AWK(1) Utility Commands AWK(1)
NAME
awk - GNU awk pattern scanning and processing language
SYNOPSIS
awk [ POSIX or GNU style options ] -f program-file [ -- ]
file ...
awk [ POSIX or GNU style options ] [ -- ] program-text
file ...
DESCRIPTION
Gawk is the GNU Project's implementation of the AWK pro-
gramming language. It conforms to the definition of the
language in the POSIX 1003.2 Command Language And Utili-
ties Standard. This version in turn is based on the
description in The AWK Programming Language, by Aho,
Kernighan, and Weinberger, with the additional features
defined in the System V Release 4 version of UNIX awk.
Gawk also provides some GNU-specific extensions.
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.
OPTIONS
Gawk options may be either the traditional POSIX one let-
ter options, or the GNU style long options. POSIX style
options start with a single ``-'', while GNU long options
start with ``--''. GNU style long options are provided
for both GNU-specific features and for POSIX mandated fea-
tures. Other implementations of the AWK language are
likely to only accept the traditional one letter options.
Following the POSIX standard, gawk-specific options are
supplied via arguments to the -W option. Multiple -W
options may be supplied, or multiple arguments may be sup-
plied together if they are separated by commas, or
enclosed in quotes and separated by white space. Case is
ignored in arguments to the -W option. Each -W option has
a corresponding GNU style long option, as detailed below.
Arguments to GNU style 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.
Gawk accepts the following options.
-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 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 argu-
ment. Multiple -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 the AT&T Bell Labs
research version of UNIX awk. They are ignored by
gawk, since gawk has no pre-defined limits.
-W compat
--compat Run in compatibility mode. In compatibility
mode, gawk behaves identically to UNIX awk;
none of the GNU-specific extensions are recog-
nized. See GNU EXTENSIONS, below, for more
information.
-W copyleft
-W copyright
--copyleft
--copyright Print the short version of the GNU copyright
information message on the error output.
-W help
-W usage
--help
--usage Print a relatively short summary of the avail-
able options on the error output. Per the GNU
Coding Standards, these options cause an imme-
diate, successful exit.
-W lint
--lint Provide warnings about constructs that are
dubious or non-portable to other AWK implemen-
tations.
-W posix
--posix This turns on compatibility mode, with the
following additional restrictions:
o \x escape sequences are not recognized.
o The synonym func for the keyword function is
not recognized.
o The operators ** and **= cannot be used in
place of ^ and ^=.
-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 com-
mand line. It is intended primarily for
medium to large size AWK programs used in
shell scripts.
The -W source= form of this option uses the
rest of the command line argument for program-
text; no other options to -W will be recog-
nized in the same argument.
-W version
--version Print version information for this particular
copy of gawk on the error 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 Founda-
tion is distributing. 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 is mainly
for consistency with the argument parsing con-
vention used by most other POSIX programs.
In compatibility mode, any other options are flagged as
illegal, 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.
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 -W source=, or
from the first non-option argument on the command line.
The -f and -W source= options may be used multiple times
on the command line. Gawk will read 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/lib/awk:/usr/local/lib/awk". 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 inter-
nal 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
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 line in the input, gawk tests to see if it
matches any pattern in the AWK program. For each pattern
that the line matches, the associated action is executed.
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 block(s) (if any).
VARIABLES 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
multiple dimensions may be simulated. Several pre-defined
variables are set as a program runs; these will be
described as needed and summarized below.
Fields
As each input line is read, gawk splits the line into
fields, using the value of the FS variable as the field
separator. If FS is a single character, fields are sepa-
rated by that character. Otherwise, FS is expected to be
a full regular expression. In the special case that FS is
a single blank, fields are separated by runs of blanks
and/or tabs. Note that the value of IGNORECASE (see
below) will also affect how fields are split when FS 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 will split up the record using the speci-
fied widths. The value of FS is ignored. Assigning a new
value to FS overrides the use of FIELDWIDTHS, and restores
the default behavior.
Each field in the input line may be referenced by its
position, $1, $2, and so on. $0 is the whole line. The
value of a field may be assigned to as well. Fields need
not be referenced by constants:
n = 5
print $n
prints the fifth field in the input line. The variable NF
is set to the total number of fields in the input line.
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) will increase the value of
NF, create any intervening fields with the null string as
their value, and cause the value of $0 to be recomputed,
with the fields being separated by the value of OFS. Ref-
erences to negative numbered fields cause a fatal error.
Built-in Variables
AWK'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.
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 /u/arnold). Changing this array does
not affect the environment seen by programs
which gawk spawns via redirection or the sys-
tem() function. (This may change in a future
version of gawk.)
ERRNO If a system error occurs either doing a redi-
rection for getline, during a read for get-
line, or during a close(), then ERRNO will
contain a string describing the error.
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. The fixed
field width facility is still experimental;
expect the semantics to change as gawk evolves
over time.
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.
FNR The input record number in the current input
file.
FS The input field separator, a blank by default.
IGNORECASE Controls the case-sensitivity of all regular
expression operations. If IGNORECASE has a
non-zero value, then pattern matching in
rules, field splitting with FS, regular
expression matching with ~ and !~, and the
gsub(), index(), match(), split(), and sub()
pre-defined functions will all ignore case
when doing regular expression operations.
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 ini-
tial value of IGNORECASE is zero, so all regu-
lar expression operations are normally case-
sensitive.
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 blank by
default.
ORS The output record separator, by default a new-
line.
RS The input record separator, by default a new-
line. RS is exceptional in that only the
first character of its string value is used
for separating records. (This will probably
change in a future release of gawk.) If RS is
set to the null string, then records are sepa-
rated by blank lines. When RS is set to the
null string, then the newline character always
acts as a field separator, in addition to
whatever value FS may have.
RSTART The index of the first character matched by
match(); 0 if no match.
RLENGTH The length of the string matched by match();
-1 if no match.
SUBSEP The character used to separate multiple sub-
scripts in array elements, by default "\034".
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 multi-
ply 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 in an if or while
statement to see 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.
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 conver-
sion is accomplished using atof(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 vari-
able as the argument. However, even though all numbers in
AWK are floating-point, integral values are always con-
verted as integers. Thus, given
CONVFMT = "%2.2f"
a = 12
b = a ""
the variable b has a string value of "12" and not "12.00".
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 numeri-
cally. Otherwise, the numeric value is converted to a
string and a string comparison is performed. Two strings
are compared, of course, as strings. According to the
POSIX standard, even if two strings are numeric strings, a
numeric comparison is performed. However, this is clearly
incorrect, and gawk does not do this.
Uninitialized variables have the numeric value 0 and the
string value "" (the null, or empty, string).
PATTERNS AND ACTIONS
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 will be executed for every single
line of input. A missing action is equivalent to
{ print }
which prints the entire line.
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, however, this is not the case for lines ending in
a ``,'', ``{'', ``?'', ``:'', ``&&'', or ``||''. Lines
ending in do or else also have their statements automati-
cally 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 written 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 expressions. BEGIN and END patterns cannot have
missing action parts.
For /regular expression/ patterns, the associated state-
ment is executed for each input line that matches the reg-
ular 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 expres-
sions.
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 combin-
ing more primitive pattern expressions. As in most lan-
guages, 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 line that matches pattern1, and continuing until a
record that matches pattern2, inclusive. It does not com-
bine 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 except newline.
^ matches the beginning of a line or a string.
$ matches the end of a line or a string.
[abc...] character class, matches any of the characters
abc....
[^abc...] negated character class, matches any character
except abc... and newline.
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.
The escape sequences that are valid in string constants
(see below) are also legal in regular expressions.
Actions
Action statements are enclosed in braces, { and }. Action
statements consist of the usual assignment, conditional,
and looping statements found in most languages. The opera-
tors, control statements, and input/output statements
available are patterned after those in C.
Operators
The operators in AWK, in order of increasing precedence,
are
= += -=
*= /= %= ^= Assignment. Both absolute assignment (var =
value) and operator-assignment (the other
forms) are supported.
?: The C conditional expression. This has the
form expr1 ? expr2 : expr3. If expr1 is true,
the value of the expression is expr2, other-
wise it is expr3. Only one of expr2 and expr3
is evaluated.
|| Logical OR.
&& Logical AND.
~ !~ 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.
< >
<= >=
!= == The regular relational operators.
blank String concatenation.
+ - Addition and subtraction.
* / % Multiplication, division, and modulus.
+ - ! Unary plus, unary minus, and logical negation.
^ Exponentiation (** may also be used, and **=
for the assignment operator).
++ -- Increment and decrement, both prefix and post-
fix.
$ Field reference.
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(filename) Close file (or pipe, see below).
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
NF, FNR.
getline var <file Set var from next record of file.
next Stop processing the current input
record. The next input record is
read 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.
next file Stop processing the current input
file. The next input record read
comes from the next input file.
FILENAME is 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.
print expr-list Prints expressions. Each expression
is separated by the value of the OFS
variable. The output record is ter-
minated with the value of the ORS
variable.
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 sys-
tems.)
Other input/output redirections are also allowed. For
print and printf, >>file appends output to the file, while
| command writes on a pipe. In a similar fashion, command
| getline pipes into getline. The getline command will
return 0 on end of file, and -1 on an error.
The printf Statement
The AWK versions of the printf statement and sprintf()
function (see below) accept the following conversion spec-
ification 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 A decimal number (the integer part).
%i Just like %d.
%e A floating point number of the form
[-]d.ddddddE[+-]dd.
%f A floating point number of the form [-]ddd.dddddd.
%g Use e or f conversion, whichever is shorter, with
nonsignificant zeros suppressed.
%o An unsigned octal number (again, an integer).
%s A character string.
%x An unsigned hexadecimal number (an integer).
%X Like %x, but using ABCDEF instead of abcdef.
%% A single % character; no argument is converted.
There are optional, additional parameters that may lie
between the % and the control letter:
- The expression should be left-justified within its
field.
width The field should be padded to this width. If the
number has a leading zero, then the field will be
padded with zeros. Otherwise it is padded with
blanks. This applies even to the non-numeric out-
put formats.
.prec A number indicating the maximum width of strings or
digits to the right of the decimal point.
The dynamic width and prec capabilities of the ANSI C
printf() routines are supported. A * in place of either
the width or prec specifications will cause their values
to be taken from the argument list to printf or sprintf().
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). Other special
filenames provide access information about the running
gawk process. 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, termi-
nated 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 ter-
minated with a newline. The fields are sepa-
rated with blanks. $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 getegid(2) system call. If there are any
additional fields, they are the group IDs
returned by getgroups(2). Multiple groups may
not be supported on all systems.
/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"
These file names may also be used on the command line to
name data files.
Numeric Functions
AWK has the following pre-defined arithmetic functions:
atan2(y, x) returns the arctangent of y/x in radians.
cos(expr) returns the cosine in radians.
exp(expr) the exponential function.
int(expr) truncates to integer.
log(expr) the natural logarithm function.
rand() returns a random number between 0 and 1.
sin(expr) returns the sine in radians.
sqrt(expr) the square root function.
srand(expr) use expr as a new seed for the random number
generator. If no expr is provided, the time of
day will be used. The return value is the
previous seed for the random number generator.
String Functions
AWK has the following pre-defined string functions:
gsub(r, s, t) for each substring matching the
regular expression r in the string
t, substitute the string s, and
return the number of substitu-
tions. If t is not supplied, use
$0.
index(s, t) returns the index of the string t
in the string s, or 0 if t is not
present.
length(s) returns the length of the string
s, or the length of $0 if s is not
supplied.
match(s, r) returns the position in s where
the regular expression r occurs,
or 0 if r is not present, and sets
the values of RSTART and RLENGTH.
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.
sprintf(fmt, expr-list) prints expr-list according to fmt,
and returns the resulting string.
sub(r, s, t) just like gsub(), but only the
first matching substring is
replaced.
substr(s, i, n) returns the n-character substring
of s starting at i. If n is omit-
ted, 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.
Time Functions
Since one of the primary uses of AWK programs is process-
ing log files that contain time stamp information, gawk
provides the following two functions for obtaining time
stamps and formatting them.
systime() returns the current time of day as the number of
seconds since the Epoch (Midnight UTC, January
1, 1970 on POSIX systems).
strftime(format, timestamp)
formats timestamp according to the specification
in format. The timestamp should be of the same
form as returned by systime(). If timestamp is
missing, the current time of day is used. See
the specification for the strftime() function in
ANSI C for the format conversions that are guar-
anteed to be available. A public-domain version
of strftime(3) and a man page for it are shipped
with gawk; if that version was used to build
gawk, then all of the conversions described in
that man page are available to gawk.
String Constants
String constants in AWK are sequences of characters
enclosed between double quotes ("). Within strings, cer-
tain escape sequences are recognized, as in C. These are:
\\ A literal backslash.
\a The ``alert'' character; usually the ASCII BEL char-
acter.
\b backspace.
\f form-feed.
\n new line.
\r carriage return.
\t horizontal tab.
\v vertical tab.
\xhex digits
The character represented by the string of hexadeci-
mal digits following the \x. As in ANSI C, all fol-
lowing hexadecimal digits are considered part of the
escape sequence. (This feature should tell us some-
thing 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 reg-
ular expressions (e.g., /[ \t\f\n\r\v]/ matches whitespace
characters).
FUNCTIONS
Functions in AWK are defined as follows:
function name(parameter list) { statements }
Functions are executed when called from within the action
parts of regular pattern-action statements. 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
example:
function f(p, q, a, b) { # a & b are local
..... }
/abc/ { ... ; f(1, 2) ; ... }
The left parenthesis in a function call is required to
immediately follow the function name, without any inter-
vening white space. This is to avoid a syntactic ambigu-
ity 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.
The word func may be used in place of function.
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 }
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.
The GAWK Manual, Edition 0.15, published by the Free Soft-
ware Foundation, 1993.
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 awk in System V Release 4, and are in the POSIX
standard.
The -v option for assigning variables before program exe-
cution starts is new. 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 documentation, this
option was added to accommodate applications that depended
upon the old behavior. (This feature was agreed upon by
both the AT&T and GNU developers.)
The -W option for implementation specific features is from
the POSIX standard.
When processing arguments, gawk uses the special option
``--'' to signal the end of arguments. In compatibility
mode, it will warn about, but otherwise ignore, 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 System V Release 4 version of UNIX awk (and 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
AT&T's); the tolower() and toupper() built-in functions
(from AT&T); and the ANSI C conversion specifications in
printf (done first in AT&T's version).
GNU EXTENSIONS
Gawk has some extensions to POSIX awk. They are described
in this section. All the extensions described here can be
disabled by invoking gawk with the -W compat option.
The following features of gawk are not available in POSIX
awk.
o The \x escape sequence.
o The systime() and strftime() functions.
o The special file names available for I/O redirec-
tion are not recognized.
o The ARGIND and ERRNO variables are not special.
o The IGNORECASE variable and its side-effects are
not available.
o The FIELDWIDTHS variable and fixed width field
splitting.
o No path search is performed for files named via
the -f option. Therefore the AWKPATH environment
variable is not special.
o The use of next file to abandon processing of the
current input file.
o The use of delete array to delete the entire con-
tents of an array.
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 a file or pipe,
respectively.
When gawk is invoked with the -W compat option, if the fs
argument to the -F option is ``t'', then FS will be set to
the tab character. Since this is a rather ugly special
case, it is not the default behavior. This behavior also
does not occur if -W posix has been specified.
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
is the same as either of
a = length()
a = length($0)
This feature is marked as ``deprecated'' in the POSIX
standard, and gawk will issue a warning about its use if
-W lint is specified on the command line.
The other feature is the use of the continue statement
outside the body of a while, for, or do loop. Traditional
AWK implementations have treated such usage as equivalent
to the next statement. Gawk will support this usage if -W
posix has not been specified.
ENVIRONMENT VARIABLES
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 will
issue a warning message to this effect.
BUGS
The -F option is not necessary given the command line
variable assignment feature; it remains only for backwards
compatibility.
If your system actually has support for /dev/fd and the
associated /dev/stdin, /dev/stdout, and /dev/stderr files,
you may get different output from gawk than you would get
on a system without those files. When gawk interprets
these files internally, it synchronizes output to the
standard output with output to /dev/stdout, while on a
system with those files, the output is actually to differ-
ent open files. Caveat Emptor.
VERSION INFORMATION
This man page documents gawk, version 2.15.
Starting with the 2.15 version of gawk, the -c, -V, -C,
-a, and -e options of the 2.11 version are no longer rec-
ognized. This fact will not even be documented in the
manual page for version 2.16.
AUTHORS
The original version of UNIX awk was designed and imple-
mented by Alfred Aho, Peter Weinberger, and Brian
Kernighan of AT&T Bell Labs. 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 ver-
sion 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.
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.
ACKNOWLEDGEMENTS
Brian Kernighan of Bell Labs provided valuable assistance
during testing and debugging. We thank him.
