Question

I use expect in perl to do ssh, following is my code snipet.

my $exp = Expect->spawn("ssh renjithp\@192.168.1.12") or die "could not spawn ssh";
my $op = $exp->expect(undef,'renjithp>');
print "*$op*";

I wanted to handle the error if the host is not reachable (destination IP is down), I was in a impression die will hit when the ip is not reachable, but when i give a wrong IP script is not terminating and it continuous execution.

what is the right way to handle this scenario?

EDITED
I am observing $op value is 1 when the ssh is succesfull, and 0 when the destination IP is not up. is it right way to use $op to take a decision?

I have one more doubt, when the destination IP is not reachable why the control coming out of expect,i mean ‘$exp->expect(undef,’renjithp>’);’ should return only after its getting the prompt right?

Answer 1

If you need to make the ssh connection contingent on IP address reachability with the expect module, you should test connectivity with a nc first…

my $addr = "192.168.1.12";
if (system("nc -w 1 -z $addr 22")==0) {
    my $exp = Expect->spawn("ssh renjithp\@$addr") or die "could not spawn ssh";
    my $op = $exp->expect(undef,'renjithp>');
    print "*$op*";
} else {
    print "Host $addr is unreachable\n";
}

The nc command is netcat… nc -z tests for TCP port open

Alternatively, you could use a module like Net::OpenSSH that makes error handling a bit easier…

use Net::OpenSSH;

my $ssh = Net::OpenSSH->new($host);
$ssh->error and
   die "Couldn't establish SSH connection: ". $ssh->error;