Yes, you explain better :-) The idea is that shell.nix is my development environment so I would like to use that shell.nix to interactive shells (nix-shell) and to run scripts (non-interactive use). I understand I could use a nix-shell shebang in every script, but that requires maintenance (when I modify the shell.nix file, modify the shellbang of all my scripts) and it is prune to errors (for example, modify the shell.nix and forget to modify the shebang of my scripts).