code: func getPassphrase(ctx *cli.Context) string {
  	// Look for the --passwordfile flag.
  	passphraseFile := ctx.String(passphraseFlag.Name)
  	if passphraseFile != "" {
  		content, err := ioutil.ReadFile(passphraseFile)
  		if err != nil {
  			utils.Fatalf("Failed to read passphrase file '%s': %v",
  				passphraseFile, err)
  		}
  		return strings.TrimRight(string(content), "\r\n")
  	}
  
  	// Otherwise prompt the user for the passphrase.
  	return promptPassphrase(false)
  }
docs: // getPassphrase obtains a passphrase given by the user.  It first checks the
  // --passfile command line flag and ultimately prompts the user for a
  // passphrase.