On 2024-01-10 Jason Loughead wrote:
Check this tutorial out for creating a systemd unit: https://linuxhandbook.com/create-systemd-services/
Also, forget about using a terminal printing "hello world" as your test basis. That's actually the opposite of what you want to do (probably). Opening "GUI things" (terminals) with background processes, like daemons being started by systemd, is harder than what it is you're actually trying to achieve, and thus counterproductive as a test case.
Instead, just see if you can get the thing to log a line to a file, which in bash would be:
echo "hello world" > /home/foo/testoutput
or even just create a file:
touch /home/foo/testfile
That way you can tell something is happening. Or if raspbian has email setup (I have no idea if it does):
mail -s 'it worked' foo@bar.com </dev/null