You can debug in Ruby using a few different ways:
$ruby -r debug filename
Example Run debugger with:
$ruby -r debug my_ruby_file.rb
List of debug commands
v l to view local variablesv g to view global variablesw to display stack frameInstall
gem install byebug
github.com/deivid-rodriguez/pry-byebug
$gem install pry-byebug --user-install
Pry is a runtime developer console and IRB alternative with introspection capabilities.
Install Pry
sudo apt-get install pry
gem install pry --user-install
Using Pry
require 'pry' # equivalent of python's `import pdb`
# Misc code
binding.pry # equivalent of `pdb.set_trace()`
To run a program with pry (and require pry, add -rpry) and run:
ruby -rpry myrubyprogram.rb
Example usage (basically binding.pry is the Python pdb.set_trace() equivalent)
william.liu@us-wliu ~/workspace/ruby-examples/ruby_lang (master) $ ruby -rpry pry_example.rb
From: /Users/william.liu/workspace/ruby-examples/ruby_lang/pry_example.rb @ line 15 :
10: x = 10
11:
12: # start a REPL session
13: binding.pry
14:
=> 15: puts "Program will resume here. Value of x is: #{x}."
16:
17: puts "End here!"
[1] pry(main)> ls
self.methods: inspect to_s
locals: _ __ _dir_ _ex_ _file_ _in_ _out_ _pry_ a x
[2] pry(main)> puts a
#<A:0x007fcc981925f0>
=> nil
[3] pry(main)> a
=> #<A:0x007fcc981925f0>
[4] pry(main)> exit
Program will resume here. Value of x is: 10.
End here!
Pry Help to see a list of commands inside of pry:
$ pry
[1] pry(main)> help
Help
help Show a list of commands or information about a specific command.
Context
cd Move into a new context (object or scope).
find-method Recursively search for a method within a class/module or the current namespace.
ls Show the list of vars and methods in the current scope.
pry-backtrace Show the backtrace for the pry session.
raise-up Raise an exception out of the current pry instance.
reset Reset the repl to a clean state.
watch Watch the value of an expression and print a notification whenever it changes.
whereami Show code surrounding the current context.
wtf? Show the backtrace of the most recent exception.
Editing
/^\s*!\s*$/ Clear the input buffer.
amend-line Amend a line of input in multi-line mode.
edit Invoke the default editor on a file.
hist Show and replay readline history.
play Playback a string variable, method, line, or file as input.
show-input Show the contents of the input buffer for the current multi-line expression.
Introspection
ri View ri documentation.
show-doc Show the documentation for a method or class.
show-source Show the source for a method or class.
stat View method information and set _file_ and _dir_ locals.
Gems
gem-cd Change working directory to specified gem's directory.
gem-install Install a gem and refresh the gem cache.
gem-list List and search installed gems.
gem-open Opens the working directory of the gem in your editor.
gem-readme Show the readme bundled with a rubygem
gem-search Search for a gem with the rubygems.org json api
gem-stat Show the statistics of a gem (requires internet connection)
Commands
import-set Import a pry command set.
install-command Install a disabled command.
Aliases
!!! Alias for `exit-program`
!!@ Alias for `exit-all`
$ Alias for `show-source`
(?-mix:whereami[!?]+) Alias for `whereami`
? Alias for `show-doc`
@ Alias for `whereami`
clipit Alias for `gist --clip`
file-mode Alias for `shell-mode`
history Alias for `hist`
quit Alias for `exit`
quit-program Alias for `exit-program`
reload-method Alias for `reload-code`
show-method Alias for `show-source`
Byebug
backtrace Display the current stack.
break Set or edit a breakpoint.
continue Continue program execution and end the pry session.
down Move current frame down.
finish Execute until current stack frame returns.
frame Move to specified frame #.
next Execute the next line within the current stack frame.
step Step execution into the next line or method.
up Move current frame up.
Input and output
.<shell command> All text following a '.' is forwarded to the shell.
cat Show code from a file, pry's input buffer, or the last exception.
change-inspector Change the current inspector proc.
change-prompt Change the current prompt.
Good commands to know:
helpls --helpls, ls some_objectcdwhereamisome_object.inspectsome_object.classshow-method some_functionedit some_function # or some class method, e.g. edit String#my_func.ls.cat.pwdselfInspect an object with:
my_object.class
"MyStringObject".methods.sort
my_object.instance_of? String #=> True
my_object.is_a?(String)
You can remove an object’s methods, e.g.
>my_object.methods
:public_foo, :public_bar
>my_object.methods-Object.methods
:something, :another
If you run a program with debugger instead of binding.pry, you’ll get the debugger. You then run with
ruby --debug my_progrma.rb
set autolist on - will show where you are
n to skip down a line
e to evaluate an object (e[val]
Command Line
pry -r ./config/app_init_file.rb - load your app into a pry session (look at the file loaded by config.ru)
pry -r ./config/environment.rb - load your rails into a pry session
Debugger
help ls -- Display command options for pry command ls
ls <Object> -- Show all of the available methods that can be called by an object
_ -- Last eval
? <Object> -- Shows more information (doc) about an object, or method
_file_ -- Represent the last file Pry touched
wtf? -- Print the stack trace, same as _ex_.backtrace
$ -- Show source, shortcut for show-source
edit Class -- Open file in $EDITOR
edit Class#instance_method -- Open file in $EDITOR
<ctrl+r> -- Search history
_out_ -- Array of all outputs values, also _in_
cd <var> -- Step into an object, change the value of self
cd .. -- Take out of a level
binding.pry -- Breakpoint
edit --ex -- Edit the file where the last exception was thrown
.<Shell> -- Runs the command
whereami -- Print the context where the debugger is stopped
whereami 20 -- Print the context 20 lines where the debugger is stopped
; -- Would mute the return output by Ruby
play -l -- Execute the line in the current debugging context
pry-nav
next -- execute next line
step -- step into next function call
continue -- continue through stack
pry-rescue
rescue rspec -- break on exception in rspec
rescue rails server -- break on exception in rails server
try-again -- run last failing spec, reloads the file not the enviornment
IRB stands for interactive ruby and allows you to interactively execute Ruby expressions.
https://github.com/microsoft/vscode-recipes/tree/master/debugging-Ruby-on-Rails
Add ‘ruby-debug-ide’, ‘debase’, and ‘rspec’ to your Gemfile.
group :development do
gem 'ruby-debug-ide', '~> 0.6'
gem 'debase', '~> 0.2'
gem 'rspec', '~> 3.9'
end
After a bundle install, find out where your files are:
which bundle
bundle info ruby-debug-ide
which rspec
Add this to your Debugger launch.json configurations.
Time Travel Debugging - None that I know of at the moment
Conditional Breakpoint Debugging - set a condition when a variable is a certain value (e.g. x == 100);
Yes in VSCode, add a Breakpoint, then ‘Edit Breakpoint’, then set your example like here
Data Breakpoints - debugger breaks when the variable is a certain value
Logging - Just puts or log info can really help, especially for distributed systems
Logpoints - Lets you more easily log what’s in your system (when you don’t want to stop execution in a part of your
application, but instead you want to inspect how state mutates throughout the lifetime of the application).
You don’t have to add logging statements into your application since logpoints are injected at execution time.
Git Bisect - if you know a good and bad commit, narrow down what changes happened since then