php匹配字符中链接地址的方法

$str="ssdsf<a target='_blank' href='https://.jb51./' >sdf</a>sdfss";
if(preg_match("/<a/s+href=[^>]>|<//[^a]a[^>]>/i",$str))
{
echo "该字符串有超链接";
}
else
{
echo "该字符串没有超链接标记";
}
?>

<?php 
echo preg_replace("/(?<=href=)([^>])(?=>)/i","#", "<a href='.jb51.'>你好，点这里看看</a><a href='.jb51.'>你好，点这里看看</a>"); 
?>

function match_links($document) {   
    preg_match_all("'<sas.?hrefs=s(["'])?(?(1)(.?)\1|([^s>]+))[^>]>?(.?)</a>'isx",$document,$links);                       
    while(list($key,$val) = each($links[2])) {
        if(!emptyempty($val))
            $match['link'][] = $val;
    }
    while(list($key,$val) = each($links[3])) {
        if(!emptyempty($val))
            $match['link'][] = $val;
    }       
    while(list($key,$val) = each($links[4])) {
        if(!emptyempty($val))
            $match['content'][] = $val;
    }
    while(list($key,$val) = each($links[0])) {
        if(!emptyempty($val))
            $match['all'][] = $val;
    }               
    return $match;
}