Find Debian/Ubuntu packages without installed dependencies

bash

First of all we list packages during upgrade, that are not marked as automatically handled:

aptitude search -F '%p' --disable-columns '~U' | while read PACKAGE; do sudo apt-mark showmanual $PACKAGE; done

Second I want to find even those packages, that are already automatically handled but are still installed although nothing
installed depends on it

aptitude search -F '%p' --disable-columns '~U' | while read PACKAGE; do echo -n "$PACKAGE "; apt-cache rdepends $PACKAGE | tail +3 | while read RDEPEND; do dpkg --get-selections | egrep "^${RDEPEND}.*\s" | wc -l; done | paste -sd+ | bc; done