Greetings all,
Here is my suggested solution:

#!/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;
[download]

It outputs:

ABCDEFGH<= before
 
ABCD-EFGH<= after
[download]

However this assumes you wanted to split the string in half.
Just a thought

-injunjoel