含if/case条件的Bash脚本执行异常，始终输出错误结果

以下是导致脚本无论输入什么都输出“It’s not the city”的常见原因及对应修正方法：

常见错误点及修正示例 #

1. 输入捕获错误 #

如果read命令没有正确将输入赋值给变量，会导致后续条件判断全不匹配。
错误写法：

echo "Enter city:"
read $city  # 错误：变量名前多了$符号

正确写法：

echo "Enter city:"
read city
# 或者带提示的写法
read -p "Enter city: " city

2. if条件判断语法错误 #

bash中[ ]和[[ ]]的语法规则不同，混用逻辑符会导致条件失效。
错误写法（[ ]中误用||）：

if [ $city = Kyiv || $city = Berlin ]  # 语法错误，[ ]不支持||
then
    echo "Valid city"
else
    echo "It’s not the city"
fi

正确写法：

# 用[ ]时用-o表示“或”，且变量必须加引号避免空值报错
if [ "$city" = "Kyiv" -o "$city" = "Berlin" -o "$city" = "California" ]
then
    # 对应逻辑处理
else
    echo "It’s not the city"
fi

# 推荐用[[ ]]，支持||/&&，语法更灵活
if [[ "$city" == "Kyiv" || "$city" == "Berlin" || "$city" == "California" ]]
then
    # 对应逻辑处理
else
    echo "It’s not the city"
fi

3. case语句格式错误 #

case分支缺少;;会导致代码继续执行到默认分支，模式后漏写)也会直接失效。
错误写法：

case $city in
    Kyiv echo "Capital of Ukraine"  # 漏写)和;;
    Berlin echo "Capital of Germany"
    *) echo "It’s not the city"
esac

正确写法：

case "$city" in
    "Kyiv")
        echo "Capital of Ukraine"
        ;;  # 终止当前分支，避免执行后续代码
    "Berlin")
        echo "Capital of Germany"
        ;;
    "California")
        echo "US State"
        ;;
    *)
        echo "It’s not the city"
        ;;
esac

4. 大小写不匹配 #

脚本中判断的是大写开头的Kyiv，如果输入小写kyiv会直接不匹配。若要忽略大小写，可开启bash的不区分大小写匹配：

shopt -s nocasematch  # 开启不区分大小写
case "$city" in
    "Kyiv") echo "Capital of Ukraine" ;;
    # ...其他分支
esac
shopt -u nocasematch  # 关闭不区分大小写（可选）

完整可运行脚本示例 #

if-elif分支结构 #

#!/bin/bash
read -p "Enter city: " city

if [[ "$city" == "Kyiv" ]]; then
    echo "Capital of Ukraine"
elif [[ "$city" == "Berlin" ]]; then
    echo "Capital of Germany"
elif [[ "$city" == "California" ]]; then
    echo "US State"
else
    echo "It’s not the city"
fi

if多条件+case语句 #

#!/bin/bash
read -p "Enter city: " city

if [[ "$city" == "Kyiv" || "$city" == "Berlin" || "$city" == "California" ]]; then
    case "$city" in
        "Kyiv") echo "Capital of Ukraine" ;;
        "Berlin") echo "Capital of Germany" ;;
        "California") echo "US State" ;;
    esac
else
    echo "It’s not the city"
fi

内容的提问来源于stack exchange，提问作者Rom24