def whoami_root(cmd)
  if `#{cmd}`.strip.chomp != 'root'
    $stderr.puts $run_as_root_msg || 'You need to be root to run this command.'
    exit $run_as_root_exit_code || 1
  end
end

['/usr/bin/whoami', '/bin/whoami'].each do |w|
  if File.exist? w
    whoami_root w
  end
end