- my $prefix = substr($file, 0, 3);
- my $suffix = substr($file, 3);
+ $file .= '_' x (length($file) + 1 - $prefix_length) if length($file) + 1 < $prefix_length;
+ my $prefix = substr($file, 0, $prefix_length);
+ my $suffix = substr($file, $prefix_length);