awk
(1g)
Name
awk - pattern scanning and processing language
Synopsis
gawk [ POSIX or GNU style options ] -f program-file [ -- ]
file ...
gawk [ POSIX or GNU style options ] [ -- ] program-text file
...
pgawk [ POSIX or GNU style options ] -f program-file [ -- ]
file ...
pgawk [ POSIX or GNU style options ] [ -- ] program-text
file ...
Description
Utility Commands GAWK(1)
NAME
gawk - pattern scanning and processing language
SYNOPSIS
gawk [ POSIX or GNU style options ] -f program-file [ -- ]
file ...
gawk [ POSIX or GNU style options ] [ -- ] program-text file
...
pgawk [ POSIX or GNU style options ] -f program-file [ -- ]
file ...
pgawk [ POSIX or GNU style options ] [ -- ] program-text
file ...
DESCRIPTION
Gawk is the GNU Project's implementation of the AWK program-
ming language. It conforms to the definition of the lan-
guage 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, with the additional features
found in the System V Release 4 version of UNIX awk. Gawk
also provides more recent Bell Laboratories awk extensions,
and a number of GNU-specific extensions.
Pgawk is the profiling version of gawk. It is identical in
every way to gawk, except that programs run more slowly, and
it automatically produces an execution profile in the file
awkprof.out when done. See the --profile option, below.
The command line consists of options to gawk itself, the AWK
program text (if not supplied via the -f or --file options),
and values to be made available in the ARGC and ARGV pre-
defined AWK variables.
OPTION FORMAT
Gawk options may be either traditional POSIX 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.
Following the POSIX standard, gawk-specific options are sup-
plied via arguments to the -W option. Multiple -W options
may be supplied Each -W option has a corresponding long
option, as detailed below. Arguments to long options are
either joined with the option by an = sign, with no inter-
vening spaces, or they may be provided in the next command
line argument. Long options may be abbreviated, as long as
the abbreviation remains unique.
OPTIONS
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Utility Commands GAWK(1)
Gawk accepts the following options, listed by frequency.
-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 execu-
tion of the program begins. Such variable values are
available to the BEGIN block of an AWK program.
-f program-file
--file program-file
Read the AWK program source from the file program-file,
instead of from the first command line argument. Mul-
tiple -f (or --file) options may be used.
-mf NNN
-mr NNN
Set various memory limits to the value NNN. The f flag
sets the maximum number of fields, and the r flag sets
the maximum record size. These two flags and the -m
option are from an earlier version of the Bell Labora-
tories research version of UNIX awk. They are ignored
by gawk, since gawk has no pre-defined limits. (Cur-
rent versions of the Bell Laboratories awk no longer
accept them.)
-O
--optimize
Enable optimizations upon the internal representation
of the program. Currently, this includes just simple
constant-folding. The gawk maintainer hopes to add
additional optimizations over time.
-W compat
-W traditional
--compat
--traditional
Run in compatibility mode. In compatibility mode, gawk
behaves identically to UNIX awk; none of the GNU-spe-
cific extensions are recognized. The use of --tradi-
tional is preferred over the other forms of this
option. See GNU EXTENSIONS, below, for more informa-
tion.
-W copyleft
-W copyright
--copyleft
--copyright
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Print the short version of the GNU copyright informa-
tion message on the standard output and exit success-
fully.
-W dump-variables[=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.)
-W exec file
--exec file
Similar to -f, however, this is option is the last one
processed. This should be used with #! scripts, par-
ticularly 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.
-W gen-po
--gen-po
Scan and parse the AWK program, and generate a GNU .po
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 .po files.
-W help
-W usage
--help
--usage
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.)
-W lint[=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 cer-
tainly encourage the development of cleaner AWK pro-
grams. With an optional argument of invalid, only
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Utility Commands GAWK(1)
warnings about things that are actually invalid are
issued. (This is not fully implemented yet.)
-W lint-old
--lint-old
Provide warnings about constructs that are not portable
to the original version of Unix awk.
-W non-decimal-data
--non-decimal-data
Recognize octal and hexadecimal values in input data.
Use this option with great caution!
-W posix
--posix
This turns on compatibility mode, with the following
additional restrictions:
o \x escape sequences are not recognized.
o Only space and tab act as field separators when FS is
set to a single space, newline does not.
o You cannot continue lines after ? and :.
o The synonym func for the keyword function is not rec-
ognized.
o The operators ** and **= cannot be used in place of ^
and ^=.
o The fflush() function is not available.
-W profile[=prof_file]
--profile[=prof_file]
Send profiling data to prof_file. The default is
awkprof.out. When run with gawk, the profile is just a
"pretty printed" version of the program. When run with
pgawk, the profile contains execution counts of each
statement in the program in the left margin and func-
tion call counts for each user-defined function.
-W re-interval
--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. How-
ever, their use is likely to break old AWK programs, so
gawk only provides them if they are requested with this
option, or when --posix is specified.
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Utility Commands GAWK(1)
-W source 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 --file options) with source code
entered on the command line. It is intended primarily
for medium to large AWK programs used in shell scripts.
-W use-lc-numeric
--use-lc-numeric
This forces 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 tradi-
tional 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.
-W version
--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 fur-
ther 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 process-
ing. This is particularly useful for running AWK programs
via the "#!" executable interpreter mechanism.
AWK PROGRAM EXECUTION
An AWK program consists of a sequence of pattern-action
statements and optional function definitions.
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
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--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.
The environment variable AWKPATH specifies a search path to
use when finding source files named with the -f option. 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.
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 block(s)
(if any), and then proceeds to read each file named in the
ARGV array. 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
block(s) have been run.) Command line variable assignment
is most useful for dynamically assigning values to the vari-
ables 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 record in the input, gawk tests to see if it
matches any pattern in the AWK program. For each pattern
that the record matches, the associated action is executed.
The patterns are tested in the order they occur in the pro-
gram.
Finally, after all the input is exhausted, gawk executes the
code in the END block(s) (if any).
VARIABLES, RECORDS AND FIELDS
AWK variables are dynamic; they come into existence when
they are first used. Their values are either floating-point
numbers or strings, or both, depending upon how they are
used. AWK also has one dimensional arrays; arrays with mul-
tiple dimensions may be simulated. Several pre-defined
variables are set as a program runs; these are described as
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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 regu-
lar 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 blank 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 sep-
arator. 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 spe-
cial case that FS is a single space, fields are separated by
runs of spaces and/or tabs and/or newlines. (But see the
section POSIX COMPATIBILITY, below). NOTE: The value of
IGNORECASE (see below) also affects how fields are split
when FS is a regular expression, and how records are sepa-
rated 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. The
value of FS is ignored. Assigning a new value to FS over-
rides the use of FIELDWIDTHS, and restores the default
behavior.
Each field in the input record may be referenced by its
position, $1, $2, and so on. $0 is the whole record.
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-exis-
tent field (e.g., $(NF+2) = 5) increases the value of NF,
creates any intervening fields with the null string as their
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value, 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 pro-
cessed.
ARGV Array of command line arguments. The array is
indexed from 0 to ARGC - 1. Dynamically chang-
ing 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" spec-
ify that all files should use binary I/O. Any
other string value is treated as "rw", but gen-
erates 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 envi-
ronment variables, each element being the value
of that variable (e.g., ENVIRON["HOME"] might be
/home/arnold). Changing this array does not
affect the environment seen by programs which
gawk spawns via redirection or the system()
function.
ERRNO If a system error occurs either doing a redi-
rection for getline, during a read for getline,
or during a close(), then ERRNO will contain a
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string describing the error. The value is sub-
ject to translation in non-English locales.
FIELDWIDTHS A white-space separated list of fieldwidths.
When set, gawk parses the input into fields of
fixed width, instead of using the value of the
FS variable as the field separator.
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 block (unless set by getline).
FNR The input record number in the current input
file.
FS The input field separator, a space by default.
See Fields, above.
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, record separating with RS, regular
expression matching with ~ and !~, and the gen-
sub(), gsub(), index(), match(), 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. Under Unix, the full ISO 8859-1
Latin-1 character set is used when ignoring
case. As of gawk 3.1.4, the case equivalencies
are fully locale-aware, based on the C <ctype.h>
facilities such as isalpha(), and toupper().
LINT Provides dynamic control of the --lint option
from within an AWK program. When true, gawk
prints lint warnings. When false, it does not.
When assigned the string value "fatal", lint
warnings become fatal errors, exactly like
--lint=fatal. Any other true value just prints
warnings.
NF The number of fields in the current input
record.
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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 new-
line.
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["egid"] the value of the getegid(2)
system call.
PROCINFO["euid"] the value of the geteuid(2)
system call.
PROCINFO["FS"] "FS" if field splitting with
FS is in effect, or "FIELD-
WIDTHS" if field splitting
with FIELDWIDTHS is in
effect.
PROCINFO["gid"] the value of the getgid(2)
system call.
PROCINFO["pgrpid"] the process group ID of the
current process.
PROCINFO["pid"] the process ID of the cur-
rent process.
PROCINFO["ppid"] the parent process ID of the
current process.
PROCINFO["uid"] the value of the getuid(2)
system call.
PROCINFO["version"] the version of gawk. This
is available from version
3.1.4 and later.
RS The input record separator, by default a new-
line.
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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 character used to separate multiple sub-
scripts in array elements, by default "\034".
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 con-
sisting 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 val-
ues.
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.
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.
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Variable Typing And Conversion
Variables and fields may be (floating point) numbers, or
strings, or both. How the value of a variable is inter-
preted 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 0 to it;
to force it to be treated as a string, concatenate it with
the null 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".
When operating in POSIX mode (such as with the --posix com-
mand line option), beware that locale settings may interfere
with the way decimal numbers are treated: the decimal sepa-
rator 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. Other-
wise, 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() that are numeric strings. The basic idea
is that user input, and only user input, that looks numeric,
should be treated that way.
Uninitialized variables have the numeric value 0 and the
string value "" (the null, or empty, string).
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Octal and Hexadecimal Constants
Starting with version 3.1 of gawk , 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 ("). 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. As in ANSI C, all following
hexadecimal digits are considered part of the escape
sequence. (This feature should tell us something about
language design by committee.) 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.
The escape sequences may also be used inside constant regu-
lar expressions (e.g., /[ \t\f\n\r\v]/ matches whitespace
characters).
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/.
PATTERNS AND ACTIONS
AWK is a line-oriented language. The pattern comes first,
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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 is executed 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. Blank lines may be used to separate
statements. Normally, a statement ends with a newline, how-
ever, this is not the case for lines ending in a ",", {, ?,
:, &&, 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 will be ignored.
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
/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 writ-
ten in a single BEGIN block. They are executed before any
of the input is read. Similarly, all the END blocks 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 expres-
sions. BEGIN and END patterns cannot have missing action
parts.
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
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Utility Commands GAWK(1)
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-cir-
cuit 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...] character list, matches any of the characters
abc....
[^abc...] 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.
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(r) grouping: matches r.
r{n}
r{n,}
r{n,m} One or two numbers inside braces denote an inter-
val expression. If there is one number in the
braces, the preceding regular expression r is
repeated n times. If there are two numbers sepa-
rated 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.
Interval expressions are only available if either
--posix or --re-interval is specified on the com-
mand line.
\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.
\w matches any word-constituent character (letter,
digit, or underscore).
\W matches any character that is not word-con-
stituent.
\` 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
below) 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 alpha-
betic 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:
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[: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:] Lower-case 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 form-
feed, to name a few).
[:upper:] Upper-case alphabetic characters.
[:xdigit:] Characters that are hexadecimal digits.
For example, before the POSIX standard, to match alphanu-
meric 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 col-
lated 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 "`" are equivalent.)
Collating Symbols
A collating symbol is a multi-character collating ele-
ment enclosed in [. and .]. For example, if ch is a
collating element, then [[.ch.]] is a regular
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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," "'," and "`." In this
case, [[=e=]] is a regular expression that matches any
of e, ', or `.
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 equiva-
lence classes.
The \y, \B, \<, \>, \w, \W, \`, and \' operators are spe-
cific 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 provide all the facilities of
POSIX regular expressions and the GNU regular expres-
sion operators described above. However, interval
expressions are not supported.
--posix
Only POSIX regular expressions are supported, the GNU
operators are not special. (E.g., \w matches a literal
w). Interval expressions are allowed.
--traditional
Traditional Unix awk regular expressions are matched.
The GNU operators are not special, interval expressions
are not available, and neither are the POSIX character
classes ([[:alnum:]] and so on). 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
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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 post-
fix.
^ 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 was
intended.
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 evalu-
ated.
= += -= *= /= %= ^=
Assignment. Both absolute assignment (var =
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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 }
I/O Statements
The input/output statements are as follows:
close(file [, how]) Close file, pipe or co-process. The
optional how should only be used when
closing one end of a two-way pipe to a
co-process. It must be a string
value, either "to" or "from".
getline Set $0 from next input record; set NF,
NR, FNR.
getline <file Set $0 from next record of file; set
NF.
getline var Set var from next input record; set
NR, FNR.
getline var <file Set var from next record of file.
command | getline [var]
Run command piping the output either
into $0 or var, as above.
command |& getline [var]
Run command as a co-process piping the
output either into $0 or var, as
above. Co-processes are a gawk exten-
sion. (command can also be a socket.
See the subsection Special File Names,
below.)
next Stop processing the current input
record. The next input record is read
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and processing starts over with the
first pattern in the AWK program. If
the end of the input data is reached,
the END block(s), if any, are exe-
cuted.
nextfile Stop processing the current input
file. The next input record read
comes from the next input file. FILE-
NAME and ARGIND are updated, FNR is
reset to 1, and processing starts over
with the first pattern in the AWK pro-
gram. If the end of the input data is
reached, the END block(s), if any, are
executed.
print Prints the current record. The output
record is terminated with the value of
the ORS variable.
print expr-list Prints expressions. Each expression
is separated by the value of the OFS
variable. The output record is termi-
nated with the value of the ORS vari-
able.
print expr-list >file Prints expressions on file. Each
expression is separated by the value
of the OFS variable. The output
record is terminated with the value of
the ORS variable.
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.)
fflush([file]) Flush any buffers associated with the
open output file or pipe file. If
file is missing, then standard output
is flushed. If file is the null
string, then all open output files and
pipes have their buffers flushed.
Additional output redirections are allowed for print and
printf.
print ... >> file
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Appends output to the file.
print ... | command
Writes on a pipe.
print ... |& command
Sends data to a co-process or socket. (See also the
subsection Special File Names, below.)
The getline command returns 1 on success, 0 on end of file,
and -1 on an error. Upon an error, ERRNO contains a string
describing the problem.
NOTE: Failure in opening a two-way socket will result in a
non-fatal error being returned to the calling function. If
using a pipe, co-process, or socket to getline, or from
print or printf within a loop, you must use close() to cre-
ate new instances of the command or socket. AWK does not
automatically close pipes, sockets, or co-processes when
they return EOF.
The printf Statement
The AWK versions of the printf statement and sprintf() func-
tion (see below) accept the following conversion specifica-
tion formats:
%c An ASCII 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).
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%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 format-
ting. 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 pro-
gram. 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 con-
versions, 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, that indicates out-
put 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.
width
The field should be padded to this width. The field is
normally padded with spaces. If the 0 flag has been
used, 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
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formats, it specifies the maximum number of significant
digits. For the %d, %o, %i, %u, %x, and %X formats, it
specifies the minimum number of digits to print. For
%s, it specifies the maximum number of characters from
the string that should be printed.
The dynamic width and prec capabilities of the ANSI 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, sup-
ply the count$ after the * in the format string. For exam-
ple, "%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:
/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 descrip-
tor n.
These are particularly useful for error messages. For exam-
ple:
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 |& co-
process operator for creating TCP/IP network connections.
/inet/tcp/lport/rhost/rport File for 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.
/inet/udp/lport/rhost/rport Similar, but use UDP/IP instead
of TCP/IP.
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/inet/raw/lport/rhost/rport Reserved for future use.
Other special filenames provide access to information about
the running gawk process. These filenames are now obsolete.
Use the PROCINFO array to obtain the information they pro-
vide. The filenames are:
/dev/pid Reading this file returns the process ID of the
current process, in decimal, terminated with a
newline.
/dev/ppid Reading this file returns the parent process ID
of the current process, in decimal, terminated
with a newline.
/dev/pgrpid Reading this file returns the process group ID
of the current process, in decimal, terminated
with a newline.
/dev/user Reading this file returns a single record termi-
nated with a newline. The fields are separated
with spaces. $1 is the value of the getuid(2)
system call, $2 is the value of the geteuid(2)
system call, $3 is the value of the getgid(2)
system call, and $4 is the value of the gete-
gid(2) system call. If there are any additional
fields, they are the group IDs returned by get-
groups(2). Multiple groups may not be supported
on all systems.
Numeric Functions
AWK has the following built-in arithmetic functions:
atan2(y, x) Returns the arctangent of y/x in radians.
cos(expr) Returns the cosine of expr, which is in radi-
ans.
exp(expr) The exponential function.
int(expr) Truncates to integer.
log(expr) The natural logarithm function.
rand() Returns a random number N, between 0 and 1,
such that 0 <= N < 1.
sin(expr) Returns the sine of expr, which is in radians.
sqrt(expr) The square root function.
srand([expr]) Uses expr as a new seed for the random number
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generator. If no expr is provided, the time
of day is used. The return value is the pre-
vious seed for the random number generator.
String Functions
Gawk has the following built-in string functions:
asort(s [, d]) Returns the number of elements in
the source array s. The contents of
s are sorted using gawk's normal
rules for comparing values, and the
indices of the sorted values of s
are replaced with sequential inte-
gers starting with 1. If the
optional destination array d is
specified, then s is first dupli-
cated into d, and then d is sorted,
leaving the indices of the source
array s unchanged.
asorti(s [, d]) Returns 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 numeri-
cally, and the values are those of
the original indices. The original
values are lost; thus provide a sec-
ond array if you wish to preserve
the original.
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, $0
is used 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 rep-
resents the entire matched text, as
does the character &. Unlike sub()
and gsub(), the modified string is
returned as the result of the func-
tion, and the original target string
is not changed.
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gsub(r, s [, t]) For each substring matching the reg-
ular 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
&'s and backslashes in the replace-
ment text of sub(), gsub(), and gen-
sub().)
index(s, t) Returns the index of the string t in
the string s, or 0 if t is not
present. (This implies that charac-
ter indices start at one.)
length([s]) Returns the length of the string s,
or the length of $0 if s is not sup-
plied. Starting with version 3.1.5,
as a non-standard extension, with an
array argument, length() returns the
number of elements in the array.
match(s, r [, a]) Returns the position in s where the
regular expression r occurs, or 0 if
r is not present, and sets the val-
ues 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 parenthe-
sized subexpression in r. The 0'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 match-
ing substring.
split(s, a [, r]) Splits the string s into the array a
on the regular expression r, and
returns the number of fields. If r
is omitted, FS is used instead. The
array a is cleared first. Splitting
behaves identically to field
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splitting, described above.
sprintf(fmt, expr-list) Prints expr-list according to fmt,
and returns the resulting string.
strtonum(str) Examines str, and returns its
numeric value. If str begins with a
leading 0, strtonum() assumes that
str is an octal number. If str
begins with a leading 0x or 0X, str-
tonum() assumes that str is a hexa-
decimal number.
sub(r, s [, t]) Just like gsub(), but only the first
matching substring is replaced.
substr(s, i [, n]) Returns the at most n-character sub-
string of s starting at i. If n is
omitted, the rest of s is used.
tolower(str) Returns a copy of the string str,
with all the upper-case characters
in str translated to their corre-
sponding lower-case counterparts.
Non-alphabetic characters are left
unchanged.
toupper(str) Returns a copy of the string str,
with all the lower-case characters
in str translated to their corre-
sponding upper-case counterparts.
Non-alphabetic characters are left
unchanged.
As of version 3.1.5, 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 for-
matting them.
mktime(datespec)
Turns datespec into a time stamp of the same form
as returned by systime(). 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
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23, the minute from 0 to 59, and 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. The time is assumed
to be in the local timezone. If the daylight sav-
ing 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 speci-
fied 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]]])
Formats 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. See
the specification for the strftime() function in
ANSI C for the format conversions that are guaran-
teed to be available.
systime() Returns 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
Starting with version 3.1 of gawk, the following bit manipu-
lation functions are available. They work by converting
double-precision floating point values to uintmax_t inte-
gers, doing the operation, and then converting the result
back to floating point. The functions are:
and(v1, v2) Return the bitwise AND of the values
provided by v1 and v2.
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 pro-
vided by v1 and v2.
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rshift(val, count) Return the value of val, shifted right
by count bits.
xor(v1, v2) Return the bitwise XOR of the values
provided by v1 and v2.
Internationalization Functions
Starting with version 3.1 of gawk, 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])
Specifies the directory where gawk looks for the .mo
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 bindtextdo-
main() returns the current binding for the given
domain.
dcgettext(string [, domain [, category]])
Returns 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 sup-
ply a text domain. Use TEXTDOMAIN if you want to use
the current domain.
dcngettext(string1 , string2 , number [, domain [, cate-
gory]])
Returns the plural form used for number of the transla-
tion 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 sup-
ply a text domain. Use TEXTDOMAIN if you want to use
the current domain.
USER-DEFINED FUNCTIONS
Functions in AWK are defined as follows:
function name(parameter list) { statements }
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Functions are executed when they are called from within
expressions in either patterns or actions. Actual parame-
ters 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 lan-
guage, 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 exam-
ple:
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 imme-
diately follow the function name, without any intervening
white space. 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. Func-
tion parameters used as local variables are initialized to
the null string and the number zero upon function invoca-
tion.
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.
If --lint has been provided, gawk warns about calls to unde-
fined 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.
DYNAMICALLY LOADING NEW FUNCTIONS
Beginning with version 3.1 of gawk, you can dynamically add
new built-in functions to the running gawk interpreter. The
full details are beyond the scope of this manual page; see
GAWK: Effective AWK Programming for the details.
extension(object, function)
Dynamically link the shared object file named by
object, and invoke function in that object, to per-
form initialization. These should both be provided
as strings. Returns the value returned by function.
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This function is provided and documented in GAWK: Effective
AWK Programming, but everything about this feature is likely
to change eventually. We STRONGLY recommend that you do not
use this feature for anything that you aren't willing to
redo.
SIGNALS
pgawk accepts two signals. SIGUSR1 causes it to dump a pro-
file 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
pgawk to dump the profile and function call stack and then
exit.
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") }'
INTERNATIONALIZATION
String constants are sequences of characters enclosed in
double quotes. In non-English speaking environments, it is
possible to mark strings in the AWK program as requiring
translation to the native 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.
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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 .mo 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 bindtextdo-
main() functions in your program, as appropriate.
4. Run gawk --gen-po -f myprog.awk > myprog.po to generate
a .po file for your program.
5. Provide appropriate translations, and build and install
the corresponding .mo files.
The internationalization features are described in full
detail in GAWK: Effective AWK Programming.
POSIX COMPATIBILITY
A primary goal for gawk is compatibility with the POSIX
standard, as well as with the latest version of UNIX awk.
To this end, gawk incorporates the following user visible
features which are not described in the AWK book, but are
part of the Bell Laboratories 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 block is executed. However,
in earlier implementations, when such an assignment appeared
before any file names, the assignment would happen before
the BEGIN block was run. Applications came to depend on
this "feature." When awk was changed to match its documen-
tation, 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 and the GNU developers.)
The -W option for implementation specific features is from
the POSIX standard.
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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 new 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 Labora-
tories version); the tolower() and toupper() built-in func-
tions (from the Bell Laboratories version); and the ANSI C
conversion specifications in printf (done first in the Bell
Laboratories version).
HISTORICAL FEATURES
There are two features of historical AWK implementations
that gawk supports. First, 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)
This feature is marked as "deprecated" in the POSIX stan-
dard, and gawk issues a warning about its use if --lint is
specified on the command line.
The other feature is the use of either the continue or the
break statements outside the body of a while, for, or do
loop. Traditional AWK implementations have treated such
usage as equivalent to the next statement. Gawk supports
this usage if --traditional has been specified.
GNU EXTENSIONS
Gawk has a 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.
o No path search is performed for files named via the -f
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option. Therefore the AWKPATH environment variable is not
special.
o The \x escape sequence. (Disabled with --posix.)
o The fflush() function. (Disabled with --posix.)
o The ability to continue lines after ? and :. (Disabled
with --posix.)
o Octal and hexadecimal constants in AWK programs.
o The ARGIND, BINMODE, ERRNO, LINT, RT and TEXTDOMAIN vari-
ables are not special.
o The IGNORECASE variable and its side-effects are not
available.
o The FIELDWIDTHS variable and fixed-width field splitting.
o The PROCINFO array is not available.
o The use of RS as a regular expression.
o The special file names available for I/O redirection are
not recognized.
o The |& operator for creating co-processes.
o The ability to split out individual characters using the
null string as the value of FS, and as the third argument
to split().
o The optional second argument to the close() function.
o The optional third argument to the match() function.
o The ability to use positional specifiers with printf and
sprintf().
o The ability to pass an array to length().
o The use of delete array to delete the entire contents of
an array.
o The use of nextfile to abandon processing of the current
input file.
o The and(), asort(), asorti(), bindtextdomain(), compl(),
dcgettext(), dcngettext(), gensub(), lshift(), mktime(),
or(), rshift(), strftime(), strtonum(), systime() and
xor() functions.
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Utility Commands GAWK(1)
o Localizable strings.
o Adding new built-in functions dynamically with the exten-
sion() function.
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, respec-
tively. It returns the process's exit status when closing
an input pipe. The return value is -1 if the named file,
pipe or co-process 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' ....
If gawk is configured with the --enable-switch option to the
configure command, then it accepts an additional control-
flow statement:
switch (expression) {
case value|regex : statement
...
[ default: statement ]
}
If gawk is configured with the --disable-directories-fatal
option, then it will silently skip directories named on the
command line. Otherwise, it will do so only if invoked with
the --traditional option.
ENVIRONMENT VARIABLES
The AWKPATH environment variable can be used to provide a
list of directories that gawk searches when looking for
files named via the -f and --file options.
For socket communication, two special environment variables
can be used to control the number of retries
(GAWK_SOCK_RETRIES), and the interval between retries
(GAWK_MSEC_SLEEP). The interval is in milliseconds. On sys-
tems 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 com-
mand line. If --lint has been specified, gawk issues a
warning message to this effect.
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Utility Commands GAWK(1)
EXIT STATUS
If the exit statement is used with a value, then gawk exits
with the numeric value given to it.
Otherwise, if there were no problems during execution, gawk
exits with the value of the C constant EXIT_SUCCESS. This
is usually zero.
If an error occurs, gawk exits with the value of the C con-
stant 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.
ATTRIBUTES
See attributes(5) for descriptions of the following
attributes:
+---------------+------------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+------------------+
|Availability | text/gawk |
+---------------+------------------+
|Stability | Volatile |
+---------------+------------------+
SEE ALSO
egrep(1), getpid(2), getppid(2), getpgrp(2), getuid(2),
geteuid(2), getgid(2), getegid(2), getgroups(2)
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 3.0, published by
the Free Software Foundation, 2001. The current version of
this document is available online at
http://www.gnu.org/software/gawk/manual.
BUGS
The -F option is not necessary given the command line vari-
able assignment feature; it remains only for backwards com-
patibility.
Syntactically invalid single character programs tend to
overflow the parse stack, generating a rather unhelpful mes-
sage. Such programs are surprisingly difficult to diagnose
in the completely general case, and the effort to do so
really is not worth it.
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Utility Commands GAWK(1)
AUTHORS
The original version of UNIX awk was designed and imple-
mented 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 Founda-
tion, wrote gawk, to be compatible with the original version
of awk distributed in Seventh Edition UNIX. John Woods con-
tributed a number of bug fixes. David Trueman, with contri-
butions from Arnold Robbins, made gawk compatible with the
new version of UNIX awk. Arnold Robbins is the current
maintainer.
The initial DOS port was done by Conrad Kwok and Scott
Garfinkle. Scott Deifik is the current DOS maintainer. Pat
Rankin did the port to VMS, and Michal Jaegermann did the
port to the Atari ST. The port to OS/2 was done by Kai Uwe
Rommel, with contributions and help from Darrel Hankerson.
Andreas Buening now maintains the OS/2 port. Fred Fish sup-
plied support for the Amiga, and Martin Brown provided the
BeOS port. Stephen Davies provided the original Tandem
port, and Matthew Woehlke provided changes for Tandem's
POSIX-compliant systems. Ralf Wildenhues now maintains that
port.
See the README file in the gawk distribution for current
information about maintainers and which ports are currently
supported.
VERSION INFORMATION
This man page documents gawk, version 3.1.8.
BUG REPORTS
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),
what 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.
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Utility Commands GAWK(1)
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. Instead, please use the electronic mail addresses
given above.
If you're using a GNU/Linux system or BSD-based system, you
may wish to submit a bug report to the vendor of your dis-
tribution. That's fine, but please send a copy to the offi-
cial email address as well, since there's no guarantee that
the bug will be forwarded to the gawk maintainer.
ACKNOWLEDGEMENTS
Brian Kernighan of Bell Laboratories provided valuable
assistance during testing and debugging. We thank him.
COPYING PERMISSIONS
Copyright (C) 1989, 1991, 1992, 1993, 1994, 1995, 1996,
1997, 1998, 1999, 2001, 2002, 2003, 2004, 2005, 2007, 2009,
2010 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 ver-
sions 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 con-
ditions for modified versions, except that this permission
notice may be stated in a translation approved by the Foun-
dation.
NOTES
This software was built from source available at
https://java.net/projects/solaris-userland. The original
community source was downloaded from
http://ftp.gnu.org/gnu/gawk/gawk-3.1.8.tar.bz2
Further information about this software can be found on the
open source community website at http://www.gnu.org/soft-
ware/gawk/.
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