              riod as the decimal point, even in locales where the  period  is  not  the  decimal
              point character.  This option overrides the default behavior, without the full dra-
              conian strictness of the --posix option.

       -O
       --optimize
              Enable optimizations upon the internal representation of the  program.   Currently,
              this  includes just simple constant-folding. The gawk maintainer hopes to add addi-
              tional optimizations over time.

       -p [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.

       -P
       --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.

       -r
       --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.

       -S
       --sandbox
              Runs  gawk  in  sandbox mode, disabling the system function, input redirection with
              getline, output redirection with printand printf, and dynamic  extensions  loading.
              Command  execution (through pipelines) is also disabled.  This effectively blocks a
              script from accessing local resources (except for the files specified on  the  com-
              mand line).

       -V
       --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 provides consistency  with  the  argument
              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).

   Command Line Directories
       According  to POSIX, files named on the awk command line must be text files.  The behavior
       is ``undefined'' if they are not.  Most versions of awk treat a directory on  the  command
       line as a fatal error.

       Starting with version 3.x of gawk, a directory on the command line produces a warning, but
       is otherwise skipped.  If either of the --posix or --traditional options  is  given,  then
       gawk reverts to treating directories on the command line as a fatal error.

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  are  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 section POSIX COMPATIBILITY, below).  NOTE: The value of IGNORE-
       CASE (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 or FPAT overrides the use of FIELD-
       WIDTHS.

       Similarly, if the FPAT variable is set to a string representing a regular expression, each
       field  is  made up of text that matches that regular expression. In this case, the regular
       expression describes the fields themselves, instead of the text that separates the fields.
       Assigning a new value to FS or FIELDWIDTHS overrides the use of FPAT.

       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.

       FPAT        A regular expression describing the contents of the fields in a record.   When
                   set, gawk parses the input into fields, where the fields match the regular ex-
                   pression, instead of using the value of the FS variable as the  field  separa-
                   tor.  See Fields, above.

       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(),
                   patsplit(),  split(),  and sub() built-in functions all ignore case when doing
                   regular expression 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
                   toupper().

       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,  "FPAT"  if
                                       field  splitting  with FPAT is in effect, or "FIELDWIDTHS"
                                       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 to test if an array has an index consisting of a  par-
       ticular 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".

       When  operating  in POSIX mode (such as with the --posix command line option), beware that
       locale settings may interfere with the way decimal numbers are treated: the decimal  sepa-
       rator  of  the  numbers you are feeding to gawk must conform to what your locale would ex-
       pect, be it a comma (,) or a period (.).

       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 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()  or  pat-
       split() that are numeric strings.  The basic idea is that user input, and only user input,
       that looks numeric, 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
              BEGINFILE
              ENDFILE
              /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.

       BEGINFILE and ENDFILE are additional special patterns whose  bodies  are  executed  before
       reading the first record of each command line input file and after reading the last record
       of each file.  Inside the BEGINFILE rule, the value of ERRNO will be the empty  string  if
       the file could be opened successfully.  Otherwise, there is some problem with the file and
       the code should use nextfile to skip it. If that is not done, gawk will produce its  usual
       fatal error for files that cannot be opened.

       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.

       \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.

       \s         matches any whitespace character.

       \S         matches any nonwhitespace character.

       \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 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  char-
       acter  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 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, no matter what it is.

       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,  \<, \>, \s, \S, \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.

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

       --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.

       gawk accepts an additional control-flow statement not allowed in other awk versions:
              switch (expression) {
              case value|regex : statement
              ...
              [ default: statement ]
              }

   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.

       | |&        Piped I/O for getline, print, and printf.

       < > <= >= != ==
                   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.  (command can also be
                             a socket.  See the subsection Special File Names, below.)

       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 or socket.  (See also the subsection Special File Names,
              below.)

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

       NOTE: Failure in opening a two-way socket will result in a non-fatal error being  returned
       to  the calling function. If using a pipe, co-process, or socket to getline, or from print
       or printf within a loop, you must use close() to create new instances of  the  command  or
       socket.  AWK does not automatically close pipes, sockets, 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, %F  A floating point number of the form [-]ddd.dddddd.  If the system library supports
               it, %F is available as well. This is like %f, but uses capital letters for special
               "not a number" and "infinity" values. If %F is not available, gawk uses %f.

       %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.

       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,
              %f  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 only to the 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, %f 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 %s, it specifies the maximum number of
              characters 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
       /inet4/tcp/lport/rhost/rport
       /inet6/tcp/lport/rhost/rport
              Files for a TCP/IP connection on local port lport to remote host  rhost  on  remote
              port  rport.   Use a port of 0 to have the system pick a port.  Use /inet4 to force
              an IPv4 connection, and /inet6 to force an IPv6 connection.  Plain /inet  uses  the
              system default (most likely IPv4).

       /inet/udp/lport/rhost/rport
       /inet4/udp/lport/rhost/rport
       /inet6/udp/lport/rhost/rport
              Similar, but use UDP/IP instead of TCP/IP.

       /inet/raw/lport/rhost/rport
       /inet4/raw/lport/rhost/rport
       /inet6/raw/lport/rhost/rport
              Reserved for future use.

   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 indices 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 indices 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.  Starting with version 3.1.5, as a non-standard ex-
                               tension, with an array argument, length() returns  the  number  of
                               elements in the array.

       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.

       patsplit(s, a [, r [, seps] ])
                               Splits the string s into the array a and the separators array seps
                               on  the  regular  expression  r, and returns the number of fields.
                               Element values are the portions of s that matched r.  The value of
                               seps[i]  is  the separator that appeared in front of a[i+1].  If r
                               is omitted, FPAT is used instead.   The  arrays  a  and  seps  are
                               cleared  first.   seps[i] is the field separator text between a[i]
                               and a[i+1].  Splitting behaves identically to field splitting with
                               FPAT, described above.

       split(s, a [, r [, seps] ])
                               Splits the string s into the array a and the separators array seps
                               on the regular expression r, and returns the number of fields.  If
                               r  is  omitted,  FS  is  used  instead.  The arrays a and seps are
                               cleared first.  seps[i] is the field separator matched  by  r  be-
                               tween  a[i]  and  a[i+1].   If  r  is a single space, then leading
                               whitespace in s goes into the  extra  array  element  seps[0]  and
                               trailing  whitespace  goes  into  the extra array element seps[n],
                               where n is the return value of split(s, a,  r,  seps).   Splitting
                               behaves identically 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.

       As of version 3.1.5, gawk is multibyte aware.  This means that index(), length(), substr()
       and match() all work in terms of characters, not bytes.

   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[, utc-flag]]])
                 Formats  timestamp  according  to  the  specification in format.  If utc-flag is
                 present and is non-zero or non-null, the result is in UTC, otherwise the  result
                 is  in local time.  The timestamp should be of the same form as returned by sys-
                 time().  If timestamp is missing, the current time of day is used.  If format is
                 missing,  a default format equivalent 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 available.

       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 uintmax_t integers, do-
       ing 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 avoids 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.

       As a gawk extension, functions may be called indirectly. To do this, assign  the  name  of
       the  function  to  be  called, as a string, to a variable.  Then use the variable as if it
       were the name of a function, prefixed with an ``at'' sign, like so:
              function  myfunc()
              {
                   print "myfunc called"
                   ...
              }

              {    ...
                   the_func = "myfunc"
                   @the_func()    # call through the_func to myfunc
                   ...
              }

       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 eventually.  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 pgawk to dump the profile and func-
       tion 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-pot -f myprog.awk > myprog.po to generate a .po file for your program.

       5.  Provide appropriate translations, and build and install the corresponding .mo files.

       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 or
       --posix options.

       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 FPAT variable and field splitting based on field values.

       +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 ability to pass an array to length().

       +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(), patsplit(), 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' ....

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.

       For  socket  communication,  two  special environment variables can be used to control the
       number of retries (GAWK_SOCK_RETRIES), and the interval between retries (GAWK_MSEC_SLEEP).
       The  interval  is  in milliseconds. On systems that do not support usleep(3), the value is
       rounded up to an integral number of seconds.

       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.

EXIT STATUS
       If the exit statement is used with a value, then gawk exits with the numeric  value  given
       to it.

       Otherwise,  if there were no problems during execution, gawk exits with the value of the C
       constant EXIT_SUCCESS.  This is usually zero.

       If an error occurs, gawk exits with the value of the C  constant  EXIT_FAILURE.   This  is
       usually one.

       If  gawk exits because of a fatal error, the exit status is 2.  On non-POSIX systems, this
       value may be mapped to EXIT_FAILURE.

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.     The    current    version    of   this   document   is   available   online   at
       http://www.gnu.org/software/gawk/manual.

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.  Andreas Buening now maintains the OS/2 port.  Fred Fish  sup-
       plied support for the Amiga, and Martin Brown provided the BeOS port.  Stephen Davies pro-
       vided the original Tandem port, and Matthew Woehlke provided changes for  Tandem's  POSIX-
       compliant systems.

Ralf Wildenhues now maintains that port.
       See the README file in the gawk distribution for current information about maintainers and
       which ports are currently supported.  VERSION INFORMATION This man  page  documents  gawk,
       version 4.0.

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 the following 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 see
       if  setting the environment variable LC_ALL to LC_ALL=C causes things to behave as you ex-
       pect. If so, it's a locale issue, and may or may not really be  a  bug.   Finally,  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, 2005, 2007, 2009, 2010 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                   Apr 20 2010                                    GAWK(1)