This document provides an introduction to regular expressions (regex). It explains that regex allows you to find text patterns through wildcards and defines patterns. Examples are given of how regex can be used to validate input, find and replace text, check for text in proximity to other text, and apply conditionals. The document suggests regex can help tasks like formatting exam questions from a list to a table format. Resources for learning more about regex are also provided.

1. (?<=REGEX)
PRIMER
D A L L A S H A C K E R S A S S O C I AT I O N
C H R I S M E R C E R – D H A @ Z A I M O R . C O M

2. DISCLAIMER
• IANARE: I am not a RegEx expert
• This is a crash course in what RegEx
is and what it can do
• Hopefully this will teach you some
new tricks to make your text
transforming bearable

3. DID YOU KNOW…
• Raise your hand if you’ve heard of RegEx!
• Put them DOWN if you DIDN’T know you could use RegEx to:
– Validate input (make sure someone put in a correctly formed email)
– Find text in code, in commands, and in text apps like vim, atom,
notepad++
– Find matches before or after other text (like finding a q without a u)
– Find text based on conditions (find A followed by T if it starts with C,
otherwise followed by S)
– Find AND REPLACE variable pieces of text (replace full names with
initials)
• If your hand is still up, go pick locks. You’re not learning anything
from me today. For the rest of you…

4. WTF IS REGEX?
• RegEx, or Regular Expressions, is a defined
“pattern” used for finding a specific string of text
• Wildcards on steroids
• You can find text that:
– Is before or after other text
– Is made up of a set of characters
– Is grouped together/saved to reference later
– Includes of tabs, spaces, new lines, special characters
• Several flavors/implementations, all “mostly”
compatible

5. VALIDATE/SEARCH
• Easiest, most well-known way to use RegEx
• Find a variable string of text, or validate that user input matches a required format

6. USE IT ANYWHERE

7. FIND TEXT IN PROXIMITY
• Lookahead (Positive or Negative)
– Find “bob” but only before “saget”
– Find “bob” but NOT before “saget”
• Lookbehind (Positive or Negative)
– Find “saget” but only after “bob”
– Find “saget” but NOT after “bob”

8. CONDITIONALS
• Home-grown syntax checking
• Assume anything starting with { must end with }, ( must end with ):

9. REPLACE
^([A-Z])(?:[a-z])*(?:s(?:([A-Z])(?:[a-z])*))?s(?:([A-Z])(?:[a-z])*)$
• Find (F)irst (optional (M)iddle) (L)ast, save initials to $1, $2, $3
– James Bond
– Rory Gilmore
– Johnny Appleseed
– George W Bush
– Jimmy Jo Bob
• Replace with “First: $1 Middle: $2 Last: $3":
– First: J Middle: Last: B
– First: R Middle: Last: G
– First: J Middle: Last: A
– First: G Middle: W Last: B
– First: J Middle: J Last: B

10. HOW DOES THIS HELP AVERAGE JOE?
What if…
I’m a teacher, and I want to take an old exam with 100 questions that looked like this:
1. Question
Answer 1
Answer 2
Answer 3
Answer 4
And format it for importing to another system like this:
Question 1|Question|A. Answer 1|B. Answer 2|C. Answer 3|D. Answer 4
Question 2|Question|A. Answer 1|B. Answer 2|C. Answer 3|D. Answer 4

11. RESOURCES
• https://www.regular-expressions.info/tutorial.html
• https://regex101.com/
• http://www.regexe.com
• https://en.wikipedia.org/wiki/Comparison_of_regular_expression_engines
• This Slideshow: