PHP 4 >= 4.0.5, PHP 5, PHP 7, PHP 8
preg_replace_callback - Perform a regular expression search and replace using a callback

     [int$limit = -1],
     [intcount = null],
     [int$flags = 0]
): string|array|null

The behavior of this function is almost identical to preg_replace, except for the fact that instead of replacement parameter, one should specify a callback.



The pattern to search for. It can be either a string or an array with strings.


A callback that will be called and passed an array of matched elements in the subject string. The callback should return the replacement string. This is the callback signature:

handler( array$matches ): string

You'll often need the callback function for a preg_replace_callback in just one place. In this case you can use an anonymous function to declare the callback within the call to preg_replace_callback. By doing it this way you have all information for the call in one place and do not clutter the function namespace with a callback function's name not used anywhere else.

preg_replace_callback and anonymous function
/* a unix-style command line filter to convert uppercase
 * letters at the beginning of paragraphs to lowercase */
$fp fopen("php://stdin""r") or die("can't read stdin");
while (!
feof($fp)) {
$line fgets($fp);
$line preg_replace_callback(
        function (
$matches) {


The string or an array with strings to search and replace.


The maximum possible replacements for each pattern in each subject string. Defaults to -1 (no limit).


If specified, this variable will be filled with the number of replacements done.


flags can be a combination of the PREG_OFFSET_CAPTURE and PREG_UNMATCHED_AS_NULL flags, which influence the format of the matches array. See the description in preg_match for more details.

Return Values

preg_replace_callback returns an array if the subject parameter is an array, or a string otherwise. On errors the return value is null

If matches are found, the new subject will be returned, otherwise subject will be returned unchanged.

Exceptions and Errors

If the regex pattern passed does not compile to a valid regex, an E_WARNING is emitted.


Version Description
7.4.0 The flags parameter was added.

Related Functions

Example of preg_replace_callback

Show all examples for preg_replace_callback

PHP Version:

Function preg_replace_callback:

Regular Expressions (Perl-Compatible) Functions

Most used PHP functions