preg_replace_callback

(PHP 4 >= 4.0.5, PHP 5, PHP 7)

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 ]] )

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. 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.

Changelog

Version	Description
5.1.0	The `count` parameter was added

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;
?>

User Contributed Notes

Richard

3 years ago


The easiest way to pass more than one parameters to the callback function is with the 'use' keyword. 



[This is better than using global, because it works even when we are already inside a function.]



In this example, the callback function is an anonymous function, which takes one argument, $match, supplied by preg_replace_callback().  The extra 

"use ($ten)" puts the $ten variable into scope for the function.



<?php

$string = "Some numbers: one: 1; two: 2; three: 3 end";

$ten = 10;

$newstring = preg_replace_callback(

    '/(\\d+)/',

    function($match) use ($ten) { return (($match[0] + $ten)); },

    $string

    );

echo $newstring;

#prints "Some numbers: one: 11; two: 12; three: 13 end";

?>

Fredow

1 year ago


<?php

// Nice little function that convert a string to uppercase by keeping the HTMLentities intact.

public static function strtoupper_entities($str) {



    $patternMajEntities = '/(\&([A-Z])(ACUTE|CEDIL|CARON|CIRC|GRAVE|ORN|RING|SLASH|TH|TILDE|UML)\;)+/';

    $str = preg_replace_callback ($patternMajEntities, 

        function ($matches) {

            return "&" . $matches[2] . strtolower($matches[3]) . ";";

        }, strtoupper($str));

    

    return $str;

}

Yuri

3 years ago


If you want to call non-static function inside your class, you can do something like this. 

For PHP 5.2 use second argument like array($this, 'replace'):
<?php
class test_preg_callback{

  private function process($text){
    $reg = "/\{([0-9a-zA-Z\- ]+)\:([0-9a-zA-Z\- ]+):?\}/";
    return preg_replace_callback($reg, array($this, 'replace'), $text);
  }
  
  private function replace($matches){
    if (method_exists($this, $matches[1])){
      return @$this->$matches[1]($matches[2]);     
    }
  }  
}
?>

For PHP 5.3 use second argument like "self::replace":
<?php
class test_preg_callback{

  private function process($text){
    $reg = "/\{([0-9a-zA-Z\- ]+)\:([0-9a-zA-Z\- ]+):?\}/";
    return preg_replace_callback($reg, "self::replace", $text);
  }
  
  private function replace($matches){
    if (method_exists($this, $matches[1])){
      return @$this->$matches[1]($matches[2]);     
    }
  }  
}
?>

development at HashNotAdam dot com

3 years ago


From PHP 5.3 you can use an anonymous function to pass local variables into the callback.



<?php



public function replace_variables( $subject, $otherVars ) {

    $linkPatterns = array(

        '/(<a .*)href=(")([^"]*)"([^>]*)>/U',

        "/(<a .*)href=(')([^']*)'([^>]*)>/U"

    );



    $callback = function( $matches ) use ( $otherVars ) {

        $this->replace_callback($matches, $otherVars);

    };



    return preg_replace_callback($this->patterns, $callback, $subject);

}



public function replace_callback($matches, $otherVars) {

    return $matches[1] . $otherVars['myVar'];

}

?>

nene at triin dot net

7 years ago


The first example is bad, because it creates function for every line it processes. When the file has many lines, you could easily run out of memory. The code should be changed so, that create_function() is used outside of loop.

Florian Arndt

4 years ago


This small class allows PHP users to read JSON files with include statements in them. For instance the include {{{ "relative/to/including.json" }}} is replaced by the content of the json file located at "relative/to/including.json".

<?php
    /**
     * Handles JSON files with includes
     * Purpose: handle bigger JSON files by featuring "includes"
     * 
     * @author Florian Arndt
     */
    class JWI {
        /**
         * Parses a JSON file and returns its contents
         * @param String $filename
         */
        static function read($filename) {
            if(!file_exists($filename))
                throw new Exception('<b>JWI Error: JSON file <tt>'.$filename.'</tt> not found!</b>');
            $content = join('', file($filename));
            $dir = dirname($filename);
            /**
             * replace
             *   include statements
             * with
             *   content of the file to include
             * recursively
             */
            $content = preg_replace_callback(
                '/{{{\s*"\s*(.+)\s*"\s*}}}/', // >include file< - pattern
                create_function(
                    '$matches', // callback parameter
                    sprintf(
                        '$fn = "%s/".$matches[1];'.
                        'return JWI::read($fn);',
                        realpath(dirname($filename))
                    )
                ),
                $content
            );
            return $content;
        }
    }

matt at languesvivantes dot com

3 years ago


Actually, this only works from php 5.4, see the changelog on http://php.net/manual/en/functions.anonymous.php

henzeberkheij at gmail dot com

4 years ago


also note that when you are using this functionality in a class and you need variables in that class, you can use a non static function as callback. array($this, functionName) should be enough to call an function of the class. 

Either use create_function if you require the code only once, 
use a static class function if no need for accessing variables in that class. or use the array metioned earlier in my post for having access to class variables or other functions!

Anteaus

1 year ago


Be aware that as of php5.4 you MUST NOT pass variables by reference, as in  '[, int &$count ]' - if you do it will result in a fatal error. 
I think the writer is trying to say that the function accepts the parameter by reference, but that is not how it reads. -Manual needs updating/clarifying ?

aleksander at throw dot pl

5 years ago


I needed a simple code to tidy up a string. It simply had to upper-case letters after dot. Simple code to do so:



<?php

$string = preg_replace_callback(

'|(?:\.)(?:\s*)(\w{1})|Ui', 

create_function('$matches', 'return ". ".strtoupper($matches[1]);'), ucfirst($string)

);

?>



<?php

$string = 'lorem ipsum dolor sit amet, consectetur adipiscing elit. sed ullamcorper diam eu lorem varius nec porta elit iaculis.';



echo preg_replace_callback(

'|(?:\.)(?:\s*)(\w{1})|Ui', 

create_function('$matches', 'return ". ".strtoupper($matches[1]);'), ucfirst($string)

);

?>



Will output: Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed ullamcorper diam eu lorem varius nec porta elit iaculis.



<?php

$string = 'lorem ipsum dolor sit amet, consectetur adipiscing elit.                 sed ullamcorper diam eu lorem varius nec porta elit iaculis.';



echo preg_replace_callback(

'|(?:\.)(?:\s*)(\w{1})|Ui', 

create_function('$matches', 'return ". ".strtoupper($matches[1]);'), ucfirst($string)

);

?>



Will output: Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed ullamcorper diam eu lorem varius nec porta elit iaculis.



Nothing fancy, but useful :)

chris at ocproducts dot com

5 years ago


The pcre.backtrack_limit option (added in PHP 5.2) can trigger a NULL return, with no errors. The default pcre.backtrack_limit value is 100000. If you have a match that exceeds about half this limit it triggers a NULL response.
e.g. My limit was at 100000 but 500500 triggered a NULL response. I'm not running unicode but I *guess* PCRE runs in utf-16.

Anonymous

5 years ago


Created this to fetch the link and name of an anchor tag. I use this when cleaning an HTML email to text. Using regex for HTML is not recommended but for this purpose I see no issue with it. This is not designed to work for nested anchors.

A note to keep in mind:
I was primarily concerned with valid HTML so if attributes do no use ' or " to contain the values then this will need to be tweaked.
If you can edit this to work better, please let me know.
<?php
/**
 * Replaces anchor tags with text
 * - Will search string and replace all anchor tags with text (case insensitive)
 * 
 * How it works:
 * - Searches string for an anchor tag, checks to make sure it matches the criteria
 *         Anchor search criteria:
 *             - 1 - <a (must have the start of the anchor tag )
 *             - 2 - Can have any number of spaces or other attributes before and after the href attribute
 *             - 3 - Must close the anchor tag
 * 
 * - Once the check has passed it will then replace the anchor tag with the string replacement
 * - The string replacement can be customized
 * 
 * Know issue:
 * - This will not work for anchors that do not use a ' or " to contain the attributes. 
 *         (i.e.- <a href=http: //php.net>PHP.net</a> will not be replaced)
 */
function replaceAnchorsWithText($data) {
    /**
     * Had to modify $regex so it could post to the site... so I broke it into 6 parts.
     */
    $regex  = '/(<a\s*'; // Start of anchor tag
    $regex .= '(.*?)\s*'; // Any attributes or spaces that may or may not exist
    $regex .= 'href=[\'"]+?\s*(?P<link>\S+)\s*[\'"]+?'; // Grab the link
    $regex .= '\s*(.*?)\s*>\s*'; // Any attributes or spaces that may or may not exist before closing tag 
    $regex .= '(?P<name>\S+)'; // Grab the name
    $regex .= '\s*<\/a>)/i'; // Any number of spaces between the closing anchor tag (case insensitive)
    
    if (is_array($data)) {
        // This is what will replace the link (modify to you liking)
        $data = "{$data['name']}({$data['link']})";
    }
    return preg_replace_callback($regex, 'replaceAnchorsWithText', $data);
}

$input  = 'Test 1: <a href="http: //php.net1">PHP.NET1</a>.<br />';
$input .= 'Test 2: <A name="test" HREF=\'HTTP: //PHP.NET2\' target="_blank">PHP.NET2</A>.<BR />';
$input .= 'Test 3: <a hRef=http: //php.net3>php.net3</a><br />';
$input .= 'This last line had nothing to do with any of this';

echo replaceAnchorsWithText($input).'<hr/>';
?>
Will output:
Test 1: PHP.NET1(http: //php.net1).
Test 2: PHP.NET2(HTTP: //PHP.NET2).
Test 3: php.net3 (is still an anchor)
This last line had nothing to do with any of this

Drake

6 years ago


The good version of the class PhpHex2Str
<?php
class PhpHex2Str
{
    private $strings;

    private static function x_hex2str($hex) {
        $hex = substr($hex[0], 1);
        $str = '';
        for($i=0;$i < strlen($hex);$i+=2) {
            $str.=chr(hexdec(substr($hex,$i,2)));
        }
        return $str;
    }

    public function decode($strings = null) {
        $this->strings = (string) $strings;
        return preg_replace_callback('#\%[a-zA-Z0-9]{2}#', 'PhpHex2Str::x_hex2str', $this->strings);
    }
}

// Exemple
$obj = new PhpHex2Str;

$strings = $obj->decode($strings);
var_dump($strings);
?>

Drake

6 years ago


Decode Hexa to Strings =)
<?php
class PhpHex2Str
{
    private $strings;

    private function x_hex2str($hex) {
        $hex = substr($hex[0], 1);
        $str = '';
        for($i=0;$i < strlen($hex);$i+=2) {
            $str.=chr(hexdec(substr($hex,$i,2)));
        }
        return $str;
    }

    public function decode($strings = null) {
        $this->strings = (string) $strings;
        return preg_replace_callback('#\%[a-zA-Z0-9]{2}#', 'x_hex2str', $this->strings);
    }
}

// Example
$strings = 'a %20 b%0A h %27 h %23';

$obj = new PhpHex2Str;
$strings = $obj->decode($strings);
var_dump($strings);
?>

ixiter at gmail dot com

6 years ago


When you use preg_replace_callback in a class and have the callback function as a private method of that class, you need to set the callback function name like className::CallBack.

self::CallBack does not work and returns an error:

"Cannot call method self::CallBack() or method does not exist"!



<?php

class myClass{

    public function parsetext($text){

        // parses text and sets literals A - C to lower case

        // this works 

        return preg_replace_callback('|([a-c])|i', 'myClass::preg_tolower', $text);

    }

    public function parsefail($text){

        // parses text and sets literals A - C to lower case

        // this fails

        return preg_replace_callback('|([a-c])|i', 'self::preg_tolower', $text);

    }

    

    private static function preg_tolower($matches){

        return strtolower($matches[1]);

    }

}



$parser = new myClass;

echo $parser->parsetext('ABCDEFGH');

// echoes abcDEFGH



echo $parser->parsefail('ABCDEFGH');

// throws the error

?>

carlos dot ballesteros at softonic dot com

6 years ago


A simple function to replace a list of complete words or terms in a string (for PHP 5.3 or above because of the closure):

<?php
function replace_words($list, $line, $callback) {
    return preg_replace_callback(
        '/(^|[^\\w\\-])(' . implode('|', array_map('preg_quote', $list)) . ')($|[^\\w\\-])/mi',
        function($v) use ($callback) { return $v[1] . $callback($v[2]) . $v[3]; },
        $line
    );
}
?>

Example of usage:
<?php
$list = array('php', 'apache web server');
$str = "php and the apache web server work fine together. php-gtk, for example, won't match. apache web servers shouldn't too.";

echo replace_words($list, $str, function($v) {
    return "<strong>{$v}</strong>";
});
?>

chris AT cmbuckley DOT co DOT uk

6 years ago


This function does not support named subpatterns, so you can't do

<?php

preg_replace_callback('/(?<char>[a-z])/', 'callback', 'word');

function callback($matches) {
    var_dump($matches);
}

?>

and expect to get $matches['char'] in your function.

tijn at q-go dot com

7 years ago


To access a local variable within a callback, use currying (delayed argument binding). For example
<?php
function curry($func, $arity) {
    return create_function('', "
        \$args = func_get_args();
        if(count(\$args) >= $arity)
            return call_user_func_array('$func', \$args);
        \$args = var_export(\$args, 1);
        return create_function('','
            \$a = func_get_args();
            \$z = ' . \$args . ';
            \$a = array_merge(\$z,\$a);
            return call_user_func_array(\'$func\', \$a);
        ');
    ");
}

function on_match($transformation, $matches)
{
    return $transformation[strtolower($matches[1])];
}

$transform = array('a' => 'Well,', 'd'=>'whatever', 'b'=>' ');

$callback = curry(on_match, 2);
echo preg_replace_callback('/([a-z])/i', $callback($transform), 'Abcd');

echo "\n";
?>

outputs:

"Well, whatever"

The magic lies in this curry function I found here: http://www.sitepoint.com/forums/showthread.php?threadid=336758

nicolaspar at gmail dot com

7 years ago


To spend more than one parameter can do the following (note the "e" parameter in preg_replace function)
<?
$array = array(
1=>'ONE',
2=>'TWO',
3=>'Three'
);

function search(&$array, $str, $foo, $bar){
    return ( empty($array[$str]) ? '['.$foo.'-'.$bar.']' : $array[$str] );
}

function keys(&$array, $str,$foo,$bar){
    return preg_replace('/\[(.*?)\]/e',"search(\$array,$1,\$foo,\$bar)",$str);
}

$str = "One [1] Two [2] Three [3], Other parameter [22]";

echo keys($array, $str,'Foo','Bar');
?>
Nice

Underdog

2 years ago


For the callback I advise only to use a permanent or anonymous function. 

Depending on the usage you may encounter memory issues when using create_function for the callback possibly due to attempts at being compatible with PHP 5.2 or prior. Some servers  refuse to update their PHP  for whatever reason.

Please peruse the create_function documentation for more details regarding its memory usage.

Regards.

Sjon at hortensius dot net

8 years ago


preg_replace_callback returns NULL when pcre.backtrack_limit is reached; this sometimes occurs faster then you might expect. No error is raised either; so don't forget to check for NULL yourself

matt at mattsoft dot net

10 years ago


it is much better on preformance and better practice to use the preg_replace_callback function instead of preg_replace with the e modifier.

function a($text){return($text);}

// 2.76 seconds to run 50000 times
preg_replace("/\{(.*?)\}/e","a('\\1','\\2','\\3',\$b)",$a);

// 0.97 seconds to run 50000 times
preg_replace_callback("/\{(.*?)\}/s","a",$a);

webmaster at mp3s dot pl

4 years ago


I noticed that 'e' modifier use addslashed on result

<?
function wyczysc_strongi($string) {
    if(mb_strlen($string,'UTF-8')>60) {
        return $string;
    } else {
        return '<strong>'.$string.'</strong>';
    }
}

$tresc = "<strong>fajna dupa's</strong>";

$tresc = preg_replace("/<strong>(.*?)<\/strong>/ie",'wyczysc_strongi("$1")',$tresc);

echo $tresc will give: <strong>fajna dupa\'s</strong>
?>

solution: $tresc = stripslashes($tresc);
after callback

Matt

6 years ago


If you're looking to show only the first digit and last four digits of a credit card number (4xxxxxxxxxxxx2331) use something like this:
preg_replace_callback('/((.)(.*))?(.{4})/', create_function('$x', 'return $x[2].str_repeat("x", strlen($x[3])).$x[4];'), '$CCNUMBER')

kkatpki

2 years ago


Note that, as of PHP 5.3, it seems that named subpatterns are now included in the matches array by their named key as well as their numerical key.

To build off of Chris' previous example, as of PHP 5.3, you *can* do

<?php

preg_replace_callback('/(?<char>[a-z])/', 'callback', 'word');

function callback($matches) {
    var_dump($matches);
}

?>

and expect to get $matches['char'] in your function. * BUT ONLY AS OF PHP 5.3 *

Please be mindful of this if you intend to support PHP 5.2.

T-Soloveychik at ya dot ru

2 years ago


Text lines numeration:
<?PHP
// Multieline text:
    $Text = "
Some 
Multieline
text
for
numeration";

// For count:
    $GLOBALS["LineNUMBER"] = 1;

// Replace linestart on number:
    PRINT preg_replace_callback("/^/m",function ()
        {
            return $GLOBALS["LineNUMBER"]++."  ";
        },
        $Text);

?>

1
2 Some
3 Multieline
4 text
5 for
6 numeration

alex dot cs00 at yahoo dot ca

5 years ago


Don't use this function to fetch BBCode, as explained. If you have some text that runs over 5000 chars (average), it will run out of its limit and makes you download the PHP page. 



According to this, you should instead use something more advanced yet complex. You will need a function called "str_replace_once()" (search for it), one called "countWord()", the famous "after()", "before()", "between()". 



str_replace_once does same as str_replace, but only replace first occurence. As for countWord, I guess you know how to count the number of a word occurence. As for after, before and between, this is a function that you may find easily somewhere on the site by a user. Else, you can do it. 



The following function is able to do all blocks, supposing [code] and [/code], you might wish things between parents dont get parsed, including [code] if inside of another [code]. 



<?php

function prepareCode($code, $op, $end)

{

    $ix = 0;

    $iy = 0;

    $nbr_Op = countWord($op, $code);

    while($ix < $nbr_Op)

    {

        if(in_string($op, before($end, $code), false))

        {

            // The following piece of code replace the default [tag] by [tag:#]

            $code = str_replace_once($op, substr($op, 0, -1).':'.$ix.']', $code); 

            $iy++;

        }

        elseif(in_string($end, before($op, $code), false))

        {

            $iy = $iy-1;

            $code = str_replace_once($end, substr($end, 0, -1).':'.($ix-1).']', $code);

            $ix = $ix-2;

        }

        $ix++;

    }

    while(in_string($end, $code))

    {

        $code = str_replace_once($end, substr($end, 0, -1).':'.($iy-1).']', $code);

        $iy=$iy-1;

    }



    $code = preg_replace('#\\'.substr($end, 0, 1).':-[0-9]\]#i', '', $code);

    if(in_string(substr($op, 0, -1).':0]', $code) && !in_string(substr($end, 0, -1).':0]', $code))

    {

        $code .= substr($end, 0, -1).":0]";

    }

    return $code;

}

?>



$code returns the whole text semi-formated. You only need to use it as :

$code = prepareCode($code="Your text", $op="[tag]" , $end="[/tag]");

Then just replace the parent tags :

str_replace("[tag:0]", "<tag>", $code);

str_replace("[/tag:0]", "</tag>", $code);

So at the end something like :

[

preg_replace_callback

Description

Parameters

Return Values

Changelog

Examples

See Also

User Contributed Notes