code: func getVariable(image *api.Image, name string) string {
  	envName := name + "="
  	for _, v := range image.Config.Env {
  		if strings.HasPrefix(v, envName) {
  			return strings.TrimSpace(v[len(envName):])
  		}
  	}
  
  	return ""
  }
docs: // getVariable gets environment variable's value from the image metadata