Hello Monks, first-time poster, and Perl newbie here. (I'm a Java & C coder.) Thank you for reading my question.

So I am struggling to write a Perl script that uses telnet to see if a remote host is responsive. This script needn't be complex; basically, this is a "Are you alive?" test done on the remote machine. (I would normally use ICMP/ping, but my network traffic must pass through my company's firewall.) A bit of a spoiler; this question leans a lot on how to interpret the Net::Telnet module documentation. (https://metacpan.org/pod/Net::Telnet)

First, here's the behavior I'm hoping to emulate. If I manually telnet to a remote host from the command line, it looks like this:

me@ubuntu01$ telnet 10.0.0.1 1234
Trying 10.0.0.1...
Connected to 10.0.0.1.
Escape character is '^]'.
SSH-2.0-OpenSSH_7.4
[download]

That "SSH-2.0-OpenSSH_7.4" message tells me that the telnet session is successful, and the remote server opened a valid TCP/IP connection for me. I will have to manually issue a ^C character to break out of the session.

Okay, here's an example of an trying to contact a server which is unavailable:

me@ubuntu01$ telnet 10.0.0.2 1235
Trying 10.0.0.2...
[download]

Here, I get nothing back, because the remote host is down. The telnet session will ultimately fail.

So now, I contimplate how to automate these actions in Perl. Ultimately, I'd like to have a subroutine that could take a remote host by IP address (expressed as a string) and then try my telnet test:

#!/usr/bin/perl
use warnings;
use strict;
use Net::Telnet;

sub attemptTelnetCheck
{
    # host is a string, expressing an IPv4 address:
    my ($host) = @_;

    # Create a telnet object to use TCP port 1234, timeout 3 seconds:
    my $telnetObj = new Net::Telnet( Port => '1234', Timeout => 3 );

    # Set errormode to "return error message upon failure", not die im
+mediately:
    # (I'm not sure this works)
    my $telnetMode = $telnetObj->errmode("return");

    # Try to open telnet session to host:
    $telnetObj->open($host);

    # How do I check to see if $telnetObj is valid???
    if(exists($telnetObj))            # Line 22
    {
        # Close telnet session:
        $telnetObj->print('exit');
        # Return TRUE:
        return 1;
    }
    else
    {
        # Failure!  Return FALSE:
        return 0;
    }
}

if(attemptTelnetCheck('10.0.0.1')
{
    print "SUCCESS!";
}
else
{
    print "failure.";
}
[download]

So right away, you can prob tell that I really don't know what I'm doing. I've made my best attempt. Right now, the code fails with the error message:

exists argument is not a HASH or ARRAY element or a subroutine at ./te
+lnetTest.perl line 22.
[download]

Line 22 is:

if(exists($telnetObj))
[download]

I've been reading and rereading the Net::Telnet module documentation over and over, and I'm getting no-where. Does anyone have any practical advice? I'll take whatever I can get. Thank you.

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