Plz help me in the following code.Where is the $bio_seq. I am new to this area plz help. How can i run the code???? Its showing error message "MSG:Target sequence not defined."

use Bio::Tools::SiRNA;

my $sirna_designer = Bio::Tools::SiRNA->new( -target => $bio_seq,
                                             -rules  => 'tuschl');
my @pairs = $sirna_designer->design;

foreach $pair (@pairs) {
  my $sense_oligo_sequence = $pair->sense->seq;
  my $antisense_oligo_sequence = $pair->antisense->seq;
  # print out results
  print join ("\t", $pair->start, $pair->end, $pair->rank,
              $sense_oligo_sequence, $antisense_oligo_sequence), "\n";
}