getopt, getopts - Process single-character switches with switch clustering


    use Getopt::Std;
    getopt('oDI');    # -o, -D & -I take arg.  Sets $opt_* as a side effect.
    getopt('oDI', \%opts);    # -o, -D & -I take arg.  Values in %opts
    getopts('oif:');  # -o & -i are boolean flags, -f takes an argument
                      # Sets $opt_* as a side effect.
    getopts('oif:', \%opts);  # options as above. Values in %opts


The getopt() function processes single-character switches with switch clustering. Pass one argument which is a string containing all switches that take an argument. For each switch found, sets $opt_x (where x is the switch name) to the value of the argument if an argument is expected, or 1 otherwise. Switches which take an argument don't care whether there is a space between the switch and the argument.

The getopts() function is similar, but you should pass to it the list of all switches to be recognized. If unspecified switches are found on the command-line, the user will be warned that an unknown option was given.

Note that, if your code is running under the recommended use strict 'vars' pragma, you will need to declare these package variables with ``our'':

    our($opt_x, $opt_y);

For those of you who don't like additional global variables being created, getopt() and getopts() will also accept a hash reference as an optional second argument. Hash keys will be x (where x is the switch name) with key values the value of the argument or 1 if no argument is specified.

To allow programs to process arguments that look like switches, but aren't, both functions will stop processing switches when they see the argument --. The -- will be removed from @ARGV.

--help and --version

If - is not a recognized switch letter, getopts() supports arguments --help and --version. If main::HELP_MESSAGE() and/or main::VERSION_MESSAGE() are defined, they are called; the arguments are the output file handle, the name of option-processing package, its version, and the switches string. If the subroutines are not defined, an attempt is made to generate intelligent messages; for best results, define $main::VERSION.

If embedded documentation (in pod format, see the perlpod manpage) is detected in the script, --help will also show how to access the documentation.

Note that due to excessive paranoia, if $Getopt::Std::STANDARD_HELP_VERSION isn't true (the default is false), then the messages are printed on STDERR, and the processing continues after the messages are printed. This being the opposite of the standard-conforming behaviour, it is strongly recommended to set $Getopt::Std::STANDARD_HELP_VERSION to true.

One can change the output file handle of the messages by setting $Getopt::Std::OUTPUT_HELP_VERSION. One can print the messages of --help (without the Usage: line) and --version by calling functions help_mess() and version_mess() with the switches string as an argument.