Visit Our UNIX and Linux User Community

Linux and UNIX Man Pages

Test Your Knowledge in Computers #810
Difficulty: Medium
The CSS3 RGB Decimal Code for Turquoise is 64,224,218.
True or False?
Linux & Unix Commands - Search Man Pages

preg_replace_callback(3) [php man page]


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

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)

Featured Tech Videos