How Can I Use PHP Regex to Avoid Modifying HTML Tags During Text Replacement?

PHP Regex to Exclude Matches Within HTML Tags

When performing text replacements using preg_replace in HTML documents, it's essential to avoid modifying HTML tags inadvertently. For instance, consider the task of wrapping certain words within tags:

<p>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...</p>

The following regex attempts to replace "yasar" with tags:

preg_replace("/(asf|gfd|oyws)/", '<span>

Unfortunately, this regex also matches "yasar" within the alt attribute of an anchor tag, resulting in undesired changes.

Using Assertions to Exclude Matches Within Tags

To prevent such unwanted matches, an assertion can be utilized. By asserting that the word being searched (i.e., "asf," "gfd," or "oyws") does not appear before a "<" or after a ">," we can effectively exclude matches within HTML tags. Here's a modified regex that employs this approach:

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

The lookahead assertion (?=[^>]*(<|$)) ensures that the word must be followed by either an HTML tag opener ("<") or the end of the string (represented by "$"). This effectively excludes matches within tags.

By incorporating this assertion into the regex, we can perform replacements without modifying HTML tags, ensuring that yasar in the alt attribute remains untouched:

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

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