Php/docs/function.preg-replace-callback
preg_replace_callback
(PHP 4 >= 4.0.5, PHP 5, PHP 7)
preg_replace_callback — Perform a regular expression search and replace using a callback
Description
preg_replace_callback
( string|array $pattern
, callable $callback
, string|array $subject
[, int $limit
= -1
[, int &$count
= NULL
[, int $flags
= 0
]]] ) : string|array|null
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
.
Parameters
pattern
The pattern to search for. It can be either a string or an array with strings.
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:handler ( array
$matches
) : stringYou'll often need the
callback
function for a preg_replace_callback() in just one place. In this case you can use an anonymous function to declare the callback within the call to preg_replace_callback(). By doing it this way you have all information for the call in one place and do not clutter the function namespace with a callback function's name not used anywhere else.Example #1 preg_replace_callback() and anonymous function
<?php/* a unix-style command line filter to convert uppercase * letters at the beginning of paragraphs to lowercase */$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);?>
subject
The string or an array with strings to search and replace.
limit
The maximum possible replacements for each pattern in each
subject
string. Defaults to-1
(no limit).count
If specified, this variable will be filled with the number of replacements done.
flags
flags
can be a combination of thePREG_OFFSET_CAPTURE
andPREG_UNMATCHED_AS_NULL
flags, which influence the format of the matches array. See the description in preg_match() for more details.
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.
Changelog
Version | Description |
---|---|
7.4.0 | The flags parameter was added.
|
Examples
Example #2 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 functionfunction 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", $text);?>
The above example will output:
April fools day is 04/01/2003 Last christmas was 12/24/2002
Example #3 preg_replace_callback() using recursive structure to handle encapsulated BB code
<?php$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_replace_callback_array() - Perform a regular expression search and replace using callbacks
- preg_quote() - Quote regular expression characters
- preg_replace() - Perform a regular expression search and replace
- preg_last_error() - Returns the error code of the last PCRE regex execution
- Anonymous functions