Regular Expressions

(aka RegEx)

/ˈrɛɡɛks/ or /ˈrɛdʒɛks/

What is a RegEx?

Example

var str1 = "Chicken soup"

var str2 = "crispy chicken burger"

var str3 = "fish burger"

/chicken/i

Set of characters that represent RULES for SEARCHING or MATCHING text in a string

Regex

Subject

Why bother learning RegEx?

Common Uses

Data Validations
Find / Replace text
Heavily used in parsers

Because I'm sure you have used RegEx before. And if not, you should start using it

Regex Format

/ pattern / flags

Flags

Flags change the default behaviour of your Regex

They are written after the ending forward slash

3 kinds of flags

1. ignore case (i)

2. global (g)

3. multiline (m)

Metacharacters

Characters with special meaning

\ ^ $ . | ? * + ( ) [ {

Note: Can be used as a literal character if preceded by a backslash

Character Class/Set

It matches a character from a specific set. Can be custom of predefined

Examples (Custom CS)

CS of uppercase vowels [AEIOU]

CS of special characters [!@#$%^&*()_+]

CS of a range of characters from a-z [a-z]

CS of all alphabets (uppercase and lowercase) [a-zA-Z]

Note: The order of characters does not matter inside a character set

Note: The only metacharacters inside CS are \ - and ^

Examples (Predefined CS)

\d === [0-9]

\s === space character

\w === [a-zA-Z0-9_ ]

Negated:

\D === [^0-9]

\S === [^\s]

\W === [^a-zA-Z0-9_ ]

Repetation

+ 1 or more

* 0 or more

? 0 or 1

{ a specific number of times

Anchors

Match positions

Word Boundary \b

Beginning of subject ^

End of subject $

Lazy vs Greedy

(Time permitting)

Use of RegEx for

Data Validation
Text find / replace
Making Parsers

Learning Resources

https://www.codeschool.com/courses/breaking-the-ice-with-regular-expressions

Testing Tools:

http://regexr.com/
https://regex101.com/

Copy of R

By sarahsga