比如域名是html.org.cn,正則表達式如下：

 

$s = 'http://www.html.org.cn/'
$domain = array('com','cn','name','org','net');
$ss = $s;
$dd = implode('|',$domain);
$ss = preg_replace('/(.*)((/w+)(/.('.$dd.'))*/.('.$dd.'))$/iu','$2',$ss);
echo $ss ;