编写Linux bash脚本时if条件判断异常，选择yes反复输出==yes如何解决？

问题原因 #

你编写的条件判断语法不符合Bash的[[测试结构规范：[[与后续判断表达式之间、]]与前面的判断表达式之间必须保留空格，你代码中的[["$Response"和"Y"]]缺少必要空格，会被Bash识别为无效命令，最终导致逻辑运行异常。

修复后的可用代码 #

echo "Found a previously saved file. Do you want to continue with this? (Yes/No)"
read Response
if [[ "$Response" == "Yes" || "$Response" == "yes" || "$Response" == "y" || "$Response" == "Y" ]]; then
    echo "Success"
else
    echo "Fail"
fi

可选优化方案 #

• 统一将输入转为小写判断，减少重复的判断分支：

echo "Found a previously saved file. Do you want to continue with this? (Yes/No)"
read Response
# ${Response,,} 会将变量内容全部转为小写
if [[ "${Response,,}" =~ ^(yes|y)$ ]]; then
    echo "Success"
else
    echo "Fail"
fi

• 开启Bash不区分大小写匹配选项，简化判断逻辑：

echo "Found a previously saved file. Do you want to continue with this? (Yes/No)"
read Response
shopt -s nocasematch
if [[ "$Response" == "yes" || "$Response" == "y" ]]; then
    echo "Success"
else
    echo "Fail"
fi
# 关闭不区分大小写匹配，恢复默认行为
shopt -u nocasematch

内容的提问来源于stack exchange，提问作者Bipul Dey