Add Specify Dependencies For A Rake Task as a Ruby TIL

ruby/specify-dependencies-for-a-rake-task.md

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+# Specify Dependencies For A Rake Task
+
+Let's say you have rake task that performs some important business task. For
+instance, a book seller might want a task that can tell them the top selling
+books from a CSV report.
+
+```ruby
+task :top_selling_books do
+  # read in CSV and process for top selling books
+end
+```
+
+This works great if the CSV file already exists on the machine from which this
+task is run. What if it isn't tho?
+
+The CSV is a prerequesite for this task. We explicitly define it as a
+prerequisite using the task dependency syntax.
+
+```ruby
+task :download_latest_book_sales_csv do
+  # saves a CSV of book sales
+end
+
+task top_selling_books: :download_latest_book_sales_csv do
+  # read in CSV and process for top selling books
+end
+```
+
+We can even define multiple task dependencies with an array.
+
+```ruby
+task top_selling_books: [:download_latest_book_sales_csv, :clean_csv] do
+  # read in CSV and process for top selling books
+end
+```
+
+[source](https://subscription.packtpub.com/book/hardware_and_creative/9781783280773/1/ch01lvl1sec13/task-dependencies-prerequisites)