php正则自动添加nofollow

<?php

$content = '<a href="http://www.forasp.cn">php正则自动添加nofollow</a><a href="http://www.forasp.cn">百度</a><a href="http://www.forasp.cn">php正则自动添加nofollow</a><a href="http://www.forasp.cn">百度</a><a href="http://www.forasp.cn">百度</a><a href="http://www.forasp.cn">百度</a><a href="http://www.forasp.cn">百度</a><a href="http://www.forasp.cn">php正则自动添加nofollow</a><a href="http://www.forasp.cn">百度</a>';

$content = "<a name='asdf' href='forasp.com'>asdf</a><a href='forasp.com'>asdf</a><a href='forasp.com'>php正则自动添加nofollow</a>";

 

$content = preg_replace('/<a(.*?)href=(["\'])(.*?)(["\'])/', "<a$1href=$2$3$4 ref=\"nofellow\"" , $content);

echo $content;