php regex to match outside of html tags

Question

I am making a preg_replace on html page. My pattern is aimed to add surrounding tag to some words in html. However, sometimes my regular expression modifies html tags. For example, when I try to replace this text:

<a href="example.com" alt="yasar home page">yasar</a>

So that yasar reads <span class="selected-word">yasar</span> , my regular expression also replaces yasar in alt attribute of anchor tag. Current preg_replace() I am using looks like this:

preg_replace("/(asf|gfd|oyws)/", '<span class=something>${1}</span>',$target);

How can I make a regular expression, so that it doesn't match anything inside a html tag?

Answer 1

You can use an assertion for that, as you just have to ensure that the searched words occur somewhen after an >, or before any <. The latter test is easier to accomplish as lookahead assertions can be variable length:

/(asf|foo|barr)(?=[^>]*(<|$))/

See also http://www.regular-expressions.info/lookaround.html for a nice explanation of that assertion syntax.

Answer 2

Yasar, resurrecting this question because it had another solution that wasn't mentioned.

Instead of just checking that the next tag character is an opening tag, this solution skips all <full tags>.

With all the disclaimers about using regex to parse html, here is the regex:

<[^>]*>(*SKIP)(*F)|word1|word2|word3

Here is a demo. In code, it looks like this:

$target = "word1 <a skip this word2 >word2 again</a> word3";
$regex = "~<[^>]*>(*SKIP)(*F)|word1|word2|word3~";
$repl= '<span class="">\0</span>';
$new=preg_replace($regex,$repl,$target);
echo htmlentities($new);

Here is an online demo of this code.

Reference

1. How to match pattern except in situations s1, s2, s3
2. How to match a pattern unless...