`[cpan://perldoc] [http://search.cpan.org/perldoc?WWW::Mechanize|WWW::Mechanize]':

...
Constructor and startup
  new()

    Creates and returns a new WWW::Mechanize object, hereafter referred to
    as the 'agent'.

        my $mech = WWW::Mechanize->new()

    The constructor for WWW::Mechanize overrides two of the parms to the
    LWP::UserAgent constructor:

        agent => "WWW-Mechanize/#.##"
        cookie_jar => {}    # an empty, memory-only HTTP::Cookies object
...

use WWW::Mechanize;
my $mechanize_with_a_memory_only_cookie_jar = WWW::Mechanize->new ( cookie_jar => {} );

Using an existing file of cookies with [cpan://WWW::Mechanize] can be done as follows:

...
my $agent = WWW::Mechanize->new();
my $cj = HTTP::Cookies->new(file => "/file/to/cookie_jar");
$agent->cookie_jar($cj);
...

Arjen

use WWW::Mechanize;
use HTTP::Cookies;
my $agent = WWW::Mechanize->new();
$agent->cookie_jar(HTTP::Cookies->new);