The problem with doing this with a regex is you don't know whether or not there are multiple repeating substrings, and if there are, which has the most repeats. This is much better suited to a linear / hash approach, perhaps something like the following: 
use strict;
use warnings;

my (%count, $str, $size, $min);

$str = 'abczdefzabcghijklzabczaerabrtyuabcethdauthabkudiabc';
$size = 3; # Size of substrings to look for
$min = 2;  # Minimum number of times substring appears

$count{substr($str, $_, $size)}++ for 0..(length($str) - $size);

for (sort {$count{$b} <=> $count{$a} || $a cmp $b} keys %count) {
    last if $count{$_} < $min;
    print "$_ :";
    print ' '.(pos($str)-$size) while $str =~ /$_/g;
    print " ($count{$_} matches)\n";
}

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In reply to Re: Finding a repeating substring with a regex by TedPride
in thread Finding a repeating substring with a regex by chargrill

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