使用默认值时访问COMPOSE_PROJECT_NAME

与COMPOSE_PROJECT_NAME docker-compose的文档相反，我似乎COMPOSE_PROJECT_NAME在我docker-compose.yml文件中访问COMPOSE_PROJECT_NAME值。

$ cat docker-compose.yml version: '3' services: web: build: . ports: - "5000:5000" environment: - "PROJECT_NAME=${COMPOSE_PROJECT_NAME}" redis: image: "redis:alpine"

该variables未设置为默认值：

$ docker-compose config|grep PROJECT WARNING: The COMPOSE_PROJECT_NAME variable is not set. Defaulting to a blank string. PROJECT_NAME: ''

传入-p foobar时也没有设置：

$ docker-compose -p foobar config|grep PROJECT WARNING: The COMPOSE_PROJECT_NAME variable is not set. Defaulting to a blank string. PROJECT_NAME: ''

将COMPOSE_NAME_PROJECT定义为使用.env文件还是将其设置在环境中的唯一方法是？