error while running rake task – “Don’t know how to build task”

The default method to pass arguments to Rake tasks is to give the parameters in square brackets –

desc 'Method #1: Use the default rake way to add two numbers and log the result'
task :add, [:num1, :num] do |t, args|
  puts args[:num1].to_i + args[:num].to_i
end

Reference: 4 ways to pass arguments to a Rake task

$ rake add[1,2]
# => 3

However, I would rather pass the arguments like this –

$ rake add 1 2
# => 3

This is Method #3, in the article above.

The key part here is that all the arguments passed should be symbolized. The rake task should then be –

desc 'Method #3: Use ARGV to add two numbers and log the result'
task :add do
  ARGV.each { |a| task a.to_sym do ; end }
  puts ARGV[1].to_i + ARGV[2].to_i
end

For whatever reason, if the arguments don’t get symbolized, we get this error

$ rake add 1 2
["add", "1", "2"]
3
rake aborted!
Don't know how to build task '1' (See the list of available tasks with `rake --tasks`)

So, the way to avoid this error, even when the arguments are not symbolized, is to add exit! at the end of the rake task –

desc 'Method #3: Use ARGV to add two numbers and log the result'
task :add do
  puts ARGV[1].to_i + ARGV[2].to_i
  exit!
end