Cron + Whenever + Rake

Sample Rake code

namespace :test do
desc "Pick a random participant from database"
task :pick_participant => :environment do
if Rails.env.production?
 # MySQL is used as the production DB, its random function is RAND()
 p = Participant.find(:first, :order => 'RAND()')
else
 # sqlite3 is used as the development DB, its random function is random()
 p = Participant.find(:first, :order => 'random()')
end
puts "#{Time.now}"
puts "* environment is: #{Rails.env}"
puts "* picked participant: #{p.first_name}"
end
end

To test the rake task from command line

$ bundle exec rake test:pick_participant

2011-11-04 10:49:08 -0700
* environment is: development
* picked participant: Macy

Add the rake task to Whenever gem's schedule.rb

every 1.minutes do
 rake "test:pick_participant"
end

Whenever defaults the environment to "production", to specify a different environment to run:

every 1.minutes do
  rake "test:pick_participant RAILS_ENV=development"
  #rake "test:pick_participant"
end

Call Whenever to update the crontab

$ whenever --update-crontab app_0515
[write] crontab file updated

$ crontab -l

# Begin Whenever generated tasks for: app_0515
* * * * * /bin/bash -l -c 'cd /Users/[username]/Development/rails_projects/app_0515 && RAILS_ENV=production bundle exec rake test:pick_participant --silent'

# End Whenever generated tasks for: app_0515