Recently I’ve been trying to work out how to update packages that I define declaratively in my Nix config. I think I figured out how to do it using my Nix flake. By running nix flake update and then sudo nixos-rebuild switch --flake ~/dotfiles#framework to update the packages.

However, I have some plugins say for tmux which are defined like so:

  t-smart-manager = pkgs.tmuxPlugins.mkTmuxPlugin
      pluginName = "t-smart-tmux-session-manager";
      version = "unstable-2023-06-05";
      rtpFilePath = "t-smart-tmux-session-manager.tmux";
      src = pkgs.fetchFromGitHub {
        owner = "joshmedeski";
        repo = "t-smart-tmux-session-manager";
        rev = "0a4c77c5c3858814621597a8d3997948b3cdd35d";
        sha256 = "1dr5w02a0y84q2iw4jp1psxvkyj4g6pr87gc22syw1jd4ibkn925";

Note the fetchFromGitHub function, where we specify a specific git revision to get. I was looking at ways we could update this automatically. Then I came across this tool update-nix-fetchgit. When run it will update the rev, sha256 and version for us.

Which will update various functions we use to fetch from git. All we need to do is install it then we can do something like fd .nix --exec update-nix-fetchgit. Which will run the update-nix-fetchgit on all nix files in our directory. The fd command (a find replacement) will find all nix files recursively in the current directory.

This should save us a lot of time doing it manually.


For my specific setup, I use devenv. I have added it to my devenv.nix file, and set it up with direnv. So it automatically loads a shell for me when I go navigate to the directory where my dotfiles are.

I will do a more detailed post on this setup, once I’ve played around with it more. But by devenv.nix file looks like this:

{ pkgs, ... }:

  # ....

  packages = [ pkgs.git pkgs.nixpkgs-fmt pkgs.update-nix-fetchgit ];

  # languages.nix.enable = true;
  languages.nix.enable = true;

  # pre-commit.hooks.shellcheck.enable = true;
  pre-commit.hooks = {
    nixpkgs-fmt.enable = true;

  # = "ping";

  # See full reference at

I install some packages when I run devenv shell, it makes the update-nix-fetchgit command available for me to run. Or anyone else for that matter, in a new “shell”.

Future Actions

  • Run the command automatically
  • Use with neovim to update the line under cursor see here