php正则替换非站内链接 替换zencart描述内的非本站链接

<?php
//要替换的文本，比如产品描述中的文字
header("content-Type: text/html; charset=utf-8"); 
$content = ‘
<li><a href="http://afish.cnblogs.com" target="_blank">小鱼阁</a></li>
<li><a href="http://afish.cnblogs.com" target="_blank">小鱼阁</a></li>
<li><a href="http://afish.cnblogs.com" target="_blank">小鱼阁</a></li>
<li><a href="http://www.baidu.com" target="_blank">百度</a></li>
<li><a href="http://www.baidu.com" target="_blank">百度</a></li>
<li><a href="http://www.baidu.com" target="_blank">百度</a></li>
<li><a href="http://www.soso.com" target="_blank">搜搜</a></li>
<li><a href="http://www.soso.com" target="_blank">搜搜</a></li>
<li><a href="http://www.soso.com" target="_blank">搜搜</a></li>
‘;

//本站域名
$host_url = str_replace(".", "\.", str_replace("www.", "", $_SERVER[‘HTTP_HOST‘]));
//echo $host_url;

//替换正则
$pattern = ‘/<[^>]*href=[\‘\"]http?:\/\/(?!‘.str_replace("http://","",$host_url).‘|‘.str_replace("http://www.","",$host_url).‘|[\w\_]+\.‘.str_replace("http://www.","",$host_url).‘)[^\‘^\"]*[\‘\"][^>]*>(.+?)<\/a>/is‘;
//替换成的内容
//$replace = ‘<a href="http://‘.$_SERVER[‘HTTP_HOST‘].‘" target="_blank">$1</a>‘;
$replace = ‘<a href="http://‘.$_SERVER[‘HTTP_HOST‘].‘" target="_blank">本站链接</a>‘;
//进行替换
$content = preg_replace($pattern, $replace, $content);
//输出替换后的内容
echo $content;
?>