Using systemd services and timers to run scheduled maintenances jobs, I usually create dedicated scripts that I call from ExecStart since it's not suitable to put non-trivial tasks in there. That in turn makes the systemd service depend on and external file that I have to place and maintain separately from it. But most of the time I'd prefer to have self-contained services without the need for external files...
...so one day I attached a script to a service, disguised as comment block ("payload"). The service would then extract that payload from itself, put it into a script and execute that - et voilà!
To compensate for the loss of maintainability - e.g. a shellscript is developed and tested best as a shellscript, not as a comment block in a foreign file - I am creating little helpers named <something>2service.sh to assist with turning a script into a systemd service and the other way around.
You need bash.
TBD
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