How to pass command line arguments to a rake task

Question

I have a rake task that needs to insert a value into multiple databases.

I\'d like to pass this value into the rake task from the command line, or from another

Answer 1

I like the "querystring" syntax for argument passing, especially when there are a lot of arguments to be passed.

Example:

rake "mytask[width=10&height=20]"

The "querystring" being:

width=10&height=20

Warning: note that the syntax is rake "mytask[foo=bar]" and NOT rake mytask["foo=bar"]

When parsed inside the rake task using Rack::Utils.parse_nested_query , we get a Hash:

=> {"width"=>"10", "height"=>"20"}

(The cool thing is that you can pass hashes and arrays, more below)

This is how to achieve this:

require 'rack/utils'

task :mytask, :args_expr do |t,args|
  args.with_defaults(:args_expr => "width=10&height=10")
  options = Rack::Utils.parse_nested_query(args[:args_expr])
end

Here's a more extended example that I'm using with Rails in my delayed_job_active_record_threaded gem:

bundle exec rake "dj:start[ebooks[workers_number]=16&ebooks[worker_timeout]=60&albums[workers_number]=32&albums[worker_timeout]=120]"

Parsed the same way as above, with an environment dependency (in order load the Rails environment)

namespace :dj do
  task :start, [ :args_expr ] => :environment do |t, args|
    # defaults here...
    options = Rack::Utils.parse_nested_query(args[:args_expr])  
  end
end

Gives the following in options

=> {"ebooks"=>{"workers_number"=>"16", "worker_timeout"=>"60"}, "albums"=>{"workers_number"=>"32", "worker_timeout"=>"120"}}