Using PHP preg_replace() for String Replacement: Syntax, Examples, and Tips

In PHP, the preg_replace() function is a powerful and flexible tool that allows searching and replacing strings using regular expressions, enabling tasks such as removing specific characters or substituting patterned text.

Basic Syntax of preg_replace()

preg_replace(pattern, replacement, subject);

The pattern is the regular expression to match, replacement is the string to replace matches with, and subject is the target string on which the operation is performed.

Below are concrete examples demonstrating how to use preg_replace() for various replacement scenarios.

Replacing Specific Characters in a String

Given a string containing the character “#”, the following code replaces all “#" with “_”.

$str = "Hello#World#";
$newStr = preg_replace('/#/', '_', $str);
echo $newStr; // Output: Hello_World_

Replacing Multiple Optional Characters

This example replaces any occurrence of “a”, “b”, or “c” with “x”.

$str = "abcde";
$newStr = preg_replace('/[abc]/', 'x', $str);
echo $newStr; // Output: xxxde

Replacing Digits in a String

To replace all digits with “*”, the \d token is used.

$str = "abc123def456";
$newStr = preg_replace('/\d/', '*', $str);
echo $newStr; // Output: abc***def***

Case‑Insensitive Replacement

Adding the /i modifier makes the pattern case‑insensitive.

$str = "Hello World";
$newStr = preg_replace('/world/i', 'PHP', $str);
echo $newStr; // Output: Hello PHP

Replacing Email Addresses

This example masks email addresses using a regular expression that matches typical email patterns.

$str = "My email is [email protected]";
$newStr = preg_replace('/[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}/', '***', $str);
echo $newStr; // Output: My email is ***

These examples illustrate basic uses of preg_replace(); the function also offers many additional options and features for advanced string manipulation.