Fish

fish, the Friendly Interactive Shell, is a command shell designed around user-friendliness.

Installation

A basic user-specific installation with Home Manager may look like this:

home-manager.users.myuser = {
  programs.fish.enable = true;
};

Change myuser to the username of the user you want to configure.

You can enable the fish shell and manage fish configuration and plugins with Home Manager, but to enable vendor fish completions provided by Nixpkgs you will also want to enable the fish shell in /etc/nixos/configuration.nix:

  programs.fish.enable = true;

Setting fish as your shell

Warning! As noted in the fish documentation, using fish as your *login* shell (referenced in /etc/passwd) may cause issues because fish is not POSIX compliant. In particular, this author found systemd's emergency mode to be completely broken when fish was set as the login shell.

This issue is discussed extensively on the Gentoo and Arch wikis. There they present an alternative, keeping bash as the system shell but having it exec fish when run interactively.

Here is one solution, which launches fish unless the parent process is already fish:

programs.bash = {
  interactiveShellInit = ''
    if [[ $(${pkgs.procps}/bin/ps --no-header --pid=$PPID --format=comm) != "fish" && -z ''${BASH_EXECUTION_STRING} ]]
    then
      shopt -q login_shell && LOGIN_OPTION='--login' || LOGIN_OPTION=""
      exec ${pkgs.fish}/bin/fish $LOGIN_OPTION
    fi
  '';
};

If you still want to set fish as the login shell, see Command Shell#Changing default shell.

Running fish interactively with zsh as system shell on darwin

Zsh users on darwin will need to use a modified version of the above snippet. As written, it presents two incompatibilities. First, being BSD-derived, MacOS's ps command accepts different options. Second, this is a script intended for bash, not zsh. MacOS uses zsh as its default shell.

programs.zsh = {
  initExtra = ''
    if [[ $(ps -o command= -p "$PPID" | awk '{print $1}') != 'fish' ]]
    then
        exec fish -l
    fi
  ''
};

Configuration

System wide

To enable fish plugins, add your preferred plugins to `environment.systemPackages`:

environment.systemPackages = with pkgs; [
  fishPlugins.done
  fishPlugins.fzf-fish
  fishPlugins.forgit
  fishPlugins.hydro
  fzf
  fishPlugins.grc
  grc
];

programs.fish.enable = true;

Home Manager

An example configuration in Home Manager for adding plugins and changing options could look like this:

home-manager.users.myuser = {
  programs.fish = {
    enable = true;
    interactiveShellInit = ''
      set fish_greeting # Disable greeting
    '';
    plugins = [
      # Enable a plugin (here grc for colorized command output) from nixpkgs
      { name = "grc"; src = pkgs.fishPlugins.grc.src; }
      # Manually packaging and enable a plugin
      {
        name = "z";
        src = pkgs.fetchFromGitHub {
          owner = "jethrokuan";
          repo = "z";
          rev = "e0e1b9dfdba362f8ab1ae8c1afc7ccf62b89f7eb";
          sha256 = "0dbnir6jbwjpjalz14snzd3cgdysgcs3raznsijd6savad3qhijc";
        };
      }
    ];
  };
};

Full list of home-manager options for fish can be found See also here.

See fishPlugins package set for available plugins in nixpkgs.

Useful scripts

Show that you are in a nix-shell

Add this to the fish_prompt function (usually placed in ~/.config/fish/functions/fish_prompt.fish):

set -l nix_shell_info (
  if test -n "$IN_NIX_SHELL"
    echo -n "<nix-shell> "
  end
)

and $nix_shell_info to the echo in that function, e.g.:

echo -n -s "$nix_shell_info ~>"

Now your prompt looks like this:

• outside: ~>
• inside: <nix-shell> ~>

You can directly start nix-shell in fish with nix-shell --run fish.

Environments

Here are some examples of helper functions that put you in a nix-shell with the given packages installed.

You can either put these in programs.fish.functions with home-manager or in ~/.config/fish/functions/fish_prompt.fish without.

haskellEnv

function haskellEnv
  nix-shell -p "haskellPackages.ghcWithPackages (pkgs: with pkgs; [ $argv ])"
end

# Invocation: haskellEnv package1 packages2 .. packageN

pythonEnv

function pythonEnv --description 'start a nix-shell with the given python packages' --argument pythonVersion
  if set -q argv[2]
    set argv $argv[2..-1]
  end
 
  for el in $argv
    set ppkgs $ppkgs "python"$pythonVersion"Packages.$el"
  end
 
  nix-shell -p $ppkgs
end

# Invocation: pythonEnv 3 package1 package2 .. packageN
# or:         pythonEnv 2 ..

See also

• Command Shell