I see many .env files with unquoted values, like the first example in OP

   REDIS_URL=redis://localhost:6379

and it triggers me big time. Always quoting shell variable values is so deeply ingrained from very painful experiences decades ago that it still causes a somatic flashback whenever I see it.

This is what went wrong with .env

Yes, I know

    docker --env-file 

doesn't work with quotes but that's just docker being broken and why they fixed it in docker compose.

Also see jt2290's comment:

https://news.ycombinator.com/item?id=49171684