如何写gem

第一步：用bundle gem gem_name生成基本结构，如下：

[root@arch demo]$ bundle gem rename_url      create  rename_url/Gemfile      create  rename_url/Rakefile      create  rename_url/.gitignore      create  rename_url/rename_url.gemspec      create  rename_url/lib/rename_url.rb      create  rename_url/lib/rename_url/version.rbInitializating git repo in /home/suchj/programs/demo/rename_url

注：

Gemfile # 描述依赖

Rakefile # 发布和打包的 rake tasksGEM_NAME.gemspec # gem 的 specGEM_NAME/lib/GEM_NAME.rb 与 GEM_NAME/lib/GEMNAME/ # gem 里的 libraryGEM_NAME/lib/GEM_NAME/version.rb # 版本记录
第二步：写Gems规范文件，rename_url.gemspec

# -*- encoding: utf-8 -*-$:.push File.expand_path("../lib", __FILE__)require "rename_url/version"Gem::Specification.new do |s|  s.name        = "rename_url"  s.version     = RenameUrl::VERSION  s.authors     = ["xx"]  s.email       = ["xx@gmail.com"]  s.homepage    = ""  s.summary     = %q{TODO: Write a gem summary}  s.description = %q{TODO: Write a gem description}  s.rubyforge_project = "rename_url"  s.files         = `git ls-files`.split("\n")  s.test_files    = `git ls-files -- {test,spec,features}/*`.split("\n")  s.executables   = `git ls-files -- bin/*`.split("\n").map{ |f| File.basename(f) }  s.require_paths = ["lib"]  # specify any dependencies here; for example:  # s.add_development_dependency "rspec"  # s.add_runtime_dependency "rest-client"end

?第三步：写实现，lib/rename_url.rb

require "rename_url/version"module RenameUrl  def self.included(base)    base.extend(ClassMethods)  end  module ClassMethods    def urlize      include RenameUrl::InstanceMethods    end  end  module InstanceMethods    def to_param      "#{id}_#{title}"    end  endendActiveRecord::Base.send(:include, RenameUrl) #在model中引入

?第四步：打包gem

[root@arch rename_url]$ gem build rename_url.gemspec WARNING:  no homepage specified  Successfully built RubyGem  Name: rename_url  Version: 0.0.1  File: rename_url-0.0.1.gem

?注：如果规范文件有信息没写全，会有警告
第五步：使用，在项目的Gemfile中加入

gem 'rename_url', :path => '~/programs/rename_url'

?注：gem文件在哪就写哪个路径post.rb

class Post < ActiveRecord::Base  urlize #相当于include RenameUrl::InstanceMethodsend

测试：

[root@arch demo]$ rails cLoading development environment (Rails 3.0.4)1.8.7 :001 > Post => Post(id: integer, name: string, title: string, content: text, created_at: datetime, updated_at: datetime) 1.8.7 :002 > Post.create(:title => "test") => #<Post id: 2, name: nil, title: "test", content: nil, created_at: "2012-02-03 08:38:53", updated_at: "2012-02-03 08:38:53"> 1.8.7 :003 > Post.find_by_title("test").to_param => "2_test" 

?OK，一个简单的gem就完成了。当然，一个完整的gem有完整的测试，还可能会放到git和rubygems上供大家使用，此例子纯粹供练手，仅供参考。

1 楼 ruby_windy 2012-02-03 1. 完成测试.

2. gem push 发送到rubygems.org