From: "David A. Black" <dblack@...>
Date: 2009-09-07T19:34:50+09:00
Subject: Re: regular expression NOT operator

Hi --

On Mon, 7 Sep 2009, Phil Cooper-king wrote:

> Regex is something I've managed to ignore for some time, only learning
> bits when needed.
>
> I'm trying to do code highlighting, so I've been using Reg to find parts
> of the code
> I've run into an issue with comments
>
> # A comment can contain control statements like if and Constants
>
> things like if and a Constant get picked up by my reg, I'm trying to put
> a not operator in my regex but cant seem to get it to work.
>
> so for constants I search /([A-Z].*?\b)/
> how can I add "when theres no # on the left"?
>
> I've been trying to use the ?! as the not operator. (is that even a not
> operator)
> this is what i've been trying /([A-Z].*?\b)(?!<regex>)/

There's negative look-behind in Oniguruma, but you're going to run
into some difficulties anyway, I suspect. For example:

   x = 3
   puts "This has no comments, and x is #{x}" if x < 5

My advice would be to keep it (relatively) straightforward by doing
something like this as you scan the lines of text:

   comment_re = /^\s*#/

   if comment_re.match(line)
     # treat line as a comment
   else
     # line is not a comment
   end


David

-- 
David A. Black / Ruby Power and Light, LLC / http://www.rubypal.com
Ruby/Rails training, mentoring, consulting, code-review
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