如何在脚本中同时选择两个值？

Question

我有一个从数组创建菜单的脚本。现在，我可以从数组中选择所有8个值。我只允许同时选择两个。我该怎么办？

function db_select {
    clear
    echo "">$DB_SELECTION
    GENERIC_OPTIONS="Q W E R T Y U I"

    for DBS in $GENERIC_OPTIONS;
    do
        options=("${options[@]}" "$DBS")
    done

    menu() {
        echo "Avaliable options:"
        for i in ${!options[@]}; do
            printf "\033[32m%3d%s)\033[0m. %s\n" $((i+1)) "${choices[i]:- }" "${options[i]}"
        done
        [[ "$db_list" ]] && echo "$db_list"; :
    }

    prompt="Check an option (again to uncheck, ENTER when done): "
    while menu && read -rp "$prompt" num && [[ "$num" ]]; do
        [[ "$num" != *[![:digit:]]* ]] &&
        (( num > 0 && num <= ${#options[@]} )) ||
        { db_list="Invalid option: $num"; continue; }
        ((num--)); #db_list="${options[num]} ${choices[num]:+un}checked"
        [[ "${choices[num]}" ]] && choices[num]="" || choices[num]="+"
    done

    printf "You selected:"; msg=" nothing"
    for i in ${!options[@]}; do
        [[ "${choices[i]}" ]] && { printf " %s" "${options[i]}"; msg=""; }  && printf "%s\n" "${options[i]}" >> $DB_SELECTION && db_download_remote "${options[i]}"
    done
    echo "$msg"
    }