Code:
# Both vars are undefined
[ ! "$DESTDIR" ] && echo "TRUE that '\$DESTDIR' doesn't exist!"
[ "$changing_kern" ] || echo "TRUE that '\$changing_kern' doesn't exist!"
echo
# NONE if statement, should echo anything !!!
# + [ ! '' -a '' ]
if [ ! "$DESTDIR" -a "$changing_kern" ]; then
echo "If statement returned TRUE, with '-a'"
fi
# + [ ! '' ]
# + [ '' ]
if [ ! "$DESTDIR" ] && [ "$changing_kern" ]; then
echo "If statement returned TRUE, with '&&'"
fi