code: func ipRunAFOutput(family seesaw.AF, cmd string, args ...interface{}) (string, error) {
  	switch family {
  	case seesaw.IPv4:
  		cmd = fmt.Sprintf("-f inet %s", cmd)
  	case seesaw.IPv6:
  		cmd = fmt.Sprintf("-f inet6 %s", cmd)
  	default:
  		return "", fmt.Errorf("Unknown address family %s", family)
  	}
  	return ipRunOutput(cmd, args...)
  }
docs: // ipRunAFOutput runs the Linux ip(1) command with the given address family
  // and specified arguments and returns the output.