Describe the bug

ExecStart is hard to read and write.

• Cryptic prefixes
• Surprising escaping (ref unescaping: nixos: add functions and documentation for escaping systemd Exec* directives #154113, although perhaps a clean slate is preferable nixos: add functions and documentation for escaping systemd Exec* directives #154113 (comment))

script is only suitable for a subset of use cases. (#135557, maybe other problems?)

• No prefixes
• No substitutions whatsoever
• Only ExecStart

Expected behavior

• Uphold the rule that a string is a string unless explicitly requested to be modified.
• Use module system enums instead of cryptic prefixes (or perhaps add a bool if a prefix can always be combined etc; haven't fully dissected those)
• Manage expectations: these aren't bash statements

It might look like this:

systemd.services.foo = {
  execStarts = [  # plural; it's a list
    { mode = "privileged";  # `+` prefix; TODO need to research exactly how prefixes combine
      exe = "echoAll";
      args = [ "$a" { substitute = "%i"; } ];  # escaped by default. not escaped when in { substitute = x; }
    }
  ]
}

Maybe even s/args/argv. More explicit, but also cryptic if you don't know C.

Additional context

man systemd.service (Exec* family of fields)
man systemd.unit (substitutions)

Notify maintainers

@NixOS/systemd

Metadata

Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

[user@system:~]$ nix-shell -p nix-info --run "nix-info -m"
output here