my $s1 = 'abcdefghijklmnopqrstuvwxyzabcdefgab';
my $s2 = 'abcdefgab';
my $MIN_LENGTH = 2;
my @subseq = ();

for my $i (0..length($s2)-$MIN_LENGTH) {
    for my $j ($MIN_LENGTH..length($s2)-$i) {
        push @subseq, substr($s2,$i,$j);
    }
}
print "$_\n" for @subseq;

@subseq = sort{length($b)<=>length($a)}@subseq;

SUBSEQ:
for my $subseq (@subseq) {
    for my $i (0..length($s1)-length($subseq)) {
        if ($subseq eq substr($s1,$i,length($subseq))) {
            print "Match $subseq @ $i\n";
            #last SUBSEQ
        }
    }
}