From: Daniel Sheppard <daniels@...>
Date: 2007-11-30T10:24:05+09:00
Subject: Re: Negate a character sequence in a regular expression?

> For the following string:
> 
> 'cat sheep horse cat tac dog'
> 
> I would like to write a regular expression that matches any substring
> that is prefixed by the word 'cat', is then followed by any characters
> as long as those characters do not comprise the word 'cat', and then
> finally suffixed by the string 'dog'.  Therefore, this expression
> should match the substring 'cat tac dog' in the above string.

Working out negative regular expressions is normally best avoided.

One step is hard. Two steps is not:

x = 'cat sheep horse cat tac dog'
/(cat.*?dog)/.match(x) && $1.sub(/.*cat/,'cat')

Or if you want multiple matches:

x = 'cat sheep horse cat tac dog cat cat sheep dog'
x.scan(/cat.*?dog/).map {|x| x.sub(/.*cat/,'cat')}
=> ["cat tac dog", "cat sheep dog"]

Dan.