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. This is the callback signature:
$matches
) 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 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); ?>
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.
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.
The count
parameter was added
<?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); ?>
<?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); ?>
The above example will output:
April fools day is 04/01/2003 Last christmas was 12/24/2002
<?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; ?>
preg_replace_callback_array() -
callback -
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