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@echo off
setlocal enabledelayedexpansion
set row=2
set line=5
set file=a.txt
set newFile=b.txt 4>b.txt
set /a newLine = %line% - 1
set /a before = %row% - 1
for /l %%i in (1,1,%before%) do set "str=^^%%i:!str!"
for /f "delims=: tokens=1*" %%i in ('findstr /n .* %file% ^| findstr /ir "%str%"') do (echo.%%j)>>%newFile%
for /f "skip=%before% delims=" %%i in (%file%) do set "midRow=%%i" & goto next
:next
(echo,!midRow:~0,%newLine%!cn-dos!midRow:~%line%!)>>%newFile%
more +%row% %file% >>%newFile%
exit /b 0