How to print program usage in Perl?

What's the easiest to maintain way of printing a Perl program's usage to stdout? I am looking for he开发者_JAVA百科redoc tricks or anything similarly useful. Forget individual successive prints.

EDIT 1: the issue I have faced many times is to have to maintain usage, general script documentation and option processing separately. I was looking for a way to combine some or all of this with minimal overhead. Thanks for the many suggestions. I will accept an answer when I have an opportunity to experiment proposed solutions.

Pod::Usage maybe? This was suggested by GetOpt::Long.

Getopt::Std::WithCheck allows you to combine the definition of options along a description, and Getopt::Simple does the same.

I think you just answered your own question. A heredoc clause is the usual way to go, if the usage information is not automatically generated (e.g. by Getopt::Long::Descriptive or MooseX::Getopt).

package ClassA;
use Getopt::Long::Descriptive;

my ($opt, $usage) = describe_options(
    'my-program %o <some-arg>',
    [ 'server|s=s', "the server to connect to"                  ],
    [ 'port|p=i',   "the port to connect to", { default => 79 } ],
    [],
    [ 'verbose|v',  "print extra stuff"            ],
    [ 'help',       "print usage message and exit" ],
);

print($usage->text), exit if $opt->help;


package ClassB;
use Moose;
with' MooseX::Getopt';

has server => (
    is => 'ro', isa => 'Str',
    traits    => [ 'Getopt' ],
    cmd_aliases => ['s'],
    documentation => 'the server to connect to',
);
has port => (
    is => 'ro', isa => 'Int',
    traits    => [ 'Getopt' ],
    cmd_aliases => ['p'],
    default => 79,
    documentation => 'the port to connect to',
);
has verbose => (
    is => 'ro', isa => 'Bool',
    traits    => [ 'Getopt' ],
    cmd_aliases => ['v'],
    documentation => 'print extra stuff',
);

You can call ClassB like so (if you're not using MooseX::Runnable or a script to construct the object):

    perl -I. -MClassB -wle'my $obj = ClassB->new_with_options;' -- --help

And produces:

    usage: -e [-?psv] [long options...]
            -? --usage --help  Prints this usage information.
            -s --server        the server to connect to
            -p --port          the port to connect to
            -v --verbose       print extra stuff

something like :

print <<END;
Usage : foo bar

Foobar foobar.
END

?

Damian Conway has two interesting modules that use the documentation of your command-line interface to produce the parsing code:

• Getopt::Euclid: declare your interface in the POD
• Getopt::Declare: declare your interface in a string that you can output in case of error

They will help (force) you to maintain a documentation matching the code.

You can use a here-doc :

use Getopt::Long;

my $USAGE = <<"USAGE";
Usage: some_script.pl -env=[dev|qa|pr]

Regular options:

-env        -- Valid values for env are 'dev', 'qa', 'pr'

USAGE

our ($opt_env);

die $USAGE
  unless GetOptions ("env=s"   => \$opt_env); # string