Xojo Plugin

SSH Commands to a Cisco Switch

Demonstrates establishing an SSH session with a Cisco switch (or similar device) and sending commands in a device console session. Each command is sent, and its output is read up to the device's next prompt.

Note: QuickShell allocates a PTY, which is what a network device console expects. The device presents an interactive prompt, and each command's output is read up to the next prompt.

Background: Network devices differ from general-purpose servers in that they expose a menu- or prompt-driven console rather than a Unix shell, so exec requests are usually unavailable and driving the interactive console is the only option. That makes prompt matching the synchronization mechanism, and it is why a PTY is appropriate here despite the general advice to avoid one. Retrieving the received text between commands is essential: a prompt left in the buffer would make the next receive return immediately with the wrong output.

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Dim success As Boolean
success = False

//  This example requires the Chilkat API to have been previously unlocked.
//  See Global Unlock Sample for sample code.

//  Demonstrates establishing an SSH session with a Cisco switch (or similar device) and sending
//  commands in a device console session.
//  
//  Note: QuickShell allocates a PTY, which is what a network device console expects.  The device
//  presents an interactive prompt, and each command's output is read up to the next prompt.

Dim ssh As New Chilkat.Ssh

Dim port As Int32
port = 22
success = ssh.Connect("172.16.16.100",port)
If (success = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
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
password = "mySshPassword"

success = ssh.AuthenticatePw("mySshLogin",password)
If (success = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

//  Start a shell session.
Dim channelNum As Int32
channelNum = ssh.QuickShell()
If (channelNum < 0) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

//  IMPORTANT: Set a read timeout before receiving until a match.  ReadTimeoutMs defaults to 0,
//  which means no limit -- without it, this call waits forever if the received data never
//  contains a match.
ssh.ReadTimeoutMs = 15000

Dim caseSensitive As Boolean
caseSensitive = True

//  The switch presents a prompt ending in "#".  Reading up to it confirms the session is ready.
success = ssh.ChannelReceiveUntilMatch(channelNum,"#","utf-8",caseSensitive)
If (success = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

Dim cmdOutput As String
cmdOutput = ssh.GetReceivedText(channelNum,"utf-8")
If (ssh.LastMethodSuccess = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

System.DebugLog(cmdOutput)

//  Send a command and read its output up to the next prompt.
success = ssh.ChannelSendString(channelNum,"show clock" + EndOfLine.Unix,"utf-8")
If (success = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

success = ssh.ChannelReceiveUntilMatch(channelNum,"#","utf-8",caseSensitive)
If (success = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

//  Retrieving the text also clears the receive buffer, which matters: if the prompt were left
//  buffered, the next receive would match it immediately and return the wrong output.
cmdOutput = ssh.GetReceivedText(channelNum,"utf-8")
If (ssh.LastMethodSuccess = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

System.DebugLog(cmdOutput)

//  Additional commands follow the same send / read-to-prompt / retrieve pattern.
success = ssh.ChannelSendString(channelNum,"show version" + EndOfLine.Unix,"utf-8")
If (success = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

success = ssh.ChannelReceiveUntilMatch(channelNum,"#","utf-8",caseSensitive)
If (success = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

cmdOutput = ssh.GetReceivedText(channelNum,"utf-8")
If (ssh.LastMethodSuccess = False) Then
    System.DebugLog(ssh.LastErrorText)
    Return
End If

System.DebugLog(cmdOutput)

ssh.Disconnect