envade

Cross-platform environment variable utility. I recommend including it as a dependency and using it in your npm scripts:

$ npm install --save envade

"scripts": {
  "dev": "envade NODE_ENV=development -- node index.js"
},

It can also be used as a command-line tool on Windows and Linux:

$ npm install -g envade
$ envade -- node -e "console.log(process.env.NODE_ENV)"
undefined
$ envade NODE_ENV=production -- node -e "console.log(process.env.NODE_ENV)"
production