I read through the direnv docs, but I'm trying to think of how I'd use it. Can you or anyone else give me some examples? Even just listing which directories you have .env or .envrc files in, and what environment variables you use in them.
Also, many scripts start by just defining a bunch of variables -- and many of those, in terms of other variables. Say, a PROJECT_ROOT directory, and a PROJECT_DOCS directory defined relative to that, etc. Then, a bunch of command parsing logic, after defining all those default values, so the user can set values of their own. Then, finally, the script can start doing the thing it was put there for in the first place.
With the .envrc approach, some of that stuff is pulled out of the script (making it shorter and simpler) and considered part of the directory environment.
[1] https://12factor.net/configExample server pattern to default to production:
if "PROJECT_IS_DEBUG" in os.environ:
DEBUG = True
ALLOWED_HOSTS = ["*"]
else:
# production configuration by default
Projects I'm on also tend to wind up with an etc/ directory that configures things like PATH and tab completions for a good baseline experience - think of it as standardizing and isolating the snippets many projects tell you to put in your ~/.bashrc to work on the project.
Direnv makes it easy to automatically load those, too.
It really did revolutionize the way I work, by making it trivial to make projects much more self-contained, the way I'd always wanted them to be but hadn't been quite sure how to achieve.
I've only used Nix for managing my personal installed package on OS X so far, but I believe direnv works really well in tandem with Nix - use a Nix file to define your project's dependencies and use direnv to automatically activate all those dependencies whenever you're in the project's directory.
It makes it a breeze to pull in a commit and set up a development harness that pokes at whatever thing I need to poke at in my local environment. And it does it without changing a line of code or command line invocation, which is a big deal in polyglot environments with various build constraints (not passing -DFLAG=thing is enormous in a big C/C++ code base, for example).
Even just being able to point whether a service is looking at a dev/production/local service/database is a big deal if you've invested in IaC and don't want to mess with any config files to do your work (as .envrc is probably in your .gitignore).
Kind of imagine if git didn't change repo when you switched directory, that was how it felt.