NAME

gawk - pattern scanning and processing language

SYNOPSIS

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

README FIRST

This manual page is provided as a courtesy. Please note that the One
Source Of Truth for gawk is the Texinfo manual, available online in
several formats at https://www.gnu.org/software/gawk/manual. It may also
be installed in the Info subsystem on your system, and available
therefore via the info(1) command.

In the case of any contradiction between the Texinfo manual and this
manual page, the Texinfo manual should be considered to be
authoritative.

Note that the Info documentation, HTML web page(s), and PDF version of
the manual all have the same content, since they are all generated from
the same Texinfo source file.

Furthermore, the gawk maintainer reserves the right in the future to
remove this manual page from the distribution or to severely truncate
the content in order to ease his maintenance burden.

DESCRIPTION

Gawk is the GNU Project's implementation of the AWK programming
language. It conforms to the definition of the language in the POSIX
1003.1 standard. This version in turn is based on the description in The
AWK Programming Language, by Aho, Kernighan, and 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.

PREFACE

This manual page is intentionally as terse as possible. Full details are
provided in GAWK: Effective AWK Programming, and you should look there
for the full story on any specific feature. Where possible, links to the
online version of the manual are provided.

OPTION FORMAT

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 features.

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

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 options may be
    used. Files read with -f are treated as if they begin with an
    implicit @namespace "awk" statement.

-F fs, - -field-separator fs

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

-v var = val, - -assign var = val

    Assign the value val to the variable var, before execution of the
    program begins. Such variable values are available to the BEGIN rule
    of an AWK program.

-b, - -characters-as-bytes

    Treat all input data as single-byte characters. The - -posix option
    overrides this one.

-c, - -traditional

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

-C, - -copyright

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

-d[file], - -dump-variables[=file]

    Print a sorted list of global variables, their types and final
    values to file. The default file is awkvars.out in the current
    directory.

-D[file], - -debug[=file]

    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-interactively.

    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; see
    https://www.gnu.org/software/gawk/manual/html_node/Debugger.html#Debugger.

-e program-text, - -source program-text

    Use program-text as AWK program source code. 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 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.

-g, - -gen-pot

    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.

-h, - -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.

-I, - -trace

    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.

-k, - -csv

    Enable CSV special processing. See Comma Separated Values, below,
    for more detail.

-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], - -lint[=value]

    Provide warnings about constructs that are dubious or non-portable
    to other AWK implementations. See
    https://www.gnu.org/software/gawk/manual/html_node/Options.html#Options
    for the list of possible values for value.

-M, - -bignum

    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.)

    NOTE: This feature is on parole. The primary gawk maintainer is no
    longer supporting it, although there is a member of the development
    team who is. If this situation changes, the feature will be removed
    from gawk.

Set GAWK_NO_MPFR_WARN in the environment to silence the warning.

-n, - -non-decimal-data

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

-N, - -use-lc-numeric

    Force gawk to use the locale's decimal point character when parsing
    input data.

-o[file], - -pretty-print[=file]

    Output a pretty printed version of the program to file. The default
    file is awkprof.out in the current directory. This option implies
    - -no-optimize.

-O, - -optimize

    Enable gawk's default optimizations upon the internal representation
    of the program. This option is on by default.

-p[prof-file], - -profile[=prof-file]

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

-P, - -posix

    This turns on compatibility mode, and disables a number of common
    extensions.

-r, - -re-interval

    Enable the use of interval expressions in regular expression
    matching. Interval expressions are enabled by default, but this
    option remains for backwards compatibility.

-s, - -no-optimize

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

-S, - -sandbox

    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.

-t, - -lint-old

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

-V, - -version

    Print version information for this particular copy of gawk on the
    standard output. This is 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 “-”.

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.

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

AWK PROGRAM EXECUTION

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

  @include "filename "
  @nsinclude "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.

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

Lines beginning with @nsinclude also include files, but with two
differences. First, the namespace in the included file is not reset to
the default of awk, and such files may be included multiple times.

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

The environment variable AWKPATH specifies a search path to use when
finding source files named with the -f and - -include options. If this
variable does not exist, the default path is ".:/usr/local/share/awk".
(The actual directory may vary, depending upon how gawk was built and
installed.) If a file name given to the -f option contains a “/”
character, no path search is performed.

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

Gawk executes AWK programs in the following order. First, all variable
assignments specified via the -v option are performed. Next, gawk
compiles the program into an internal form. Then, gawk executes the code
in the BEGIN rule(s) (if any), and then proceeds to read each file named
in the ARGV array (up to ARGV[ARGC-1]). If there are no files named on
the command line, gawk reads the standard input.

If a filename on the command line has the form var=val it is treated as
a variable assignment. The variable var will be assigned the value val.
(This happens after any BEGIN rule(s) have been run.)

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 rules 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.

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

VARIABLES, RECORDS AND FIELDS

AWK variables are dynamic; they come into existence when they are first
used. Their 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. However, gawk
provides true arrays of arrays. Several pre-defined variables are set as
a program runs; these are described as needed and summarized below.

Records

Normally, records are separated by newline characters. You can control
how records are separated by assigning values to the built-in variable
RS. See https://www.gnu.org/software/gawk/manual/html_node/Records.html
for the details.

Fields

As each input record is read, gawk splits the record into fields, using
the value of the FS variable as the field separator. Additionally,
FIELDWIDTHS and FPAT may be used to control input field splitting. See
the details, starting at
https://www.gnu.org/software/gawk/manual/html_node/Fields.html.

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.

The variable NF is set to the total number of fields in the input
record.

References to non-existent fields (i.e., fields after $NF) produce the
null string. 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.

Comma Separated Values

When invoked with either the -k or the - -csv option, gawk does not use
regular record determination and field splitting as described above.
Instead, records are terminated by unquoted newlines, and fields are
separated by commas. Double-quotes may be used to enclose fields
containing commas, newlines, or doubled double-quotes. See
https://www.gnu.org/software/gawk/manual/html_node/Comma-Separated-Fields.html
for more details.

Built-in Variables

Gawk 's built-in variables are listed below. This list is purposely
terse. For details, see
https://www.gnu.org/software/gawk/manual/html_node/Built_002din-Variables.

ARGC

    The number of command line arguments.

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.

BINMODE

    On non-POSIX systems, specifies use of “binary” mode for all file
    I/O. See
    https://www.gnu.org/software/gawk/manual/html_node/PC-Using.html for
    the details.

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.

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.

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.

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.

FS

    The input field separator, a space by default. See
    https://www.gnu.org/software/gawk/manual/html_node/Field-Separators.html
    for the details.

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. See
    https://www.gnu.org/software/gawk/manual/html_node/Case_002dsensitivity.html
    for details.

LINT

    Provides dynamic control of the - -lint option from within an AWK
    program.

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. See
    https://www.gnu.org/software/gawk/manual/html_node/Auto_002dset for
    the details.

ROUNDMODE

    The rounding mode to use for arbitrary precision arithmetic on
    numbers, by default "N" (IEEE-754 roundTiesToEven mode). See
    https://www.gnu.org/software/gawk/manual/html_node/Setting-the-rounding-mode
    for the details.

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.

RLENGTH

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

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. 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

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++. See
https://www.gnu.org/software/gawk/manual/html_node/Arrays for details.

Namespaces

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
https://www.gnu.org/software/gawk/manual/html_node/Namespaces.html#Namespaces.

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 string.

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.

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. See
https://www.gnu.org/software/gawk/manual/html_node/Escape-Sequences for
the details.

Regexp Constants

A regular expression constant is a sequence of characters enclosed
between forward slashes (like /value/).

The escape sequences described in the manual 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.

PATTERNS AND ACTIONS

AWK is a line-oriented language. The pattern comes first, and then the
action. Action statements are enclosed in { and }. Either the pattern
may be missing, or the action may be missing, but, of course, not both.
If the pattern is missing, the action 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.

Patterns

AWK patterns may be one of the following:

  BEGIN
      END
      BEGINFILE
      ENDFILE
      /regular expression/
      relational expression
      pattern && pattern
      pattern || pattern
      pattern ? pattern : pattern
      (pattern)
      ! pattern
      pattern1, pattern2

BEGIN and END are two special kinds of patterns which are not tested
against the input. The action parts of all BEGIN patterns are merged as
if all the statements had been written in a single BEGIN rule. They are
executed before any of the input is read. Similarly, all the END rules
are merged, and executed when all the input is exhausted (or when an
exit statement is executed). BEGIN and END patterns cannot be combined
with other patterns in pattern expressions. BEGIN and END patterns
cannot have missing action parts.

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

For /regular expression/ patterns, the associated statement is executed
for each input record that matches the regular expression. Regular
expressions are essentially the same as those in egrep(1). See
https://www.gnu.org/software/gawk/manual/html_node/Regexp.html for the
details on regular expressions.

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.

Actions

Action statements are enclosed in braces, { and }. Action statements
consist of the usual assignment, conditional, and looping statements
found in most languages. The operators, control statements, and
input/output statements available are patterned after those in C.

Operators

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

(. . .)

    Grouping

$

    Field reference.

++ - -

    Increment and decrement, both prefix and postfix.

^

    Exponentiation.

+ - !

    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.

in

    Array membership.

&&

    Logical AND.

||

    Logical OR.

?:

    The C conditional expression. This has the form expr1 ? expr2 :
    expr3. If expr1 is true, the value of the expression is expr2,
    otherwise it is expr3. Only one of expr2 and expr3 is evaluated.

= += -= *= /= %= ^=

    Assignment. Both absolute assignment (var = value) and
    operator-assignment (the other forms) are supported.

Control Statements

The control statements are as follows:

  if (condition) statement [ else statement ]
      while (condition) statement
      do statement while (condition)
      for (expr1; expr2; expr3) statement
      for (var in array) statement
      break
      continue
      delete array [ index ]
      delete array 
      exit [ expression ]
      { statements }
      switch (expression) {
      case value|regex : statement
      . . .
      [ default: statement ]
      }

I/O Statements

The input/output statements are as follows:

close(file [, how])

    Close an open 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, RT.

getline var

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

getline var <file

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

command | getline [var]

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

command |& getline [var]

    Run command as a coprocess piping the output either into $0 or var,
    as above, and RT. (The command can also be a socket. See the
    subsection Special File Names, below.)

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.

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.

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
    https://www.gnu.org/software/gawk/manual/html_node/I_002fO-Functions.html#I_002fO-Functions
    for the full details on the exit status.

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

NOTE: Failure in opening a two-way socket results in a non-fatal error
being returned to the calling function. If using a pipe, coprocess, or
socket to getline, or from print or printf within a loop, you must use
close() to create new instances of the command or socket. AWK does not
automatically close pipes, sockets, or coprocesses when they return EOF.

The AWK versions of the printf statement and sprintf() function are
similar to those of C. For details, see
https://www.gnu.org/software/gawk/manual/html_node/Printf.html.

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.

The following special filenames may be used with the |& coprocess
operator for creating TCP/IP network connections:

/inet/tcp/lport/rhost/rport

/inet4/tcp/lport/rhost/rport

/inet6/tcp/lport/rhost/rport Files for a TCP/IP connection on local port
lport to remote host rhost on remote port rport. Use a port of 0 to have
the system pick a port. Use /inet4 to force an IPv4 connection, and
/inet6 to force an IPv6 connection. Plain /inet uses the system default
(most likely IPv4). Usable only with the |& two-way I/O operator.

/inet/udp/lport/rhost/rport

/inet4/udp/lport/rhost/rport

/inet6/udp/lport/rhost/rport Similar, but use UDP/IP instead of TCP/IP.
UDP support is obsolete and will be removed in the future.

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.

intdiv(num, denom, result)

    Truncate num and denom to integers. Return the quotient of num
    divided by denom in result["quotient"] and the remainder in
    result["remainder"]. This is a gawk extension, primarily of value
    when working with arbitrarily large integers.

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 generator.

String Functions

Gawk has the following built-in string functions; details are provided
in https://www.gnu.org/software/gawk/manual/html_node/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
    described in
    https://www.gnu.org/software/gawk/manual/html_node/String-Functions.html#String-Functions.
    s and d are allowed to be the same array; this only makes sense when
    supplying the third argument as well.

asorti(s [, d [, how] ])

    Return the number of elements in the source array s. The behavior is
    the same as that of asort(), except that the array indices are used
    for sorting, not the array values. When done, the array is indexed
    numerically, and the values are those of the original indices. The
    original values are lost; thus provide a second array if you wish to
    preserve the original. The purpose of the optional string how is the
    same as for asort(). Here too, s and d are allowed to be the same
    array; this only makes sense when supplying the third argument as
    well.

gensub(r, s, h [, t])

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

gsub(r, s [, t])

    For each substring matching the regular expression r in the string
    t, substitute the string s, and return the number of substitutions.
    If t is not supplied, use $0. An & in the replacement text is
    replaced with the text that was actually matched. Use \& to get a
    literal &. (This must be typed as "\\&"; see
    https://www.gnu.org/software/gawk/manual/html_node/Gory-Details.html#Gory-Details
    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.)

length([s])

    Return the length of the string s, or the length of $0 if s is not
    supplied. 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.

See
https://www.gnu.org/software/gawk/manual/html_node/String-Functions.html#String-Functions
for a description of how the array a is filled if it is provided.

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.

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]. Splitting behaves identically to field splitting.

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 number.

sub(r, s [, t])

    Just like gsub(), but replace only the first matching substring.
    Return either zero or one.

substr(s, i [, n])

    Return the at most n-character substring of s starting at i. If n is
    omitted, use the rest of s.

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

Gawk provides the following functions for obtaining time stamps and
formatting them. Details are provided in
https://www.gnu.org/software/gawk/manual/html_node/Time-Functions.

mktime(datespec [, utc-flag])

    Turn datespec into a time stamp of the same form as returned by
    systime(), and return the result. 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 datespec does not contain enough elements or if the resulting
    time is out of range, mktime() returns -1. See
    https://www.gnu.org/software/gawk/manual/html_node/Time-Functions.html#Time-Functions
    for the details of datespec.

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. 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 bits.

or(v1, v2 [, ...])

    Return the bitwise OR of the values provided in the argument list.
    There must be at least two.

rshift(val, count)

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

xor(v1, v2 [, ...])

    Return the bitwise XOR of the values provided in the argument list.
    There must be at least two.

Type Functions

The following functions provide type related information about their
arguments.

isarray(x)

    Return true if x is an array, false otherwise.

typeof(x)

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

Internationalization Functions

The following functions may be used from within your AWK program for
translating strings at run-time. For full details, see
https://www.gnu.org/software/gawk/manual/html_node/I18N-Functions.html#I18N-Functions.

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. 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".

dcngettext(string1, string2, number [, domain [, category]])

    Return the plural form used for number of the translation of string1
    and string2 in text domain domain for locale category category. The
    default value for domain is the current value of TEXTDOMAIN. The
    default value for category is "LC_MESSAGES".

Boolean Valued Functions

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

mkbool(expression )

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

USER-DEFINED FUNCTIONS

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.

Local variables 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
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.

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
      	. . .
      }

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.

DYNAMICALLY LOADING NEW FUNCTIONS

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
https://www.gnu.org/software/gawk/manual/html_node/Dynamic-Extensions.html#Dynamic-Extensions.

SIGNALS

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.

INTERNATIONALIZATION

String constants are sequences of characters enclosed in double quotes.
In non-English speaking environments, it is possible to mark strings in
the AWK program as requiring translation to the 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. See
https://www.gnu.org/software/gawk/manual/html_node/Internationalization.html#Internationalization
for the steps involved in producing and running a localizable AWK
program.

GNU EXTENSIONS

Gawk has a too-large number of extensions to POSIX awk. They are
described in
https://www.gnu.org/software/gawk/manual/html_node/POSIX_002fGNU.html.
All the extensions can be disabled by invoking gawk with the
- -traditional or - -posix options.

ENVIRONMENT VARIABLES

The AWKPATH environment variable can be used to provide a list of
directories that gawk searches when looking for files named via the -f,
- -file, -i and - -include options, and the @include and @nsinclude
directives. 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_PERSIST_FILE environment variable, if present, specifies a file
to use as the backing store for persistent memory. See GAWK: Effective
AWK Programming for the details.

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 effect.

Set GAWK_NO_MPFR_WARN in the environment to silence the warning about
MPFR mode being deprecated.

EXIT STATUS

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

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

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

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

VERSION INFORMATION

This man page documents gawk, version 5.4.

AUTHORS

The original version of UNIX awk was designed and implemented by Alfred
Aho, Peter Weinberger, and Brian Kernighan of Bell Laboratories. Ozan
Yigit is the current maintainer. Brian Kernighan occasionally dabbles in
its development.

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 supported.

BUG REPORTS AND QUESTIONS

If you find a bug in gawk, please use the gawkbug(1) program to report
it.

Full instructions for reporting a bug are provided in
https://www.gnu.org/software/gawk/manual/html_node/Bugs.html. Please
carefully read and follow the instructions given there. This will make
bug reporting and resolution much easier for everyone involved. Really.

On the other hand, if you have a question as to how to accomplish a
particular task using awk or gawk, send an email to help-gawk@gnu.org
with your request for help.

BUGS

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

This manual page is too long; gawk has too many features.

SEE ALSO

egrep(1), sed(1), gawkbug(1), printf(3), and strftime(3).

The AWK Programming Language, second edition, Alfred V. Aho, Brian W.
Kernighan, Peter J. Weinberger, Addison-Wesley, 2023. ISBN
9-780138-269722.

GAWK: Effective AWK Programming, Edition 5.4, shipped with the gawk
source. The current version of this document is available online at
https://www.gnu.org/software/gawk/manual.

The GNU gettext documentation, available online at
https://www.gnu.org/software/gettext.

EXAMPLES

    Print and sort the login names of all users:

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

    Count lines in a file:

    		{ nlines++ }
    	END	{ print nlines }

    Precede each line by its number in the file:

    	{ print FNR, $0 }

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

    	{ print NR, $0 }

    Run an external command for particular lines of data:

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

ACKNOWLEDGEMENTS

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

COPYING PERMISSIONS

Copyright © 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2001, 2002, 2003, 2004, 2005, 2007, 2009, 2010, 2011, 2012, 2013, 2014,
2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022, 2023, 2024, 2025, 2026
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 process this file through troff and print the
results, provided the printed document carries copying permission notice
identical to this one except for the removal of this paragraph (this
paragraph not being relevant to the printed manual page).

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.
