You should put your code in <code> tags. And without knowing a little Perl this is unlikely to get you far but this is roughly equivalent. I didn't use the if block because it is unperly (to me) when there is no real else.

use strict;   # DO NOT LEAVE OUT.
use warnings; # What did I just say?!
use CGI ":standard";

my $comment;
$comment = param("comment") if request_method() eq "POST";

# Note, $comment could be undefined/uninitialized here
# but this is similar to your logical block.
[download]