Hate to give you the party line, but where's strict and warnings? ;-) Also, consider using the referer() method.

#!/usr/bin/perl -w
use strict;
use CGI;

my $q = new CGI;

my ($url, $ref, $sendmail) = (
    $q->url(-base),
    $q->referer,
    "/usr/sbin/sendmail",
);

# can't use list assingnment here because param()
# may return more than one value
my ($stmail, $tmail, $tnmail);
$stmail=$q->param('category');
$tmail=$q->param('email');
$tnmail=$q->param('password');
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Makeshifts last the longest.