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.

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Perl

use chilkat();

$success = 0;

#  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.

$ssh = chilkat::CkSsh->new();

$sshPort = 22;
$success = $ssh->Connect("ssh.example.com",$sshPort);
if ($success == 0) {
    print $ssh->lastErrorText() . "\r\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.
$password = "mySshPassword";

$success = $ssh->AuthenticatePw("mySshLogin",$password);
if ($success == 0) {
    print $ssh->lastErrorText() . "\r\n";
    exit;
}

$channelNum = $ssh->OpenSessionChannel();
if ($channelNum < 0) {
    print $ssh->lastErrorText() . "\r\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 == 0) {
    print $ssh->lastErrorText() . "\r\n";
    exit;
}

$success = $ssh->ChannelSendString($channelNum,"uname -a\n","utf-8");
if ($success == 0) {
    print $ssh->lastErrorText() . "\r\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.
$result = $ssh->ChannelRead($channelNum);
if ($result == -1) {
    print $ssh->lastErrorText() . "\r\n";
    exit;
}

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

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

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

$output = $ssh->getReceivedText($channelNum,"utf-8");
if ($ssh->get_LastMethodSuccess() == 0) {
    print $ssh->lastErrorText() . "\r\n";
    exit;
}

print $output . "\r\n";

$ssh->Disconnect();