为什么在Bash中[[和]]周围应该有空格? [英] Why should there be spaces around '[' and ']' in Bash?

问题描述

我试图编写一个使用if语句的Bash脚本.

I was trying to write a Bash script that uses an if statement.

if[$CHOICE -eq 1];

该脚本给了我错误，直到我在[之前和之后以及]之前给出一个空格，如下所示:

The script was giving me errors until I gave a space before and after [ and before ] as shown below:

if [ $CHOICE -eq 1 ];

我的问题是，为什么Bash中方括号周围的空间如此重要?

My question here is, why is the space around the square brackets so important in Bash?

推荐答案

一旦您意识到 [ 是 命令 ，整个过程变得更加清晰！

Once you grasp that [ is a command, a whole lot becomes clearer!

[ 是拼写"test"的另一种方法.

help [

尽管它们确实完全相同，但test却具有更详细的帮助页面.检查

However while they do exactly the same, test turns out to have a more detailed help page. Check

help test

...了解更多信息.

...for more information.

此外，请注意，我故意使用的是help test而不是man test.这是因为test和[是当今的shell内置命令.它们的功能集可能与man页面中描述的命令的coreutils的/bin/test和/bin/[不同.

Furthermore note that I'm using, by intention, help test and not man test. That's because test and [ are shell builtin commands nowadays. Their feature set might differ from /bin/test and /bin/[ from coreutils which are the commands described in the man pages.

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