while (<DATA>)
    {
    print $_;
    }

__DATA__
Hello world

##</code><code>##

use warnings;
use strict;

while (<DATA>)
    {
    chomp;
    my @sentences = split /(?<=\.)\s*/;
    print '>', join ("<\n>", @sentences), '<';
    }

__DATA__
Hello world. Hello Bretheren. Goodbye spaces. All I really want are sentences.

##</code><code>##

>Hello world.<
>Hello Bretheren.<
>Goodbye spaces.<
>All I really want are sentences.<