gistfile1.rb

def prepend_handler(signal, &handler)
  previous = Signal.trap(signal) do
    previous = -> { raise SignalException, signal } unless previous.respond_to?(:call)
    handler.call(previous)
  end
end

prepend_handler("TERM") do |old|
  do_something
  old.call
end

I've handled this by resetting the old handler and then resending the signal:

$ ruby -e '
   old = trap("INT") {
     puts "\e[35mWhy hello, thar!\e[39m"
     trap "INT", old
     Process.kill "INT", Process.pid
   }

   Process.kill "INT", Process.pid
'
Why hello, thar!
-e:8:in `kill': Interrupt
    from -e:8:in `<main>'
fish: Job 6, 'ruby -e '' terminated by signal SIGINT (Quit request from job control (^C))