Add Invoking Rake Tasks Multiple Times as a ruby til.

ruby/invoking-rake-tasks-multiple-times.md

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+# Invoking Rake Tasks Multiple Times
+
+I have a rake task, `build`, that builds a single record for development
+purposes. I want a supplemental rake task, `build:all`, that builds a bunch
+of different records. To keep things dry, `build:all` should just invoke
+`build` a number of times.
+
+```ruby
+namespace :build do
+  task :all do
+    predefined_list.each do |data|
+      Rake::Task["build"].invoke(data)
+    end
+  end
+end
+```
+
+This doesn't work though. No matter how many items are in the list, the
+`build` task only seems to get run once. This is because by default tasks
+can only be invoked once in a given context. To get around this, the task
+needs to be reenabled after each invocation.
+
+```ruby
+namespace :build do
+  task :all do
+    predefined_list.each do |data|
+      Rake::Task["build"].invoke(data)
+      Rake::Task["build"].reenable
+    end
+  end
+end
+```