code: func (l *EnvfileLookup) Lookup(key string, config *config.ServiceConfig) []string {
  	envs, err := opts.ParseEnvFile(l.Path)
  	if err != nil {
  		return []string{}
  	}
  	for _, env := range envs {
  		e := strings.Split(env, "=")
  		if e[0] == key {
  			return []string{env}
  		}
  	}
  	return []string{}
  }
docs: // Lookup creates a string slice of string containing a "docker-friendly" environment string
  // in the form of 'key=value'. It gets environment values using a '.env' file in the specified
  // path.