Forum: Ruby Hopefully simple regex

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stephen O'D (Guest)
on 2008-12-18 00:20
(Received via mailing list)
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.
stephen O'D (Guest)
on 2008-12-18 00:33
(Received via mailing list)
On Dec 17, 10:15 pm, "stephen O'D" <removed_email_address@domain.invalid> wrote:
>   def setup
>     ]
>       "sometext@bar text",
> 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?
David A. Black (Guest)
on 2008-12-18 00:35
(Received via mailing list)
Hi --

On Thu, 18 Dec 2008, stephen O'D wrote:

>
>  def setup
>    # this doesn't work correctly for the fails scenarios
>    @regex = /(@{1,1}\w+)/
>  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?

Try this:

   @regex = /(?:^|\s)(@\w+)/


David
stephen O'D (Guest)
on 2008-12-18 00:45
(Received via mailing list)
> Coming in 2009: The Well-Grounded Rubyist (http://manning.com/black2)
Perfect - I didn't know you could (or even think to try) putting the
'start of string' anchor inside a group with an alternative!  At least
I have learned something from the last hour of trying!
Richard C. (Guest)
on 2008-12-18 14:09
(Received via mailing list)
On Wed, Dec 17, 2008 at 10:37 PM, stephen O'D
<removed_email_address@domain.invalid> wrote:
> I have learned something from the last hour of trying!
>

http://www.rubular.com is an awesome way of composing and testing ruby
regular expressions. Highly recommended.
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