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preg_replace_callback

Perform a regular expression search and replace using a callback (PHP 4 >= 4.0.5, PHP 5)
mixed 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 1723. 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);
?>


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

VersionDescription
5.1.0 The count parameter was added

Examples

Example 1724. 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 1725. 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
preg_replace()
create_function()
information about the callback type