Handling .env file with option to override them with flags. This example read .env into a map instead of writing into the OS environment variables.

.env

AMI_USERNAME="YOUR_AMI_USERNAME"
AMI_PASSWORD="YOUR_AMI_PASSWORD"
AMI_HOST="YOUR_AMI_HOST"

.env.dev

AMI_USERNAME="developer"
AMI_PASSWORD="secret-dev-password"
AMI_HOST="www.developing.com.my"

loadConfig.go

package main

import (
	"flag"
	"fmt"
	"github.com/joho/godotenv"
)

var(
	// parse config flag
	envFlag = flag.String("env", ".env", "The .env file to load.")

	usernameFlag = flag.String("u", "", "Username for AMI authentication.")
	passwordFlag = flag.String("p", "", "Password for AMI authentication.")
	hostnameFlag = flag.String("h", "", "Hostname for AMI.")
)
func main() {
	loadConfig()
	fmt.Println("after flags")
	fmt.Println(*usernameFlag)
	fmt.Println(*passwordFlag)
	fmt.Println(*hostnameFlag)
}
func loadConfig() {
	// parse first to load the env value
	flag.Parse()

	// load .env
	env, _ := godotenv.Read(*envFlag)

	// set env as flag default
	_ = flag.Set("u", env["AMI_USERNAME"])
	_ = flag.Set("p", env["AMI_PASSWORD"])
	_ = flag.Set("h", env["AMI_HOST"])
	fmt.Println(*usernameFlag)
	fmt.Println(*passwordFlag)
	fmt.Println(*hostnameFlag)

	// parse flags again to make user input flags override default
	flag.Parse()
}