Issue description

I'm currently trying to write a script to interactively pipe-panes. Part of this involves asking the user which direction they want the pipe to go (in, out, both), followed by the command name and confirming whether they'd like to kill an open pipe.

command-prompt by itself doesn't have a flag to output the result to stdout so I've been trying to do indirectly through display-message but It seems to me that the command-prompt command implicitly runs a subshell which captures the output preventing my script from recieving it.

For example I have a script ~/tmux-pipe-ctrl which I've bound to | (bind | $HOME/tmux-pipe-ctrl) containing this:

choice=$(tmux command-prompt -1 -p "Direction (i|o|b):" "display-message -p '%%'")

How do I access the command-prompt result from within my script?

If there's no way (as of yet) I'd like to propose a flag that dumps the prompts result to stdout.

Required information

Please provide the following information:

• tmux version (tmux -V). tmux next-3.3
• Platform (uname -sp). Linux unknown
• $TERM inside and outside of tmux (echo $TERM). screen-256color
• Logs from tmux (tmux kill-server; tmux -vv new).