path: root/_posts/2009-06-22-modules-i-like-getopt-long-and-moosex-getopt.md

---
layout: post
summary: In which I talk about GetOpt::Long and Moosex::Getopt
title: Modules I like Getopt::Long and MooseX::Getopt
---

## Getopt::Long

[Getopt::long](http://search.cpan.org/perldoc?Getopt::Long) is a useful module to parse command line arguements.

A basic usage is something like this:

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

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

my $config = LoadFile $cfg_file
{% endhighlight %}

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 :

{% highlight bash %}
% 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
{% endhighlight %}

The three syntaxes are understood.

A good practices is to combine this module with [Pod::Usage](http://search.cpan.org/perldoc?Pod::Usage). Let's do some modifications on the example:

{% highlight perl %}
#!/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
{% endhighlight %}

then

{% highlight bash %}
% perl uberscript

Usage:
    uberscript [options]

    Options:
        --config  config file
{% endhighlight %}

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

## MooseX::Getopt

[MooseX::Getopt](http://search.cpan.org/perldoc?MooseX::Getopt) is a Role that add a `new_with_options` to your object. We create a basic Object :

{% highlight perl %}
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 }
);

...
{% endhighlight %}

create a script to call this object

{% highlight perl %}
#!/usr/bin/perl -w
use strict;
use OurShinyObject;

my $obj = OurShinyObject->new_from_options();

{% endhighlight %}

{% highlight sh%}
% script.pl --config file.yml
{% endhighlight %}

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 :).