filter fasta file by size (less than)

filter_fasta.rb

#!/usr/bin/env ruby
# usage: ruby filter_fasta.rb size fasta.file 

require 'bio'

s = ARGV.shift.to_i

Bio::FlatFile.auto(ARGF) do |ff|
  ff.each do |entry|
    if entry.seq.length < s
            puts entry.seq.to_fasta(entry.definition)
    end
  end
end