[regex-coach] negative lookahead assertion bug? message 9 of 20)

[recoach.z.pbowers at spamgourmet.com]

Break it down into elements.
 
[^a-z]{3}
 
This says MATCH if you find 3 characters in a row which are not lowercase
alphas.  None of A-D match in this case because all of them have at least
one lower-case alpha within those first 3 chars.
 
Add the negative lookahead:
 
(?![^a-z]{3})
 
Since NONE of them matched and we're doing a NEGATIVE lookahead then we end
up with a positive and so all of A-D match here.
 
-Peter


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From: Arian Hojat - armyofda12mnkeys at gmail.com
[mailto:+recoach+pbowers+7ef1bd310e.armyofda12mnkeys#gmail.com at spamgourmet.c
om] 
Sent: Wednesday, May 21, 2008 4:32 PM
To: General purpose mailing list for The Regex Coach
Subject: Re: [regex-coach] negative lookahead assertion bug?
message 9 of 20)


i think the last email was right about the pattern needing to be
([A-Z]-)(?![^a-z]{3})([a-z0-9A-Z]* ),
this one is like a double NOT, almost right?

Now I'm just curious with a pattern like this.... This pattern 
([A-Z]-)(?![^a-z]{3}) 
for text: A-xyz37 # B-ab6142 # C-Wxy66 # D-qrs93
matches
A-xyz37 # B-ab6142 # C-Wxy66 # D-qrs93

Its looking to make sure the next thing after Capital Letter dash isnt 3
lower case letters, then 'nots' it? 
aka it really looks ahead for 3 lowercase letters, and i thought would only
match A- and D-.

Thanks for the help btw, I wasnt sure if these were problems with program or
just me understanding regexes bad :) which is most likely the case.
Arian



2008/5/21 Laurent TAUPIAC <ltaupiac at lfdj.com>:


Negative lookup assertion should match to be validate.
If "Wxy" not match, the positive assertion failed.

If you want a Capital letter followed by a dash but not followed by 3 lower
case, you should match "not 3 lower case" 

([A-Z]-)(?![^a-z]{3})([a-z0-9]* )



Regards

Arian Hojat a écrit : 

Hello all,

had a question/possible bug report...
For the example on this webpage:
http://www.nuclearblender.com/leftovers/howto/regex/

this pattern is presented and i tried a positive lookup assertion which
worked, but this first negative one only matched the first pattern (global
option is on btw, so not sure why wont match).
Pattern: ([A-Z]-)(?![a-z]{3})([a-z0-9]* )
Text to lookup: A-xyz37 # B-ab6142 # C-Wxy66 # D-qrs93

Should match B-ab6142 and C-Wxy66 as they both (have a capital letter
followed by a dash), then (dont have 3 lower case letters), and (are
following by letters/numbers and a space)
only matches first one in the program.

Thanks, let me know if it should match only one if im wrong. Running latest
version on Windows XP.
Great Tool!
Arian



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