[megaloman]

Код:

@Echo Off
cls
	Set "BoxIn=Z:\Box_In"
	Set "Mask=*.txt"
	Set "Delim=."

	For /F "usebackq delims=" %%f In (`2^>nul Dir "%BoxIn%\%Mask%" /B /A:-D`) Do (
		For /F "usebackq delims=" %%s in (`type "%BoxIn%\%%f" ^& Del "%BoxIn%\%%f"`) Do (
			>>"%BoxIn%\%%f" (Echo %%s%Delim%%%~nf)
		)
	)
pause
Exit /B