awk
There are two ways to run awk: with an explicit program, or with
one or more program files. Here are templates for both of them; items
enclosed in `[...]' in these templates are optional.
Besides traditional one-letter POSIX-style options, gawk also
supports GNU long options.
awk [options] -f progfile [--] file ... awk [options] [--] 'program' file ...
It is possible to invoke awk with an empty program:
$ awk " datafile1 datafile2
Doing so makes little sense though; awk will simply exit
silently when given an empty program (d.c.). If `--lint' has
been specified on the command line, gawk will issue a
warning that the program is empty.
awk programs.
gawk.
Options begin with a dash, and consist of a single character. GNU style long options consist of two dashes and a keyword. The keyword can be abbreviated, as long the abbreviation allows the option to be uniquely identified. If the option takes an argument, then the keyword is either immediately followed by an equals sign (`=') and the argument's value, or the keyword and the argument's value are separated by whitespace. For brevity, the discussion below only refers to the traditional short options; however the long and short options are interchangeable in all contexts.
Each long option for gawk has a corresponding
POSIX-style option. The options and their meanings are as follows:
-F fs
--field-separator fs
FS variable to fs
(see section Specifying How Fields are Separated).
-f source-file
--file source-file
awk program is to be found in source-file
instead of in the first non-option argument.
-v var=val
--assign var=val
BEGIN rule
(see section Other Command Line Arguments).
The `-v' option can only set one variable, but you can use
it more than once, setting another variable each time, like this:
`awk -v foo=1 -v bar=2 ...'.
-mf=NNN
-mr=NNN
awk. They are provided
for compatibility, but otherwise ignored by
gawk, since gawk has no predefined limits.
-W gawk-opt
gawk,
these arguments may be separated by commas, or quoted and separated by
whitespace. Case is ignored when processing these options. These options
also have corresponding GNU style long options.
See below.
--
The following gawk-specific options are available:
-W traditional
-W compat
--traditional
--compat
awk language are disabled, so that gawk behaves just
like the Bell Labs research version of Unix awk.
`--traditional' is the preferred form of this option.
See section Extensions in gawk Not in POSIX awk,
which summarizes the extensions. Also see
section Downward Compatibility and Debugging.
-W copyleft
-W copyright
--copyleft
--copyright
gawk.
-W help
-W usage
--help
--usage
gawk accepts, and then exit.
-W lint
--lint
awk implementations.
Some warnings are issued when gawk first reads your program. Others
are issued at run-time, as your program executes.
-W lint-old
--lint-old
awk
(see section Major Changes between V7 and SVR3.1).
-W posix
--posix
gawk
extensions (just like `--traditional'), and adds the following additional
restrictions:
\x escape sequences are not recognized
(see section Escape Sequences).
func for the keyword function is not
recognized (see section Function Definition Syntax).
FS to be a single tab character
(see section Specifying How Fields are Separated).
fflush built-in function is not supported
(see section Built-in Functions for Input/Output).
gawk
will also issue a warning if both options are supplied.
-W re-interval
--re-interval
awk,
gawk does not provide them by default. This prevents old awk
programs from breaking.
-W source program-text
--source program-text
AWKPATH Environment Variable).
-W version
--version
gawk.
This allows you to determine if your copy of gawk is up to date
with respect to whatever the Free Software Foundation is currently
distributing.
It is also useful for bug reports
(see section Reporting Problems and Bugs).
Any other options are flagged as invalid with a warning message, but are otherwise ignored.
In compatibility mode, as a special case, if the value of fs supplied
to the `-F' option is `t', then FS is set to the tab
character ("\t"). This is only true for `--traditional', and not
for `--posix'
(see section Specifying How Fields are Separated).
The `-f' option may be used more than once on the command line.
If it is, awk reads its program source from all of the named files, as
if they had been concatenated together into one big file. This is
useful for creating libraries of awk functions. Useful functions
can be written once, and then retrieved from a standard place, instead
of having to be included into each individual program.
You can type in a program at the terminal and still use library functions,
by specifying `-f /dev/tty'. awk will read a file from the terminal
to use as part of the awk program. After typing your program,
type Control-d (the end-of-file character) to terminate it.
(You may also use `-f -' to read program source from the standard
input, but then you will not be able to also use the standard input as a
source of data.)
Because it is clumsy using the standard awk mechanisms to mix source
file and command line awk programs, gawk provides the
`--source' option. This does not require you to pre-empt the standard
input for your source code, and allows you to easily mix command line
and library source code
(see section The AWKPATH Environment Variable).
If no `-f' or `--source' option is specified, then gawk
will use the first non-option command line argument as the text of the
program source code.
If the environment variable POSIXLY_CORRECT exists,
then gawk will behave in strict POSIX mode, exactly as if
you had supplied the `--posix' command line option.
Many GNU programs look for this environment variable to turn on
strict POSIX mode. If you supply `--lint' on the command line,
and gawk turns on POSIX mode because of POSIXLY_CORRECT,
then it will print a warning message indicating that POSIX
mode is in effect.
You would typically set this variable in your shell's startup file. For a Bourne compatible shell (such as Bash), you would add these lines to the `.profile' file in your home directory.
POSIXLY_CORRECT=true export POSIXLY_CORRECT
For a csh compatible shell,(14)
you would add this line to the `.login' file in your home directory.
setenv POSIXLY_CORRECT true
Any additional arguments on the command line are normally treated as
input files to be processed in the order specified. However, an
argument that has the form var=value, assigns
the value value to the variable var---it does not specify a
file at all.
All these arguments are made available to your awk program in the
ARGV array (see section Built-in Variables). Command line options
and the program text (if present) are omitted from ARGV.
All other arguments, including variable assignments, are
included. As each element of ARGV is processed, gawk
sets the variable ARGIND to the index in ARGV of the
current element.
The distinction between file name arguments and variable-assignment
arguments is made when awk is about to open the next input file.
At that point in execution, it checks the "file name" to see whether
it is really a variable assignment; if so, awk sets the variable
instead of reading a file.
Therefore, the variables actually receive the given values after all
previously specified files have been read. In particular, the values of
variables assigned in this fashion are not available inside a
BEGIN rule
(see section The BEGIN and END Special Patterns),
since such rules are run before awk begins scanning the argument list.
The variable values given on the command line are processed for escape sequences (d.c.) (see section Escape Sequences).
In some earlier implementations of awk, when a variable assignment
occurred before any file names, the assignment would happen before
the BEGIN rule was executed. awk's behavior was thus
inconsistent; some command line assignments were available inside the
BEGIN rule, while others were not. However,
some applications came to depend
upon this "feature." When awk was changed to be more consistent,
the `-v' option was added to accommodate applications that depended
upon the old behavior.
The variable assignment feature is most useful for assigning to variables
such as RS, OFS, and ORS, which control input and
output formats, before scanning the data files. It is also useful for
controlling state if multiple passes are needed over a data file. For
example:
awk 'pass == 1 { pass 1 stuff }
pass == 2 { pass 2 stuff }' pass=1 mydata pass=2 mydata
Given the variable assignment feature, the `-F' option for setting
the value of FS is not
strictly necessary. It remains for historical compatibility.
AWKPATH Environment Variable
The previous section described how awk program files can be named
on the command line with the `-f' option. In most awk
implementations, you must supply a precise path name for each program
file, unless the file is in the current directory.
But in gawk, if the file name supplied to the `-f' option
does not contain a `/', then gawk searches a list of
directories (called the search path), one by one, looking for a
file with the specified name.
The search path is a string consisting of directory names
separated by colons. gawk gets its search path from the
AWKPATH environment variable. If that variable does not exist,
gawk uses a default path, which is
`.:/usr/local/share/awk'.(15) (Programs written for use by
system administrators should use an AWKPATH variable that
does not include the current directory, `.'.)
The search path feature is particularly useful for building up libraries
of useful awk functions. The library files can be placed in a
standard directory that is in the default path, and then specified on
the command line with a short file name. Otherwise, the full file name
would have to be typed for each file.
By using both the `--source' and `-f' options, your command line
awk programs can use facilities in awk library files.
See section A Library of awk Functions.
Path searching is not done if gawk is in compatibility mode.
This is true for both `--traditional' and `--posix'.
See section Command Line Options.
Note: if you want files in the current directory to be found, you must include the current directory in the path, either by including `.' explicitly in the path, or by writing a null entry in the path. (A null entry is indicated by starting or ending the path with a colon, or by placing two colons next to each other (`::').) If the current directory is not included in the path, then files cannot be found in the current directory. This path search mechanism is identical to the shell's.
Starting with version 3.0, if AWKPATH is not defined in the
environment, gawk will place its default search path into
ENVIRON["AWKPATH"]. This makes it easy to determine
the actual search path gawk will use.
This section describes features and/or command line options from
previous releases of gawk that are either not available in the
current version, or that are still supported but deprecated (meaning that
they will not be in the next release).
For version 3.0 of gawk, there are no command line options
or other deprecated features from the previous version of gawk.
This section
is thus essentially a place holder,
in case some option becomes obsolete in a future version of gawk.
This section intentionally left blank.
gawkFS
(see section Command Line Options)
is not necessary given the command line variable
assignment feature; it remains only for backwards compatibility.
gawk
than you would get on a system without those files. When gawk
interprets these files internally, it synchronizes output to the
standard output with output to `/dev/stdout', while on a system
with those files, the output is actually to different open files
(see section Special File Names in gawk).