title: How to echo environment variables in Docker
body: <p>My docker-compose.yml is:</p>
  
  <pre><code>version: '2'
  
  volumes:
    postgres_data: {}
    postgres_backup: {}
  
  services:
    postgres:
      build: ./compose/postgres
      volumes:
        - postgres_data:/var/lib/postgresql/data
        - postgres_backup:/backups
      env_file: .env
  
    django:
      build:
        context: .
        dockerfile: ./compose/django/Dockerfile
      user: django
      depends_on:
        - postgres
        - redis
      command: /gunicorn.sh
      env_file: .env
  
    nginx:
      build: ./compose/nginx
      depends_on:
        - django
  
      ports:
        - "0.0.0.0:80:80"
  
  
    redis:
      image: redis:latest
      restart: always
  </code></pre>
  
  <p>And in my .env file, I have:</p>
  
  <pre><code># PostgreSQL
  POSTGRES_PASSWORD=mysecretpass
  POSTGRES_USER=postgresuser
  </code></pre>
  
  <p>How do I test if the environment variables are effectively set?</p>
  
  <p>I've tried tu run on the remote machine:</p>
  
  <pre><code>docker run sorbetcitron_django echo $POSTGRES_USER
  </code></pre>
  
  <p>where <strong>sorbetcitron_django</strong> is my django image, but it outputs nothing.</p>