copy file1+file2 file3

@if exist file1.txt if exist file2.txt if exist file3.txt  copy file1.txt+file2.txt+file3.txt result.txt

@echo off

echo First file:
set /p first=

echo Second file:
set /p second=

echo Third file:
set /p third=

if not exist %first%.txt goto CLOSE
if not exist %second%.txt goto CLOSE
if not exist %third%.txt goto CLOSE

copy %first%.txt+%second%.txt+%third%.txt result.txt
:CLOSE
exit

@echo off
echo Enter file name:
set /p file=

echo Enter catalog name:
set /p catalog=

cd %catalog%

DIR | SORT /+10 > %file%

pause > null
exit