php man page for preg_replace_callback

PREG_REPLACE_CALLBACK(3)						 1						  PREG_REPLACE_CALLBACK(3)

preg_replace_callback - Perform a regular expression search and replace using a callback

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

DESCRIPTION
	The  behavior  of  this  function  is almost identical to preg_replace(3), except for the fact that instead of $replacement parameter, one
       should specify a $callback.

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

	      o $callback
		- 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:
		string	handler  (array   $matches)  You'll often need the $callback function for a preg_replace_callback(3) in just one place. In
		this case you can use an anonymous function to declare the callback within the call to preg_replace_callback(3). 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(3) and anonymous function

		     <?php
		     /* 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);
			 $line = preg_replace_callback(
			     '|<p>s*w|',
			     function ($matches) {
				 return strtolower($matches[0]);
			     },
			     $line
			 );
			 echo $line;
		     }
		     fclose($fp);
		     ?>

	      o $subject
		- The string or an array with strings to search and replace.

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

	      o $count
		- If specified, this variable will be filled with the number of replacements done.

RETURN VALUES
       preg_replace_callback(3) 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.

CHANGELOG
       +--------+---------------------------------+
       |Version |				  |
       |	|				  |
       |	|	    Description 	  |
       |	|				  |
       +--------+---------------------------------+
       | 5.1.0	|				  |
       |	|				  |
       |	|  The $count parameter was added |
       |	|				  |
       +--------+---------------------------------+
EXAMPLES
       Example #2

	      preg_replace_callback(3) example

	      <?php
	      // this text was used in 2002
	      // we want to get this up to date for 2003
	      $text = "April fools day is 04/01/2002
";
	      $text.= "Last christmas was 12/24/2001
";
	      // the callback function
	      function next_year($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);
	      }
	      echo preg_replace_callback(
			  "|(d{2}/d{2}/)(d{4})|",
			  "next_year",
			  $text);

	      ?>

	      The above example will output:

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

       Example #3

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

	      <?php
	      $input = "plain [indent] deep [indent] deeper [/indent] deep [/indent] plain";

	      function parseTagsRecursive($input)
	      {

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

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

		  return preg_replace_callback($regex, 'parseTagsRecursive', $input);
	      }

	      $output = parseTagsRecursive($input);

	      echo $output;
	      ?>

SEE ALSO
       PCRE Patterns, preg_quote(3), preg_replace(3), preg_last_error(3), Anonymous functions, information about the callback type.

PHP Documentation Group 												  PREG_REPLACE_CALLBACK(3)