negative lookahed won't work
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#135 negative lookahed won't work
Invalid
nobody
None
Medium
Defect
2010-06-11
2010-06-01
Anonymous
No
Originally created by: matteo.t... (code.google.com)@gmail.com
What steps will reproduce the problem?
1. try a regex with a negative lookahed on a text file, for example
"javascript:\s*(?!history)" is the one I was using
What is the expected output? What do you see instead?
I expected to see only the string "javascript:" NOT followed by the word
"history", instead those were returned too.
What version of the product are you using? On what operating system?
version 1.4.2 on windows7 32 bit
Discussion
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Originally posted by: tortoisesvn
Works just fine for me.
Using a file with two lines:
javascript:history
javascript:test
and the regex 'javascript:\s*(?!history)'
I get one match on line two, and not two matches.
Status: NeedsInfo
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Originally posted by: matteo.t... (code.google.com)@gmail.com
mine had lines like "javascript: history.go(-1);" but they would be reported too...
I'll do another test, perhaps I've made some mistake.
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Originally posted by: matteo.t... (code.google.com)@gmail.com
Ok, here is what I've discovered: some of my files contained pieces like
href="javascript: history.go(-1)"
which I need to keep, while there are other parts like
onlick="javascript: [...]"
where I want to cut out the "javascript: " part.
Please notice the space after the colon.
it seems that if I use the regex "javascript:\s*(?!history)" I get also the strings I want to preserve, while if I use the regex "javascript:\s+(?!history)" I get the correct result, though I do not understand why this happens. Is it a "bug" or a problem with me not understanding regex?
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Originally posted by: tortoisesvn
The negative lookahead has priority, so even though the '*' is greedy, it won't match until the lookahead is triggered.
Use 'atomic grouping' to group the first part together:
(?>javascript:\s*)(?!history)
Status: Invalid
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Originally posted by: matteo.t... (code.google.com)@gmail.com
I see. Well then, sorry for having opened an issue that was not related to your program.
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Originally posted by: tortoisesvn
no problem :)