Ruby finding OS

To find the Operating System that you ruby script/program is running on you can do:
puts RUBY_PLATFORM

To return one of Windows, Mac, Linux you could do:

if (RUBY_PLATFORM.include? ("darwin"))
   os = "Mac"
elsif (RUBY_PLATFORM.include? ("nix"))
   os = "Linux"
elsif (RUBY_PLATFORM.include? ("Win"))
   os = "Windows"
else
   os = ""
end

there is also
puts ENV['OS']
but this only works on windows and is empty for Linux and Mac OS X