I'm not sure I understand what you're looking for.

Are you looking for how parse a FASTA file? Or are you asking about how to find the >500 nucleotide sequences?

The previous responder, Anonymous Monk, provided an ideal strategy for easily reading FASTA files. My very first foray into learning Perl several years back was via the "Perl for Bioinformatics" book. It referenced that package; but I changed to a different learning text before I really did anything with that package. Hence, I don't know what all it does. It may also have utilities for doing things like you finding the kind of nucleotide sequences you're seeking.

If you're looking for strategies for finding the >500 nucleotide sequences and Anonymous Monk's suggested package doesn't help, then I'd be happy to try to help. But I don't want to invest that effort if that's not what you're after.

ack Albuquerque, NM

In reply to Re: Parse DNA fasta file by ack
in thread Parse DNA fasta file by Anonymous Monk

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