windows 意外“系统找不到指定的驱动器。” 在批处理文件中
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Unexpected "The system cannot find the drive specified." in batch file
提问by Matthew Strawbridge
I've got a problem with a batch file (Windows 7 x64). I've managed to reduce it to the following (there are two empty comment lines; it doesn't seem to matter whether there's an actual comment):
我的批处理文件（Windows 7 x64）有问题。我设法将其缩减为以下内容（有两个空注释行；是否有实际注释似乎并不重要）：
@echo off
if /i [%1]==[] (
echo A
::
::
echo B
)
Putting this in a batch file and then running it with no parameters produces the following output:
把它放在一个批处理文件中，然后不带参数运行它会产生以下输出：
A
The system cannot find the drive specified.
B
Deleting one of the ::lines, or deleting the surrounding if, fixesthings so you get the expected output:
删除其中::一行，或删除周围的if，修复问题，以便您获得预期的输出：
A
B
What's going on here? Why is it looking for a drive?
这里发生了什么？为什么要寻找驱动器？
Edit
编辑
Thanks for the responses for far. So my question really boils down to this:
感谢您的答复。所以我的问题实际上归结为：
What are the rules for determining whether
::means "start of comment" or "drive letter colon"?
确定是
::“评论开始”还是“驱动器号冒号”的规则是什么？
Perhaps it's easier to just switch back to REMfor adding comments so there's no scope for ambiguity, but I do find the ::style easier to read.
也许切换回REM添加评论更容易，因此没有歧义的余地，但我确实发现这种::风格更容易阅读。
回答by jeb
It's an obscoure effect in batch code blocks.
这是批处理代码块中的一种晦涩的效果。
In a code block a label in one line requires always a secondary line with quite different syntax rules (for a secondaryline).
SO: goto command not working
在代码块中，一行中的标签总是需要一个具有完全不同语法规则的辅助行（对于辅助行）。
SO：goto 命令不起作用
The secondary line must be a command or simple label, but not a parenthesis nor a double colon nor an internal command appended with a parenthesis.
第二行必须是命令或简单标签，但不能是括号、双冒号或附加括号的内部命令。
MC ND explained that the :is used here like a normal drive letter, that's really true!
But only in the secondary line and even you can suppress the error by a subst :: C:\, the line is handled like a label (You can't start anything).
MC ND 解释说，:这里使用的就像一个普通的驱动器号，这是真的！
但只有在辅助行中，甚至您可以通过 a 抑制错误subst :: C:\，该行就像标签一样处理（您无法启动任何东西）。
subst :: C:\
(
:label
::\windows\system32\calc.exe
)
And the secondary line accepts &even when the line is a label.
&即使该行是标签，辅助行也接受。
Failing samples
不合格样品
(
:Label at the end fails
)
(
:label
(
echo new Block fails
)
echo ...
)
(
:label
:: Double colon fails
)
(
:label
echo( fails also, as now a file named "echo(" is searched for execution
)
And now working ones
现在工作的
(
::Works
:with a "normal" label in the second line
)
(
:But this label! & echo This will not echo'd
:but & echo You can see this !
)
(
:label
echo or a simple command works too
)
Sometimes ::is used as a comment style, this can cause problems inside blocks, if you don't care about the secondary line.
有时::用作注释样式，如果您不关心辅助行，这可能会导致块内出现问题。
Edit: To answer your second question
编辑：回答你的第二个问题
What are the rules for determining whether :: means "start of comment" or "drive letter colon"?
确定 :: 是“评论开始”还是“驱动器号冒号”的规则是什么？
The first ::is always a comment or label, in the next line it's always a drive letter colon.
第一个::总是一个注释或标签，在下一行它总是一个drive letter colon.
回答by MC ND
::is a valid drive. Just as c:or d:but the letter is :
::是一个有效的驱动器。就像c:或d:但是字母是:
So, your lines are trying to change from the current drive to drive ::
因此，您的线路正试图从当前驱动器更改为驱动器 ::
Example: try subst :: c:\and then dir ::\
示例：尝试subst :: c:\然后dir ::\
