use Algorithm::Diff qw(LCS traverse_sequences);

my @seq1 = split //, 'abcdefghijklmnopqrstuvwxyz';
my @seq2 = split //,'flubberabcdubberdofghijklm';
my $lcs    = join '', LCS( \@seq1, \@seq2 );
print "LCS: $lcs\n";

my $lcss = lcss( \@seq1, \@seq2 );
print "All CSS: @$lcss\n";
my $index;
my $length = 0;
for( my $i = 0; $i < @$lcss; $i++ ) {
   next unless length($lcss->[$i])>$length;
   $index = $i;
   $length = length($lcss->[$i]);
}
print "LCSS: ", $lcss->[$index], "\n";
# optional sort method
print "LCSS: ", (sort{length{$a}<=>length{$b}}@$lcss)[-1];

sub lcss {
    my ( $seq1, $seq2 ) = @_;
    my ( @match, $from_match );
    my $i = 0;
    traverse_sequences( $seq1, $seq2, {
        MATCH => sub { $match[$i] .= $seq1->[$_[0]]; $from_match = 1 },
        DISCARD_A => sub { do{$i++; $from_match = 0} if $from_match },
        DISCARD_B => sub { do{$i++; $from_match = 0} if $from_match },
    });
   return \@match;
}

__DATA__
LCS: abcdefghijklm
All CSS: abcd e fghijklm
LCSS: fghijklm
LCSS: fghijklm