ID: 14893
User updated by: [EMAIL PROTECTED]
Reported By: [EMAIL PROTECTED]
Status: Bogus
Bug Type: PCRE related
Operating System: SunOS
PHP Version: 4.1.1
New Comment:
The bug is in PCRE, as the category states -- I am merely bringing to
the attention of the PHP developers that this bug exists in the regex
engine it employs. I have contacted the author of PCRE, and he'll fix
it when the next version of PCRE is released.
As for why it is properly a bug:
"ab1b" =~ /(.*)\d+\1/
should match as follows (assuming absolutely no optimizations are
done);
[] [ab1b] OPEN 1
[] [ab1b] STAR ANY
[ab1b] [] CLOSE 1
[ab1b] [] PLUS DIGIT
fail
[ab1] [b] CLOSE 1
[ab1] [b] PLUS DIGIT
fail
[ab] [1b] CLOSE 1
[ab] [1b] PLUS DIGIT
[ab1] [b] REF 1
fail
[a] [b1b] CLOSE 1
[a] [b1b] PLUS DIGIT
fail
start over
[a] [b1b] OPEN 1
[a] [b1b] STAR ANY
[ab1b] [] CLOSE 1
[ab1b] [] PLUS DIGIT
fail
[ab1] [b] CLOSE 1
[ab1] [b] PLUS DIGIT
fail
[ab] [1b] CLOSE 1
[ab] [1b] PLUS DIGIT
[ab1] [b] REF 1
[ab1b] [] DONE
You can see that this regex should succeed (at least, I hope I've made
that clear). The problem is that the PCRE engine optimizes a .* at the
beginning of a regex to be implicitly anchored with ^, since it seems
obvious that if .* is going to match anywhere, it will end up matching
at the beginning of the string. This is perfectly sensible except in
the case where that .* is captured and used later in the regex, as my
case shows.
Previous Comments:
------------------------------------------------------------------------
[2002-01-27 01:03:39] [EMAIL PROTECTED]
a) Not a PHP bug (but its good to be aware of this issue, if you
wouldn't mind please send a mail to [EMAIL PROTECTED] with any updates,
etc.)
b) not sure if this is really a bug, the way I read the 1st regex is:
read in ab
put that as \1
after a digit match \1
which is ab
after the digit there is only b
whereas in the second example you make the regex non-greedy, so
therefore it matches from the beginning of the string and matches the
ab from the lookahead assertion.
I could be wrong, but either way its not a PHP bug ;) If you disagree
please follow up at [EMAIL PROTECTED]
regards,
sterling
------------------------------------------------------------------------
[2002-01-06 17:57:14] [EMAIL PROTECTED]
Here's the problem:
<? echo preg_match('/(.*)\d+\1/', 'ab1b'); ?>
It fails, but it really shouldn't. You can fool the engine into not
having the bug:
<? echo preg_match('/(?=)(.*)\d+\1/', 'ab1b'); ?>
The bug is thus: a regex that starts with .* can logically be made to
start with an implicit anchor to the beginning of the string. However,
this optimization can break the success of a regex if the .* is
captured (as above) and used later (the back-reference \1). I've
contacted the author of the PCRE package.
------------------------------------------------------------------------
Edit this bug report at http://bugs.php.net/?id=14893&edit=1
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