是什么在一个cmd文件％和%%之间的区别？ [英] What is the difference between % and %% in a cmd file?
问题描述
我最近包括在.cmd文件类似这样的一行：
I recently included a line similar to this in a .cmd file:
for /f %%f in ('dir /b .\directory\*.sql') DO sqlcmd -b -o ".\directory\output\%%f.txt" -i ".\directory\%%f"
我原本只是用来％F，并在命令行上运行，而不是在通过文件来看，它做工精细。当我切换到%%楼它的工作的文件中。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
的（更详细的说明，可在的此Microsoft知识库。）的
三件事知道的：
- 百分号在批处理文件用于重新present命令行参数：
％1，％2... -
在他们之间的任何字符两个百分号PTED都作为变量间$ P $：
- The percent sign is used in batch files to represent command line parameters:
%1,%2, ... Two percent signs with any characters in between them are interpreted as a variable:
回声％MYVAR％
为什么？
例如，如果我们执行你（简体）命令行
For example, if we execute your (simplified) command line
FOR /f %f in ('dir /b .') DO somecommand %f
在一个批处理文件，的规则2 的会尽力间preT
in a batch file, rule 2 would try to interpret
%f in ('dir /b .') DO somecommand %
作为一个变量。为了prevent的是，你必须申请的规则3 的并与第二个逃避：％％
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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