The main reason your code doesn't work, is that you
have sent two \n's to the browser, before you attempt
to redirect it. Once you have sent the double carriage
returns, it's game over, anything printed to the browser
after that is considered content. That is, as long as you've
specified the Content-Type at some point before the carriage
returns.
The key is to redirect the browser, if you need to,
before printing the Content-Type, and sending the
double carriage returns.
The follow code snippet will allow you to specify a
list of bad domains, and redirects the user back to the
bad domain if a match is found:
#!/usr/bin/perl -wT
use strict;
use CGI;
use URI;
use constant BAD_DOMAINS => qw(
www.baddomain.com
);
#create lookup table
my %bad_domains;
undef @bad_domains{ BAD_DOMAINS() };
my $cgi = CGI->new;
print $cgi->redirect($cgi->referer)
if exists $bad_domains{ URI->new($cgi->referer, 'http')->host };
print $cgi->header;
#...