Set an Environment Variable on an SSH Channel

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Demonstrates the Chilkat Ssh.SendReqSetEnv method, which asks the server to set an environment variable for a session channel. The arguments are the channel number, the variable name, and its value. Send these requests before the exec, shell, or subsystem request.

import 'package:chilkat/chilkat.dart';

void main() {
  // Demonstrates the Ssh.SendReqSetEnv method, which asks the server to set an environment
  // variable for a session channel.  The 1st argument is the channel number, the 2nd is the
  // variable name, and the 3rd is its value.  Send it before the exec, shell, or subsystem
  // request.

  final ssh = CkSsh();

  final sshPort = 22;
  try {
    ssh.connect('ssh.example.com', sshPort);
  } 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;
  }

  // Open a session channel.  A negative return value indicates failure.
  final channelNum = ssh.openSessionChannel();
  if (channelNum < 0) {
    print(ssh.lastErrorText);
    return;
  }

  // Set environment variables for the channel.  Multiple variables may be requested.
  try {
    ssh.sendReqSetEnv(channelNum, 'LANG', 'en_US.UTF-8');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  try {
    ssh.sendReqSetEnv(channelNum, 'MY_APP_MODE', 'production');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Now run the command, which sees the requested environment.
  try {
    ssh.sendReqExec(channelNum, 'echo \$MY_APP_MODE');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // IMPORTANT: Set a read timeout.  ReadTimeoutMs defaults to 0, which means no limit -- without
  // it, this call waits forever if the server never sends channel close.
  ssh.readTimeoutMs = 15000;

  try {
    ssh.channelReceiveToClose(channelNum);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

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

  print(output);

  ssh.disconnect();
}