#!/usr/bin/perl -w
use strict;

my ($str);
open(DF, q{43.txt}) or die(qq{Can't open 43.txt for input: $!\n"});
{
  my @string = <DF>;
  chomp(@string);
  $str = join('', @string);
}
close(DF);

foreach my $to_consider (reverse(1..length($str) - 2)) {
  foreach my $start_at (0..length($str) - $to_consider - 1) {
    my $str1 = substr($str, $start_at, $to_consider);
    foreach my $against (1..length($str) - $to_consider) {
      if (substr($str, $start_at + $against, $to_consider) eq $str) {
        printf qq{Found at %d and %d, of length %d\n}, 
            $start_at, $start_at + $against, $to_consider;
        exit;
      }
    }
  }
}