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VBscript regexp - optional submatch problem

Posted on 2004-09-12
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Last Modified: 2008-01-09
I have a text string as below

"outside/1.1.2.3/12 customermex-148-244-192-88.alestra.net.mx (0) -> dmz/66.193.215.3"

I want to match the
"outside/" as submatch 1
"1.1.2.3" as submatch 2
the "/12" as optional submatch 3
the "(0)" as optional submatch 4

ie all of these four strings would be matched by the pattern

1 "outside/1.1.2.3/12 customermex-148-244-192-88.alestra.net.mx (0) -> dmz/66.193.215.3"
2 "discarded outside/2.2.2.2/service"
3 "discarded outside/2.5.2.2/as (service)"
4 "discarded outside/2.2.552.2/178 (service)"

I have been trying this pattern,

"outside/"........"IP addresss"...... optional match "/number"......."match anything"......optional match "(xxxx)"
ie
(outside\/)(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})(\/\d+)?.+?(\(.+?\))?

This last optional submatch,  (\(.+?\))? doesn't match the "(0)" portion. If I make the last match required, ie
(outside\/)(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})(\/\d+)?.+?(\(.+?\))
Then this works fine with the three strings with this match occurs, but not for string 2 wheres the "(xxxx)" portion is missing

What do I need to change in the pattern?

Cheers

Dave


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Question by:Dave Brett
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Author Comment

by:Dave Brett
ID: 12041693
This works but it is a little clumsy

"(outside\/)(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})(\/\d+)?(.+?(\(.+?\)){1}|.+?)"

any improvements?
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Expert Comment

by:_kiew
ID: 12046970
Did you tried

(outside\/)(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})(\/\d+)?[^(]+?(\(.+?\))?

???
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Author Comment

by:Dave Brett
ID: 12061493
Hi _kiew

This pattern misses the
"(0)"
portion

Cheers

Dave

 
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Accepted Solution

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_kiew earned 500 total points
ID: 12061591
You are right. I have just understood why you made your "match anything" subpattern reluctant (to avoid matching the opening paren)
Of course, you don't have to do so if you want to "match anything but opening paren"

This does work (it has been tested with Perl, if your VBScript regex engine behaves differently, then I cannot help you)

(outside\/)(\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3})(\/\d+)?[^(]*(\(.+?\))?

(use * instead of + for example nr 2 to match)

Sorry for the untested answer (at least I learned something today ;-)
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Author Comment

by:Dave Brett
ID: 12061865
Hi _kiew

Thats very interesting

By replacing my "find anything after the IP and before parens" in my original pattern
.+?
with "find anyhting after the IP that is not a paren"
[^(]*
then suddenly the optional parens match is found

But I'm still unclear why my initial attempt failed, any ideas?

Cheers

Dave





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Expert Comment

by:_kiew
ID: 12068988
With a string matched by your 1st, 2nd and optional 3rd subpattern, one more character is enough for the global match to succeed, then, if the next characters are "(xxxx)" they will be matched, but that is the only case because then "\(.+?\)" subpattern is optional. This is why your examples 3 and 4 were working, I think.

The most important to grab the "(xxxx)" successfully is to make the "find anything after the IP that is not a paren" subpattern greedy (you see, no "?"). A greedy subpattern will match as much as possible, so this one is matching until the first opening parenthesis, and then you can capture the "(xxxx)" with your optional subpattern.
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Author Comment

by:Dave Brett
ID: 12070514
Thanks

> A greedy subpattern will match as much as possible,
I made it non-greedy with the "?" deliberately as otherwise a string such as

"outside/1.1.2.3/12 customermex-148-244-192-88.alestra.net.mx (0) -> dmz/66.193.215.3 (otherstuff)"
would match
(otherstuff)
rather then
(0)

Thanks for your assistance, your pattern is neater than my workaround second post

Welcome to EE :)

Cheers

Dave
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Author Comment

by:Dave Brett
ID: 12157887
Hi kiew,

I came back here as I realised that I'd mis-interpreted your last post and talked about something different after your "A greedy subpattern will match as much as possible". Your negated class was a better method than my lazy +  ...... which kind of goes without saying as my orginal method didn't work

One aspect of VBscript RegExp that I hadn't realised that I was missing till I started posted in the Perl TA was the Lookaround. Boy I could do with that functionality.

Cheers

Dave


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