try the login command, see the documentation for the module.

Otherwise, if you don't use the shell interactivly, why not use Cyrus::IMAP::Admin and do the full monty directly in perl?

use Cyrus::IMAP::Admin;

#
# assuming all necessary variables have been declared and filled accor
+dingly:
#

my $client = Cyrus::IMAP::Admin->new($host);

my $auth = {
    -mechanism => 'login',
    -service => 'imap',
    -authz => $admin,
    -user => $admin,
    -minssf => 0,
    -maxssf => 10000,
    -password => $admin_pass,
};

$client->authenticate( \%$auth);

(print $client->{error} && return(1)) if $client->{error};

# e.g. create a new mailbox:
$client->createmailbox('user.' . $mailuser);
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