How Can I Replace Whole Words Only Using Regex in PHP?

Regex-Based Word Replacement in PHP Strings

Replacing specific words within a string can be tricky if you want to ensure that only entire words are matched. In this particular case, the string text contains the word "Hello" in various forms, but we want to replace only complete occurrences of "Hello."

To achieve this, we can utilize PHP's regular expression functions. Regular expressions provide a powerful tool for matching patterns within strings. The key to limiting the replacement to whole words is the b metacharacter, which matches a word boundary.

By modifying the str_replace function to incorporate a regular expression, we can accomplish our goal:

$text = "Hello hellol hello, Helloz";
$newtext = preg_replace('/\bHello\b/', 'NEW', $text);

The b in the regular expression ensures that only entire occurrences of "Hello" are matched, excluding any partial or overlapped matches. The result will be:

NEW hellol hello, Helloz

This correctly replaces only the complete instances of "Hello" with "NEW" while leaving other variations untouched.

UTF-8 Unicode Handling:

If the text contains UTF-8 characters, an additional step is necessary to ensure proper recognition of word boundaries. UTF-8 encoding for Unicode characters requires the use of the "u" modifier in the regular expression:

$text = "Hello hellol こんにちは, Helloz";
$newtext = preg_replace('/\bHello\b/u', 'NEW', $text);

This will correctly replace all complete occurrences of "Hello" regardless of language or character encoding.

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