This is the most basic regular expression in the universe, and it will make you cry tears of frustration.
Given a string, it will find all occurrences of the word "cat" and replace them with "CAT" using the power of regex!
But be warned, it's not just any regex, it's the most basic regex in the universe, with the most basic syntax.
It's like a kindergartener trying to build a house with blocks, but with more code and less understanding.
cat|CAT
Just copy and paste this regex into your favorite editor and watch it fail in a blaze of glory.
Or, if you're feeling adventurous, you can try to modify it and see if you can make it slightly less basic.
Example 2: The Slightly Less Basic Regular Expression