# File lib/rubygems/commands/update_command.rb, line 47
  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.source_index.each do |name, spec|
      if hig[spec.name].nil? or hig[spec.name].version < spec.version then
        hig[spec.name] = spec
      end
    end

    gems_to_update = which_to_update hig, options[:args]

    updated = []

    installer = Gem::DependencyInstaller.new options

    gems_to_update.uniq.sort.each do |name|
      next if updated.any? { |spec| spec.name == name }

      say "Updating #{name}"
      installer.install name

      installer.installed_gems.each do |spec|
        updated << spec
        say "Successfully installed #{spec.full_name}"
      end
    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
      if updated.empty? then
        say "Nothing to update"
      else
        say "Gems updated: #{updated.map { |spec| spec.name }.join ', '}"
      end
    end
  end