process.env.DATABASE_SERVICE_NAME is undefined #167

I dont understand if i have to set the value for all the env variables :
var mongoServiceName = process.env.DATABASE_SERVICE_NAME.toUpperCase(),
mongoHost = process.env[mongoServiceName + '_SERVICE_HOST'],
mongoPort = process.env[mongoServiceName + '_SERVICE_PORT'],
mongoDatabase = process.env[mongoServiceName + '_DATABASE'],
mongoPassword = process.env[mongoServiceName + '_PASSWORD']
mongoUser = process.env[mongoServiceName + '_USER'];

And if i have to which value is for each one of these env variables.Please help.