From: stephen O'D <stephen.odonnell@...>
Date: 2008-12-18T07:22:15+09:00
Subject: Re: Hopefully simple regex

On Dec 17, 10:15 pm, "stephen O'D" <stephen.odonn...@gmail.com> wrote:
> Hi,
>
> I am trying to make a regex that will capture strings that look like
> '@string' surrounded by whitespace or at the start or end of a line -
> here is the spec:
>
> require 'test/unit'
>
> class RegexTest < Test::Unit::TestCase
>
>   def setup
>     # this doesn't work correctly for the fails scenarios
>     @regex = /(@{1,1}\w+)/
>   end
>
>   def test_regex_matches
>     str = [
>       "@bar some more text",
>       "@bar",
>       "sometext @bar text",
>       "sometext @bar"
>     ]
>     str.each do |s|
>       s =~ @regex
>       assert_equal('@bar', $1)
>     end
>   end
>
>   def test_regex_fails
>     str = [
>       "@@bar",
>       "sometext @@bar text",
>       "sometext@bar text",
>       "sometext@bar"
>     ]
>     str.each do |s|
>       s =~ @regex
>       assert_equal(nil, $1)
>     end
>   end
>
> end
>
> I have tried all sorts of combinations of character class and negated
> classes etc until my eyes have started glazing over - I really though
> this should be easy - can anyone suggest a regex that pass my spec
> above?
>
> Thanks,
>
> Stephen.

It seems like this regex works:

 /^(?:.*\s+(@{1,1}\w+)|(@{1,1}\w+))/

Although you have to change the spec a little to check $1 and $2 for
matches.  Still seems a bit over complex to me - any better
suggestions?