Java

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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import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.Ssh;

public class ChilkatExample {

    public static void main(String[] args) {
        // 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 ssh = new Ssh();

        int port = 22;
        try {
            ssh.connect("172.16.16.100", port);
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            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.
        String password = "mySshPassword";

        try {
            ssh.authenticatePw("mySshLogin", password);
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        // Start a shell session.
        int channelNum = ssh.quickShell();
        if (channelNum < 0) {
            System.out.println(ssh.getLastErrorText());
            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.setReadTimeoutMs(15000);

        boolean caseSensitive = true;

        // The switch presents a prompt ending in "#".  Reading up to it confirms the session is ready.
        String cmdOutput;
        try {
            ssh.channelReceiveUntilMatch(channelNum, "#", "utf-8", caseSensitive);

            cmdOutput = ssh.getReceivedText(channelNum, "utf-8");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        System.out.println(cmdOutput);

        // Send a command and read its output up to the next prompt.
        try {
            ssh.channelSendString(channelNum, "show clock\n", "utf-8");

            ssh.channelReceiveUntilMatch(channelNum, "#", "utf-8", caseSensitive);

            // 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");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        System.out.println(cmdOutput);

        // Additional commands follow the same send / read-to-prompt / retrieve pattern.
        try {
            ssh.channelSendString(channelNum, "show version\n", "utf-8");

            ssh.channelReceiveUntilMatch(channelNum, "#", "utf-8", caseSensitive);

            cmdOutput = ssh.getReceivedText(channelNum, "utf-8");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        System.out.println(cmdOutput);

        ssh.disconnect();
    }
}