Add Zero Padding as a ruby til.

README.md

@@ -141,6 +141,7 @@ smart people at [Hashrocket](http://hashrocket.com/).
 - [Summing Collections](ruby/summing-collections.md)
 - [Uncaught Exceptions In Pry](ruby/uncaught-exceptions-in-pry.md)
 - [`undef_method` And The Inheritance Hierarchy](ruby/undef-method-and-the-inheritance-hierarchy.md)
+- [Zero Padding](ruby/zero-padding.md)
 
 ### tmux
 

ruby/zero-padding.md

@@ -0,0 +1,22 @@
+# Zero Padding
+
+Ruby makes zero-padding strings to a fixed length easy with `String#rjust`.
+
+```ruby
+> "1234".rjust(6, "0")
+=> "001234"
+> "123456".rjust(6, "0")
+=> "123456"
+```
+
+In the same way, you can pad zeros on the other side of the string with
+`String#ljust`.
+
+```ruby
+> "12".ljust(4, "0")
+=> "1200"
+> "".ljust(4, "0")
+=> "0000"
+```
+
+h/t Dillon Hafer