No need to use while loops, use backreferences in your pattern. In the following code I make arrays of references to substrings of 2, 4 & 8 characters without converting bytes to string representations. I then test by matching each dereferenced element against the pattern and print an error if I find repeats. I test a clean string first then introduce some repeats and test it again.

use strict;
use warnings;

use 5.014;

my $str = q{};
$str   .= chr for 0 .. 31;
say qq{\n}, q{| . . . ^ . . . } x 4; 
say unpack q{H*}, $str;

for my $len ( 8, 4, 2 )
{
    say qq{\nChecking groups of $len};
    my $quant  = $len - 1;
    my @groups =
       map { \ substr $str, $_ * $len, $len }
       0 .. ( length( $str ) / $len ) - 1;

    for my $idx ( 0 .. $#groups )
    {
        say
           qq{Found @{ [ unpack q{H*}, $1 ] } },
           qq{at offset @{ [ $len * $idx ] }}
           if ${ $groups[ $idx ] } =~ m{((.)\2{$quant})};
    }
}

substr $str,  0, 2, qq{\x3e\x3e};
substr $str, 16, 8, qq{\xac} x 8;
substr $str,  4, 4, qq{\x7f} x 4;
substr $str, 26, 4, qq{\x45} x 4;
say qq{\n}, q{| . . . ^ . . . } x 4; 
say unpack q{H*}, $str;

for my $len ( 8, 4, 2 )
{
    say qq{\nChecking groups of $len};
    my $quant  = $len - 1;
    my @groups =
       map { \ substr $str, $_ * $len, $len }
       0 .. ( length( $str ) / $len ) - 1;

    for my $idx ( 0 .. $#groups )
    {
        say
           qq{Found @{ [ unpack q{H*}, $1 ] } },
           qq{at offset @{ [ $len * $idx ] }}
           if ${ $groups[ $idx ] } =~ m{((.)\2{$quant})};
    }
}

[download]

The output.


| . . . ^ . . . | . . . ^ . . . | . . . ^ . . . | . . . ^ . . . 
000102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f

Checking groups of 8

Checking groups of 4

Checking groups of 2

| . . . ^ . . . | . . . ^ . . . | . . . ^ . . . | . . . ^ . . . 
3e3e02037f7f7f7f08090a0b0c0d0e0facacacacacacacac1819454545451e1f

Checking groups of 8
Found acacacacacacacac at offset 16

Checking groups of 4
Found 7f7f7f7f at offset 4
Found acacacac at offset 16
Found acacacac at offset 20

Checking groups of 2
Found 3e3e at offset 0
Found 7f7f at offset 4
Found 7f7f at offset 6
Found acac at offset 16
Found acac at offset 18
Found acac at offset 20
Found acac at offset 22
Found 4545 at offset 26
Found 4545 at offset 28

[download]

I hope this helps you along.

Cheers,

JohnGG

In reply to Re^3: matching characters and numbers with regex by johngg
in thread matching characters and numbers with regex by james28909

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