I popped up here
to ask
how to configure my terminal program to work together with my sketches,
realized by the given answer that my serial menu was highly dependent on
my former use cases with the Arduino GUI Serial Monitor window
but did not work well in situations like running 'screen' on the Raspberry Pi by design,
so
started to rewrite code,
adapted the other parts to fit,
deleted this and added that,
run tests over and over again,
and ended up with code that seems to work well for me now
but needs much more testing...
I like the way it went 
thanks for the given feedback so far.
If someone feels like testing the result, please do so GitHub - reppr/softboard: arduino software breadboard
It´s an example using a serial menu to access Arduino pins, a kind of 'software breadboard'.
It can be useful in development for testing hardware units, or calling your own code from the menu, before you fit it all together.
Defaults to 115200 baud.
Before I might try to implement serial menu as library I would appreciate user feedback...