gawk

NAME

SYNOPSIS

DESCRIPTION

PREFACE

OPTION FORMAT

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

-F fs, --field-separator fs

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

-v var=val, --assign var =val

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

-b, --characters-as-bytes

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

-c, --traditional

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

-C, --copyright

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

-d[file], --dump-variables[=file]

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

-D[file], --debug[=file]

Enable debugging of AWK programs. By default, the debugger reads commands interactively from the keyboard (standard input). The optional file argument specifies a file with a list of commands for the debugger to execute non-interactively. In this mode of execution, gawk loads the AWK source code and then prompts for debugging commands. Gawk can only debug AWK program source provided with the -f and --include options. The debugger is documented in GAWK: Effective AWK Programming; see https://www.gnu.org/software/gawk/manual/html_node/Debugger.html#Debugger.

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

Use program-text as AWK program source code. Each argument supplied via -e is treated as if it begins with an implicit @namespace "awk" statement.

-E file, --exec file

Similar to -f, however, this is option is the last one processed. This should be used with #! scripts, particularly for CGI applications, to avoid passing in options or source code (!) on the command line from a URL. This option disables command-line variable assignments.

-g, --gen-pot

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

-h, --help

Print a relatively short summary of the available options on the standard output. Per the GNU Coding Standards, these options cause an immediate, successful exit.

-i include-file, --include include-file

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

-I, --trace

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

-l lib, --load lib

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

-L [value], --lint[=value]

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

-M, --bignum

Force arbitrary precision arithmetic on numbers. This option has no effect if gawk is not compiled to use the GNU MPFR and GMP libraries. (In such a case, gawk issues a warning.) NOTE: This feature is on parole. The primary gawk maintainer is no longer supporting it, although there is a member of the development team who is. If this situation changes, the feature will be removed from gawk.

-n, --non-decimal-data

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

-N, --use-lc-numeric

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

-o[file], --pretty-print[=file]

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

-O, --optimize

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

-p[prof-file], --profile[=prof-file]

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

-P, --posix

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

-r, --re-interval

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

-s, --no-optimize

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

-S, --sandbox

Run gawk in sandbox mode, disabling the system() function, input redirection with getline, output redirection with print and printf, and loading dynamic extensions. Command execution (through pipelines) is also disabled.

-t, --lint-old

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

-V, --version

Print version information for this particular copy of gawk on the standard output. This is useful when reporting bugs. Per the GNU Coding Standards, these options cause an immediate, successful exit.

--

Signal the end of options. This is useful to allow further arguments to the AWK program itself to start with a “-”.

AWK PROGRAM EXECUTION

Command Line Directories

VARIABLES, RECORDS AND FIELDS

Records

Fields

Built-in Variables

ARGC

The number of command line arguments.

ARGIND

The index in ARGV of the current file being processed.

ARGV

Array of command line arguments. The array is indexed from 0 to ARGC - 1.

BINMODE

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

CONVFMT

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

ENVIRON

An array containing the values of the current environment. The array is indexed by the environment variables, each element being the value of that variable.

ERRNO

If a system error occurs either doing a redirection for getline, during a read for getline, or during a close(), then ERRNO is set to a string describing the error. The value is subject to translation in non-English locales.

FIELDWIDTHS

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

FILENAME

The name of the current input file. If no files are specified on the command line, the value of FILENAME is “-”. However, FILENAME is undefined inside the BEGIN rule (unless set by getline).

FNR

The input record number in the current input file.

FPAT

A regular expression describing the contents of the fields in a record. When set, gawk parses the input into fields, where the fields match the regular expression, instead of using the value of FS as the field separator.

FS

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

FUNCTAB

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

IGNORECASE

Controls the case-sensitivity of all regular expression and string operations. See https://www.gnu.org/software/gawk/manual/html_node/Case_002dsensitivity.html for details.

LINT

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

NF

The number of fields in the current input record.

NR

The total number of input records seen so far.

OFMT

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

OFS

The output field separator, a space by default.

ORS

The output record separator, by default a newline.

PREC

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

PROCINFO

The elements of this array provide access to information about the running AWK program. See https://www.gnu.org/software/gawk/manual/html_node/Auto_002dset for the details.

ROUNDMODE

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

RS

The input record separator, by default a newline.

RT

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

RSTART

The index of the first character matched by match(); 0 if no match.

RLENGTH

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

SUBSEP

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

SYMTAB

An array whose indices are the names of all currently defined global variables and arrays in the program. You may not use the delete statement with the SYMTAB array, nor assign to elements with an index that is not a variable name.

TEXTDOMAIN

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

Arrays

if (val in array)
	print array[val]

Namespaces

Variable Typing And Conversion

Octal and Hexadecimal Constants

String Constants

Regexp Constants

PATTERNS AND ACTIONS

Patterns

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

Actions

Operators

(...)

Grouping

$

Field reference.

++ --

Increment and decrement, both prefix and postfix.

^

Exponentiation.

+ - !

Unary plus, unary minus, and logical negation.

* / %

Multiplication, division, and modulus.

+ -

Addition and subtraction.

space

String concatenation.

| |&

Piped I/O for getline, print, and printf.

< > <= >= == !=

The regular relational operators.

~ !~

Regular expression match, negated match.

in

Array membership.

&&

Logical AND.

||

Logical OR.

?:

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

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

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

Control Statements

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

close(file [, how])

Close an open file, pipe or coprocess. The optional how should only be used when closing one end of a two-way pipe to a coprocess. It must be a string value, either "to" or "from".

getline

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

getline <file

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

getline var

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

getline var <file

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

command | getline [var]

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

command |& getline [var]

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

fflush([file])

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

next

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

nextfile

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

print

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

print expr-list

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

print expr-list >file

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

printf fmt, expr-list

Format and print.

printf fmt, expr-list >file

Format and print on file.

system(cmd-line)

Execute the command cmd-line, and return the exit status. (This may not be available on non-POSIX systems.) See https://www.gnu.org/software/gawk/manual/html_node/I_002fO-Functions.html#I_002fO-Functions for the full details on the exit status.

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.)

Special File Names

-

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.

/inet/tcp/lport/rhost/rport

/inet4/tcp/lport/rhost/rport

/inet6/tcp/lport/rhost/rport

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

/inet/udp/lport/rhost/rport

/inet4/udp/lport/rhost/rport

/inet6/udp/lport/rhost/rport

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

Numeric 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

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

Return the number of elements in the source array s. Sort the contents of s using gawk's normal rules for comparing values, and replace the indices of the sorted values s with sequential integers starting with 1. If the optional destination array d is specified, first duplicate s into d, and then sort d, leaving the indices of the source array s unchanged. The optional string how controls the direction and the comparison mode. Valid values for how are described in https://www.gnu.org/software/gawk/manual/html_node/String-Functions.html#String-Functions. s and d are allowed to be the same array; this only makes sense when supplying the third argument as well.

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

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

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

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

gsub(r, s [, t])

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

index(s, t)

Return the index of the string t in the string s, or zero if t is not present. (This implies that character indices start at one.)

length([s])

Return the length of the string s, or the length of $0 if s is not supplied. With an array argument, length() returns the number of elements in the array.

match(s, r [, a])

Return the position in s where the regular expression r occurs, or zero if r is not present, and set the values of RSTART and RLENGTH. Note that the argument order is the same as for the ~ operator: str ~ re. See https://www.gnu.org/software/gawk/manual/html_node/String-Functions.html#String-Functions for a description of how the array a is filled if it is provided.

patsplit(s, a [, r [ , seps] ])

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

split(s, a [, r [, seps] ])

Split the string s into the array a and the separators array seps on the regular expression r, and return the number of fields. If r is omitted, FS is used instead. The arrays a and seps are cleared first. seps[i] is the field separator matched by r between a[i] and a[i+1]. Splitting behaves identically to field splitting.

sprintf(fmt, expr-list)

Print expr-list according to fmt, and return the resulting string.

strtonum(str)

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

sub(r, s [, t])

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

substr(s, i [, n])

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

tolower(str)

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

toupper(str)

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

Time Functions

mktime(datespec [, utc-flag])

Turn datespec into a time stamp of the same form as returned by systime(), and return the result. If utc-flag is present and is non-zero or non-null, the time is assumed to be in the UTC time zone; otherwise, the time is assumed to be in the local time zone. If datespec does not contain enough elements or if the resulting time is out of range, mktime() returns -1. See https://www.gnu.org/software/gawk/manual/html_node/Time-Functions.html#Time-Functions for the details of datespec.

strftime([format [, timestamp[, utc-flag]]])

Format timestamp according to the specification in format. If utc-flag is present and is non-zero or non-null, the result is in UTC, otherwise the result is in local time. The timestamp should be of the same form as returned by systime(). If timestamp is missing, the current time of day is used. If format is missing, a default format equivalent to the output of date(1) is used. The default format is available in PROCINFO["strftime"]. See the specification for the strftime() function in ISO C for the format conversions that are guaranteed to be available.

systime()

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

Bit Manipulations Functions

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

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", "regexp", "string", "strnum", "unassigned", or "undefined".

Internationalization Functions

bindtextdomain(directory [, domain] )

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

dcgettext(string [, domain [, category]])

Return the translation of string in text domain domain for locale category category. The default value for domain is the current value of TEXTDOMAIN. The default value for category is "LC_MESSAGES".

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

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

Boolean Valued Functions

mkbool(expression)

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

USER-DEFINED FUNCTIONS

function  f(p, q,     a, b)	# a and b are local
{
	...
}

/abc/	{ ... ; f(1, 2) ; ... }

function myfunc()
{
	print "myfunc called"
	...
}

{	...
	the_func = "myfunc"
	@the_func()	# call through the_func to myfunc
	...
}

DYNAMICALLY LOADING NEW FUNCTIONS

SIGNALS

INTERNATIONALIZATION

GNU EXTENSIONS

ENVIRONMENT VARIABLES

EXIT STATUS

VERSION INFORMATION

AUTHORS

BUG REPORTS

BUGS

SEE ALSO

EXAMPLES

Print and sort the login names of all users:

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

Count lines in a file:

		{ nlines++ }
	END	{ print nlines }

Precede each line by its number in the file:

	{ print FNR, $0 }

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

	{ print NR, $0 }

Run an external command for particular lines of data:

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

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