PowerShell

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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Add-Type -Path "C:\chilkat\ChilkatDotNet47-x64\ChilkatDotNet47.dll"

$success = $false

#  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 = New-Object Chilkat.Ssh

$sshPort = 22
$success = $ssh.Connect("ssh.example.com",$sshPort)
if ($success -eq $false) {
    $($ssh.LastErrorText)
    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 -eq $false) {
    $($ssh.LastErrorText)
    exit
}

$channelNum = $ssh.OpenSessionChannel()
if ($channelNum -lt 0) {
    $($ssh.LastErrorText)
    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 -eq $false) {
    $($ssh.LastErrorText)
    exit
}

$success = $ssh.ChannelSendString($channelNum,"uname -a`n","utf-8")
if ($success -eq $false) {
    $($ssh.LastErrorText)
    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 -eq -1) {
    $($ssh.LastErrorText)
    exit
}

if ($result -eq -2) {
    $("No channel data arrived before the timeout.")
}

if ($result -eq 0) {
    $("EOF or channel close was processed.  Buffered data may still remain.")
}

if ($result -gt 0) {
    $("Total bytes buffered: " + $result)
}

$output = $ssh.GetReceivedText($channelNum,"utf-8")
if ($ssh.LastMethodSuccess -eq $false) {
    $($ssh.LastErrorText)
    exit
}

$($output)

$ssh.Disconnect()