Stan Lo
Mostly Debugging

Mostly Debugging

ruby/debug cheatsheet

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Stan Lo
·Sep 8, 2022·

3 min read

This cheatsheet can help you get started with ruby/debug as well as use it in your daily development. It's not an exhausting list of its features or commands, so please go through its document as well.

If you're migrating from byebug, I also recommend checking my byebug to ruby/debug migration guide.

Getting Started

  1. Add gem "debug" to your Gemfile
  2. Run bundle install
  3. Add require "debug"
  4. Use binding.b or debugger to set initial breakpoints (they're same)

The rdbg Executable

(Running with bundle exec is usually recommended)

ActionCommand
Debug a Ruby script with executable$ rdbg foo.rb
Debug a Ruby command with executable$ rdbg -c -- bundle exec <cmd>
Debug without the initial stop$ rdbg -n ...

Need Any Help?

ActionCommand
See document of all the commandsh[elp]
See document of <cmd>h[elp] <cmd>
See configurationsconfig
Learn how to configure the debuggerh config

Step Debugging & Frame Navigation

ActionCommand
Step ins[tep]
Step overn[ext]
Finishfin[ish]
Move to <id> framef[rame] <id>
Move up a frameup
Move down a framedown
Continue the programc[ontinue]
Quit the debuggerq[uit]!
Kill the programkill

Breakpoint Commands

Setting Breakpoints

TargetCommand
A lineb[reak] <line>
A file:lineb[reak] <file>:<line>
An instance methodb[reak] <class>#<method>
An object's methodb[reak] <obj>.<method>
A class methodb[reak] <class>.<method>
An exceptioncatch <ExceptionClass>
Mutation of instance variablewatch <@ivar>

Options (applies to all 3 breakpoint commands)

Condition TypeOption
With an if condition... if: <expr>
With a path condition... path: /path/
To run a command and continue... do: <cmd>
To run a command before stopping... pre: <cmd>

Managing Breakpoints

ActionCommand
List all breakpointsb[reak]
Delete a breakpointdel[ete] <id>
Delete all breakpointsdel[ete]

Information Commands

InformationCommand
Current scope's outlne (methods and avialble ivars, locals)ls
obj's outlne (methods and avialble ivars, locals)ls obj
Backtracebt
Only <n> backtracebt <n>
Source codel[ist]
Local variables, instance variables, and current scope's constantsi[nfo]
Local varibalesi[nfo] l
Instance variablesi[nfo] i
Global varibalesi[nfo] g
Constantsi[nfo] c
Filter variables/constants by namesi[nfo] ... /regexp/

Scriptable Breakpoints

DescriptionCode
Run the <cmd> and stop the programbinding.b(pre: "<cmd>")
Run the <cmd> and continue the programbinding.b(do: "<cmd>")
Run multiple commandsbinding.b(do: "<cmd1> ;; <cmd2>")

My Favourites

DescriptionCode
Glance through variables before I start typingbinding.b(pre: "i")
Quickly get the surrounding contextbinding.b(pre: "ls ;; bt 10")
Start tracing exceptionsbinding.b(do: "trace exception")
Stop me when there's an exceptionbinding.b(do: "catch StandardError")
 
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