Learn ruby
ruby_tour
sudo apt-get install ruby-full
ruby -v
ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-linux-gnu]
evan@myxps:~/lx/ssh/intra$
交互式 Ruby（IRb）
交互式 Ruby（IRb）为体验提供了一个 shell。在 IRb shell 内，您可以逐行立即查看解释结果。
这个工具会随着 Ruby 的安装自动带有，所以您不需要做其他额外的事情，IRb 即可正常工作。
只需要在命令提示符中键入 irb，一个交互式 Ruby Session 将会开始，
intra$ irb
irb(main):001:0> puts "hey evan"
hey evan
=> nil
* base 20分钟学会Ruby
evan@myxps:~$ irb
irb(main):001:0> 3+2
=> 5
irb(main):002:0> 3*4
=> 12
irb(main):003:0> 3**2
=> 9
irb(main):004:0> Math.sqrt(9)
=> 3.0
方法 function
rb(main):005:0> def h
irb(main):006:1* puts "hey ruby"
irb(main):007:0> end
=> :h
irb(main):008:0> h
hey ruby
=> nil
irb(main):009:1* def h(name)
irb(main):010:1* puts "hello #{name}"
irb(main):011:0> end
=> :h
irb(main):012:0> h("eva")
hello eva
=> nil
irb(main):014:1* def h(name="world")
irb(main):015:1* puts "hello #{name.capitalize}!"
irb(main):016:0> end
=> :h
如果不输入参数，那么就会使用默认参数world。
irb(main):017:0> h "evan"
hello Evan!
=> nil
irb(main):018:0> h
hello World!
=> nil
irb(main):019:1* class Greeter
irb(main):020:2* def initialize(name = "world")
irb(main):021:2* @name = name
irb(main):022:1* end
irb(main):023:2* def say_hi
irb(main):024:2* puts "HI #{@name}!"
irb(main):025:1* end
irb(main):026:2* def say_bye
irb(main):027:2* puts "bye #{@name}. come back soon."
irb(main):028:1* end
irb(main):029:0> end
=> :say_bye
这里有一个新的关键词class，图中定义了一个名叫Greeter的类，里面有一些方法。注意这里的name，现在是一个实例变量，它对于Greeter中的所有类都是可用的。
irb(main):013:0> g = Greeter.new("pat")
irb(main):014:0> g.say_hi
HI pat!
=> nil
irb(main):015:0> g.say_bye
bye pat. come back soon.
=> nil
irb(main):016:0> g.@name
Traceback (most recent call last):
3: from /usr/bin/irb:23:in `<main>'
2: from /usr/bin/irb:23:in `load'
1: from /usr/lib/ruby/gems/2.7.0/gems/irb-1.2.3/exe/irb:11:in `<top (required)>'
SyntaxError ((irb):16: syntax error, unexpected instance variable)
g.@name
^~~~~
对象内部
rb(main):017:0> Greeter.instance_methods
=> [:say_hi, :say_bye, :dup, :itself, :yield_self, :then, :taint, :tainted?, :untaint, :untrust, :untrusted?, :trust, :frozen?, :methods, :singleton_methods, :protected_methods, :private_methods, :public_methods, :instance_variables, :instance_variable_get, :instance_variable_set, :instance_variable_defined?, :remove_instance_variable, :instance_of?, :kind_of?, :is_a?, :tap, :clone, :display, :hash, :class, :singleton_class, :public_send, :method, :public_method, :singleton_method, :define_singleton_method, :extend, :to_enum, :enum_for, :<=>, :===, :=~, :!~, :nil?, :eql?, :respond_to?, :freeze, :inspect, :object_id, :send, :to_s, :__send__, :!, :==, :!=, :equal?, :__id__, :instance_eval, :instance_exec]
这里有好多方法，但我们只定义了两个方法，这里是怎么回事呢？这是对象Greeter的全部方法，一个完整的列表，包含了父类定义的一些方法。如果要列出定义在Greeter中的且不包含父类的方法，那就使用参数false：
Greeter.instance_methods(false)
=> [:say_hi, :say_bye]
irb(main):019:0> g.respond_to?("say_hi")
=> true
see also
https://blog.csdn.net/mmiww/article/details/1363960
https://blog.csdn.net/mmiww/article/details/1355157
https://www.runoob.com/ruby/ruby-installation-unix.html
https://www.cnblogs.com/xuliangxing/p/7132656.html
https://linuxize.com/post/how-to-install-ruby-on-debian-9/
https://flicsdb.com/how-to-install-ruby-on-rails-on-ubuntu-or-kali-linux/
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