function rvm
  set -l gems ''
  set -l ruby ''

  if test ! $argv[1]
    set argv[1] '<nothing>'
  end

  switch $argv[1]
    case system
      set gems $HOME/.gem-system
      set ruby /usr/bin/ruby

    # for other rubies add somthing like the following.
    # the important principle is that I don't want to mix gems between versions
    # cause its bad for space-time.

    # case r19
    #   set gems $HOME/.gem-1.9
    #   set ruby ~/homebrew/.../ruby19/bin/ruby # whatever the path is

    case '*'
      echo 'hey, ruby needs to be one of [system]'
      return
  end

  echo $argv[1] > ~/.lastruby

  set -xg GEM_HOME $gems
  set -xg GEM_PATH $gems
  set -xg PATH $gems/bin (dirname $ruby) $PATH
end