External Env File on Dockerfile

Hi everyone. I have a question about Dockerfile and I can’t find the answer on Docker documentation.
It is possible to have something like .env file for a Dockerfile?

The reason I’m looking for this is simple. I made a Laravel App and I want to distribuite it within a single container (Webserver, Database, app files, etc…) but I would like to store some values inside a diferent file instead of having them hardcoded.

I already thought in docker-compose, but my idea is to have only one single image to get easy using this service.