Rake task with an arbitrary number of arguments

Rake gives you a way of specifying arguments for a given task like this:

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desc "A task that can accept a optional 'foo' argument"
task :thing, [:foo] do |task, args|
  puts args[:foo]
end

This will make the value of foo available in the args variable. When you run rake -T, it will show you that argument like this:

$> rake -T
rake thing[foo]  # A task that can accept a optional 'foo' argument

But what if you want to allow an arbitrary number of arguments, like a list of usernames to report on?

A solution

You could use an alternative method of passing arguments in, such as ARGV or Environment Variables, but Rake does provide a way. The args block parameter behaves like a hash, but it is actually a Rake::TaskArguments object. This object responds to an #extras method that will return an array of any extra arguments.

For example:

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task :thing, [:foo] do |task, args|
  puts args[:foo]     # First argument
  puts args.extras    # The rest of the arguments
end

This will allow you to call the task like this:

$> rake thing[foo]
foo

$> rake thing[foo,extra1,extra2]
foo
extra1
extra2

Caveats

While you can specify many arguments on the command line, (unless they are quoted) the arguments can not be separated by spaces, for example:

$> rake thing[foo,extra1]    # GOOD
foo
extra1
$> rake thing[foo, extra1]   # BAD
Don't know how to build task 'thing[foo,'

This means you may want to include some explanation in the desc section.

Also, rake -T will not show the “extra” arguments, only the named arguments:

$> rake -T
rake thing[foo]  # A task that can accept a optional 'foo' argument