Last updated: Fri, 03 Sep 2010

preg_replace_callback

(PHP 4 >= 4.0.5, PHP 5)

preg_replace_callback — Perform a regular expression search and replace using a callback

Description

mixed preg_replace_callback ( mixed $pattern , callback $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.

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 (since PHP 5.3.0) or 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()


<?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. 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;
?>


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
09-Jun-2010 07:01


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
22-Mar-2010 01:48


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
21-Mar-2010 08:05


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);

?>

Matt
14-Sep-2009 04:24


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')

ixiter at gmail dot com
29-Jul-2009 02:06


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
02-Jul-2009 03:02


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
09-Jun-2009 02:44


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.

mariush
12-May-2009 08:17


If you're planning to use preg_replace_callback inside a class, you need to use the array() function:





<?php


class MyClass


{





  function preg_callback_url($matches)


  {


    //var_dump($matches);


    $url = $matches[1].$matches[2];


    $text = '';


    $pos = strpos($url,' ');


    if ($pos!==FALSE) {


      $text = trim(substr($url,$pos+1));


      $url = substr($url,0,$pos);


    }


    return '<a href="'.$url.'" rel="nofollow">'.(($text!='') ? $text : $url).'</a>';


  }





  function ParseText($text)


  {


    return preg_replace_callback('/\[(http|https|ftp)(.*?)\]/iS',array( &$this, 'preg_callback_url'), $text);


  }





}


?>

james dot records at gmail dot com
26-Apr-2009 07:22


This is what i use to read log files and do dns lookups on the ip's from the file.





<?php


function resolve_logs($arr) {


        return gethostbyaddr($arr[0]);


}





$logent=file('yourlogfile');





$ipaddr = '/\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}/';


$logent = preg_replace_callback($ipaddr, resolve_logs, $logent);


?>

long2hu3 ATT yahoo DOTT com
02-Apr-2009 07:25


When you access variables from outside in a callback function, use the $global keyword:



<?php



// global # 1:

global $x;



$x = 0;

$str = '&Bla bla. &#x25ba;';



$find = '/(\&)([^#])/';



// global # 2:

$replace = create_function('$f',

    'global $x; $x ++; return $f[2];';



$str2 = preg_replace_callback($find, $replace, $str);



// $x == 1

// $str2 == 'Bla bla. &#x25ba;'

// without global, $x would be 0



?>

tijn at q-go dot com
06-Jan-2009 10:01


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

tijn at q-go dot com
05-Jan-2009 04:48


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
20-Dec-2008 02:33


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

nene at triin dot net
20-May-2008 10:14


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.

Sjon at hortensius dot net
24-Jun-2007 11:56


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
26-Apr-2006 09:16


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);

add a note

preg_replace

preg_quote