Commit 3e27219

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+# [Topic Exchanges](http://www.rabbitmq.com/tutorials/tutorial-five-ruby.html)
+
+In this example we publish and subscribe to a topic exchange.
+Which gives us if more granularity with the type of messages we
+subscribe to.
+
+Topic Exchanges allows us to specify routing keys in form of:
+
+```ruby
+"canada.alberta.calgary"
+"canada.alberta.*"
+"canada.#"
+```
+
+* \* to substitute exactly one word.
+* # to substitue zero or more words
+
+To publish:
+
+```bash
+λ ruby lib/4-topic-exchange/publish.rb git.error 'just kidding'
+ [x] Sent 'blah'
+λ ruby lib/4-topic-exchange/publish.rb vim.warning 'too good'
+ [x] Sent 'blah'
+```
+
+To subscribe:
+
+```bash
+λ ruby lib/5-topic-exchange/subscribe.rb vim.warning
+ [*] Waiting for logs. To exit press CTRL+C
+ [x] vim.warning:too good
+```
+or 
+```bash
+λ ruby lib/5-topic-exchange/subscribe.rb git.#
+ [*] Waiting for logs. To exit press CTRL+C
+ [x] git.error:just kidding
+```