PHP mb_ereg_replace_callback() Function

The mb_ereg_replace_callback() function is an inbuilt function in PHP that is used to replace a regular expression match in a string using the callback function.

Syntax:

mb_ereg_replace_callback( $pattern, $callback,$string,$options): string|false|null

Parameters: The function accepts four parameters that are described below.

• $pattern: A pattern is a regular expression pattern that is used for replacing a string. It must be a valid regular expression pattern.
• $callback:  A callback function is to be called for each match. The function should accept one parameter (an array containing the match information) and return the replacement string.
• $string: The input string to search in.
• $options: This is an optional parameter. Possible values for this parameter are: ‘m’ for multiline, ‘s’ for single line, and ‘r’ using Unicode rules when matching.

Return values: This function is the input string with all matches of the pattern replaced by the result of the callback function, as a string when it is true, & when it is false then it will give an error. The null will be returned when the string is invalid for the current encoding.

Example 1: The following program demonstrates the mb_ereg_replace_callback() function.

PHP

<?php

$string = "I love cats and dogs";
$pattern = "[a-z]";

$callback = function ($match) {
    return mb_strtoupper($match[0]);
};

$replaced_string = mb_ereg_replace_callback($pattern, $callback, $string);
echo "The string '$string' with matches replaced is '$replaced_string'.";

?>

Output

The string 'I love cats and dogs' with matches replaced is 'I LOVE CATS AND DOGS'.

Example 2: The following program demonstrates the mb_ereg_replace_callback() function.

PHP

<?php

$string = "Hello world";
$pattern = "[w]";
$replaced_string = mb_ereg_replace_callback(
    $pattern,
    function ($matches) {
        $first_letter = $matches[0];
        if (mb_strtolower($first_letter) == "w") {
            return mb_strtoupper($first_letter);
        } else {
            return $first_letter;
        }
    },
    $string
);
echo "The string '$string' with matches replaced is '
    $replaced_string'.";
?>

Output:

The string 'Hello world' with matches replaced is 'Hello World'. 

Reference: https://www.php.net/manual/en/function.mb-ereg-replace-callback.php