test.rb

#ruby -v # 1.9.2
#gem list|grep em-ssh # em-ssh(0.1.0)
require 'em-ssh'

# runs the command on server and gives the callback call
def do_ssh(cmd)
  do_ssh_var = 'ssh'
  EM::Ssh.start('localhost','goutham') do |ssh|
    puts 'ssh start'
    ssh.exec!(cmd) do |channel, stream, data|
      puts 'callback'
      yield data
      puts do_ssh_var
    end
  end

end
# modifies command and runs it on server. 
# After commands are run on server rest of code is exec in callback block
def prepare_server(cmd)
  cmd += ' /home'
  callback_var = 'callback var'
  do_ssh(cmd) do |data|
    puts "\n#{data}"
    puts "pre callback_val", callback_val
    yield()
    puts "post callback_val", callback_val
  end

end
begin
  EM.run do
    puts 'run'
    main_var = 'main'
    prepare_server('ls -l') do 
      puts 'main context', main_var # callback after the server is prepared
    end
    EM.add_timer(3) { EM.stop}
  end
rescue => e
  puts e.message 
end