Rebuild FASTA

#!/usr/bin/ruby
fasta = ARGF.gets.split.drop(1).map do |in_file|
  open(in_file).slice_before(/\A>/).map do |lines|
    [lines.first.match(/\A>(\S+)/)[1], lines]
  end
end.flatten(1).to_h
ARGF.each do |line|
  out_file, *ids = line.split
  open(out_file, 'w') do |f|
    ids.each do |id|
      f.puts fasta[id].join
    end
  end
end