#! /usr/local/bin/perl -w

### NOT TESTED CODE-- I'm not a bio guy, and don't have BioPerl...

use strict;

use constant IDEAL => 250;

use Bio::SeqIO;

MAIN: {
  my $seq_file = Bio::SeqIO->new(
                                 -file => $ARGV[0],
                                 -format => 'fasta'
                                )
    or die "Couldn't open $ARGV[0]: $!; stopped";

  while ( my $seq = $seq_file->next_seq() ) {
    if ( $seq->length() > IDEAL ) {
      print $seq->seq(), "\n";
    }
  }
}