相关疑难解决方法(0)

我可以读取数字和操作：

echo "First number please"
read num1
echo "Second number please"
read num2
echo "Operation?"
read op

但随后我所有添加数字的尝试都失败了：

case "$op" in
  "+")
    echo num1+num2;;
  "-")
    echo `num1-num2`;;
esac

跑：

First number please
1
Second mumber please
2
Operation?
+

输出：

num1+num2

...或者...

echo $num1+$num2;;

# results in: 1+2    

...或者...

echo `$num1`+`$num2`;;

# results in: ...line 9: 1: command not found

当我尝试添加添加（“2+2”而不是“4”）时，似乎我仍然得到字符串。