%%是什么意思？批量

Question

%% a是什么意思？ 我知道背景但不知道如何使用它 有人请告诉我 例如

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

Answer 1

%%a指的是for循环将写入的变量的名称。

引自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

可生产

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)

可生产

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