gnuwin32 程序：[.exe 的作用是什么？

发布于 2024-07-09 06:24:16 字数 469 浏览 11 评论 0 原文

查看 gnuwin32/bin 目录，有一个名为 [.exe 的奇怪程序文件，

我在文档、gnuwin32.sourceforge.net 或 google 搜索中找不到它，所以我运行它并得到：

$ [
[: missing `]'
$

所以我给它 ] 作为参数并得到

$ [ ]

$

它没有抱怨，所以我认为它处于正确的轨道上。我

$ [ hello ]

再次尝试：没有抱怨。所以我尝试了一个算术表达式：

$ [ 1 + 1 ]
[: +: binary operator expected
$

我尝试了一堆不同的组合，包括前缀和; 后缀表示法，但似乎没有任何作用。这个东西有什么作用？

原文

Looking in the gnuwin32/bin directory, there is an odd-looking program file named [.exe

I couldn't find it in the documentation, gnuwin32.sourceforge.net or in a google search, so I ran it and got:

$ [
[: missing `]'
$

so I gave it ] as a parameter and got

$ [ ]

$

It didn't complain, so I assumed it was on the right track. I tried:

$ [ hello ]

again, no complaints. so I tried an arithmetic expression:

$ [ 1 + 1 ]
[: +: binary operator expected
$

I tried a bunch of different combinations, including prefix & postfix notation but nothing seemed to work. What does this thing do?

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烟酉 2024-07-16 06:24:16

test a

[ a ]

这只是糖

编辑：澄清一下，这是条件语法，例如 [“a”=“a”]

test a

[ a ]

It's just sugar

Edit: To clarify, that's the conditional syntax, e.g. [ "a" = "a" ]

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情话难免假 2024-07-16 06:24:16

它用于评估条件表达式。
它相当于（可能是符号链接？）test 可执行文件。
手册页位于此处。

您可能会在很多 bash 脚本中看到这一点：

if [ "$LOGNAME" = "scott" ]
then
    echo "Logged in as Scott"
else
     echo "incorrect user"
fi

有趣的是， [ 不是 bash 语言的一部分，它实际上是一个可执行文件，其返回代码由“如果”。这就是为什么 [ 及其第一个参数后面的空格是强制性的 - 如果省略它，脚本将尝试执行 [ “$LOGNAME” 并失败。

您不能用它进行算术运算 - 使用 expr （请参阅此处）。
但是，您可以测试各种文件属性（是否存在？它是什么类型？等）以及对字符串和数字使用比较运算符。

It's used to evaluate conditional expressions.
It is equivalent to (possibly a symlink to?) the test executable.
The manpage is here.

You may see this in a lot of bash scripts:

if [ "$LOGNAME" = "scott" ]
then
    echo "Logged in as Scott"
else
     echo "incorrect user"
fi

The funny thing is, the [ is not part of the bash language, it's actually an executable whose return code is used by the 'IF'. This is the reason why the space after the [ and its first argument is mandatory - if it would be omitted, the script would try to execute ["$LOGNAME" and fail.

You can't do arithmetical operations with it - use expr for that (see here).
However, you can test for a wide range of file properties (does it exist? what type is it? etc) as well as use comparison operators on strings and numbers.