lambdas.rb

Net::SSH::Simple.new do |s|
  s.servers "server1"

  exit_code = s.run "ls -la" do |cmd|
    cmd.on_stdout do |stdout|
    end

    cmd.on_stderr do |stderr|
    end
  end
end

subclasses.rb

class DataHandler
  def on_stdout(stdout)
  end

  def on_stderr(stderr)
  end
end

Net::SSH::Simple.new do |s|
  s.servers "server1"
  exit_code = s.run "ls -la", DataHandler.new
end

subclasses_2.rb

class DataHandler
  def on_stdout(stdout)
  end

  def on_stderr(stderr)
  end
end

ssh = Net::SSH::Simple.new("server1", :data_handler => DataHandler.new)
exit_code = ssh.run "ls -la"

begin
  ssh.run! "thiscommandclearlydoesn'texist"
rescue Net::SSH::Simple::CommandFailedError => e
  exit_code = e.exit_code
end