Last updated: Fri, 18 Jul 2008

preg_replace

(PHP 4, PHP 5)

preg_replace — Perform a regular expression search and replace

Description

mixed preg_replace ( mixed $pattern , mixed $replacement , mixed $subject [, int $limit [, int &$count ]] )

Searches subject for matches to pattern and replaces them with replacement .

Parameters

pattern

The pattern to search for. It can be either a string or an array with strings.

The e modifier makes preg_replace() treat the replacement parameter as PHP code after the appropriate references substitution is done. Tip: make sure that replacement constitutes a valid PHP code string, otherwise PHP will complain about a parse error at the line containing preg_replace().

replacement

The string or an array with strings to replace. If this parameter is a string and the pattern parameter is an array, all patterns will be replaced by that string. If both pattern and replacement parameters are arrays, each pattern will be replaced by the replacement counterpart. If there are fewer elements in the replacement array than in the pattern array, any extra pattern s will be replaced by an empty string.

replacement may contain references of the form \\n or (since PHP 4.0.4) $n, with the latter form being the preferred one. Every such reference will be replaced by the text captured by the n'th parenthesized pattern. n can be from 0 to 99, and \\0 or $0 refers to the text matched by the whole pattern. Opening parentheses are counted from left to right (starting from 1) to obtain the number of the capturing subpattern.

When working with a replacement pattern where a backreference is immediately followed by another number (i.e.: placing a literal number immediately after a matched pattern), you cannot use the familiar \\1 notation for your backreference. \\11, for example, would confuse preg_replace() since it does not know whether you want the \\1 backreference followed by a literal 1, or the \\11 backreference followed by nothing. In this case the solution is to use \${1}1. This creates an isolated $1 backreference, leaving the 1 as a literal.

When using the e modifier, this function escapes some characters (namely ', ", \ and NULL) in the strings that replace the backreferences. This is done to ensure that no syntax errors arise from backreference usage with either single or double quotes (e.g. 'strlen(\'$1\')+strlen("$2")'). Make sure you are aware of PHP's string syntax to know exactly how the interpreted string will look like.

subject

The string or an array with strings to search and replace.

If subject is an array, then the search and replace is performed on every entry of subject , and the return value is an array as well.

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() 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 or NULL if an error occurred.

ChangeLog

Version	Description
5.1.0	Added the `count` parameter
4.0.4	Added the '$n' form for the `replacement` parameter
4.0.2	Added the `limit` parameter

Examples

Example #1 Using backreferences followed by numeric literals


<?php
$string = 'April 15, 2003';
$pattern = '/(\w+) (\d+), (\d+)/i';
$replacement = '${1}1,$3';
echo preg_replace($pattern, $replacement, $string);
?>

The above example will output:

April1,2003

Example #2 Using indexed arrays with preg_replace()


<?php
$string = 'The quick brown fox jumped over the lazy dog.';
$patterns[0] = '/quick/';
$patterns[1] = '/brown/';
$patterns[2] = '/fox/';
$replacements[2] = 'bear';
$replacements[1] = 'black';
$replacements[0] = 'slow';
echo preg_replace($patterns, $replacements, $string);
?>

The above example will output:

The bear black slow jumped over the lazy dog.

By ksorting patterns and replacements, we should get what we wanted.


<?php
ksort($patterns);
ksort($replacements);
echo preg_replace($patterns, $replacements, $string);
?>

The above example will output:

The slow black bear jumped over the lazy dog.

Example #3 Replacing several values


<?php
$patterns = array ('/(19|20)(\d{2})-(\d{1,2})-(\d{1,2})/',
                   '/^\s*{(\w+)}\s*=/');
$replace = array ('\3/\4/\1\2', '$\1 =');
echo preg_replace($patterns, $replace, '{startDate} = 1999-5-27');
?>

The above example will output:

$startDate = 5/27/1999

Example #4 Using the 'e' modifier


<?php
preg_replace("/(<\/?)(\w+)([^>]*>)/e", 
             "'\\1'.strtoupper('\\2').'\\3'", 
             $html_body);
?>

This would capitalize all HTML tags in the input text.

Example #5 Strip whitespace

This example strips excess whitespace from a string.


<?php
$str = 'foo   o';
$str = preg_replace('/\s\s+/', ' ', $str);
// This will be 'foo o' now
echo $str;
?>

Example #6 Using the count parameter


<?php
$count = 0;

echo preg_replace(array('/\d/', '/\s/'), '*', 'xp 4 to', -1 , $count);
echo $count; //3
?>

The above example will output:

xp***to
3

Notes

Note: When using arrays with pattern and replacement , the keys are processed in the order they appear in the array. This is not necessarily the same as the numerical index order. If you use indexes to identify which pattern should be replaced by which replacement , you should perform a ksort() on each array prior to calling preg_replace().


When you use the '$1', '$2', etc. replacement values, they can be either in double or single quotes. There is no need to worry about the dollar sign being interpreted as a variable or not:



<?php

print preg_replace("/I want (\S+) one/", "$1 is the one I want", "I want that one") . "\n";

print preg_replace("/I want (\S+) one/", '$1 is the one I want', "I want that one") . "\n";

?>



Both lines will print "that is the one I want".

David
11-Jul-2008 12:59


Take care when you try to strip whitespaces out of an UTF-8 text. Using something like:



<?php

$text = preg_replace( "{\s+}", ' ', $text );

?>



brokes in my case the letter à which is hex c3a0. But a0 is a whitespace. So use 



<?php

$text = preg_replace( "{[ \t]+}", ' ', $text );

?>



to strip all spaces and tabs, or better, use a multibyte function like mb_ereg_replace.

akniep at rayo dot info
07-Jul-2008 11:22


preg_replace (and other preg-functions) return null instead of a string when encountering problems you probably did not think about!

-------------------------



It may not be obvious to everybody that the function returns NULL if an error of any kind occurres. An error I happen to stumple about quite often was the back-tracking-limit:

http://de.php.net/manual/de/pcre.configuration.php

#ini.pcre.backtrack-limit



When working with HTML-documents and their parsing it happens that you encounter documents that have a length of over 100.000 characters and that may lead to certain regular-expressions to fail due the back-tracking-limit of above.



A regular-expression that is ungreedy ("U", http://de.php.net/manual/de/reference.pcre.pattern.modifiers.php) often does the job, but still: sometimes you just need a greedy regular expression working on long strings ...



Since, an unhandled return-value of NULL usually creates a consecutive error in the application with unwanted and unforeseen consequences, I found the following solution to be quite helpful and at least save the application from crashing:



<?php



$string_after = preg_replace( '/some_regexp/', "replacement", $string_before );



// if some error occurred we go on working with the unchanged original string

if (PREG_NO_ERROR !== preg_last_error())

{

    $string_after = $string_before;

    

    // put email-sending or a log-message here

} //if



// free memory

unset( $string_before );



?>



You may or should also put a log-message or the sending of an email into the if-condition in order to get informed, once, one of your regular-expressions does not have the effect you desired it to have.

php at PointedEars dot de
07-Jul-2008 11:46


A bit easier to read and probably more efficient will be



<?php



function preg_escape($s = '')

{

  return preg_replace('/[]\\\\^$.|?*+(){}[]/', '\\\\$0', $s);

}



?>

patrick dot d dot hayes at gmail dot com
25-Jun-2008 10:15


Here's some handy-dandy code that will properly escape a string that includes regex special characters.



<?php

$x = "

/\\[|\\\\|\\^|\\$|\\.|\\||\\?

|\\*|\\+|\\(|\\)|\\{|\\}/

";



$escaped_string = preg_replace($x, "\\\\$0", $in_string);



?>



This is useful if you are generating dynamic regular expressions based on user input.  With the above example, the $escaped_string variable is now ready to be used in another regular expression as the search variable.

da_pimp2004_966 at hotmail dot com
21-Jun-2008 07:09


A simple BB like thing..



function AddBB($var) {

        $search = array(

                '/\[b\](.*?)\[\/b\]/is',

                '/\[i\](.*?)\[\/i\]/is',

                '/\[u\](.*?)\[\/u\]/is',

                '/\[img\](.*?)\[\/img\]/is',

                '/\[url\](.*?)\[\/url\]/is',

                '/\[url\=(.*?)\](.*?)\[\/url\]/is'

                );



        $replace = array(

                '<strong>$1</strong>',

                '<em>$1</em>',

                '<u>$1</u>',

                '<img src="$1" />',

                '<a href="$1">$1</a>',

                '<a href="$1">$2</a>'

                );



        $var = preg_replace ($search, $replace, $var);

        return $var;

}

 <!-- -->

Let me know of any error(s) :)

Michael W
16-Apr-2008 11:35


For filename tidying I prefer to only ALLOW certain characters rather than converting particular ones that we want to exclude. To this end I use ...



<?php

  $allowed = "/[^a-z0-9\\040\\.\\-\\_\\\\]/i";

  preg_replace($allowed,"",$str));

?>



Allows letters a-z, digits, space (\\040), hyphen (\\-), underscore (\\_) and backslash (\\\\), everything else is removed from the string.

Misha
25-Mar-2008 02:45


This is in response to iasmin at amazingdiscoveries dot org's URL text to link function. Hope this is helpful to someone.



I played with it a bit and came up with this version (there were one or two little errors in the regex I think, also -- it didn't allow various necessary characters).



I start with a URL in brackets (this works for my case):

[http://www.site.com/path/that/may/be_long.php?fun=1]



It returns a link of the URL after the "http://":

www.site.com/path/that/may/b...



-----------

    // Cuts off long URLs at $url_length, and appends "..."

    function reduceurl($url, $url_length) {

        $reduced_url = substr($url, 0, $url_length);

        if (strlen($url) > $url_length) $reduced_url .= '...';

        

        return $reduced_url;

    }



    // Makes URLs with brackets into links

    // The regex searches for "http://" or equivalent, then various character possibilities (I don't know if it might be possible to exploit this if more characters were allowed). The "e" after the regex allows the reduceurl() to be evaluated.



    function url2link($linktext) {

        $linktext = preg_replace("#\[(([a-zA-Z]+://)([a-zA-Z0-9?&%.;:/=+_-]*))\]#e", "'<a href=\"$1\" target=\"_blank\">' . reduceurl(\"$3\", 30) . '</a>'", $linktext);

                

        return $linktext;

    }

php-comments-REMOVE dot ME at dotancohen dot com
29-Feb-2008 08:02


Below is a function for converting Hebrew final characters to their

normal equivelants should they appear in the middle of a word.

The /b argument does not treat Hebrew letters as part of a word,

so I had to work around that limitation.



<?php



$text="עברית מבולגנת";



function hebrewNotWordEndSwitch ($from, $to, $text) {

   $text=

    preg_replace('/'.$from.'([א-ת])/u','$2'.$to.'$1',$text);

   return $text;

}



do {

   $text_before=$text;

   $text=hebrewNotWordEndSwitch("ך","כ",$text);

   $text=hebrewNotWordEndSwitch("ם","מ",$text);

   $text=hebrewNotWordEndSwitch("ן","נ",$text);

   $text=hebrewNotWordEndSwitch("ף","פ",$text);

   $text=hebrewNotWordEndSwitch("ץ","צ",$text);

}   while ( $text_before!=$text );



print $text; // עברית מסודרת!



?>



The do-while is necessary for multiple instances of letters, such

as "אנני" which would start off as "אןןי". Note that there's still the

problem of acronyms with gershiim but that's not a difficult one

to solve. The code is in use at http://gibberish.co.il which you can

use to translate wrongly-encoded Hebrew, transliterize, and some

other Hebrew-related functions.



To ensure that there will be no regular characters at the end of a

word, just convert all regular characters to their final forms, then

run this function. Enjoy!

Bryan Roach
15-Jan-2008 09:53


Jacob Fogg's clean_filename function is good, but there is a typo. Replace "\\x00-\\x40" with "\\x00-\\x20" or you will exclude too many characters.



Also keep in mind when checking file names to look for the special directory names ".." and ".". A user could potentially use those to reach an unexpected directory.

Jacob Fogg
14-Jan-2008 09:29


Here is my attempt at cleaning up a file name... it's similar to  what someone else has done however a little cleaner with the addition of the | in the reserved characters... also I clean any characters from x00 to x40 (all non display characters and space) as well as everything greater than 7f and greater (removes the Del character and other non English characters), replacing them with an '_'.



function clean_filename($filename){//function to clean a filename string so it is a valid filename

$reserved = preg_quote('\/:*?"<>|', '/');//characters that are  illegal on any of the 3 major OS's

//replaces all characters up through space and all past ~ along with the above reserved characters

return preg_replace("/([\\x00-\\x40\\x7f-\\xff{$reserved}])/e", "_", $filename);

}

admin[a-t]saltwaterc[d0t]net
11-Dec-2007 04:17


Actually I made a mistake in my previous post. In order to make the function more effective ... I broke it. The original which works (really) looks like this:



<?php

function repl_amp($text)

    {

    $text=preg_replace("/&(?!amp;)/i", "&amp;", $text);

    $text=preg_replace("/&amp;#(\d+);/i", "&#$1;", $text); // For numeric entities

    $text=preg_replace("/&amp;(\w+);/i", "&$1;", $text); // For literal entities

    return $text;

    }

?>



The RegEx Tester says that the first expression is OK, but when testing with various entities, some of them came out broken. I'd tried to use only 2 preg_replace(); calls instead of three by using the alternative branch from the pattern syntax - which didn't came out well. Sorry for the previous error, and I still hope that someone can find a better alternative.

ulf dot reimers at tesa dot com
07-Dec-2007 06:28


Hi,



as I wasn't able to find another way to do this, I wrote a function converting any UTF-8 string into a correct NTFS filename (see http://en.wikipedia.org/wiki/Filename).



<?php

function strToNTFSFilename($string)

{

  $reserved = preg_quote('\/:*?"<>', '/');

  return preg_replace("/([\\x00-\\x1f{$forbidden}])/e", "_", $string);

}

?>



It converts all control characters and filename characters which are reserved by Windows ('\/:*?"<>') into an underscore.

This way you can safely create an NTFS filename out of any UTF-8 string.

Anonymous
30-Nov-2007 08:26


This code is much easier than preg_replaces current implementation, I stole some of this from someone else here, but to make it more explicit:



$relation['/pattern/'] = "replacement";



$text_out = preg_replace(array_keys($relation), array_values($relation), $text_in);



Fast, efficient, no guess work..

Santosh Patnaik
23-Oct-2007 07:35


@giel dot berkers



Use the 'PCRE_DOTALL' ('s') option so that the '.' covers newline characters:



$code = preg_replace('/\/\*.*\*\//ms', '', $code);

mike dot hayward at mikeyskona dot co dot uk
18-Oct-2007 04:49


Hi.

Not sure if this will be a great help to anyone out there, but thought i'd post just in case.

I was having an Issue with a project that relied on $_SERVER['REQUEST_URI']. Obviously this wasn't working on IIS.

(i am using mod_rewrite in apache to call up pages from a database and IIS doesn't set REQUEST_URI). So i knocked up this simple little preg_replace to use the query string set by IIS when redirecting to a PHP error page.



<?

//My little IIS hack :)

if(!isset($_SERVER['REQUEST_URI'])){ 

$_SERVER['REQUEST_URI'] = preg_replace( '/404;([a-zA-Z]+:\/\/)(.*?)\//i', "/" , $_SERVER['QUERY_STRING'] );

}

?>



Hope this helps someone else out there trying to do the same thing :)



If anyone finds a better way, please let met know, I'm still learning ;)

matt
28-Sep-2007 04:52


at below post:

<?php

 $template = "Price: #price#";

 $price    = '&#36;5';

 print "Price: $price\n";

 $res    = preg_replace("/#price#/", $price, $template);

 print "From template: -> $res\n";



 ?>

jefkin at gmail dot com
20-Sep-2007 02:52


@ Santosh Patnaik



The perl regular expression engine will handle this expression better and much faster by using the word boundry escape code \b.  Though it may not be obvious except to long time perl geeks such as I :)



so:



// Expect and get 'pa pa pa pa'

echo preg_replace('`\bma\b`', 'pa', 'ma ma ma ma');



Jeff

Santosh Patnaik
14-Sep-2007 07:11


Once a match is identified, the regular expression engine appears to set aside the matching segment of the target string. A second segment that you expect to match may therefore end up not getting matched:



// Expect 'pa pa pa pa' but get 'pa ma pa ma'

echo preg_replace('`(^|\s)ma(\s|$)`', '$1pa$2', 'ma ma ma ma');



Here the issue can be solved by using a 'lookahead':



// Expect and get 'pa pa pa pa'

echo preg_replace('`(^|\s)ma(?=\s|$)`', '$1pa', 'ma ma ma ma');

iasmin at amazingdiscoveries dot org
13-Sep-2007 03:37


I thought that someone could use this hyperlink function. 

preg_replace is about 6 times faster than ereg_replace. I took the original example from the ereg_replace function page and modified so that it works perfect. I gave a comment of what it matches.

One thing is that I added a space at the beginning so that only links that don't have <a href="" around them or anything else touching will be replaced. 



<i>NOTE! I had to break the long lines otherwise I couldn't have posted this. So take the new line out and it will work</i>

<?php

function hyperlink(&$text)

    {

       // match protocol://address/path/file.extension?some=variable&another=asf%

       $text = preg_replace("/\s(([a-zA-Z]+:\/\/)([a-z][a-z0-9_\..-]*

[a-z]{2,6})([a-zA-Z0-9\/*-?&%]*))\s/i", " <a href=\"$1\">$3</a> ", $text);

    

       // match www.something.domain/path/file.extension?some=variable&another=asf%

       $text = preg_replace("/\s(www\.([a-z][a-z0-9_\..-]*

[a-z]{2,6})([a-zA-Z0-9\/*-?&%]*))\s/i", " <a href=\"http://$1\">$2</a> ", $text);

       

       return $text;

    }

?>



Play around with it and see how it works. 

Courtesy of AmazingDiscoveries.org 

God bless, Iasmin Balaj

sternkinder at gmail dot com
24-Aug-2007 11:10


From what I can see, the problem is, that if you go straight and substitute all 'A's wit 'T's you can't tell for sure which 'T's to substitute with 'A's afterwards. This can be for instance solved by simply replacing all 'A's by another character (for instance '_' or whatever you like), then replacing all 'T's by 'A's, and then replacing all '_'s (or whatever character you chose) by 'A's:



$dna = "AGTCTGCCCTAG";

echo str_replace(array("A","G","C","T","_","-"), array("_","-","G","A","T","C"), $dna); //output will be TCAGACGGGATC



Although I don't know how transliteration in perl works (though I remember that is kind of similar to the UNIX command "tr") I would suggest following function for "switching" single chars:



function switch_chars($subject,$switch_table,$unused_char="_") {

    foreach ( $switch_table as $_1 => $_2 ) {

        $subject = str_replace($_1,$unused_char,$subject);

        $subject = str_replace($_2,$_1,$subject);

        $subject = str_replace($unused_char,$_2,$subject);

    }

    return $subject;

}



echo switch_chars("AGTCTGCCCTAG", array("A"=>"T","G"=>"C")); //output will be TCAGACGGGATC

rob at ubrio dot us
21-Aug-2007 09:48


Also worth noting is that you can use array_keys()/array_values() with preg_replace like:



$subs = array(

  '/\[b\](.+)\[\/b\]/Ui' => '<strong>$1</strong>',

  '/_(.+)_/Ui' => '<em>$1</em>'

  ...

  ...

);



$raw_text = '[b]this is bold[/b] and this is _italic!_';



$bb_text = preg_replace(array_keys($subs), array_values($subs), $raw_text);

lehongviet at gmail dot com
25-Jul-2007 09:15


I got problem echoing text that contains double-quotes into a text field. As it confuses value option. I use this function below to match and replace each pair of them by smart quotes. The last one will be replaced by a hyphen(-).



It works for me.



function smart_quotes($text) {

 $pattern = '/"((.)*?)"/i';

 $text = preg_replace($pattern,"&#147;\\1&#148;",stripslashes($text));

$text = str_replace("\"","-",$text);

$text = addslashes($text);

return $text;

}

131 dot php at cloudyks dot org
17-Jul-2007 12:37


Based on previous comment, i suggest 

( this function already exist in php 6 )



function unicode_decode($str){

    return preg_replace(

        '#\\\u([0-9a-f]{4})#e',

        "unicode_value('\\1')",

        $str);

}

function unicode_value($code) {

    $value=hexdec($code);

    if($value<0x0080)

        return chr($value);

    elseif($value<0x0800)

        return chr((($value&0x07c0)>>6)|0xc0)

            .chr(($value&0x3f)|0x80);

    else

        return chr((($value&0xf000)>>12)|0xe0)

        .chr((($value&0x0fc0)>>6)|0x80)

        .chr(($value&0x3f)|0x80);

}

ismith at nojunk dot motorola dot com
21-Mar-2007 05:47


Be aware that when using the "/u" modifier, if your input text contains any bad UTF-8 code sequences, then preg_replace will return an empty string, regardless of whether there were any matches.



This is due to the PCRE library returning an error code if the string contains bad UTF-8.

mrozenoer at overstream dot net
07-Mar-2007 04:30


I could not find a function to unescape javascript unicode escapes anywhere (e.g., "\u003c"=>"<"). 





<?php


function js_uni_decode($s) {


    return preg_replace('/\\\u([0-9a-f]{4})/ie', "chr(hexdec('\\1'))",  $s);


}


echo js_uni_decode("\u003c");


?>

dani dot church at gmail dot youshouldknowthisone
07-Feb-2007 07:09


Note that it is in most cases much more efficient to use preg_replace_callback(), with a named function or an anonymous function created with create_function(), instead of the /e modifier.  When preg_replace() is called with the /e modifier, the interpreter must parse the replacement string into PHP code once for every replacement made, while preg_replace_callback() uses a function that only needs to be parsed once.

Alexey Lebedev
07-Sep-2006 10:21


Wasted several hours because of this:



$str='It&#039;s a string with HTML entities';

preg_replace('~&#(\d+);~e', 'code2utf($1)', $str);



This code must convert numeric html entities to utf8. And it does with a little exception. It treats wrong codes starting with &#0



The reason is that code2utf will be called with leading zero, exactly what the pattern matches - code2utf(039).

And it does matter! PHP treats 039 as octal number.

Try print(011);



Solution:

preg_replace('~&#0*(\d+);~e', 'code2utf($1)', $str);

robvdl at gmail dot com
21-Apr-2006 01:15


For those of you that have ever had the problem where clients paste text from msword into a CMS, where word has placed all those fancy quotes throughout the text, breaking the XHTML validator... I have created a nice regular expression, that replaces ALL high UTF-8 characters with HTML entities, such as &#8217;.



Note that most user examples on php.net I have read, only replace selected characters, such as single and double quotes. This replaces all high characters, including greek characters, arabian characters, smilies, whatever.



It took me ages to get it just downto two regular expressions, but it handles all high level characters properly.



$text = preg_replace('/([\xc0-\xdf].)/se', "'&#' . ((ord(substr('$1', 0, 1)) - 192) * 64 + (ord(substr('$1', 1, 1)) - 128)) . ';'", $text);

$text = preg_replace('/([\xe0-\xef]..)/se', "'&#' . ((ord(substr('$1', 0, 1)) - 224) * 4096 + (ord(substr('$1', 1, 1)) - 128) * 64 + (ord(substr('$1', 2, 1)) - 128)) . ';'", $text);

gabe at mudbuginfo dot com
18-Oct-2004 09:39


It is useful to note that the 'limit' parameter, when used with 'pattern' and 'replace' which are arrays, applies to each individual pattern in the patterns array, and not the entire array.

<?php



$pattern = array('/one/', '/two/');

$replace = array('uno', 'dos');

$subject = "test one, one two, one two three";



echo preg_replace($pattern, $replace, $subject, 1);

?>



If limit were applied to the whole array (which it isn't), it would return:

test uno, one two, one two three



However, in reality this will actually return:

test uno, one dos, one two three

steven -a-t- acko dot net
08-Feb-2004 05:45


People using the /e modifier with preg_replace should be aware of the following weird behaviour. It is not a bug per se, but can cause bugs if you don't know it's there.



The example in the docs for /e suffers from this mistake in fact.



With /e, the replacement string is a PHP expression. So when you use a backreference in the replacement expression, you need to put the backreference inside quotes, or otherwise it would be interpreted as PHP code. Like the example from the manual for preg_replace:



preg_replace("/(<\/?)(\w+)([^>]*>)/e",

             "'\\1'.strtoupper('\\2').'\\3'",

             $html_body);



To make this easier, the data in a backreference with /e is run through addslashes() before being inserted in your replacement expression. So if you have the string



 He said: "You're here"



It would become:



 He said: \"You\'re here\"



...and be inserted into the expression.

However, if you put this inside a set of single quotes, PHP will not strip away all the slashes correctly! Try this:



 print ' He said: \"You\'re here\" ';

 Output: He said: \"You're here\"



This is because the sequence \" inside single quotes is not recognized as anything special, and it is output literally.



Using double-quotes to surround the string/backreference will not help either, because inside double-quotes, the sequence \' is not recognized and also output literally. And in fact, if you have any dollar signs in your data, they would be interpreted as PHP variables. So double-quotes are not an option.



The 'solution' is to manually fix it in your expression. It is easiest to use a separate processing function, and do the replacing there (i.e. use "my_processing_function('\\1')" or something similar as replacement expression, and do the fixing in that function).



If you surrounded your backreference by single-quotes, the double-quotes are corrupt:

$text = str_replace('\"', '"', $text);



People using preg_replace with /e should at least be aware of this.



I'm not sure how it would be best fixed in preg_replace. Because double-quotes are a really bad idea anyway (due to the variable expansion), I would suggest that preg_replace's auto-escaping is modified to suit the placement of backreferences inside single-quotes (which seemed to be the intention from the start, but was incorrectly applied).

thewolf at pixelcarnage dot com
23-Oct-2003 03:38


I got sick of trying to replace just a word, so I decided I would write my own string replacement code. When that code because far to big and a little faulty I decided to use a simple preg_replace:





<?php


/**


 * Written by Rowan Lewis of PixelCarnage.com


 * $search(string), the string to be searched for


 * $replace(string), the string to replace $search


 * $subject(string), the string to be searched in


 */


function word_replace($search, $replace, $subject) {


    return preg_replace('/[a-zA-Z]+/e', '\'\0\' == \'' . $search . '\' ? \'' . $replace . '\': \'\0\';', $subject);


}


?>





I hope that this code helpes someone!

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preg_replace_callback

Last updated: Fri, 18 Jul 2008

preg_replace

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