Add Ins And Outs Of Pry as a ruby til

README.md

@@ -10,7 +10,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 For a steady stream of TILs from a variety of rocketeers, checkout
 [til.hashrocket.com](https://til.hashrocket.com/).
 
-_528 TILs and counting..._
+_529 TILs and counting..._
 
 ---
 
@@ -393,6 +393,7 @@ _528 TILs and counting..._
 - [Finding The Source of Ruby Methods](ruby/finding-the-source-of-ruby-methods.md)
 - [Identify Outdated Gems](ruby/identify-outdated-gems.md)
 - [If You Detect None](ruby/if-you-detect-none.md)
+- [Ins And Outs Of Pry](ruby/ins-and-outs-of-pry.md)
 - [Invoking Rake Tasks Multiple Times](ruby/invoking-rake-tasks-multiple-times.md)
 - [Last Raised Exception In The Call Stack](ruby/last-raised-exception-in-the-call-stack.md)
 - [Limit Split](ruby/limit-split.md)

ruby/ins-and-outs-of-pry.md

@@ -0,0 +1,26 @@
+# Ins And Outs Of Pry
+
+When executing commands during a [Pry](http://pryrepl.org/) session, you'll
+see an incrementing number for each prompt as you enter each statement.
+These numbers can be used to look up the inputs and outputs of each
+statement executed during the session. The statements and their results are
+made available in the array-like `_in_` and `_out_` objects.
+
+```ruby
+[1] pry(main)> :one
+=> :one
+[2] pry(main)> 1 + 1
+=> 2
+[3] pry(main)> ["t", "h", "r", "e", "e"].join
+=> "three"
+[4] pry(main)> _in_.to_a
+=> [nil, ":one\n", "1 + 1\n", "[\"t\", \"h\", \"r\", \"e\", \"e\"].join\n"]
+[5] pry(main)> _out_.to_a
+=> [nil, :one, 2, "three", [nil, ":one\n", "1 + 1\n", "[\"t\", \"h\", \"r\", \"e\", \"e\"].join\n"]]
+[6] pry(main)> _out_[2]
+=> 2
+[7] pry(main)> _in_[2]
+=> "1 + 1\n"
+```
+
+[source](https://github.com/pry/pry/wiki/Special-Locals#In_and_out)