while ($w =~ /((.)(\2{7}|\2{3}|\2))/sg) {
   ... do something ...
}

##</code><code>##

#!/usr/bin/perl
use strict;
use warnings;

my $t = pack "H*",
        '0a0a0a0a0b0b0a0a0c0c0c0c0c0c0c0c'
      . '1f1f2b2b2b2b3e3e7b7b7b7b7b7b7b7b'
      . '8f8f8f8f8f8f8f8f6c6c4b4b4b4b3f3f'
      . '9d9d0f0f0f0f0f0f0f0f3a3a2e2e2e2e';

repeats($t);
repeats('abbcccddddeeeeeffffffggggggghhhhhhhhiiiiiiiii');

sub repeats {
    my $w = shift;
    print "\nBYTES: ", unpack("H*",$w),"\n";
    while ($w =~ /((.)(\2{7}|\2{3}|\2))/sg) {
        my $bytes = $1;
        my $hex = unpack "H*", $bytes;
        $bytes =~ s/[\x00-\x1f\x80-\xff]/_/g;
        print "repeat: $hex ($bytes) pos:", pos($w)-length($bytes), "\n";
    }
}