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GAWK(1) Utility Commands GAWK(1)
gawk - pattern scanning and processing language
gawk [ POSIX or GNU style options ] -f program-file [ -- ] file
...
gawk [ POSIX or GNU style options ] [ -- ] program-text file ...
This manual page is provided as a courtesy. Please note that the
One Source Of Truth for gawk is the Texinfo manual, GAWK:
Effective AWK Programming, available online in several formats at
this link ⟨https://www.gnu.org/software/gawk/manual⟩. The Texinfo
manual should always be considered to be authoritative.
This manual page is intentionally as terse as possible. Full
details are provided in in the manual, 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.
Furthermore, the gawk maintainer reserves the right in the future
to remove this manual page from the distribution in order to ease
his maintenance burden.
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 first edition (1987) of 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.
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 “--”.
Gawk accepts the following options. Standard options are listed
first, followed by options for gawk extensions, listed
alphabetically by short option. A full description of the options
is provided at this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Options⟩.
-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.
-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.
-b, --characters-as-bytes
Treat all input data as single-byte characters. The
--posix option overrides this one.
-c, --traditional
Run in compatibility mode.
-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. For details about the
debugger, see this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Debugger⟩.
-e program-text, --source program-text
Use program-text as AWK program source code.
-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 doesn't run.
-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. For more information, see this
link
⟨https://www.gnu.org/software/gawk/manual/html_node/AWKPATH-
Variable⟩.
-I, --trace
Print to standard error the internal byte code names as
they are executed when running the program.
-k, --csv
Enable CSV special processing. See Comma Separated Values,
below, for more information.
-l lib, --load lib
Load a gawk extension from the shared library lib. For
more information, see this link
⟨https://www.gnu.org/software/gawk/manual/html_node/AWKLIBPATH-
Variable⟩.
-L [value], --lint[=value]
Provide warnings about constructs that are dubious or non-
portable to other AWK implementations. See this link
⟨https://www.gnu.org/software/gawk/manual/html_node/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.)
-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
Apply gawk's default optimizations to the program's
internal representation. This is the 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. This option implies --no-optimize.
-P, --posix
Turn on compatibility mode, and disable a number of common
extensions.
-s, --no-optimize
Disable gawk's default optimizations upon the internal
representation of the program.
-S, --sandbox
Run gawk in sandbox mode.
-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.
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. 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.
See this link
⟨https://www.gnu.org/software/gawk/manual/html_node/AWKPATH-
Variable⟩.
The environment variable AWKLIBPATH specifies a search path to use
when finding source files named with the --load option. See this
link
⟨https://www.gnu.org/software/gawk/manual/html_node/AWKLIBPATH-
Variable⟩.
Gawk executes AWK programs as follows: 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.
A filename on the command line of the form var=val is treated as a
variable assignment. The variable var is 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).
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
You control how records are separated by assigning values to the
built-in variable RS. See this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Records⟩ for
the details. Normally, records are separated by newline
characters.
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 this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Fields⟩.
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.
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 record
determination and field splitting are different: 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 this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Comma-
Separated-Fields⟩ for more details.
Built-in Variables
Gawk's built-in variables are listed below. This list is
purposely terse. For details, see this link
⟨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 this link
⟨https://www.gnu.org/software/gawk/manual/html_node/PC-
Using⟩ for the details.
CONVFMT
The conversion format for numbers, "%.6g", by default.
ENVIRON
An array containing the values of the current environment.
ERRNO A string describing the problem if a system error occurs
doing a redirection for getline, during a read for getline,
or during a close().
FIELDWIDTHS
A whitespace-separated list of field widths. See this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Constant-
Size⟩.
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. See this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Splitting-
By-Content⟩.
FS The input field separator, a space by default. See this
link
⟨https://www.gnu.org/software/gawk/manual/html_node/Field-
Separators⟩.
FUNCTAB
An array whose indices and corresponding values are the
names of all the user-defined or extension functions in the
program.
IGNORECASE
Controls the case-sensitivity of all regular expression and
string operations. See this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Case_002dsensitivity⟩.
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 this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Auto_002dset⟩.
ROUNDMODE
The rounding mode to use for arbitrary precision arithmetic
on numbers, by default "N" (IEEE-754 roundTiesToEven mode).
See this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Setting-
the-rounding-mode⟩.
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.
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 simulates
multidimensional 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. See this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Arrays⟩.
Namespaces
Gawk provides a simple namespace facility to help work around the
fact that all variables in AWK are global. For more details, see
this link
⟨https://www.gnu.org/software/gawk/manual/html_node/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).
Much more (important!) detail may be found in the manual. See this
link
⟨https://www.gnu.org/software/gawk/manual/html_node/Typing-and-
Comparison⟩.
Octal and Hexadecimal Constants
You may use C-style octal and hexadecimal constants in your AWK
program source code.
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 this link
⟨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.
Gawk provides strongly typed regular expression constants. These
are written with a leading @ symbol like so: @/value/. Such
constants may be assigned to scalars (variables, array elements)
and passed to user-defined functions. Variables that have been so
assigned have regular expression type.
AWK is a line-oriented language. The pattern comes first, and
then the action. Action statements are enclosed in { and }.
Either the pattern may be missing, or the action may be missing,
but, of course, not both. If the pattern is missing, the action
executes for every single record of input. A missing action is
equivalent to { print } which prints the entire record.
Comments begin with the # character, and continue until the end of
the line. Empty lines may be used to separate statements. See
this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Statements_002fLines⟩
for the rules about when statements continue across lines.
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
execute in order as if all the statements had been written in a
single BEGIN rule. They execute before any of the input is read.
Similarly, all the END rule statements execute 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, nor may they have missing action parts.
BEGINFILE and ENDFILE are additional special patterns whose
actions execute before reading the first record of each command-
line input file and after reading the last record of each file.
See this link
⟨https://www.gnu.org/software/gawk/manual/html_node/BEGINFILE_002fENDFILE⟩.
For more information on patterns and their constituent elements,
see this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Pattern-
Overview⟩.
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, of 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. See this link
⟨https://www.gnu.org/software/gawk/manual/html_node/I_002fO-
Functions⟩.
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.
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.
See this link
⟨https://www.gnu.org/software/gawk/manual/html_node/I_002fO-
Functions⟩ for more details.
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. Upon an error, ERRNO describes the problem.
It may be possible to retry failing I/O; see this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Retrying-
Input⟩.
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. See this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Printf⟩.
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.
Numeric Functions
AWK has the following built-in arithmetic functions:
atan2(y, x)
Return the arctangent of y/x in radians.
cos(expr)
Return the cosine of expr, which is in radians.
exp(expr)
The exponential function.
int(expr)
Truncate to integer.
log(expr)
The natural logarithm function.
rand() Return a random number N, between zero and one, such that 0
≤ N < 1.
sin(expr)
Return the sine of expr, which is in radians.
sqrt(expr)
Return the square root of expr.
srand([expr])
Use expr as the new seed for the random number generator.
If no expr is provided, use the time of day. Return the
previous seed for the random number generator.
String Functions
Gawk has the following built-in string functions; details are
provided in this link
⟨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, replacing the indices of the sorted
values with integers starting with 1. If given the
destination array d, duplicate s into d, and then sort d,
leaving the indices of s unchanged. The optional string
how controls the direction and the comparison mode. See
this link
⟨https://www.gnu.org/software/gawk/manual/html_node/String-
Functions⟩ for valid values for how. s and d may 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. Like
asort(), except that the array indices are used for
sorting.
gensub(r, s, h [, t])
Search the target string t for matches of the regular
expression r. See this link
⟨https://www.gnu.org/software/gawk/manual/html_node/String-
Functions⟩.
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 &.
index(s, t)
Return the index of the string t in the string s, or zero
if t is not present.
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.
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. 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. 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. See the manual
for the details.
sub(r, s [, t])
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.
toupper() and tolower() are locale-aware.
Time Functions
Gawk provides the following functions for obtaining time stamps
and formatting them. Details are provided in this link
⟨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.
strftime([format [, timestamp[, utc-flag]]])
Format timestamp according to the specification in format.
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. 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 this
link
⟨https://www.gnu.org/software/gawk/manual/html_node/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.”
dcgettext(string [, domain [, category]])
Return the translation of string in text domain domain for
locale category category.
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.
Boolean Valued Functions
You can create special Boolean-typed values; see this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Boolean-
Functions⟩ 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.
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. Functions may be called
indirectly; see this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Indirect-Calls⟩
for the details.
The left parenthesis in a function call is required to immediately
follow the function name, without any intervening whitespace.
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.
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 this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Dynamic-
Extensions⟩.
The gawk profiler accepts two signals. SIGUSR1 causes it to dump
a profile and function call stack to the profile file, which is
either awkprof.out, or whatever file was named with the --profile
option. It then continues to run. SIGHUP causes gawk to dump the
profile and function call stack and then exit.
String constants are sequences of characters enclosed in double
quotes. In non-English speaking environments, it is possible to
mark strings in the AWK program as requiring translation to the
local natural language. Such strings are marked in the AWK
program with a leading underscore (“_”). See this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Internationalization⟩
for the steps involved in producing and running a localizable AWK
program.
Gawk has a too-large number of extensions to POSIX awk. They are
described in this link
⟨https://www.gnu.org/software/gawk/manual/html_node/POSIX_002fGNU⟩.
All the extensions can be disabled by invoking gawk with the
--traditional or --posix options.
AWKPATH provides 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.
AWKLIBPATH provides a list of directories that gawk searches when
looking for files named via the -l and --load options and the
@load directive.
GAWK_PERSIST_FILE, if present, specifies a file to use as the
backing store for persistent memory. See this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Persistent-
Memory⟩.
GAWK_READ_TIMEOUT specifies 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, gawk behaves exactly
as if --posix had been specified on the command line. With
--lint, gawk issues a warning message to this effect.
If the exit statement is used with a value, then gawk exits with
the numeric value given to it. Otherwise, if there were no
problems during execution, gawk exits with the value of the C
constant EXIT_SUCCESS. This is usually zero.
If an error occurs, gawk exits with the value of the C constant
EXIT_FAILURE. This is usually one. If gawk exits because of a
fatal error, the exit status is 2. On non-POSIX systems, this
value may be mapped to EXIT_FAILURE.
This man page documents gawk, version 5.4.
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 this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Contributors⟩
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.
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 this link
⟨https://www.gnu.org/software/gawk/manual/html_node/Bugs⟩. 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.
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.
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 this link ⟨https://www.gnu.org/software/gawk/manual⟩.
The GNU gettext documentation, available online at this link
⟨https://www.gnu.org/software/gettext⟩.
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") }'
Copyright © 1989, 1991–1999, 2001–2005, 2007, 2009–2026, 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 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.
This page is part of the gawk (GNU awk) project. Information
about the project can be found at
⟨http://www.gnu.org/software/gawk/⟩. If you have a bug report for
this manual page, see
⟨http://pkg-shadow.alioth.debian.org/getinvolved.php⟩. This page
was obtained from the project's upstream Git repository
⟨git://git.savannah.gnu.org/gawk.git⟩ on 2026-08-03. (At that
time, the date of the most recent commit that was found in the
repository was 2026-08-01.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
Free Software Foundation June 25 2026 GAWK(1)
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