How to automatically parse environment variables without setting configuration files?

[zc2638]

Hello,

	home, err := homedir.Dir()
	if err != nil {
		return err
	}
	viper.AddConfigPath(home)
	viper.SetConfigName("config.yaml")	

	viper.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
	viper.AutomaticEnv()
	if err := viper.ReadInConfig(); err != nil {
		if _, ok := err.(*os.PathError); !ok {
			return err
		}
	}
	return viper.Unmarshal(data, func(dc *mapstructure.DecoderConfig) {
		dc.TagName = "json"
	})

Question:
When the configuration file does not exist, how can I make the environment variable automatically parse to the data structure?

Expect:
When the configuration file does not exist, the configuration can be parsed into data according to environment variables.

Actual:
Before formatting data, all field values ​​will be parsed first, according to the v.AllSettings() method