PHP获取文件的扩展名

<?php   $url = 'dir/upload.image.jpg';      function getExt1($url){      return strrchr($url,'.');   }      function getExt2($url){      return substr($url,strrpos($url,'.'));   }      function getExt3($url){      $a = explode('.',$url);      return array_pop($a);   }      function getExt4($url){      $p = pathinfo($url);      return $p['extension'];   }      function getExt5($url){      return strrev(substr(strrev($url), 0, strpos(strrev($url), '.')));   }      $s = getExt5($url);   echo $s;?>