Ruby-Debug uses rdebug (instead of irb) as the debugger when you run a Ruby on Rails app.
This means that you can see the code around your breakpoint, and examine variables more easily.

WINDOWS ERROR with ROR 2.0.2: seems to be broken for win32..had to go back to gem before ruby-debug was split into base & debug..like this.. gem install ruby-debug -v 0.7.5

Ruby-debug Home Page

an (outdated) example

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Instructions

(These steps were tested using Ruby 1.8.6 and Rails 1.2.3. They should work for earlier versions as well, unless ruby-debug specifically says ‘Nope!’. The install and usage will probably be different once Rails 2.0 comes out.)

• To install, type:

gem install ruby-debug

• In your config/environments/development.rb file, add this to the bottom line:

require 'ruby-debug'

• Then, if using mongrel or webBrick (lighttpd or anything using FastCGI won’t work with this), start your server as normal:

script/server

• (In EDGE Rails and Rails 2.0, it should be possible to use the—debugger flag when starting the server: script/server --debugger or ruby script/server --debugger for Windows people)

• In your code, add debugger to the lines where you want to inspect your code (use just like breakpoint)

• When your application gets to that point, the console window in which you started the server will drop into the debugger program where you can play with it!

• Typing help will allow you to see a list of commands: help command will give you more detail on each one.

• If you want to inspect variables once in debugger mode, you can type p insert_variable_name_here to print it. Also typing “set autoeval” makes everything you type print out.

• Since you aren’t exactly in a console mode by default, type irb to drop into an interactive ruby console (equivalent to irb or script/console). Now you can really have fun!

• See the Railscasts: Debugging with ruby-debug movie to get up to speed.

- Adam G.

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