#!/usr/bin/perl

# http://perlmonks.org/?node_id=1176775

use strict;
use warnings;

print /x(.*)x(??{$1 =~ tr##.#cr})x/ ? 'pass' : 'fail', ' ', $_ while <
+DATA>;

__DATA__
xxxxx
x1x2x...x
xxx
x.x.x
x12x..x
x123x...x
x123x.x.x
x12x1x
[download]

outputs:

pass xxxxx
pass x1x2x...x
pass xxx
pass x.x.x
pass x12x..x
pass x123x...x
pass x123x.x.x
fail x12x1x
[download]