gistfile1.txt

~/projects/jruby ➔ jruby -rreal_unix -e 'trap("INT") { puts :there; exit }; puts :here; select(nil, nil, nil, nil)'
here
^Cthere

~/projects/jruby ➔ jruby -rreal_unix -e 'puts $$; exec "echo $$"'
461
461

~/projects/jruby ➔ cat real_unix.rb 
require 'ffi'

module RealUnix
  extend FFI::Library

  ffi_lib 'c'

  attach_function :execv, [ :string, :buffer_in ], :int
  attach_function :exit, [ :int ], :void
  
  def self.exec(*args)
    args.unshift "/bin/sh", "-c"
    cmd = args[0]
    exec_args = FFI::MemoryPointer.new(:pointer, args.length + 1)
    args.each_with_index do |arg, i|
      exec_args[i].put_pointer(0, FFI::MemoryPointer.from_string(arg))
    end
    execv(cmd, exec_args)
  end
end

module Kernel
  alias :old_exec :exec
  alias :old_exit :exit
  
  def exec(*args); RealUnix.exec(*args); end
  def exit(code = 0); RealUnix.exit(code); end
end