@rl_dane @golemwire ok, nerdsniping completed.
Create a file WEISS.BAS in your DOSBOX C: or whereever:
10 X%=INP(&h3DA):OUT &h3C0,&h10:OUT &h3C0,4:COLOR 16,15:CLS
Make sure the file ends with CR+LF (I think I don’t need to spell out how for you). In case of doubt, jupp for DOS should default to CRLF mode and pressing ^OZ toggles it (the status line will show you which one is then active) in both jupp for DOS and jupp for Unix. (The change only affects newlines created AFTER that, so if you do need to toggle it, backspace/delete that newline and hit Enter to create it anew.)
Then, run gwbasic weiss on DOS. Enjoy.