- substr: documentation ( source)
- var_dump: documentation ( source)
- parse_url: documentation ( source)
<?php
$url = 'http://33c5def5fd5303508478-404edcebd16173bc1f7617706b5a3522.r34.cf2.rackcdn.com/91@2x.png';
$urlParts = parse_url($url);
$ext = substr($urlParts['path'], 0, -3);
var_dump($ext);