post_install() {
        echo "Adding '/bin/csh' to '/etc/shells'..."
        grep -qe '^/bin/csh$' etc/shells || echo '/bin/csh' >> etc/shells
}

post_upgrade() {
        post_install
}

pre_remove() {
        echo "Removing '/bin/csh' from '/etc/shells'..."
        sed -i '\|^/bin/csh$|d' etc/shells
}