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# preg_replace_callback

(PHP 4 >= 4.0.5, PHP 5)

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

## Description

mixed preg_replace_callback ( mixed pattern, callback callback, mixed subject [, int limit [, 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 that will be called and passed an array of matched elements in the subject string. The callback should return the replacement string. See preg_replace() for description of other parameters.

Example 1. preg_replace_callback() 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\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); } echo preg_replace_callback( "|(\d{2}/\d{2}/)(\d{4})|", "next_year", $text); // result is: // April fools day is 04/01/2003 // Last christmas was 12/24/2002 ?>`

You'll often need the callback function for a preg_replace_callback() in just one place. In this case you can use 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 functions name not used anywhere else.

Example 2. preg_replace_callback() and create_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|', create_function( // single quotes are essential here, // or alternative escape all $ as \$ '$matches', 'return strtolower($matches[0]);' ), $line ); echo $line; } fclose($fp); ?>`

Example 3. preg_replace_callback() 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; ?>`

> Note: count parameter is available since PHP 5.1.0.

See also preg_replace(), create_function(), and information about the callback type.

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