在 bash 中检查空字符串
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Checking for null string in bash
提问by ?imon Tóth
Is there any difference between the following tests?
以下测试之间有什么区别吗？
[[ "$STRING" = "" ]] && exit 1;
[[ "x$STRING" = "x" ]] && exit 1;
[[ -z $STRING ]] && exit 1;
回答by Sodved
Nope, they are all the same. But couple of defensive habits to get into.
不，他们都是一样的。但是要养成一些防御习惯。
- You should quote the
$STRINGin the-zone as well - If you are running with the -u option (I always do) then you should reference the possibly optional variable as
${STRING-}just in case its not set at all
- 你要引用
$STRING的-z一个，以及 - 如果您使用 -u 选项运行（我总是这样做），那么您应该引用可能的可选变量，
${STRING-}以防万一它根本没有设置
回答by Guilherme David da Costa
Apparently, they all do the same thing, that is check if the given string its "empty", except that the first one checks if $string its empty, the second checks whether x plus $string its equals to x and finally, -z that checks the length. Personally I'd ratter go with -z that's more realiable.
显然，他们都做同样的事情，即检查给定的字符串是否为“空”，除了第一个检查 $string 是否为空，第二个检查 x 加 $string 是否等于 x，最后，-z检查长度。我个人认为 -z 更可靠。
