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GAWK(1) 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 programming lan-
guage. It conforms to the definition of the language in the POSIX
1003.2 Command Language And Utilities 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 supplied via
arguments to the -W option. Multiple -W options may be supplied Each
-W option has a corresponding long option, as detailed below. Argu-
ments to long options are either joined with the option by an = sign,
with no intervening spaces, or they may be provided in the next com-
mand line argument. Long options may be abbreviated, as long as the
abbreviation remains unique.
OPTIONS
Gawk accepts the following options, listed alphabetically.
-F fs
--field-separator fs
Use fs for the input field separator (the value of the FS pre-
defined 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 argument. 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
Bell Laboratories research version of UNIX awk. They are
ignored by gawk, since gawk has no pre-defined limits.
-W compat
-W traditional
--compat
--traditional
Run in compatibility mode. In compatibility mode, gawk behaves
identically to UNIX awk; none of the GNU-specific extensions
are recognized. The use of --traditional is preferred over the
other forms of this option. See GNU EXTENSIONS, below, for
more information.
-W copyleft
-W copyright
--copyleft
--copyright
Print the short version of the GNU copyright information mes-
sage on the standard output and exit successfully.
-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 func-
tions, and you want to be sure that your functions don't inad-
vertently use global variables that you meant to be local.
(This is a particularly easy mistake to make with simple vari-
able names like i, j, and so on.)
-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 argu-
ment of fatal, lint warnings become fatal errors. This may be
drastic, but its use will certainly encourage the development
of cleaner AWK programs. With an optional argument of invalid,
only warnings about things that are actually invalid are
issued. (This is not fully implemented yet.)
-W lint-old
--lint-old
Provide warnings about constructs that are not portable to the
original version of Unix awk.
-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 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:
? \x escape sequences are not recognized.
? Only space and tab act as field separators when FS is set to
a single space, newline does not.
? You cannot continue lines after ? and :.
? The synonym func for the keyword function is not recognized.
? The operators ** and **= cannot be used in place of ^ and ^=.
? 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" ver-
sion of the program. When run with pgawk, the profile contains
execution counts of each statement in the program in the left
margin and function 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 expres-
sions were not traditionally available in the AWK language.
The POSIX standard added them, to make awk and egrep consistent
with each other. However, 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.
-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 pro-
grams used in shell scripts.
-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 Stan-
dards, 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 convention
used by most other POSIX programs.
In compatibility mode, any other options are flagged as invalid, but
are otherwise ignored. In normal operation, as long as program text
has been supplied, unknown options are passed on to the AWK program in
the ARGV array for processing. This is particularly useful for run-
ning 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 speci-
fied, from arguments to --source, or from the first non-option argu-
ment on the command line. The -f and --source options may be used
multiple times on the command line. Gawk reads the program text as if
all the program-files and command line source texts had been concate-
nated together. This is useful for building libraries of AWK func-
tions, 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 vari-
able 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 val-
ues to the variables AWK uses to control how input is broken into
fields and records. It is also useful for controlling state if multi-
ple 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 pat-
tern 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 program.
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 multiple dimensions may be simulated.
Several pre-defined variables are set as a program runs; these will be
described as needed and summarized below.
Records
Normally, records are separated by newline characters. You can con-
trol how records are separated by assigning values to the built-in
variable RS. If RS is any single character, that character separates
records. Otherwise, RS is a regular expression. Text in the input
that matches this regular expression separates the record. However,
in compatibility mode, only the first character of its string value is
used for separating records. If RS is set to the null string, then
records are separated by 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 separator. If FS is a
single character, fields are separated by that character. If FS is
the null string, then each individual character becomes a separate
field. Otherwise, FS is expected to be a full regular expression. In
the special case that FS is a single space, fields are separated by
runs of spaces and/or tabs and/or newlines. (But see the discussion
of --posix, below). NOTE: The value of IGNORECASE (see below) also
affects how fields are split when FS is a regular expression, and how
records are separated when RS is a regular expression.
If the FIELDWIDTHS variable is set to a space separated list of num-
bers, 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 overrides 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-existent field (e.g.,
$(NF+2) = 5) increases the value of NF, creates any intervening fields
with the null string as their value, and causes 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. Decrementing
NF causes the values of fields past the new value to be lost, and the
value of $0 to be recomputed, with the fields being separated by the
value of OFS.
Assigning a value to an existing field causes the whole record to be
rebuilt when $0 is referenced. Similarly, assigning a value to $0
causes the record to be resplit, creating new values for the fields.
Built-in Variables
Gawk's built-in variables are:
ARGC The number of command line arguments (does not include
options to gawk, or the program source).
ARGIND The index in ARGV of the current file being processed.
ARGV Array of command line arguments. The array is indexed
from 0 to ARGC - 1. Dynamically changing the contents of
ARGV can control the files used for data.
BINMODE On non-POSIX systems, specifies use of "binary" mode for
all file I/O. Numeric values of 1, 2, or 3, specify that
input files, output files, or all files, respectively,
should use binary I/O. String values of "r", or "w" spec-
ify that input files, or output files, respectively,
should use binary I/O. String values of "rw" or "wr"
specify that all files should use binary I/O. Any other
string value is treated as "rw", but generates a warning
message.
CONVFMT The conversion format for numbers, "%.6g", by default.
ENVIRON An array containing the values of the current environment.
The array is indexed by the environment variables, each
element being the value of that variable (e.g., ENVI-
RON["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 redirection for
getline, during a read for getline, or during a close(),
then ERRNO will contain a string describing the error.
The value is subject 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 separa-
tor.
FILENAME The name of the current input file. If no files are spec-
ified 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.
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.
NR The total number of input records seen so far.
OFMT The output format for numbers, "%.6g", by default.
OFS The output field separator, a space by default.
ORS The output record separator, by default a newline.
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 "FIELDWIDTHS" 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 current process.
PROCINFO["ppid"] the parent process ID of the current
process.
PROCINFO["uid"] the value of the getuid(2) system call.
RS The input record separator, by default a newline.
RT The record terminator. Gawk sets RT to the input text
that matched the character or regular expression specified
by RS.
RSTART The index of the first character matched by match(); 0 if
no match. (This implies that character indices start at
one.)
RLENGTH The length of the string matched by match(); -1 if no
match.
SUBSEP The character used to separate multiple subscripts 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 consisting of the concatenation
of the (string) value of each expression, separated by the value of
the SUBSEP variable. This facility is used to simulate multiply
dimensioned arrays. For example:
i = "A"; j = "B"; k = "C"
x[i, j, k] = "hello, world\n"
assigns the string "hello, world\n" to the element of the array x
which is indexed by the string "A\034B\034C". All arrays in AWK are
associative, i.e. indexed by string values.
The special operator in may be used 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, just by specifying the array name without a subscript.
Variable Typing And Conversion
Variables and fields may be (floating point) numbers, or strings, or
both. How the value of a variable is interpreted depends upon its
context. If used in a numeric expression, it will be treated as a
number, if used as a string it will be treated as a string.
To force a variable to be treated as a number, add 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 accom-
plished 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 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 numerically. Otherwise, the numeric value is converted to a
string and a string comparison is performed. Two strings are com-
pared, of course, as strings. Note that the POSIX standard applies
the concept of "numeric string" everywhere, even to string constants.
However, this is clearly incorrect, and gawk does not do this. (For-
tunately, this is fixed in the next version of the standard.)
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).
Octal and Hexadecimal Constants
Starting with version 3.1 of gawk , you may use C-style octal and hex-
adecimal 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 rec-
ognized, 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 regular expres-
sions (e.g., /[ \t\f\n\r\v]/ matches whitespace characters).
In compatibility mode, the characters represented by octal and hex-
adecimal 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, 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, however, 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 state-
ments 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 can-
not be combined with other patterns in pattern expressions. BEGIN and
END patterns cannot have missing action parts.
For /regular expression/ patterns, the associated statement is exe-
cuted for each input record that matches the regular expression. Reg-
ular expressions are the same as those in egrep(1), and are summarized
below.
A relational expression may use any of the operators defined below in
the section on actions. These generally test whether certain fields
match certain regular expressions.
The &&, ||, and ! operators are logical AND, logical OR, and logical
NOT, respectively, as in C. They do short-circuit evaluation, also as
in C, and are used for combining more primitive pattern expressions.
As in most languages, parentheses may be used to change the order of
evaluation.
The ?: operator is like the same operator in C. If the first pattern
is true then the pattern used for testing is the second pattern, oth-
erwise 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 pat-
tern. 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 expres-
sion.
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.
(r) grouping: matches r.
r{n}
r{n,}
r{n,m} One or two numbers inside braces denote an interval expres-
sion. If there is one number in the braces, the preceding
regular expression r is repeated n times. If there are two
numbers separated by a comma, r is repeated n to m times.
If there is one number followed by a comma, then r is
repeated at least n times.
Interval expressions are only available if either --posix
or --re-interval is specified on the command 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-constituent.
\' matches the empty string at the beginning of a buffer
(string).
\' matches the empty string at the end of a buffer.
The escape sequences that are valid in string constants (see below)
are also valid in regular expressions.
Character classes are a new feature introduced in the POSIX standard.
A character class is a special notation for describing lists of char-
acters that have a specific attribute, but where the actual characters
themselves can vary from country to country and/or from character set
to character set. For example, the notion of what is an alphabetic
character differs in the USA and in France.
A character class is only valid in a regular expression inside the
brackets of a character list. Character classes consist of [:, a key-
word denoting the class, and :]. The character classes defined by the
POSIX standard are:
[:alnum:] Alphanumeric characters.
[:alpha:] Alphabetic characters.
[:blank:] Space or tab characters.
[:cntrl:] Control characters.
[:digit:] Numeric characters.
[:graph:] Characters that are both printable and visible. (A space
is printable, but not visible, while an a is both.)
[:lower:] Lower-case alphabetic characters.
[:print:] Printable characters (characters that are not control char-
acters.)
[:punct:] Punctuation characters (characters that are not letter,
digits, control characters, or space characters).
[:space:] Space characters (such as space, tab, and formfeed, to name
a few).
[:upper:] Upper-case alphabetic characters.
[:xdigit:] Characters that are hexadecimal digits.
For example, before the POSIX standard, to match alphanumeric charac-
ters, you would have had to write /[A-Za-z0-9]/. If your character
set had other alphabetic characters in it, this would not match them,
and if your character set collated differently from ASCII, this might
not even match the ASCII alphanumeric characters. With the POSIX
character classes, you can write /[[:alnum:]]/, and this matches the
alphabetic and numeric characters in your character set.
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 col-
lating, or sorting, purposes. (E.g., in French, a plain "e" and a
grave-accented e` are equivalent.)
Collating Symbols
A collating symbol is a multi-character collating element
enclosed in [. and .]. For example, if ch is a collating ele-
ment, then [[.ch.]] is a regular expression that matches this
collating element, while [ch] is a regular expression that
matches either c or h.
Equivalence Classes
An equivalence class is a locale-specific name for a list of
characters that are equivalent. The name is enclosed in [= and
=]. For example, the name e might be used to represent all of
"e," "?," and "`." In this case, [[=e=]] is a regular expres-
sion 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 cur-
rently only recognize POSIX character classes; they do not recognize
collating symbols or equivalence classes.
The \y, \B, \<, \>, \w, \W, \', and \' operators are specific to gawk;
they are extensions based on facilities in the GNU regular expression
libraries.
The various command line options control how gawk interprets charac-
ters in regular expressions.
No options
In the default case, gawk provide all the facilities of POSIX
regular expressions and the GNU regular expression operators
described above. However, interval expressions are not sup-
ported.
--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 avail-
able, 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 looping statements
found in most languages. The operators, control statements, and
input/output statements available are patterned after those in C.
Operators
The operators in AWK, in order of decreasing precedence, are
(...) Grouping
$ Field reference.
++ -- Increment and decrement, both prefix and postfix.
^ Exponentiation (** may also be used, and **= for the
assignment operator).
+ - ! Unary plus, unary minus, and logical negation.
* / % Multiplication, division, and modulus.
+ - Addition and subtraction.
space String concatenation.
< >
<= >=
!= == 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 expres-
sion is expr2, otherwise it is expr3. Only one of expr2
and expr3 is evaluated.
= += -=
*= /= %= ^= Assignment. Both absolute assignment (var = value) and
operator-assignment (the other forms) are supported.
Control Statements
The control statements are as follows:
if (condition) statement [ else statement ]
while (condition) statement
do statement while (condition)
for (expr1; expr2; expr3) statement
for (var in array) statement
break
continue
delete array[index]
delete array
exit [ expression ]
{ statements }
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 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 extension.
next Stop processing the current input record. The
next input record is read 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 executed.
nextfile Stop processing the current input file. The
next input record read comes from the next input
file. FILENAME and ARGIND are updated, FNR is
reset to 1, 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 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 sepa-
rated by the value of the OFS variable. The
output record is terminated 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 systems.)
fflush([file]) Flush any buffers associated with the open out-
put 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
appends output to the file.
print ... | command
writes on a pipe.
print ... |& command
sends data to a co-process.
The getline command returns 0 on end of file and -1 on an error. Upon
an error, ERRNO contains a string describing the problem.
NOTE: If using a pipe or co-process to getline, or from print or
printf within a loop, you must use close() to create new instances of
the command. AWK does not automatically close pipes or co-processes
when they return EOF.
The printf Statement
The AWK versions of the printf statement and sprintf() function (see
below) accept the following conversion specification formats:
%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 charac-
ter 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 A floating point number of the form [-]ddd.dddddd.
%g , %G
Use %e or %f conversion, whichever is shorter, with nonsignif-
icant zeros suppressed. The %G format uses %E instead of %e.
%o An unsigned octal number (also an integer).
%u An unsigned decimal number (again, an integer).
%s A character string.
%x , %X
An unsigned hexadecimal number (an integer). The %X format
uses ABCDEF instead of abcdef.
%% A single % character; no argument is converted.
NOTE: When using the integer format-control letters for values that
are outside the range of a C long integer, gawk switches to the %g
format specifier. If --lint is provided on the command line gawk warns
about this. Other versions of awk may print invalid values or do
something else entirely.
Optional, additional parameters may lie between the % and the control
letter:
count$ Use the count'th argument at this point in the formatting.
This is called a positional specifier and is intended primarily
for use in translated versions of format strings, not in the
original text of an AWK program. It is a gawk extension.
- The expression should be left-justified within its field.
space For numeric conversions, prefix positive values with a space,
and negative values with a minus sign.
+ The plus sign, used before the width modifier (see below), says
to always supply a sign for numeric conversions, even if the
data to be formatted is positive. The + overrides the space
modifier.
# Use an "alternate form" for certain control letters. For %o,
supply a leading zero. For %x, and %X, supply a leading 0x or
0X for a nonzero result. For %e, %E, 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 output should
be padded with zeroes instead of spaces. This applies even to
non-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 nor-
mally 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, and %f formats, this specifies the number of
digits you want printed to the right of the decimal point. For
the %g, and %G formats, it specifies the maximum number of sig-
nificant 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() rou-
tines are supported. A * in place of either the width or prec speci-
fications causes their values to be taken from the argument list to
printf or sprintf(). To use a positional specifier with a dynamic
width or precision, supply the count$ after the * in the format
string. For example, "%3$*2$.*1$s".
Special File Names
When doing I/O redirection from either print or printf into a file, or
via getline from a file, gawk recognizes certain special filenames
internally. These filenames allow access to open file descriptors
inherited from gawk's parent process (usually the shell). These file
names may also be used on the command line to name data files. The
filenames are:
/dev/stdin The standard input.
/dev/stdout The standard output.
/dev/stderr The standard error output.
/dev/fd/n The file associated with the open file descriptor n.
These are particularly useful for error messages. For example:
print "You blew it!" > "/dev/stderr"
whereas you would otherwise have to use
print "You blew it!" | "cat 1>&2"
The following special filenames may be used with the |& 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 sys-
tem pick a port.
/inet/udp/lport/rhost/rport Similar, but use UDP/IP instead of
TCP/IP.
/inet/raw/lport/rhost/rport Reserved for future use.
Other special filenames provide access to information about the run-
ning gawk process. These filenames are now obsolete. Use the
PROCINFO array to obtain the information they provide. 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 cur-
rent process, in decimal, terminated with a newline.
/dev/user Reading this file returns a single record terminated 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 get-
gid(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.
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 radians.
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 generator.
If no expr is provided, the time of day is used. The
return value is the previous 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 indexes of the sorted values of s are
replaced with sequential integers starting
with 1. If the optional destination array d is
specified, then s is first duplicated into d,
and then d is sorted, leaving the indexes 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 numerically, and
the values are those of the original indices.
The original values are lost; thus provide a
second array if you wish to preserve the orig-
inal.
gensub(r, s, h [, t]) Search the target string t for matches of the
regular expression r. If h is a string begin-
ning 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 sup-
plied, $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 indi-
cate just the text that matched the n'th
parenthesized subexpression. The sequence \0
represents the entire matched text, as does
the character &. Unlike sub() and gsub(), the
modified string is returned as the result of
the function, and the original target string
is not changed.
gsub(r, s [, t]) For each substring matching the regular
expression r in the string t, substitute the
string s, and return the number of substitu-
tions. 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 back-
slashes in the replacement text of sub(),
gsub(), and gensub().)
index(s, t) Returns the index of the string t in the
string s, or 0 if t is not present. (This
implies that character indices start at one.)
length([s]) Returns the length of the string s, or the
length of $0 if s is not supplied.
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 values of RSTART and RLENGTH.
Note that the argument order is the same as
for the ~ operator: str ~ re. If array a is
provided, a is cleared and then elements 1
through n are filled with the portions of s
that match the corresponding parenthesized
subexpression in r. The 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 matching 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 split-
ting, 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, strtonum()
assumes that str is a hexadecimal 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 substring 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 corresponding 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 corresponding upper-case counterparts.
Non-alphabetic characters are left unchanged.
Time Functions
Since one of the primary uses of AWK programs is processing log files
that contain time stamp information, gawk provides the following func-
tions for obtaining time stamps and formatting 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 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 saving flag is posi-
tive, the time is assumed to be daylight saving time; if
zero, the time is assumed to be standard time; and if nega-
tive (the default), mktime() attempts to determine whether
daylight saving time is in effect for the specified time.
If datespec does not contain enough elements or if the
resulting time is out of range, mktime() returns -1.
strftime([format [, timestamp]])
Formats timestamp according to the specification in format.
The timestamp should be of the same form as returned by sys-
time(). 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 guaranteed to be available. A public-domain ver-
sion of strftime(3) and a man page for it come with gawk; if
that version was used to build gawk, then all of the conver-
sions described in that man page are available to gawk.
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 manipulation
functions are available. They work by converting double-precision
floating point values to unsigned long integers, 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 provided by v1
and v2.
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 bindtextdomain() 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: Effec-
tive AWK Programming. You must also supply a text domain. Use
TEXTDOMAIN if you want to use the current domain.
dcngettext(string1 , string2 , number [, domain [, category]])
Returns the plural form used for number of the translation of
string1 and string2 in text domain domain for locale category
category. The default value for domain is the current value of
TEXTDOMAIN. The default value for category is "LC_MESSAGES".
If you supply a value for category, it must be a string equal
to one of the known locale categories described in GAWK: Effec-
tive AWK Programming. You must also supply 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 }
Functions are executed when they are called from within expressions in
either patterns or actions. Actual parameters supplied in the func-
tion call are used to instantiate the formal parameters declared in
the function. Arrays are passed by reference, other variables are
passed by value.
Since functions were not originally part of the AWK language, the pro-
vision for local variables is rather clumsy: They are declared as
extra parameters in the parameter list. The convention is to separate
local variables from real parameters by extra spaces in the parameter
list. For example:
function f(p, q, a, b) # a and b are local
{
...
}
/abc/ { ... ; f(1, 2) ; ... }
The left parenthesis in a function call is required to immediately
follow the function name, without any intervening white space. This
is to avoid a syntactic ambiguity with the concatenation operator.
This restriction does not apply to the built-in functions listed
above.
Functions may call each other and may be recursive. Function parame-
ters used as local variables are initialized to the null string and
the number zero upon function invocation.
Use return expr to return a value from a function. The return value
is undefined if no value is provided, or if the function returns by
"falling off" the end.
If --lint has been provided, gawk warns about calls to undefined func-
tions 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 Program-
ming for the details.
extension(object, function)
Dynamically link the shared object file named by object, and
invoke function in that object, to perform initialization.
These should both be provided as strings. Returns the value
returned by function.
This function is provided and documented in GAWK: Effective AWK Pro-
gramming, but everything about this feature is likely to change in the
next release. 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 profile and
function call stack to the profile file, which is either awkprof.out,
or whatever file was named with the --profile option. It then contin-
ues to run. SIGHUP causes it 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 nat-
ural language. Such strings are marked in the AWK program with a lead-
ing underscore ("_"). For example,
gawk 'BEGIN { print "hello, world" }'
always prints hello, world. But,
gawk 'BEGIN { print _"hello, world" }'
might print bonjour, monde in France.
There are several steps involved in producing and running a localiz-
able 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 pro-
gram. 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 under-
scores.
3. If necessary, use the dcgettext() and/or bindtextdomain() func-
tions 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 a corre-
sponding .mo file.
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 incor-
porates 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.
When processing arguments, gawk uses the special option "--" to signal
the end of arguments. In compatibility mode, it warns about but oth-
erwise 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 Laboratories version); the tolower()
and toupper() built-in functions (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 func-
tion 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 standard, 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 speci-
fied.
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 option.
The following features of gawk are not available in POSIX awk.
? No path search is performed for files named via the -f option.
Therefore the AWKPATH environment variable is not special.
? The \x escape sequence. (Disabled with --posix.)
? The fflush() function. (Disabled with --posix.)
? The ability to continue lines after ? and :. (Disabled with
--posix.)
? Octal and hexadecimal constants in AWK programs.
? The ARGIND, BINMODE, ERRNO, LINT, RT and TEXTDOMAIN variables are
not special.
? The IGNORECASE variable and its side-effects are not available.
? The FIELDWIDTHS variable and fixed-width field splitting.
? The PROCINFO array is not available.
? The use of RS as a regular expression.
? The special file names available for I/O redirection are not recog-
nized.
? The |& operator for creating co-processes.
? The ability to split out individual characters using the null string
as the value of FS, and as the third argument to split().
? The optional second argument to the close() function.
? The optional third argument to the match() function.
? The ability to use positional specifiers with printf and sprintf().
? The use of delete array to delete the entire contents of an array.
? The use of nextfile to abandon processing of the current input file.
? The and(), asort(), asorti(), bindtextdomain(), compl(), dcget-
text(), dcngettext(), gensub(), lshift(), mktime(), or(), rshift(),
strftime(), strtonum(), systime() and xor() functions.
? Localizable strings.
? Adding new built-in functions dynamically with the extension() func-
tion.
The AWK book does not define the return value of the close() function.
Gawk's close() returns the value from fclose(3), or pclose(3), when
closing an output file or pipe, respectively. It returns the pro-
cess'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 redirec-
tion.
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 charac-
ter as the field separator, it is best to use single quotes: gawk
-F'\t' ....
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.
If POSIXLY_CORRECT exists in the environment, then gawk behaves
exactly as if --posix had been specified on the command line. If
--lint has been specified, gawk issues a warning message to this
effect.
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.
BUGS
The -F option is not necessary given the command line variable assign-
ment feature; it remains only for backwards compatibility.
Syntactically invalid single character programs tend to overflow the
parse stack, generating a rather unhelpful message. Such programs are
surprisingly difficult to diagnose in the completely general case, and
the effort to do so really is not worth it.
AUTHORS
The original version of UNIX awk was designed and implemented by
Alfred Aho, Peter Weinberger, and Brian Kernighan of Bell Laborato-
ries. Brian Kernighan continues to maintain and enhance it.
Paul Rubin and Jay Fenlason, of the Free Software Foundation, wrote
gawk, to be compatible with the original version of awk distributed in
Seventh Edition UNIX. John Woods contributed a number of bug fixes.
David Trueman, with contributions from Arnold Robbins, made gawk com-
patible with the new version of UNIX awk. Arnold Robbins is the cur-
rent 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. Fred Fish supplied support for the Amiga, Stephen
Davies provided the Tandem port, and Martin Brown provided the BeOS
port.
VERSION INFORMATION
This man page documents gawk, version 3.1.3.
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 two 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 read this man page and
the reference manual carefully to be sure that what you think is a bug
really is, instead of just a quirk in the language.
Whatever you do, do NOT post a bug report in comp.lang.awk. While the
gawk developers occasionally read this newsgroup, posting bug reports
there is an unreliable way to report bugs. Instead, please use the
electronic mail addresses given above.
ACKNOWLEDGEMENTS
Brian Kernighan of Bell Laboratories provided valuable assistance dur-
ing testing and debugging. We thank him.
COPYING PERMISSIONS
Copyright (C) 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
1999, 2001, 2002, 2003 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this
manual page provided the copyright notice and this permission notice
are preserved on all copies.
Permission is granted to copy and distribute modified versions of this
manual page under the conditions for verbatim copying, provided that
the entire resulting derived work is distributed under the terms of a
permission notice identical to this one.
Permission is granted to copy and distribute translations of this man-
ual page into another language, under the above conditions for modi-
fied versions, except that this permission notice may be stated in a
translation approved by the Foundation.
Free Software Foundation June 25 2003 GAWK(1)
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