class Gem::Commands::UpdateCommand

def update_rubygems
  if Gem.disable_system_update_message
    alert_error Gem.disable_system_update_message
    terminate_interaction 1
  end
  check_update_arguments
  version, requirement = rubygems_target_version
  check_latest_rubygems version
  check_oldest_rubygems version
  update_gem 'rubygems-update', version
  installed_gems = Gem::Specification.find_all_by_name 'rubygems-update', requirement
  version        = installed_gems.first.version
  install_rubygems version
end