#! perl
use strict;
use warnings;

while (<DATA>)
{
    if    (/^([0-9a-fA-F]{2})\1/)
    {
        print "Found  4 repeating characters: $1$1\n";
    }
    elsif (/^([0-9a-fA-F]{4})\1/)
    {
        print "Found  8 repeating characters: $1$1\n";
    }
    elsif (/^([0-9a-fA-F]{8})\1/)
    {
        print "Found 16 repeating characters: $1$1\n";
    }
    else
    {
        print "Found  0 repeating characters\n";
    }
}

__DATA__
1234FBABCBED062405E56F853AAE238C4428FBABCBED0624
0A0AFBABCBED062405E56F853AAE238C4428FBABCBED0624
0A1B0A1BCBED062405E56F853AAE238C4428FBABCBED0624
0A1B2C3D0A1B2C3DCBED062405E56F853AAE238C4428FBAB
01230A0AFBABCBED062405E56F853AAE238C4428FBABCBED

##</code><code>##

13:12 >perl 914_SoPW.pl
Found  0 repeating characters
Found  4 repeating characters: 0A0A
Found  8 repeating characters: 0A1B0A1B
Found 16 repeating characters: 0A1B2C3D0A1B2C3D
Found  0 repeating characters

13:12 >

##</code><code>##

while (my $string = <DATA>)
{
    for my $chars (2, 4, 8)
    {
        printf "Found %2d repeating characters: %s\n", $chars * 2, $1 . $1
            if $string =~ /^([0-9a-fA-F]{$chars})\1/;
    }
}