Pry
Ruby ships with an interactive shell, or REPL (Read-Eval-Print Loop) called
irb. It’s pretty handy for quick ruby evaluations, or running rails console
commands.
You can also require files or gems to do more complicated stuff, you can
bundle exec irb to run your shell with the local gemset installed.
I’ll assume you know about it and what it does.
Pry is like irb, but better. The big benefits include:
- syntax highlighting
- source code and documentation browsing
- breakpoint debugging
- state and stack navigation
- customisation options
Combining it with plugins like pry-byebug and pry-remote allows you to step through code, or debug through a network connection.
Source code and documentation browsing
Using this code:
pry example pry_example.rb
require 'pry'
require 'pry-byebug'
# This class stores a value when initialized, and provides a multiply method
# to multiply a given value by the initial value
class SimpleTest
def initialize(v)
binding.pry
@v = v
end
def multiply m
@v * m
end
end
binding.pry
t = SimpleTest.new(3)
t.multiply 7
You can spelunk around the code, inspect classes and methods and view their source code or documentation.
Breakpoint debugging
The best use for pry, is with binding.pry Add this to your code, and when
executed, you will drop straight into the pry REPL at that point in the code.
You can then inspect objects, and navigate through the stack and step through
the code.
These features are shown in the playthough below:
$ ruby pry_example.rb
From: .../blog_code_examples/pry_example.rb:19 :
14: end
15: end
16:
17: binding.pry
18:
=> 19: t = SimpleTest.new(3)
20: t.multiply 7
21:
[1] pry(main)> ls
self.methods: inspect to_s
locals: _ __ _dir_ _ex_ _file_ _in_ _out_ pry_instance t
[2] pry(main)> cd SimpleTest
[3] pry(SimpleTest):1> show-source
From: pry_example.rb:4
Class name: SimpleTest
Number of lines: 10
class SimpleTest
def initialize(v)
binding.pry
@v = v
end
def multiply m
@v * m
end
end
[4] pry(SimpleTest):1> show-doc
From: pry_example.rb:4
Class name: SimpleTest
Number of lines: 2
This class stores a value when initialized, and provides a multiply method
to multiply a given value by the initial value
WARNING: the show-doc command is deprecated. It will be removed from future Pry versions.
Please use 'show-source' with the -d (or --doc) switch instead
Example: show-source -d
[5] pry(SimpleTest):1> nesting
Nesting status:
--
0. main (Pry top level)
1. SimpleTest
[6] pry(SimpleTest):1> cd ..
[7] pry(main)> next
From: .../blog_code_examples/pry_example.rb:9 SimpleTest#initialize:
7: def initialize(v)
8: binding.pry
=> 9: @v = v
10: end
[7] pry(#<SimpleTest>)> v
=> 3
[8] pry(#<SimpleTest>)> next
From: .../blog_code_examples/pry_example.rb:20 :
15: end
16:
17: binding.pry
18:
19: t = SimpleTest.new(3)
=> 20: t.multiply 7
21:
[9] pry(main)> t.interesting_methods
=> [:multiply]
[10] pry(main)>continue
Customisation
You can add features and configurations in $HOME/.pryrc. This is a ruby file,
mine currently looks like this:
.pryrc .pryrc
class Object
def interesting_methods
case self.class
when Class
self.public_methods.sort - Object.public_methods
when Module
self.public_methods.sort - Module.public_methods
else
self.public_methods.sort - Object.new.public_methods
end
end
end
if defined?(PryDebugger) || defined?(PryByebug)
Pry.commands.alias_command 'c', 'continue'
Pry.commands.alias_command 's', 'step'
Pry.commands.alias_command 'n', 'next'
Pry.commands.alias_command 'f', 'finish'
end
Extra
You can also edit an object, open your configured editor.
w 20 shows 20 lines of context around your current breakpoint.
Type help at any point to get a whole bunch of useful information.