From: G_ F_ <8si.greg@...>
Date: 2009-09-08T02:31:57+09:00
Subject: Re: regular expression NOT operator

Phil Cooper-king wrote:
[...]
> so for constants I search /([A-Z].*?\b)/

This regex is not going to match a constant. It matches any upper-case 
letter followed by a non-greedy wildcard followed by a word boundary.

A constant has to begin with an upper-case letter, possibly followed by 
mixed-case letters, numbers and underscores ("_").

The following show the problem: The first two are your regex, and the 
second two show a fix.

    /([A-Z].*?\b)/ =~ 'noT a constant'  # => 2
    /([A-Z].*?\b)/ =~ 'a Constant'  # => 2

    /\b([A-Z]\w*\b)/ =~ 'noT a constant.'    # => nil
    /\b([A-Z]\w*\b)/ =~ 'a Constant.'    # => 2

The # => at the end of the line show where the match occurred. The first 
set shows a non-constant having a false-positive.

Regex are extremely powerful, but you have to think out what can go 
wrong with them. When you are searching you can get false-positives 
easily. If you are searching and replacing, you can get destroyed 
content.

Also, "?!" is not a NOT operator, it's a negative look-ahead. A match 
succeeds if the initial condition matches followed by no match.

http://www.ruby-doc.org/docs/ProgrammingRuby/html/language.html#UN
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