springcm

我的答案：
要求一

@echo off
setlocal enabledelayedexpansion
set n=0
set count=0
goto :loop
:up
set /a count=!n!-2
for /f "skip=%count% tokens=*" %%j in (a.txt) do (
    echo %%j>>b.txt
    goto :eof
    )
:loop
for /f "tokens=*" %%i in (a.txt) do (
    set /a n+=1
    set temp=%%i
    if "!temp:~0,4!"=="abcd" (
    echo %%i>>b.txt
    call :up
    )
    )
start b.txt
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要求二

@echo off
setlocal enabledelayedexpansion
set n=0
set count=0
goto :loop
:up
set /a count=!n!-2
for /f "skip=%count% tokens=*" %%j in (a.txt) do (
    echo %%j>>b.txt
    goto :eof
    )
:low
set /a count=!n!
for /f "skip=%count% tokens=*" %%j in (a.txt) do (
    echo %%j>>b.txt
    goto :eof
    )
:loop
for /f "tokens=*" %%i in (a.txt) do (
    set /a n+=1
    set temp=%%i
    if "!temp:~0,4!"=="abcd" (
    echo %%i>>b.txt
    call :up
    call :low
    )
    )
start b.txt
复制代码

如果原文件以abcd开头行出现的位置<2的话就要加判断语句,否则会报错.
不过按照楼主的a.txt文件,我测试是通过的.

[ 本帖最后由 springcm 于 2008-6-2 07:59 编辑 ]

springcm

:: 在标签:loop处,我用了
set /a n+=1 
:: 相当于FOR 语句每处理一行N值递增1.
set /a count=!n!-2
:: 然后把n-2赋值给变量count
复制代码