I have a script I want to run with a systemd timer on my user.
User Service file:
```
[Unit]
Description=BlaBla

[Service]
WorkingDirectory=/foo
ExecStart=/foo/bar.sh
```

Script to run:
```
#! /usr/bin/env nix-shell
#! nix-shell -i bash

command
```
Shell.nix:
```
with import <nixpkgs> {};
stdenv.mkDerivation {
  name = "bar_shell";
  buildInputs = [
    bar
    bash
  ];
}
```

But the unit fails with: /usr/bin/env: ‘nix-shell’: No such file or directory

Is sytemd not aware of nixos and stuff at all? Do I need to add environment paths to systemd somehow?