use Bio::Index::Fasta;

my $idx = new Bio::Index::Fasta(-filename => 'seqs.idx',
                                -write_flag => 1);
$idx->id_parser(\&myidparser);

$idx->make_index($seqfile);
my @idlist = qw(456-3210 4670-5490);

my @seqlist;
for my $id ( @idlist ) {
 if( my $seq = $idx->get_Seq_by_acc($id) ) {
    push @seqlist, $seq;
  }
}


# define your own ID parser if you wanted to strip out
# the gb| part of the id
# alternatively don't do this and make sure the IDs
# you input exactly match the IDs of the sequences
sub myidparser {
 if( $_[0] =~ /^>\s*gb\|(\S+)/ ) {
  return $1;
 } elsif ($_[0] =~ /^>\s*(\S+)/) {
        return $1;
 } else {
     return;
 }
}