How does bot receives user command but hide message from public?

I’m thinking of a simple Rock Paper Scissors game.

I want user to type a command like !ROCK to make his decision but it should be not shown in public because if opponent notice his message, the opponent will type !PAPER to win. So basically chat bot read user’s command such as !ROCK / !PAPER , hide their commands from public and whisper users that your command is successfully received. About 10 seconds after, the result will be announced in public.(!PAPER user won)

So my question is,
How do I receive user’s command but hide them from public? Is it possible?

Thank you.

You can’t, basically

Users would have to whisper the bot
The bot may be able to reply to the whisper.

(Bots generally have problems with whispers as the whisper product is not designed for bots to use)

Basically chat doesn’t work for the use case you have described.