#!/usr/bin/perl
use warnings;
use strict;
# 856624

my $str = 'abccabbcabc';
my @chars = split(//, $str);
my $seen = '-';
for my $char(@chars) {
	if ($char =~ $seen ) {
		print $char . "\t|\t"; # skip the tabs and pipe if desired
	} else {
		$seen = $char;
	}
}

=head Output:
c       |       b       |
=cut