split line at period

#!/usr/bin/perl
use strict;
use warnings;
use utf8;
use open qw(:encoding(utf8) :std);
open my $in, '<', 'dat' or die;
my $prev = 0;
while (<$in>) {
  chomp;
  if (/\A\.\z/) {
    print ".\n";
    $prev = 0;
    next;
  }
  if ($prev) {
    print ' ';
  }
  print $_;
  $prev = $_;
}