This module parses .env files to make environment variables stored in them accessible via os.Getenv("key")

This is a port of the Symfony Dotenv Component

go get https://github.com/Valgard/godotenv 

Sensitive information and environment-dependent settings should be defined as environment variables (as recommended for twelve-factor applications). Using a .env file to store those environment variables eases development and CI management by keeping them in one "standard" place and agnostic of the technology stack you are using.

Load a .env file in your application via Dotenv::Load():

package main

import (
	"github.com/Valgard/godotenv"
)

func main() {
	dotenv := godotenv.New()
	if err := dotenv.Load(".env"); err != nil {
		panic(err)
	}

	// You can also load several files
	if err := dotenv.Load(".env", ".env.dev"); err != nil {
		panic(err)
	}
}

Given the following .env file content:

# .env
DB_USER=root
DB_PASS=pass

Access the value with os.Getenv() in your code:

dbUser := os.Getenv("DB_USER")

The Load() method never overwrites existing environment variables. Use the Overload() method if you need to overwrite them:

if err := dotenv.Overload(".env"); err != nil {
	panic(err)
}

As you're working with this module you'll notice that you might want to have different files depending on the environment you're working in. Typically this happens for local development or Continuous Integration where you might want to have different files for your test and dev environments.

You can use Dotenv::LoadEnv() to ease this process:

	dotenv := godotenv.New()
	if err := dotenv.LoadEnv(".env"); err != nil {
		panic(err)
	}

The Dotenv module will then look for the correct .env file to load in the following order whereas the files loaded later override the variables defined in previously loaded files:

1. If .env exists, it is loaded first. In case there's no .env file but a .env.dist, this one will be loaded instead.
2. If one of the previously mentioned files contains the APP_ENV variable, the variable is populated and used to load environment-specific files hereafter. If APP_ENV is not defined in either of the previously mentioned files, dev is assumed for APP_ENV and populated by default.
3. If there's a .env.local representing general local environment variables it's loaded now.
4. If there's a .env.{env}.local file, this one is loaded. Otherwise, it falls back to .env.{env}.

This might look complicated at first glance but it gives you the opportunity to commit multiple environment-specific files that can then be adjusted to your local environment. Given you commit .env, .env.test and .env.dev to represent different configuration settings for your environments, each of them can be adjusted by using .env.local, .env.test.local and .env.dev.local respectively.

.env.local is always ignored in test environment because tests should produce the same results for everyone.

You can adjust the variable defining the environment, default environment and test environments by passing them as additional options to Dotenv::LoadEnv() (see LoadEnv() for details).

You should never store a .env.local file in your code repository as it might contain sensitive information; create a .env file (or multiple environment-specific ones as shown above) with sensible defaults instead.

This dotenv module can be used in any environment of your application: development, testing, staging and even production. However, in production it's recommended to configure real environment variables to avoid the performance overhead of parsing the .env file for every request.

As a .env file is a regular shell script, you can source it in your own shell scripts:

source .env

Add comments by prefixing them with #:

# Database credentials
DB_USER=root
DB_PASS=pass # This is the secret password

Use environment variables in values by prefixing variables with $:

DB_USER=root
DB_PASS=${DB_USER}pass # Include the user as a password prefix

The order is important when some env var depends on the value of other env vars. In the above example, DB_PASS must be defined after DB_USER. Moreover, if you define multiple .env files and put DB_PASS first, its value will depend on the DB_USER value defined in other files instead of the value defined in this file.

Define a default value in case the environment variable is not set:

DB_USER=
DB_PASS=${DB_USER:-root}pass # results in DB_PASS=rootpass

Embed commands via $() (not supported on Windows):

START_TIME=$(date)

Note that using $() might not work depending on your shell.

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.