No, there are alternatives like runit and SMF that do not use shell scripts.

Its conveniently ignored by systemd-supporters and the conversation always revolves around the fact that we used to use shell scripts. Despite the fact that there are sensible inits that predate systemd that did not use shell languages.

Hey, systemd supporter here and yes, I do ignore runit and SMF.

systemd is great and has essentially solved the system management problem once and for all. it's license is open enough not to worry about it.

SMF is proprietary oracle stuff.

Runit... tried a few years ago on void linux (I think?) and was largely unimpressed.

Runit absolutely uses shell scripts. All services are started via a shell script that exec's the final process with the right environment / arguments. If you use runit as your system init, the early stages are also shell scripts.