use strict;
use warnings;
use Data::Dumper;
use Bio::SeqIO;

my %hash; #updated.
#Reading sequence files in Fasta format
my $in=Bio::SeqIO->new(
	-file=> "sequences.fa",
	-format=>"fasta",
	);
#getting the IDs of the identical sequences into a data structure
while(my $seq=$in->next_seq()){
	#print $seq->id,$/;
	push @{$hash{$seq->seq}}, $seq->id;
	}

#print each group of identical IDs into a separate line
foreach my $key(keys %hash){
	if(scalar @{$hash{$key}}>=1){
		print scalar @{$hash{$key}},"\t";
		print "@{$hash{$key}}","\n";
		}
	}


##</code><code>##