Dart

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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Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // 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.

  final ssh = CkSsh();

  final port = 22;
  try {
    ssh.connect('172.16.16.100', port);
  } on ChilkatException catch (e) {
    print(e.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.
  final password = 'mySshPassword';

  try {
    ssh.authenticatePw('mySshLogin', password);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Start a shell session.
  final channelNum = ssh.quickShell();
  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;

  final caseSensitive = true;

  // The switch presents a prompt ending in "#".  Reading up to it confirms the session is ready.
  try {
    ssh.channelReceiveUntilMatch(channelNum, '#', 'utf-8', caseSensitive);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  String cmdOutput;
  try {
    cmdOutput = ssh.getReceivedText(channelNum, 'utf-8');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print(cmdOutput);

  // Send a command and read its output up to the next prompt.
  try {
    ssh.channelSendString(channelNum, 'show clock\n', 'utf-8');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  try {
    ssh.channelReceiveUntilMatch(channelNum, '#', 'utf-8', caseSensitive);
  } on ChilkatException catch (e) {
    print(e.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.
  try {
    cmdOutput = ssh.getReceivedText(channelNum, 'utf-8');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print(cmdOutput);

  // Additional commands follow the same send / read-to-prompt / retrieve pattern.
  try {
    ssh.channelSendString(channelNum, 'show version\n', 'utf-8');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  try {
    ssh.channelReceiveUntilMatch(channelNum, '#', 'utf-8', caseSensitive);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  try {
    cmdOutput = ssh.getReceivedText(channelNum, 'utf-8');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print(cmdOutput);

  ssh.disconnect();
}