use strict;
use LWP::UserAgent;
use HTTP::Cookies;
my $cookie_jar = HTTP::Cookies->new ('file' => 'cookie.txt', 'autosave' => 1);
my $ua = LWP::UserAgent->new;
$ua->cookie_jar ($cookie_jar);

$ua->cookie_jar (HTTP::Cookies->new ('file' => 'cookie.txt', 'autosave' => 1));