execute (Gem::Commands::UpdateCommand)

    # File lib/rubygems/commands/update_command.rb, line 46
      def execute
        if options[:system] then
          say "Updating RubyGems..."

          unless options[:args].empty? then
            fail "No gem names are allowed with the --system option"
          end

          options[:args] = ["rubygems-update"]
        else
          say "Updating installed gems..."
        end

        hig = highest_installed_gems = {}

        Gem::SourceIndex.from_installed_gems.each do |name, spec|
          if hig[spec.name].nil? or hig[spec.name].version < spec.version then
            hig[spec.name] = spec
          end
        end

        remote_gemspecs = Gem::SourceInfoCache.search(//)

        gems_to_update = if options[:args].empty? then
                           which_to_update(highest_installed_gems, remote_gemspecs)
                         else
                           options[:args]
                         end

        options[:domain] = :remote # install from remote source

        # HACK use the real API
        install_command = Gem::CommandManager.instance['install']

        gems_to_update.uniq.sort.each do |name|
          say "Attempting remote update of #{name}"
          options[:args] = [name]
          options[:ignore_dependencies] = true # HACK skip seen gems instead
          install_command.merge_options(options)
          install_command.execute
        end

        if gems_to_update.include? "rubygems-update" then
          latest_ruby_gem = remote_gemspecs.select do |s|
            s.name == 'rubygems-update'
          end

          latest_ruby_gem = latest_ruby_gem.sort_by { |s| s.version }.last

          say "Updating version of RubyGems to #{latest_ruby_gem.version}"
          installed = do_rubygems_update latest_ruby_gem.version

          say "RubyGems system software updated" if installed
        else
          updated = gems_to_update.uniq.sort.collect { |g| g.to_s }

          if updated.empty? then
            say "Nothing to update"
          else
            say "Gems updated: #{updated.join ', '}"
          end
        end
      end