I meant no critcism towards your post, but I'm not sure whether Bio::SeqIO can read a file where all the sequence is on 1 line rather than 60 chars to a line. Perhaps it can. :-)
I just wanted readers to know that there is a 'write_seq()' method so they don't have to manually, (and without error), write out the 'id', 'decscription' or 'sequence'.
Again, I didn't mean to be critical of your post, but just to make readers aware of the write_seq method. (And I wasn't aware of the 'width' method and how it might be used).