Try something like this below. Since you know what the prompt is when logging in manually, use it during creation of the object. 
use Net::Telnet;
 
my $telnet3;
$telnet3 = new Net::Telnet(timeout => 10,
                Errmode => 'die'
                Prompt => '/ENTER USERNAME </');
 
$telnet3->open('10.200.16.58'); 
$telnet3->login('IATEST', 'TESTBED');
@lines = $telnet3->cmd("who");
 
 
open(FILE, ">file.txt");
 
    print FILE ("@lines\n");

print("logged in to the device.\n");

[download]
Maybe that helps?

regexes

In reply to Re^4: Net::Telnet timed out when logging in by regexes
in thread Net::Telnet timed out when logging in by poolboi

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