#!/usr/bin/perl -w
use strict;
my $string = "ABCDEFGH";
print $string."<= before\n\n";
my $regexp = '\w{'.int(length($string)/2).'}';
$string =~ s/($regexp)/$1-/;
print $string."<= after\n\n";

exit;

##</code><code>##

ABCDEFGH<= before
 
ABCD-EFGH<= after