Proper way to search information about nixos preprocessor variables

I’m trying to use some Nix package manager variables inside the .nix configuration files. I’m learning NixOS and Nix package manager about 2 months now and I know that if I want to get information about NixOS package configuration, I can go to nixpkgs repository on GitHub( and open folder /nixos/modules There I can find .nix config files, related to different packages, with configuration options described.

So I want to know, how to get list and description of different Nix package manager variables in a similar way(or if there’s no way to do so, if there’s alternative way to get info about NixPkgs variables)
For example, in one of my NixOS configs, I use variable ${} What should I do, if I want to get all available variables inside submodule

Can the nix read-event-print-loop help you?

nix repl


nix repl
:l <nixpkgs>
:l <nixpkgs/nixos>

nix repl support tab completion. like the shell, so config. can really help.

does this help at all?

For me personally, I’m not sure how nix repl is evalating /etc/nixos/configration.nix … but it is.
I presume nix repl just looks in NIX_PATH and NIXPKGS_CONFIG, and evaluates those from there…



if you on nixos you can use the handy

nixos-option services.nginx.enable

again it supports tab smashing completion…

is this the ‘proper’ way of doing? I’m not sure, but seeing as nix and nixos has many ways of doing things, i don’t think there is any ‘standard’ or ‘proper way of doing things’. That’s what makes nix/nixos so brilliant and so terrifying at the same time.