In article <3454c9680807250045q6d3ecbe8n2692c899dc62a94a / mail.gmail.com>,
  "Vladimir Sizikov" <vsizikov / gmail.com> writes:

> It could just be "mri'. For version numbers, you could then inspect

RubyGems uses RUBY_ENGINE as a directory name:

lib/rubygems/defaults.rb:

  def self.default_dir
    if defined? RUBY_FRAMEWORK_VERSION then
      File.join File.dirname(ConfigMap[:sitedir]), 'Gems',
                ConfigMap[:ruby_version]
    elsif defined? RUBY_ENGINE then
      File.join ConfigMap[:libdir], RUBY_ENGINE, 'gems',
                ConfigMap[:ruby_version]
    else
      File.join ConfigMap[:libdir], 'ruby', 'gems', ConfigMap[:ruby_version]
    end
  end

If RUBY_ENGINE is "mri", libdir/mri/gems/version is used as default_dir.

I guess RubyGems expects "ruby".
-- 
Tanaka Akira