#!/usr/bin/perl

use strict; # https://perlmonks.org/?node_id=11138432
use warnings;

sub randomstring { join '', map +(qw(a b))[rand 2], 1 .. shift }

for (1 .. 10)
  {
  match( $_, randomstring(4), randomstring(4), 1);
  }

sub match
  {
  my ($n, $x, $y, $m) = @_;
  $x =~ /(.+)$(??{
    ($1 ^ substr $y, 0, length $1) =~ tr!\0!!c <= $m ? '' : '(*FAIL)'
    })/ and print "$n:($-[1],@{[ length $1 ]})($x,$y)\n";
  }