Dockerfile
FROM ubuntu:latest ARG hoge ENV HOGE=${hoge}
$ sudo docker build ./ -t test –build-arg hoge=”abc”
$ sudo docker run -itd –rm –name my_container test:latest
$ sudo docker exec -it my_container /bin/bash
root@1ae829aee3fc:/# echo $HOGE
abc
なるほどー
次はdockerでpostfix