12 Gems of Christmas #3 – thor


Ever try to write a rake task that took one or more arguments? How about calling a rake task from another task? Rake makes basic invocation simple but everything else obtuse. Enter thor, courtesy of the unstoppable Yehuda Katz. Thor aims to make command line script development simpler by making your scripts standard Ruby objects and providing good documentation in its wiki for many common use cases. Consider a simple example, create a task to process a CSV file:

# inventory.thor
class Inventory < Thor
  include Thor::Actions

  desc "process_csv FILE", "process the nightly inventory update"
  method_option :delete, :aliases => "-d", :desc => "Delete the file after parsing it"
  def process_csv(file)
    # do something, maybe like:
    #require 'inventory_file'
    remove_file(file) if options[:delete]

You invoke the task via thor inventory:process_csv some_file.csv. Tasks are just public methods within a subclass of Thor. The desc and method_option methods describe those tasks and any expected options on the command line. Thor::Actions gives us some filesystem helper methods, like remove_file. The wiki goes into further detail on things like inter-task dependencies, task grouping, namespaces, etc. Next time you need to write a command line script, give Thor a try and see if it doesn’t make your life easier.

Tomorrow, I’ll show you a tool for detecting and fixing a common Rails performance problem.