Question

我正在使用while命令编写一个shell程序，以防止被零除，并在用户键入99时退出程序。每次运行它时，我得到第二个数字的输入错误不给我答案。以下是我对此问题的尝试：

#!/bin/bash
firstNum=0
secondNum=0
answer=0
while true firstNum != 99, secondNum != 99 do
read -p "Enter first number" firstNum
read -p "Enter second number" secondNum
echo "first num $firstNum"
echo "second Num $secondNum"
if ["$secondNum" = "0"]
then
    exit 1
else
    echo "first number / second Number = $((firstNum/secondNum))"
    echo "Answer = $answer"
fi
do 
exit
done

以下是我收到的错误消息

./example.sh: 10: ./example.sh: [2: not found

非常感谢任何帮助。感谢

Answer 1

看起来像是一些错别字。

替换它：

if ["$secondNum" = "0"] then
    exit 1
then
    echo "1st number / 2nd number = $((firstNum/secondNum))"
    echo "Answer = $answer"
fi

用这个：

if [ "$secondNum" = "0" ]
then
    exit 1
else
    echo "1st number / 2nd number = $((firstNum/secondNum))"
    echo "Answer = $answer"
fi

巴什很挑剔。确保then位于下一行，与if不在同一行，您的第3行也有then而不是else。

Answer 2

您的代码可以简化

while true; do
    read -p "Enter first number: " firstNum
    [[ "$firstNum" -eq 99 ]] && break

    read -p "Enter second number: " secondNum
    case "$secondNum" in
        99) break ;;
        0) echo "div by zero, try again"; continue ;;
    esac

    echo "first number / second Number = $(bc -l <<< "$firstNum/$secondNum")"
done

我呼吁bc获取浮点运算。使用shell，你只能限制为整数。

<<<是＆＃34; here-string＆＃34;，一个传递给bc＆＃39; sdin的字符串

Answer 3

你的代码看起来对我很好，但是我稍微改变了POSIX shell测试以测试小于99而不是99本身的值。并且我删除了脚本底部附近的一个流浪do。 Bash也有[[]]样式测试语法，你可能希望在某些时候切换到它。

#!/bin/bash

firstNum=0
secondNum=0
answer=0

while [ "$firstNum" -lt 99 -a "$secondNum" -lt 99 ]
do
    read -p "Enter first number " firstNum
    read -p "Enter second number " secondNum
    printf "first num $firstNum\n"
    printf "second Num $secondNum\n"
    if [ "$secondNum" = 0 ]
    then
        printf "$secondNum was a zero, exiting!\n"
        exit 1
    else
        printf "first num / second Num = \$(($firstNum / $secondNum))\n"
        answer=$(( firstNum / secondNum))
        printf "Answer = $answer\n"
    fi
done

如果您有兴趣学习Bash测试语法[[]]（它比POSIX shell的测试（1）[]更强大），这里有一个使用的示例它：

#!/bin/bash

firstNum=0
secondNum=0
answer=0

while [[ "$firstNum" < 99 && "$secondNum" < 99 ]]
do
    read -p "Enter first number " firstNum
    read -p "Enter second number " secondNum
    printf "first num $firstNum\n"
    printf "second Num $secondNum\n"
    if [[ "$secondNum" == 0 ]]
    then
        printf "$secondNum was a zero, exiting!\n"
        exit 1
    else
        printf "first num / second Num = \$(($firstNum / $secondNum))\n"
        answer=$(( firstNum / secondNum))
        printf "Answer = $answer\n"
    fi
done

建议将测试移到while循环的主体中，而不是使用约定，而[[1]]＆＃39;创建一个连续循环。下面是一个示例（使用bash测试语法[[]]）并使用bc，因此脚本支持浮点运算：

#!/bin/bash

firstNum=0
secondNum=0
answer=0

while [[ 1 ]]
do
    read -p "Enter first number " firstNum
    read -p "Enter second number " secondNum
    printf "first num $firstNum\n"
    printf "second Num $secondNum\n"
    case "$firstNum" in
        99) printf "Invalid values\n"
            exit 1
            ;;
    esac

    case "$secondNum" in
        99) printf "Invalid values\n"
            exit 1
            ;;
         0) printf "Invalid values\n"
            exit 1
            ;;
    esac

    answer=$(printf "$firstNum / $secondNum\n" | bc -l)
    printf "Floating point supported answer using bc: = $answer \n"
done

使用shell除以零

3 个答案: