use strict;
use warnings;
use Regexp::Assemble;

my $r = Regexp::Assemble->new;

$r->add('2L', 'bar.2L');

my $pattern = qr/($r)/;
[download]

oops, no, I didn't see it was just the '2L' part you were interested. Oh well, rather than removing the code I may as well leave it in case it solves someone else's problem :)