Nix

Nix patterns

Getting a recent version of a package from nixpkgs-unstable

By default, new devenv projects are configured to use a fork of nixpkgs called devenv-nixpkgs/rolling.

devenv-nixpkgs/rolling is tested against devenv’s test suite and receives monthly updates, as well as interim stability patches that affect devenv’s most popular services and integrations.

For some packages that are updated frequently, you may want to use a more recent version from nixpkgs-unstable.

inputs:  nixpkgs:    url: github:cachix/devenv-nixpkgs/rolling  nixpkgs-unstable:    url: github:NixOS/nixpkgs/nixpkgs-unstable

devenv.yaml

{ pkgs, inputs, ... }:let  pkgs-unstable = import inputs.nixpkgs-unstable { system = pkgs.stdenv.system; };in{  packages = [    pkgs-unstable.elmPackages.elm-test-rs  ];}

devenv.nix

How do I contribute a package or a fix to nixpkgs?

For temporary fixes, we recommend using either overlays or a different nixpkgs input.

You can also consider contributing your changes back to nixpkgs. Follow the nixpkgs contributing guide to get started.

Once you’ve forked and cloned nixpkgs, test your changes with devenv:

inputs:  nixpkgs:    url: github:username/nixpkgs/branch    # Or a local path to nixpkgs    # url: path:/path/to/local/nixpkgs/clone

Add a directory to $PATH

This example adds Elixir install scripts to ~/.mix/escripts:

{ ... }:
{  languages.elixir.enable = true;
  enterShell = ''    export PATH="$HOME/.mix/escripts:$PATH"  '';}

devenv.nix

Skip the C compiler toolchain

If your project doesn’t need a C compiler toolchain, set stdenv to pkgs.stdenvNoCC to drop it from the shell. This saves a few hundred MB of storage and shell startup time:

{ pkgs, ... }: {  stdenv = pkgs.stdenvNoCC;}

devenv.nix

This is equivalent to using nixpkgs’ mkShellNoCC instead of mkShell.

Escape Nix curly braces inside shell scripts

{ pkgs, ... }: {  scripts.myscript.exec = ''    foobar=1    echo ''${foobar}  '';}

devenv.nix

Last updated Oct 08, 2026