use strict;
use warnings;

use LWP::UserAgent;

my $ua = LWP::UserAgent->new();
my $url = "http://www.perlmonks.org";
my $buffer;

$ua->get($url, ':content_cb' => \&first_chunk, ':read_size_hint' => 512 );

print $buffer;

sub first_chunk {
    my ($chunk, $response_ref, $protocol_ref) = @_;
    $buffer .= $chunk;
    die() if length($buffer) >= 512;
}