From: Jason Sweat <jason.sweat@...>
Date: 2005-03-24T11:09:15+09:00
Subject: Re: (Maybe) a simple question about regex

On Thu, 24 Mar 2005 10:49:49 +0900, Sam Kong <sam.s.kong@gmail.com> wrote:
> Hello!
> 
> I think that I am missing a very simple concept about regex.
> 
> s = '0123456789'
> s.scan(/\d\d/) #-> ["01", "23", "45", "67", "89"]
> 
> Now I want to exclude "45".
> How can I express it in the regex?
> When it's only one character, I can use ^.
> But for 2 characters, I don't think I can use it.
> 
> What I want is:
> 
> s = '0123456789'
> s.scan(some_regex) #-> ["01", "23", "67", "89"]
> 
> What should some_regex be?

You can use a negative assertion to say you want to skip "45", but it
will bump forward one space and you will end up with the last matches
being "56" and "78"

>> s.scan(/(?!45)\d\d/)
=> ["01", "23", "56", "78"]

So with a little uglier assertion, you can say:

>> s.scan(/(?!45|5)\d\d/)
=> ["01", "23", "67", "89"]

and get what you specified, but though it works for your toy case, I
would be worried that this might not extrapolate out to your real goal
well.

HTH 

Regards,
Jason
http://blog.casey-sweat.us/