I am writing my first Sinatra application and would like to use Pry to inspect/debug some things going on in the application. I haven't used Pry before either, but I would like to try it out. How would I get started using Pry with my Sinatra application?
Answer
Summary
- Use
require 'pry'at the top of your application. - Call
binding.pryin your code whenever you want to drop into the interactive session. For information on using Pry, see Turning IRB on its head with Pry and the Pry wiki. - When you are done with a particular interactive session, type
exitor Ctrl-D; Sinatra will resume running where it left off.
Example
require 'sinatra'
require 'pry'
get '/' do
@cats = rand(100)
html = haml :index
binding.pry
html
end
__END__
@@index
%html
<head><title>Hello World</title></head>
%body
%p I have #{@cats} cat#{:s unless @cats==1}!
Here's what it looks like when I start the web server:
C:\>ruby pry_into_sinatra.rb
== Sinatra/1.2.6 has taken the stage on 4567 for development with backup from Thin
>> Thin web server (v1.2.11 codename Bat-Shit Crazy)
>> Maximum connections set to 1024
>> Listening on 0.0.0.0:4567, CTRL+C to stop
When I make a request in a web browser to http://localhost:4567 the console drops into the Pry debugger before sending the result:
From: pry_into_sinatra.rb @ line 7 in Sinatra::Application#HEAD /:
2: require 'pry'
3:
4: get '/' do
5: @cats = rand(100)
6: html = haml :index
=> 7: binding.pry
8: html
9: end
10:
11: __END__
12: @@index
pry(#<Sinatra::Application:0x3300ac8>)> @cats
=> 42
pry(#<Sinatra::Application:0x3300ac8>)> puts html
<html>
<head><title>Hello World</title></head>
<body>
<p>I have 42 cats!</p>
</body>
</html>
=> nil
pry(#<Sinatra::Application:0x3300ac8>)> exit
127.0.0.1 - - [24/Aug/2011 13:25:57] "GET / HTTP/1.1" 200 96 28.5390
127.0.0.1 - - [24/Aug/2011 13:25:57] "GET /favicon.ico HTTP/1.1" 404 447 0.0010
Further Debugging
If you want to be able to use traditional debugging commands, such as setting line-based breakpoints, or stepping, or breaking when exceptions are raised, see the PryDebug library by Mon-Ouie.