Shell – Escape sequences in output of script called from ncurses application

escape-charactersncursesshellterminaltmux

I'm currently running mcabber as my Jabber client (which uses ncurses) in a tmux session on my homeserver. Locally i run iTerm2 as a terminal emulator, which supports the triggering of growl notifications through character escape sequences.

Note: All echo in this question works like printf %b, or echo -e in bash and GNU echo.

e.g. echo "\e]9;foobar\007" makes iTerm2 send a Growl message with the text "foobar".

However, when in a tmux session, the escape sequences get eaten up. Therefore using the proprietary character escape sequence \Ptmux can be used like this: 

echo "\ePtmux;\e\e]9;foobar\007\e\\"

This triggers a growl message from within a tmux session.

However, when I use this in my mcabber event script that gets fired when a new message is received, no notification is triggerd, as if the echo is send to the wrong terminal.

I suppose this has to do with that mcabber which triggers the script is a ncurses application so the output from my normal bash script gets lost and iTerm 2 does never see it.

I also tried calling smcup without success before echoing accoring to some ideas I discovered

tput smcup
echo "\ePtmux;\e\e]9;$FROM: $MSG\007\e\\"
tput rmcup

I suppose this does not work as the issue is not switching back to the "real terminal window", but more directing the output at the ncurses window.

Any ideas on this one?

Best Answer

The reason why an event-script fails to send a "growler" message is that mcabber closes the standard input, output and error streams when it runs an event command. You can see this in hooks.c:

  if ((pid=fork()) == -1) {
    scr_LogPrint(LPRINT_LOGNORM, "Fork error, cannot launch external command.");
    g_free(datafname);
    return;   
  }    
  if (pid == 0) { // child
    // Close standard file descriptors
    close(STDIN_FILENO);
    close(STDOUT_FILENO);
    close(STDERR_FILENO);
    if (execl(extcmd, extcmd, arg_type, arg_info, bjid, arg_data,
              (char *)NULL) == -1) {
      // scr_LogPrint(LPRINT_LOGNORM, "Cannot execute external command.");
      exit(1);
    }
  }
  g_free(datafname);

That makes the event script run without interfering with the streams used by mcabber.

There is no special ncurses mode intercepting the message (after all, tmux is already running as a terminfo application). You can probably work around the problem by redirecting your echo (preferably printf) to /dev/tty, e.g.,

#!/bin/sh
printf '\033Ptmux;\033\033]9;foobar\007\033\\' >/dev/tty
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