unless works like if not

until is while not

swap values: x, y = y, x

FILE - name of current source file

irb(main):024:0> puts __FILE__
(irb)

$0 - name of top level program executed

irb(main):024:0> puts $0
irb
=> nil

$: is array of paths

$! is current exeption raised. nil if no exeption being raised

$SAFE is current safe level

ENV is hash of environment vairables

methods ending wiht ‘?’ are boolean

puts ('ok') if File.exists?('filename')

methods ending wiht ‘!’ modify current object

str = "   hello world   "
str.strip!
p str   # -> "hello world"
  = or-equal operator  
a   = b means assign b to a if a is nil or false 
a = nil
b = 2
a ||= b
=> 2

ruby’s getters and setters are attr_reader, attr_writer and attr_accessor

class Awesome
	attr_accessor: :name, :date
end

ruby’s analog to try-catch-finally is begin-rescue-ensure

== operator checks if two ojects are equal .eql? check if objects types and values are equal .equal? checks if two object are the same object

1 == 1.0
=> true

1.eql?(1.0)
=> false