before_all Rake hook

gistfile1.txt

$ rake one
> always_run_before_one
> always_run_before_two
> one

$ rake nested:two
> always_run_before_one
> always_run_before_two
> two

$ rake three
> three

Rakefile

module Rake::DSL
  def before_all(*args)
    args.each do |pair|
      matchers, task_names = pair.to_a.first

      tasks = []
      [ *matchers ].each do |matcher|
        matcher = matcher.to_s if matcher.is_a?(Symbol)
        tasks += Rake::Task.tasks.select { |task| !!task.name.match(matcher) }
      end

      tasks.each { |task| task.enhance([ *task_names ]) }
    end
  end
end

task :one do
  puts '> one'
end

namespace :nested do
  task :two do
    puts '> two'
  end
end

task :three do
  puts '> three'
end

task :always_run_before_one do
  puts '> always_run_before_one'
end

task :always_run_before_two do
  puts '> always_run_before_two'
end

before_all [ /^one$/, 'nested:two' ] => [ 'always_run_before_one', 'always_run_before_two' ]