If you docker-compose up with this, you should see the environment var from .env passed and printed out...

Example output

> docker-compose up
Starting exampleworkingdockercomposeenvironmentvars_some_server_1
Attaching to exampleworkingdockercomposeenvironmentvars_some_server_1
some_server_1  | ENV Var Passed in: Test value from .env file!
exampleworkingdockercomposeenvironmentvars_some_server_1 exited with code 0