I think I got it figured out. There already exist a UCI interface for every emulated old chess computer. It's written in lua. This is how Arena can communicate with the chess computers in UCI. I just need to figure out how I can use the keyboard (console) to send and receive UCI data. For example, if you start the Stockfish engine from a command line, you can communicate with it in UCI. How would I do that for the old chess computers? E.g. if I open a command line and type "messchess boris" the emulated chess computer starts up but I don't have UCI communications from my keyboard.

Hi John
I play against all the old chess computer ROMS on my Certabo electronic board.
Have a look on Certabo's GitHub page, it might help you but I'm not sure.
https://github.com/CERTABO/CERTABO-CHESSBOARDS-SOFTWARE

Regards
Bryan

Hi John,

A command line cannot simply send commands to a program with a graphical user interface. You need a separate, simple program that starts MessChess and then uses the standard input/output channels of this process to send commands to the program and receive the responses.

Lars

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BearChess: https://www.solanosoft.com/index.php?page=bearchess

Thanks Lars, Bryan!