You could also use the scan() method to duplicate the stored cookies. It takes a callback which is invoked for each cookie and given arguments in the same order needed for set_cookie()

my $cookie_jar = HTTP::Cookies->new();
# ...
my $netscape_cookie_jar = HTTP::Cookies::Netscape->new();
my $callback = sub {
    $netscape_cookie_jar->set_cookie(@_);
};
$cookie_jar->scan( $callback );
$netscape_cookie_jar->save("mycookies.txt");
[download]