gistfile1.rb

s1 = {:host=>'foo', :user => 'foobar'}
s2 = {:host=>'bar', :user => 'foobar'}
s3 = {:host=>'baz', :user => 'foobar'}
s4 = {:host=>'moo', :user => 'foobar', :options => {:password => 'barfoo'}}

def gate(s, s2, opts={})
  gw = Net::SSH::Gateway.new(s[:host], s[:user], {:port => 22}.merge(opts))
  gw_port = gw.open(s2[:host], s2[:port])
  yield(gw_port)
ensure
  gw.shutdown!
end

gate(s, s2) do |gw_port|
  gate(s2, s3, {:port => gw_port}) do |gw2_port|
    gw3 = Net::SSH::Gateway.new(s3[:host], s3[:user], {:port => gw2_port})
    gw3.ssh(s4[:host], s4[:user], s4[:options]) do |session|
      session.exec!('uptime')
    end
  end
end