With this method you can open any config file that supported by viper

pars config file with viper

// go run main.go --config ./config/config.yaml
// go run main.go --config ./config/config.json
// go run main.go --config ./config/config.toml
// file name also can be any name : config, app and etc.

var configFile = flag.String("config", "./config/config.yaml", "Address of config file")

func parseConfig() {
	dir, file := path.Split(*configFile)
	ext := path.Ext(file)
	viper.SetConfigName(strings.ReplaceAll(file, ext, ""))
	viper.SetConfigType(strings.ReplaceAll(ext, ".", ""))

	viper.AddConfigPath(dir)
	if err := viper.ReadInConfig(); err != nil {
		panic(fmt.Errorf("Fatal error config file: %s ", err))
	}
}