to be pedantic, if you're using `tmux`, you're already in a "box" and are using what amounts to a "nested terminal emulator" Emacs and Vim are perfectly capabl

to be pedantic, if you're using `tmux`, you're already in a "box" and are using what amounts to a "nested terminal emulator" Emacs and Vim are perfectly capable of taking arbitrary strings (which can be lines from the same terminal buffer that match a given regex) and putting them onto the command line of a terminal buffer. And more importantly, you can customize that whole process without writing C.