Poll an SSH Channel for Incoming Data

See more SSH Examples

Demonstrates the Chilkat Ssh.ChannelPoll method, which polls a channel for incoming messages, waiting at most the given number of milliseconds. The first argument is the channel number and the second is the poll timeout; pass 0 for a nonblocking poll.

The integer return value is -1 on error, -2 if nothing arrived before the timeout, 0 if EOF or channel close was processed, or — when greater than 0 — the total bytes currently buffered for the channel (not the bytes newly received by this call).

use strict;
use warnings;
use Chilkat2;

# Demonstrates the Ssh.ChannelPoll method, which polls a channel for incoming messages, waiting
# at most the given number of milliseconds.  The 1st argument is the channel number and the 2nd
# is the poll timeout.  Pass 0 for a nonblocking poll.

my $ssh = Chilkat2::Ssh->new;

my $sshPort = 22;
my $success = $ssh->Connect('ssh.example.com', $sshPort);
if (!$success) {
    print $ssh->LastErrorText, "\n";
    exit;
}

# Normally you would not hard-code the password in source.  You should instead obtain it
# from an interactive prompt, environment variable, or a secrets vault.
my $password = 'mySshPassword';

$success = $ssh->AuthenticatePw('mySshLogin', $password);
if (!$success) {
    print $ssh->LastErrorText, "\n";
    exit;
}

my $channelNum = $ssh->OpenSessionChannel();
if ($channelNum < 0) {
    print $ssh->LastErrorText, "\n";
    exit;
}

# Start a shell WITHOUT requesting a PTY.  Without a PTY the shell sees it is connected to a
# raw data pipe and enters non-interactive mode: it suppresses the command prompt, does not
# echo typed commands back, and skips interactive login scripts.  The output is therefore
# clean and easily parseable -- but because no prompt is ever sent, code must not wait for
# one.  Instead, have each command print a predictable marker, or wait for EOF / channel close.
$success = $ssh->SendReqShell($channelNum);
if (!$success) {
    print $ssh->LastErrorText, "\n";
    exit;
}

$success = $ssh->ChannelSendString($channelNum, "date\n", 'utf-8');
if (!$success) {
    print $ssh->LastErrorText, "\n";
    exit;
}

# Wait up to 3 seconds for channel data.
my $pollTimeoutMs = 3000;
# The return value is: -1 on error, -2 if nothing arrived before the timeout, 0 if EOF or
# channel close was processed, or the total number of buffered bytes when greater than 0.
my $result = $ssh->ChannelPoll($channelNum, $pollTimeoutMs);
if ($result == -1) {
    print $ssh->LastErrorText, "\n";
    exit;
}

if ($result == -2) {
    print "No channel data arrived before the timeout.\n";
}

if ($result == 0) {
    print "EOF or channel close was processed.  Buffered data may still remain.\n";
}

if ($result > 0) {
    print 'Total bytes buffered: ', $result, "\n";
}

my $output = $ssh->GetReceivedText($channelNum, 'utf-8');
if (!$ssh->LastMethodSuccess) {
    print $ssh->LastErrorText, "\n";
    exit;
}

print $output, "\n";

$ssh->Disconnect();