gawk(1) — Linux manual page


GAWK(1)                     Utility Commands                     GAWK(1)

NAME         top

       gawk - pattern scanning and processing language

SYNOPSIS         top

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

DESCRIPTION         top

       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 Weinberger.  Gawk provides the additional features found in
       the current version of Brian Kernighan's awk and numerous GNU-
       specific extensions.

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

       When gawk is invoked with the --profile option, it starts
       gathering profiling statistics from the execution of the program.
       Gawk runs more slowly in this mode, and automatically produces an
       execution profile in the file awkprof.out when done.  See the
       --profile option, below.

       Gawk also has an integrated debugger. An interactive debugging
       session can be started by supplying the --debug option to the
       command line. In this mode of execution, gawk loads the AWK
       source code and then prompts for debugging commands.  Gawk can
       only debug AWK program source provided with the -f and --include
       options.  The debugger is documented in GAWK: Effective AWK

OPTION FORMAT         top

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

       Gawk-specific options are typically used in long-option form.
       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, every long option has a corresponding short option,
       so that the option's functionality may be used from within #!
       executable scripts.

OPTIONS         top

       Gawk accepts the following options.  Standard options are listed
       first, followed by options 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.  Files read with -f
              are treated as if they begin with an implicit @namespace
              "awk" statement.

       -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 rule of an AWK program.

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

              Run in compatibility mode.  In compatibility mode, gawk
              behaves identically to Brian Kernighan's awk; none of the
              GNU-specific extensions are recognized.  See GNU
              EXTENSIONS, below, for more information.

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

              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 program with a
              lot of functions, and you want to be sure that your
              functions don't inadvertently use global variables that
              you meant to be local.  (This is a particularly easy
              mistake to make with simple variable names like i, j, and
              so on.)

              Enable debugging of AWK programs.  By default, the
              debugger reads commands interactively from the keyboard
              (standard input).  The optional file argument specifies a
              file with a list of commands for the debugger to execute

       -e program-text
       --source program-text
              Use program-text as AWK program source code.  This option
              allows the easy intermixing of library functions (used via
              the -f and --include options) with source code entered on
              the command line.  It is intended primarily for medium to
              large AWK programs used in shell scripts.  Each argument
              supplied via -e is treated as if it begins with an
              implicit @namespace "awk" statement.

       -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
              options or source code (!) on the command line from a URL.
              This option disables command-line variable assignments.

              Scan and parse the AWK program, and generate a GNU .pot
              (Portable Object Template) format file on standard output
              with entries for all localizable strings in the program.
              The program itself is not executed.  See the GNU gettext
              distribution for more information on .pot files.

       --help 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.)

       -i include-file
       --include include-file
              Load an awk source library.  This searches for the library
              using the AWKPATH environment variable.  If the initial
              search fails, another attempt will be made after appending
              the .awk suffix.  The file will be loaded only once (i.e.,
              duplicates are eliminated), and the code does not
              constitute the main program source.  Files read with
              --include are treated as if they begin with an implicit
              @namespace "awk" statement.

              Print the internal byte code names as they are executed
              when running the program. The trace is printed to standard
              error. Each ``op code'' is preceded by a + sign in the

       -l lib
       --load lib
              Load a gawk extension from the shared library lib.  This
              searches for the library using the AWKLIBPATH environment
              variable.  If the initial search fails, another attempt
              will be made after appending the default shared library
              suffix for the platform.  The library initialization
              routine is expected to be named dl_load().

       -L [value]
              Provide warnings about constructs that are dubious or non-
              portable to other AWK implementations.  With an optional
              argument of fatal, lint warnings become fatal errors.
              This may be drastic, but its use will certainly encourage
              the development of cleaner AWK programs.  With an optional
              argument of invalid, only warnings about things that are
              actually invalid are issued.  (This is not fully
              implemented yet.)  With an optional argument of no-ext,
              warnings about gawk extensions are disabled.

              Force arbitrary precision arithmetic on numbers. This
              option has no effect if gawk is not compiled to use the
              GNU MPFR and GMP libraries.  (In such a case, gawk issues
              a warning.)

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

              Force 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 period 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
              draconian strictness of the --posix option.

              Output a pretty printed version of the program to file.
              If no file is provided, gawk uses a file named awkprof.out
              in the current directory.  This option implies

              Enable gawk's default optimizations upon the internal
              representation of the program.  Currently, this just
              includes simple constant folding.  This option is on by

              Start a profiling session, and send the profiling data to
              prof-file.  The default is awkprof.out.  The profile
              contains execution counts of each statement in the program
              in the left margin and function call counts for each user-
              defined function.  This option implies --no-optimize.

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

              •      \x escape sequences are not recognized.

              •      You cannot continue lines after ?  and :.

              •      The synonym func for the keyword function is not

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

              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.  They are
              enabled by default, but this option remains for use
              together with --traditional.

              Disable gawk's default optimizations upon the internal
              representation of the program.

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

              Provide warnings about constructs that are not portable to
              the original version of UNIX awk.

              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 options 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 ignored.  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.

       For POSIX compatibility, the -W option may be used, followed by
       the name of a long option.


       An AWK program consists of a sequence of optional directives,
       pattern-action statements, and optional function definitions.

              @include "filename"
              @load "filename"
              @namespace "name"
              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 together.  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.

       In addition, lines beginning with @include may be used to include
       other source files into your program, making library use even
       easier.  This is equivalent to using the --include option.

       Lines beginning with @load may be used to load extension
       functions into your program.  This is equivalent to using the
       --load option.

       The environment variable AWKPATH specifies a search path to use
       when finding source files named with the -f and --include
       options.  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.

       The environment variable AWKLIBPATH specifies a search path to
       use when finding source files named with the --load option.  If
       this variable does not exist, the default path is
       "/usr/local/lib/gawk".  (The actual directory may vary, depending
       upon how gawk was built and installed.)

       Gawk executes AWK programs in the following order.  First, all
       variable assignments specified via the -v option are performed.
       Next, gawk compiles the program into an internal form.  Then,
       gawk executes the code in the BEGIN rule(s) (if any), and then
       proceeds to read each file named in the ARGV array (up to
       ARGV[ARGC-1]).  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 assignment.  The variable var will be
       assigned the value val.  (This happens after any BEGIN rule(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 input file, if a BEGINFILE rule exists, gawk executes
       the associated code before processing the contents of the file.
       Similarly, gawk executes the code associated with ENDFILE after
       processing the file.

       For each record in the input, gawk tests to see if it matches any
       pattern in the AWK program.  For each pattern that the record
       matches, gawk executes the associated action.  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 rule(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

       Starting with version 4.0 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.


       AWK variables are dynamic; they come into existence when they are
       first used.  Their values are either floating-point numbers or
       strings, or both, depending upon how they are used.
       Additionally, gawk allows variables to have regular-expression
       type.  AWK also has one dimensional arrays; arrays with multiple
       dimensions may be simulated.  Gawk provides true arrays of
       arrays; see Arrays, below.  Several pre-defined variables are set
       as a program runs; these are described as needed and summarized

       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 input 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 empty 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.

       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 separate 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.  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 expected to have fixed width, and gawk
       splits up the record using the specified widths.  Each field
       width may optionally be preceded by a colon-separated value
       specifying the number of characters to skip before the field
       starts.  The value of FS is ignored.  Assigning a new value to FS
       or FPAT overrides the use of FIELDWIDTHS.

       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, including leading and
       trailing whitespace.  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

       References to non-existent fields (i.e., fields after $NF)
       produce the null string.  However, assigning to a non-existent
       field (e.g., $(NF+2) = 5) increases the value of NF, creates any
       intervening fields with the null string as their values, 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.

              On non-POSIX systems, specifies use of “binary” mode for
              all file I/O.  Numeric values of 1, 2, or 3, specify that
              input files, output files, or all files, respectively,
              should use binary I/O.  String values of "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

              The conversion format for numbers, "%.6g", by default.

              An array containing the values of the current environment.
              The array is indexed by the environment variables, each
              element being the value of that variable (e.g.,
              ENVIRON["HOME"] might be "/home/arnold").

              In POSIX mode, changing this array does not affect the
              environment seen by programs which gawk spawns via
              redirection or the system() function.  Otherwise, gawk
              updates its real environment so that programs it spawns
              see the changes.

       ERRNO  If a system error occurs either doing a redirection for
              getline, during a read for getline, or during a close(),
              then ERRNO is set to a string describing the error.  The
              value is subject to translation in non-English locales.
              If the string in ERRNO corresponds to a system error in
              the errno(3) variable, then the numeric value can be found
              in PROCINFO["errno"].  For non-system errors,
              PROCINFO["errno"] will be zero.

              A whitespace-separated list of field widths.  When set,
              gawk parses the input into fields of fixed width, instead
              of using the value of the FS variable as the field
              separator.  Each field width may optionally be preceded by
              a colon-separated value specifying the number of
              characters to skip before the field starts.  See Fields,

              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 rule
              (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 expression, instead of
              using the value of FS as the field separator.  See Fields,

       FS     The input field separator, a space by default.  See
              Fields, above.

              An array whose indices and corresponding values are the
              names of all the user-defined or extension functions in
              the program.  NOTE: You may not use the delete statement
              with the FUNCTAB array.

              Controls the case-sensitivity of all regular expression
              and string operations.  If IGNORECASE has a non-zero
              value, then string comparisons and pattern matching in
              rules, field splitting with FS and FPAT, record separating
              with RS, regular expression 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 normally

       LINT   Provides dynamic control of the --lint option from within
              an AWK program.  When true, gawk prints lint warnings.
              When false, it does not.  The values allowed for the
              --lint option may also be assigned to LINT, with the same
              effects.  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.

       PREC   The working precision of arbitrary precision floating-
              point numbers, 53 by default.

              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 following elements are guaranteed to be

                     The command line arguments as received by gawk at
                     the C-language level.  The subscripts start from

                     The value of the getegid(2) system call.

                     The value of errno(3) when ERRNO is set to the
                     associated error message.

                     The value of the geteuid(2) system call.

                     "FS" if field splitting with FS is in effect,
                     "FPAT" if field splitting with FPAT is in effect,
                     "FIELDWIDTHS" if field splitting with FIELDWIDTHS
                     is in effect, or "API" if API input parser field
                     splitting is in effect.

                     The value of the getgid(2) system call.

                     A subarray, indexed by the names of all identifiers
                     used in the text of the AWK program.  The values
                     indicate what gawk knows about the identifiers
                     after it has finished parsing the program; they are
                     not updated while the program runs.  For each
                     identifier, the value of the element is one of the

                            The identifier is an array.

                            The identifier is a built-in function.

                            The identifier is an extension function
                            loaded via @load or --load.

                            The identifier is a scalar.

                            The identifier is untyped (could be used as
                            a scalar or array, gawk doesn't know yet).

                     "user" The identifier is a user-defined function.

                     The value of the getpgrp(2) system call.

                     The value of the getpid(2) system call.

                     A string indicating the platform for which gawk was
                     compiled.  It is one of:

                     "djgpp", "mingw"
                            Microsoft Windows, using either DJGPP, or
                            MinGW, respectively.

                     "os2"  OS/2.

                            GNU/Linux, Cygwin, Mac OS X, and legacy Unix

                     "vms"  OpenVMS or Vax/VMS.

                     The value of the getppid(2) system call.

                     The default time format string for strftime().
                     Changing its value affects how strftime() formats
                     time values when called with no arguments.

                     The value of the getuid(2) system call.

                     The version of gawk.

              The following elements are present if loading dynamic
              extensions is available:

                     The major version of the extension API.

                     The minor version of the extension API.

              The following elements are available if MPFR support is
              compiled into gawk:

                     The version of the GNU GMP library used for
                     arbitrary precision number support in gawk.

                     The version of the GNU MPFR library used for
                     arbitrary precision number support in gawk.

                     The maximum precision supported by the GNU MPFR
                     library for arbitrary precision floating-point

                     The minimum precision allowed by the GNU MPFR
                     library for arbitrary precision floating-point

              The following elements may set by a program to change
              gawk's behavior:

                     If this exists, then I/O errors for all
                     redirections become nonfatal.

              PROCINFO["name", "NONFATAL"]
                     Make I/O errors for name be nonfatal.

              PROCINFO["command", "pty"]
                     Use a pseudo-tty for two-way communication with
                     command instead of setting up two one-way pipes.

              PROCINFO["input", "READ_TIMEOUT"]
                     The timeout in milliseconds for reading data from
                     input, where input is a redirection string or a
                     filename. A value of zero or less than zero means
                     no timeout.

              PROCINFO["input", "RETRY"]
                     If an I/O error that may be retried occurs when
                     reading data from input, and this array entry
                     exists, then getline returns -2 instead of
                     following the default behavior of returning -1 and
                     configuring input to return no further data.  An
                     I/O error that may be retried is one where errno(3)
                     has the value EAGAIN, EWOULDBLOCK, EINTR, or
                     ETIMEDOUT.  This may be useful in conjunction with
                     PROCINFO["input", "READ_TIMEOUT"] or in situations
                     where a file descriptor has been configured to
                     behave in a non-blocking fashion.

                     If this element exists in PROCINFO, then its value
                     controls the order in which array elements are
                     traversed in for loops.  Supported values are
                     "@ind_str_asc", "@ind_num_asc", "@val_type_asc",
                     "@val_str_asc", "@val_num_asc", "@ind_str_desc",
                     "@ind_num_desc", "@val_type_desc", "@val_str_desc",
                     "@val_num_desc", and "@unsorted".  The value can
                     also be the name (as a string) of any comparison
                     function defined as follows:

                          function cmp_func(i1, v1, i2, v2)

                     where i1 and i2 are the indices, and v1 and v2 are
                     the corresponding values of the two elements being
                     compared.  It should return a number less than,
                     equal to, or greater than 0, depending on how the
                     elements of the array are to be ordered.

              The rounding mode to use for arbitrary precision
              arithmetic on numbers, by default "N" (IEEE-754
              roundTiesToEven mode).  The accepted values are:

              "A" or "a"
                     for rounding away from zero.  These are only
                     available if your version of the GNU MPFR library
                     supports rounding away from zero.

              "D" or "d"
                     for roundTowardNegative.

              "N" or "n"
                     for roundTiesToEven.

              "U" or "u"
                     for roundTowardPositive.

              "Z" or "z"
                     for roundTowardZero.

       RS     The input record separator, by default a newline.

       RT     The record terminator.  Gawk sets RT to the input text
              that matched the character or regular expression specified
              by RS.

       RSTART The index of the first character matched by match(); 0 if
              no match.  (This implies that character indices start at

              The length of the string matched by match(); -1 if no

       SUBSEP The string used to separate multiple subscripts in array
              elements, by default "\034".

       SYMTAB An array whose indices are the names of all currently
              defined global variables and arrays in the program.  The
              array may be used for indirect access to read or write the
              value of a variable:

                   foo = 5
                   SYMTAB["foo"] = 4
                   print foo    # prints 4

              The typeof() function may be used to test if an element in
              SYMTAB is an array.  You may not use the delete statement
              with the SYMTAB array, nor assign to elements with an
              index that is not a variable name.

              The text domain of the AWK program; used to find the
              localized translations for the program's strings.

       Arrays are subscripted with an expression between square brackets
       ([ and ]).  If the expression is an expression list (expr, expr
       ...)  then the array subscript is a string consisting 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 arrays.  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 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 array.  However, the (i, j) in array
       construct only works in tests, not in for loops.

       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.

       gawk supports true multidimensional arrays. It does not require
       that such arrays be ``rectangular'' as in C or C++.  For example:

              a[1] = 5
              a[2][1] = 6
              a[2][2] = 7

       NOTE: You may need to tell gawk that an array element is really a
       subarray in order to use it where gawk expects an array (such as
       in the second argument to split()).  You can do this by creating
       an element in the subarray and then deleting it with the delete

       Gawk provides a simple namespace facility to help work around the
       fact that all variables in AWK are global.

       A qualified name consists of a two simple identifiers joined by a
       double colon (::).  The left-hand identifier represents the
       namespace and the right-hand identifier is the variable within
       it.  All simple (non-qualified) names are considered to be in the
       ``current'' namespace; the default namespace is awk.  However,
       simple identifiers consisting solely of uppercase letters are
       forced into the awk namespace, even if the current namespace is

       You change the current namespace with an @namespace "name"

       The standard predefined builtin function names may not be used as
       namespace names.  The names of additional functions provided by
       gawk may be used as namespace names or as simple identifiers in
       other namespaces.  For more details, see GAWK: Effective AWK

   Variable Typing And Conversion
       Variables and fields may be (floating point) numbers, or strings,
       or both.  They may also be regular expressions. 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 zero to it; to
       force it to be treated as a string, concatenate it with the null

       Uninitialized variables have the numeric value zero and the
       string value "" (the null, or empty, string).

       When a string must be converted to a number, the conversion is
       accomplished using strtod(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".

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

       Gawk performs comparisons as follows: If two variables are
       numeric, they are compared numerically.  If one value is numeric
       and the other has a string value that is a “numeric string,” then
       comparisons are also done numerically.  Otherwise, the numeric
       value is converted to a string and a string comparison is
       performed.  Two strings are compared, of course, as strings.

       Note that string constants, such as "57", are not numeric
       strings, they are string constants.  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 patsplit() that are numeric strings.  The basic idea is that
       user input, and only user input, that looks numeric, should be
       treated that way.

   Octal and Hexadecimal Constants
       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

   String Constants
       String constants in AWK are sequences of characters enclosed
       between double quotes (like "value").  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.  Up to two following hexadecimal
              digits are considered part of the escape sequence.  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.

       In compatibility mode, the characters represented by octal and
       hexadecimal escape sequences are treated literally when used in
       regular expression constants.  Thus, /a\52b/ is equivalent to

   Regexp Constants
       A regular expression constant is a sequence of characters
       enclosed between forward slashes (like /value/).  Regular
       expression matching is described more fully below; see Regular

       The escape sequences described earlier may also be used inside
       constant regular expressions (e.g., /[ \t\f\n\r\v]/ matches
       whitespace characters).

       Gawk provides strongly typed regular expression constants. These
       are written with a leading @ symbol (like so: @/value/).  Such
       constants may be assigned to scalars (variables, array elements)
       and passed to user-defined functions. Variables that have been so
       assigned have regular expression type.


       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
       executes 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.  Empty lines may be used to separate statements.
       Normally, a statement ends with a newline, however, this is not
       the case for lines ending in a comma, {, ?, :, &&, or ||.  Lines
       ending in do or else also have their statements automatically
       continued on the following line.  In other cases, a line can be
       continued by ending it with a “\”, in which case the newline is
       ignored.  However, a “\” after a # is not special.

       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.

       AWK patterns may be one of the following:

              /regular expression/
              relational expression
              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 written in a single
       BEGIN rule.  They are executed before any of the input is read.
       Similarly, all the END rules 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
       actions 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 is the empty
       string if the file was 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 produces 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 actions.  These generally test whether
       certain fields match certain regular expressions.

       The &&, ||, and !  operators are logical AND, logical OR, and
       logical NOT, respectively, as in C.  They do short-circuit
       evaluation, also as in C, and are used for combining more
       primitive pattern expressions.  As in most languages, parentheses
       may be used to change the order of evaluation.

       The ?: operator is like the same operator in C.  If the first
       pattern 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 expression.

   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.

              A character list: matches any of the characters abc....
              You may include a range of characters by separating them
              with a dash.  To include a literal dash in the list, put
              it first or last.

              A negated character list: matches any character except

       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,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

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

       \`     Matches the empty string at the beginning of a buffer

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

       The escape sequences that are valid in string constants (see
       String Constants) are also valid in regular 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 character set to character set.  For example, the notion of
       what is an alphabetic character differs in the USA and in France.

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

              Alphanumeric characters.

              Alphabetic characters.

              Space or tab characters.

              Control characters.

              Numeric characters.

              Characters that are both printable and visible.  (A space
              is printable, but not visible, while an a is both.)

              Lowercase alphabetic characters.

              Printable characters (characters that are not control

              Punctuation characters (characters that are not letter,
              digits, control characters, or space characters).

              Space characters (such as space, tab, and formfeed, to
              name a few).

              Uppercase alphabetic characters.

              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 represented with
       more than one character, as well as several characters that are
       equivalent for collating, or sorting, purposes.  (E.g., in
       French, a plain “e” and a grave-accented “e`” are equivalent.)

       Collating Symbols
              A collating symbol is a multi-character collating element
              enclosed in [.  and .].  For example, if ch is a collating
              element, then [[.ch.]]  is a 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 expression 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 expressions.

       No options
              In the default case, gawk provides all the facilities of
              POSIX regular expressions and the GNU regular expression
              operators described above.

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

              Traditional UNIX awk regular expressions are matched.  The
              GNU operators are not special, and interval expressions
              are not available.  Characters described by octal and
              hexadecimal escape sequences are treated literally, even
              if they represent regular expression metacharacters.

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

       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.

       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 you want.

       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
              delete array[index]
              delete array
              exit [ expression ]
              { statements }
              switch (expression) {
              case value|regex : statement
              [ default: statement ]

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

       close(file [, how])
              Close file, pipe or coprocess.  The optional how should
              only be used when closing one end of a two-way pipe to a
              coprocess.  It must be a string value, either "to" or

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

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

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

       getline var <file
              Set var from the next record of file; set RT.

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

       command |& getline [var]
              Run command as a coprocess piping the output either into
              $0 or var, as above, and RT.  Coprocesses are a gawk
              extension.  (The command can also be a socket.  See the
              subsection Special File Names, below.)

       next   Stop processing the current input record.  Read the next
              input record and start processing over with the first
              pattern in the AWK program.  Upon reaching the end of the
              input data, execute any END rule(s).

              Stop processing the current input file.  The next input
              record read comes from the next input file.  Update
              FILENAME and ARGIND, reset FNR to 1, and start processing
              over with the first pattern in the AWK program.  Upon
              reaching the end of the input data, execute any ENDFILE
              and END rule(s).

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

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

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

       printf fmt, expr-list
              Format and print.  See The printf Statement, below.

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

              Execute the command cmd-line, and return the exit status.
              (This may not be available on non-POSIX systems.)  See
              GAWK: Effective AWK Programming for the full details on
              the exit status.

              Flush any buffers associated with the open output file or
              pipe file.  If file is missing or if it is the null
              string, then flush all open output files and pipes.

       Additional output redirections are allowed for print and printf.

       print ... >> file
              Append output to the file.

       print ... | command
              Write on a pipe.

       print ... |& command
              Send data to a coprocess or socket.  (See also the
              subsection Special File Names, below.)

       The getline command returns 1 on success, zero on end of file,
       and -1 on an error.  If the errno(3) value indicates that the I/O
       operation may be retried, and PROCINFO["input", "RETRY"] is set,
       then -2 is returned instead of -1, and further calls to getline
       may be attempted.  Upon an error, ERRNO is set to a string
       describing the problem.

       NOTE: Failure in opening a two-way socket results in a non-fatal
       error being returned to the calling function. If using a pipe,
       coprocess, 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
       coprocesses when they return EOF.

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

       %a, %A A floating point number of the form [-]0xh.hhhhp+-dd (C99
              hexadecimal floating point format).  For %A, uppercase
              letters are used instead of lowercase ones.

       %c     A single 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 instead 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 suppressed.  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 positional specifier and is intended
              primarily for use in translated versions of format
              strings, not in the original text of an AWK program.  It
              is a 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, indicating that output
              should be padded with zeroes 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.

       '      A single quote character instructs gawk to insert the
              locale's thousands-separator character into decimal
              numbers, and to also use the locale's decimal point
              character with floating point formats.  This requires
              correct locale support in the C library and in the
              definition of the current locale.

       width  The field should be padded to this width.  The field is
              normally padded with spaces.  With the 0 flag, 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, %i, %o, %u, %x, and %X formats, it specifies
              the minimum number of digits to print.  For the %s format,
              it specifies the maximum number of characters from the
              string that should be printed.

       The dynamic width and prec capabilities of the ISO 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:

       -      The standard input.

              The standard input.

              The standard output.

              The standard error output.

              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 |& coprocess
       operator for creating TCP/IP network connections:

              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).
              Usable only with the |& two-way I/O operator.

              Similar, but use UDP/IP instead of TCP/IP.

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

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

              Return the cosine of expr, which is in radians.

              The exponential function.

              Truncate to integer.

              The natural logarithm function.

       rand() Return a random number N, between zero and one, such that
              0 ≤ N < 1.

              Return the sine of expr, which is in radians.

              Return the square root of expr.

              Use expr as the new seed for the random number generator.
              If no expr is provided, use the time of day.  Return the
              previous seed for the random number generator.

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

       asort(s [, d [, how] ])
              Return the number of elements in the source array s.  Sort
              the contents of s using gawk's normal rules for comparing
              values, and replace the indices of the sorted values s
              with sequential integers starting with 1. If the optional
              destination array d is specified, first duplicate s into
              d, and then sort d, leaving the indices of the source
              array s unchanged. The optional string how controls the
              direction and the comparison mode.  Valid values for how
              are any of the strings valid for PROCINFO["sorted_in"].
              It can also be the name of a user-defined comparison
              function as described in PROCINFO["sorted_in"].  s and d
              are allowed to be the same array; this only makes sense
              when supplying the third argument as well.

       asorti(s [, d [, how] ])
              Return the number of elements in the source array s.  The
              behavior 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 array if you wish
              to preserve the original.  The purpose of the optional
              string how is the same as described previously for
              asort().  Here too, s and d are allowed to be the same
              array; this only makes sense when supplying the third
              argument as well.

       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, use $0 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 substitutions.  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: Effective AWK
              Programming for a fuller discussion of the rules for
              ampersands and backslashes in the replacement text of
              sub(), gsub(), and gensub().)

       index(s, t)
              Return the index of the string t in the string s, or zero
              if t is not present.  (This implies that character indices
              start at one.)  It is a fatal error to use a regexp
              constant for t.

              Return the length of the string s, or the length of $0 if
              s is not supplied.  As a non-standard extension, with an
              array argument, length() returns the number of elements in
              the array.

       match(s, r [, a])
              Return the position in s where the regular expression r
              occurs, or zero if r is not present, and set 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 zero'th element of
              a contains the portion of s matched by the entire regular
              expression r.  Subscripts a[n, "start"], and a[n,
              "length"] provide the starting index in the string and
              length respectively, of each matching substring.

       patsplit(s, a [, r [, seps] ])
              Split the string s into the array a and the separators
              array seps on the regular expression r, and return the
              number of fields.  Element values are the portions of s
              that matched r.  The value of seps[i] is the possibly null
              separator that appeared after a[i].  The value of seps[0]
              is the possibly null leading separator.  If r is omitted,
              FPAT is used instead.  The arrays a and seps are cleared
              first.  Splitting behaves identically to field splitting
              with FPAT, described above.

       split(s, a [, r [, seps] ])
              Split the string s into the array a and the separators
              array seps on the regular expression r, and return 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 between 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.  In particular, if r is a single-
              character string, that string acts as the separator, even
              if it happens to be a regular expression metacharacter.

       sprintf(fmt, expr-list)
              Print expr-list according to fmt, and return the resulting

              Examine str, and return its numeric value.  If str begins
              with a leading 0, treat it as an octal number.  If str
              begins with a leading 0x or 0X, treat it as a hexadecimal
              number.  Otherwise, assume it is a decimal number.

       sub(r, s [, t])
              Just like gsub(), but replace only the first matching
              substring.  Return either zero or one.

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

              Return a copy of the string str, with all the uppercase
              characters in str translated to their corresponding
              lowercase counterparts.  Non-alphabetic characters are
              left unchanged.

              Return a copy of the string str, with all the lowercase
              characters in str translated to their corresponding
              uppercase counterparts.  Non-alphabetic characters are
              left unchanged.

       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

       mktime(datespec [, utc-flag])
              Turn datespec into a time stamp of the same form as
              returned by systime(), and return the result.  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 including century,
              the month from 1 to 12, the day of the month from 1 to 31,
              the hour of the day from 0 to 23, the minute from 0 to 59,
              the second from 0 to 60, and an optional daylight saving
              flag.  The values of these numbers need not be within the
              ranges specified; for example, an hour of -1 means 1 hour
              before midnight.  The origin-zero Gregorian calendar is
              assumed, with year 0 preceding year 1 and year -1
              preceding year 0.  If utc-flag is present and is non-zero
              or non-null, the time is assumed to be in the UTC time
              zone; otherwise, the time is assumed to be in the local
              time zone.  If the DST 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]]])
              Format 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
              systime().  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.  The default
              format is available in PROCINFO["strftime"].  See the
              specification for the strftime() function in ISO C for the
              format conversions that are guaranteed to be available.

              Return the current time of day as the number of seconds
              since the Epoch (1970-01-01 00:00:00 UTC on POSIX

   Bit Manipulations Functions
       Gawk supplies the following bit manipulation functions.  They
       work by converting double-precision floating point values to
       uintmax_t integers, doing the operation, and then converting the
       result back to floating point.

       NOTE: Passing negative operands to any of these functions causes
       a fatal error.

       The functions are:

       and(v1, v2 [, ...])
              Return the bitwise AND of the values provided in the
              argument list.  There must be at least two.

              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 in the
              argument list.  There must be at least two.

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

       xor(v1, v2 [, ...])
              Return the bitwise XOR of the values provided in the
              argument list.  There must be at least two.

   Type Functions
       The following functions provide type related information about
       their arguments.

              Return true if x is an array, false otherwise.  This
              function is mainly for use with the elements of
              multidimensional arrays and with function parameters.

              Return a string indicating the type of x.  The string will
              be one of "array", "number", "regexp", "string", "strnum",
              "unassigned", or "undefined".

   Internationalization Functions
       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])
              Specify the directory where gawk looks for the .gmo files,
              in case they will not or cannot be placed in the
              ``standard'' locations (e.g., during testing).  It returns
              the directory where domain is ``bound.''
              The default domain is the value of TEXTDOMAIN.  If
              directory is the null string (""), then bindtextdomain()
              returns the current binding for the given domain.

       dcgettext(string [, domain [, category]])
              Return the translation of string in text domain domain for
              locale category category.  The default value for domain is
              the current value of TEXTDOMAIN.  The default value for
              category is "LC_MESSAGES".
              If you supply a value for category, it must be a string
              equal to one of the known locale categories described in
              GAWK: Effective AWK Programming.  You must also supply a
              text domain.  Use TEXTDOMAIN if you want to use the
              current domain.

       dcngettext(string1, string2, number [, domain [, category]])
              Return 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_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 supply a
              text domain.  Use TEXTDOMAIN if you want to use the
              current domain.

   Boolean Valued Functions
       You can create special Boolean-typed values; see the manual for
       how they work and why they exist.

              Based on the boolean value of expression return either a
              true value or a false value.  True values have numeric
              value one.  False values have numeric value zero.


       Functions in AWK are defined as follows:

              function name(parameter list) { statements }

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

       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
       whitespace.  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 @ sign, like so:
              function myfunc()
                   print "myfunc called"

              {    ...
                   the_func = "myfunc"
                   @the_func()    # call through the_func to myfunc
       As of version 4.1.2, this works with user-defined functions,
       built-in functions, and extension functions.

       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, although this is


       You can dynamically add new functions written in C or C++ to the
       running gawk interpreter with the @load statement.  The full
       details are beyond the scope of this manual page; see GAWK:
       Effective AWK Programming.

SIGNALS         top

       The gawk profiler 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 --profile
       option.  It then continues to run.  SIGHUP causes gawk to dump
       the profile and function call stack and then exit.


       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
       local 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 .gmo 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

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

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

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

       The internationalization features are described in full detail in
       GAWK: Effective AWK Programming.


       A primary goal for gawk is compatibility with the POSIX standard,
       as well as with the latest version of Brian Kernighan's awk.  To
       this end, gawk incorporates the following user visible features
       which are not described in the AWK book, but are part of the
       Brian Kernighan's version 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 rule is executed.  However, in earlier
       implementations, when such an assignment appeared before any file
       names, the assignment would happen before the BEGIN rule 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 developers and the
       GNU developers.)

       When processing arguments, gawk uses the special option “--” to
       signal the end of arguments.  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 return the seed it was using, to allow
       keeping track of random number sequences.  Therefore srand() in
       gawk also returns its current seed.

       Other 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 Laboratories
       version); the tolower() and toupper() built-in functions (from
       the Bell Laboratories version); and the ISO C conversion
       specifications in printf (done first in the Bell Laboratories


       There is one feature of historical AWK implementations that gawk
       supports: It is possible to call the length() built-in function
       not only with no argument, but even without parentheses!  Thus,

              a = length     # Holy Algol 60, Batman!

       is the same as either of

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

       Using this feature is poor practice, and gawk issues a warning
       about its use if --lint is specified on the command line.

GNU EXTENSIONS         top

       Gawk has a too-large 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

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

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

       •      There is no facility for doing file inclusion (gawk's
              @include mechanism).

       •      There is no facility for dynamically adding new functions
              written in C (gawk's @load mechanism).

       •      The \x escape sequence.

       •      The ability to continue lines after ?  and :.

       •      Octal and hexadecimal constants in AWK programs.

              TEXTDOMAIN variables are not special.

       •      The IGNORECASE variable and its side-effects are not

       •      The FIELDWIDTHS variable and fixed-width field splitting.

       •      The FPAT variable and field splitting based on field

       •      The FUNCTAB, SYMTAB, and PROCINFO arrays are not

       •      The use of RS as a regular expression.

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

       •      The |& operator for creating coprocesses.

       •      The BEGINFILE and ENDFILE special patterns are not

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

       •      An optional fourth argument to split() to receive the
              separator texts.

       •      The optional second argument to the close() function.

       •      The optional third argument to the match() function.

       •      The ability to use positional specifiers with printf and

       •      The ability to pass an array to length().

       •      The and(), asort(), asorti(), bindtextdomain(), compl(),
              dcgettext(), dcngettext(), gensub(), lshift(), mktime(),
              or(), patsplit(), rshift(), strftime(), strtonum(),
              systime() and xor() functions.

       •      Localizable strings.

       •      Non-fatal I/O.

       •      Retryable I/O.

       The AWK book does not define the return value of the close()
       function.  Gawk's close() returns the value from fclose(3), or
       pclose(3), when closing an output file or pipe, respectively.  It
       returns the process's exit status when closing an input pipe.
       The return value is -1 if the named file, pipe or coprocess 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 occur 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' ....


       The AWKPATH environment variable can be used to provide a list of
       directories that gawk searches when looking for files named via
       the -f, --file, -i and --include options, and the @include
       directive.  If the initial search fails, the path is searched
       again after appending .awk to the filename.

       The AWKLIBPATH environment variable can be used to provide a list
       of directories that gawk searches when looking for files named
       via the -l and --load options.

       The GAWK_READ_TIMEOUT environment variable can be used to specify
       a timeout in milliseconds for reading input from a terminal, pipe
       or two-way communication including sockets.

       For connection to a remote host via socket, GAWK_SOCK_RETRIES
       controls the number of retries, and GAWK_MSEC_SLEEP the interval
       between retries.  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

EXIT STATUS         top

       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

       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.


       This man page documents gawk, version 5.1.

AUTHORS         top

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

       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 contributed 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 maintainer.

       See GAWK: Effective AWK Programming for a full list of the
       contributors to gawk and its documentation.

       See the README file in the gawk distribution for up-to-date
       information about maintainers and which ports are currently

BUG REPORTS         top

       If you find a bug in gawk, please send electronic mail to  Please include your operating system and its
       revision, the version of gawk (from gawk --version), which 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 expect. 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 occasionally read this newsgroup,
       posting bug reports there is an unreliable way to report bugs.
       Similarly, do NOT use a web forum (such as Stack Overflow) for
       reporting bugs.  Instead, please use the electronic mail
       addresses given above.  Really.

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

BUGS         top

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

SEE ALSO         top

       egrep(1), sed(1), getpid(2), getppid(2), getpgrp(2), getuid(2),
       geteuid(2), getgid(2), getegid(2), getgroups(2), printf(3),
       strftime(3), usleep(3)

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

       GAWK: Effective AWK Programming, Edition 5.1, shipped with the
       gawk source.  The current version of this document is available
       online at .

       The GNU gettext documentation, available online at .

EXAMPLES         top

       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") }'


       Brian Kernighan provided valuable assistance during testing and
       debugging.  We thank him.


       Copyright © 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
       1999, 2001, 2002, 2003, 2004, 2005, 2007, 2009, 2010, 2011, 2012,
       2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021, 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.

COLOPHON         top

       This page is part of the gawk (GNU awk) project.  Information
       about the project can be found at 
       ⟨⟩.  If you have a bug report for
       this manual page, see
       ⟨⟩.  This page
       was obtained from the project's upstream Git repository
       ⟨git://⟩ on 2021-08-27.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2021-08-26.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

Free Software Foundation       Jul 05 2021                       GAWK(1)