A solution to https://twitter.com/garybernhardt/status/253708758964903936

extensions.rb

module Extensions
  module_function

  def separate(path)
    extensions = path.reverse
                     .scan(/\G\w+\./)
                     .map { |e| e[0..-2].reverse }
                     .reverse
    file_name  = path.split(".")[0..-(extensions.size + 1)].join(".")
    [file_name, extensions]
  end
end

if $PROGRAM_NAME == __FILE__
  require "minitest/autorun"

  class SeparateExtensions < MiniTest::Unit::TestCase
    def test_extensions_are_pulled_off_the_end
      assert_equal(
        ["some file name with", ["dots", "html", "markdown"]],
        Extensions.separate("some file name with.dots.html.markdown")
      )
    end

    def test_sections_with_spaces_are_ignored
      assert_equal(
        ["some file name.with dots", ["html", "markdown"]],
        Extensions.separate("some file name.with dots.html.markdown")
      )
    end

    def test_treats_the_leading_section_as_part_of_the_file_name
      assert_equal(
        ["some.file name with.multiple dots", ["html", "markdown"]],
        Extensions.separate("some.file name with.multiple dots.html.markdown")
      )
    end
  end
end