Swift

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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Swift


func chilkatTest() {
    var success: Bool = 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.

    let ssh = CkoSsh()!

    var port: Int = 22
    success = ssh.connect(hostname: "172.16.16.100", port: port)
    if success == false {
        print("\(ssh.lastErrorText!)")
        return
    }

    //  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.
    var password: String? = "mySshPassword"

    success = ssh.authenticatePw(login: "mySshLogin", password: password)
    if success == false {
        print("\(ssh.lastErrorText!)")
        return
    }

    //  Start a shell session.
    var channelNum: Int = ssh.quickShell().intValue
    if channelNum < 0 {
        print("\(ssh.lastErrorText!)")
        return
    }

    //  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

    var caseSensitive: Bool = true

    //  The switch presents a prompt ending in "#".  Reading up to it confirms the session is ready.
    success = ssh.channelReceive(untilMatch: channelNum, matchPattern: "#", charset: "utf-8", caseSensitive: caseSensitive)
    if success == false {
        print("\(ssh.lastErrorText!)")
        return
    }

    var cmdOutput: String? = ssh.getReceivedText(channelNum: channelNum, charset: "utf-8")
    if ssh.lastMethodSuccess == false {
        print("\(ssh.lastErrorText!)")
        return
    }

    print("\(cmdOutput!)")

    //  Send a command and read its output up to the next prompt.
    success = ssh.channelSendString(channelNum: channelNum, strData: "show clock\n", charset: "utf-8")
    if success == false {
        print("\(ssh.lastErrorText!)")
        return
    }

    success = ssh.channelReceive(untilMatch: channelNum, matchPattern: "#", charset: "utf-8", caseSensitive: caseSensitive)
    if success == false {
        print("\(ssh.lastErrorText!)")
        return
    }

    //  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: channelNum, charset: "utf-8")
    if ssh.lastMethodSuccess == false {
        print("\(ssh.lastErrorText!)")
        return
    }

    print("\(cmdOutput!)")

    //  Additional commands follow the same send / read-to-prompt / retrieve pattern.
    success = ssh.channelSendString(channelNum: channelNum, strData: "show version\n", charset: "utf-8")
    if success == false {
        print("\(ssh.lastErrorText!)")
        return
    }

    success = ssh.channelReceive(untilMatch: channelNum, matchPattern: "#", charset: "utf-8", caseSensitive: caseSensitive)
    if success == false {
        print("\(ssh.lastErrorText!)")
        return
    }

    cmdOutput = ssh.getReceivedText(channelNum: channelNum, charset: "utf-8")
    if ssh.lastMethodSuccess == false {
        print("\(ssh.lastErrorText!)")
        return
    }

    print("\(cmdOutput!)")

    ssh.disconnect()

}