Golang - check env is loaded.

config.go

import (
	"fmt"
	"reflect"
	log "github.com/sirupsen/logrus"
	"github.com/spf13/viper"
)


type Config struct {
	MongoHost     string
	MongoPort     int
	MongoUserName string
	MongoPassword string
	AppPort       int
}

var AppConfig Config

func Load() error {
	viper.AutomaticEnv()
    
	AppConfig = Config{
		MongoHost:     viper.GetString("MongoHost"),
		MongoPort:     viper.GetInt("MongoPort"),
		MongoUserName: viper.GetString("MongoUserName"),
		MongoPassword: viper.GetString("MongoPassword"),
		AppPort:       viper.GetString("AppPort"),
	}

	v := reflect.ValueOf(AppConfig)
	typeOfV := v.Type()

	for i := 0; i < v.NumField(); i++ {
        
		if fmt.Sprintf("%v", v.Field(i).Interface()) == "" {
			log.Warn(fmt.Sprintf("Value of environment var %s is empty.", typeOfV.Field(i).Name))
		}
        
	}

	return nil
}

Fields in struct has to be exported (big caps) else warning will be thrown.

This is also a demonstration on how we can loop through structs to get key/value pair.