code: func Fatalf(format string, args ...interface{}) {
  	w := io.MultiWriter(os.Stdout, os.Stderr)
  	if runtime.GOOS == "windows" {
  		// The SameFile check below doesn't work on Windows.
  		// stdout is unlikely to get redirected though, so just print there.
  		w = os.Stdout
  	} else {
  		outf, _ := os.Stdout.Stat()
  		errf, _ := os.Stderr.Stat()
  		if outf != nil && errf != nil && os.SameFile(outf, errf) {
  			w = os.Stderr
  		}
  	}
  	fmt.Fprintf(w, "Fatal: "+format+"\n", args...)
  	os.Exit(1)
  }
docs: // Fatalf formats a message to standard error and exits the program.
  // The message is also printed to standard output if standard error
  // is redirected to a different file.