docker-compose，无法在 docker 容器中打印环境变量

Question

我想打印 docker-compose 文件中定义的环境变量。

这是我的docker-compose-1.yml：

version: '3.6'

services:
  busybox:
    image: busybox
    command: 'echo $DEBUG'
    environment:
      - DEBUG='123456'

并且，尝试在 docker 容器中打印 DEBUG 环境变量：

☁  environment-variables-in-compose [master] ⚡  docker-compose -f docker-compose-1.yml up
WARNING: The DEBUG variable is not set. Defaulting to a blank string.
Creating network "environmentvariablesincompose_default" with the default driver
Creating environmentvariablesincompose_busybox_1 ... done
Attaching to environmentvariablesincompose_busybox_1
busybox_1  |
environmentvariablesincompose_busybox_1 exited with code 0

如你所见，得到WARNING: The DEBUG variable is not set. Defaulting to a blank string.

我错了吗？

更新 1：

docker-compose-1.yml:

version: '3.6'

services:
  busybox:
    image: busybox
    command: 'echo $$DEBUG'
    environment:
      DEBUG: 123456

我使用双$ 符号更改command，但结果仍然不是我想要的。

☁  environment-variables-in-compose [master] ⚡  docker-compose -f docker-compose-1.yml up
Creating network "environmentvariablesincompose_default" with the default driver
Creating environmentvariablesincompose_busybox_1 ... done
Attaching to environmentvariablesincompose_busybox_1
busybox_1  | $DEBUG
environmentvariablesincompose_busybox_1 exited with code 0

如您所见，环境变量打印为$DEBUG，而不是预期值123456

Answer 1

Compose 将从您运行 compose 的环境中扩展变量。要在容器中展开变量，请使用 $$ 转义 $：

command: '/bin/sh -c "echo $$DEBUG"'

更多详情请见：https://docs.docker.com/compose/compose-file/#variable-substitution

编辑：我还在容器内添加了一个外壳来扩展变量。