A .env file is a configuration file used to store environment variables, typically as a file in the project root. It’s commonly used in development to keep sensitive information (like API keys) out of source code.

This is similar to config.properties in Java - see article.

Basic usage

  • Create a file named .env in your project’s root directory.
  • Add variables in KEY=VALUE format, one per line.
  • Access variables in your code using process.env.KEY (Node.js) or similar methods in other languages

Top tips

  • The contents of the file are not encrypted, so it should be kept private and not shared with others.
  • Never commit .env files to version control. Or only if there are no sensitive secrets in them.
  • Use .env.template to share template of required variables.
  • Load .env files as early as possible in your application.
  • Validate required environment variables on startup.
  • You can use different .env files for different environments (e.g. .env.development, .env.production). Though you could set those variables instead as environment variables in your build pipeline such that as dotenv file is not needed in a deploymed environment.

Syntax

  • It must be a valid shell script (usually Bash).
  • No spaces around = sign: API_KEY=abcdef123456
  • Use quotes for values with spaces: MESSAGE="Hello World"
  • Multi-line values: 
    MULTI_LINE="line 1
line 2"

Sample content

# Database configuration
DB_HOST=localhost
DB_PORT=5432

# API Keys
API_KEY=sk_test_abcdef

# Multi-line example.
MULTI_LINE_VALUE="This is a
multi-line
value example"

Load dotenv

Manually

Run this in Bash to read the contents of the file and then set each as exported variables with export

$ export $(< .env)

Or this (does not work with comments in the file).

$ export $(xargs < .env)

Run that once in a terminal window. Then start your app.

In a Makefile, you can set this to make that easier:

run:
	export $(< .env) \
		&& npm start

Then run:

$ make run

Related - see the export command cheatsheet.

Automatic

Use a package that can read the .env file when your app starts. This does add an extra dependency though.

Node

See dotenv package for Node.js

  • Install the package in your project with: 
      $ npm install --save-dev dotenv
  • Load environment variables from the “.env” file with: 
      $ dotenv -e .env
  • Test with this in a JS script: 
      console.log(process.env.API_KEY)

Python

See Python dotenv cheatsheet.

Resources