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PHP Manual


(PHP 4 >= 4.0.5, PHP 5)

preg_replace_callbackPerform a regular expression search and replace using a callback


mixed preg_replace_callback ( mixed $pattern , callable $callback , mixed $subject [, int $limit = -1 [, int &$count ]] )

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.

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 (since PHP 5.3.0) or create_function() to declare an anonymous function as 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.

Example #1 preg_replace_callback() and create_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(
// single quotes are essential here,
            // or alternative escape all $ as \$
'return strtolower($matches[0]);'


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.

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.


Version Description
5.1.0 The count parameter was added


Example #2 preg_replace_callback() example

// this text was used in 2002
// we want to get this up to date for 2003
$text "April fools day is 04/01/2002\n";
$text.= "Last christmas was 12/24/2001\n";
// the callback function
function next_year($matches)
// as usual: $matches[0] is the complete match
  // $matches[1] the match for the first subpattern
  // enclosed in '(...)' and so on
return $matches[1].($matches[2]+1);


The above example will output:

April fools day is 04/01/2003
Last christmas was 12/24/2002

Example #3 preg_replace_callback() using recursive structure to handle encapsulated BB code

"plain [indent] deep [indent] deeper [/indent] deep [/indent] plain";


$regex '#\[indent]((?:[^[]|\[(?!/?indent])|(?R))+)\[/indent]#';

    if (
is_array($input)) {
$input '<div style="margin-left: 10px">'.$input[1].'</div>';


$output parseTagsRecursive($input);


See Also

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