PHP preg_replace_callback function

preg_replace_callback

(PHP 4 >= 4.0.5, PHP 5)

preg_replace_callback -- Perform a regular expression search and replace using a callbackDescriptionmixed preg_replace_callback ( mixed pattern, callback callback, mixed subject [, int limit [, int &count]] )

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.

You'll often need the callback function
for a preg_replace_callback() in just one place.
In this case you can use 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()

/* 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);

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.

If matches are found, the new subject will be returned, otherwise
subject will be returned unchanged.

ChangeLog

VersionDescription5.1.0 The count parameter was added

Examples

Example 2. preg_replace_callback() example

// 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

$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>';
}