- var_dump: documentation ( source)
- preg_match: documentation ( source)
<?php
$str = 'https://www.youtube.com/watch?v=UiyDmqO59QE';
if (preg_match('/(youtu\.be\/|youtube\.com\/(watch\?(.*&)?v=|(embed|v)\/))([^\?&"\'>]+)/', $str, $matches)) {
var_dump( $matches );
}