::might be relative|short|full|...whatever... (take it as is)
if [%FILE_INPUT%] ==  ( goto NOFILE )
:: "f"=convert to a fully qualified path, with standard naming (if input is short naming, might still look like short-naming).
for /f %%a in ("%FILE_INPUT%")do (set "FILE_INPUT_FULL_RAW=%%~fa" )
:: "s"=convert to a fully qualified path, with 8.3-naming "short-DOS-naming".
for /f %%a in ("%FILE_INPUT%")do (set "FILE_INPUT_FULL_SHORT=%%~fsa" )
echo ERROR: Argument missing.
echo Please supply a file or folder path (relative or full),
echo You may also simply drag^&drop any file or folder over this batch file to make it work..
Also at this GitHub's GIST:
', 'Any Relative PATH To A Fully Qualified