.ds PX \s-1POSIX\s+1
.ds UX \s-1UNIX\s+1
.ds GN \s-1GNU\s+1
.ds AK \s-1AWK\s+1
.ds EP \fIGAWK: Effective AWK Programming\fP
.if !\n(.g \{\
.	if !\w|\*(lq| \{\
.		ds lq ``
.		if \w'\(lq' .ds lq "\(lq
.	\}
.	if !\w|\*(rq| \{\
.		ds rq ''
.		if \w'\(rq' .ds rq "\(rq
.	\}
.\}
.TH GAWK 1 "Jun 09 2022" "Free Software Foundation" "Utility Commands"
.SH NAME
gawk \- pattern scanning and processing language
.SH SYNOPSIS
.B gawk
[ \*(PX or \*(GN style options ]
.B \-f
.I program-file
[
.B \-\^\-
] file .\|.\|.
.br
.B gawk
[ \*(PX or \*(GN style options ]
[
.B \-\^\-
]
.I program-text
file .\|.\|.
.SH DESCRIPTION
.I Gawk
is the \*(GN Project's implementation of the \*(AK programming language.
It conforms to the definition of the language in
the \*(PX 1003.1 standard.
This version in turn is based on the description in
.IR "The AWK Programming Language" ,
by Aho, Kernighan, and Weinberger.
.I Gawk
provides the additional features found in the current version
of Brian Kernighan's
.I awk
and numerous \*(GN-specific extensions.
.PP
The command line consists of options to
.I gawk
itself, the \*(AK program text (if not supplied via the
.B \-f
or
.B \-\^\-include
options), and values to be made
available in the
.B ARGC
and
.B ARGV
pre-defined \*(AK variables.
.SH PREFACE
This manual page is intentionally as terse as possible.
Full details are provided in \*(EP, 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.
.SH OPTION FORMAT
.I Gawk
options may be either traditional \*(PX-style one letter options,
or \*(GN-style long options.  \*(PX options start with a single \*(lq\-\*(rq,
while long options start with \*(lq\-\^\-\*(rq.
Long options are provided for both \*(GN-specific features and
for \*(PX-mandated features.
.PP
.IR Gawk -specific
options are typically used in long-option form.
Arguments to long options are either joined with the option
by an
.B =
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.
.PP
Additionally, every long option has a corresponding short
option, so that the option's functionality may be used from
within
.B #!
executable scripts.
.SH OPTIONS
.I Gawk
accepts the following options.
Standard options are listed first, followed by options for
.I gawk
extensions, listed alphabetically by short option.
.TP
.BI \-f " program-file\fR,\fP "\c
.BI \-\^\-file " program-file"
Read the \*(AK program source from the file
.IR program-file ,
instead of from the first command line argument.
Multiple
.B \-f
options may be used.
Files read with
.B \-f
are treated as if they begin with an implicit \fB@namespace "awk"\fR statement.
.TP
.BI \-F " fs\fR, \fP"\c
.BI \-\^\-field-separator " fs"
Use
.I fs
for the input field separator (the value of the
.B FS
predefined
variable).
.TP
\fB\-v\fI var\fB\^=\^\fIval\fR, \fB\-\^\-assign \fIvar\fB\^=\^\fIval\fR
Assign the value
.I val
to the variable
.IR var ,
before execution of the program begins.
Such variable values are available to the
.B BEGIN
rule of an \*(AK program.
.TP
.BR \-b ", "\c
.B \-\^\-characters\-as\-bytes
Treat all input data as single-byte characters.
The
.B \-\^\-posix
option overrides this one.
.TP
.BR \-c ", "\c
.B \-\^\-traditional
Run in
.I compatibility
mode.  In compatibility mode,
.I gawk
behaves identically to Brian Kernighan's
.IR awk ;
none of the \*(GN-specific extensions are recognized.
.TP
.BR \-C ", "\c
.B \-\^\-copyright
Print the short version of the \*(GN copyright information message on
the standard output and exit successfully.
.TP
\fB\-d\fR[\fIfile\fR], \fB\-\^\-dump-variables\fR[\fB=\fIfile\fR]
Print a sorted list of global variables, their types and final values to
.IR file .
The default file is
.B awkvars.out
in the current directory.
.TP
\fB\-D\fR[\fIfile\fR], \fB\-\^\-debug\fR[\fB=\fIfile\fR]
Enable debugging of \*(AK programs.
By default, the debugger reads commands interactively from the keyboard
(standard input).
The optional
.I file
argument specifies a file with a list
of commands for the debugger to execute non-interactively.
.sp .5
In this mode of execution,
.I gawk
loads the
AWK source code and then prompts for debugging commands.
.I Gawk
can only debug AWK program source provided with the
.B \-f
and
.B \-\^\-include
options.
The debugger is documented in \*(EP; see
.IR https://www.gnu.org/software/gawk/manual/html_node/Debugger.html#Debugger .
.TP
.BI \-e " program-text\fR, \fP"\c
.BI \-\^\-source " program-text"
Use
.I program-text
as \*(AK program source code.
Each argument supplied via
.B \-e
is treated as if it begins with an implicit \fB@namespace "awk"\fR statement.
.TP
\fB\-E \fIfile\fR, \fB\-\^\-exec \fIfile\fR
Similar to
.BR \-f ,
however, this is option is the last one processed.
This should be used with
.B #!
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.
.TP
.BR \-g ", "\c
.B \-\^\-gen\-pot
Scan and parse the \*(AK program, and generate a \*(GN
.B \&.pot
(Portable Object Template)
format file on standard output with entries for all localizable
strings in the program.  The program itself is not executed.
.TP
.BR \-h ", "\c
.B \-\^\-help
Print a relatively short summary of the available options on
the standard output.
Per the
.IR "GNU Coding Standards" ,
these options cause an immediate, successful exit.
.TP
\fB\-i \fIinclude-file\fR, \fB\-\^\-include \fIinclude-file\fR
Load an awk source library.
This searches for the library using the
.B AWKPATH
environment variable.  If the initial search fails, another attempt will
be made after appending the
.B \&.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
.B \-\^\-include
are treated as if they begin with an implicit \fB@namespace "awk"\fR statement.
.TP
.BR \-I ", "\c
.B \-\^\-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
.B +
sign in the output.
.TP
.BI \-l " lib\fR, "\c
.BI \-\^\-load " lib"
Load a
.I gawk
extension from the shared library
.IR lib .
This searches for the library using the
.B 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
.BR dl_load() .
.TP
\fB\-L \fR[\fIvalue\fR], \fB\-\^\-lint\fR[\fB=\fIvalue\fR]
Provide warnings about constructs that are
dubious or non-portable to other \*(AK implementations.
See
.I https://www.gnu.org/software/gawk/manual/html_node/Options.html#Options
for the list of possible values for
.IR value .
.TP
.BR \-M ", "\c
.B \-\^\-bignum
Force arbitrary precision arithmetic on numbers. This option has
no effect if
.I gawk
is not compiled to use the GNU MPFR and GMP libraries.
(In such a case,
.I gawk
issues a warning.)
.sp
.B NOTE:
This feature is
.IR "on parole" .
The primary
.I 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
.IR gawk .
.ig
Set
.B GAWK_NO_MPFR_WARN
in the environment to silence the warning.
..
.TP
.BR \-n ", "\c
.B \-\^\-non\-decimal\-data
Recognize octal and hexadecimal values in input data.
.I "Use this option with great caution!"
.TP
.BR \-N ", "\c
.B \-\^\-use\-lc\-numeric
Force
.I gawk
to use the locale's decimal point character when parsing input data.
.ig
.\" This option is left undocumented, on purpose.
.TP
.BR "\-W nostalgia" ", "\c
.B \-\^\-nostalgia
Provide a moment of nostalgia for long time
.I awk
users.
..
.TP
\fB\-o\fR[\fIfile\fR], \fB\-\^\-pretty-print\fR[\fB=\fIfile\fR]
Output a pretty printed version of the program to
.IR file .
The default file is
.B awkprof.out
in the current directory.
This option implies
.BR \-\^\-no\-optimize .
.TP
.BR \-O ", "\c
.B \-\^\-optimize
Enable
.IR gawk 's
default optimizations upon the internal representation of the program.
This option is on by default.
.TP
\fB\-p\fR[\fIprof-file\fR], \fB\-\^\-profile\fR[\fB=\fIprof-file\fR]
Start a profiling session, and send the profiling data to
.IR prof-file .
The default is
.B 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.
.I Gawk
runs more slowly in this mode.
This option implies
.BR \-\^\-no\-optimize .
.TP
.BR \-P ", "\c
.B \-\^\-posix
This turns on
.I compatibility
mode, and disables a number of common extensions.
.TP
.BR \-r ", "\c
.B \-\^\-re\-interval
Enable the use of
.I "interval expressions"
in regular expression matching.
Interval expressions
are enabled by default, but this option remains for backwards compatibility.
.TP
.BR \-s ", "\c
.B \-\^\-no\-optimize
Disable
.IR gawk 's
default optimizations upon the internal representation of the program.
.TP
.BR \-S ", "\c
.B \-\^\-sandbox
Run
.I gawk
in sandbox mode, disabling the
.B system()
function, input redirection with
.BR getline ,
output redirection with
.BR print " and " printf ,
and loading dynamic extensions.
Command execution (through pipelines) is also disabled.
.TP
.BR \-t ", "\c
.B \-\^\-lint\-old
Provide warnings about constructs that are
not portable to the original version of \*(UX
.IR awk .
.TP
.BR \-V ", "\c
.B \-\^\-version
Print version information for this particular copy of
.I gawk
on the standard output.
This is useful when reporting bugs.
Per the
.IR "GNU Coding Standards" ,
these options cause an immediate, successful exit.
.TP
.B \-\^\-
Signal the end of options. This is useful to allow further arguments to the
\*(AK program itself to start with a \*(lq\-\*(rq.
.PP
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 \*(AK program in the
.B ARGV
array for processing.
.PP
For \*(PX compatibility, the
.B \-W
option may be used, followed by the name of a long option.
.SH AWK PROGRAM EXECUTION
An \*(AK program consists of a sequence of
optional directives,
pattern-action statements,
and optional function definitions.
.RS
.PP
\fB@include "\fIfilename\^\fB"
.br
\fB@load "\fIfilename\^\fB"
.br
\fB@namespace "\fIname\^\fB"
.br
\fIpattern\fB	{ \fIaction statements\fB }\fR
.br
\fBfunction \fIname\fB(\fIparameter list\fB) { \fIstatements\fB }\fR
.RE
.PP
.I Gawk
first reads the program source from the
.IR program-file (s)
if specified,
from arguments to
.BR \-\^\-source ,
or from the first non-option argument on the command line.
The
.B \-f
and
.B \-\^\-source
options may be used multiple times on the command line.
.I Gawk
reads the program text as if all the
.IR program-file s
and command line source texts
had been concatenated together.
.PP
In addition, lines beginning with
.B @include
may be used to include other source files into your program.
This is equivalent
to using the
.B \-\^\-include
option.
.PP
Lines beginning with
.B @load
may be used to load extension functions into your program.  This is equivalent
to using the
.B \-\^\-load
option.
.PP
The environment variable
.B AWKPATH
specifies a search path to use when finding source files named with
the
.B \-f
and
.B \-\^\-include
options.  If this variable does not exist, the default path is
\fB".:/usr/local/share/awk"\fR.
(The actual directory may vary, depending upon how
.I gawk
was built and installed.)
If a file name given to the
.B \-f
option contains a \*(lq/\*(rq character, no path search is performed.
.PP
The environment variable
.B AWKLIBPATH
specifies a search path to use when finding source files named with
the
.B \-\^\-load
option.  If this variable does not exist, the default path is
\fB"/usr/local/lib/gawk"\fR.
(The actual directory may vary, depending upon how
.I gawk
was built and installed.)
.PP
.I Gawk
executes \*(AK programs in the following order.
First,
all variable assignments specified via the
.B \-v
option are performed.
Next,
.I gawk
compiles the program into an internal form.
Then,
.I gawk
executes the code in the
.B BEGIN
rule(s) (if any),
and then proceeds to read
each file named in the
.B ARGV
array (up to
.BR ARGV[ARGC\-1] ).
If there are no files named on the command line,
.I gawk
reads the standard input.
.PP
If a filename on the command line has the form
.IB var = val
it is treated as a variable assignment.  The variable
.I var
will be assigned the value
.IR val .
(This happens after any
.B BEGIN
rule(s) have been run.)
.PP
If the value of a particular element of
.B ARGV
is empty (\fB""\fR),
.I gawk
skips over it.
.PP
For each input file,
if a
.B BEGINFILE
rule exists,
.I gawk
executes the associated code
before processing the contents of the file. Similarly,
.I gawk
executes
the code associated with
.B ENDFILE
rules
after processing the file.
.PP
For each record in the input,
.I gawk
tests to see if it matches any
.I pattern
in the \*(AK program.
For each pattern that the record matches,
.I gawk
executes the associated
.IR action .
The patterns are tested in the order they occur in the program.
.PP
Finally, after all the input is exhausted,
.I gawk
executes the code in the
.B END
rule(s) (if any).
.SS Command Line Directories
According to POSIX, files named on the
.I awk
command line must be
text files.  The behavior is ``undefined'' if they are not.  Most versions
of
.I awk
treat a directory on the command line as a fatal error.
.PP
For
.IR gawk ,
a directory on the command line
produces a warning, but is otherwise skipped.  If either of the
.B \-\^\-posix
or
.B \-\^\-traditional
options is given, then
.I gawk
reverts to
treating directories on the command line as a fatal error.
.SH VARIABLES, RECORDS AND FIELDS
\*(AK 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,
.I gawk
allows variables to have regular-expression type.
\*(AK also has one dimensional
arrays; arrays with multiple dimensions may be simulated.
However,
.I gawk
provides true arrays of arrays.
Several pre-defined variables are set as a program
runs; these are described as needed and summarized below.
.SS Records
Normally, records are separated by newline characters.  You can control how
records are separated by assigning values to the built-in variable
.BR RS .
See
.I https://www.gnu.org/software/gawk/manual/html_node/Records.html
for the details.
.SS Fields
As each input record is read,
.I gawk
splits the record into
.IR fields ,
using the value of the
.B FS
variable as the field separator.
Additionally,
.B FIELDWIDTHS
and
.B FPAT
may be used to control input field splitting.
See the details, starting at
.IR https://www.gnu.org/software/gawk/manual/html_node/Fields.html .
.PP
Each field in the input record may be referenced by its position:
.BR $1 ,
.BR $2 ,
and so on.
.B $0
is the whole record,
including leading and trailing whitespace.
.PP
The variable
.B NF
is set to the total number of fields in the input record.
.PP
References to non-existent fields (i.e., fields after
.BR $NF )
produce the null string.  However, assigning to a non-existent field
(e.g.,
.BR "$(NF+2) = 5" )
increases the value of
.BR NF ,
creates any intervening fields with the null string as their values, and
causes the value of
.B $0
to be recomputed, with the fields being separated by the value of
.BR OFS .
References to negative numbered fields cause a fatal error.
Decrementing
.B NF
causes the values of fields past the new value to be lost, and the value of
.B $0
to be recomputed, with the fields being separated by the value of
.BR OFS .
.PP
Assigning a value to an existing field
causes the whole record to be rebuilt when
.B $0
is referenced.
Similarly, assigning a value to
.B $0
causes the record to be resplit, creating new
values for the fields.
.SS Built-in Variables
.IR Gawk\^ "'s"
built-in variables are listed below.
This list is purposely terse. For details, see
.IR https://www.gnu.org/software/gawk/manual/html_node/Built_002din-Variables .
.TP "\w'\fBFIELDWIDTHS\fR'u+1n"
.B ARGC
The number of command line arguments.
.TP
.B ARGIND
The index in
.B ARGV
of the current file being processed.
.TP
.B ARGV
Array of command line arguments.  The array is indexed from
0 to
.B ARGC
\- 1.
.TP
.B BINMODE
On non-POSIX systems, specifies use of \*(lqbinary\*(rq mode for all file I/O.
See
.I https://www.gnu.org/software/gawk/manual/html_node/PC-Using.html
for the details.
.TP
.B CONVFMT
The conversion format for numbers, \fB"%.6g"\fR, by default.
.TP
.B 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.
.TP
.B ERRNO
If a system error occurs either doing a redirection for
.BR getline ,
during a read for
.BR getline ,
or during a
.BR close() ,
then
.B ERRNO
is set to
a string describing the error.
The value is subject to translation in non-English locales.
.TP
.B FIELDWIDTHS
A whitespace-separated list of field widths.  When set,
.I gawk
parses the input into fields of fixed width, instead of using the
value of the
.B 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.
.TP
.B FILENAME
The name of the current input file.
If no files are specified on the command line, the value of
.B FILENAME
is \*(lq\-\*(rq.
However,
.B FILENAME
is undefined inside the
.B BEGIN
rule
(unless set by
.BR getline ).
.TP
.B FNR
The input record number in the current input file.
.TP
.B FPAT
A regular expression describing the contents of the
fields in a record.
When set,
.I gawk
parses the input into fields, where the fields match the
regular expression, instead of using the
value of
.B FS
as the field separator.
.TP
.B FS
The input field separator, a space by default.
See
.I https://www.gnu.org/software/gawk/manual/html_node/Field-Separators.html
for the details.
.TP
.B FUNCTAB
An array whose indices and corresponding values
are the names of all the user-defined
or extension functions in the program.
.BR NOTE :
You may not use the
.B delete
statement with the
.B FUNCTAB
array.
.TP
.B IGNORECASE
Controls the case-sensitivity of all regular expression
and string operations.
See
.I https://www.gnu.org/software/gawk/manual/html_node/Case_002dsensitivity.html
for details.
.TP
.B LINT
Provides dynamic control of the
.B \-\^\-lint
option from within an \*(AK program.
.TP
.B NF
The number of fields in the current input record.
.TP
.B NR
The total number of input records seen so far.
.TP
.B OFMT
The output format for numbers, \fB"%.6g"\fR, by default.
.TP
.B OFS
The output field separator, a space by default.
.TP
.B ORS
The output record separator, by default a newline.
.TP
.B PREC
The working precision of arbitrary precision floating-point
numbers, 53 by default.
.TP
.B PROCINFO
The elements of this array provide access to information about the
running \*(AK program.
See
.I https://www.gnu.org/software/gawk/manual/html_node/Auto_002dset
for the details.
.TP
.B ROUNDMODE
The rounding mode to use for arbitrary precision arithmetic on
numbers, by default \fB"N"\fR (IEEE-754 roundTiesToEven mode).
See
.I https://www.gnu.org/software/gawk/manual/html_node/Setting-the-rounding-mode
for the details.
.TP
.B RS
The input record separator, by default a newline.
.TP
.B RT
The record terminator.
.I Gawk
sets
.B RT
to the input text that matched the character or regular expression
specified by
.BR RS .
.TP
.B RSTART
The index of the first character matched by
.BR match() ;
0 if no match.
.TP
.B RLENGTH
The length of the string matched by
.BR match() ;
\-1 if no match.
.TP
.B SUBSEP
The string used to separate multiple subscripts in array
elements, by default \fB"\e034"\fR.
.TP
.B SYMTAB
An array whose indices are the names of all currently defined
global variables and arrays in the program.
You may not use the
.B delete
statement with the
.B SYMTAB
array, nor assign to elements with an index that is
not a variable name.
.TP
.B TEXTDOMAIN
The text domain of the \*(AK program; used to find the localized
translations for the program's strings.
.SS Arrays
Arrays are subscripted with an expression between square brackets
.RB ( [ " and " ] ).
If the expression is an expression list
.RI ( 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
.B SUBSEP
variable.
This facility is used to simulate multiply dimensioned
arrays.  For example:
.PP
.RS
.ft B
i = "A";\^ j = "B";\^ k = "C"
.br
x[i, j, k] = "hello, world\en"
.ft R
.RE
.PP
assigns the string \fB"hello,\ world\en"\fR to the element of the array
.B x
which is indexed by the string \fB"A\e034B\e034C"\fR.  All arrays in \*(AK
are associative, i.e., indexed by string values.
.PP
The special operator
.B in
may be used to test if an array has an index consisting of a particular
value:
.PP
.RS
.ft B
.nf
if (val in array)
	print array[val]
.fi
.ft
.RE
.PP
If the array has multiple subscripts, use
.BR "(i, j) in array" .
.PP
The
.B in
construct may also be used in a
.B for
loop to iterate over all the elements of an array.
However, the
.B "(i, j) in array"
construct only works in tests, not in
.B for
loops.
.PP
An element may be deleted from an array using the
.B delete
statement.
The
.B delete
statement may also be used to delete the entire contents of an array,
just by specifying the array name without a subscript.
.PP
.I gawk
supports true multidimensional arrays. It does not require that
such arrays be ``rectangular'' as in C or C++.
See
.I https://www.gnu.org/software/gawk/manual/html_node/Arrays
for details.
.SS Namespaces
.I Gawk
provides a simple
.I namespace
facility to help work around the fact that all variables in
AWK are global.
.PP
A
.I "qualified name"
consists of a two simple identifiers joined by a double colon
.RB ( :: ).
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
.BR awk .
However, simple identifiers consisting solely of uppercase
letters are forced into the
.B awk
namespace, even if the current namespace is different.
.PP
You change the current namespace with an
\fB@namespace "\fIname\^\fB"\fR
directive.
.PP
The standard predefined builtin function names may not be used as
namespace names.  The names of additional functions provided by
.I gawk
may be used as namespace names or as simple identifiers in other
namespaces.
For more details, see
.IR https://www.gnu.org/software/gawk/manual/html_node/Namespaces.html#Namespaces .
.SS 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.
.PP
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.
.PP
Uninitialized variables have the numeric value zero and the string value ""
(the null, or empty, string).
.PP
When a string must be converted to a number, the conversion is accomplished
using
.IR strtod (3).
A number is converted to a string by using the value of
.B CONVFMT
as a format string for
.IR sprintf (3),
with the numeric value of the variable as the argument.
However, even though all numbers in \*(AK are floating-point,
integral values are
.I always
converted as integers.
.PP
.I 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
\*(lqnumeric string,\*(rq 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.
.PP
Note that string constants, such as \fB"57"\fP, are
.I not
numeric strings, they are string constants.
The idea of \*(lqnumeric string\*(rq
only applies to fields,
.B getline
input,
.BR FILENAME ,
.B ARGV
elements,
.B ENVIRON
elements and the elements of an array created by
.B split()
or
.B patsplit()
that are numeric strings.
The basic idea is that
.IR "user input" ,
and only user input, that looks numeric,
should be treated that way.
.SS Octal and Hexadecimal Constants
You may use C-style octal and hexadecimal constants in your AWK
program source code.
For example, the octal value
.B 011
is equal to decimal
.BR 9 ,
and the hexadecimal value
.B 0x11
is equal to decimal 17.
.SS String Constants
String constants in \*(AK are sequences of characters enclosed
between double quotes (like \fB"value"\fR).  Within strings, certain
.I "escape sequences"
are recognized, as in C.
See
.I https://www.gnu.org/software/gawk/manual/html_node/Escape-Sequences
for the details.
.SS Regexp Constants
A regular expression constant is a sequence of characters enclosed
between forward slashes (like
.BR /value/ ).
.PP
The escape sequences described in the manual may also be used inside
constant regular expressions
(e.g.,
.B "/[\ \et\ef\en\er\ev]/"
matches whitespace characters).
.PP
.I Gawk
provides
.I "strongly typed"
regular expression constants. These are written with a leading
.B @
symbol (like so:
.BR @/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.
.SH PATTERNS AND ACTIONS
\*(AK is a line-oriented language.  The pattern comes first, and then the
action.  Action statements are enclosed in
.B {
and
.BR } .
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
.RS
.PP
.B "{ print }"
.RE
.PP
which prints the entire record.
.PP
Comments begin with the
.B #
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,
.BR { ,
.BR ? ,
.BR : ,
.BR && ,
or
.BR || .
Lines ending in
.B do
or
.B else
also have their statements automatically continued on the following line.
In other cases, a line can be continued by ending it with a \*(lq\e\*(rq,
in which case the newline is ignored.  However, a \*(lq\e\*(rq after a
.B #
is not special.
.PP
Multiple statements may
be put on one line by separating them with a \*(lq;\*(rq.
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.
.SS Patterns
\*(AK patterns may be one of the following:
.PP
.RS
.nf
.B BEGIN
.B END
.B BEGINFILE
.B ENDFILE
.BI / "regular expression" /
.I "relational expression"
.IB pattern " && " pattern
.IB pattern " || " pattern
.IB pattern " ? " pattern " : " pattern
.BI ( pattern )
.BI ! " pattern"
.IB pattern1 ", " pattern2
.fi
.RE
.PP
.B BEGIN
and
.B END
are two special kinds of patterns which are not tested against
the input.
The action parts of all
.B BEGIN
patterns are merged as if all the statements had
been written in a single
.B BEGIN
rule.  They are executed before any
of the input is read.  Similarly, all the
.B END
rules are merged,
and executed when all the input is exhausted (or when an
.B exit
statement is executed).
.B BEGIN
and
.B END
patterns cannot be combined with other patterns in pattern expressions.
.B BEGIN
and
.B END
patterns cannot have missing action parts.
.PP
.B BEGINFILE
and
.B 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
.B BEGINFILE
rule, the value of
.B ERRNO
is the empty string if the file was opened successfully.
Otherwise, there is some problem with the file and the code should
use
.B nextfile
to skip it. If that is not done,
.I gawk
produces its usual fatal error for files that cannot be opened.
.PP
For
.BI / "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
.IR egrep (1).
See
.I https://www.gnu.org/software/gawk/manual/html_node/Regexp.html
for the details on regular expressions.
.PP
A
.I "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.
.PP
The
.BR && ,
.BR || ,
and
.B !
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.
.PP
The
.B ?\^:
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.
.PP
The
.IB pattern1 ", " pattern2
form of an expression is called a
.IR "range pattern" .
It matches all input records starting with a record that matches
.IR pattern1 ,
and continuing until a record that matches
.IR pattern2 ,
inclusive.  It does not combine with any other sort of pattern expression.
.SS Actions
Action statements are enclosed in braces,
.B {
and
.BR } .
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.
.SS Operators
The operators in \*(AK, in order of decreasing precedence, are:
.TP "\w'\fB*= /= %= ^=\fR'u+1n"
.BR ( \&.\|.\|. )
Grouping
.TP
.B $
Field reference.
.TP
.B "++ \-\^\-"
Increment and decrement, both prefix and postfix.
.TP
.B ^
Exponentiation.
.TP
.B "+ \- !"
Unary plus, unary minus, and logical negation.
.TP
.B "* / %"
Multiplication, division, and modulus.
.TP
.B "+ \-"
Addition and subtraction.
.TP
.I space
String concatenation.
.TP
.B "|   |&"
Piped I/O for
.BR getline ,
.BR print ,
and
.BR printf .
.TP
.B "< > <= >= == !="
The regular relational operators.
.TP
.B "~ !~"
Regular expression match, negated match.
.TP
.B in
Array membership.
.TP
.B &&
Logical AND.
.TP
.B ||
Logical OR.
.TP
.B ?:
The C conditional expression.  This has the form
.IB expr1 " ? " expr2 " : " expr3\c
\&.
If
.I expr1
is true, the value of the expression is
.IR expr2 ,
otherwise it is
.IR expr3 .
Only one of
.I expr2
and
.I expr3
is evaluated.
.TP
.B "= += \-= *= /= %= ^="
Assignment.  Both absolute assignment
.BI ( var " = " value )
and operator-assignment (the other forms) are supported.
.SS Control Statements
The control statements are
as follows:
.PP
.RS
.nf
\fBif (\fIcondition\fB) \fIstatement\fR [ \fBelse\fI statement \fR]
\fBwhile (\fIcondition\fB) \fIstatement\fR
\fBdo \fIstatement \fBwhile (\fIcondition\fB)\fR
\fBfor (\fIexpr1\fB; \fIexpr2\fB; \fIexpr3\fB) \fIstatement\fR
\fBfor (\fIvar \fBin\fI array\fB) \fIstatement\fR
\fBbreak\fR
\fBcontinue\fR
\fBdelete \fIarray\^\fB[\^\fIindex\^\fB]\fR
\fBdelete \fIarray\^\fR
\fBexit\fR [ \fIexpression\fR ]
\fB{ \fIstatements \fB}\fR
\fBswitch (\fIexpression\fB) {
\fBcase \fIvalue\fB|\fIregex\fB : \fIstatement
\&.\^.\^.
\fR[ \fBdefault: \fIstatement \fR]
\fB}\fR
.fi
.RE
.SS "I/O Statements"
The input/output statements are as follows:
.TP "\w'\fBprintf \fIfmt, expr-list\fR'u+1n"
\fBclose(\fIfile \fR[\fB, \fIhow\fR]\fB)\fR
Close an open file, pipe or coprocess.
The optional
.I how
should only be used when closing one end of a
two-way pipe to a coprocess.
It must be a string value, either
\fB"to"\fR or \fB"from"\fR.
.TP
.B getline
Set
.B $0
from the next input record; set
.BR NF ,
.BR NR ,
.BR FNR ,
.BR RT .
.TP
.BI "getline <" file
Set
.B $0
from the next record of
.IR file ;
set
.BR NF ,
.BR RT .
.TP
.BI getline " var"
Set
.I var
from the next input record; set
.BR NR ,
.BR FNR ,
.BR RT .
.TP
.BI getline " var" " <" file
Set
.I var
from the next record of
.IR file ;
set
.BR RT .
.TP
\fIcommand\fB | getline \fR[\fIvar\fR]
Run
.IR command ,
piping the output either into
.B $0
or
.IR var ,
as above, and
.BR RT .
.TP
\fIcommand\fB |& getline \fR[\fIvar\fR]
Run
.I command
as a coprocess
piping the output either into
.B $0
or
.IR var ,
as above, and
.BR RT .
.RI "(The " command
can also be a socket.  See the subsection
.BR "Special File Names" ,
below.)
.TP
\&\fBfflush(\fR[\fIfile\^\fR]\fB)\fR
Flush any buffers associated with the open output file or pipe
.IR file .
If
.I file
is missing or if it
is the null string,
then flush all open output files and pipes.
.TP
.B next
Stop processing the current input record.
Read the next input record
and start processing over with the first pattern in the
\*(AK program.
Upon reaching the end of the input data,
execute any
.B END
rule(s).
.TP
.B nextfile
Stop processing the current input file.  The next input record read
comes from the next input file.
Update
.B FILENAME
and
.BR ARGIND ,
reset
.B FNR
to 1, and start processing over with the first pattern in the
\*(AK program.
Upon reaching the end of the input data,
execute any
.B ENDFILE
and
.B END
rule(s).
.TP
.B print
Print the current record.
The output record is terminated with the value of
.BR ORS .
.TP
.BI print " expr-list"
Print expressions.
Each expression is separated by the value of
.BR OFS .
The output record is terminated with the value of
.BR ORS .
.TP
.BI print " expr-list" " >" file
Print expressions on
.IR file .
Each expression is separated by the value of
.BR OFS .
The output record is terminated with the value of
.BR ORS .
.TP
.BI printf " fmt, expr-list"
Format and print.
.TP
.BI printf " fmt, expr-list" " >" file
Format and print on
.IR file .
.TP
.BI system( cmd-line )
Execute the command
.IR cmd-line ,
and return the exit status.
(This may not be available on non-\*(PX systems.)
See
.I https://www.gnu.org/software/gawk/manual/html_node/I_002fO-Functions.html#I_002fO-Functions
for the full details on the exit status.
.PP
Additional output redirections are allowed for
.B print
and
.BR printf .
.TP
.BI "print .\|.\|.\& >>" " file"
Append output to the
.IR file .
.TP
.BI "print .\|.\|.\& |" " command"
Write on a pipe.
.TP
.BI "print .\|.\|.\& |&" " command"
Send data to a coprocess or socket.
(See also the subsection
.BR "Special File Names" ,
below.)
.PP
The
.B getline
command returns 1 on success, zero on end of file, and \-1 on an error.
If the
.IR errno (3)
value indicates that the I/O operation may be retried,
and \fBPROCINFO["\fIinput\^\fP", "RETRY"]\fR
is set, then \-2 is returned instead of \-1, and further calls to
.B getline
may be attempted.
Upon an error,
.B ERRNO
is set to a string describing the problem.
.PP
.BR 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
.BR getline ,
or from
.B print
or
.B printf
within a loop, you
.I must
use
.B close()
to create new instances of the command or socket.
\*(AK does not automatically close pipes, sockets, or coprocesses when
they return EOF.
.PP
The \*(AK versions of the
.B printf
statement and
.B sprintf()
function
are similar to those of C. For details, see
.IR https://www.gnu.org/software/gawk/manual/html_node/Printf.html .
.SS Special File Names
When doing I/O redirection from either
.B print
or
.B printf
into a file,
or via
.B getline
from a file,
.I gawk
recognizes certain special filenames internally.  These filenames
allow access to open file descriptors inherited from
.IR 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:
.TP "\w'\fB/dev/stdout\fR'u+1n"
.B \-
The standard input.
.TP
.B /dev/stdin
The standard input.
.TP
.B /dev/stdout
The standard output.
.TP
.B /dev/stderr
The standard error output.
.TP
.BI /dev/fd/\^ n
The file associated with the open file descriptor
.IR n .
.PP
The following special filenames may be used with the
.B |&
coprocess operator for creating TCP/IP network connections:
.TP
.PD 0
.BI /inet/tcp/ lport / rhost / rport
.TP
.PD 0
.BI /inet4/tcp/ lport / rhost / rport
.TP
.PD
.BI /inet6/tcp/ lport / rhost / rport
Files for a TCP/IP connection on local port
.I lport
to
remote host
.I rhost
on remote port
.IR rport .
Use a port of
.B 0
to have the system pick a port.
Use
.B /inet4
to force an IPv4 connection,
and
.B /inet6
to force an IPv6 connection.
Plain
.B /inet
uses the system default (most likely IPv4).
Usable only with the
.B |&
two-way I/O operator.
.TP
.PD 0
.BI /inet/udp/ lport / rhost / rport
.TP
.PD 0
.BI /inet4/udp/ lport / rhost / rport
.TP
.PD
.BI /inet6/udp/ lport / rhost / rport
Similar, but use UDP/IP instead of TCP/IP.
.SS Numeric Functions
\*(AK has the following built-in arithmetic functions:
.TP "\w'\fBsrand(\fR[\fIexpr\^\fR]\fB)\fR'u+1n"
.BI atan2( y , " x" )
Return the arctangent of
.I y/x
in radians.
.TP
.BI cos( expr )
Return the cosine of
.IR expr ,
which is in radians.
.TP
.BI exp( expr )
The exponential function.
.TP
.BI int( expr )
Truncate to integer.
.ig
.TP
.BI intdiv( num ", " denom ", " result )
Truncate
.I num
and
.I denom
to integers. Return the quotient of
.I num
divided by
.I denom
in \fIresult\fB["quotient"]\fR
and the remainder in
\fIresult\fB["remainder"]\fR.
This is a
.I gawk
extension, primarily of value when working with
arbitrarily large integers.
..
.TP
.BI log( expr )
The natural logarithm function.
.TP
.B rand()
Return a random number
.IR N ,
between zero and one,
such that 0 \(<= \fIN\fP < 1.
.TP
.BI sin( expr )
Return the sine of
.IR expr ,
which is in radians.
.TP
.BI sqrt( expr )
Return the square root of
.IR expr .
.TP
\&\fBsrand(\fR[\fIexpr\^\fR]\fB)\fR
Use
.I expr
as the new seed for the random number generator.  If no
.I expr
is provided, use the time of day.
Return the previous seed for the random
number generator.
.SS String Functions
.I Gawk
has the following built-in string functions; details are provided in
.IR https://www.gnu.org/software/gawk/manual/html_node/String-Functions .
.TP "\w'\fBsprintf(\fIfmt\^\fB, \fIexpr-list\^\fB)\fR'u+1n"
\fBasort(\fIs \fR[\fB, \fId\fR [\fB, \fIhow\fR] ]\fB)\fR
Return the number of elements in the source
array
.IR s .
Sort
the contents of
.I s
using
.IR gawk\^ "'s"
normal rules for
comparing values, and replace the indices of the
sorted values
.I s
with sequential
integers starting with 1. If the optional
destination array
.I d
is specified,
first duplicate
.I s
into
.IR d ,
and then sort
.IR d ,
leaving the indices of the
source array
.I s
unchanged. The optional string
.I how
controls the direction and the comparison mode.
Valid values for
.I how
are
described in
.IR https://www.gnu.org/software/gawk/manual/html_node/String-Functions.html#String-Functions .
.IR s " and " d
are allowed to be the same array; this only makes sense when
supplying the third argument as well.
.TP
\fBasorti(\fIs \fR[\fB, \fId\fR [\fB, \fIhow\fR] ]\fB)\fR
Return the number of elements in the source
array
.IR s .
The behavior is the same as that of
.BR asort() ,
except that the array
.I 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
.I how
is the same as for
.BR asort() .
Here too,
.IR s " and " d
are allowed to be the same array; this only makes sense when
supplying the third argument as well.
.TP
\fBgensub(\fIr\fB, \fIs\fB, \fIh \fR[\fB, \fIt\fR]\fB)\fR
Search the target string
.I t
for matches of the regular expression
.IR r .
If
.I h
is a string beginning with
.B g
or
.BR G ,
then replace all matches of
.I r
with
.IR s .
Otherwise,
.I h
is a number indicating which match of
.I r
to replace.
If
.I t
is not supplied, use
.B $0
instead.
Within the replacement text
.IR s ,
the sequence
.BI \e n\fR,
where
.I n
is a digit from 1 to 9, may be used to indicate just the text that
matched the
.IR n 'th
parenthesized subexpression.  The sequence
.B \e0
represents the entire matched text, as does the character
.BR & .
Unlike
.B sub()
and
.BR gsub() ,
the modified string is returned as the result of the function,
and the original target string is
.I not
changed.
.TP
\fBgsub(\fIr\fB, \fIs \fR[\fB, \fIt\fR]\fB)\fR
For each substring matching the regular expression
.I r
in the string
.IR t ,
substitute the string
.IR s ,
and return the number of substitutions.
If
.I t
is not supplied, use
.BR $0 .
An
.B &
in the replacement text is replaced with the text that was actually matched.
Use
.B \e&
to get a literal
.BR & .
(This must be typed as \fB"\e\e&"\fP; see
.I 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
.BR sub() ,
.BR gsub() ,
and
.BR gensub() .)
.TP
.BI index( s , " t" )
Return the index of the string
.I t
in the string
.IR s ,
or zero if
.I t
is not present.
(This implies that character indices start at one.)
.TP
\fBlength(\fR[\fIs\fR]\fB)
Return the length of the string
.IR s ,
or the length of
.B $0
if
.I s
is not supplied.
With an array argument,
.B length()
returns the number of elements in the array.
.TP
\fBmatch(\fIs\fB, \fIr \fR[\fB, \fIa\fR]\fB)\fR
Return the position in
.I s
where the regular expression
.I r
occurs, or zero if
.I r
is not present, and set the values of
.B RSTART
and
.BR RLENGTH .
Note that the argument order is the same as for the
.B ~
operator:
.IB str " ~"
.IR re .
.ft R
See
.I https://www.gnu.org/software/gawk/manual/html_node/String-Functions.html#String-Functions
for a description of how the array
.I a
is filled if it is provided.
.TP
\fBpatsplit(\fIs\fB, \fIa \fR[\fB, \fIr\fR [\fB, \fIseps\fR] ]\fB)\fR
Split the string
.I s
into the array
.I a
and the separators array
.I seps
on the regular expression
.IR r ,
and return the number of fields.
Element values are the portions of
.I s
that matched
.IR r .
The value of
.BI seps[ i ]
is the possibly null separator that appeared after
.BI a[ i ]\fR.
The value of
.B seps[0]
is the possibly null leading separator.
If
.I r
is omitted,
.B FPAT
is used instead.
The arrays
.I a
and
.I seps
are cleared first.
Splitting behaves identically to field splitting with
.BR FPAT .
.TP
\fBsplit(\fIs\fB, \fIa \fR[\fB, \fIr\fR [\fB, \fIseps\fR] ]\fB)\fR
Split the string
.I s
into the array
.I a
and the separators array
.I seps
on the regular expression
.IR r ,
and return the number of fields.  If
.I r
is omitted,
.B FS
is used instead.
The arrays
.I a
and
.I seps
are cleared first.
.BI seps[ i ]
is the field separator matched by
.I r
between
.BI a[ i ]
and
.BI a[ i +1]\fR.
Splitting behaves identically to field splitting.
.TP
.BI sprintf( fmt\^ , " expr-list\^" )
Print
.I expr-list
according to
.IR fmt ,
and return the resulting string.
.TP
.BI strtonum( str )
Examine
.IR str ,
and return its numeric value.
If
.I str
begins
with a leading
.BR 0 ,
treat it
as an octal number.
If
.I str
begins
with a leading
.B 0x
or
.BR 0X ,
treat it
as a hexadecimal number.
Otherwise, assume it is a decimal number.
.TP
\fBsub(\fIr\fB, \fIs \fR[\fB, \fIt\fR]\fB)\fR
Just like
.BR gsub() ,
but replace only the first matching substring.
Return either zero or one.
.TP
\fBsubstr(\fIs\fB, \fIi \fR[\fB, \fIn\fR]\fB)\fR
Return the at most
.IR n -character
substring of
.I s
starting at
.IR i .
If
.I n
is omitted, use the rest of
.IR s .
.TP
.BI tolower( str )
Return a copy of the string
.IR str ,
with all the uppercase characters in
.I str
translated to their corresponding lowercase counterparts.
Non-alphabetic characters are left unchanged.
.TP
.BI toupper( str )
Return a copy of the string
.IR str ,
with all the lowercase characters in
.I str
translated to their corresponding uppercase counterparts.
Non-alphabetic characters are left unchanged.
.PP
.I Gawk
is multibyte aware.  This means that
.BR index() ,
.BR length() ,
.B substr()
and
.B match()
all work in terms of characters, not bytes.
.SS Time Functions
.I Gawk
provides the following functions for obtaining time stamps and
formatting them. Details are provided in
.IR https://www.gnu.org/software/gawk/manual/html_node/Time-Functions .
.TP "\w'\fBsystime()\fR'u+1n"
\fBmktime(\fIdatespec\fR [\fB, \fIutc-flag\fR]\fB)\fR
Turn
.I datespec
into a time stamp of the same form as returned by
.BR systime() ,
and return the result.
If
.I 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
.I datespec
does not contain enough elements or if the resulting time
is out of range,
.B mktime()
returns \-1.
See
.I https://www.gnu.org/software/gawk/manual/html_node/Time-Functions.html#Time-Functions
for the details of
.IR datespec .
.TP
\fBstrftime(\fR[\fIformat \fR[\fB, \fItimestamp\fR[\fB, \fIutc-flag\fR]]]\fB)\fR
Format
.I timestamp
according to the specification in
.IR format .
If
.I utc-flag
is present and is non-zero or non-null, the result
is in UTC, otherwise the result is in local time.
The
.I timestamp
should be of the same form as returned by
.BR systime() .
If
.I timestamp
is missing, the current time of day is used.
If
.I format
is missing, a default format equivalent to the output of
.IR date (1)
is used.
The default format is available in
.BR PROCINFO["strftime"] .
See the specification for the
.B strftime()
function in ISO C for the format conversions that are
guaranteed to be available.
.TP
.B systime()
Return the current time of day as the number of seconds since the Epoch
(1970-01-01 00:00:00 UTC on \*(PX systems).
.SS Bit Manipulations Functions
.I Gawk
supplies the following bit manipulation functions.
They work by converting double-precision floating point
values to
.B 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.
.PP
The functions are:
.TP "\w'\fBrshift(\fIval\fB, \fIcount\fB)\fR'u+2n"
\fBand(\fIv1\fB, \fIv2 \fR[, ...]\fB)\fR
Return the bitwise AND of the values provided in the argument list.
There must be at least two.
.TP
\fBcompl(\fIval\fB)\fR
Return the bitwise complement of
.IR val .
.TP
\fBlshift(\fIval\fB, \fIcount\fB)\fR
Return the value of
.IR val ,
shifted left by
.I count
bits.
.TP
\fBor(\fIv1\fB, \fIv2 \fR[, ...]\fB)\fR
Return the bitwise OR of the values provided in the argument list.
There must be at least two.
.TP
\fBrshift(\fIval\fB, \fIcount\fB)\fR
Return the value of
.IR val ,
shifted right by
.I count
bits.
.TP
\fBxor(\fIv1\fB, \fIv2 \fR[, ...]\fB)\fR
Return the bitwise XOR of the values provided in the argument list.
There must be at least two.
.SS Type Functions
The following functions provide type related information about
their arguments.
.TP \w'\fBisarray(\fIx\fB)\fR'u+1n
\fBisarray(\fIx\fB)\fR
Return true if
.I x
is an array, false otherwise.
.TP
\fBtypeof(\fIx\fB)\fR
Return a string indicating the type of
.IR x .
The string will be one of
\fB"array"\fP,
\fB"number"\fP,
\fB"regexp"\fP,
\fB"string"\fP,
\fB"strnum"\fP,
\fB"unassigned"\fP,
or
\fB"undefined"\fP.
.SS Internationalization Functions
The following functions may be used from within your AWK program for
translating strings at run-time.
For full details, see
.IR https://www.gnu.org/software/gawk/manual/html_node/I18N-Functions.html#I18N-Functions .
.TP
\fBbindtextdomain(\fIdirectory \fR[\fB, \fIdomain\fR]\fB)\fR
Specify the directory where
.I gawk
looks for the
.B \&.gmo
files, in case they
will not or cannot be placed in the ``standard'' locations.
It returns the directory where
.I domain
is ``bound.''
.sp .5
The default
.I domain
is the value of
.BR TEXTDOMAIN .
If
.I directory
is the null string (\fB""\fR), then
.B bindtextdomain()
returns the current binding for the
given
.IR domain .
.TP
\fBdcgettext(\fIstring \fR[\fB, \fIdomain \fR[\fB, \fIcategory\fR]]\fB)\fR
Return the translation of
.I string
in text domain
.I domain
for locale category
.IR category .
The default value for
.I domain
is the current value of
.BR TEXTDOMAIN .
The default value for
.I category
is \fB"LC_MESSAGES"\fR.
.TP
\fBdcngettext(\fIstring1\fB, \fIstring2\fB, \fInumber \fR[\fB, \fIdomain \fR[\fB, \fIcategory\fR]]\fB)\fR
Return the plural form used for
.I number
of the translation of
.I string1
and
.I string2
in
text domain
.I domain
for locale category
.IR category .
The default value for
.I domain
is the current value of
.BR TEXTDOMAIN .
The default value for
.I category
is \fB"LC_MESSAGES"\fR.
.SS Boolean Valued Functions
You can create special Boolean-typed values; see the manual for how
they work and why they exist.
.TP
.BI mkbool( expression\^ )
Based on the boolean value of
.I expression
return either a true value or a false value.
True values have numeric value one.
False values have numeric value zero.
.SH USER-DEFINED FUNCTIONS
Functions in \*(AK are defined as follows:
.PP
.RS
\fBfunction \fIname\fB(\fIparameter list\fB) { \fIstatements \fB}\fR
.RE
.PP
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.
.PP
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:
.PP
.RS
.ft B
.nf
function  f(p, q,     a, b)	# a and b are local
{
	\&.\|.\|.
}

/abc/	{ .\|.\|.\& ; f(1, 2) ; .\|.\|.\& }
.fi
.ft R
.RE
.PP
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.
.PP
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.
.PP
Use
.BI 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 \*(lqfalling off\*(rq the
end.
.PP
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
.B @
sign, like so:
.RS
.ft B
.nf
function myfunc()
{
	print "myfunc called"
	\&.\|.\|.
}

{	.\|.\|.
	the_func = "myfunc"
	@the_func()	# call through the_func to myfunc
	.\|.\|.
}
.fi
.ft R
.RE
.PP
If
.B \-\^\-lint
has been provided,
.I 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.
.SH DYNAMICALLY LOADING NEW FUNCTIONS
You can dynamically add new functions written in C or C++ to the running
.I gawk
interpreter with the
.B @load
statement.
The full details are beyond the scope of this manual page;
see
.IR https://www.gnu.org/software/gawk/manual/html_node/Dynamic-Extensions.html#Dynamic-Extensions .
.SH SIGNALS
The
.I gawk
profiler accepts two signals.
.B SIGUSR1
causes it to dump a profile and function call stack to the
profile file, which is either
.BR awkprof.out ,
or whatever file was named with the
.B \-\^\-profile
option.  It then continues to run.
.B SIGHUP
causes
.I gawk
to dump the profile and function call stack and then exit.
.SH INTERNATIONALIZATION
String constants are sequences of characters enclosed in double
quotes.  In non-English speaking environments, it is possible to mark
strings in the \*(AK program as requiring translation to the local
natural language. Such strings are marked in the \*(AK program with
a leading underscore (\*(lq_\*(rq).  For example,
.sp
.RS
.ft B
gawk 'BEGIN { print "hello, world" }'
.RE
.sp
.ft R
always prints
.BR "hello, world" .
But,
.sp
.RS
.ft B
gawk 'BEGIN { print _"hello, world" }'
.RE
.sp
.ft R
might print
.B "bonjour, monde"
in France.
See
.I https://www.gnu.org/software/gawk/manual/html_node/Internationalization.html#Internationalization
for the steps involved in producing and running a localizable
\*(AK program.
.SH GNU EXTENSIONS
.I Gawk
has a too-large number of extensions to \*(PX
.IR awk .
They are described in
.IR https://www.gnu.org/software/gawk/manual/html_node/POSIX_002fGNU.html .
All the extensions
can be disabled by
invoking
.I gawk
with the
.B \-\^\-traditional
or
.B \-\^\-posix
options.
.SH ENVIRONMENT VARIABLES
The
.B AWKPATH
environment variable can be used to provide a list of directories that
.I gawk
searches when looking for files named via the
.BR \-f ,
.BR \-\^\-file ,
.B \-i
and
.B \-\^\-include
options, and the
.B @include
directive.  If the initial search fails, the path is searched again after
appending
.B \&.awk
to the filename.
.PP
The
.B AWKLIBPATH
environment variable can be used to provide a list of directories that
.I gawk
searches when looking for files named via the
.B \-l
and
.B \-\^\-load
options.
.PP
The
.B GAWK_PERSIST_FILE
environment variable, if present, specifies a file to use as
the backing store for persistent memory.
.IR "This is an experimental feature" .
See \*(EP for the details.
.PP
The
.B 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.
.PP
For connection to a remote host via socket,
.B GAWK_SOCK_RETRIES
controls the number of retries, and
.B GAWK_MSEC_SLEEP
the interval between retries.
The interval is in milliseconds. On systems that do not support
.IR usleep (3),
the value is rounded up to an integral number of seconds.
.PP
If
.B POSIXLY_CORRECT
exists in the environment, then
.I gawk
behaves exactly as if
.B \-\^\-posix
had been specified on the command line.
If
.B \-\^\-lint
has been specified,
.I gawk
issues a warning message to this effect.
.ig
.PP
Set
.B GAWK_NO_MPFR_WARN
in the environment to silence the warning about MPFR mode
being deprecated.
..
.SH EXIT STATUS
If the
.B exit
statement is used with a value,
then
.I gawk
exits with
the numeric value given to it.
.PP
Otherwise, if there were no problems during execution,
.I gawk
exits with the value of the C constant
.BR EXIT_SUCCESS .
This is usually zero.
.PP
If an error occurs,
.I gawk
exits with the value of
the C constant
.BR EXIT_FAILURE .
This is usually one.
.PP
If
.I gawk
exits because of a fatal error, the exit
status is 2.  On non-POSIX systems, this value may be mapped to
.BR EXIT_FAILURE .
.SH VERSION INFORMATION
This man page documents
.IR gawk ,
version 5.2.
.SH AUTHORS
The original version of \*(UX
.I awk
was designed and implemented by Alfred Aho,
Peter Weinberger, and Brian Kernighan of Bell Laboratories.  Brian Kernighan
continues to maintain and enhance it.
.PP
Paul Rubin and Jay Fenlason,
of the Free Software Foundation, wrote
.IR gawk ,
to be compatible with the original version of
.I awk
distributed in Seventh Edition \*(UX.
John Woods contributed a number of bug fixes.
David Trueman, with contributions
from Arnold Robbins, made
.I gawk
compatible with the new version of \*(UX
.IR awk .
Arnold Robbins is the current maintainer.
.PP
See \*(EP for a full list of the contributors to
.I gawk
and its documentation.
.PP
See the
.B README
file in the
.I gawk
distribution for up-to-date information about maintainers
and which ports are currently supported.
.SH BUG REPORTS
If you find a bug in
.IR gawk ,
please use the
.IR gawkbug (1)
program to report it.
.PP
Full instructions for reporting a bug are provided in
.IR https://www.gnu.org/software/gawk/manual/html_node/Bugs.html .
.I Please
carefully read and follow the instructions given there.
This will make bug reporting and resolution much easier for everyone involved.
Really.
.SH BUGS
The
.B \-F
option is not necessary given the command line variable assignment feature;
it remains only for backwards compatibility.
.PP
This manual page is too long;
.I gawk
has too many features.
.SH SEE ALSO
.IR egrep (1),
.IR sed (1),
.IR gawkbug (1),
.IR printf (3),
and
.IR strftime (3).
.PP
.IR "The AWK Programming Language" ,
Alfred V.\& Aho, Brian W.\& Kernighan, Peter J.\& Weinberger,
Addison-Wesley, 1988.  ISBN 0-201-07981-X.
.PP
\*(EP,
Edition 5.2, shipped with the
.I gawk
source.
The current version of this document is available online at
.IR https://www.gnu.org/software/gawk/manual .
.PP
The GNU
.B gettext
documentation, available online at
.IR https://www.gnu.org/software/gettext .
.SH EXAMPLES
.nf
Print and sort the login names of all users:

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

.ft R
Count lines in a file:

.ft B
		{ nlines++ }
	END	{ print nlines }

.ft R
Precede each line by its number in the file:

.ft B
	{ print FNR, $0 }

.ft R
Concatenate and line number (a variation on a theme):

.ft B
	{ print NR, $0 }

.ft R
Run an external command for particular lines of data:

.ft B
	tail \-f access_log |
	awk '/myhome.html/ { system("nmap " $1 ">> logdir/myhome.html") }'
.ft R
.fi
.ig
.SH ACKNOWLEDGEMENTS
Brian Kernighan
provided valuable assistance during testing and debugging.
We thank him.
..
.SH COPYING PERMISSIONS
Copyright \(co 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
Free Software Foundation, Inc.
.PP
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.
.ig
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).
..
.PP
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.
.PP
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.