Writing your own Perl modules

Making your own Perl modules is actually really easy, only involving a few special alterations to a script and an environment variable to make them easy to utilize. To make Perl modules, you first need to understand Object Oriented Perl, so if that’s new to you, check out Tom’s object-oriented Perl Tutorial. Onward.

For this example, I’ll just use a simplified version of the ‘Person’ class from the above-mentioned tutorial:

package Person;
use strict;


sub new {
    my $self  = {
        NAME => undef,
        AGE => undef,
        PEERS => [],
    };
    bless($self);
    return $self;
}
sub name {
    my $self = shift;
    if (@) { $self->{NAME} = shift }
    return $self->{NAME};
}
sub age {
    my $self = shift;
    if (@) { $self->{AGE} = shift }
    return $self->{AGE};
}
sub peers {
    my $self = shift;
    if (@) { @{ $self->{PEERS} } = @ }
    return @{ $self->{PEERS} };
}
1;

To begin with, let’s make a directory where you will put all the modules you make; say, ~/perl-modules. Take the code above and save it as Person.pm in your new perl-modules directory. Notice the .pm extension that perl will look for when you go to use this module. Now, we need to let perl know where to look for the modules you write. When you ask for a Perl module by writing use foo in a script, perl, by default, it looks in a bunch of system directories and in the current directory for anything named foo.pm. You can tell it to look other places by adding to the PERL5LIB environment variable. For ease, I simply put this into my .bashrc:

export PERL5LIB=~/perl-modules

Now, anywhere that I write a perl script, I can simply say use Person and the Person class will be grabbed from my perl-modules directory.

Another thing to keep in mind when writing modules is that you should load the Carp module and use the functions carp and croak rather than warn and die respectively. Carp’s functions produce errors that reference the proper context in the user’s code when an error occurs, rather then saying there is a problem in your module.