2.2 Command-Line Options

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 as the abbreviation allows the option to be uniquely identified. If the option takes an argument, either the keyword is immediately followed by an equals sign (‘=’) and the argument’s value, or the keyword and the argument’s value are separated by whitespace. If a particular option with a value is given more than once, it is the last value that counts.

Each long option for gawk has a corresponding POSIX-style short option. The long and short options are interchangeable in all contexts. The following list describes options mandated by the POSIX standard:

-F fs

--field-separator fs

Set the FS variable to fs (see Field Separators).

-f source-file

--file source-file

Read the awk program source from source-file instead of in the first nonoption argument. This option may be given multiple times; the awk program consists of the concatenation of the contents of each specified source-file.

-v var=val

--assign var=val

Set the variable var to the value val before execution of the program begins. Such variable values are available inside the BEGIN rule (see Other Arguments).

The -v option can only set one variable, but it can be used more than once, setting another variable each time, like this: ‘awk -v foo=1 -v bar=2 …’.

CAUTION: Using -v to set the values of the built-in variables may lead to surprising results. awk will reset the values of those variables as it needs to, possibly ignoring any initial value you may have given.

-W gawk-opt

Provide an implementation-specific option. This is the POSIX convention for providing implementation-specific options. These options also have corresponding GNU-style long options. Note that the long options may be abbreviated, as long as the abbreviations remain unique. The full list of gawk-specific options is provided next.

--

Signal the end of the command-line options. The following arguments are not treated as options even if they begin with ‘-’. This interpretation of -- follows the POSIX argument parsing conventions.

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 that could start with ‘-’. It is also useful for passing options on to the awk program; see Getopt Function.

The following list describes gawk-specific options:

-b

--characters-as-bytes

Cause gawk to treat all input data as single-byte characters. In addition, all output written with print or printf is treated as single-byte characters.

Normally, gawk follows the POSIX standard and attempts to process its input data according to the current locale (see Locales). This can often involve converting multibyte characters into wide characters (internally), and can lead to problems or confusion if the input data does not contain valid multibyte characters. This option is an easy way to tell gawk, “Hands off my data!”

-c

--traditional

Specify compatibility mode, in which the GNU extensions to the awk language are disabled, so that gawk behaves just like BWK awk. See POSIX/GNU, which summarizes the extensions. Also see Compatibility Mode.

-C

--copyright

Print the short version of the General Public License and then exit.

-d[file]

--dump-variables[=file]

Print a sorted list of global variables, their types, and final values to file. If no file is provided, print this list to a file named awkvars.out in the current directory. No space is allowed between the -d and file, if file is supplied.

Having a list of all 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, etc.)

-D[file]

--debug[=file]

Enable debugging of awk programs (see Debugging). By default, the debugger reads commands interactively from the keyboard (standard input). The optional file argument allows you to specify a file with a list of commands for the debugger to execute noninteractively. No space is allowed between the -D and file, if file is supplied.

-e program-text

--source program-text

Provide program source code in the program-text. This option allows you to mix source code in files with source code that you enter on the command line. This is particularly useful when you have library functions that you want to use from your command-line programs (see AWKPATH Variable).

-E file

--exec file

Similar to -f, read awk program text from file. There are two differences from -f:

• This option terminates option processing; anything else on the command line is passed on directly to the awk program.
• Command-line variable assignments of the form ‘var=value’ are disallowed.

This option is particularly necessary for World Wide Web CGI applications that pass arguments through the URL; using this option prevents a malicious (or other) user from passing in options, assignments, or awk source code (via -e) to the CGI application.¹¹ This option should be used with ‘#!’ scripts (see Executable Scripts), like so:

#! /usr/local/bin/gawk -E

awk program here …

-g

--gen-pot

Analyze the source program and generate a GNU gettext portable object template file on standard output for all string constants that have been marked for translation. See Internationalization, for information about this option.

-h

--help

Print a “usage” message summarizing the short- and long-style options that gawk accepts and then exit.

-i source-file

--include source-file

Read an awk source library from source-file. This option is completely equivalent to using the @include directive inside your program. It is very similar to the -f option, but there are two important differences. First, when -i is used, the program source is not loaded if it has been previously loaded, whereas with -f, gawk always loads the file. Second, because this option is intended to be used with code libraries, gawk does not recognize such files as constituting main program input. Thus, after processing an -i argument, gawk still expects to find the main source code via the -f option or on the command line.

-l ext

--load ext

Load a dynamic extension named ext. Extensions are stored as system shared libraries. This option searches for the library using the AWKLIBPATH environment variable. The correct library suffix for your platform will be supplied by default, so it need not be specified in the extension name. The extension initialization routine should be named dl_load(). An alternative is to use the @load keyword inside the program to load a shared library. This advanced feature is described in detail in Dynamic Extensions.

-L[value]

--lint[=value]

Warn about constructs that are dubious or nonportable to other awk implementations. No space is allowed between the -L and value, if value is supplied. Some warnings are issued when gawk first reads your program. Others are issued at runtime, as your program executes. 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.)

Some warnings are only printed once, even if the dubious constructs they warn about occur multiple times in your awk program. Thus, when eliminating problems pointed out by --lint, you should take care to search for all occurrences of each inappropriate construct. As awk programs are usually short, doing so is not burdensome.

-M

--bignum

Select arbitrary-precision arithmetic on numbers. This option has no effect if gawk is not compiled to use the GNU MPFR and MP libraries (see Arbitrary Precision Arithmetic).

-n

--non-decimal-data

Enable automatic interpretation of octal and hexadecimal values in input data (see Nondecimal Data).

CAUTION: This option can severely break old programs. Use with care. Also note that this option may disappear in a future version of gawk.

-N

--use-lc-numeric

Force the use of the locale’s decimal point character when parsing numeric input data (see Locales).

-o[file]

--pretty-print[=file]

Enable pretty-printing of awk programs. By default, the output program is created in a file named awkprof.out (see Profiling). The optional file argument allows you to specify a different file name for the output. No space is allowed between the -o and file, if file is supplied.

NOTE: Due to the way gawk has evolved, with this option your program still executes. This will change in the next major release, such that gawk will only pretty-print the program and not run it.

-O

--optimize

Enable some optimizations on the internal representation of the program. At the moment, this includes just simple constant folding.

-p[file]

--profile[=file]

Enable profiling of awk programs (see Profiling). By default, profiles are created in a file named awkprof.out. The optional file argument allows you to specify a different file name for the profile file. No space is allowed between the -p and file, if file is supplied.

The profile contains execution counts for each statement in the program in the left margin, and function call counts for each function.

-P

--posix

Operate in strict POSIX mode. This disables all gawk extensions (just like --traditional) and disables all extensions not allowed by POSIX. See Common Extensions for a summary of the extensions in gawk that are disabled by this option. Also, the following additional restrictions apply:

• Newlines do not act as whitespace to separate fields when FS is equal to a single space (see Fields).
• Newlines are not allowed after ‘?’ or ‘:’ (see Conditional Exp).
• Specifying ‘-Ft’ on the command line does not set the value of FS to be a single TAB character (see Field Separators).
• The locale’s decimal point character is used for parsing input data (see Locales).

If you supply both --traditional and --posix on the command line, --posix takes precedence. gawk issues a warning if both options are supplied.

-r

--re-interval

Allow interval expressions (see Regexp Operators) in regexps. This is now gawk’s default behavior. Nevertheless, this option remains (both for backward compatibility and for use in combination with --traditional).

-S

--sandbox

Disable the system() function, input redirections with getline, output redirections with print and printf, and dynamic extensions. This is particularly useful when you want to run awk scripts from questionable sources and need to make sure the scripts can’t access your system (other than the specified input data file).

-t

--lint-old

Warn about constructs that are not available in the original version of awk from Version 7 Unix (see V7/SVR3.1).

-V

--version

Print version information for this particular copy of 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 Bugs).

As long as program text has been supplied, 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 true only for --traditional and not for --posix (see Field Separators).

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. These functions can be written once and then retrieved from a standard place, instead of having to be included in each individual program. The -i option is similar in this regard. (As mentioned in Definition Syntax, function names must be unique.)

With standard awk, library functions can still be used, even if the program is entered at the keyboard, by specifying ‘-f /dev/tty’. After typing your program, type Ctrl-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 -e option. This does not require you to preempt the standard input for your source code; it allows you to easily mix command-line and library source code (see AWKPATH Variable). As with -f, the -e and -i options may also be used multiple times on the command line.

If no -f or -e option is specified, then gawk uses the first nonoption command-line argument as the text of the program source code.

If the environment variable POSIXLY_CORRECT exists, then gawk behaves in strict POSIX mode, exactly as if you had supplied --posix. Many GNU programs look for this environment variable to suppress extensions that conflict with POSIX, but gawk behaves differently: it suppresses all extensions, even those that do not conflict with POSIX, and behaves in strict POSIX mode. If --lint is supplied on the command line and gawk turns on POSIX mode because of POSIXLY_CORRECT, then it issues 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 C shell-compatible shell,¹² you would add this line to the .login file in your home directory:

setenv POSIXLY_CORRECT true

Having POSIXLY_CORRECT set is not recommended for daily use, but it is good for testing the portability of your programs to other environments.