sub get_oldest_file
{
   my $path = shift;  # name of directory to search
   opendir( D, $path ) or return "Unable to read directory $path\n";

   my $oldest_age = 0;
   my $oldest_name = '';

   for ( readdir( D ))
   {
      next unless ( -f "$path/$_");
      my $age = ( -M _ );   # note the "_" : uses stat data loaded by "-f" above
      if ( $age > $oldest_age ) {
         $oldest_name = $_;
         $oldest_age = $age;
      }
   }
   closedir D;
   return $oldest_name;
}