打出来的结果有问题

脚本如下

#!/bin/bash

read -t 30 -p "请输入数值1：" num1

read -t 30 -p "请输入数值2：" num2

read -t 30 -p "请输入运算符：" ope

if [ -n "$num1" -a -n "$num2" -a -n "$ope" ]

then

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

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

if [ -z "$test1" -a -z "$test2" ]

then

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

then

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

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

then

sum = $(($num1-$num2))

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

then

sum = $(($num1*$num2))

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

then

sum = $(($num1/$num2))

else

echo "只支持加减乘除四种运算符！"

exit 10

fi

else

echo "必须输入数字！"

exit 11

fi

else

echo "输入的数值或运算符不能为空！"

exit 12

fi

echo "$num1 $ope $num2 = $sum"