Hi
You did not put a question mark in your character class ([\/\w\.-] and
instead you put it together with the session id.
The expression looks for a sequence without which is not followed by the
next expression --- ?PHPSESSID\=2u0cca.....
If it would count the last `p` of `.php` then the next expression would
violate the negative lookahead.
Instead it stops just before it, after the `.ph` which is the longest
expression it could find that fulfills your negative lookahead, and then it
inserts the new sessionid over there.
Try instead
$buffer =
preg_replace('/"http\:\/\/www\.domain\.com([\/\w\.\-]*\??)(?!PHPSESSID\=2u0c
caffoh6jaeapkke35qpp87;?)/',
'"http://www.domain.com$1?PHPSESSID=t9gksvpdcuobsnqt98qloe6lg4;', $buffer);
(not tested)
Simcha Younger
-----Original Message-----
From: Cameron B. Prince [mailto:cplists@xxxxxxxxxxxxxxxxxx]
Sent: Monday, August 18, 2008 12:56 AM
To: php-general@xxxxxxxxxxxxx
Subject: Negative Look Ahead Regex - Code Mistake or Bug?
Hello,
I¹ve run into a problem with a regex and need help determining if this is my
mistake or a bug. The regex is for inserting a SID into every link in the
buffer before it¹s flushed, but only when each link doesn¹t already have a
SID.
An example of the code is here:
$buffer =
preg_replace('/"http\:\/\/www\.domain\.com([\/\w\.-]*)(?!\?PHPSESSID\=2u0cca
ffoh6jaeapkke35qpp87;?)/',
'"http://www.domain.com$1?PHPSESSID=t9gksvpdcuobsnqt98qloe6lg4;', $buffer);
The code works correctly in most cases except when a SID already exists and
there is a path after the .com such as:
http://www.domain.com/path1/path2.php?PHPSESSID=2u0ccaffoh6jaeapkke35qpp87;
When this URL is processed by the regex, it becomes:
http://www.domain.com/path1/path2.ph?PHPSESSID=t9gksvpdcuobsnqt98qloe6lg4;p?
PHPSESSID=2u0ccaffoh6jaeapkke35qpp87;
So the problem is the regex not only falsely matches, it's inserting the SID
in between 2nd and 3rd letters of the extension.
You can see the code in action here:
http://kottmann.com/test.php
The full source for the test code is also available when viewing the source
of this page.
I've tested this on PHP v5.1.6 and PHP v5.2.6.
TIA,
Cameron
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