Perl

Read Data from an SSH Channel

Demonstrates the Chilkat Ssh.ChannelRead method, which reads incoming SSH channel messages. The only argument is the channel number; the ReadTimeoutMs property limits how long it waits. Received data is appended to the channel's receive buffer, then retrieved with a GetReceived... method.

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).

Background: SSH reading is a two-step pattern that trips people up at first: the Channel* read/poll methods move bytes from the network into an internal per-channel buffer, and a separate GetReceived... call hands that buffer to your code. A positive return is therefore a buffer total, not a count of what this call fetched. Note that a 0 return means EOF or close — buffered data can still remain and should be drained.

Chilkat Perl Downloads

Download Chilkat for Perl

Chilkat2 Perl

use strict;
use warnings;
use Chilkat2;

# Demonstrates the Ssh.ChannelRead method, which reads incoming SSH channel messages.  The only
# argument is the channel number.  The ReadTimeoutMs property limits how long it waits.

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, "uname -a\n", 'utf-8');
if (!$success) {
    print $ssh->LastErrorText, "\n";
    exit;
}

# 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 = $ssh->ChannelRead($channelNum);
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();