Add Evaluating One-Off Commands as a ruby til.

ruby/evaluating-one-off-commands.md

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+# Evaluating One-Off Commands
+
+When I need to quickly test something out in Ruby, I will often reach for
+`irb`. There is an even quicker way to send a line of code to ruby for
+evaluation. Use the `ruby` binary with the `-e` flag followed by your line
+of ruby. For instance,
+
+```
+$ ruby -e 'puts Class.ancestors'
+[Class, Module, Object, Kernel, BasicObject]
+```