How to Use PHP Regular Expressions to Match Keywords Excluding Those in Anchor Tags?

How to Match Keywords Outside HTML Anchor Tags Using PHP Regular Expressions

In PHP, matching and replacing specific keywords in HTML content can be achieved using regular expressions. A common scenario is the need to match keywords while excluding their occurrences within HTML anchor tags. Consider the following requirements:

• Match the keyword "keyword" and its bold equivalent "keyword", disregarding any instances within anchor tags.
• Issue: Anchor tags with "keyword" as the link text should not be modified, such as " keyword " and "already linked keyword ".

To address this challenge, we can employ a regular expression solution in PHP that ensures keyword matches only occur outside anchor tags.

The following code snippet demonstrates how to achieve this:

<code class="php">$str = preg_replace('~Moses(?!(?>[^<]*(?:<(?!/?a\b)[^<]*)*)</a>)~i',
                    '<a href="novo-mega-link.php"></a>', $str);</code>

Explanation:

The core component of this regular expression is the negative lookahead. This lookahead checks for the presence of closing anchor tags "" and an opening anchor tag "" in that order. If this pattern is found, the expression within the lookahead is considered true, and the keyword match is canceled.

Therefore, the regular expression ensures that matches are made only when the keyword appears outside of HTML anchor tags. This enables us to subsequently replace the keyword with an anchor tag linking to a specified URL.

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