老师交待的作业，不用if嵌套写了个加减乘除，大神们有BUG吗？

#!/bin/bash

read -p "Please input num1:" num1

read -p "Please input num2:" num2

read -p "Please input operator:" operator

if [ -z "$num1" -o -z "$operator" -o -z "$num2" ]

        then

        echo "输入数值有空值，请重新输入"

        exit 10

fi

test1=$( echo $num1 | sed 's/[0-9]//g' )

test2=$( echo $num2 | sed 's/[0-9]//g' )

if [ -n "$test1" -o -n "$test2" ]

        then

        echo "请输入数值" 

        exit 11

fi

if [ "$operator" == '+' ]

        then

                sum=$(( $num1 + $num2 ))

elif [ "$operator" == '-' ]

        then

                diff=$(( $num1 - $num2 ))

elif [ "$operator" == '*' ]

        then

                pro=$(( $num1 * $num2 ))

elif [ "$operator" == '/' ]

        then

                quo=$(( $num1 / $num2 ))

else

        echo "请输入正确的运算符"

        exit 12

fi

echo "运算结果：$num1 $operator $num2："$sum$diff$pro$quo