PHP – mb_ereg_replac_callback() function

In PHP, mb_ereg_replace_callback() function is used to perform a regular expression search and replace with multibyte support using a callback. It scans strings, matches them with a pattern, then replaces the matched text with the output of the callback function. This function is similar to mb_ereg_replace() but allows custom replacement logic through callbacks. It is supported in PHP 5.4 or higher versions.

Syntax

string mb_ereg_replace_callback(str $pattern, callback $callback, str $string, str $options)

Parameters

The function accepts the following four parameters −

• $pattern − The regular expression pattern. May use multibyte characters.

• $callback − A callback function that receives an array of matched elements and returns the replacement string.

• $string − The input string to search and replace.

• $options − Optional search options (default is null).

Return Value

Returns the modified string on success, FALSE on error, or NULL if the string is invalid for the current encoding.

Example 1: Using Named Function

This example demonstrates incrementing years in date strings using a named callback function −

<?php
   $result = "April Fools day is 04/01/2019<br>";
   $result.= "Next match is 12/24/2021<br>";

   // callback function
   function next_year($matches)
   {
      return $matches[1].($matches[2]+1);
   }
   
   echo mb_ereg_replace_callback(
      "(\d{2}/\d{2}/)(\d{4})",
      "next_year",
      $result
   );
?>

April Fools day is 04/01/2020
Next match is 12/24/2022

Example 2: Using Anonymous Function

This example shows the same functionality using an anonymous function −

<?php
   // anonymous function is used
   $result = "April Fools day is 04/01/2019<br>";
   $result.= "Next match is 12/24/2021<br>";

   echo mb_ereg_replace_callback(
      "(\d{2}/\d{2}/)(\d{4})",
      function ($matches) {
         return $matches[1].($matches[2]+1);
      },
      $result
   );
?>

April Fools day is 04/01/2020
Next match is 12/24/2022

Key Points

• Anonymous functions are often preferred for simple callbacks to keep code concise

• The callback receives an array where $matches[0] is the full match and $matches[1], $matches[2], etc. are captured groups

• Supports multibyte character encoding unlike standard regex functions

Conclusion

The mb_ereg_replace_callback() function provides powerful pattern replacement with custom logic through callbacks. Use anonymous functions for simple operations and named functions for complex or reusable logic.