Just looked at the CPAN docs for this mod. Shows this example:

use Net::Telnet ();
    $t = new Net::Telnet (Timeout => 10,
                          Prompt => '/bash\$ $/');
    $t->open("sparky");
    $t->login($username, $passwd);
    @lines = $t->cmd("who");
    print @lines;
[download]

Maybe use the list that comes back from your command to trim things down to what you want, like popping of the last line or two, then printing to your output.txt file yourself? If your not looking at that doc already, it is Here