Container runs systemd, what's the easiest way to execute a script that uses systemd?

I have a container that runs systemd, the setup instructions followed can be found at * [*Dockerfile for systemd base image*](https://hub.docker.com/_/centos) Now I have a script install.sh which I need to run in the build phase over the base image created above. The problem is that the install.sh is systemd aware. So what is the easiest way to have systemd's init run that install.sh, what I want is something like buildah run $ctr -- sh /tmp/install.sh But this will **not** run install.sh under systemd, as I require.