require(name)

它将返回bolean true/false

作为参数传递给require的名称，ruby将尝试在加载路径中找到具有该名称的源文件。 如果你尝试在第一次之后加载相同的库，require方法将返回' false '。require方法仅在您正在加载的库定义在单独的文件中时才需要使用。 所以它会跟踪那个库是否已经被加载。

include module_name

假设你需要在两个不同的类中有一些方法。这样就不需要在两个类中都写了。相反，你可以在module中定义它。然后将此模块包含在其他类中。 它是由Ruby提供的，只是为了保证DRY原则。它用于DRY代码以避免重复

What's the difference between "include" and "require" in Ruby? Answer: The include and require methods do very different things. The require method does what include does in most other programming languages: run another file. It also tracks what you've required in the past and won't require the same file twice. To run another file without this added functionality, you can use the load method. The include method takes all the methods from another module and includes them into the current module. This is a language-level thing as opposed to a file-level thing as with require. The include method is the primary way to "extend" classes with other modules (usually referred to as mix-ins). For example, if your class defines the method "each", you can include the mixin module Enumerable and it can act as a collection. This can be confusing as the include verb is used very differently in other languages.

源

所以如果你只是想使用一个模块，而不是扩展它或做一个混合，那么你会想要使用require。

奇怪的是，Ruby的require类似于C的include，而Ruby的include几乎与C的include完全不同。

如果你正在使用一个模块，这意味着你要把所有的方法都带入你的类中。 如果你用一个模块扩展一个类，这意味着你把模块的方法作为类方法“引入”了。 如果你在模块中包含了一个类，这意味着你将模块的方法作为实例方法“引入”了。

EX:

 module A
   def say
     puts "this is module A"
   end
 end

 class B
   include A
 end

 class C
   extend A
 end

B.say =>未定义的方法'说'的B:类

B.new.say 这是模块A

C.say 这是模块A

C.new.say =>未定义的方法'说' C:类

例如:当你使用require 'math'时，你必须写math::PI。 但是当你使用include math时，你可以简单地写成PI。

下面是require和include之间的一些基本区别:

要求:

Require从文件系统读取文件，解析它，保存到内存中，并在给定的位置运行它，这意味着如果你在脚本运行时更改了任何内容，那么这些更改将不会反映出来。 我们按名称要求文件，而不是按模块名。 它通常用于库和扩展。

包括:

当你将一个模块包含到你的类中时，它的行为就像你将模块中定义的代码插入到你的类中一样。 我们包含模块名，而不是文件名。 它通常用于干涸代码和删除代码中的重复。

来自编程Ruby 1.9

We’ll make a couple of points about the include statement before we go on. First, it has nothing to do with files. C programmers use a preprocessor directive called #include to insert the contents of one file into another during compilation. The Ruby include statement simply makes a reference to a module. If that module is in a separate file, you must use require (or its less commonly used cousin, load) to drag that file in before using include. Second, a Ruby include does not simply copy the module’s instance methods into the class. Instead, it makes a reference from the class to the included module. If multiple classes include that module, they’ll all point to the same thing. If you change the definition of a method within a module, even while your program is running, all classes that include that module will exhibit the new behavior.