Stop Accidental Bourne-Shell Logouts (Unix Power Tools, 3rd Edition)

4.19. Stop Accidental Bourne-Shell Logouts

It's pretty easy to type one too many CTRL-d characters and log out of a Bourne shell without meaning to. The C shell has an ignoreeof shell variable that won't let you log out with CTRL-d. So do the Korn shell and bash; use set -o ignoreeof.

Here's a different sort of solution for the Bourne shell. When you end the shell, it asks if you're sure. If you don't answer yes, a new shell is started to replace your old one.

First, make a file like the C shell's .logout that will be read when your Bourne shell exits (Section 4.18). Save your tty (Section 2.7) name in an environment variable (Section 35.3), too -- you'll need it later:

trap Section 35.17

TTY=`tty`; export TTY
trap '. $HOME/.sh_logout; exit' 0

(Your system may need $LOGDIR instead of $HOME.) Put the following lines in your new .sh_logout file:

exec < Section 36.15, case Section 35.11, exec Section 24.2, -sh Section 3.19

exec < $TTY
echo "Do you really want to log out? \c"
read ans
case "$ans" in
[Yy]*) ;;
*)  exec $HOME/bin/-sh ;;
esac

The last line uses some trickery to start a new login shell (Section 3.19). The shell closes your tty (Section 36.15) before reading your .sh_logout file; the exec < $TTY reconnects the shell's standard input to your terminal.

Note that if your system is very slow, you may not get the reminder message for a couple of seconds -- consequently, you might forget that it's coming and walk away. That hasn't been a problem where I've tested this. If it is for you, though, replace the read ans with a program like grabchars that times out and gives a default answer after a while. There may be some Bourne shells that need other tricks -- and others that don't need these tricks -- but this should give you an idea of what to do.

--JP and SJC