code: func checkDockerClient() {
  	output, err := commandOutput("docker", []string{"--version"})
  	if err != nil {
  		panic(StatusError{errors.New("Error when probing Docker's client version. Is docker installed and within the $PATH?"), 69})
  	}
  	re := regexp.MustCompile("([0-9]+)\\.([0-9]+)\\.?([0-9]+)?")
  	rawVersions := re.FindStringSubmatch(output)
  	var versions []int
  	for _, rawVersion := range rawVersions[1:] {
  		version, err := strconv.Atoi(rawVersion)
  		if err != nil {
  			printErrorf("Error when parsing Docker's version %v: %v", rawVersion, err)
  			break
  		}
  		versions = append(versions, version)
  	}
  
  	for i, expectedVersion := range requiredDockerVersion {
  		if versions[i] > expectedVersion {
  			break
  		}
  		if versions[i] < expectedVersion {
  			printErrorf("Unsupported client version! Please upgrade to Docker %v or later.\n", intJoin(requiredDockerVersion, "."))
  		}
  	}
  }
docs: // Ensure there is a docker binary in the path,
  // and printing an error if its version is below the minimal requirement.