code: func main() {
  	errQuit := func(err error) {
  		fmt.Fprintf(os.Stderr, "error updating gTLD map: %s\n", err)
  		os.Exit(1)
  	}
  
  	// Default to writing to standard out
  	writer := os.Stdout
  	if flag.NArg() > 0 {
  		// If a filename is specified as a command line flag then open it (creating
  		// if needed), truncate the existing contents, and use the file as the
  		// writer instead of standard out
  		filename := flag.Args()[0]
  		f, err := os.OpenFile(filename, os.O_CREATE|os.O_TRUNC|os.O_WRONLY, 0664)
  		if err != nil {
  			errQuit(err)
  		}
  		defer f.Close()
  		writer = f
  	}
  
  	if err := renderGTLDMap(writer); err != nil {
  		errQuit(err)
  	}
  }
docs: // main handles rendering a gTLD map to either standard out (when no argument is
  // provided) or to the provided filename. If an error occurs it is printed to
  // standard err and the program terminates with a non-zero exit status.