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Bug #39695 preg_replace returns NULL if no match, instead of unmodified subject
Submitted: 2006-11-30 16:55 UTC Modified: 2006-11-30 21:36 UTC
From: ivo_gelov at abv dot bg Assigned:
Status: Not a bug Package: PCRE related
PHP Version: 5.2.0 OS: Linux Fedora Core 4
Private report: No CVE-ID: None
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 [2006-11-30 16:55 UTC] ivo_gelov at abv dot bg 
Description:
------------
There are 2 strange effects/bugs, may be one depends on the other, I do not know.
1. PREG_REPLACE does not recognize $n as a back reference in its second argument. It will recognize only \\n references.
2. PREG_REPLACE returns NULL if no match is found, instead of returning unmodified subject

This symptom is present only in 5.2.0 - there are no problems with 5.1.0

Reproduce code:
---------------
$pat = '/^([a-zA-Z])(\d*)$/';
$rep = '\$2\$1';
$b = preg_replace($pat,$rep,'D764209812');


Expected result:
----------------
$b should be '764209812D'

Actual result:
--------------
$b is NULL

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 [2006-11-30 17:36 UTC] tony2001@php.net 
Not reproducible.
Btw, this code - $rep = '\$2\$1'; apparently won't work.
 [2006-11-30 18:05 UTC] ivo_gelov at abv dot bg 
I checked "$2$1" instead of "\$2\$1" and it worked.
So this is my fault since I was looking an example in an old manual, not the current one.
Sorry for disturbing.

But there is another issue - when I used preg_replace in PHP 5.1.4 with a relatively long string as a subject, it worked without problems. But after upgrade to 5.2.0, it now gives me an error PREG_BACKTRACK_LIMIT_ERROR with default value for "pcre.backtrack_limit" (not listed in PHP.INI at all). What can I do ? Should I revert back to 5.1.4 ?
Or just compile 5.2.0 with the 6.6 version of PCRE library ?
 [2006-11-30 18:17 UTC] tony2001@php.net 
Just increase pcre.backtrack_limit.
 [2006-11-30 18:58 UTC] ivo_gelov at abv dot bg 
But what is the limit for this setting ?
 [2006-11-30 21:36 UTC] tony2001@php.net 
AFAIK both maximum for recursion and match limits is set to 10000000.
 
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