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，得到了 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 command 符号更改了 $，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。要扩展容器内的变量，请转义 $使用 $$ :

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 shell 来扩展变量。