multiple git identities with home-manager and fzf

If you have multiple git identities (a personal and a work email, say) and would like to use both in different projects on the same machine it can be a hassle. Hopefully you've never committed to your work repo with your personal email address! If this happens you're looking at an unwieldy git filter-branch invocation to fix it.

To avoid the issue in the future you can use a feature of git called conditional includes, but I still find them easy to forget to include in each repo that needs a different identity (and I don't use a separate ~/dev/work and ~/dev/personal so there isn't a good place to set and forget them). I found the solution that works best for me in a blog post by Micah Henning. You should go check it out, but I'm quoting the first paragraph because it is almost exactly the solution I was looking for.

Working on many projects across multiple identities can be difficult to manage. This is a procedure for leveraging git aliases to set an identity at the project level for any project with support for GPG-based commit signing.

Henning's needs include PGP which I won't be touching on here, but my approach will work if you do need pgp keys as well. The other difference is that I use home-manager which allow you to declaratively define all your dotfiles including their dependencies (copy your home.nix to a new machine and watch as everything is setup just the way you want it, it's magical the first time you see it work). home-manager uses nix as a package manager. The downside (such as it is) is that nix wants everything in the nix language so that it can track it and give you atomic upgrades and painless rollbacks.

So, with the table-setting out of the way, how did I combine the ideas of the git config in Henning's blog post with the git support in home-manager? It starts with a home.nix that contains at least


{ config, pkgs, ... }:

  # Let Home Manager install and manage itself.
  programs.home-manager.enable = true;
  targets.genericLinux.enable = true;

  imports = [
  # This value determines the Home Manager release that your
  # configuration is compatible with. This helps avoid breakage
  # when a new Home Manager release introduces backwards
  # incompatible changes.
  # You can update Home Manager without changing this value. See
  # the Home Manager release notes for a list of state version
  # changes in each release.
  home.stateVersion = "20.03";

The important piece here is:

imports = [

when you import ./git in your home.nix it will attempt to import the file called default.nix from that directory.


{ config, lib, pkgs, ... }:

  # put a shell script into the nix store
  gitIdentity =
    pkgs.writeShellScriptBin "git-identity" (builtins.readFile ./git-identity);
in {
  # we will use the excellent fzf in our `git-identity` script, so let's make sure it's available
  # let's add the gitIdentity script to the path as well
  home.packages = with pkgs; [

  programs.git = {
    enable = true;
    extraConfig = {
      # extremely important, otherwise git will attempt to guess a default user identity. see `man git-config` for more details
      user.useConfigOnly = true;

      # the `work` identity = "Spider-Man"; = "";

      # the `personal` identity = "Peter Parker"; = "";
      # I think spider-man might be peter parker! somebody get j jonah jameson on the line
    # This is optional, as `git identity` will call the `git-identity` script by itself, however
    # setting it up explicitly as an alias gives you autocomplete
    aliases = {
      identity = "! git-identity";
      id = "! git-identity";


the default.nix relies on a script called git-identity

  gitIdentity =
    pkgs.writeShellScriptBin "git-identity" (builtins.readFile ./git-identity);
in {

so let's go ahead and create it. It is also in the ./git directory


#!/usr/bin/env bash

# get each set of usernames from the git config (which will be generated from our `default.nix` above)
IDENTITIES=$(git config --global --name-only --get-regexp "user.*" | sed -e 's/^user.//' -e 's/.name$//')
# filter them with fzf
ID=$(echo "${IDENTITIES}" | fzf -e -1 +m -q "$1")
if ! git config --global --get-regexp "user.${ID}.name" > /dev/null; then
    echo "Please use a valid git identity
    git config --global --name-only --get-regexp "user.*" | sed -e 's/^user.//' -e 's/.name$//' -e 's/^/\t/'
    exit 1
# set the ID locally in each repo (eg in the repo's .git/config)
git config "$(git config user.${ID}.name)"
git config "$(git config user.${ID}.email)"

echo "Name: $(git config"
echo "Email: $(git config"

To make that all a little more concrete, once that is all in your home.nix and ./git, run

home-manager switch

and attempt to commit something to your favorite repo

ยป git commit
Author identity unknown

*** Please tell me who you are.


  git config --global ""
  git config --global "Your Name"

to set your account's default identity.
Omit --global to set the identity only in this repository.

fatal: no email was given and auto-detection is disabled

simply type git identity to get an fzf-powered list of all your various identities.