1.
Regular Expressions and You
An introduction to regular expressions.
James I. Armes
Web Developer, AllPlayers.com
@jamesiarmes

2.
Email Validation Examples
^[w.%+-]+@[w.-]+.[A-Za-z]{2,4}$

3.
Email Validation Examples
(?:(?:rn)?[ t])*(?:(?:(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:
[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[]
000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[
["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*|(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:
(?:rn)?[ t])*)*<(?:(?:rn)?[ t])*(?:@(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[
t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*(?:,@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+
(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[
["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*)*:(?:(?:rn)?[ t])*)?(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:
(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:
(?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:
[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*>(?:(?:rn)?[ t])*)|(?:[^()<>@,;:".[] 000-031]+(?:(?:
(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)*:(?:(?:rn)?[ t])*(?:(?:(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?
=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:
[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?
[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*|(?:[^()<>@,;:".[] 000-031]+
(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)*<(?:(?:rn)?[ t])*(?:@(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])
+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^
[]r]|.)*](?:(?:rn)?[ t])*))*(?:,@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:
(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*)*:(?:(?:rn)?[ t])*)?(?:[^()<>@,;:".[]
000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:
(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[
["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:
(?:rn)?[ t])*))*>(?:(?:rn)?[ t])*)(?:,s*(?:(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)
(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:(?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?:
[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:
(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*|(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:
(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)*<(?:(?:rn)?[ t])*(?:@(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.
(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*(?:,@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[]
000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[
["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*)*:(?:(?:rn)?[ t])*)?(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:
(?:rn)?[ t]))*"(?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|"(?:[^"r]|.|(?:(?:rn)?[ t]))*"(?:
(?:rn)?[ t])*))*@(?:(?:rn)?[ t])*(?:[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*)(?:.(?:(?:rn)?[ t])*(?:
[^()<>@,;:".[] 000-031]+(?:(?:(?:rn)?[ t])+|Z|(?=[["()<>@,;:".[]]))|[([^[]r]|.)*](?:(?:rn)?[ t])*))*>(?:(?:rn)?[ t])*))*)?;s*)

4.
Types of Regular Expressions
● Simple Regular Expressions
● POSIX Basic Regular Expressions
● POSIX Extended Regular Expressions
● Perl Regular Expressions

5.
Simple Regular Expressions
● Traditional regular expressions.
● Not a standard.
● Support by some applications for backwards
compatibility.
● Deprecated.

6.
POSIX Basic Regular
Expressions
● Created to provide a common standard for Unix
tools.
● Designed to be backwards compatible with
traditional regular expressions.
● Adopted as the default syntax of many Unix
tools.
● Some metacharacters require escaping.

7.
POSIX Extended Regular
Expressions
● Adds some new metacharacters.
● Metacharacters do not require escaping.
● Dropped support for back references (n).
● Many Unix tools provide support with a
command line argument (usually -E).

8.
Perl Regular Expressions
● Adds lazy quantification, named capture groups
and recursive patterns.
● Adopted by many programming languages due
to its power.
● Requires non-alphanumeric delimiters around
expression.
● Other languages only implement a subset, so
implementations vary.

9.
Syntax

10.
Basic Metacharacters
. Match any single character.
^ Matches beginning of a string.
$ Matches end of a string.
| Matches the expression before or after (think ||).

11.
Character Classes
[] Match any characters within the group.
[^ ] Match any characters NOT within the group.
[n-m] Match a range of characters.
Examples:
[A-Za-z0-9]
[^G-Zg-z _]

12.
Shorthand Character Classes
s Any whitespace character such as space, tab and newlines.
Same as [nrt ]
w Any word character.
Same as [A-Za-z0-9_]
d Any digit character.
Same as [0-9]
S, W, D Negated version of the above. Can be used inside character
classes but could be confusing.

13.
Quantifiers
* Match the preceding expression 0 or more times.
+ Match the preceding expression 1 or more times.
? Match the preceding expression 0 or 1 time.
{m,n} Match the preceding expression at least m times but no more than n times.
{m,} Match the preceding expression at least m times with no maximum.
{,n} Match the preceding expression no more than n times with no minimum.
{n} Match the preceding expression exactly n times.

14.
Lazy Quantifiers
Standard Quantifiers are greedy.
Example:
Many programming courses start with a "Hello World" example.
That would be "Hallo Welt" in German.
"Hello .*"
Many programming courses start with a "Hello World" example.
That would be "Hallo Welt" in German.

15.
Lazy Quantifiers
Use ? to make a quantifier lazy.
Example:
Many programming courses start with a "Hello World" example.
That would be "Hallo Welt" in German.
"Hello .*?"
Many programming courses start with a "Hello World" example.
That would be "Hallo Welt" in German.

16.
Grouping
() Group the expression and capture the text.
(?: ) Group the expression but DO NOT capture the text.

17.
Backreferences
1 through 9 reference previously captured text.
Example:
Many programming courses start with a "Hello World"
example. 'Hello World' examples are extremely simple,
especially when they just output "Hello World'.
('|")Hello World(1)
Many programming courses start with a "Hello World"
example. 'Hello World' examples are extremely simple,
especially when they just output "Hello World'.

18.
Word Boundaries
b matches the position between a word character
(w) and a non-word character (W).
Example:
Hello World
ob
Hello| World

19.
Word Boundaries
B matches the position between two word
characters (ww).
Example:
Hello World
oB
Hello Wo|rld

20.
Lookaheads
(?= ) matches the position directly before the
expression is matched.
Example:
Hello World sounds better than "Hello Earth".
Hello(?= World)
Hello World sounds better than "Hello Earth".

21.
Lookbehinds
(?<= ) matches the position directly after the
expression is matched.
Example:
Hello World sounds better than "Hello Earth".
(?<=")Hello
Hello World sounds better than "Hello Earth".

22.
Lookaheads
(?! ) matches the position directly before the
expression is NOT matched.
Example:
Hello World sounds better than "Hello Earth".
Hello(?! World)
Hello World sounds better than "Hello Earth".

23.
Lookbehinds
(?<! ) matches the position directly after the
expression is NOT matched.
Example:
Hello World sounds better than "Hello Earth".
(?<!")Hello
Hello World sounds better than "Hello Earth".

24.
Conditionals
(?(condition)then|else)
● condition must be a lookahead or a lookbehind.
● If condition is matched, then must match for the
expression to pass.
● If condition is not matched, else must match for
the expression to pass.

25.
Conditionals
Example:
Hello World sounds better than "Hello Earth".
Hello (?(?<=World)World|Earth)
Hello World sounds better than "Hello Earth".
Hello (?(?<=People)People|Earth)
Hello World sounds better than "Hello Earth".

26.
Modifiers
i Case insensitive matching.
s . matches newline characters.
m ^ and $ match after and before newlines (respectively).
x Whitespace within the expression is ignored unless escaped.
g Match globally.

27.
Modifiers
● (?a) to turn modifiers on.
●(?-a) to turn modifiers off.
Examples:
(?i)WORLD(?-i)
(?i-s)WORLD.(?s-i)
(?i:WORLD)

28.
Language
Implementations

29.
JavaScript
● RegExp object.
– var expression = new RegExp('World', 'g');
– var expression = /World/g;
● String.match()
● String.replace()
● String.split()

30.
Perl
● if ($string =~ /regex/)
● $string =~ s/regex/replacement/
● Regexp::Common
– http://search.cpan.org/dist/Regexp-Common/
– Provides common expressions.
– Examples:
● IP Address
● Credit Card Number
● Profanity

31.
PHP
● ereg vs. preg
– preg uses Perl syntax.
– ereg uses POSIX Extended syntax.
– preg is much faster.
– ereg has been deprecated as of PHP 5.3.

32.
PHP
● preg_match()
● preg_match_all()
● preg_replace()
● preg_split()
● preg_quote()
● http://www.php.net/manual/en/book.pcre.php
● http://php.net/manual/reference.pcre.pattern.modifiers.php

33.
Tools and Resources
● txt2regex - http://aurelio.net/txt2regex/
● Reggy (mac) - http://reggyapp.com/
● Patterns (mac) - http://krillapps.com/patterns/
● Web based - http://regex.larsolavtorvik.com/
● Regular-Expressions.info (reference) -
http://www.regular-expressions.info/

34.
Thanks!
http://xkcd.com/208/