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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?

lordmj
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  • To clarify, which is a match: (1) `a` tags with the specified URL pattern *and* the `rel="shadowbox[a]"` attribute, or (2) `a` tags with the specified URL pattern *or* the `rel="shadowbox[a]"` attribute? – elixenide Mar 05 '14 at 21:33
  • P.S. You are better off not using regex at all and using a parser instead, for [the reasons set forth in this answer](http://stackoverflow.com/a/1732454/2057919). – elixenide Mar 05 '14 at 21:35
  • It's a tag with the rel="shadowbox[a]" attribute. I want to keep those urls (along with all hyperlinks that link to http://keepthisdomain.com/foo/bar) – lordmj Mar 05 '14 at 21:42

1 Answers1

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

Details on the regex:

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

Regular expression visualization

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 \.

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elixenide
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