From: nobu.nokada@...
Date: 2004-05-13T20:56:55+09:00
Subject: Re: Strange regexp behaviour in gsub

Hi,

At Wed, 12 May 2004 09:13:51 +0900,
Florian Gross wrote in [ruby-talk:99884]:
> > Yes, that would clarify the situation, but is it the correct
> > behaviour?  I would think that (?!a)a doesn't mean the same
> > character, but consecutive ones.  Because it doesn't consume
> > the character, it effectively is the character 'before' the
> > match (if any).  The other behaviour wouldn't make sense,
> > because (?!a)b is then exactly the same as b.
> 
> I think that it's the intended behavior. Just use /(?!a).b/ if you want 
> to consume the character.
> 
> Thinking about this, it is indeed possible to implement fixed-width 
> look-behind -- interesting.

Ruby 1.9 (Oniguruma) has look-behind feature.

  $ ruby -v -e 'p "bab".gsub(/(?<!a)ab/, "cd")'
  ruby 1.9.0 (2004-05-12) [i686-linux]
  "bcd"

-- 
Nobu Nakada