thank you for your answer. It seems that my use of the :pty (and /dev/tty) could be improper.
Actually I tried to open explicitly the tty for the child process, but normally the child process
should do that itself. I have to investigate further. What puzzles me is that when I test this
function under clisp, with the equivalent syntax for run-program, less functions correctly as
expected (displays the string and then waits that I type 'q' to quit and return). I have to look