260

I have a rake task where I do some checks at the beginning, if one of the checks fails I would like to return early from the rake task, I don't want to execute any of the remaining code.

I thought the solution would be to place a return where I wanted to return from the code but I get the following error

unexpected return
Simone Carletti
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Janak
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7 Answers7

336

A Rake task is basically a block. A block, except lambdas, doesn't support return but you can skip to the next statement using next which in a rake task has the same effect of using return in a method.

task :foo do
  puts "printed"
  next
  puts "never printed"
end

Or you can move the code in a method and use return in the method.

task :foo do
  do_something
end

def do_something
  puts "startd"
  return
  puts "end"
end

I prefer the second choice.

Pablo Fernandez
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Simone Carletti
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    I like the second one best, too. The more I use rake, the more I like to keep non-trivial code outside of the task definition. Not a 100% firm rule, but seems to be a good guideline to work to. – Mike Woodhouse Feb 23 '10 at 09:02
  • I absolutely agree. Also, methods are much more easier to test. – Simone Carletti Feb 23 '10 at 10:43
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    The second solution is nicer. In your first solution, I would prefer to use break instead of next to get out of the block... Should work too, shouldn't it? – severin Feb 23 '10 at 13:34
  • @severin Yes, it should. I agree, break makes more sense. – Simone Carletti Feb 23 '10 at 13:47
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    I've tried with `break` and I've got this error: rake aborted! break from proc-closure (See full trace by running task with --trace) – Pablo Fernandez Jun 19 '10 at 07:27
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    I prefer using next. Why should we declare a new method just to support early returns? – Derek Greer Dec 01 '11 at 16:16
  • I agree, Derek. I'd prefer to keep the code for my rake task within the task definition itself rather than be required to split it into two places (there and a method def). Of course sometimes it makes sense to extract the code into a class or method to make it more testable/reusable, but you shouldn't be forced to. – Tyler Rick Feb 15 '12 at 22:11
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    Does anyone know why "next" works and "break" doesn't?? "next" sounds like you're in a loop; "break" sounds more appropriate, but I get a "break from proc-closure" if I try that. – Tyler Rick Feb 15 '12 at 22:12
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    What do you do if you're deeply nested within multiple blocks? (`next` only works if there's on "level" of block to break out of. – mjs Jan 30 '13 at 17:16
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    Warning: declaring methods in Rake tasks is a bad idea because they are global to all loaded Rake tasks, irrelevant of namespace. Next is used instead of break because the code in the block may be called multiple times by whatever is executing the block (think of the .each method). – Leslie Viljoen Oct 04 '16 at 22:04
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    I can't stress enough what @LeslieViljoen said. Declaring the method `do_something` in your rake file means it pollutes _all_ other rake files. There is no "private" methods in rake files. So if you have another rake file that also defined `do_something` you'll get a collision, but worse than that, they will collide silently and you'll find yourself running a completely different method without knowing it. Very dangerous. – Joshua Pinter May 09 '18 at 18:40
  • To avoid the nameclash / global namespace pollution, just define your methods as static methods inside a named module. – Qortex Jul 19 '19 at 09:00
  • @JoshuaPinter I've seen this go beyond just affecting other Rake files to actually clobbering methods in a Rails app. Definitely not a good idea – Casey Nov 02 '20 at 21:10
  • I treat rake tasks as a controller. Ideally, a rake task is a single call to a model or service method, with *zero* knowledge of what's under the hood. Sometimes it makes sense to process input and format output in the task, when parameters or output are essential. That code is appropriate in the task (aka controller). – David Hempy Aug 31 '22 at 14:33
  • The answers with the `exit` / `abort` approaches are superior for the reasons noted of correctly setting the exit status. They are also more idiomatic. – dferrazm May 11 '23 at 08:30
209

You can use abort(message) from inside the task to abort that task with a message.

Sergikon
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    @TylerRick No, it's [Kernel#abort](http://www.ruby-doc.org/core-1.9.3/Kernel.html#method-i-abort). – Jo Liss Jun 11 '12 at 02:42
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    This way is superior for exiting in non-success situations as it automatically sets exit status. – samuil May 28 '14 at 08:44
  • This is a winner. Also an easy way to provide usage feedback for argument errors. – David Hempy Dec 12 '17 at 05:28
  • Inline and much more explanatory than `next`. Love it. – SomeSchmo May 04 '18 at 15:24
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    This might not be a good idea if you are testing your rake task, this will most likely have the test fail. – user2953607 Mar 30 '21 at 22:15
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    I like this in code, but just discovered a problem with it. `abort` goes all the way up the stack. That includes your rspec test. I had `expect(Logger).to receive... call_task()` This did not fail, and in fact did not complete the test. So it *looked* like the test pass, even when I still had a bug in my rake task's `abort` logic. For this reason, I'll go back to `next`. YMMV – David Hempy Aug 31 '22 at 14:46
47

Return with an Error ❌

If you're returning with an error (i.e. an exit code of 1) you'll want to use abort, which also takes an optional string param that will get outputted on exit:

task :check do
  
  # If any of your checks fail, you can exit early like this.
  abort( "One of the checks has failed!" ) if check_failed?

end

On the command line:

$ rake check && echo "All good"
#=> One of the checks has failed!

Return with Success ✅

If you're returning without an error (i.e. an exit code of 0) you'll want to use exit, which does not take a string param.

task :check do
  
  # If any of your checks fail, you can exit early like this.
  exit if check_failed?
  
end

On the command line:

$ rake check && echo "All good"
#=> All good

This is important if you're using this in a cron job or something that needs to do something afterwards based on whether the rake task was successful or not.

Bonus: Return with an Error from a rescue block without the stacktrace.

By default, if you use abort inside of a rescue block, it will output the entire stack trace, even if you just use abort without re-raising the error.

To get around this, you can supply a non-zero exit code to the exit command, like:


task :check do

  begin
    do_the_thing_that_raises_an_exception
  rescue => error
    puts error.message
 
    exit( 1 )
  end

end
Joshua Pinter
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    This one should be accepted answer @simone-carletti – Daniel Gomez Rico Jan 19 '22 at 12:44
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    No, it shouldn't. This will not just bump you out of the task, it will bump you out of the entire stack, terminating the entire process that invoked it. This will crash your application if you invoke them inline, or give you false positives when you're writing tests for them. Using `next` is the only "right" way of doing it. – Pelle Nov 14 '22 at 11:37
23

I tend to use abort which is a better alternative in such situations, for example:

task :foo do
  something = false
  abort 'Failed to proceed' unless something
end
khelll
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    But how do you `abort` without exiting with a `1` exit code? Rake tasks are often use in the command line to determine success or failure. Is there a "successful" `abort`? – Joshua Pinter May 09 '18 at 18:41
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    Answered my own questions: looks like `exit` is a good way to exit successfully. – Joshua Pinter May 09 '18 at 18:50
13

If you need to break out of multiple block levels, you can use fail.

For example

task :something do
  [1,2,3].each do |i|
    ...
    fail "some error" if ...
  end
end

(See https://stackoverflow.com/a/3753955/11543.)

Community
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mjs
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9

If you meant exiting from a rake task without causing the "rake aborted!" message to be printed, then you can use either "abort" or "exit". But "abort", when used in a rescue block, terminates the task as well as prints the whole error (even without using --trace). So "exit" is what I use.

ZX12R
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    In general, I think using "exit" instead of return/break is a bad idea since it doesn't just jump out of the *current* proc/method/etc. -- it exits the entire process and skips any code that the caller method may have intended to be run afterwards (including possibly some cleanup). But for a rake task I guess it's probably not a problem... – Tyler Rick Feb 15 '12 at 22:18
  • _"abort", when used in a rescue block, terminates the task as well as prints the whole error (even without using --trace)._ Boy were you right with this! Couldn't find this anywhere else. I've updated my answer to indicate this as well. Thanks! – Joshua Pinter Apr 18 '21 at 00:27
0

I used next approach suggested by Simone Carletti, since when testing rake task, abort, which in fact is just a wrapper for exit, is not the desired behavior.

Example:

task auto_invoice: :environment do
  if Application.feature_disabled?(:auto_invoice)
    $stderr.puts 'Feature is disabled, aborting.'
  next
end
Artur INTECH
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