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 ...
Gawk is the GNU Project's implementation of the AWK programming
language. It conforms to the definition of the language in the POSIX
1003.1 standard. This version in turn is based on the description in
The AWK Programming Language, by Aho, Kernighan, and Weinberger.
Gawk provides the additional features found in the current version of
Brian Kernighan's awk and numerous GNU-specific extensions.
The command line consists of options to gawk itself, the AWK program
text (if not supplied via the -f or --include options), and values to
be made available in the ARGC and ARGV pre-defined AWK variables.
When gawk is invoked with the --profile option, it starts gathering
profiling statistics from the execution of the program. Gawk runs
more slowly in this mode, and automatically produces an execution
profile in the file awkprof.out when done. See the --profile option,
below.
Gawk also has an integrated debugger. An interactive debugging
session can be started by supplying the --debug option to the command
line. In this mode of execution, gawk loads the AWK source code and
then prompts for debugging commands. Gawk can only debug AWK program
source provided with the -f and --include options. The debugger is
documented in GAWK: Effective AWK Programming.
Gawk options may be either traditional POSIX-style one letter
options, or GNU-style long options. POSIX options start with a
single “-”, while long options start with “--”. Long options are
provided for both GNU-specific features and for POSIX-mandated
features.
Gawk-specific options are typically used in long-option form.
Arguments to long options are either joined with the option by an =
sign, with no intervening spaces, or they may be provided in the next
command line argument. Long options may be abbreviated, as long as
the abbreviation remains unique.
Additionally, every long option has a corresponding short option, so
that the option's functionality may be used from within #!
executable scripts.
Gawk accepts the following options. Standard options are listed
first, followed by options for gawk extensions, listed alphabetically
by short option.
-f program-file
--file program-file
Read the AWK program source from the file program-file,
instead of from the first command line argument. Multiple -f
(or --file) options may be used. Files read with -f are
treated as if they begin with an implicit @namespace "awk"
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. In other
words, don't pay any attention to the locale information when
attempting to process strings as multibyte characters. The
--posix option overrides this one.
-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. See GNU EXTENSIONS,
below, for more information.
-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. If no file is provided, gawk uses a file
named awkvars.out in the current directory.
Having a list of all the global variables is a good way to
look for typographical errors in your programs. You would
also use this option if you have a large program with a lot of
functions, and you want to be sure that your functions don't
inadvertently use global variables that you meant to be local.
(This is a particularly easy mistake to make with simple
variable names like i, j, and so on.)
-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.
-e program-text
--source program-text
Use program-text as AWK program source code. This option
allows the easy intermixing of library functions (used via the
-f and --include options) with source code entered on the
command line. It is intended primarily for medium to large
AWK programs used in shell scripts. Each argument supplied
via -e is treated as if it begins with an implicit @namespace
"awk" statement.
-E file
--exec file
Similar to -f, however, this is option is the last one
processed. This should be used with #! scripts, particularly
for CGI applications, to avoid passing in options or source
code (!) on the command line from a URL. This option disables
command-line variable assignments.
-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. See the GNU gettext
distribution for more information on .pot files.
-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.
-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. With an optional
argument of fatal, lint warnings become fatal errors. This
may be drastic, but its use will certainly encourage the
development of cleaner AWK programs. With an optional
argument of invalid, only warnings about things that are
actually invalid are issued. (This is not fully implemented
yet.) With an optional argument of no-ext, warnings about
gawk extensions are disabled.
-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. Although the POSIX standard requires this
behavior, and gawk does so when --posix is in effect, the
default is to follow traditional behavior and use a period as
the decimal point, even in locales where the period is not the
decimal point character. This option overrides the default
behavior, without the full draconian strictness of the --posix
option.
-o[file]
--pretty-print[=file]
Output a pretty printed version of the program to file. If no
file is provided, gawk uses a file named awkprof.out in the
current directory. This option implies --no-optimize.
-O
--optimize
Enable gawk's default optimizations upon the internal
representation of the program. Currently, this just includes
simple constant folding. This option is on by default.
-p[prof-file]
--profile[=prof-file]
Start a profiling session, and send the profiling data to
prof-file. The default is awkprof.out. The profile contains
execution counts of each statement in the program in the left
margin and function call counts for each user-defined
function. This option implies --no-optimize.
-P
--posix
This turns on compatibility mode, with the following
additional restrictions:
· \x escape sequences are not recognized.
· You cannot continue lines after ? and :.
· The synonym func for the keyword function is not recognized.
· The operators ** and **= cannot be used in place of ^ and
^=.
-r
--re-interval
Enable the use of interval expressions in regular expression
matching (see Regular Expressions, below). Interval
expressions were not traditionally available in the AWK
language. The POSIX standard added them, to make awk and
egrep consistent with each other. They are enabled by
default, but this option remains for use together with
--traditional.
-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. This effectively blocks
a script from accessing local resources, except for the files
specified on the command line.
-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 mainly for knowing if the
current copy of gawk on your system is up to date with respect
to whatever the Free Software Foundation is distributing.
This is also useful when reporting bugs. (Per the GNU Coding
Standards, these options cause an immediate, successful exit.)
-- Signal the end of options. This is useful to allow further
arguments to the AWK program itself to start with a “-”. This
provides consistency with the argument parsing convention used
by most other POSIX programs.
In compatibility mode, any other options are flagged as invalid, but
are otherwise ignored. In normal operation, as long as program text
has been supplied, unknown options are passed on to the AWK program
in the ARGV array for processing. This is particularly useful for
running AWK programs via the #! executable interpreter mechanism.
For POSIX compatibility, the -W option may be used, followed by the
name of a long option.
An AWK program consists of a sequence of optional directives,
pattern-action statements, and optional function definitions.
@include "filename"
@load "filename"
@namespace "name"
pattern { action statements }
function name(parameter list) { statements }
Gawk first reads the program source from the program-file(s) if
specified, from arguments to --source, or from the first non-option
argument on the command line. The -f and --source options may be
used multiple times on the command line. Gawk reads the program text
as if all the program-files and command line source texts had been
concatenated together. This is useful for building libraries of AWK
functions, without having to include them in each new AWK program
that uses them. It also provides the ability to mix library
functions with command line programs.
In addition, lines beginning with @include may be used to include
other source files into your program, making library use even easier.
This is equivalent to using the --include option.
Lines beginning with @load may be used to load extension functions
into your program. This is equivalent to using the --load option.
The environment variable AWKPATH specifies a search path to use when
finding source files named with the -f and --include options. If
this variable does not exist, the default path is
".:/usr/local/share/awk". (The actual directory may vary, depending
upon how gawk was built and installed.) If a file name given to the
-f option contains a “/” character, no path search is performed.
The environment variable AWKLIBPATH specifies a search path to use
when finding source files named with the --load option. If this
variable does not exist, the default path is "/usr/local/lib/gawk".
(The actual directory may vary, depending upon how gawk was built and
installed.)
Gawk executes AWK programs in the following order. First, all
variable assignments specified via the -v option are performed.
Next, gawk compiles the program into an internal form. Then, gawk
executes the code in the BEGIN rule(s) (if any), and then proceeds to
read each file named in the ARGV array (up to ARGV[ARGC-1]). If
there are no files named on the command line, gawk reads the standard
input.
If a filename on the command line has the form var=val it is treated
as a variable assignment. The variable var will be assigned the
value val. (This happens after any BEGIN rule(s) have been run.)
Command line variable assignment is most useful for dynamically
assigning values to the variables AWK uses to control how input is
broken into fields and records. It is also useful for controlling
state if multiple passes are needed over a single data file.
If the value of a particular element of ARGV is empty (""), gawk
skips over it.
For each input file, if a BEGINFILE rule exists, gawk executes the
associated code before processing the contents of the file.
Similarly, gawk executes the code associated with ENDFILE after
processing the file.
For each record in the input, gawk tests to see if it matches any
pattern in the AWK program. For each pattern that the record
matches, gawk executes the associated action. The patterns are
tested in the order they occur in the program.
Finally, after all the input is exhausted, gawk executes the code in
the END rule(s) (if any).
Command Line Directories
According to POSIX, files named on the awk command line must be text
files. The behavior is ``undefined'' if they are not. Most versions
of awk treat a directory on the command line as a fatal error.
Starting with version 4.0 of gawk, a directory on the command line
produces a warning, but is otherwise skipped. If either of the
--posix or --traditional options is given, then gawk reverts to
treating directories on the command line as a fatal error.
AWK variables are dynamic; they come into existence when they are
first used. Their values are either floating-point numbers or
strings, or both, depending upon how they are used. Additionally,
gawk allows variables to have regular-expression type. AWK also has
one dimensional arrays; arrays with multiple dimensions may be
simulated. Gawk provides true arrays of arrays; see Arrays, below.
Several pre-defined variables are set as a program runs; these are
described as needed and summarized below.
Records
Normally, records are separated by newline characters. You can
control how records are separated by assigning values to the built-in
variable RS. If RS is any single character, that character separates
records. Otherwise, RS is a regular expression. Text in the input
that matches this regular expression separates the record. However,
in compatibility mode, only the first character of its string value
is used for separating records. If RS is set to the null string,
then records are separated by empty lines. When RS is set to the
null string, the newline character always acts as a field separator,
in addition to whatever value FS may have.
Fields
As each input record is read, gawk splits the record into fields,
using the value of the FS variable as the field separator. If FS is
a single character, fields are separated by that character. If FS is
the null string, then each individual character becomes a separate
field. Otherwise, FS is expected to be a full regular expression.
In the special case that FS is a single space, fields are separated
by runs of spaces and/or tabs and/or newlines. NOTE: The value of
IGNORECASE (see below) also affects how fields are split when FS is a
regular expression, and how records are separated when RS is a
regular expression.
If the FIELDWIDTHS variable is set to a space-separated list of
numbers, each field is expected to have fixed width, and gawk splits
up the record using the specified widths. Each field width may
optionally be preceded by a colon-separated value specifying the
number of characters to skip before the field starts. The value of
FS is ignored. Assigning a new value to FS or FPAT overrides the use
of FIELDWIDTHS.
Similarly, if the FPAT variable is set to a string representing a
regular expression, each field is made up of text that matches that
regular expression. In this case, the regular expression describes
the fields themselves, instead of the text that separates the fields.
Assigning a new value to FS or FIELDWIDTHS overrides the use of FPAT.
Each field in the input record may be referenced by its position: $1,
$2, and so on. $0 is the whole record, including leading and
trailing whitespace. Fields need not be referenced by constants:
n = 5
print $n
prints the fifth field in the input record.
The variable NF is set to the total number of fields in the input
record.
References to non-existent fields (i.e., fields after $NF) produce
the null string. However, assigning to a non-existent field (e.g.,
$(NF+2) = 5) increases the value of NF, creates any intervening
fields with the null string as their values, and causes the value of
$0 to be recomputed, with the fields being separated by the value of
OFS. References to negative numbered fields cause a fatal error.
Decrementing NF causes the values of fields past the new value to be
lost, and the value of $0 to be recomputed, with the fields being
separated by the value of OFS.
Assigning a value to an existing field causes the whole record to be
rebuilt when $0 is referenced. Similarly, assigning a value to $0
causes the record to be resplit, creating new values for the fields.
Built-in Variables
Gawk's built-in variables are:
ARGC The number of command line arguments (does not include
options to gawk, or the program source).
ARGIND The index in ARGV of the current file being processed.
ARGV Array of command line arguments. The array is indexed
from 0 to ARGC - 1. Dynamically changing the contents of
ARGV can control the files used for data.
BINMODE On non-POSIX systems, specifies use of “binary” mode for
all file I/O. Numeric values of 1, 2, or 3, specify that
input files, output files, or all files, respectively,
should use binary I/O. String values of "r", or "w"
specify that input files, or output files, respectively,
should use binary I/O. String values of "rw" or "wr"
specify that all files should use binary I/O. Any other
string value is treated as "rw", but generates a warning
message.
CONVFMT The conversion format for numbers, "%.6g", by default.
ENVIRON An array containing the values of the current
environment. The array is indexed by the environment
variables, each element being the value of that variable
(e.g., ENVIRON["HOME"] might be "/home/arnold").
In POSIX mode, changing this array does not affect the
environment seen by programs which gawk spawns via
redirection or the system() function. Otherwise, gawk
updates its real environment so that programs it spawns
see the changes.
ERRNO If a system error occurs either doing a redirection for
getline, during a read for getline, or during a close(),
then ERRNO is set to a string describing the error. The
value is subject to translation in non-English locales.
If the string in ERRNO corresponds to a system error in
the errno(3) variable, then the numeric value can be
found in PROCINFO["errno"]. For non-system errors,
PROCINFO["errno"] will be zero.
FIELDWIDTHS A whitespace-separated list of field widths. When set,
gawk parses the input into fields of fixed width, instead
of using the value of the FS variable as the field
separator. Each field width may optionally be preceded
by a colon-separated value specifying the number of
characters to skip before the field starts. See Fields,
above.
FILENAME The name of the current input file. If no files are
specified on the command line, the value of FILENAME is
“-”. However, FILENAME is undefined inside the BEGIN
rule (unless set by getline).
FNR The input record number in the current input file.
FPAT A regular expression describing the contents of the
fields in a record. When set, gawk parses the input into
fields, where the fields match the regular expression,
instead of using the value of FS as the field separator.
See Fields, above.
FS The input field separator, a space by default. See
Fields, above.
FUNCTAB An array whose indices and corresponding values are the
names of all the user-defined or extension functions in
the program. NOTE: You may not use the delete statement
with the FUNCTAB array.
IGNORECASE Controls the case-sensitivity of all regular expression
and string operations. If IGNORECASE has a non-zero
value, then string comparisons and pattern matching in
rules, field splitting with FS and FPAT, record
separating with RS, regular expression matching with ~
and !~, and the gensub(), gsub(), index(), match(),
patsplit(), split(), and sub() built-in functions all
ignore case when doing regular expression operations.
NOTE: Array subscripting is not affected. However, the
asort() and asorti() functions are affected.
Thus, if IGNORECASE is not equal to zero, /aB/ matches
all of the strings "ab", "aB", "Ab", and "AB". As with
all AWK variables, the initial value of IGNORECASE is
zero, so all regular expression and string operations are
normally case-sensitive.
LINT Provides dynamic control of the --lint option from within
an AWK program. When true, gawk prints lint warnings.
When false, it does not. The values allowed for the
--lint option may also be assigned to LINT, with the same
effects. Any other true value just prints warnings.
NF The number of fields in the current input record.
NR The total number of input records seen so far.
OFMT The output format for numbers, "%.6g", by default.
OFS The output field separator, a space by default.
ORS The output record separator, by default a newline.
PREC The working precision of arbitrary precision floating-
point numbers, 53 by default.
PROCINFO The elements of this array provide access to information
about the running AWK program. On some systems, there
may be elements in the array, "group1" through "groupn"
for some n, which is the number of supplementary groups
that the process has. Use the in operator to test for
these elements. The following elements are guaranteed to
be available:
PROCINFO["argv"] The command line arguments as
received by gawk at the C-language
level. The subscripts start from
zero.
PROCINFO["egid"] The value of the getegid(2) system
call.
PROCINFO["errno"] The value of errno(3) when ERRNO is
set to the associated error message.
PROCINFO["euid"] The value of the geteuid(2) system
call.
PROCINFO["FS"] "FS" if field splitting with FS is
in effect, "FPAT" if field splitting
with FPAT is in effect,
"FIELDWIDTHS" if field splitting
with FIELDWIDTHS is in effect, or
"API" if API input parser field
splitting is in effect.
PROCINFO["gid"] The value of the getgid(2) system
call.
PROCINFO["identifiers"]
A subarray, indexed by the names of
all identifiers used in the text of
the AWK program. The values
indicate what gawk knows about the
identifiers after it has finished
parsing the program; they are not
updated while the program runs. For
each identifier, the value of the
element is one of the following:
"array" The identifier is an
array.
"builtin" The identifier is a
built-in function.
"extension" The identifier is an
extension function
loaded via @load or
--load.
"scalar" The identifier is a
scalar.
"untyped" The identifier is
untyped (could be used
as a scalar or array,
gawk doesn't know yet).
"user" The identifier is a
user-defined function.
PROCINFO["pgrpid"] The value of the getpgrp(2) system
call.
PROCINFO["pid"] The value of the getpid(2) system
call.
PROCINFO["platform"] A string indicating the platform for
which gawk was compiled. It is one
of:
"djgpp", "mingw"
Microsoft Windows, using
either DJGPP, or MinGW,
respectively.
"os2" OS/2.
"posix"
GNU/Linux, Cygwin, Mac OS X,
and legacy Unix systems.
"vms" OpenVMS or Vax/VMS.
PROCINFO["ppid"] The value of the getppid(2) system
call.
PROCINFO["strftime"] The default time format string for
strftime(). Changing its value
affects how strftime() formats time
values when called with no
arguments.
PROCINFO["uid"] The value of the getuid(2) system
call.
PROCINFO["version"] The version of gawk.
The following elements are present if loading dynamic
extensions is available:
PROCINFO["api_major"]
The major version of the extension API.
PROCINFO["api_minor"]
The minor version of the extension API.
The following elements are available if MPFR support is
compiled into gawk:
PROCINFO["gmp_version"]
The version of the GNU GMP library used for
arbitrary precision number support in gawk.
PROCINFO["mpfr_version"]
The version of the GNU MPFR library used for
arbitrary precision number support in gawk.
PROCINFO["prec_max"]
The maximum precision supported by the GNU MPFR
library for arbitrary precision floating-point
numbers.
PROCINFO["prec_min"]
The minimum precision allowed by the GNU MPFR
library for arbitrary precision floating-point
numbers.
The following elements may set by a program to change
gawk's behavior:
PROCINFO["NONFATAL"]
If this exists, then I/O errors for all
redirections become nonfatal.
PROCINFO["name", "NONFATAL"]
Make I/O errors for name be nonfatal.
PROCINFO["command", "pty"]
Use a pseudo-tty for two-way communication with
command instead of setting up two one-way pipes.
PROCINFO["input", "READ_TIMEOUT"]
The timeout in milliseconds for reading data from
input, where input is a redirection string or a
filename. A value of zero or less than zero means
no timeout.
PROCINFO["input", "RETRY"]
If an I/O error that may be retried occurs when
reading data from input, and this array entry
exists, then getline returns -2 instead of
following the default behavior of returning -1 and
configuring input to return no further data. An
I/O error that may be retried is one where
errno(3) has the value EAGAIN, EWOULDBLOCK, EINTR,
or ETIMEDOUT. This may be useful in conjunction
with PROCINFO["input", "READ_TIMEOUT"] or in
situations where a file descriptor has been
configured to behave in a non-blocking fashion.
PROCINFO["sorted_in"]
If this element exists in PROCINFO, then its value
controls the order in which array elements are
traversed in for loops. Supported values are
"@ind_str_asc", "@ind_num_asc", "@val_type_asc",
"@val_str_asc", "@val_num_asc", "@ind_str_desc",
"@ind_num_desc", "@val_type_desc",
"@val_str_desc", "@val_num_desc", and "@unsorted".
The value can also be the name (as a string) of
any comparison function defined as follows:
function cmp_func(i1, v1, i2, v2)
where i1 and i2 are the indices, and v1 and v2 are
the corresponding values of the two elements being
compared. It should return a number less than,
equal to, or greater than 0, depending on how the
elements of the array are to be ordered.
ROUNDMODE The rounding mode to use for arbitrary precision
arithmetic on numbers, by default "N" (IEEE-754
roundTiesToEven mode). The accepted values are:
"A" or "a"
for rounding away from zero. These are only
available if your version of the GNU MPFR library
supports rounding away from zero.
"D" or "d" for roundTowardNegative.
"N" or "n" for roundTiesToEven.
"U" or "u" for roundTowardPositive.
"Z" or "z" for roundTowardZero.
RS The input record separator, by default a newline.
RT The record terminator. Gawk sets RT to the input text
that matched the character or regular expression
specified by RS.
RSTART The index of the first character matched by match(); 0 if
no match. (This implies that character indices start at
one.)
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. The
array may be used for indirect access to read or write
the value of a variable:
foo = 5
SYMTAB["foo"] = 4
print foo # prints 4
The typeof() function may be used to test if an element
in SYMTAB is an array. You may not use the delete
statement with the SYMTAB array, nor assign to elements
with an index that is not a variable name.
TEXTDOMAIN The text domain of the AWK program; used to find the
localized translations for the program's strings.
Arrays
Arrays are subscripted with an expression between square brackets ([
and ]). If the expression is an expression list (expr, expr ...)
then the array subscript is a string consisting of the concatenation
of the (string) value of each expression, separated by the value of
the SUBSEP variable. This facility is used to simulate multiply
dimensioned arrays. For example:
i = "A"; j = "B"; k = "C"
x[i, j, k] = "hello, world\n"
assigns the string "hello, world\n" to the element of the array x
which is indexed by the string "A\034B\034C". All arrays in AWK are
associative, i.e., indexed by string values.
The special operator in may be used to test if an array has an index
consisting of a particular value:
if (val in array)
print array[val]
If the array has multiple subscripts, use (i, j) in array.
The in construct may also be used in a for loop to iterate over all
the elements of an array. However, the (i, j) in array construct
only works in tests, not in for loops.
An element may be deleted from an array using the delete statement.
The delete statement may also be used to delete the entire contents
of an array, just by specifying the array name without a subscript.
gawk supports true multidimensional arrays. It does not require that
such arrays be ``rectangular'' as in C or C++. For example:
a[1] = 5
a[2][1] = 6
a[2][2] = 7
NOTE: You may need to tell gawk that an array element is really a
subarray in order to use it where gawk expects an array (such as in
the second argument to split()). You can do this by creating an
element in the subarray and then deleting it with the delete
statement.
Namespaces
Gawk provides a simple namespace facility to help work around the
fact that all variables in AWK are global.
A qualified name consists of a two simple identifiers joined by a
double colon (::). The left-hand identifier represents the namespace
and the right-hand identifier is the variable within it. All simple
(non-qualified) names are considered to be in the ``current''
namespace; the default namespace is awk. However, simple identifiers
consisting solely of uppercase letters are forced into the awk
namespace, even if the current namespace is different.
You change the current namespace with an @namespace "name" directive.
The standard predefined builtin function names may not be used as
namespace names. The names of additional functions provided by gawk
may be used as namespace names or as simple identifiers in other
namespaces. For more details, see GAWK: Effective AWK Programming.
Variable Typing And Conversion
Variables and fields may be (floating point) numbers, or strings, or
both. They may also be regular expressions. How the value of a
variable is interpreted depends upon its context. If used in a
numeric expression, it will be treated as a number; if used as a
string it will be treated as a string.
To force a variable to be treated as a number, add zero to it; to
force it to be treated as a string, concatenate it with the null
string.
Uninitialized variables have the numeric value zero and the string
value "" (the null, or empty, string).
When a string must be converted to a number, the conversion is
accomplished using strtod(3). A number is converted to a string by
using the value of CONVFMT as a format string for sprintf(3), with
the numeric value of the variable as the argument. However, even
though all numbers in AWK are floating-point, integral values are
always converted as integers. Thus, given
CONVFMT = "%2.2f"
a = 12
b = a ""
the variable b has a string value of "12" and not "12.00".
NOTE: When operating in POSIX mode (such as with the --posix option),
beware that locale settings may interfere with the way decimal
numbers are treated: the decimal separator of the numbers you are
feeding to gawk must conform to what your locale would expect, be it
a comma (,) or a period (.).
Gawk performs comparisons as follows: If two variables are numeric,
they are compared numerically. If one value is numeric and the other
has a string value that is a “numeric string,” then comparisons are
also done numerically. Otherwise, the numeric value is converted to
a string and a string comparison is performed. Two strings are
compared, of course, as strings.
Note that string constants, such as "57", are not numeric strings,
they are string constants. The idea of “numeric string” only applies
to fields, getline input, FILENAME, ARGV elements, ENVIRON elements
and the elements of an array created by split() or patsplit() that
are numeric strings. The basic idea is that user input, and only
user input, that looks numeric, should be treated that way.
Octal and Hexadecimal Constants
You may use C-style octal and hexadecimal constants in your AWK
program source code. For example, the octal value 011 is equal to
decimal 9, and the hexadecimal value 0x11 is equal to decimal 17.
String Constants
String constants in AWK are sequences of characters enclosed between
double quotes (like "value"). Within strings, certain escape
sequences are recognized, as in C. These are:
\\ A literal backslash.
\a The “alert” character; usually the ASCII BEL character.
\b Backspace.
\f Form-feed.
\n Newline.
\r Carriage return.
\t Horizontal tab.
\v Vertical tab.
\xhex digits
The character represented by the string of hexadecimal digits
following the \x. Up to two following hexadecimal digits are
considered part of the escape sequence. E.g., "\x1B" is the
ASCII ESC (escape) character.
\ddd The character represented by the 1-, 2-, or 3-digit sequence of
octal digits. E.g., "\033" is the ASCII ESC (escape) character.
\c The literal character c.
In compatibility mode, the characters represented by octal and
hexadecimal escape sequences are treated literally when used in
regular expression constants. Thus, /a\52b/ is equivalent to /a\*b/.
Regexp Constants
A regular expression constant is a sequence of characters enclosed
between forward slashes (like /value/). Regular expression matching
is described more fully below; see Regular Expressions.
The escape sequences described earlier may also be used inside
constant regular expressions (e.g., /[ \t\f\n\r\v]/ matches
whitespace characters).
Gawk provides strongly typed regular expression constants. These are
written with a leading @ symbol (like so: @/value/). Such constants
may be assigned to scalars (variables, array elements) and passed to
user-defined functions. Variables that have been so assigned have
regular expression type.
AWK is a line-oriented language. The pattern comes first, and then
the action. Action statements are enclosed in { and }. Either the
pattern may be missing, or the action may be missing, but, of course,
not both. If the pattern is missing, the action executes for every
single record of input. A missing action is equivalent to
{ print }
which prints the entire record.
Comments begin with the # character, and continue until the end of
the line. Empty lines may be used to separate statements. Normally,
a statement ends with a newline, however, this is not the case for
lines ending in a comma, {, ?, :, &&, or ||. Lines ending in do or
else also have their statements automatically continued on the
following line. In other cases, a line can be continued by ending it
with a “\”, in which case the newline is ignored. However, a “\”
after a # is not special.
Multiple statements may be put on one line by separating them with a
“;”. This applies to both the statements within the action part of a
pattern-action pair (the usual case), and to the pattern-action
statements themselves.
Patterns
AWK patterns may be one of the following:
BEGIN
END
BEGINFILE
ENDFILE
/regular expression/
relational expression
pattern && pattern
pattern || pattern
pattern ? pattern : pattern
(pattern)
! pattern
pattern1, pattern2
BEGIN and END are two special kinds of patterns which are not tested
against the input. The action parts of all BEGIN patterns are merged
as if all the statements had been written in a single BEGIN rule.
They are executed before any of the input is read. Similarly, all
the END rules are merged, and executed when all the input is
exhausted (or when an exit statement is executed). BEGIN and END
patterns cannot be combined with other patterns in pattern
expressions. BEGIN and END patterns cannot have missing action
parts.
BEGINFILE and ENDFILE are additional special patterns whose actions
are executed before reading the first record of each command-line
input file and after reading the last record of each file. Inside
the BEGINFILE rule, the value of ERRNO is the empty string if the
file was opened successfully. Otherwise, there is some problem with
the file and the code should use nextfile to skip it. If that is not
done, gawk produces its usual fatal error for files that cannot be
opened.
For /regular expression/ patterns, the associated statement is
executed for each input record that matches the regular expression.
Regular expressions are the same as those in egrep(1), and are
summarized below.
A relational expression may use any of the operators defined below in
the section on actions. These generally test whether certain fields
match certain regular expressions.
The &&, ||, and ! operators are logical AND, logical OR, and logical
NOT, respectively, as in C. They do short-circuit evaluation, also
as in C, and are used for combining more primitive pattern
expressions. As in most languages, parentheses may be used to change
the order of evaluation.
The ?: operator is like the same operator in C. If the first pattern
is true then the pattern used for testing is the second pattern,
otherwise it is the third. Only one of the second and third patterns
is evaluated.
The pattern1, pattern2 form of an expression is called a range
pattern. It matches all input records starting with a record that
matches pattern1, and continuing until a record that matches
pattern2, inclusive. It does not combine with any other sort of
pattern expression.
Regular Expressions
Regular expressions are the extended kind found in egrep. They are
composed of characters as follows:
c Matches the non-metacharacter c.
\c Matches the literal character c.
. Matches any character including newline.
^ Matches the beginning of a string.
$ Matches the end of a string.
[abc...] A character list: matches any of the characters abc....
You may include a range of characters by separating them
with a dash. To include a literal dash in the list, put
it first or last.
[^abc...] A negated character list: matches any character except
abc....
r1|r2 Alternation: matches either r1 or r2.
r1r2 Concatenation: matches r1, and then r2.
r+ Matches one or more r's.
r* Matches zero or more r's.
r? Matches zero or one r's.
(r) Grouping: matches r.
r{n}
r{n,}
r{n,m} One or two numbers inside braces denote an interval
expression. If there is one number in the braces, the
preceding regular expression r is repeated n times. If
there are two numbers separated by a comma, r is repeated
n to m times. If there is one number followed by a comma,
then r is repeated at least n times.
\y Matches the empty string at either the beginning or the
end of a word.
\B Matches the empty string within a word.
\< Matches the empty string at the beginning of a word.
\> Matches the empty string at the end of a word.
\s Matches any whitespace character.
\S Matches any nonwhitespace character.
\w Matches any word-constituent character (letter, digit, or
underscore).
\W Matches any character that is not word-constituent.
\` Matches the empty string at the beginning of a buffer
(string).
\' Matches the empty string at the end of a buffer.
The escape sequences that are valid in string constants (see String
Constants) are also valid in regular expressions.
Character classes are a feature introduced in the POSIX standard. A
character class is a special notation for describing lists of
characters that have a specific attribute, but where the actual
characters themselves can vary from country to country and/or from
character set to character set. For example, the notion of what is
an alphabetic character differs in the USA and in France.
A character class is only valid in a regular expression inside the
brackets of a character list. Character classes consist of [:, a
keyword denoting the class, and :]. The character classes defined by
the POSIX standard are:
[:alnum:] Alphanumeric characters.
[:alpha:] Alphabetic characters.
[:blank:] Space or tab characters.
[:cntrl:] Control characters.
[:digit:] Numeric characters.
[:graph:] Characters that are both printable and visible. (A space
is printable, but not visible, while an a is both.)
[:lower:] Lowercase alphabetic characters.
[:print:] Printable characters (characters that are not control
characters.)
[:punct:] Punctuation characters (characters that are not letter,
digits, control characters, or space characters).
[:space:] Space characters (such as space, tab, and formfeed, to
name a few).
[:upper:] Uppercase alphabetic characters.
[:xdigit:] Characters that are hexadecimal digits.
For example, before the POSIX standard, to match alphanumeric
characters, you would have had to write /[A-Za-z0-9]/. If your
character set had other alphabetic characters in it, this would not
match them, and if your character set collated differently from
ASCII, this might not even match the ASCII alphanumeric characters.
With the POSIX character classes, you can write /[[:alnum:]]/, and
this matches the alphabetic and numeric characters in your character
set, no matter what it is.
Two additional special sequences can appear in character lists.
These apply to non-ASCII character sets, which can have single
symbols (called collating elements) that are represented with more
than one character, as well as several characters that are equivalent
for collating, or sorting, purposes. (E.g., in French, a plain “e”
and a grave-accented “e`” are equivalent.)
Collating Symbols
A collating symbol is a multi-character collating element
enclosed in [. and .]. For example, if ch is a collating
element, then [[.ch.]] is a regular expression that matches
this collating element, while [ch] is a regular expression
that matches either c or h.
Equivalence Classes
An equivalence class is a locale-specific name for a list of
characters that are equivalent. The name is enclosed in [=
and =]. For example, the name e might be used to represent
all of “e”, “e´”, and “e`”. In this case, [[=e=]] is a regular
expression that matches any of e, e´, or e`.
These features are very valuable in non-English speaking locales.
The library functions that gawk uses for regular expression matching
currently only recognize POSIX character classes; they do not
recognize collating symbols or equivalence classes.
The \y, \B, \<, \>, \s, \S, \w, \W, \`, and \' operators are specific
to gawk; they are extensions based on facilities in the GNU regular
expression libraries.
The various command line options control how gawk interprets
characters in regular expressions.
No options
In the default case, gawk provides all the facilities of POSIX
regular expressions and the GNU regular expression operators
described above.
--posix
Only POSIX regular expressions are supported, the GNU
operators are not special. (E.g., \w matches a literal w).
--traditional
Traditional UNIX awk regular expressions are matched. The GNU
operators are not special, and interval expressions are not
available. Characters described by octal and hexadecimal
escape sequences are treated literally, even if they represent
regular expression metacharacters.
--re-interval
Allow interval expressions in regular expressions, even if
--traditional has been provided.
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 (** may also be used, and **= for the
assignment operator).
+ - ! Unary plus, unary minus, and logical negation.
* / % Multiplication, division, and modulus.
+ - Addition and subtraction.
space String concatenation.
| |& Piped I/O for getline, print, and printf.
< > <= >= == !=
The regular relational operators.
~ !~ Regular expression match, negated match. NOTE: Do not
use a constant regular expression (/foo/) on the left-
hand side of a ~ or !~. Only use one on the right-hand
side. The expression /foo/ ~ exp has the same meaning as
(($0 ~ /foo/) ~ exp). This is usually not what you want.
in Array membership.
&& Logical AND.
|| Logical OR.
?: The C conditional expression. This has the form expr1 ?
expr2 : expr3. If expr1 is true, the value of the
expression is expr2, otherwise it is expr3. Only one of
expr2 and expr3 is evaluated.
= += -= *= /= %= ^=
Assignment. Both absolute assignment (var = value) and
operator-assignment (the other forms) are supported.
Control Statements
The control statements are as follows:
if (condition) statement [ else statement ]
while (condition) statement
do statement while (condition)
for (expr1; expr2; expr3) statement
for (var in array) statement
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 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.
Coprocesses are a gawk extension. (The command
can also be a socket. See the subsection
Special File Names, below.)
next Stop processing the current input record. Read
the next input record and start processing over
with the first pattern in the AWK program.
Upon reaching the end of the input data,
execute any END rule(s).
nextfile Stop processing the current input file. The
next input record read comes from the next
input file. Update FILENAME and ARGIND, reset
FNR to 1, and start processing over with the
first pattern in the AWK program. Upon
reaching the end of the input data, execute any
ENDFILE and END rule(s).
print Print the current record. The output record is
terminated with the value of ORS.
print expr-list Print expressions. Each expression is
separated by the value of OFS. The output
record is terminated with the value of ORS.
print expr-list >file Print expressions on file. Each expression is
separated by the value of OFS. The output
record is terminated with the value of ORS.
printf fmt, expr-list Format and print. See The printf Statement,
below.
printf fmt, expr-list >file
Format and print on file.
system(cmd-line) Execute the command cmd-line, and return the
exit status. (This may not be available on
non-POSIX systems.) See GAWK: Effective AWK
Programming for the full details on the exit
status.
fflush([file]) Flush any buffers associated with the open
output file or pipe file. If file is missing
or if it is the null string, then flush all
open output files and pipes.
Additional output redirections are allowed for print and printf.
print ... >> file
Append output to the file.
print ... | command
Write on a pipe.
print ... |& command
Send data to a coprocess or socket. (See also the subsection
Special File Names, below.)
The getline command returns 1 on success, zero on end of file, and -1
on an error. If the errno(3) value indicates that the I/O operation
may be retried, and PROCINFO["input", "RETRY"] is set, then -2 is
returned instead of -1, and further calls to getline may be
attempted. Upon an error, ERRNO is set to a string describing the
problem.
NOTE: Failure in opening a two-way socket results in a non-fatal
error being returned to the calling function. If using a pipe,
coprocess, or socket to getline, or from print or printf within a
loop, you must use close() to create new instances of the command or
socket. AWK does not automatically close pipes, sockets, or
coprocesses when they return EOF.
The printf Statement
The AWK versions of the printf statement and sprintf() function (see
below) accept the following conversion specification formats:
%a, %A A floating point number of the form [-]0xh.hhhhp+-dd (C99
hexadecimal floating point format). For %A, uppercase
letters are used instead of lowercase ones.
%c A single character. If the argument used for %c is numeric,
it is treated as a character and printed. Otherwise, the
argument is assumed to be a string, and the only first
character of that string is printed.
%d, %i A decimal number (the integer part).
%e, %E A floating point number of the form [-]d.dddddde[+-]dd. The
%E format uses E instead of e.
%f, %F A floating point number of the form [-]ddd.dddddd. If the
system library supports it, %F is available as well. This is
like %f, but uses capital letters for special “not a number”
and “infinity” values. If %F is not available, gawk uses %f.
%g, %G Use %e or %f conversion, whichever is shorter, with
nonsignificant zeros suppressed. The %G format uses %E
instead of %e.
%o An unsigned octal number (also an integer).
%u An unsigned decimal number (again, an integer).
%s A character string.
%x, %X An unsigned hexadecimal number (an integer). The %X format
uses ABCDEF instead of abcdef.
%% A single % character; no argument is converted.
Optional, additional parameters may lie between the % and the control
letter:
count$ Use the count'th argument at this point in the formatting.
This is called a positional specifier and is intended
primarily for use in translated versions of format strings,
not in the original text of an AWK program. It is a gawk
extension.
- The expression should be left-justified within its field.
space For numeric conversions, prefix positive values with a space,
and negative values with a minus sign.
+ The plus sign, used before the width modifier (see below),
says to always supply a sign for numeric conversions, even if
the data to be formatted is positive. The + overrides the
space modifier.
# Use an “alternate form” for certain control letters. For %o,
supply a leading zero. For %x, and %X, supply a leading 0x or
0X for a nonzero result. For %e, %E, %f and %F, the result
always contains a decimal point. For %g, and %G, trailing
zeros are not removed from the result.
0 A leading 0 (zero) acts as a flag, indicating that output
should be padded with zeroes instead of spaces. This applies
only to the numeric output formats. This flag only has an
effect when the field width is wider than the value to be
printed.
' A single quote character instructs gawk to insert the locale's
thousands-separator character into decimal numbers, and to
also use the locale's decimal point character with floating
point formats. This requires correct locale support in the C
library and in the definition of the current locale.
width The field should be padded to this width. The field is
normally padded with spaces. With the 0 flag, it is padded
with zeroes.
.prec A number that specifies the precision to use when printing.
For the %e, %E, %f and %F, formats, this specifies the number
of digits you want printed to the right of the decimal point.
For the %g, and %G formats, it specifies the maximum number of
significant digits. For the %d, %i, %o, %u, %x, and %X
formats, it specifies the minimum number of digits to print.
For the %s format, it specifies the maximum number of
characters from the string that should be printed.
The dynamic width and prec capabilities of the ISO C printf()
routines are supported. A * in place of either the width or prec
specifications causes their values to be taken from the argument list
to printf or sprintf(). To use a positional specifier with a dynamic
width or precision, supply the count$ after the * in the format
string. For example, "%3$*2$.*1$s".
Special File Names
When doing I/O redirection from either print or printf into a file,
or via getline from a file, gawk recognizes certain special filenames
internally. These filenames allow access to open file descriptors
inherited from gawk's parent process (usually the shell). These file
names may also be used on the command line to name data files. The
filenames are:
- The standard input.
/dev/stdin The standard input.
/dev/stdout The standard output.
/dev/stderr The standard error output.
/dev/fd/n The file associated with the open file descriptor n.
These are particularly useful for error messages. For example:
print "You blew it!" > "/dev/stderr"
whereas you would otherwise have to use
print "You blew it!" | "cat 1>&2"
The following special filenames may be used with the |& coprocess
operator for creating TCP/IP network connections:
/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
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:
asort(s [, d [, how] ]) Return the number of elements in the source
array s. Sort the contents of s using gawk's
normal rules for comparing values, and
replace the indices of the sorted values s
with sequential integers starting with 1. If
the optional destination array d is
specified, first duplicate s into d, and then
sort d, leaving the indices of the source
array s unchanged. The optional string how
controls the direction and the comparison
mode. Valid values for how are any of the
strings valid for PROCINFO["sorted_in"]. It
can also be the name of a user-defined
comparison function as described in
PROCINFO["sorted_in"].
asorti(s [, d [, how] ])
Return the number of elements in the source
array s. The behavior is the same as that of
asort(), except that the array indices are
used for sorting, not the array values. When
done, the array is indexed numerically, and
the values are those of the original indices.
The original values are lost; thus provide a
second array if you wish to preserve the
original. The purpose of the optional string
how is the same as described previously for
asort().
gensub(r, s, h [, t]) Search the target string t for matches of the
regular expression r. If h is a string
beginning with g or G, then replace all
matches of r with s. Otherwise, h is a
number indicating which match of r to
replace. If t is not supplied, use $0
instead. Within the replacement text s, the
sequence \n, where n is a digit from 1 to 9,
may be used to indicate just the text that
matched the n'th parenthesized subexpression.
The sequence \0 represents the entire matched
text, as does the character &. Unlike sub()
and gsub(), the modified string is returned
as the result of the function, and the
original target string is not changed.
gsub(r, s [, t]) For each substring matching the regular
expression r in the string t, substitute the
string s, and return the number of
substitutions. If t is not supplied, use $0.
An & in the replacement text is replaced with
the text that was actually matched. Use \&
to get a literal &. (This must be typed as
"\\&"; see GAWK: Effective AWK Programming
for a fuller discussion of the rules for
ampersands and backslashes in the replacement
text of sub(), gsub(), and gensub().)
index(s, t) Return the index of the string t in the
string s, or zero if t is not present. (This
implies that character indices start at one.)
It is a fatal error to use a regexp constant
for t.
length([s]) Return the length of the string s, or the
length of $0 if s is not supplied. As a non-
standard extension, with an array argument,
length() returns the number of elements in
the array.
match(s, r [, a]) Return the position in s where the regular
expression r occurs, or zero if r is not
present, and set the values of RSTART and
RLENGTH. Note that the argument order is the
same as for the ~ operator: str ~ re. If
array a is provided, a is cleared and then
elements 1 through n are filled with the
portions of s that match the corresponding
parenthesized subexpression in r. The
zero'th element of a contains the portion of
s matched by the entire regular expression r.
Subscripts a[n, "start"], and a[n, "length"]
provide the starting index in the string and
length respectively, of each matching
substring.
patsplit(s, a [, r [, seps] ])
Split the string s into the array a and the
separators array seps on the regular
expression r, and return the number of
fields. Element values are the portions of s
that matched r. The value of seps[i] is the
possibly null separator that appeared after
a[i]. The value of seps[0] is the possibly
null leading separator. If r is omitted,
FPAT is used instead. The arrays a and seps
are cleared first. Splitting behaves
identically to field splitting with FPAT,
described above.
split(s, a [, r [, seps] ])
Split the string s into the array a and the
separators array seps on the regular
expression r, and return the number of
fields. If r is omitted, FS is used instead.
The arrays a and seps are cleared first.
seps[i] is the field separator matched by r
between a[i] and a[i+1]. If r is a single
space, then leading whitespace in s goes into
the extra array element seps[0] and trailing
whitespace goes into the extra array element
seps[n], where n is the return value of
split(s, a, r, seps). Splitting behaves
identically to field splitting, described
above. In particular, if r is a single-
character string, that string acts as the
separator, even if it happens to be a regular
expression metacharacter.
sprintf(fmt, expr-list) Print expr-list according to fmt, and return
the resulting string.
strtonum(str) Examine str, and return its numeric value.
If str begins with a leading 0, treat it as
an octal number. If str begins with a
leading 0x or 0X, treat it as a hexadecimal
number. Otherwise, assume it is a decimal
number.
sub(r, s [, t]) Just like gsub(), but replace only the first
matching substring. Return either zero or
one.
substr(s, i [, n]) Return the at most n-character substring of s
starting at i. If n is omitted, use the rest
of s.
tolower(str) Return a copy of the string str, with all the
uppercase characters in str translated to
their corresponding lowercase counterparts.
Non-alphabetic characters are left unchanged.
toupper(str) Return a copy of the string str, with all the
lowercase characters in str translated to
their corresponding uppercase counterparts.
Non-alphabetic characters are left unchanged.
Gawk is multibyte aware. This means that index(), length(), substr()
and match() all work in terms of characters, not bytes.
Time Functions
Since one of the primary uses of AWK programs is processing log files
that contain time stamp information, gawk provides the following
functions for obtaining time stamps and formatting them.
mktime(datespec [, utc-flag])
Turn datespec into a time stamp of the same form as
returned by systime(), and return the result. The datespec
is a string of the form YYYY MM DD HH MM SS[ DST]. The
contents of the string are six or seven numbers
representing respectively the full year including century,
the month from 1 to 12, the day of the month from 1 to 31,
the hour of the day from 0 to 23, the minute from 0 to 59,
the second from 0 to 60, and an optional daylight saving
flag. The values of these numbers need not be within the
ranges specified; for example, an hour of -1 means 1 hour
before midnight. The origin-zero Gregorian calendar is
assumed, with year 0 preceding year 1 and year -1 preceding
year 0. If utc-flag is present and is non-zero or non-
null, the time is assumed to be in the UTC time zone;
otherwise, the time is assumed to be in the local time
zone. If the DST daylight saving flag is positive, the
time is assumed to be daylight saving time; if zero, the
time is assumed to be standard time; and if negative (the
default), mktime() attempts to determine whether daylight
saving time is in effect for the specified time. If
datespec does not contain enough elements or if the
resulting time is out of range, mktime() returns -1.
strftime([format [, timestamp[, utc-flag]]])
Format timestamp according to the specification in format.
If utc-flag is present and is non-zero or non-null, the
result is in UTC, otherwise the result is in local time.
The timestamp should be of the same form as returned by
systime(). If timestamp is missing, the current time of
day is used. If format is missing, a default format
equivalent to the output of date(1) is used. The default
format is available in PROCINFO["strftime"]. See the
specification for the strftime() function in ISO C for the
format conversions that are guaranteed to be available.
systime() Return the current time of day as the number of seconds
since the Epoch (1970-01-01 00:00:00 UTC on POSIX systems).
Bit Manipulations Functions
Gawk supplies the following bit manipulation functions. They work by
converting double-precision floating point values to uintmax_t
integers, doing the operation, and then converting the result back to
floating point.
NOTE: Passing negative operands to any of these functions causes a
fatal error.
The functions are:
and(v1, v2 [, ...]) Return the bitwise AND of the values provided in
the argument list. There must be at least two.
compl(val) Return the bitwise complement of val.
lshift(val, count) Return the value of val, shifted left by count
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. This
function is mainly for use with the elements of
multidimensional arrays and with function parameters.
typeof(x) Return a string indicating the type of x. The string will
be one of "array", "number", "regexp", "string", "strnum",
"unassigned", or "undefined".
Internationalization Functions
The following functions may be used from within your AWK program for
translating strings at run-time. For full details, see GAWK:
Effective AWK Programming.
bindtextdomain(directory [, domain])
Specify the directory where gawk looks for the .gmo files, in
case they will not or cannot be placed in the ``standard''
locations (e.g., during testing). It returns the directory
where domain is ``bound.''
The default domain is the value of TEXTDOMAIN. If directory
is the null string (""), then bindtextdomain() returns the
current binding for the given domain.
dcgettext(string [, domain [, category]])
Return the translation of string in text domain domain for
locale category category. The default value for domain is the
current value of TEXTDOMAIN. The default value for category
is "LC_MESSAGES".
If you supply a value for category, it must be a string equal
to one of the known locale categories described in GAWK:
Effective AWK Programming. You must also supply a text
domain. Use TEXTDOMAIN if you want to use the current domain.
dcngettext(string1, string2, number [, domain [, category]])
Return the plural form used for number of the translation of
string1 and string2 in text domain domain for locale category
category. The default value for domain is the current value
of TEXTDOMAIN. The default value for category is
"LC_MESSAGES".
If you supply a value for category, it must be a string equal
to one of the known locale categories described in GAWK:
Effective AWK Programming. You must also supply a text
domain. Use TEXTDOMAIN if you want to use the current domain.
Functions in AWK are defined as follows:
function name(parameter list) { statements }
Functions execute when they are called from within expressions in
either patterns or actions. Actual parameters supplied in the
function call are used to instantiate the formal parameters declared
in the function. Arrays are passed by reference, other variables are
passed by value.
Since functions were not originally part of the AWK language, the
provision for local variables is rather clumsy: They are declared as
extra parameters in the parameter list. The convention is to
separate local variables from real parameters by extra spaces in the
parameter list. For example:
function f(p, q, a, b) # a and b are local
{
...
}
/abc/ { ... ; f(1, 2) ; ... }
The left parenthesis in a function call is required to immediately
follow the function name, without any intervening whitespace. This
avoids a syntactic ambiguity with the concatenation operator. This
restriction does not apply to the built-in functions listed above.
Functions may call each other and may be recursive. Function
parameters used as local variables are initialized to the null string
and the number zero upon function invocation.
Use return expr to return a value from a function. The return value
is undefined if no value is provided, or if the function returns by
“falling off” the end.
As a gawk extension, functions may be called indirectly. To do this,
assign the name of the function to be called, as a string, to a
variable. Then use the variable as if it were the name of a
function, prefixed with an @ sign, like so:
function myfunc()
{
print "myfunc called"
...
}
{ ...
the_func = "myfunc"
@the_func() # call through the_func to myfunc
...
}
As of version 4.1.2, this works with user-defined functions, built-in
functions, and extension functions.
If --lint has been provided, gawk warns about calls to undefined
functions at parse time, instead of at run time. Calling an
undefined function at run time is a fatal error.
The word func may be used in place of function, although this is
deprecated.
You can dynamically add new functions written in C or C++ to the
running gawk interpreter with the @load statement. The full details
are beyond the scope of this manual page; see GAWK: Effective AWK
Programming.
The gawk profiler accepts two signals. SIGUSR1 causes it to dump a
profile and function call stack to the profile file, which is either
awkprof.out, or whatever file was named with the --profile option.
It then continues to run. SIGHUP causes gawk to dump the profile and
function call stack and then exit.
String constants are sequences of characters enclosed in double
quotes. In non-English speaking environments, it is possible to mark
strings in the AWK program as requiring translation to the local
natural language. Such strings are marked in the AWK program with a
leading underscore (“_”). For example,
gawk 'BEGIN { print "hello, world" }'
always prints hello, world. But,
gawk 'BEGIN { print _"hello, world" }'
might print bonjour, monde in France.
There are several steps involved in producing and running a
localizable AWK program.
1. Add a BEGIN action to assign a value to the TEXTDOMAIN variable
to set the text domain to a name associated with your program:
BEGIN { TEXTDOMAIN = "myprog" }
This allows gawk to find the .gmo file associated with your
program. Without this step, gawk uses the messages text domain,
which likely does not contain translations for your program.
2. Mark all strings that should be translated with leading
underscores.
3. If necessary, use the dcgettext() and/or bindtextdomain()
functions in your program, as appropriate.
4. Run gawk --gen-pot -f myprog.awk > myprog.pot to generate a .pot
file for your program.
5. Provide appropriate translations, and build and install the
corresponding .gmo files.
The internationalization features are described in full detail in
GAWK: Effective AWK Programming.
A primary goal for gawk is compatibility with the POSIX standard, as
well as with the latest version of Brian Kernighan's awk. To this
end, gawk incorporates the following user visible features which are
not described in the AWK book, but are part of the Brian Kernighan's
version of awk, and are in the POSIX standard.
The book indicates that command line variable assignment happens when
awk would otherwise open the argument as a file, which is after the
BEGIN rule is executed. However, in earlier implementations, when
such an assignment appeared before any file names, the assignment
would happen before the BEGIN rule was run. Applications came to
depend on this “feature.” When awk was changed to match its
documentation, the -v option for assigning variables before program
execution was added to accommodate applications that depended upon
the old behavior. (This feature was agreed upon by both the Bell
Laboratories developers and the GNU developers.)
When processing arguments, gawk uses the special option “--” to
signal the end of arguments. In compatibility mode, it warns about
but otherwise ignores undefined options. In normal operation, such
arguments are passed on to the AWK program for it to process.
The AWK book does not define the return value of srand(). The POSIX
standard has it return the seed it was using, to allow keeping track
of random number sequences. Therefore srand() in gawk also returns
its current seed.
Other features are: The use of multiple -f options (from MKS awk);
the ENVIRON array; the \a, and \v escape sequences (done originally
in gawk and fed back into the Bell Laboratories version); the
tolower() and toupper() built-in functions (from the Bell
Laboratories version); and the ISO C conversion specifications in
printf (done first in the Bell Laboratories version).
There is one feature of historical AWK implementations that gawk
supports: It is possible to call the length() built-in function not
only with no argument, but even without parentheses! Thus,
a = length # Holy Algol 60, Batman!
is the same as either of
a = length()
a = length($0)
Using this feature is poor practice, and gawk issues a warning about
its use if --lint is specified on the command line.
Gawk has a too-large number of extensions to POSIX awk. They are
described in this section. All the extensions described here can be
disabled by invoking gawk with the --traditional or --posix options.
The following features of gawk are not available in POSIX awk.
· No path search is performed for files named via the -f option.
Therefore the AWKPATH environment variable is not special.
· There is no facility for doing file inclusion (gawk's @include
mechanism).
· There is no facility for dynamically adding new functions written
in C (gawk's @load mechanism).
· The \x escape sequence.
· The ability to continue lines after ? and :.
· Octal and hexadecimal constants in AWK programs.
· The ARGIND, BINMODE, ERRNO, LINT, PREC, ROUNDMODE, RT and
TEXTDOMAIN variables are not special.
· The IGNORECASE variable and its side-effects are not available.
· The FIELDWIDTHS variable and fixed-width field splitting.
· The FPAT variable and field splitting based on field values.
· The FUNCTAB, SYMTAB, and PROCINFO arrays are not available.
· The use of RS as a regular expression.
· The special file names available for I/O redirection are not
recognized.
· The |& operator for creating coprocesses.
· The BEGINFILE and ENDFILE special patterns are not available.
· The ability to split out individual characters using the null
string as the value of FS, and as the third argument to split().
· An optional fourth argument to split() to receive the separator
texts.
· The optional second argument to the close() function.
· The optional third argument to the match() function.
· The ability to use positional specifiers with printf and sprintf().
· The ability to pass an array to length().
· The and(), asort(), asorti(), bindtextdomain(), compl(),
dcgettext(), dcngettext(), gensub(), lshift(), mktime(), or(),
patsplit(), rshift(), strftime(), strtonum(), systime() and xor()
functions.
· Localizable strings.
· Non-fatal I/O.
· Retryable I/O.
The AWK book does not define the return value of the close()
function. Gawk's close() returns the value from fclose(3), or
pclose(3), when closing an output file or pipe, respectively. It
returns the process's exit status when closing an input pipe. The
return value is -1 if the named file, pipe or coprocess was not
opened with a redirection.
When gawk is invoked with the --traditional option, if the fs
argument to the -F option is “t”, then FS is set to the tab
character. Note that typing gawk -F\t ... simply causes the shell
to quote the “t,” and does not pass “\t” to the -F option. Since
this is a rather ugly special case, it is not the default behavior.
This behavior also does not occur if --posix has been specified. To
really get a tab character as the field separator, it is best to use
single quotes: gawk -F'\t' ....
The AWKPATH environment variable can be used to provide a list of
directories that gawk searches when looking for files named via the
-f, --file, -i and --include options, and the @include directive. If
the initial search fails, the path is searched again after appending
.awk to the filename.
The AWKLIBPATH environment variable can be used to provide a list of
directories that gawk searches when looking for files named via the
-l and --load options.
The GAWK_READ_TIMEOUT environment variable can be used to specify a
timeout in milliseconds for reading input from a terminal, pipe or
two-way communication including sockets.
For connection to a remote host via socket, GAWK_SOCK_RETRIES
controls the number of retries, and GAWK_MSEC_SLEEP the interval
between retries. The interval is in milliseconds. On systems that do
not support usleep(3), the value is rounded up to an integral number
of seconds.
If POSIXLY_CORRECT exists in the environment, then gawk behaves
exactly as if --posix had been specified on the command line. If
--lint has been specified, gawk issues a warning message to this
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 5.1.
The original version of UNIX awk was designed and implemented by
Alfred Aho, Peter Weinberger, and Brian Kernighan of Bell
Laboratories. Brian Kernighan continues to maintain and enhance it.
Paul Rubin and Jay Fenlason, of the Free Software Foundation, wrote
gawk, to be compatible with the original version of awk distributed
in Seventh Edition UNIX. John Woods contributed a number of bug
fixes. David Trueman, with contributions from Arnold Robbins, made
gawk compatible with the new version of UNIX awk. Arnold Robbins is
the current maintainer.
See GAWK: Effective AWK Programming for a full list of the
contributors to gawk and its documentation.
See the README file in the gawk distribution for up-to-date
information about maintainers and which ports are currently
supported.
If you find a bug in gawk, please send electronic mail to
bug-gawk@gnu.org. Please include your operating system and its
revision, the version of gawk (from gawk --version), which C compiler
you used to compile it, and a test program and data that are as small
as possible for reproducing the problem.
Before sending a bug report, please do the following things. First,
verify that you have the latest version of gawk. Many bugs (usually
subtle ones) are fixed at each release, and if yours is out of date,
the problem may already have been solved. Second, please see if
setting the environment variable LC_ALL to LC_ALL=C causes things to
behave as you expect. If so, it's a locale issue, and may or may not
really be a bug. Finally, please read this man page and the
reference manual carefully to be sure that what you think is a bug
really is, instead of just a quirk in the language.
Whatever you do, do NOT post a bug report in comp.lang.awk. While
the gawk developers occasionally read this newsgroup, posting bug
reports there is an unreliable way to report bugs. Similarly, do NOT
use a web forum (such as Stack Overflow) for reporting bugs.
Instead, please use the electronic mail addresses given above.
Really.
If you're using a GNU/Linux or BSD-based system, you may wish to
submit a bug report to the vendor of your distribution. That's fine,
but please send a copy to the official email address as well, since
there's no guarantee that the bug report will be forwarded to the
gawk maintainer.
The -F option is not necessary given the command line variable
assignment feature; it remains only for backwards compatibility.
egrep(1), sed(1), getpid(2), getppid(2), getpgrp(2), getuid(2),
geteuid(2), getgid(2), getegid(2), getgroups(2), printf(3),
strftime(3), usleep(3)
The AWK Programming Language, Alfred V. Aho, Brian W. Kernighan,
Peter J. Weinberger, Addison-Wesley, 1988. ISBN 0-201-07981-X.
GAWK: Effective AWK Programming, Edition 5.1, shipped with the gawk
source. The current version of this document is available online at
https://www.gnu.org/software/gawk/manual .
The GNU gettext documentation, available online at
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") }'
Brian Kernighan provided valuable assistance during testing and
debugging. We thank him.
Copyright © 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
1999, 2001, 2002, 2003, 2004, 2005, 2007, 2009, 2010, 2011, 2012,
2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, Free Software
Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this
manual page provided the copyright notice and this permission notice
are preserved on all copies.
Permission is granted to copy and distribute modified versions of
this manual page under the conditions for verbatim copying, provided
that the entire resulting derived work is distributed under the terms
of a permission notice identical to this one.
Permission is granted to copy and distribute translations of this
manual page into another language, under the above conditions for
modified versions, except that this permission notice may be stated
in a translation approved by the Foundation.
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 2020-06-09. (At that time,
the date of the most recent commit that was found in the repository
was 2020-06-08.) 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 Mar 23 2020 GAWK(1)
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