function checkUpdate() {
    lastUpdateFile=$HOME/.config/last-system-update

    if [ ! -f "$lastUpdateFile" ]; then
        echo "this system hasn't ever been updated using system-upgrade.sh"
        echo "run system-upgrade.sh now"
        return
    fi

    lastUpdate=$(cat $lastUpdateFile)
    now=$(date "+%s")

    if [ $(( $now - $lastUpdate > 604800 )) ]; then
        echo "this system hasn't been updated for over a week"
        echo "run system-upgrade.sh asap"
        return
    fi
}

checkUpdate