Hopefully simple regex

ruby-talk
1

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.

2

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?

···

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.

3

Hi --

···

On Thu, 18 Dec 2008, stephen O'D 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

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

--
David A. Black / Ruby Power and Light, LLC
Ruby/Rails consulting & training: http://www.rubypal.com
Coming in 2009: The Well-Grounded Rubyist (http://manning.com/black2\)

4

Try this:

   @regex = /(?:^|\s)(@\w+)/

David

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

5

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

···

On Wed, Dec 17, 2008 at 10:37 PM, stephen O'D <stephen.odonnell@gmail.com> wrote:

Try this:

   @regex = /(?:^|\s)(@\w+)/

David

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!