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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 language. It con-
forms 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 fea-
tures 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-man-
dated 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 corre-
sponding long option, as detailed below. Arguments to long options are either
joined with the option by an = sign, with no intervening spaces, or they may be
provided in the next command line argument. Long options may be abbreviated, as
long as the abbreviation remains unique.
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 predefined vari-
able).
-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 message 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 typo-
graphical errors in your programs. You would also use this option if you
have a large program with a lot of functions, and you want to be sure that
your functions don’t inadvertently use global variables that you meant to be
local. (This is a particularly easy mistake to make with simple variable
names like i, j, and so on.)
-W help
-W usage
--help
--usage
Print a relatively short summary of the available options on the standard
output. (Per the GNU Coding Standards, these options cause an immediate,
successful exit.)
-W lint[=value]
--lint[=value]
Provide warnings about constructs that are dubious or non-portable to other
AWK implementations. With an optional argument of fatal, lint warnings
become fatal errors. This may be drastic, but its use will certainly
encourage the development of cleaner AWK programs. With an optional argu-
ment 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 ver-
sion of Unix awk.
-W gen-po
--gen-po
Scan and parse the AWK program, and generate a GNU .po format file on stan-
dard 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 restric-
tions:
· \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” version 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 expressions 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 programs 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 Founda-
tion is distributing. This is also useful when reporting bugs. (Per the
GNU Coding Standards, these options cause an immediate, successful exit.)
-- Signal the end of options. This is useful to allow further arguments to the
AWK program itself to start with a “-”. This 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 running AWK programs via the “#!” executable interpreter
mechanism.
AWK PROGRAM EXECUTION
An AWK program consists of a sequence of pattern-action statements and optional
function definitions.
pattern { action statements }
function name(parameter list) { statements }
Gawk first reads the program source from the program-file(s) if specified, from
arguments to --source, or from the first non-option argument on the command line.
The -f and --source options may be used multiple times on the command line. Gawk
reads the program text as if all the program-files and command line source texts
had been concatenated together. This is useful for building libraries of AWK 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 variable assignments
specified via the -v option are performed. Next, gawk compiles the program into an
internal form. Then, gawk executes the code in the BEGIN block(s) (if any), and
then proceeds to read each file named in the ARGV array. If there are no files
named on the command line, gawk reads the standard input.
If a filename on the command line has the form var=val it is treated as a variable
assignment. The variable var will be assigned the value val. (This happens after
any BEGIN block(s) have been run.) Command line variable assignment is most useful
for dynamically assigning values to the 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 pattern in the
AWK program. For each pattern that the record matches, the associated action is
executed. The patterns are tested in the order they occur in the 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 control how records
are separated by assigning values to the built-in variable RS. If RS is any single
character, that character separates records. Otherwise, RS is a regular expres-
sion. 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 char-
acter 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 numbers, each field
is expected to have fixed width, and gawk splits up the record using the specified
widths. The value of FS is ignored. Assigning a new value to FS 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. References to negative numbered fields cause a fatal error. Decre-
menting NF causes the values of fields past the new value to be lost, and the value
of $0 to be recomputed, with the fields being separated by the value of OFS.
Assigning a value to an existing field causes the whole record to be rebuilt when
$0 is referenced. Similarly, assigning a value to $0 causes the record to be
resplit, creating new values for the fields.
Built-in Variables
Gawk’s built-in variables are:
ARGC The number of command line arguments (does not include options to gawk,
or the program source).
ARGIND The index in ARGV of the current file being processed.
ARGV Array of command line arguments. The array is indexed from 0 to ARGC -
1. Dynamically changing the contents of ARGV can control the files
used for data.
BINMODE On non-POSIX systems, specifies use of “binary” mode for all file I/O.
Numeric values of 1, 2, or 3, specify that input files, output files,
or all files, respectively, should use binary I/O. String values of
"r", or "w" specify that input files, or output files, respectively,
should use binary I/O. String values of "rw" or "wr" specify that all
files should use binary I/O. Any other string value is treated as
"rw", but generates a warning message.
CONVFMT The conversion format for numbers, "%.6g", by default.
ENVIRON An array containing the values of the current environment. The array
is indexed by the environment variables, each element being the value
of that variable (e.g., ENVIRON["HOME"] might be /home/arnold). Chang-
ing 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 separator.
FILENAME The name of the current input file. If no files are specified on the
command line, the value of FILENAME is “-”. However, FILENAME is unde-
fined 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 compar-
isons and pattern matching in rules, field splitting with FS, record
separating with RS, regular expression matching with ~ and !~, and the
gensub(), gsub(), index(), match(), split(), and sub() built-in func-
tions all ignore case when doing regular expression operations. NOTE:
Array subscripting is not affected. However, the asort() and asorti()
functions are affected.
Thus, if IGNORECASE is not equal to zero, /aB/ matches all of the
strings "ab", "aB", "Ab", and "AB". As with all AWK variables, the
initial value of IGNORECASE is zero, so all regular expression and
string operations are normally case-sensitive. Under Unix, the full
ISO 8859-1 Latin-1 character set is used when ignoring case. As of
gawk 3.1.4, the case equivalencies are fully locale-aware, based on the
C <ctype.h> facilities such as isalpha(), and tolupper().
LINT Provides dynamic control of the --lint option from within an AWK pro-
gram. 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 run-
ning AWK program. On some systems, there may be elements in the array,
"group1" through "groupn" for some n, which is the number of supplemen-
tary 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.
PROCINFO["version"]
The version of gawk. This is available from version
3.1.4 and later.
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 transla-
tions 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 spec-
ifying 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 accomplished using
strtod(3). A number is converted to a string by using the value of CONVFMT as a
format string for sprintf(3), with the numeric value of the variable as the argu-
ment. However, even though all numbers in AWK are floating-point, integral values
are always converted as integers. Thus, given
CONVFMT = "%2.2f"
a = 12
b = a ""
the variable b has a string value of "12" and not "12.00".
Gawk performs comparisons as follows: If two variables are numeric, they are com-
pared numerically. If one value is numeric and the other has a string value that
is a “numeric string,” then comparisons are also done numerically. Otherwise, the
numeric value is converted to a string and a string comparison is performed. Two
strings are compared, of course, as strings. Note that 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. (Fortunately, 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 hexadecimal con-
stants in your AWK program source code. For example, the octal value 011 is equal
to decimal 9, and the hexadecimal value 0x11 is equal to decimal 17.
String Constants
String constants in AWK are sequences of characters enclosed between double quotes
("). Within strings, certain escape sequences are recognized, as in C. These are:
\\ A literal backslash.
\a The “alert” character; usually the ASCII BEL character.
\b backspace.
\f form-feed.
\n newline.
\r carriage return.
\t horizontal tab.
\v vertical tab.
\xhex digits
The character represented by the string of hexadecimal digits following the
\x. As in ANSI C, all following hexadecimal digits are considered part of the
escape sequence. (This feature should tell us something about language design
by committee.) E.g., "\x1B" is the ASCII ESC (escape) character.
\ddd The character represented by the 1-, 2-, or 3-digit sequence of octal digits.
E.g., "\033" is the ASCII ESC (escape) character.
\c The literal character c.
The escape sequences may also be used inside constant regular expressions (e.g.,
/[ \t\f\n\r\v]/ matches whitespace characters).
In compatibility mode, the characters represented by octal and hexadecimal escape
sequences are treated literally when used in regular expression constants. Thus,
/a\52b/ is equivalent to /a\*b/.
PATTERNS AND ACTIONS
AWK is a line-oriented language. The pattern comes first, 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 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 pat-
terns cannot have missing action parts.
For /regular expression/ patterns, the associated statement is executed for each
input record that matches the regular expression. Regular expressions are the same
as those in 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, respec-
tively, as in C. They do short-circuit evaluation, also as in C, and are used for
combining more primitive pattern expressions. As in most languages, parentheses
may be used to change the order of evaluation.
The ?: operator is like the same operator in C. If the first pattern is true then
the pattern used for testing is the second pattern, otherwise it is the third.
Only one of the second and third patterns is evaluated.
The pattern1, pattern2 form of an expression is called a range pattern. It matches
all input records starting with a record that matches pattern1, and continuing
until a record that matches pattern2, inclusive. It does not combine with any
other sort of pattern expression.
Regular Expressions
Regular expressions are the extended kind found in egrep. They are composed of
characters as follows:
c matches the non-metacharacter c.
\c matches the literal character c.
. matches any character including newline.
^ matches the beginning of a string.
$ matches the end of a string.
[abc...] 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 expression. If
there is one number in the braces, the preceding regular expression r is
repeated n times. If there are two numbers separated by a comma, r is
repeated n to m times. If there is one number followed by a comma, then
r is repeated at least n times.
Interval expressions are only available if either --posix or --re-inter-
val 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 characters that have a specific
attribute, but where the actual characters themselves can vary from country to
country and/or from character set to character set. For example, the notion of
what is an alphabetic character differs in the USA and in France.
A character class is only valid in a regular expression inside the brackets of a
character list. Character classes consist of [:, a keyword denoting the class, and
:]. The character classes defined by the POSIX standard are:
[:alnum:] Alphanumeric characters.
[:alpha:] Alphabetic characters.
[:blank:] Space or tab characters.
[:cntrl:] Control characters.
[:digit:] Numeric characters.
[:graph:] Characters that are both printable and visible. (A space is printable,
but not visible, while an a is both.)
[:lower:] Lower-case alphabetic characters.
[:print:] Printable characters (characters that are not control characters.)
[:punct:] Punctuation characters (characters that are not letter, digits, control
characters, or space characters).
[:space:] Space characters (such as space, tab, and 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 characters, you would
have had to write /[A-Za-z0-9]/. If your character set had other alphabetic char-
acters in it, this would not match them, and if your character set collated differ-
ently 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 collating, or sorting, purposes. (E.g., in French, a plain
“e” and a grave-accented e` are equivalent.)
Collating Symbols
A collating symbol is a multi-character collating element enclosed in [.
and .]. For example, if ch is a collating element, then [[.ch.]] is a reg-
ular expression that matches this collating element, while [ch] is a regular
expression that matches either c or h.
Equivalence Classes
An equivalence class is a locale-specific name for a list of characters that
are equivalent. The name is enclosed in [= and =]. For example, the name e
might be used to represent all of “e,” “,” and “`.” In this case, [[=e=]]
is a regular expression that matches any of e, e, or `.
These features are very valuable in non-English speaking locales. The library
functions that gawk uses for regular expression matching currently only recognize
POSIX character classes; they do not recognize collating symbols or 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 characters 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. How-
ever, interval expressions are not supported.
--posix
Only POSIX regular expressions are supported, the GNU operators are not spe-
cial. (E.g., \w matches a literal w). Interval expressions are allowed.
--traditional
Traditional Unix awk regular expressions are matched. The GNU operators are
not special, interval expressions are not available, and neither are the
POSIX character classes ([[:alnum:]] and so on). Characters described by
octal and hexadecimal escape sequences are treated literally, even if they
represent regular expression metacharacters.
--re-interval
Allow interval expressions in regular expressions, even if --traditional has
been provided.
Actions
Action statements are enclosed in braces, { and }. Action statements consist of
the usual assignment, conditional, and looping statements found in most languages.
The operators, control statements, and input/output statements available are pat-
terned 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 opera-
tor).
+ - ! 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 expression is expr2, otherwise it is
expr3. Only one of expr2 and expr3 is evaluated.
= += -=
*= /= %= ^= Assignment. Both absolute assignment (var = value) and operator-
assignment (the other forms) are supported.
Control Statements
The control statements are as follows:
if (condition) statement [ else statement ]
while (condition) statement
do statement while (condition)
for (expr1; expr2; expr3) statement
for (var in array) statement
break
continue
delete array[index]
delete array
exit [ expression ]
{ statements }
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-pro-
cess. It must be a string value, either "to" or "from".
getline Set $0 from next input record; set NF, NR, FNR.
getline <file Set $0 from next record of file; set NF.
getline var Set var from next input record; set NR, FNR.
getline var <file Set var from next record of file.
command | getline [var]
Run command piping the output either into $0 or var, as
above.
command |& getline [var]
Run command as a co-process piping the output either into $0
or var, as above. Co-processes are a gawk extension.
next Stop processing the current input record. The next input
record is read and processing starts over with the first pat-
tern 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 exe-
cuted.
print Prints the current record. The output record is terminated
with the value of the ORS variable.
print expr-list Prints expressions. Each expression is separated by the
value of the OFS variable. The output record is 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 termi-
nated with the value of the ORS variable.
printf fmt, expr-list Format and print.
printf fmt, expr-list >file
Format and print on file.
system(cmd-line) Execute the command cmd-line, and return the exit status.
(This may not be available on non-POSIX systems.)
fflush([file]) Flush any buffers associated with the open output file or
pipe file. If file is missing, then standard output is
flushed. If file is the null string, then all open output
files and pipes have their buffers flushed.
Additional output redirections are allowed for print and printf.
print ... >> file
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 character of that string is printed.
%d, %i A decimal number (the integer part).
%e , %E
A floating point number of the form [-]d.dddddde[+-]dd. The %E format uses
E instead of e.
%f A floating point number of the form [-]ddd.dddddd.
%g , %G
Use %e or %f conversion, whichever is shorter, with nonsignificant zeros
suppressed. The %G format uses %E instead of %e.
%o An unsigned octal number (also an integer).
%u An unsigned decimal number (again, an integer).
%s A character string.
%x , %X
An unsigned hexadecimal number (an integer). The %X format uses ABCDEF
instead of abcdef.
%% A single % character; no argument is converted.
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 ver-
sions 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 lead-
ing 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 for-
mats. This flag only has an effect when the field width is wider than the
value to be printed.
width The field should be padded to this width. The field is normally padded with
spaces. If the 0 flag has been used, it is padded with zeroes.
.prec A number that specifies the precision to use when printing. For the %e, %E,
and %f formats, this specifies the number of digits you want printed to the
right of the decimal point. For the %g, and %G formats, it specifies the
maximum number of significant digits. For the %d, %o, %i, %u, %x, and %X
formats, it specifies the minimum number of digits to print. For %s, it
specifies the maximum number of characters from the string that should be
printed.
The dynamic width and prec capabilities of the ANSI C printf() routines are sup-
ported. A * in place of either the width or prec specifications causes their val-
ues 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 system 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 running gawk pro-
cess. 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 current 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 getgid(2) system call, and $4 is the value of the gete-
gid(2) system call. If there are any additional fields, they are the
group IDs returned by getgroups(2). Multiple groups may not be sup-
ported 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 previ-
ous 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 com-
paring 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 original.
gensub(r, s, h [, t]) Search the target string t for matches of the regular
expression r. If h is a string beginning with g or G, then
replace all matches of r with s. Otherwise, h is a number
indicating which match of r to replace. If t is not 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 indicate just the text that matched the n’th paren-
thesized subexpression. The sequence \0 represents the
entire matched text, as does the character &. Unlike sub()
and gsub(), the modified string is returned as the result
of the function, and the original target string is not
changed.
gsub(r, s [, t]) For each substring matching the regular expression r in the
string t, substitute the string s, and return the number of
substitutions. If t is not supplied, use $0. An & in the
replacement text is replaced with the text that was actu-
ally matched. Use \& to get a literal &. (This must be
typed as "\\&"; see GAWK: Effective AWK Programming for a
fuller discussion of the rules for &s and backslashes in
the 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 pro-
vided, 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 respec-
tively, of each matching substring.
split(s, a [, r]) Splits the string s into the array a on the regular expres-
sion r, and returns the number of fields. If r is omitted,
FS is used instead. The array a is cleared first. Split-
ting behaves identically to field splitting, described
above.
sprintf(fmt, expr-list) Prints expr-list according to fmt, and returns the result-
ing 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 functions for obtaining time
stamps and formatting them.
mktime(datespec)
Turns datespec into a time stamp of the same form as returned by sys-
time(). 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 respec-
tively 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 sav-
ing 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 positive, the time is assumed
to be daylight saving time; if zero, the time is assumed to be standard
time; and if negative (the default), mktime() attempts to determine
whether daylight saving time is in effect for the specified time. If
datespec does not contain enough elements or if the resulting time is out
of range, mktime() returns -1.
strftime([format [, timestamp]])
Formats timestamp according to the specification in format. The times-
tamp should be of the same form as returned by systime(). If timestamp
is missing, the current time of day is used. If format is missing, a
default format equivalent to the output of date(1) is used. See the
specification for the strftime() function in ANSI C for the format con-
versions that are guaranteed to be available. A public-domain version of
strftime(3) and a man page for it come with gawk; if that version was
used to build gawk, then all of the conversions 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: Effective AWK Programming. You
must also supply a text domain. Use TEXTDOMAIN if you want to use the cur-
rent 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: Effective AWK Programming. You
must also supply a text domain. Use TEXTDOMAIN if you want to use the cur-
rent 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 pat-
terns or actions. Actual parameters supplied in the function call are used to
instantiate the formal parameters declared in the function. Arrays are passed by
reference, other variables are passed by value.
Since functions were not originally part of the AWK language, the provision for
local variables is rather clumsy: They are declared as extra parameters in the
parameter list. The convention is to separate local variables from real parameters
by extra spaces in the parameter list. For example:
function f(p, q, a, b) # a and b are local
{
...
}
/abc/ { ... ; f(1, 2) ; ... }
The left parenthesis in a function call is required to immediately follow the func-
tion name, without any intervening white space. This is to avoid a syntactic ambi-
guity with the concatenation operator. This restriction does not apply to the
built-in functions listed above.
Functions may call each other and may be recursive. Function parameters used as
local variables are initialized to the null string and the number zero upon func-
tion 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 functions at parse
time, instead of at run time. Calling an undefined function at run time is a fatal
error.
The word func may be used in place of function.
DYNAMICALLY LOADING NEW FUNCTIONS
Beginning with version 3.1 of gawk, you can dynamically add new built-in functions
to the running gawk interpreter. The full details are beyond the scope of this
manual page; see GAWK: Effective AWK Programming for the details.
extension(object, function)
Dynamically link the shared object file named by object, and invoke func-
tion in that object, to perform initialization. These should both be pro-
vided as strings. Returns the value returned by function.
This function is provided and documented in GAWK: Effective AWK Programming, 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 arent 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 continues 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 natural language. Such strings are marked in
the AWK program with a leading underscore (“_”). For example,
gawk BEGIN { print "hello, world" }
always prints hello, world. But,
gawk BEGIN { print _"hello, world" }
might print bonjour, monde in France.
There are several steps involved in producing and running a localizable AWK pro-
gram.
1. Add a BEGIN action to assign a value to the TEXTDOMAIN variable to set the text
domain to a name associated with your program.
BEGIN { TEXTDOMAIN = "myprog" }
This allows gawk to find the .mo file associated with your program. Without
this step, gawk uses the messages text domain, which likely does not contain
translations for your program.
2. Mark all strings that should be translated with leading underscores.
3. If necessary, use the dcgettext() and/or bindtextdomain() functions in your
program, as appropriate.
4. Run gawk --gen-po -f myprog.awk > myprog.po to generate a .po file for your
program.
5. Provide appropriate translations, and build and install a corresponding .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 incorporates the following user
visible features which are not described in the AWK book, but are part of the Bell
Laboratories version of awk, and are in the POSIX standard.
The book indicates that command line variable assignment happens when awk would
otherwise open the argument as a file, which is after the BEGIN block is executed.
However, in earlier implementations, when such an assignment appeared before any
file names, the assignment would happen before the BEGIN block was run. Applica-
tions 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 otherwise ignores undefined
options. In normal operation, such arguments are passed on to the AWK program for
it to process.
The AWK book does not define the return value of srand(). The POSIX standard has
it return the seed it was using, to allow keeping track of random number sequences.
Therefore srand() in gawk also returns its current seed.
Other new features are: The use of multiple -f options (from MKS awk); the ENVIRON
array; the \a, and \v escape sequences (done originally in gawk and fed back into
the Bell 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 function not only with no argu-
ment, 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 --tra-
ditional has been specified.
GNU EXTENSIONS
Gawk has a number of extensions to POSIX awk. They are described in this section.
All the extensions described here can be disabled by invoking gawk with the --tra-
ditional 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 recognized.
· 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(), dcgettext(), dcnget-
text(), gensub(), lshift(), mktime(), or(), rshift(), strftime(), strtonum(),
systime() and xor() functions.
· Localizable strings.
· Adding new built-in functions dynamically with the extension() function.
The AWK book does not define the return value of the close() function. Gawk’s
close() returns the value from fclose(3), or pclose(3), when closing an output file
or pipe, respectively. It returns the process’s exit status when closing an input
pipe. The return value is -1 if the named file, pipe or co-process was not opened
with a redirection.
When gawk is invoked with the --traditional option, if the fs argument to the -F
option is “t”, then FS is set to the tab character. Note that typing gawk -F\t ...
simply causes the shell to quote the “t,”, and does not pass “\t” to the -F option.
Since this is a rather ugly special case, it is not the default behavior. This
behavior also does not occur if --posix has been specified. To really get a tab
character as the field separator, it is best to use single quotes: gawk -F\t ....
If gawk is configured with the --enable-switch option to the configure command,
then it accepts an additional control-flow statement:
switch (expression) {
case value|regex : statement
...
[ default: statement ]
}
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. Wein-
berger, Addison-Wesley, 1988. ISBN 0-201-07981-X.
GAWK: Effective AWK Programming, Edition 3.0, published by the Free Software Foun-
dation, 2001.
BUGS
The -F option is not necessary given the command line variable assignment 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 Laboratories. Brian Kernighan continues to
maintain and enhance it.
Paul Rubin and Jay Fenlason, of the Free Software Foundation, wrote gawk, to be
compatible with the original version of awk distributed in Seventh Edition UNIX.
John Woods contributed a number of bug fixes. David Trueman, with contributions
from Arnold Robbins, made gawk compatible with the new version of UNIX awk. Arnold
Robbins is the current maintainer.
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 3.1.4.
BUG REPORTS
If you find a bug in gawk, please send electronic mail to bug-gawk AT 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 devel-
opers occasionally read this newsgroup, posting bug reports there is an unreliable
way to report bugs. Instead, please use the electronic mail addresses given above.
If you’re using a GNU/Linux system or BSD-based system, you may wish to submit a
bug report to the vendor of your distribution. That’s fine, but please send a copy
to the official email address as well, since there’s no guarantee that the bug will
be forwarded to the gawk maintainer.
ACKNOWLEDGEMENTS
Brian Kernighan of Bell Laboratories provided valuable assistance during testing
and debugging. We thank him.
COPYING PERMISSIONS
Copyright © 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002,
2003, 2004 Free Software Foundation, Inc.
Permission is granted to make and distribute verbatim copies of this manual page
provided the copyright notice and this permission notice are preserved on all
copies.
Permission is granted to copy and distribute modified versions of this manual page
under the conditions for verbatim copying, provided that the entire resulting
derived work is distributed under the terms of a permission notice identical to
this one.
Permission is granted to copy and distribute translations of this manual page into
another language, under the above conditions for modified versions, except that
this permission notice may be stated in a translation approved by the Foundation.
Free Software Foundation July 28 2004 GAWK(1)
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