Hopefully simple regex

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.