dotenv-expand

What is dotenv-expand?

The dotenv-expand npm package is an extension for dotenv. It allows you to have more complex .env files by enabling variable expansion within your environment variables. This means you can reference other environment variables within your .env file, which dotenv by itself does not support.

What are dotenv-expand's main functionalities?

Variable Expansion

This feature allows you to reference other variables in your .env file. For example, if you have a BASE_URL variable, you can use it to construct the API_URL variable.

require('dotenv').config();
require('dotenv-expand')(process.env);

// .env file
// BASE_URL=https://myapi.com
// API_URL=${BASE_URL}/v1

Nested Variable Expansion

This feature allows for nested variable expansion where you can use multiple environment variables to construct a new one.

require('dotenv').config();
require('dotenv-expand')(process.env);

// .env file
// URL=https://myapi.com
// VERSION=v1
// API_URL=${URL}/${VERSION}

Other packages similar to dotenv-expand

env-cmd

env-cmd is a simple node program for executing commands using an environment from an env file. It is similar to dotenv-expand in that it helps manage environment variables, but it does not support variable expansion.

cross-env

cross-env allows you to run scripts that set and use environment variables across platforms. It is similar to dotenv-expand in the sense that it helps with environment variables, but it does not support .env file variable expansion.

envfile

envfile is a package to parse and stringify the envfile format. It is similar to dotenv-expand in that it works with .env files, but it does not support variable expansion within the .env file itself.

README

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dotenv-expand

Dotenv-expand adds variable expansion on top of dotenv. If you find yourself needing to expand environment variables already existing on your machine, then dotenv-expand is your tool.

Install

# Install locally (recommended)
npm install dotenv-expand --save

Or installing with yarn? yarn add dotenv-expand

Usage

Create a .env file in the root of your project:

PASSWORD="s1mpl3"
DB_PASS=$PASSWORD

As early as possible in your application, import and configure dotenv and then expand dotenv:

var dotenv = require('dotenv')
var dotenvExpand = require('dotenv-expand')

var myEnv = dotenv.config({ processEnv: {} }) // important to set processEnv: {}, otherwise expansion will be attempted on your already existing machine envs
dotenvExpand.expand(myEnv)

console.log(process.env)

That's it. process.env now has the expanded keys and values you defined in your .env file.

Preload

You can use the --require (-r) command line option to preload dotenv & dotenv-expand. By doing this, you do not need to require and load dotenv or dotenv-expand in your application code. This is the preferred approach when using import instead of require.

$ node -r dotenv-expand/config your_script.js

The configuration options below are supported as command line arguments in the format dotenv_config_<option>=value

$ node -r dotenv-expand/config your_script.js dotenv_config_path=/custom/path/to/your/env/vars

Additionally, you can use environment variables to set configuration options. Command line arguments will precede these.

$ DOTENV_CONFIG_<OPTION>=value node -r dotenv-expand/config your_script.js

$ DOTENV_CONFIG_ENCODING=latin1 node -r dotenv-expand/config your_script.js dotenv_config_path=/custom/path/to/.env

Examples

See tests/.env.test for simple and complex examples of variable expansion in your .env file.

Documentation

DotenvExpand exposes one function:

• expand

Expand

expand will expand your environment variables.

const dotenv = {
  parsed: {
    BASIC: 'basic',
    BASIC_EXPAND: '${BASIC}',
    BASIC_EXPAND_SIMPLE: '$BASIC'
  }
}

const obj = dotenvExpand.expand(dotenv)

console.log(obj)

Options

processEnv

Default: process.env

Specify an object to write your secrets to. Defaults to process.env environment variables.

const myObject = {}
const dotenv = {
  processEnv: myObject,
  parsed: {
    SHOULD_NOT_EXIST: 'testing'
  }
}
const obj = dotenvExpand.expand(dotenv).parsed

console.log(obj.SHOULD_NOT_EXIST) // testing
console.log(myObject.SHOULD_NOT_EXIST) // testing
console.log(process.env.SHOULD_NOT_EXIST) // undefined

FAQ

What rules does the expansion engine follow?

The expansion engine roughly has the following rules:

• $KEY will expand any env with the name KEY
• ${KEY} will expand any env with the name KEY
• \$KEY will escape the $KEY rather than expand
• ${KEY:-default} will first attempt to expand any env with the name KEY. If not one, then it will return default
• ${KEY-default} will first attempt to expand any env with the name KEY. If not one, then it will return default

You can see a full list of rules here.

Contributing Guide

See CONTRIBUTING.md

CHANGELOG

See CHANGELOG.md

Who's using dotenv-expand?

These npm modules depend on it.

Changelog

11.0.3 (2024-02-11)

Changed

• 🐞 bug fix when processEnv set to process.env rather than empty object (also test fixes which hid the bug) (#113)