Ruby – How to return early from a rake task

rakeruby

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

Best Answer

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.

Related Solutions

Ruby – How to call shell commands from Ruby

This explanation is based on a commented Ruby script from a friend of mine. If you want to improve the script, feel free to update it at the link.

First, note that when Ruby calls out to a shell, it typically calls /bin/sh, not Bash. Some Bash syntax is not supported by /bin/sh on all systems.

Here are ways to execute a shell script:

cmd = "echo 'hi'" # Sample string that can be used

Kernel#` , commonly called backticks – `cmd`

This is like many other languages, including Bash, PHP, and Perl.

Returns the result (i.e. standard output) of the shell command.

Docs: http://ruby-doc.org/core/Kernel.html#method-i-60
```
value = `echo 'hi'`
value = `#{cmd}`
```
Built-in syntax, %x( cmd )

Following the x character is a delimiter, which can be any character. If the delimiter is one of the characters (, [, {, or <, the literal consists of the characters up to the matching closing delimiter, taking account of nested delimiter pairs. For all other delimiters, the literal comprises the characters up to the next occurrence of the delimiter character. String interpolation #{ ... } is allowed.

Returns the result (i.e. standard output) of the shell command, just like the backticks.

Docs: https://docs.ruby-lang.org/en/master/syntax/literals_rdoc.html#label-Percent+Strings
```
value = %x( echo 'hi' )
value = %x[ #{cmd} ]
```
Kernel#system

Executes the given command in a subshell.

Returns true if the command was found and run successfully, false otherwise.

Docs: http://ruby-doc.org/core/Kernel.html#method-i-system
```
wasGood = system( "echo 'hi'" )
wasGood = system( cmd )
```
Kernel#exec

Replaces the current process by running the given external command.

Returns none, the current process is replaced and never continues.

Docs: http://ruby-doc.org/core/Kernel.html#method-i-exec
```
exec( "echo 'hi'" )
exec( cmd ) # Note: this will never be reached because of the line above
```

Here's some extra advice: $?, which is the same as $CHILD_STATUS, accesses the status of the last system executed command if you use the backticks, system() or %x{}. You can then access the exitstatus and pid properties:

$?.exitstatus

For more reading see:

Ruby – How to run Rake tasks from within Rake tasks

If you need the task to behave as a method, how about using an actual method?

task :build => [:some_other_tasks] do
  build
end

task :build_all do
  [:debug, :release].each { |t| build t }
end

def build(type = :debug)
  # ...
end

If you'd rather stick to `rake`'s idioms, here are your possibilities, compiled from past answers:

This always executes the task, but it doesn't execute its dependencies:
```
Rake::Task["build"].execute
```
This one executes the dependencies, but it only executes the task if it has not already been invoked:
```
Rake::Task["build"].invoke
```
This first resets the task's already_invoked state, allowing the task to then be executed again, dependencies and all:
```
Rake::Task["build"].reenable
Rake::Task["build"].invoke
```
Note that dependencies already invoked are not automatically re-executed unless they are re-enabled. In Rake >= 10.3.2, you can use the following to re-enable those as well:
```
Rake::Task["build"].all_prerequisite_tasks.each(&:reenable)
```