超链接转换成绝对地址,能否完全使用正则解决?

从网页抓取到的超链接格式多变,怎样全部转换成绝对地址呢?<?php
$paths=array("http://we.us","x.y.z","a.b.cn/en/","http://a.b.cn/en/js","a.b.cn/js/","a.b.cn/en/js/ext","a.b.cn/en/css/ext/");
$files=array("http://so.do.i","http://a.b.cn/","./","../","../../","../js/","/js","/css/blue.css","../../en/js/ad.js");foreach($paths as $path){
  foreach($files as $file){
echo realfile($path,$file);
  }
}function realfile($path,$file){
//返回文件file的绝对地址,
//如果文件地址是相对地址,则以路径path为参照
/*
$real=$path.$file;//要完善的内容
*/
return '<li>'.$real.'</li>';
}?>