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

post_upgrade() {
        post_install
}

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