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---
layout: post
category: perl
title: Modules I like Getopt::Long and MooseX::Getopt
---
h3. 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.
h3. MooseX::Getopt
"MooseX::Getopt":http://search.cpan.org/perldoc?MooseX::Getopt) is a Role that add a <code>new_with_options</code> 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 %}
bc. script.pl --config file.yml
The role will set our attribute **context** using the value from the argument set on the command line.
The
{% highlight perl %}
traits => ['NoGetopt']
{% endhighlight %}
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 *_*.
h3. 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 :).
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