How to use environment variables in package.json

In case you use .env file, let’s use grep or eval to get a value environment variable from the .env file.

Updated start2 as @Paul suggested:

"scripts": {
    "start": "NODE_ENV=$(grep NODE_ENV .env | cut -d '=' -f2) some_script",
    "start2": "eval $(grep '^NODE_ENV' .env) && some_script"
}