regexp.php

<?php

$input = isset($argv[1]) ? $argv[1] : 'fb.com/username';
$pattern = '#(?:https?\://)?(?:www\.)?(?:facebook|fb)\.com/(\d+|[A-Za-z0-9\.]+)/?#';
var_dump(preg_match($pattern, $input, $matches));
var_dump($matches);