$s = 'xxaabcdabcabcecdecdxx';

$min_len = 2;
$min_rep = 2;
while($s=~/(.{$min_len,})(?=.*?\1)/g)
{
    for my $x (0..length $1) {
        @saw{ map {substr $1, $x, $_} $x+2..length $1 } = ();
    }
    pos($s) = pos($s) +1 -length $1; # fix
}
for (keys %saw)
{
        my $saw{$_} =()= $s=~/\Q$_/g;
        delete $saw{$_} if $saw{$_}<$min_rep;
}
____
a 4
ab 3
abc 3
bc 3
c 5
cd 3
d 3
e 2
ec 2
ecd 2
x 4
xx 2