#!/usr/bin/perl -w
use strict;
use warnings;

use List::Util qw(first);

my %test = (
	'15.01.2011' => defined,
	'17.01.2011' => defined,
	'13.02.2011' => defined,
	'16.03.2011' => defined,
	'20.12.2011' => defined,
);

foreach my $m (1..12) {
	if (first { /\.0?$m\./ } keys %test) {
		print "Monat $m gefunden!\n";
	}
}