> irb
>> 1
=> 1
>> 1+1
=> 2
>> "hello"
=> "hello"
>> puts "hello"
hello
=> nil
>> def inrc n
>>   n+1
>> end
=> nil
>> inrc 3
=> 4
>> "hello".length
=> 5
>> "hello".reverse
=> "olleh"
>> "hello".class
=> String
>> String.class
=> Class
>> "hello".class.class
=> Class
>> String.methods
=> ["private_class_method", "inspect", "name", "tap", "clone", "public_methods", "__send__", "method_defined?", "yaml_tag_subclasses?", "instance_variable_defined?", "autoload", "equal?", "freeze", "extend", "send", "const_defined?", "methods", "ancestors", "module_eval", "inrc", "hash", "dup", "object_id", "instance_methods", "public_method_defined?", "taguri", "instance_variables", "class_variable_defined?", "eql?", "yaml_as", "constants", "taguri=", "id", "instance_eval", "singleton_methods", "module_exec", "instance_method", "const_missing", "taint", "autoload?", "instance_variable_get", "frozen?", "to_enum", "private_method_defined?", "to_yaml_style", "public_instance_methods", "display", "instance_of?", "superclass", "to_a", "included_modules", "yaml_new", "const_get", "instance_exec", "type", "<", "protected_methods", "<=>", "class_eval", "==", "class_variables", ">", "===", "instance_variable_set", "enum_for", "yaml_tag_read_class", "protected_instance_methods", "protected_method_defined?", "respond_to?", "kind_of?", ">=", "method", "public_class_method", "yaml_tag_class_name", "to_s", "<=", "const_set", "allocate", "to_yaml", "class", "new", "private_methods", "=~", "tainted?", "__id__", "class_exec", "to_yaml_properties", "untaint", "nil?", "private_instance_methods", "include?", "is_a?"]
>> String.methods.class
=> Array
>> String.methods.length
=> 92
>> Array.methods
=> ["private_class_method", "inspect", "name", "tap", "clone", "public_methods", "__send__", "method_defined?", "yaml_tag_subclasses?", "instance_variable_defined?", "autoload", "equal?", "freeze", "extend", "send", "const_defined?", "methods", "ancestors", "module_eval", "inrc", "hash", "dup", "object_id", "instance_methods", "public_method_defined?", "taguri", "instance_variables", "class_variable_defined?", "eql?", "yaml_as", "constants", "taguri=", "id", "instance_eval", "singleton_methods", "module_exec", "instance_method", "const_missing", "taint", "autoload?", "instance_variable_get", "frozen?", "to_enum", "private_method_defined?", "to_yaml_style", "public_instance_methods", "display", "instance_of?", "superclass", "to_a", "included_modules", "const_get", "instance_exec", "type", "<", "protected_methods", "<=>", "class_eval", "==", "class_variables", ">", "===", "instance_variable_set", "enum_for", "yaml_tag_read_class", "protected_instance_methods", "protected_method_defined?", "respond_to?", "kind_of?", ">=", "method", "public_class_method", "yaml_tag_class_name", "to_s", "<=", "const_set", "allocate", "to_yaml", "class", "new", "private_methods", "=~", "tainted?", "__id__", "class_exec", "to_yaml_properties", "untaint", "nil?", "private_instance_methods", "include?", "is_a?", "[]"]
>> Array.methods.length
=> 92
>> 1.+(1)
=> 2
>> 1.+ 1
=> 2
>> 1.class
=> Fixnum
>> 1.methods
=> ["%", "odd?", "lcm", "inspect", "prec_i", "power!", "<<", "tap", "div", "&", "clone", ">>", "public_methods", "__send__", "instance_variable_defined?", "denominator", "equal?", "freeze", "to_sym", "*", "ord", "+", "extend", "next", "send", "round", "methods", "prec_f", "-", "even?", "gcdlcm", "singleton_method_added", "divmod", "inrc", "hash", "/", "integer?", "downto", "gcd", "dup", "object_id", "taguri", "instance_variables", "|", "eql?", "size", "taguri=", "id", "instance_eval", "truncate", "~", "to_r", "to_i", "singleton_methods", "rdiv", "modulo", "taint", "zero?", "times", "instance_variable_get", "frozen?", "to_enum", "to_yaml_style", "display", "instance_of?", "^", "to_a", "numerator", "+@", "-@", "quo", "instance_exec", "type", "**", "upto", "to_f", "<", "step", "protected_methods", "rpower", "<=>", "between?", "==", "remainder", ">", "===", "to_int", "nonzero?", "pred", "instance_variable_set", "enum_for", "coerce", "respond_to?", "kind_of?", "floor", "succ", ">=", "method", "prec", "to_s", "<=", "fdiv", "to_yaml", "class", "private_methods", "=~", "tainted?", "__id__", "to_yaml_properties", "abs", "untaint", "nil?", "chr", "id2name", "is_a?", "ceil", "[]"]
>> 3.times { puts "again" }
again
again
again
=> 3
>> 3.times { |n| puts n }
0
1
2
=> 3
>> a = nil
=> nil
>> a
=> nil
>> a.class
=> NilClass
>> a.class.methods
=> ["private_class_method", "inspect", "name", "tap", "clone", "public_methods", "__send__", "method_defined?", "yaml_tag_subclasses?", "instance_variable_defined?", "autoload", "equal?", "freeze", "extend", "send", "const_defined?", "methods", "ancestors", "module_eval", "inrc", "hash", "dup", "object_id", "instance_methods", "public_method_defined?", "taguri", "instance_variables", "class_variable_defined?", "eql?", "yaml_as", "constants", "taguri=", "id", "instance_eval", "singleton_methods", "module_exec", "instance_method", "const_missing", "taint", "autoload?", "instance_variable_get", "frozen?", "to_enum", "private_method_defined?", "to_yaml_style", "public_instance_methods", "display", "instance_of?", "superclass", "to_a", "included_modules", "const_get", "instance_exec", "type", "<", "protected_methods", "<=>", "class_eval", "==", "class_variables", ">", "===", "instance_variable_set", "enum_for", "yaml_tag_read_class", "protected_instance_methods", "protected_method_defined?", "respond_to?", "kind_of?", ">=", "method", "public_class_method", "yaml_tag_class_name", "to_s", "<=", "const_set", "allocate", "to_yaml", "class", "private_methods", "=~", "tainted?", "__id__", "class_exec", "to_yaml_properties", "untaint", "nil?", "private_instance_methods", "include?", "is_a?"]
>> nil.methods.length
=> 56
>> a=[1,2,3]
=> [1, 2, 3]
>> a
=> [1, 2, 3]
>> a.class
=> Array
>> a.length
=> 3
>> a[0]
=> 1
>> a[2]
=> 3
>> a[3]=4
=> 4
>> a
=> [1, 2, 3, 4]
>> a[-2]
=> 3
>> a[10]=17
=> 17
>> a
=> [1, 2, 3, 4, nil, nil, nil, nil, nil, nil, 17]
>> h = { "weather" => "cold" , "xyzzy" => 42 }
=> {"xyzzy"=>42, "weather"=>"cold"}
>> h["weather"]
=> "cold"
>> h["stuff"] = "something interesting"
=> "something interesting"
>> h
=> {"stuff"=>"something interesting", "xyzzy"=>42, "weather"=>"cold"}
>> h.each { |k,v| puts k; puts v }
stuff
something interesting
xyzzy
42
weather
cold
=> {"stuff"=>"something interesting", "xyzzy"=>42, "weather"=>"cold"}
>> class Toy
>>   def initialize(name,color)
>>     @name=name
>>     @color = color
>>   end
>>   def name
>>     @name
>>   end
>> end
=> nil
>> truck = Toy.new("firetruck", "red")
=> #<Toy:0x101143410 @color="red", @name="firetruck">
>> truck
=> #<Toy:0x101143410 @color="red", @name="firetruck">
>> truck.name
=> "firetruck"
>> name.color
NameError: undefined local variable or method `name' for main:Object
	from (irb):62
>> class Toy
>>   def color
>>     @color
>>   end
>> end
=> nil
>> Toy.methods
=> ["private_class_method", "inspect", "name", "tap", "clone", "public_methods", "__send__", "method_defined?", "yaml_tag_subclasses?", "instance_variable_defined?", "autoload", "equal?", "freeze", "extend", "send", "const_defined?", "methods", "ancestors", "module_eval", "inrc", "hash", "dup", "object_id", "instance_methods", "public_method_defined?", "taguri", "instance_variables", "class_variable_defined?", "eql?", "yaml_as", "constants", "taguri=", "id", "instance_eval", "singleton_methods", "module_exec", "instance_method", "const_missing", "taint", "autoload?", "instance_variable_get", "frozen?", "to_enum", "private_method_defined?", "to_yaml_style", "public_instance_methods", "display", "instance_of?", "superclass", "to_a", "included_modules", "const_get", "instance_exec", "type", "<", "protected_methods", "<=>", "class_eval", "==", "class_variables", ">", "===", "instance_variable_set", "enum_for", "yaml_tag_read_class", "protected_instance_methods", "protected_method_defined?", "respond_to?", "kind_of?", ">=", "method", "public_class_method", "yaml_tag_class_name", "to_s", "<=", "const_set", "allocate", "to_yaml", "class", "new", "private_methods", "=~", "tainted?", "__id__", "class_exec", "to_yaml_properties", "untaint", "nil?", "private_instance_methods", "include?", "is_a?"]
>> truck
=> #<Toy:0x101143410 @color="red", @name="firetruck">
>> truck.name
=> "firetruck"
>> truck.color
=> "red"
>> truck.color="green"
NoMethodError: undefined method `color=' for #<Toy:0x101143410 @color="red", @name="firetruck">
	from (irb):77
>> class Toy 
>>   def color=(color)
>>     @color=color
>>   end
>> end
=> nil
>> truck
=> #<Toy:0x101143410 @color="red", @name="firetruck">
>> truck.color
=> "red"
>> truck.color="purple"
=> "purple"
>> truck
=> #<Toy:0x101143410 @color="purple", @name="firetruck">
>> 1.class
=> Fixnum
>> 1.methods
=> ["%", "odd?", "lcm", "inspect", "prec_i", "power!", "<<", "tap", "div", "&", "clone", ">>", "public_methods", "__send__", "instance_variable_defined?", "denominator", "equal?", "freeze", "to_sym", "*", "ord", "+", "extend", "next", "send", "round", "methods", "prec_f", "-", "even?", "gcdlcm", "singleton_method_added", "divmod", "inrc", "hash", "/", "integer?", "downto", "gcd", "dup", "object_id", "taguri", "instance_variables", "|", "eql?", "size", "taguri=", "id", "instance_eval", "truncate", "~", "to_r", "to_i", "singleton_methods", "rdiv", "modulo", "taint", "zero?", "times", "instance_variable_get", "frozen?", "to_enum", "to_yaml_style", "display", "instance_of?", "^", "to_a", "numerator", "+@", "-@", "quo", "instance_exec", "type", "**", "upto", "to_f", "<", "step", "protected_methods", "rpower", "<=>", "between?", "==", "remainder", ">", "===", "to_int", "nonzero?", "pred", "instance_variable_set", "enum_for", "coerce", "respond_to?", "kind_of?", "floor", "succ", ">=", "method", "prec", "to_s", "<=", "fdiv", "to_yaml", "class", "private_methods", "=~", "tainted?", "__id__", "to_yaml_properties", "abs", "untaint", "nil?", "chr", "id2name", "is_a?", "ceil", "[]"]
>> class Fixnum
>>   def +(other)
>>     17
>>   end
>> end
=> nil
>> 1+1
=> 17
>> 2+3
=> 17
>> a
=> [1, 2, 3, 4, nil, nil, nil, nil, nil, nil, 17]
>> a[1+1]="what?"
>> a
>> a
>> a
>> ^D=> [1, 2, 3, 4, nil, nil, nil, nil, nil, nil, 17, nil, nil, nil, nil, nil, nil, "what?"]
>