Regular Expressions (regex or regexp) allow for matching patterns in strings. The document discusses regex, including what they are, common uses, and special characters. It provides examples of regex to match telephone numbers, email addresses, and URLs. While regex can be a powerful tool, patterns can become complex and regex risks becoming too restrictive. It's best to start simply and work with consistent, clean data.

1. Regular Expressions
Ben Simpson - <3 HUB

2. Introductions
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Working with web technologies for 10 years
Former HUB supervisor
Tour de jobs: http://tinyurl.com/kmsns38
Graduated from CSU with a BAS in
Technology Management 2013
● Husband and proud father
● Presenter on regular expressions!

3. What Is a Regular
Expression?
Pattern matching

4. What Could I Do With a RegExp?
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Searching
Syntax highlighting
Data validation
Sanitation
Data queries / extraction
Many tasks that require matching a pattern

5. RegExps Won’t Let You Time Travel

6. Brain Teaser
Which of the following is a valid telephone
number?
1. 678 466 4000
2. (678) 466-4000
3. 1234
4. domainuser
5. 1 (800) 1234 567

7. How did you know?
Depends on who you ask...

8. We Pattern Match Every Day
● Telephone numbers follow a pattern that we
recognize
● This pattern has rules (3 digit zip, 7 digit
number, numeric only)
● There are often many variations to a pattern
(optional intl code)

9. Literal Characters
String: The cat in the hat
RegExp: /at/
The cat in the hat

10. Regular Expressions in Javascript
var haystack = "The cat in the hat";
var needle = new RegExp(/cat/);
haystack.match(needle); // truthy
needle = new RegExp(/dog/);
haystack.match(needle); // falsey

11. Well that wasn’t so bad
The best is yet to come!

12. Special Characters (Metacharacters)
● - escape character
● ^ - beginning of line (not
inside brackets)
● $ - ending of line
● . - wildcard
● | - or junction
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? - zero or one
* - zero or more
+ - one or more
() - grouping
[] - character set
{} - repetition

14. Demonstration of Special Characters
String: ...To login to your email use the
username: “ben.simpson@mail.com” with a
password “password123”...
RegExp: /username "(.*)" .* password "(.*)"/
Results: 1. ben.simpson@mail.com
2. password123

15. Shorthand Character Classes
● d - digit [0-9]
● w - word
● s - whitespace
● D - digit [^d]
● W - word [^w]
● S - whitespace [^s]

16. Wait a Second!
You said this was easy

17. Thinking about a Telephone Pattern
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Optional international code
3 digit area code
7 digit number
Optional extension
What about alpha phrases? (e.g. 678 466-HELP)
What is the length of intl codes? (e.g. 358 for Finland)
Are parenthesis optional?
Is spacing optional?
Country specific formats (e.g. France 06 87 71 23 45)

18. Regular Expression - Telephone #
String: 678 466 4357
RegExp: d{3} d{3} d{4}
String: (678) 466-4357
RegExp: (d{3}) d{3}-d{4}

19. Telephone # - Two Variations
String: 678 466 4357
(678) 466-4357
RegExp: (?d{3})? d{3}[s-]d{4}

20. Telephone # - Three Variations
String: 678 466 4357
(678) 466-4357
1 (678) 466-4357
RegExp: d*s?(?d{3})? d{3}[s-]?d{4}

21. That Escalated Quickly

22. Surprisingly Difficult
● Seemingly simple patterns can become very
complex.
● Its best to work against data that is
consistent, or regular in its implementation of
patterns
● If the data is too dirty, a regular expression
won’t be much help

23. When RegExps Go Bad
● Websites that don’t accept special
characters in email addresses, URLs,
telephone numbers, etc
● May be RegExps that are too restrictive
● Doesn’t take into account all variations of a
pattern
● Longer expressions are difficult to grok

25. In a Nutshell
“Some people, when confronted with a
problem, think ‘I know, I'll use regular
expressions.’ Now they have two problems.”
-Jamie Zawinski

26. Brain Teaser
Which of the following a valid email address?
1. thehoagie@gmail.com
2. ben.simpson+work@analoganalytics.com
3. ben+email
4. http://www.clayton.edu
5. abc."defghi".xyz@example.com

27. Thinking about Email Address
● Has a local part (e.g. thehub@clayton.edu)
● Has a domain part (e.g. thehub@clayton.
edu)
● Has an @ symbol in the middle
● Do we need to support special characters?
● Can we verify based on minimum /
maximum length?

28. Best to Keep It Simple!
String: thehoagie@gmail.com
RegExp: .*@.*
Yeah, but isn’t here an official email Regex that
takes all the patterns into account? Yes...

29. RFC 5322 - The Email RegExp
(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*
| "(?:[x01-x08x0bx0cx0e-x1fx21x23-x5bx5d-x7f]
| [x01-x09x0bx0cx0e-x7f])*")
@ (?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?
| [(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?).){3}
(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:
(?:[x01-x08x0bx0cx0e-x1fx21-x5ax53-x7f]
| [x01-x09x0bx0cx0e-x7f])+)
])

30. Maybe this instead?
(╯°□°）╯︵ ┻━┻)

31. ┬─┬ ノ( ゜-゜ノ)
(Let me put that back for you)

32. Brain Teaser
Which is a valid zipcode?
1. 30022
2. 30022-7155
3. 300131
4. -7155
5. AB123XY

33. Thinking About a Zipcode
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Digits only
5 digits mandatory plus optional 4 digit code
4 digit code suffixed with hyphen
Do other countries use zip codes?
Pattern is easier because there is less
variation (Thank USPS!)

34. Brain Teaser
Which is a valid URL?
1. http://www.clayton.edu
2. www.clayton.edu
3. clayton.edu
4. thehub.clayton.edu
5. ben:pass@clayton.edu:80/foo?bar=baz#qux

35. Thinking about a URL

36. Ben Simpson
thehoagie@gmail.com
@mrfrosti

37. Extra Credit
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IP address
HTML Tag contents
Validating a password against requirements
Dates
Times