Environment variable names, when my development environment has multiple projects
check out https://direnv.net/ it sets environment variables based on the directory you are in.

other options are:
1.docker-compose
2.plain bash to set the variables.
3. bash source .env
4. use prefixes but you would still need to set the environment you are in via an environment variable, so back to options 1-3.

if you are going to store passwords or keys in the env variables locally that are sensitive i.e not a localhost db pass, use a secrets manager like https://pkhub.io/usecases/environments, or you could script up something with aws' secrets manager