gistfile1.txt

[agrimm@computer_name using_block_test]$ more skippy.rb 
#This is from the Pickaxe
module Kernel
  old_system_method = instance_method(:system)
  define_method(:system) do |*args|
    result = old_system_method.bind(self).call(*args)
    puts "system(#{args.join(', ')}) returned #{result.inspect}"
    result
  end
end
system("date")
system("kangaroo", "-hop 10", "skippy")
[agrimm@computer_name using_block_test]$ ruby -W2 skippy.rb 
Mon Oct 26 08:17:25 EST 2009
system(date) returned true
system(kangaroo, -hop 10, skippy) returned false
[agrimm@computer_name using_block_test]$ [alias for ruby 1.9.1] -W2 skippy.rb 
skippy.rb:3: warning: method redefined; discarding old system
Mon Oct 26 08:17:31 EST 2009
system(date) returned true
system(kangaroo, -hop 10, skippy) returned nil
[agrimm@computer_name using_block_test]$ [alias for ruby 1.9.1] -W1 skippy.rb 
Mon Oct 26 08:18:44 EST 2009
system(date) returned true
system(kangaroo, -hop 10, skippy) returned nil
[agrimm@computer_name using_block_test]$