How Can I Replace Whole Words in a String Using PHP While Preserving Word Boundaries?

Preserving Word Boundaries in String Replacements with PHP

Replacing substrings within a string is a common programming task. However, when working with words or sequences of characters, it's often desirable to only replace complete word matches.

Problem Statement:

Consider the PHP code snippet below:

$text = "Hello hellol hello, Helloz";
$newtext = str_replace("Hello", 'NEW', $text);

If we intend to replace all instances of "Hello" with "NEW," the snippet above will produce the following incorrect result:

NEW hello1 hello, NEWz

Instead of the desired:

NEW hello1 hello, Helloz

This is because PHP's str_replace function performs a character-by-character replacement, resulting in partial matches being replaced as well.

Solution Using Regular Expressions:

To only replace complete word matches, we can employ regular expressions. Regular expressions provide a more powerful pattern matching capability and allow us to match and capture substrings based on specific patterns.

In this case, we can use the b word boundary pattern to only match complete words. The b pattern matches the boundary between a word and a non-word character or vice versa.

Here's the modified code using regular expressions:

$text = preg_replace('/\bHello\b/', 'NEW', $text);

This code will produce the correct result:

NEW hello1 hello, Helloz

Unicode Compatibility:

If your text contains UTF-8 characters, it's important to use the "u" Unicode modifier in your regular expression to ensure correct word boundary matching. This prevents non-latin characters from being misinterpreted as word boundaries.

$text = preg_replace('/\bHello\b/u', 'NEW', $text);

By using regular expressions and word boundary patterns, you can effectively replace whole word matches in a string, ensuring character boundaries are preserved.

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