cmd 文件中的 % 和 %% 有什么区别? [英] What is the difference between % and %% in a cmd file?

问题描述

我最近在 .cmd 文件中包含了与此类似的一行:

I recently included a line similar to this in a .cmd file:

for /f %%f in ('dir /b .directory*.sql') DO sqlcmd -b -o ".directoryoutput\%%f.txt" -i ".directory\%%f"

最初我只使用了 %f，它在命令行上运行时可以正常工作，但在通过文件运行时却无法正常工作.当我切换到 %%f 时，它在文件中工作.只是想知道有什么区别.

Originally I had only used %f, and it would work fine when run on the command line, but not when run through the file. When I switched to %%f, it worked in the file. Just wondering what the difference is.

推荐答案

(更详细的解释可以在 存档的 Microsoft KB 文章.)

要知道的三件事:

1. 百分号在批处理文件中用于表示命令行参数:%1、%2、...

2. 中间有任何字符的两个百分号被解释为一个变量:

1. The percent sign is used in batch files to represent command line parameters: %1, %2, ...

2. Two percent signs with any characters in between them are interpreted as a variable:

echo %myvar%

<小时>

这是为什么?

---

Why's that?

例如，如果我们执行您的(简化的)命令行

For example, if we execute your (simplified) command line

FOR /f %f in ('dir /b .') DO somecommand %f

在批处理文件中，规则 2 会尝试解释

in a batch file, rule 2 would try to interpret

%f in ('dir /b .') DO somecommand %

作为变量.为了防止这种情况发生，您必须应用规则 3 并使用第二个 % 对 % 进行转义:

as a variable. In order to prevent that, you have to apply rule 3 and escape the % with an second %:

FOR /f %%f in ('dir /b .') DO somecommand %%f

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