(PHP 4 >= 4.0.5, PHP 5, PHP 7, PHP 8)
preg_replace_callback — Perform a regular expression search and replace using a callback
$pattern,$callback,$subject,$limit = -1,&$count = null,$flags = 0
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.
patternThe 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:
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);
?>subjectThe 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).
countIf specified, this variable will be filled with the number of replacements done.
flags
flags can be a combination of the
PREG_OFFSET_CAPTURE and
PREG_UNMATCHED_AS_NULL flags, which influence the
format of the matches array.
See the description in preg_match() for more details.
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.
If the regex pattern passed does not compile to a valid regex, an E_WARNING is emitted.
| Version | Description |
|---|---|
| 7.4.0 |
The flags 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;
?>