How to return some value from rake task

Question

How can I return some value from a Rake task in ruby.

Sample code:

namespace tasks
    task task1: :environment do |task|
      log = "Running task"
      puts log
      log << "Done"
      return log # suggest how to do this
    end
end

I am running the rake task as: Rake::Task['tasks:task1'].invoke. How can I get the return value in a variable as follows:

result = Rake::Task['tasks:task1'].invoke

Mortality

Looking through the source code for rake this appears to be not possible. Ultimately the return value for a rake task is determined from Task#execute which has a nil return value. You can take a look here. github.com/ruby/rake/blob/master/lib/rake/task.rb#L270 – Tao

Instead of calling other task result, in task1 I set result = 'something' and in task2 I can read the variable. Consider I created result variable outside task scopes, something like result = nil before any namespace/task. This is, assuming you want a task result in other task. – Artillery

In the past I have resorted to storing a flag somewhere either in a database table or in a txt file that can be read back in when needed – Verine

Answer 1

Assuming you want the task result in other task:

config = ''

task :load_config do
  config = 'some config' # this could be reading from a file or API
end

# this tasks depends on the other
task use_config: [:load_config] do
  puts config
end

Then:

$ bundle exec rake use_config
some config

Aureus

Answer 2

Call the Rake's action directly.

Using @vigo's example because it's simple.

task :return_a_value do
  '123'
end

result = Rake::Task['return_a_value'].actions.first.call

puts result #=> "123"

I found this out by digging through the various methods of the Rake Task in the console and this appeared to work without having to run the task twice, like @vido's answer.

However, the only caveat I've found is that I couldn't figure out how to pass arguments to the Rake Task using this method. Using .call( "myargument" ) didn't work. If you can figure out how to do this, I'd be grateful if you shared it. Thanks!

Update: Figured it out.

After a little more experimentation, I figured out how to use this method while passing arguments to the Rake Task. You just have to pass a Hash of the arguments as the second parameter and nil as the first, like so:

task :return_a_value, :mystring do
  mystring
end

result = Rake::Task['return_a_value'].actions.first.call( nil, { mystring: "hellow there" } )

puts result #=> "hellow there"

It has the added benefit of naming the parameters you pass to the Rake Task, which is a nice bonus.

---

Versions

• Rails: 7.0.7
• Ruby: 3.2.2

Ocko

One caveat I noticed when using this is that it didn't seem to preload my models. I ended up going a different direction but you may need to load in your environment manually. – Ocko

Answer 3

Try aborting with an error message and catching that.

Depending on what you're trying to return, you could try aborting the task with an error message, which would be "catchable" from where you invoked the task. You could then see what the error message was.

Your Task

namespace :tasks
  task task1: :environment do |task|
    log = "Running task... "
    puts log
    log << "Done!"
    abort( log )
  end
end

Running Your Task

begin
  Rake::Task[ "tasks:task1" ].invoke
rescue SystemExit => exit
  puts exit.message #=> "Running task... Done!" 
end

It's not exactly elegant but depending on what you're trying to return it could handle your needs.

Ocko

Answer 4

You can exit a rake task with a code and then check that with $?

But perhaps rake might not really the right tool for this job.

Polestar

Answer 5

task :return_a_value do
  '123'
end

task :hello do
  result = Rake::Task['return_a_value'].invoke.first.call
  puts result
end

now call:

$ rake hello
123

Impart

this runs task return_a_value twice. You can check this if you add a print before the return – Artillery

if you add more prints, you'll see more executions. thats why .invoke.first (from an array) important. when you inject print statement, it will be another statement to run. try with double print lines. such as print 'a' (new line) print 'b' (new line) and '123' – Impart

invoke will run the task and store it in an array, and first.call will run the task one more time – Artillery

they are all proc in the array. any suggestions? @JuanJoséRamírez – Impart