检查在bash空字符串 [英] Checking for null string in bash

问题描述

有没有下面的测试有何区别？

  [$ STRING=]]＆放大器;＆安培; 1号出口;
[X $ STRING=X]]＆放大器;＆安培; 1号出口;
[[-z $ STRING]＆放大器;＆安培; 1号出口;
 

解决方案

不，他们都是一样的。但夫妇的防守习惯进入。

• 您要引用 $ STRING 在 -z 之一，也是


• 如果您正在使用-u选项（我总是这样），那么你应该引用可能可选变量 $ {运行STRING - } 以防万一它不设置在所有

Is there any difference between the following tests?

[[ "$STRING" = "" ]] && exit 1;


[[ "x$STRING" = "x" ]] && exit 1;


[[ -z $STRING ]] && exit 1;

解决方案

Nope, they are all the same. But couple of defensive habits to get into.

• You should quote the $STRING in the -z one 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

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