假如要把字串符www.cn-dos.net插入a.txt第5行前面,同时改写a.txt:
@echo off&setlocal enabledelayedexpansion
for /f "delims=" %%i in ('type a.txt') do (
     set /a n+=1
     if !n! equ 1 (
        echo %%i>a.txt
        ) else (
        if !n! equ 5 (
          echo www.cn-dos.net>>a.txt&echo %%i>>a.txt
          ) else (
          echo %%i>>a.txt
       )
    )
)     
start a.txt
如要另存为b.txt:
@echo off&setlocal enabledelayedexpansion
for /f "delims=" %%i in (a.txt) do (
     set /a n+=1
     if !n! equ 5 (
        echo www.cn-dos.net>>b.txt&echo %%i>>b.txt
        ) else (
        echo %%i>>b.txt
    )
)
start b.txt