useful utilities (irb, ruby)

irb:

    a shell to run ruby 

    irb  -r  test.rb

    include the content of test.rb,  r is require

ruby:

-w:

turn warnings on for your script

-e:

execute the code in '  '

ex:

ruby -e  'puts "hello"  '

--->  hello

-r:

require some files

-rdebug:

debug program,

step command:  run next instruction 

-r profile:

test performance