Getopt::Long

Getopt::long is a useful module to parse command line arguements.

A basic usage is something like this:

#!/usr/bin/perl -w
use strict;
use YAML::Syck;
use Getopt::Long;

GetOptions('config=s' => \my $cfg_file,);

my $config = LoadFile $cfg_file

In GetOptions, we require a value for config with config=s. If we wante an integer, we replace ‘s’ with ‘i’, and for a floating point, with ‘f’.

Call your script :

    script.pl --config=file.yml #this one works
    script.pl --config file.yml  #this one too!
    script.pl -c file.yml          #and this one too

The three syntaxes are understood.

A good practices is to combine this module with Pod::Usage. Let’s do some modifications on the example:

#!/usr/bin/perl -w
use strict;
use YAML::Syck;
use Getopt::Long;
use Pod::Usage;

GetOptions('config=s' => \my $cfg_file,) or pod2usage(2);
pod2usage(2) unless @ARGV > 0;

my $config = LoadFile $cfg_file

__END__
=head1 NAME

uberscript

=head1 SYNOPSIS

uberscript [options]

Options:

    --config  config file

=head1 Options

=over 4

=item B<config>

Path to the config file

then

$ perl uberscript

Usage:
    uberscript [options]

    Options:
        --config  config file

From now if we call our script without argument, the POD will be printed on STDIN.

MooseX::Getopt

MooseX::Getopt) is a Role that add a new_with_options to your object. We create a basic Object :

package OurShinyObject;

use Moose;
with qw/MooseX::Getopt/;

has 'config' => (isa => 'Str', is => 'ro', required => 1);
has 'context' => (
    isa     => 'HashRef',
    is      => 'rw',
    lazy    => 1,
    traits  => ['NoGetopt'],
    default => sub { LoadFile shift->config }
);

...

create a script to call this object

#!/usr/bin/perl -w
use strict;
use OurShinyObject;

my $obj = OurShinyObject->new_from_options();

script.pl --config file.yml

The role will set our attribute context using the value from the argument set on the command line.

The

traits => ['NoGetopt']

indicate that this attributes will be not be read from the command line. An alternate way to do this is to prefix the attributes with _.

conclusion (?)

When you write a script, even if you’re sure you will never need to have more than one argument, or that you never will have to update the code, please consider to use of Getopt::Long instead of a shift @ARGV, because we all know that you will at a certain point update this script and you will more than one argument :).