regex - Replace all urls in string not matching url pattern in php

Question

I'm using the following code to filter out urls from a block of HTML text in PHP.

preg_replace('#<a(?![^>]+?href="?http://keepthisdomain.com/foo/bar"?).*?>(.*?)</a>#i', '1', $text);

It's intended to replace all url's that do not match the specified url pattern. However I do want to include all tags that have the attribute rel="shadowbox[a]" set.

How can I modify this preg_replace to do that?

Answer 1

You are better off not using regex at all and using a parser instead, for the reasons set forth in this answer.

That said, you can do it with regex, but it's tricky:

preg_replace('#<a(?![^>]+?href="?http://keepthisdomain.com/foo/bar"?|[^>]+rel="shadowbox[a]").*?>(.*?)</a>#i', '1', $text);

Details on the regex:

<a(?![^>]+?href="?http://keepthisdomain.com/foo/bar"?|[^>]+rel="shadowbox[a]").*?>(.*?)</a>

Out of the following four tags, only the third would be replaced:

<a href="http://keepthisdomain.com/foo/bar">foo</a> // left alone
<a href="http://keepthisdomain.com/foo/bar" rel="shadowbox[a]">foo</a> // left alone
<a href="http://rejectthis.com/foo/bar">foo</a> // REPLACED
<a href="http://rejectthis.com/foo/bar" rel="shadowbox[a]">foo</a> // left alone

Edited with a minor tweak to make it match a literal . in .com, using .