preg_replace_callback
Perform a regular expression search and replace using a callback
Description
mixed preg_replace_callback
( mixed $pattern
, callable $callback
, mixed $subject
[, int $limit = -1
[, int &$count
]] )
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:
string handler
( array $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);
?>
-
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.
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.
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";
$text.= "Last christmas was 12/24/2001\n";
// the callback function
function next_year($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;
?>