MongoDB Compose file using string interpolation to assign values to the environment variables

docker-compose.yml

version: '3.1'

services:
  db:
    container_name: Mongo-db
    image: mongo:latest
    restart: always
    volumes:
      - ./myData:/data/db
    environment:
      - MONGO_INITDB_DATABASE=${DATABASE}
      - MONGODB_USER=${USERNAME}
      - MONGODB_PASS=${PASS}
    ports:
      - 27020:27017