当环绕可变引号 [英] When to wrap quotes around a variable

问题描述

我在网上搜索，并不能找到一个答案，满足自己的好奇心。

I have searched the Internet and cannot find an answer to satisfy my own curiosity.

可能有人请告诉我，你是否应该环绕变量报价在shell脚本？

Could someone please tell me whether or not you should wrap quotes around variables in a shell script?

例如如下正确的：

xdg-open $URL 
[ $? -eq 2 ]

或者

xdg-open "$URL"
[ "$?" -eq "2" ]

如果是这样，为什么？

And if so, why?

非常抱歉，如果这是一个愚蠢的问题，但我无法找到答案。

Very sorry if this is a stupid question, but I could not find an answer.

提前感谢大家！

推荐答案

一般规则：报价，如果它可以是空的或包含空格（或任何空白真的）。引述不带空格的字符串往往导致破壳分离的一个参数为多。

General rule: quote it if it can either be empty or contain spaces (or any whitespace really). Not quoting strings with spaces often leads to the shell breaking apart a single argument into many.

$？，因为它是一个数值，不需要引号。无论 $网址需要它取决于你允许在那里，你是否还希望有一个说法，如果它是空的。

$? doesn't need quotes since it's a numeric value. Whether $URL needs it depends on what you allow in there and whether you still want an argument if it's empty.

我倾向于时常引用字符串只是出于习惯，因为它的安全的方式。

I tend to always quote strings just out of habit since it's safer that way.

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