Dotenv-expand NPM

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:

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

dotenvExpand(dotenv.config())

console.log(process.env) // remove this after you've confirmed it is expanding

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

dotenvExpand(dotenv.config())

...

connectdb(process.env.DB_PASS)

Preload

Note: Consider using dotenvx instead of preloading. I am now doing (and recommending) so.
It serves the same purpose (you do not need to require and load dotenv), has built-in expansion support, adds better debugging, and works with ANY language, framework, or platform. – motdotla

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

dotenv-expand exposes one function:

expand

Expand

expand will expand your environment variables.

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

console.log(dotenvExpand.expand(env))

Options

processEnv

Default: process.env

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

const myEnv = {}
const env = {
  processEnv: myEnv,
  parsed: {
    HELLO: 'World'
  }
}
dotenvExpand.expand(env)

console.log(myEnv.HELLO) // World
console.log(process.env.HELLO) // 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.

How can I avoid expanding pre-existing envs (already in my `process.env`, for example `pas$word`)?

Modify your dotenv.config to write to an empty object and pass that to dotenvExpand.processEnv.

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

const myEnv = dotenv.config({ processEnv: {} }) // prevent writing to `process.env`

dotenvExpand.expand(myEnv)