my $DIE_MSG="FATAL ERROR";

sub get_bytes_in_file_list {
    my @files = @_;
    my $size=0;

    foreach my $file (@files) {
        die "can't read $file $DIE_MSG"
          if ( !-r $file );
        if ( -d $file ) {
            opendir( DH, $file )
              or die "$! bad open directory $file $DIE_MSG\n";
            my @sub_files =
              map { "$file/$_"; }
              grep { $_ ne '.' && $_ ne '..'; } readdir(DH);

            closedir(DH) or die "$! couldn't close dir:$file\n$DIE_MSG";
            $size += get_bytes_in_file_list(@sub_files)
              if (@sub_files)    # don't check empty dir;
        }
        else {
            $size += ( stat($file) )[7];
        }
    }
    return $size;
}