while (my $line = <$DATA>){ 
    (my $file_name) = $line =~ /    
 ...........
    if ( ($file_name) and ( !$seen_file{$file_name}++ ) ) { 
	  foreach my $filename(keys %Hash_filenames) {
	  @{ $Hash_filematches{ $filename } } = grep( /\/\Q$file_name\E#/i, @{ $Hash_filenames{ $filename } });--------->@{ $Hash_filematches{ $filename } } stores only the grep of the last $file_name
	  }#for loop end
   }#if file_name end
....
for my $key (keys %Hash_filematches) {
  my $value = $Hash_filematches{$key};

   if (scalar @$value) { # check that the arrayref isn't empty
      print "KEY: $key\n";
      print "VALUES: ", join(", ", @$value), "\n\n";
   }
   }