ans='!'
while expr "X$ans" : "X!" >/dev/null; do
    read ans
    case "$ans" in
    !)
	sh
	echo " "
	echo -n "Your answer: "
	;;
    !*)
	set `expr "X$ans" : "X!\(.*\)$"`
	sh -c "$*"
	echo " "
	echo -n "Your answer: "
	;;
    esac
done