PureBasic

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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PureBasic

IncludeFile "CkSsh.pb"

Procedure ChilkatExample()

    success.i = 0

    ;  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.

    ssh.i = CkSsh::ckCreate()
    If ssh.i = 0
        Debug "Failed to create object."
        ProcedureReturn
    EndIf

    port.i = 22
    success = CkSsh::ckConnect(ssh,"172.16.16.100",port)
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    ;  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.s = "mySshPassword"

    success = CkSsh::ckAuthenticatePw(ssh,"mySshLogin",password)
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    ;  Start a shell session.
    channelNum.i = CkSsh::ckQuickShell(ssh)
    If channelNum < 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    ;  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.
    CkSsh::setCkReadTimeoutMs(ssh, 15000)

    caseSensitive.i = 1

    ;  The switch presents a prompt ending in "#".  Reading up to it confirms the session is ready.
    success = CkSsh::ckChannelReceiveUntilMatch(ssh,channelNum,"#","utf-8",caseSensitive)
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    cmdOutput.s = CkSsh::ckGetReceivedText(ssh,channelNum,"utf-8")
    If CkSsh::ckLastMethodSuccess(ssh) = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    Debug cmdOutput

    ;  Send a command and read its output up to the next prompt.
    success = CkSsh::ckChannelSendString(ssh,channelNum,"show clock" + Chr(10),"utf-8")
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    success = CkSsh::ckChannelReceiveUntilMatch(ssh,channelNum,"#","utf-8",caseSensitive)
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    ;  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 = CkSsh::ckGetReceivedText(ssh,channelNum,"utf-8")
    If CkSsh::ckLastMethodSuccess(ssh) = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    Debug cmdOutput

    ;  Additional commands follow the same send / read-to-prompt / retrieve pattern.
    success = CkSsh::ckChannelSendString(ssh,channelNum,"show version" + Chr(10),"utf-8")
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    success = CkSsh::ckChannelReceiveUntilMatch(ssh,channelNum,"#","utf-8",caseSensitive)
    If success = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    cmdOutput = CkSsh::ckGetReceivedText(ssh,channelNum,"utf-8")
    If CkSsh::ckLastMethodSuccess(ssh) = 0
        Debug CkSsh::ckLastErrorText(ssh)
        CkSsh::ckDispose(ssh)
        ProcedureReturn
    EndIf

    Debug cmdOutput

    CkSsh::ckDisconnect(ssh)


    CkSsh::ckDispose(ssh)


    ProcedureReturn
EndProcedure