%%a 是什么意思？（批）

Question

%%a 是什么意思？
我了解上下文，但不了解如何使用它。例如 ：

FOR %%a in (%HELP%) DO echo I don't Know what it means

Answer 1

%%a 指的是您的 for 循环将写入的变量的名称。

引用自for /?：

FOR %variable IN (set) DO command [command-parameters]

  %variable  Specifies a single letter replaceable parameter.
  (set)      Specifies a set of one or more files.  Wildcards may be used.
  command    Specifies the command to carry out for each file.
  command-parameters
             Specifies parameters or switches for the specified command.

To use the FOR command in a batch program, specify %%variable instead
of %variable.  Variable names are case sensitive, so %i is different
from %I.

示例 1：

for %%a in (A B C D E) do Echo %%a

生产

A
B
C
D
E

示例 2：

for %%a in (A B C) do (for %%b in (1 2 3) do Echo %%a:%%b)

生产

A:1
A:2
A:3
B:1
B:2
B:3
C:1
C:2
C:3