VB.NET

Collect Completed SSH Commands with QuickCmdCheck

Demonstrates the Chilkat Ssh.QuickCmdCheck method, which waits for any command started by QuickCmdSend to complete. The only argument is the poll timeout in milliseconds; 0 performs a nonblocking check. It returns the channel number of a completed command, -1 when commands are still pending but none finished before the timeout, or -2 when no quick commands remain or an error occurred.

Background: This is the collection half of the concurrent pattern. Each completed channel is reported only once, so looping until -2 drains every outstanding command exactly once. Distinguish the two negative values carefully: -1 simply means "still working, ask again," while -2 means there is nothing left to wait for — or that the connection failed, so check LastErrorText when the distinction matters. Manually opened exec channels are not reported here.

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Dim success As Boolean = False

'  Demonstrates the Ssh.QuickCmdCheck method, which waits for any command started by
'  QuickCmdSend to complete.  The only argument is the poll timeout in milliseconds; 0 performs
'  a nonblocking check.

Dim ssh As New Chilkat.Ssh

Dim sshPort As Integer = 22
success = ssh.Connect("ssh.example.com",sshPort)
If (success = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


'  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.
Dim password As String = "mySshPassword"

success = ssh.AuthenticatePw("mySshLogin",password)
If (success = False) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


'  Start two commands that will finish at different times.
Dim channel1 As Integer = ssh.QuickCmdSend("sleep 2; echo first done")
If (channel1 < 0) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


Dim channel2 As Integer = ssh.QuickCmdSend("echo second done")
If (channel2 < 0) Then
    Debug.WriteLine(ssh.LastErrorText)
    Exit Sub
End If


'  Collect the results as they complete.  The return value is the channel number of a completed
'  command, -1 if commands are still pending but none finished before the timeout, or -2 when
'  no quick commands remain (or an error occurred).
Dim pollTimeoutMs As Integer = 5000
Dim completedChannel As Integer = ssh.QuickCmdCheck(pollTimeoutMs)
While completedChannel <> -2
    If (completedChannel >= 0) Then
        Dim output As String = ssh.GetReceivedText(completedChannel,"utf-8")
        If (ssh.LastMethodSuccess = False) Then
            Debug.WriteLine(ssh.LastErrorText)
            Exit Sub
        End If

        Debug.WriteLine("Channel " & completedChannel & " finished: " & output)
    End If


    If (completedChannel = -1) Then
        Debug.WriteLine("Still waiting for a command to finish...")
    End If


    completedChannel = ssh.QuickCmdCheck(pollTimeoutMs)
End While

Debug.WriteLine("All quick commands have been collected.")

ssh.Disconnect()