How to Use Environment Variables in a .env file to fill out other environment variable in the same .env file

There is no way to do this in an env_file since it is not run as a bash command. This means that the variable is not created and then concatenated into the next variable it appears in. The values are just read in as they are in the env_file.

You can actually do it like this (at least in vlucas/dotenv package (php), not sure about others, please check it yourself)

MAIL_NAME=${MAIL_FROM}

Read more about it here