How to Match Keywords Outside of Anchor Tags Using PHP Regex?

Matching Keywords Outside HTML Anchor Tags () Using PHP Regular Expression

In web development, there might arise situations where you need to match and replace keywords within HTML content while avoiding certain specific areas, such as hyperlinks. This can be achieved using PHP regular expressions.

Problem Statement:

The task at hand is to find a regular expression pattern that matches the keyword "keyword" but excludes instances that are enclosed within anchor tags (keyword).

Solution:

To address this problem effectively, the following PHP regular expression can be utilized:

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

Explanation:

• Moses: This part simply matches the keyword "Moses."
• (?!: This denotes the beginning of a negative lookahead assertion.
• (?>[^<]*(?:<(?!/?ab)[^<]*)*): This part creates a recursive pattern to identify any number of non-HTML tag characters or nested tags that are not opening anchor tags.
• : Matches the closing anchor tag.
• ): This parenthesis closes the negative lookahead assertion.
• ~i: The case-insensitive modifier makes the pattern work for both upper and lower case "Moses."

Working Principle:

The regular expression initially matches "Moses." However, if the following conditions are met, it will not perform a match:

• The keyword must be followed by a sequence of non-HTML characters.
• The keyword must not be followed by an opening anchor tag.
• The keyword must be followed by a valid closing anchor tag.

If all these conditions are fulfilled, the pattern will not match the keyword. Consequently, it will be excluded from replacement.

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