#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;
use constant MIN => 2;

my $str='aabcdabcabcecdecd';

sub count {
    local $_=shift;
    my $l=length;
    my %count;
    
    for my $off (0..$l-1) {
        for my $len (MIN .. $l-$off) {
            my $s=substr $_, $off, $len;
            $count{ $s } ||= ()= /$s/g;
        }
        $count{$_} == 1 and
          delete $count{$_} for keys %count;
    }
    \%count;
}

print Dumper count $str;

__END__