(PHP 4 >= 4.0.5, PHP 5)
preg_replace_callback — Perform a regular expression search and replace using a callback
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.
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 (since PHP 5.3.0) or 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 function's name not used anywhere else.
Example #1 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);
?>
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.
| Version | Description |
|---|---|
| 5.1.0 | The count parameter was added |
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";
$text.= "Last christmas was 12/24/2001\n";
// the callback function
function next_year($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() 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;
?>