docker-compose.yml

version: "3"
services:
  test:
    env_file: ./myenv
    image: alpine
    command: env

myenv

MY_VAR=yes

stdout

$ docker version
Client:
 Version:      17.06.0-ce
 API version:  1.30
 Go version:   go1.8.3
 Git commit:   02c1d87
 Built:        Fri Jun 23 21:31:53 2017
 OS/Arch:      darwin/amd64

Server:
 Version:      17.06.0-ce
 API version:  1.30 (minimum version 1.12)
 Go version:   go1.8.3
 Git commit:   02c1d87
 Built:        Fri Jun 23 21:51:55 2017
 OS/Arch:      linux/amd64
 Experimental: false
$ docker-compose version
docker-compose version 1.14.0, build c7bdf9e
docker-py version: 2.3.0
CPython version: 2.7.12
OpenSSL version: OpenSSL 1.0.2j  26 Sep 2016
$ docker-compose up
WARNING: The Docker Engine you're using is running in swarm mode.

Compose does not use swarm mode to deploy services to multiple nodes in a swarm. All containers will be scheduled on the current node.

To deploy your application across the swarm, use `docker stack deploy`.

Creating network "envfile_default" with the default driver
Creating envfile_test_1 ... 
Creating envfile_test_1 ... done
Attaching to envfile_test_1
test_1  | PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
test_1  | HOSTNAME=9152d83d9311
test_1  | MY_VAR=yes
test_1  | no_proxy=*.local, 169.254/16
test_1  | HOME=/root
envfile_test_1 exited with code 0