webpack --config build/webpack.config.js

VAR_A=Hello World
VAR_B=format the .env file like this with new vars separated by a line break

# in config/servers/web.js
exports.production = {
  servers: {
    web: function(api){
      return {
       port: process.env.PORT
      }
    }
  }
}

"scripts": {
  "aaa": "set TMP=test && npm run bbb",
  "bbb": "echo %TMP%"
}