.env

person_name=Ben Ramsey

docker-compose.yml

version: '3.4'

services:
    quoter:
        image: php:cli
        environment:
            - person_name
        command:
            - php
            - -r
            - "print 'Hello ' . getenv('person_name') . PHP_EOL;"
            

gistfile1.txt

$ docker-compose up -d
$ docker-compose logs quoter
quoter_1  | Hello Ben Ramsey