批处理提取指定字符后面几行的字符

a
123
1234
12345
123456
b
321
4321
54321
654321

@echo off&setlocal enabledelayedexpansion
for /f "delims=" %%a in (a.txt) do (
   !var! 
   if "%%a"=="b" set "var=set /a n+=1"
   if !n! geq 1 (
      if !n! leq 3 echo %%a
   )
)
pause