如何提示用户输入两个数字，然后选择使用条件语句中的算术操作员在bash脚本中使用的算术运算符？

Question

我正在尝试编程一个代码，其中提示用户输入2个数字，然后选择执行操作员。我试图运行此操作，但是如果语句不起作用，我不知道问题所在。

  echo "Enter 1st number: "
  read num1
  echo "Enter 2nd number: "
  read num2
  echo "a. Add b. Subtract c. Multiply d. Divide"
  echo "Enter Operator: "
  read opr

  if [[$opr==A]]
  then
          sum=$(($num1 + $num2))
          echo "The sum is $sum."
  elif [[$opr==B]]
  then
          diff=$(($num1 - $num2))
          echo "The difference is $diff"
  elif [[$opr==C]]
  then
          prod=$(($num1 * $num2))
          echo "The product is $prod"
  elif [[$opr==D]]
  then
          quot=$(($num1 / $num2))
          echo "The quotient is $quot"
  else
          echo "Invalid. Please enter A, B, C, and D only."
  fi

Answer 1

中的错误[[撇开，我建议使用case语句：

case $opr in
  
  A)
      sum=$(($num1 + $num2))
      echo "The sum is $sum."
      ;;
  B)
      diff=$(($num1 - $num2))
      echo "The difference is $diff"
      ;;
  C)
      prod=$(($num1 * $num2))
      echo "The product is $prod"
      ;;
  D)
      quot=$(($num1 / $num2))
      echo "The quotient is $quot"
      ;;
  *)
      echo "Invalid. Please enter A, B, C, and D only."
      ;;
esac

Answer 2

需要在所有中放置在双方平方括号之间

if [[ $opr == A ]]

如果语句：此外：bash对案例敏感，则 ：

if [[ ${opr^^} == A ]]

上面的语法将$ opr变量的值转换为大写，无论您输入什么。

Answer 3

我建议这样做：

read -p "Enter 1st number: " num1
read -p "Enter 2nd number: " num2
echo -e "a. Add b. Subtract c. Multiply d. Divide" && read -p "Enter Operator: " opr

case $opr in
    'a'|'A')
          sum=$(($num1 + $num2))
          echo "The sum is $sum.";;
    'b'|'B')
        diff=$(($num1 - $num2))
        echo "The difference is $diff";;
    'c'|'C')
        prod=$(($num1 * $num2))
        echo "The product is $prod";;
    'd'|'D')
        quot=$(($num1 / $num2))
        echo "The quotient is $quot";;
    *)
        echo "Invalid. Please enter A, B, C, and D only.";;
esac

它更清洁，并取得了理想的结果。