Something

@echo off
cls
dir /b>> dirlist.txt
findstr /c:.bat dirlist.txt>> d.txt
del /f /q dirlist.txt
findstr /v /c:merg.bat d.txt>> dir.txt
del /f /q d.txt
for /f "tokens=*" %%G in (dir.txt) do for /f "tokens=*" %%I in (%%G) do echo %%I>> allin.bat
del /f /q dir.txt