Thing with strings and Ruby

question.rb

mystring = "something"
puts mystring

=> "something" # okay, so far so good

foobar = "test"
mystring = '#{foobar}' # note the single quotation marks!
puts mystring

=> "#{foobar}" # not what i want

puts eval mystring

=> nil # not what i want, either

=> "test" # <= this is what i wish to get back somehow...