I have `users.defaultUserShell = pkgs.fish;` set on my server and when I ran `nixos-rebuild switch --target-host …`, the command failed with the following error:
fish: Unsupported use of '='. To run 'nix-store' with a modified environment, please use 'env PATH=… nix-store…'
That is because fish requires env to set environment variables for a program. It should also work on other shells.