Say you want to do run some stats on your Ruby on Rails application nightly. Create a rake task to do what you want then use cron to execute it.

First we need to create the RoR application.

rails cron
cd cron
script/generate model my_model
vi config/database.yml (set the database username/password, and databases created in your environment)

First lets see how to call any ruby code from rake. Rake code is placed in lib/tasks/FILENAME.rake. So lets create a lib/tasks/cron.rake and place this code in it:

namespace :cron do
  desc "Just what Date is it really"
  task(:dummy ){ p Date::today.to_s  }
end

running rake -T cron gives us this:

rake -T cron
(in /Users/linda/example/cron)
rake cron:dummy  # Just what Date is it really

now lets execute the the rake task

 rake cron:dummy
(in /Users/linda/example/cron)
"2007-09-23"

Ok so that shows us how to call any kind of ruby code from rake. But what happens when you want to do something fancy and work with the database.

This is actually how I use the rake tasks the most. To do some expensive calculations on the database. For example lets say there is a model called MyModel which has a method called calc_stats. Add the following code to your model:

class MyModel < ActiveRecord::Base
  def self.calc_stats
    # Do something spiffy with the model here
    "Finished!"
  end
end

So the additional rake code /lib/tasks/cron.rake would look like this:

  desc "Example of calling a model"
  task(:calcstats => :environment){ p MyModel.calc_stats  }

rake -T cron
(in /Users/linda/example/cron)
rake cron:dummy        # Just what Date is it really
rake cron:calcstats    # Example of calling a model

Lets execute the rake task

rake RAILS_ENV=production cron:calcstats
(in /Users/linda/example/cron)
"Finished!"

To create the cron job from webmin webmin→System→Schedule Cron Jobs→Create a new cron job

• Execute cron job as: root
• Command: (See below for the proper format)
• Then set the appropriate schedule for the task

cd /path/to/rails/app && /opt/csw/bin/rake cron:dummy

cd /path/to/rails/app && /opt/csw/bin/rake RAILS_ENV=production cron:calcstats