use warnings;
use strict;

$_ = "helloworldhellohellohihellohiworld";
my %pttrns;
PTTRN: {
 if (/\G(.{2,})(?=.*?\1)/g) {
  $pttrns{$1}++;
  SKIP: {
   my $again;
   for my $pat (keys %pttrns) {
    if (substr($_, pos, length $pat) eq $pat) {
     pos() += length($pat);
     redo SKIP;
    }
   }
  }
  redo PTTRN;
 }
}
print "[$_]\n" for keys %pttrns;

~/tmp >./tst
[world]
[hello]
[hi]