From: Robert Klemme <bob.news@...>
Date: 2005-03-24T17:09:52+09:00
Subject: Re: (Maybe) a simple question about regex


"Assaph Mehr" <assaph@gmail.com> schrieb im Newsbeitrag
news:1111629894.417238.111830@l41g2000cwc.googlegroups.com...
>
> > 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"]
>
> Negative lookahead:
> s.scan /(?!4|5)\d\d/
> Note the OR sign ('|') between the digits, otherwise it would produce:
> ["01", "23", "56", "78"]

But:

>> s = '01234567894657'
=> "01234567894657"
>> s.scan /(?!4|5)\d\d/
=> ["01", "23", "67", "89", "65"]
>> s.scan /\d\d/
=> ["01", "23", "45", "67", "89", "46", "57"]

IOW, you loose "46" and "57".

I prefer a non RE solution in these cases as it's simpler

>> s.scan(/\d\d/).reject {|x| "45" == x}
=> ["01", "23", "67", "89", "46", "57"]

Otherwise RE becomes really complex if you want to make it right - if it's
possible at all (see other postings).

Kind regards

    robert