写代码时候，一些简单的 Bug 基本上打印1，2个变量就能找到原因。但是如果因为不了解 gem 而产生的 Bug 就比较难发现，这时候最好是加断点来调试。

Byebug

基础

• 开发环境下的 server 会自动加载 debugger
• byebug 是一个普通的方法，所以可以写如下代码 byebug if foo == "bar"
• 在 debugger 模式下，按回车会执行最后一条命令，输入 help 可以看到完整的命令列表
• 还可以用 info 查看一些具体信息

# The display command evaluates expressions every time the debugger stops.
(byebug) info display
There are no auto-display expressions now.

# Doing a info on line gives you the line number of the current break point.
(byebug) info line
Line 8 of "/Users/bparanj/projects/blog5/app/controllers/tasks_controller.rb"

停止

• q[uit] 退出调试并退出程序
• quit unconditionally, q! 和上一条命令一样，但略过确认的步骤
• kill 使用 kill -9 结束当前程序

主要命令

• c[ontinue] <line-number> 继续执行代码到结束，或发现到另外一处断点
• n[ext] <number> steps over the current line of code (runs the whole current line)
• s[tep] <number> steps into the current line of code (runs the current line, stopping inside any called methods)
• up 返回上一层函数，down 进入下一层函数
• eval 打印变量的值
• b[ack]t[race] — a.k.a. "w[here]" Display stack trace.
• irb 进入 irb 编辑代码
• exit 退出 irb 并继续调试
• h[elp] <command-name> 帮助

# In this case, we step into the Rails source code.
(byebug) step

[1, 10] in /Users/bparanj/.rvm/gems/ruby-2.3.0@rails5/gems/actionpack-5.0.0.beta3/lib/action_controller/metal/basic_implicit_render.rb
    1: module ActionController
    2:   module BasicImplicitRender
    3:     def send_action(method, *args)
=>  4:       super.tap { default_render unless performed? }
    5:     end
    6:
    7:     def default_render(*args)
    8:       head :no_content
    9:     end
   10:   end

# The eval command is one way to print the values of variables.
(byebug) eval performed?
false

调试

断点和捕获点 Breakpoints and Catchpoints

Pry

• pry -r ./config/enviroment
• cd
• exit
• ls -h
• ls -G map 列出所有包含 map 的方法
• ls -M Repo --grep ^b 列出 Repo 模块中以 b 开头的方法
• ls -g List global variables
• ls -c List constants
• find-method currency Spree 列出命名空间 Spree 下所有包含 currency 的方法
• show-source Spree::Product#bought_since any method in your application or its gems
• show-doc Array#in_group_of
• show-method all.in_group_of
• edit-method all.in_group_of

pry-byebug

在 Pry 的基础上，利用 Byebug 增加 step, next, finish, continue

• step Step execution into the next line or method. Takes an optional numeric argument to step multiple times.
• next Step over to the next line within the same frame. Also takes an optional numeric argument to step multiple lines.
• finish Execute until current stack frame returns.
• continue Continue program execution and end the Pry session.

相关资源

byebug

• Byebug Cheatsheet
• Byebug Cheat Sheet
• Debugging using ByeBug Gem in Rails 5
• Screencast: Debugging With Byebug

Pry

• Pry Screencast
• Debugging Ruby
• Pry with Rails
• Setting up Rails or Heroku to use Pry