@echo off

del hash_*  >nul 2>&1

rem process files
for %%a in (files\*) do (
  for /F %%b in ('md5sum "files/%%~nxa"') do (
    rem echo %%b - %%a

    if not exist hash_%%b (
      copy nul hash_%%b >nul 2>&1
    ) ELSE (
      echo dup: %%a
    )

  )
)