Presentation I did for the helpdesk of my alma mater

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