Here's what I do:

#!/usr/bin/perl -w

use strict;
use ExtUtils::Installed;

my $instmod = ExtUtils::Installed->new();
foreach my $module ($instmod->modules()) {
    my $version = $instmod->version($module) || "???";
    print " $module  -- $version\n";
}
[download]

HTH

Update: Please ignore, I mis-read op. The above returns the modules in a perl installation and the vesion numbers.