I have a perl script which, when destilled a bit, looks like this:

my $randport = int(10000 + rand(1000));          # Random port as other scripts like this run at the same time
my $localip = '192.168.100.' . ($port - 4000);   # Don't ask... backwards compatibility
system("ssh -NL $randport:$localip:23 root\@$ip -o ConnectTimeout=60 -i somekey &");    # create the tunnel in the background

sleep 10;       # Give the tunnel some time to come up

# Create the telnet object
my $telnet = new Net::Telnet(
        Timeout =>      10,
        Host    =>      'localhost',
        Port    =>      $randport,
        Telnetmode =>   0,
        Errmode =>      \&fail,
);

# SNIPPED... a bunch of parsing data from $telnet

The thing is that the target $ip is on a link with very unpredictable bandwidth, so the tunnel might come up right away, it might take a while, it might not come up at all. So a sleep is necessary to give the tunnel some time to get up and running.

So the question is: How can i test if the tunnel is up and running? 10 seconds is a really undesirable delay if the tunnel comes up straight away. Ideally, i would like to check if it's up and continue with creating the telnet object once it is, to a maximum of, say, 30 seconds.