012345678901234567890123456789 ==>
01234-56789-01234<br>56789-01234-56789

##</code><code>##

#!/perl/bin/perl -w

use strict;

my $s = "012345678901234567890123456789";
print $s, "\n";

$s =~ s/(\d{5})(\d{5})(\d{5})(\d{5})(\d{5})(\d{5})/$1-$2-$3<br>$4-$5-$6/;
print $s, "\n";