| > What’s the escape hatch to bring those into the dev environment? The function `pkgs.runCommand` is useful if you just want to run some Bash commands https://nixos.org/manual/nixpkgs/stable/#trivial-builder-run... The main difference compared to running commands in a normal terminal is that builds are sandboxed, with no network access by default: - If your commands need to download some particular files, you can have Nix fetch them separately (e.g. using `fetchurl`, `fetchGit`, etc.) and provide them to your commands via env vars. See https://nixos.org/manual/nixpkgs/stable/#chap-pkgs-fetchers - If you don't know what will be downloaded, or there's no way to run in an 'offline' mode, then you can specify hash for the result (making it a "fixed output derivation"). That will give it network access, and Nix will check that the output matches the given hash for reproducibility (you can just make up a random hash to start with; Nix will reject the result, telling you its hash, which you can copy/paste into the definition :) ) The reasons I like this approach include: - Bash is familiar/traditional and mostly-compatible with e.g. official install instructions provided by many projects, Stack Overflow answers, blog posts and tutorials, etc. - Powerful/unrestricted, in case we need to do some fiddling between some steps - Nix often reveals problems with those familiar/traditional instructions; e.g. if some deeply-nested part of an installer happens to run Python, it will fail if Python wasn't explicitly listed in its dependencies (AKA `buildInputs`). Revealing and fixing such things up-front avoids the "works on my machine" problem. - Bash commands are often tedious and inflexible; so after writing a few of these we may find ourselves wanting more structure, more reusable parts, etc. which is exactly what the helper functions in Nixpkgs provide (like `pkgs.stdenv.mkDerivation`, `pkgs.pythonPackages.buildPythonApplication`, etc.). In contrastt, starting off with those helper functions can seem overwhelming, and the benefits may be hard to appreciate immediately. |