Problem with negative lookahead at end of string

olivierp has asked for the wisdom of the Perl Monks concerning the following question:

Hi Monks ! I'm having trouble building a regex that would match as follows:
string starts with chars, contains this, but does not contain that and does not end with whatever A couple of samples:

chars at the beginning, this is right and whatever is not at the end
chars at the beginning, this is ok and the end is whatever
chars at the beginning, this is ok and that is included
chars at the beginning, that here this is not ok

This regex will match 1 and 2, and correctly skip 3 and 4:

^chars(?!.*that).*this(?!.*that).*

If I include the whatever part, as here

^chars(?!.*that).*this(?!.*that).*(?!.*whatever)$

, sample 2 still matches, whereas this:

^chars(?!.*that).*this(?!.*that).*[^w][^h][^a][^t][^e][^v][^e][^r]$

excludes sample 2 but is horrible...

Am I missing something with the negative lookahead, or is it not possible to do such a thing ?

--
Olivier

Edited by demerphq: Changed </br> to <br />

Comment on Problem with negative lookahead at end of string Select or Download Code

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•Re: Problem with negative lookahead at end of string by merlyn (Sage) on Jun 21, 2004 at 15:45 UTC
For simplicity sake, you can list a compound "and-ed" condition as a series of null assertions: `/ ^ # anchor so as not to try this at every spot (?= chars ) # stars with chars (?= .? this ) # contains this (?! .? that ) # does not contain that (?! .* whatever $ ) # does not end in whatever /xs` [download] -- Randal L. Schwartz, Perl hacker Be sure to read my standard disclaimer if this is a reply. update: edited to include additional whitespace for readability	[reply] [d/l]
Re^2: Problem with negative lookahead at end of string by melora (Scribe) on Jun 21, 2004 at 17:35 UTC
Nice. "I'd walk a mile for a (Programming Perl) Camel." Had to reach for it to get through that ?!.*? regex! I'm just an old C programmer, learning more than one way to do it...	[reply]
Re: Problem with negative lookahead at end of string by tye (Sage) on Jun 21, 2004 at 15:12 UTC
`/^chars(?!.that).this.(?<!whatever)$/` [download] If "whatever" is actually a pattern that can match more than a single length of string, then instead use: `/^chars(?!.that).this(?!.whatever$)/` [download] And note that the `(?!.*that)` part doesn't need to be repeated. - tye	[reply] [d/l] [select]
Re: Problem with negative lookahead at end of string by delirium (Chaplain) on Jun 21, 2004 at 15:25 UTC
Despite a processing slowdown, I prefer the readability of splitting criteria like this up into multiple expressions: `/^chars/ && /this/ && !/that/ && !/whatever$/`	[reply] [d/l]
Re^2: Problem with negative lookahead at end of string by runrig (Abbot) on Jun 21, 2004 at 17:40 UTC
Despite a processing slowdown... It depends on the patterns and the string, but it's often faster (and in this case it is faster) to split up the matches into multiple regexes.	[reply]