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,

       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 Programming.

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"

       -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 non-

       -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 output.

       -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

              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 --no-optimize.

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

              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 recognized.

              · 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

              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 line.

              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

       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

       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 error.

       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 below.

       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.

       BINMODE     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

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

       ENVIRON     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.

       FIELDWIDTHS 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,

       FILENAME    The name of the current input file.  If no files are
                   specified on the command line, the value of FILENAME is
                   “-”.  However, FILENAME is undefined inside the BEGIN
                   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, above.

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

       FUNCTAB     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.

       IGNORECASE  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 case-sensitive.

       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.

       PROCINFO    The elements of this array provide access to information
                   about the running AWK program.  On some systems, there
                   may be elements in the array, "group1" through "groupn"
                   for some n, which is the number of supplementary groups
                   that the process has.  Use the in operator to test for
                   these elements.  The following elements are guaranteed to
                   be available:

                   PROCINFO["argv"]     The command line arguments as
                                        received by gawk at the C-language
                                        level.  The subscripts start from

                   PROCINFO["egid"]     The value of the getegid(2) system

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

                   PROCINFO["euid"]     The value of the geteuid(2) system

                   PROCINFO["FS"]       "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.

                   PROCINFO["gid"]      The value of the getgid(2) system

                                        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 following:

                                        "array"     The identifier is an

                                        "builtin"   The identifier is a
                                                    built-in function.

                                        "extension" The identifier is an
                                                    extension function
                                                    loaded via @load or

                                        "scalar"    The identifier is a

                                        "untyped"   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.

                   PROCINFO["pgrpid"]   The value of the getpgrp(2) system

                   PROCINFO["pid"]      The value of the getpid(2) system

                   PROCINFO["platform"] A string indicating the platform for
                                        which gawk was compiled.  It is one

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

                                        "os2"  OS/2.

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

                                        "vms"  OpenVMS or Vax/VMS.

                   PROCINFO["ppid"]     The value of the getppid(2) system

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

                   PROCINFO["uid"]      The value of the getuid(2) system

                   PROCINFO["version"]  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.

       ROUNDMODE   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

       RLENGTH     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.

       TEXTDOMAIN  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 different.

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

       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 Programming.

   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 17.

   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 /a\*b/.

   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 Expressions.

       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

       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

       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.

       [abc...]   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.

       [^abc...]  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:

       [:alnum:]  Alphanumeric characters.

       [:alpha:]  Alphabetic characters.

       [:blank:]  Space or tab characters.

       [:cntrl:]  Control characters.

       [:digit:]  Numeric characters.

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

       [:lower:]  Lowercase alphabetic characters.

       [:print:]  Printable characters (characters that are not control

       [:punct:]  Punctuation characters (characters that are not letter,
                  digits, control characters, or space characters).

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

       [:upper:]  Uppercase alphabetic characters.

       [:xdigit:] Characters that are hexadecimal digits.

       For example, before the POSIX standard, to match alphanumeric
       characters, you would have had to write /[A-Za-z0-9]/.  If your
       character set had other alphabetic characters in it, this would not
       match them, and if your character set collated differently from
       ASCII, this might not even match the ASCII alphanumeric characters.
       With the POSIX character classes, you can write /[[:alnum:]]/, and
       this matches the alphabetic and numeric characters in your character
       set, no matter what it is.

       Two additional special sequences can appear in character lists.
       These apply to non-ASCII character sets, which can have single
       symbols (called collating elements) that are 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 w).

              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 "from".

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

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

       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).

       nextfile              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,

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

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

       fflush([file])        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

       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 formats:

       %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

       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

       -      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

       '      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.

       /dev/stdin  The standard input.

       /dev/stdout The standard output.

       /dev/stderr The standard error output.

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

       These are particularly useful for error messages.  For example:

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

       whereas you would otherwise have to use

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

       The following special filenames may be used with the |& 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.

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

       exp(expr)     The exponential function.

       int(expr)     Truncate to integer.

       log(expr)     The natural logarithm function.

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

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

       sqrt(expr)    Return the square root of expr.

       srand([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

   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

       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

       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.

       length([s])             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

       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 string.

       strtonum(str)           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

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

       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.

       tolower(str)            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.

       toupper(str)            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 them.

       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.

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

   Bit Manipulations Functions
       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.

       compl(val)          Return the bitwise complement of val.

       lshift(val, count)  Return the value of val, shifted left by count

       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

       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

       isarray(x) 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.

       typeof(x)  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
              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.


       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

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 version).


       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 options.

       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 special.

       · There is no facility for doing file inclusion (gawk's @include

       · 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 available.

       · The FIELDWIDTHS variable and fixed-width field splitting.

       · The FPAT variable and field splitting based on field values.

       · The FUNCTAB, SYMTAB, and PROCINFO arrays are not available.

       · The use of RS as a regular expression.

       · The special file names available for I/O redirection are not

       · The |& operator for creating coprocesses.

       · The BEGINFILE and ENDFILE special patterns are not available.

       · 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

       · 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 sprintf().

       · 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()

       · 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 zero.

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

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


       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 it.

       Paul Rubin and Jay Fenlason, of the Free Software Foundation, wrote
       gawk, to be compatible with the original version of awk distributed
       in Seventh Edition UNIX.  John Woods 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.

       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, 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 2020-08-13.  (At that time,
       the date of the most recent commit that was found in the repository
       was 2020-08-12.)  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 2 2020                          GAWK(1)