npm scripts: read .env file

Question

I have a simple requirement: In my npm scripts package.json file I have the line:

{
    "scripts": {
        "example": "some-lib --argument --domain \"https://tld.com\""
    }
}

Now I want the "domain" to be factored out.

First try is to use $npm_package_config, which works:

{
    "config": {
        "domain": "https://tld.com"
    },
    "scripts": {
        "example": "some-lib --argument --domain \"$npm_package_config_domain\""
    }
}

But I want the domain loaded from an local .env file.

I did not find any solution out there to read the contents of an env file inside npm scripts on the command line.

Can somebody give me a hint to a possible solution for this problem?

Answer 1

Short answer: There's no terse way to achieve this that works cross-platform, as per your second example which references the $npm_package_config variable.

For a cross-platform solution, i.e. one that works successfully on both *nix and Windows platforms - whereby the default shell utilized by npm scripts is either sh or cmd respectively, you'll need to execute your command (i.e. the one which is currently defined in your npm-script) via a nodejs helper script. Essentially, your nodejs script will need to:

• Utilize the dotenv package to load the .env file.
• Execute the command using the nodejs built-in module; child_process.exec() or child_process.execSync().

The nodejs helper script can then be invoked via your npm-script.

The following describes how to achieve a solution that runs cross-platform.

---

Solution

1. The .env file

Firstly, lets assume we have a .env file residing in the root of our project directory. The .env file contains the following entry:

DOMAIN=https://tld.com

2. Install

The following nodejs script utilizes the dotenv package to load the environment variable(s) from the .env file. We'll need to install it. To do this cd to your project directory and run the following command:

npm i -D dotenv

3. The Node.js script (some-lib-cmd.js)

Next create a nodejs script as follows. Let's name the file some-lib-cmd.js and save it in the root of the project directory:

// Requirements...
require('dotenv').config();
const execSync = require('child_process').execSync;
const path = require("path");

/**
 * Creates a path to an executable in the node_modules/.bin directory. Each
 * path segment is joined with the appropriate platform-specific separator as
 * a delimiter.
 * @param {String} cmd The name of the executable.
 * @returns {String} The path to the executable.
 */
function getBinFile(cmd) {
  return path.join('node_modules', '.bin', cmd);
}

// Execute the command...
execSync(`${getBinFile('some-lib')} --argument --domain ${process.env.DOMAIN}`, { stdio: [0, 1, 2] });

Notes:

• If your .env file does not reside in the root of our project directory along with some-lib-cmd.js, then you can utilize dotenv's path option to define a custom path to the location of your .env file instead. For example:

  require('dotenv').config({ path: 'path/to/another/folder/' })
  

• To reference the DOMAIN variable from within the nodejs script we utilize process.env, i.e. process.env.DOMAIN.

4. package.json

In the scripts section of your package.json define the following script:

"scripts": {
  "example": "node some-lib-cmd"
}

Note: If you have chosen to save some-lib-cmd.js elsewhere, i.e. not in the in the root of your project directory, then redefine the path in your example script as necessary. For instance:

"scripts": {
  "example": "node path/to/some/folder/some-lib-cmd"
}