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    preg_replace_callback

    (PHP 4 >= 4.0.5, PHP 5, PHP 7, PHP 8)

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

    Description

    preg_replace_callback(
        string|array $pattern,
        callable $callback,
        string|array $subject,
        int $limit = -1,
        int &$count = null,
        int $flags = 0
    ): string|array|null

    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:

    handler(array $matches): 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 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.

    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.

    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.

    Errors/Exceptions

    If the regex pattern passed does not compile to a valid regex, an E_WARNING is emitted.

    Changelog

    Version Description
    7.4.0 The flags 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;
    ?>

    See Also

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    User Contributed Notes 22 notes

    up
    104
    Richard
    12 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";
    ?>
    up
    7
    Sjon at hortensius dot net
    17 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
    up
    24
    Yuri
    12 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]);
    }
    }
    }
    ?>
    up
    3
    carlos dot ballesteros at softonic dot com
    15 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>";
    });
    ?>
    up
    2
    Drake
    14 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);
    ?>
    up
    2
    matt at mattsoft dot net
    18 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",$a);
    up
    5
    Fredow
    9 years ago
    <?php
    // Nice little function that convert a string to uppercase by keeping the HTMLentities intact.
    public static function strtoupper_entities($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;
    }
    up
    2
    T-Soloveychik at ya dot ru
    11 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
    up
    4
    development at HashNotAdam dot com
    12 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'];
    }
    ?>
    up
    1
    kkatpki
    11 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.
    up
    1
    Florian Arndt
    12 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;
    }
    }
    up
    1
    chris at ocproducts dot com
    14 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.
    up
    1
    Anonymous
    14 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
    up
    1
    Evgeny
    1 year ago
    Please note! if you have defined namespace,
    the usage format must me changed:

    echo preg_replace_callback(
    "|(\d{2}/\d{2}/)(\d{4})|",
    __NAMESPACE__ . '\\next_year',
    $text);
    up
    0
    steven at nevvix dot com
    6 years ago
    <?php
    $format     = <<<SQL
    CREATE DATABASE IF NOT EXISTS :database;
    GRANT ALL PRIVILEGES ON :database_name.* TO ':user'@':host';
    SET PASSWORD = PASSWORD(':pass');
    SQL;
    $args = ["database"=>"people", "user"=>"staff", "pass"=>"pass123", "host"=>"localhost"];

    preg_replace_callback("/:(\w+)/", function ($matches) use ($args) {
    return @    $args[$matches[1]] ?: $matches[0];
    },     $format);

    /*
    Result:

    CREATE DATABASE IF NOT EXISTS people;
    GRANT ALL PRIVILEGES ON :database_name.* TO 'staff'@'localhost';
    SET PASSWORD = PASSWORD('pass123');

    The `:database_name` placeholder doesn't exist as a matching key in `$args` so it's returned as is.
    This way you know you need to correct the array by adding the "database_name" item.
    */
    up
    -2
    2962051004 at qq dot com
    6 years ago
    <?php

    /**
    * 将中文转为Html实体
    * Turning Chinese into Html entity
    * Author QiangGe
    * Mail 2962051004@qq.com
    *
    */

    $str = <<<EOT
    你好 world
    EOT;

    function     ChineseToEntity($str) {
    return     preg_replace_callback(
    '/[\x{4e00}-\x{9fa5}]/u', // utf-8
    // '/[\x7f-\xff]+/', // if gb2312
    function ($matches) {
    $json = json_encode(array($matches[0]));
    preg_match('/\[\"(.*)\"\]/', $json, $arr);
    /*
    * 通过json_encode函数将中文转为unicode
    * 然后用正则取出unicode
    * Turn the Chinese into Unicode through the json_encode function, then extract Unicode from regular.
    * I think this idea is seamless.
    */
    return '&#x'. str_replace('\\u', '', $arr[1]). ';';
    },     $str
    );
    }

    echo     ChineseToEntity($str);
    // &#x4f60;&#x597d; world
    up
    -1
    Drake
    14 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($strings);
    ?>
    up
    -2
    Anteaus
    9 years ago
    Be aware that as of php5.4 you MUST NOT pass variables by reference, as in '[, int &$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 ?
    up
    -3
    alex dot cs00 at yahoo dot ca
    14 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>", $code);
    So at the end something like :
    [
    up
    -1
    jobowo
    2 years ago
    Note that when using the 'Use ($variable)' with preg_replace_callback, if you wish the value to be altered by the anonymous function, you must pass the value in by reference. eg preg_replace_callback($pattern, function($matches) use (&$alterThis) { $alterThis+=$something;},$string);
    up
    -5
    Underdog
    10 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.
    up
    -3
    tgage at nobigfoot dot com
    6 years ago
    To use variable from the parent scope of the anonymous callback function passed to preg_replace_callback(), utilize the use() parameter.

    $var1 = "one";
    $var2 = "two";
    $line = preg_replace_callback('/^.*$/',
    function( $matches ) use ( $var1, $var2 ) {
    return( $var1 . " " . $var2 );
    }, $line);

    Will replace the entire string with the concatenated values or $var1 and $var2 ("one two") from the parent scope.
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