while [ true ] ; do
        $ECHO ""
        $ECHO "PASSWORD"
        $ECHO ""
        stty -echo
        printf "%s" ">>> Please enter your PPPoE password:    "
        read PWD1
        $ECHO ""
        printf "%s" ">>> Please re-enter your PPPoE password: "
        read PWD2
        $ECHO ""
        stty echo
        if [ "$PWD1" = "$PWD2" ] ; then
            break
        fi
        printf "%s" ">>> Sorry, the passwords do not match. Try again? (y/n)"
        read ANS
        case "$ANS" in
            N|No|NO|Non|n|no|non)
                $ECHO "OK, quitting. Bye."
                exit 1
        esac
    done


,等用到在来看