handle-named-arguments-in-a-rake-task.md

Handle Named Arguments In A Rake Task

There are a number of ways to pass arguments into a Rake task. The standard approach only allows for positional arguments. When I need named and optional arguments, my preferred approach is to use environment variables.

Here is a skimmed down version of a user lookup task. Notice the task definition itself doesn't include any arguments. Instead, a couple optional values are extracted from the environment (ENV) at the beginngin of the task.

desc "An example task with named, optional arguments"
task :lookup_user => :environment do
  user_id = ENV['USER_ID']
  email = ENV['EMAIL']

  if user_id.present?
    user = User.find(user_id)

    if user.blank?
      puts "No user for id ##{user_id}"
    end
  elsif email.present?
    user = User.find_by(email: email)

    if user.blank?
      puts "No user for email #{email}"
    end
  end

  puts "User found" if user.present?
end

This task can be invoked in the following ways:

$ rake lookup_user USER_ID=123

$ rake lookup_user EMAIL="user@example.com"

or even with both arguments included, in which case the task has been written to give precedence to USER_ID:

$ rake lookup_user EMAIL="user@example.com" USER_ID=123