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man page(1) manual page
Table of Contents
gawk - pattern scanning and processing language
gawk [ POSIX or GNU style options ] -f program-file [ -- ] file ...
gawk [ POSIX or GNU style options ] [ -- ] program-text file ...
pgawk [ POSIX or GNU style options ] -f program-file [ -- ] file ...
pgawk [ POSIX or GNU style options ] [ -- ] program-text file ...
Gawk is the GNU Project’s implementation of the AWK programming language.
It conforms to the definition of the language in the POSIX
1003.2 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.
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. 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.
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
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 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 typographical errors in your programs. You would also use
this option if you have a large program with a lot of functions,
and you want to be sure that your functions don’t inadvertently
use global variables that you meant to be local. (This is a
particularly easy mistake to make with simple variable names
like i, j, and so on.)
- -W exec file
-
--exec file
Similar to -f, however, this is option is the last one processed.
This should be used with #! scripts, particularly for
CGI applications, to avoid passing in options or source code (!)
on the command line from a URL. This option disables commandline
variable assignments.
- -W gen-po
-
--gen-po
Scan and parse the AWK program, and generate a GNU .po format
file on standard output with entries for all localizable strings
in the program. The program itself is not executed. See the
GNU gettext distribution for more information on .po files.
- -W help
-
-W usage
--help
--usage
Print a relatively short summary of the available options on the
standard output. (Per the GNU Coding Standards, these options
cause an immediate, successful exit.)
- -W lint[=value]
-
--lint[=value]
Provide warnings about constructs that are dubious or nonportable
to other AWK implementations. With an optional
argument of fatal, lint warnings become fatal errors. This may
be drastic, but its use will certainly encourage the development
of cleaner AWK programs. With an optional argument of invalid,
only warnings about things that are actually invalid are issued.
(This is not fully implemented yet.)
- -W lint-old
-
--lint-old
Provide warnings about constructs that are not portable to the
original version of Unix awk.
- -W non-decimal-data
-
--non-decimal-data
Recognize octal and hexadecimal values in input data. Use this
option with great caution!
- -W posix
-
--posix
This turns on compatibility mode, with the following additional
restrictions:
· \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 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 running
AWK programs via the “#!” executable interpreter mechanism.
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 functions,
without having to include them in each new AWK program that uses them.
It also provides the ability to mix library functions with command line
programs.
The environment variable AWKPATH specifies a search path to use when
finding source files named with the -f option. If this variable does
not exist, the default path is “.:/usr/local/share/awk". (The actual
directory may vary, depending upon how gawk was built and installed.)
If a file name given to the -f option contains a “/” character, no path
search is performed.
Gawk executes AWK programs in the following order. First, all variable
assignments specified via the -v option are performed. Next, gawk compiles
the program into an internal form. Then, gawk executes the code
in the BEGIN block(s) (if any), and then proceeds to read each file
named in the ARGV array. If there are no files named on the command
line, gawk reads the standard input.
If a filename on the command line has the form var=val it is treated as
a variable assignment. The variable var will be assigned the value
val. (This happens after any BEGIN block(s) have been run.) Command
line variable assignment is most useful for dynamically assigning values
to the variables AWK uses to control how input is broken into
fields and records. It is also useful for controlling state if multiple
passes are needed over a single data file.
If the value of a particular element of ARGV is empty (""), gawk skips
over it.
For each 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).
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 predefined
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 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 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. Decrementing NF
causes the values of fields past the new value to be lost, and the
value of $0 to be recomputed, with the fields being separated by the
value of OFS.
Assigning a value to an existing field causes the whole record to be
rebuilt when $0 is referenced. Similarly, assigning a value to $0
causes the record to be resplit, creating new values for the fields.
Built-in Variables
Gawk’s built-in variables are:
- ARGC
- The number of command line arguments (does not include
options to gawk, or the program source).
- ARGIND
- The index in ARGV of the current file being processed.
- ARGV
- Array of command line arguments. The array is indexed from
0 to ARGC - 1. Dynamically changing the contents of ARGV
can control the files used for data.
- BINMODE
- On non-POSIX systems, specifies use of “binary” mode for
all file I/O. Numeric values of 1, 2, or 3, specify that
input files, output files, or all files, respectively,
should use binary I/O. String values of “r", or “w” specify
that input files, or output files, respectively, should
use binary I/O. String values of “rw” or “wr” specify that
all files should use binary I/O. Any other string value is
treated as “rw", but generates a warning message.
- CONVFMT
- The conversion format for numbers, “%.6g", by default.
- ENVIRON
- An array containing the values of the current environment.
The array is indexed by the environment variables, each
element being the value of that variable (e.g., ENVIRON["HOME"]
might be /home/arnold). 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 separator.
- FILENAME
- The name of the current input file. If no files are specified
on the command line, the value of FILENAME is “-”.
However, FILENAME is undefined inside the BEGIN block
(unless set by getline).
- FNR
- The input record number in the current input file.
- FS
- The input field separator, a space by default. See Fields,
above.
IGNORECASE Controls the case-sensitivity of all regular expression and
string operations. If IGNORECASE has a non-zero value,
then string comparisons and pattern matching in rules,
field splitting with FS, record separating with RS, regular
expression matching with ~ and !~, and the gensub(),
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 casesensitive.
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 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.
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
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 accomplished
using strtod(3)
. A number is converted to a string by using
the value of CONVFMT as a format string for sprintf(3)
, with the
numeric value of the variable as the argument. However, even though
all numbers in AWK are floating-point, integral values are always converted
as integers. Thus, given
CONVFMT = “%2.2f"
a = 12
b = a “"
the variable b has a string value of “12” and not “12.00".
Gawk performs comparisons as follows: If two variables are numeric,
they are compared numerically. If one value is numeric and the other
has a string value that is a “numeric string,” then comparisons are
also done numerically. Otherwise, the numeric value is converted to a
string and a string comparison is performed. Two strings are compared,
of course, as strings. Note that 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
constants in your AWK program source code. For example, the
octal value 011 is equal to decimal 9, and the hexadecimal value 0x11
is equal to decimal 17.
String Constants
String constants in AWK are sequences of characters enclosed between
double quotes ("). Within strings, certain escape sequences are recognized,
as in C. These are:
- \\
- A literal backslash.
- \a
- The “alert” character; usually the ASCII BEL character.
\b backspace.
\f form-feed.
\n newline.
- \r
- carriage return.
- \t
- horizontal tab.
- \v
- vertical tab.
\xhex digits
The character represented by the string of hexadecimal digits following
the \x. As in ANSI C, all following hexadecimal digits are
considered part of the escape sequence. (This feature should tell
us something about language design by committee.) E.g., “\x1B” is
the ASCII ESC (escape) character.
\ddd The character represented by the 1-, 2-, or 3-digit sequence of
octal digits. E.g., “\033” is the ASCII ESC (escape) character.
- \c
- The literal character c.
The escape sequences may also be used inside constant 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/.
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
patterns cannot have missing action parts.
For /regular expression/ patterns, the associated statement is executed
for each input record that matches the regular expression. Regular
expressions are the same as those in egrep(1)
, and are summarized
below.
A relational expression may use any of the operators defined below in
the section on actions. These generally test whether certain fields
match certain regular expressions.
The &&, ||, and ! operators are logical AND, logical OR, and logical
NOT, respectively, as in C. They do short-circuit evaluation, also as
in C, and are used for combining more primitive pattern expressions.
As in most languages, parentheses may be used to change the order of
evaluation.
The ?: operator is like the same operator in C. If the first pattern
is true then the pattern used for testing is the second pattern, otherwise
it is the third. Only one of the second and third patterns is
evaluated.
The pattern1, pattern2 form of an expression is called a range pattern.
It matches all input records starting with a record that matches pat_tern1,
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 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 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 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 element,
then [[.ch.]] is a regular expression that matches this
collating element, while [ch] is a regular expression that
matches either c or h.
Equivalence Classes
An equivalence class is a locale-specific name for a list of
characters that are equivalent. The name is enclosed in [= and
=]. For example, the name e might be used to represent all of
“e,” “e´,” and “e‘.” In this case, [[=e=]] is a regular expression
that matches any of e, e´´, or e‘.
These features are very valuable in non-English speaking locales. The
library functions that gawk uses for regular expression matching currently
only recognize POSIX character classes; they do not recognize
collating symbols or equivalence classes.
The \y, \B, \<, \>, \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. However, interval expressions are not supported.
- --posix
-
Only POSIX regular expressions are supported, the GNU operators
are not special. (E.g., \w matches a literal w). Interval
expressions are allowed.
- --traditional
-
Traditional Unix awk regular expressions are matched. The GNU
operators are not special, interval expressions are not available,
and neither are the POSIX character classes ([[:alnum:]]
and so on). Characters described by octal and hexadecimal
escape sequences are treated literally, even if they represent
regular expression metacharacters.
- --re-interval
-
Allow interval expressions in regular expressions, even if
--traditional has been provided.
Actions
Action statements are enclosed in braces, { and }. Action statements
consist of the usual assignment, conditional, and 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 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-process. It must be a
string value, either “to” or “from".
- getline
- Set $0 from next input record; set NF, NR, FNR.
- getline <file
- Set $0 from next record of file; set NF.
- getline var
- Set var from next input record; set NR, FNR.
- getline var <file
- Set var from next record of file.
command | getline [var]
Run command piping the output either into $0 or
var, as above.
command |& getline [var]
Run command as a co-process piping the output
either into $0 or var, as above. Co-processes
are a gawk 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 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 terminated with the value of the
ORS variable.
printf fmt, expr-list Format and print.
printf fmt, expr-list >file
Format and print on file.
- system(cmd-line)
- Execute the command cmd-line, and return the exit
status. (This may not be available on non-POSIX
systems.)
- fflush([file])
- Flush any buffers associated with the open output
file or pipe file. If file is missing, then
standard output is flushed. If file is the null
string, then all open output files and pipes have
their buffers flushed.
Additional output redirections are allowed for print and printf.
print ... >> file
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 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 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 supported. A * in place of either the width or prec specifications
causes their values to be taken from the argument list to printf or
sprintf(). To use a positional specifier with a dynamic width or precision,
supply the count$ after the * in the format string. For
example, “%3$*2$.*1$s".
Special File Names
When doing I/O redirection from either print or printf into a file, or
via getline from a file, gawk recognizes certain special filenames
internally. These filenames allow access to open file descriptors
inherited from gawk’s parent process (usually the shell). These file
names may also be used on the command line to name data files. The
filenames are:
/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 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 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 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 original.
gensub(r, s, h [, t]) Search the target string t for matches of the
regular expression r. If h is a string beginning
with g or G, then replace all matches of r
with s. Otherwise, h is a number indicating
which match of r to replace. If t is not supplied,
$0 is used instead. Within the replacement
text s, the sequence \n, where n is a
digit from 1 to 9, may be used to indicate just
the text that matched the n’th parenthesized
subexpression. The sequence \0 represents the
entire matched text, as does the character &.
Unlike sub() and gsub(), the modified string is
returned as the result of the function, and the
original target string is not changed.
- gsub(r, s [, t])
- For each substring matching the regular expression
r in the string t, substitute the string
s, and return the number of substitutions. If
t is not supplied, use $0. An & in the
replacement text is replaced with the text that
was actually matched. Use \& to get a literal
&. (This must be typed as “\\&"; see GAWK:
Effective AWK Programming for a fuller discussion
of the rules for &’’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. Starting
with version 3.1.5, as a non-standard extension,
with an array argument, length() returns
the number of elements in the array.
- match(s, r [, a])
- Returns the position in s where the regular
expression r occurs, or 0 if r is not present,
and sets the 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 splitting,
described above.
sprintf(fmt, expr-list) Prints expr-list according to fmt, and returns
the resulting string.
- strtonum(str)
- Examines str, and returns its numeric value.
If str begins with a leading 0, strtonum()
assumes that str is an octal number. If str
begins with a leading 0x or 0X, 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 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 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 timestamp should be of the same form as returned by systime().
If timestamp is missing, the current time of day is
used. If format is missing, a default format equivalent to
the output of date(1)
is used. See the specification for the
strftime() function in ANSI C for the format conversions that
are 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 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: Effective
AWK Programming. You must also supply a text domain. Use
TEXTDOMAIN if you want to use the current domain.
Functions in AWK are defined as follows:
function name(parameter list) { statements }
Functions are executed when they are called from within expressions in
either patterns or actions. Actual parameters supplied in the function
call are used to instantiate the formal parameters declared in the
function. Arrays are passed by reference, other variables are passed
by value.
Since functions were not originally part of the AWK language, the provision
for local variables is rather clumsy: They are declared as extra
parameters in the parameter list. The convention is to separate local
variables from real parameters by extra spaces in the parameter list.
For example:
function f(p, q, a, b) # a and b are local
{
...
}
- /abc/
- { ... ; f(1, 2) ; ... }
The left parenthesis in a function call is required to immediately follow
the function name, without any intervening 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 parameters
used as local variables are initialized to the null string and the
number zero upon function invocation.
Use return expr to return a value from a function. The return value is
undefined if no value is provided, or if the function returns by
“falling off” the end.
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.
Beginning with version 3.1 of gawk, you can dynamically add new builtin
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.
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.
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") }’’
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 program.
1. Add a BEGIN action to assign a value to the TEXTDOMAIN variable to
set the text domain to a name associated with your program.
BEGIN { TEXTDOMAIN = “myprog” }
This allows gawk to find the .mo file associated with your program.
Without this step, gawk uses the messages text domain, which likely
does not contain translations for your program.
2. Mark all strings that should be translated with leading underscores.
3. If necessary, use the dcgettext() and/or 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.
A primary goal for gawk is compatibility with the POSIX standard, as
well as with the latest version of UNIX awk. To this end, gawk incorporates
the following user visible features which are not described in
the AWK book, but are part of the Bell Laboratories version of awk, and
are in the POSIX standard.
The book indicates that command line variable assignment happens when
awk would otherwise open the argument as a file, which is after the
BEGIN block is executed. However, in earlier implementations, when
such an assignment appeared before any file names, the assignment would
happen before the BEGIN block was run. Applications came to depend on
this “feature.” When awk was changed to match its documentation, the
-v option for assigning variables before program execution was added to
accommodate applications that depended upon the old behavior. (This
feature was agreed upon by both the Bell Laboratories 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).
There are two features of historical AWK implementations that gawk supports.
First, it is possible to call the length() built-in function
not only with no argument, but even without parentheses! Thus,
- a = length
- # Holy Algol 60, Batman!
is the same as either of
a = length()
a = length($0)
This feature is marked as “deprecated” in the POSIX 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 specified.
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 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(),
dcngettext(), 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 ]
}
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.
egrep(1)
, getpid(2)
, getppid(2)
, getpgrp(2)
, getuid(2)
, geteuid(2)
,
getgid(2)
, getegid(2)
, getgroups(2)
The AWK Programming Language, Alfred V. Aho, Brian W. Kernighan, Peter
J. Weinberger, Addison-Wesley, 1988. ISBN 0-201-07981-X.
GAWK: Effective AWK Programming, Edition 3.0, published by the Free
Software Foundation, 2001.
The -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.
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.
This man page documents gawk, version 3.1.5.
If you find a bug in gawk, please send electronic mail to buggawk@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.
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.
Brian Kernighan of Bell Laboratories provided valuable assistance during
testing and debugging. We thank him.
Copyright © 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2001, 2002, 2003, 2004, 2005 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.
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