# 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