use strict;
use warnings;

sub ubb_txt {
          my $txt = shift;

          return "" unless ( defined $txt);
          my ($nl) = $txt =~ m{(\cM?\cJ)};
          $txt =~ s{$nl$nl}{</p><p>}gs if (defined $nl);
          $txt =~ s{$nl}{<br>}gs if (defined $nl);

          $txt;
  }


my $test = <<'--';
One fish
Two fish

Red fish
Blue fish
--

print ubb_txt ($test), "\n";
__END__
One fish<br>Two fish</p><p>Red fish<br>Blue fish<br>