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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 named options.
awk [POSIX or GNU style options] -f progfile [--] file ... awk [POSIX or GNU style options] [--] 'program' file ...
Options begin with a minus sign, and consist of a single character. GNU style long named options consist of two minus signs and a keyword that can be abbreviated if the abbreviation allows the option to be uniquely identified. If the option takes an argument, then the keyword is immediately followed by an equals sign (`=') and the argument's value. 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 named 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 below for a fuller explanation).
The `-v' option can only set one variable, but you can use it more than once, setting another variable each time, like this: `-v foo=1 -v bar=2'.
-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 named options. The following
gawk-specific options are available:
-W compat
--compat
gawk are disabled, so that gawk behaves just like Unix
awk.
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 posix
--posix
gawk
extensions (just like -W compat), and adds the following additional
restrictions:
\x escape sequences are not recognized
(see section Constant Expressions).
func for the keyword function is not
recognized (see section Syntax of Function Definitions).
FS to be a single tab character
(see section Specifying how Fields are Separated).Although you can supply both `-W compat' and `-W posix' on the command line, `-W posix' will take precedence.
-W source=program-text
--source=program-text
awk source code in files with program source
code that you would enter on the command line. This is particularly useful
when you have library functions that you wish to use from your command line
programs (see section The AWKPATH Environment Variable).
-W version
--version
gawk.
This is so you can determine if your copy of gawk is up to date
with respect to whatever the Free Software Foundation is currently
distributing. This option may disappear in a future version of gawk.
This is useful if you have file names that start with `-', or in shell scripts, if you have file names that will be specified by the user which could start with `-'.
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 `-W compat', and not
for `-W posix'
(see section Specifying how Fields are Separated).
If the `-f' option is not used, then the first non-option command line argument is expected to be the program text.
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 still
type in a program at the terminal and 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.
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, means to assign
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 the ARGV
array. All other arguments, including variable assignments, are
included.
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 specified 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 BEGIN and END Special Patterns),
since such rules are run before awk begins scanning the argument list.
The values given on the command line are processed for escape sequences
(see section Constant Expressions).
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. 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 this 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 datafile pass=2 datafile
Given the variable assignment feature, the `-F' option 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 some 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 in 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 actually 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 the default path, which is
`.:/usr/lib/awk:/usr/local/lib/awk'. (Programs written 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 combining the `--source' and `-f' options, your command line
awk programs can use facilities in awk library files.
Path searching is not done if gawk is in compatibility mode.
This is true for both `-W compat' and `-W 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 writing `.' as an entry 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.
This section describes features and/or command line options from the
previous release 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 2.15 of gawk, the following command line options
from version 2.11.1 are no longer recognized.
gawk. The POSIX standard now
specifies traditional awk regular expressions for the awk utility.
The public-domain version of strftime that is distributed with
gawk changed for the 2.14 release. The `%V' conversion specifier
that used to generate the date in VMS format was changed to `%v'.
This is because the POSIX standard for the date utility now
specifies a `%V' conversion specifier.
See section Functions for Dealing with Time Stamps, for details.
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