preg_replace_callback

Perform a regular expression search and replace using a callback.

preg_replace_callback Function synopsis

preg_replace_callback(
    array|string $pattern,
    callable $callback,
    array|string $subject,
    int $limit = -1,
    &$count = null,
    int $flags = 0
  ): array|string|null

Parameters

$pattern

Typearray|string

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

$callback

Typecallable

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:

$subject

Typearray|string

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

$limit

OptionalTypeintDefault value-1

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

$count

Passed by reference, OptionalDefault valuenull

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

$flags

OptionalTypeintDefault value0

$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.

Note that the parameter $count is passed by reference, and contains additional/updated context data that may be useful.

Return value

Typearray|string|null

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.