$request = HTTP::Request->new('GET', 'http://...');
$response = $ua->request($request, '/tmp/sss');

##</code><code>##

$request = HTTP::Request->new('GET', 'http://...');
$response = $ua->request($request, \&callback);
sub callback {
   my ($data, $response, $protocol) = @_;
   ...
}

##</code><code>##

use strict;
use warnings;

use LWP ();

sub callback {
   my ($data, $response, $protocol) = @_;

   unless ($response->{'callback_first'}) {
      $response->{'callback_first'} = 1;
      my $content_type = join('; ', $response->content_type());
      print("Content-Type: $content_type\n");
      print("\n");
   }

   # print("\n########################################\n");
   print($data);
}

my $ua = LWP::UserAgent->new();
my $request = HTTP::Request->new('GET', 'http://www.perlmonks.org/');
my $response = $ua->request($request, \&callback);