Introduction

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

Installation

Regular (non-Rails) install:

  $ gem sources -a http://gems.github.com  #you only need to run this once
  $ sudo gem install javan-whenever

In a Rails (2.1 or greater) application:

in your "config/environment.rb" file:

  Rails::Initializer.run do |config|
    config.gem 'javan-whenever', :lib => false, :source => 'http://gems.github.com'
  end

To install this gem (and all other missing gem dependencies), run rake gems:install (use sudo if necessary).

In older versions of Rails:

  $ gem sources -a http://gems.github.com  #you only need to run this once
  $ gem install javan-whenever

in your "config/environment.rb" file:

  Rails::Initializer.run do |config|
    ...
  end

  require 'whenever'

NOTE: Requiring the whenever gem inside your Rails application is technically optional. However, if you plan to use something like Capistrano to automatically deploy and write your crontab file, you’ll need to have the gem installed on your servers, and requiring it in your app is one way to ensure this.

Getting started

  $ cd /my/rails/app
  $ wheneverize .

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

Example schedule.rb file

  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

Output redirection

In your schedule.rb file you can specify the redirection options for your commands at a global or command level by setting the ‘output’ variable.

  # adds ">> /path/to/file.log 2>&1" to all commands
  set :output => '/path/to/file.log'

Or you can STDOUT and STDERR separately,

  # adds ">> cron.log 2> error.log" to all commands
  set :output => {:error => 'error.log', :standard => 'cron.log'}

  # adds ">> cron.log" to all commands
  set :output => {:standard => 'cron.log'}

  # adds "2> error.log" to all commands
  set :output => {:error => 'error.log'}

Additionally you can set these values at the command level,

  every 3.hours do
    runner "MyModel.some_process", :output => 'cron.log'
    rake "my:rake:task", :output => {:error => 'error.log', :standard => 'cron.log'}
    command "/usr/bin/cmd"
  end

In all cases you can if you explicitly set the value of any output to ‘nil’ it will add a redirect to /dev/null

  # adds ">> /dev/null 2>&1" to all commands
  set :output => nil
  set :output => {:error => nil, :standard => nil}

  # adds ">> /dev/null" to all commands
  set :output => {:standard => nil}

  # adds "2> /dev/null" to all commands
  set :output => {:error => nil}

Cron output

  $ cd /my/rails/app
  $ whenever

And you’ll see your schedule.rb converted to cron sytax

Capistrano integration

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

Credit

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

Discussion / Feedback / Issues / Bugs

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

License

Copyright © 2009 Javan Makhmali

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.