Whenever is a Ruby gem that provides a clear syntax for defining cron jobs. It outputs valid cron syntax and can even write your crontab file for you. It is designed to work well with Rails applications and can be deployed with Capistrano. Whenever works fine independently as well.

Ryan Bates created a great Railscast about Whenever: railscasts.com/episodes/164-cron-in-ruby

Discussion: groups.google.com/group/whenever-gem

$ sudo gem install whenever

$ cd /my/rails/app
$ wheneverize .

This will create an initial “config/schedule.rb” file you.

every 3.hours do
  runner "MyModel.some_process"       
  rake "my:rake:task"                 
  command "/usr/bin/my_great_command"
end

every 1.day, :at => '4:30 am' do 
  runner "MyModel.task_to_run_at_four_thirty_in_the_morning"
end

every :hour do # Many shortcuts available: :hour, :day, :month, :year, :reboot
  runner "SomeModel.ladeeda"
end

every :sunday, :at => '12pm' do # Use any day of the week or :weekend, :weekday
  runner "Task.do_something_great"
end

More examples on the wiki: wiki.github.com/javan/whenever/instructions-and-examples

Whenever ships with three pre-defined job types: command, runner, and rake. You can define your own with job_type.

For example:

job_type :awesome, '/usr/local/bin/awesome :task :fun_level'

every 2.hours do
  awesome "party", :fun_level => "extreme"
end

Would run /usr/local/bin/awesome party extreme every two hours. :task is always replaced with the first argument, and any additional :whatevers are replaced with the options passed in or by variables that have been defined with set.

The default job types that ship with Whenever are defined like so:

job_type :command, ':task'
job_type :runner,  'cd :path && script/runner -e :environment ":task"'
job_type :rake,    'cd :path && RAILS_ENV=:environment /usr/bin/env rake :task'

If a :path is not set it will default to the directory in which whenever was executed. :environment will default to ‘production’.

$ cd /my/rails/app
$ whenever

And you’ll see your schedule.rb converted to cron sytax. Note: running ‘whenever’ with no options does not display your current crontab file, it simply shows you the output of converting your schedule.rb file.

In your “config/deploy.rb” file do something like:

after "deploy:symlink", "deploy:update_crontab"

namespace :deploy do
  desc "Update the crontab file"
  task :update_crontab, :roles => :db do
    run "cd #{release_path} && whenever --update-crontab #{application}"
  end
end

This will update your crontab file, leaving any existing entries unharmed. When using the --update-crontab option, Whenever will only update the entries in your crontab file related to the current schedule.rb file. You can replace the #{application} with any identifying string you’d like. You can have any number of apps deploy to the same crontab file peacefully given they each use a different identifier.

If you wish to simply overwrite your crontab file each time you deploy, use the --write-crontab option. This is ideal if you are only working with one app and every crontab entry is contained in a single schedule.rb file.

By mixing and matching the --load-file and --user options with your various :roles in Capistrano it is entirely possible to deploy different crontab schedules under different users to all your various servers. Get creative!

If you want to override a variable (like your environment) at the time of deployment you can do so with the --set option: wiki.github.com/javan/whenever/setting-variables-on-the-fly

Whenever was created for use at Inkling (inklingmarkets.com) where I work. Their take on it: blog.inklingmarkets.com/2009/02/whenever-easy-way-to-do-cron-jobs-from.html

While building Whenever, I learned a lot by digging through the source code of Capistrano - github.com/jamis/capistrano

For general discussion and questions, please use the google group: groups.google.com/group/whenever-gem

If you’ve found a genuine bug or issue, please use the Issues section on github: github.com/javan/whenever/issues

Copyright © 2009+ Javan Makhmali

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