I have a somewhat complicated .env.{dev,staging,prod} which

source .env.common-pre RAILS_ENV="staging" MYSQL_ROOT_PASSWORD="blah" MYSQL_USER="user" MYSQL_PASS="blah" MYSQL_HOST="1.2.3.4" MYSQL_DBNAME="mydb" source .env.common-post 

All three environemnts source a common .env fragment at the beginning and end. In bash it works like a charm, of course.

I use dotenv for everything programmatic like passing env vars to docker, docker-compose and I LOVE it.
I would love if dotenv was able to expand on additional .env based on bash command "source".