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;
?>