Tutorial for Regex Matching a URL

gistfile1.md

Tutorial for a Regex Matching a URL

A regular expression, or regex, is a sequence of characters that defines a search pattern that can be used to validate user input. This tutorial breaks down a regex used for matching a URL.

Summary

The following regex can be used to validate a URL and has been broken down in this tutorial by its components (anchor, quantifies, grouping constructs, bracket expressions, character classes, and character escapes). Each section describes the symbol, a description, and where the code is found within the regex.

Regex Matching a URL:

`/^(https?:\/\/)?([\da-z\.-]+)\.([a-z\.]{2,6})([\/\w \.-]*)*\/?$/`

Table of Contents

• Anchors
• Quantifiers
• Grouping Constructs
• Bracket Expressions
• Character Classes
• Character Escapes

Regex Components

Anchors

Symbol	Description	Code in Regex
^	Asserts the position at the start of the string.	``/^(h`
$	Asserts the position at the end of the string (or before the end of the string's line terminator, if present).	`/?$/``

Quantifiers

Symbol	Description	Code in Regex
?	Matches the previous token between 0 and 1 times, as many times as possible, giving back as needed.	(https?:\/\/)? matches the characters https : // literally \/?$/ matches the character / literally
(*)	Matches the prevoius token between 0 and unlimited times, as many times as possible, giving back as needed.	([\/\w \.-]*)*
(+)	Matches the previous token between 1 and unlimited times, as many times as possible, giving back as needed.	([\da-z\.-]+)
{2,6}	Matches the previous token between 2 and 6 times, as many times as possible, giving back as needed.	([a-z\.]{2,6})

Grouping Constructs

Symbol	Description	Code in Regex
(?:...)	Matches everything enclosed.	(https?:\/\/)?

Bracket Expressions

Symbol	Description	Code in Regex
[a-z]	Matches a single character in the range between a and z.	[a-z\.] matches a single character in the range between a & z with a character. [\da-z\.-] matches a single character in the range between a & z, before one digit equivalent to [0-9] & the characters . & -
[ \/ \w \.-]	Matching a single character present in the list to the right:	\/ = matches the character / \w = matches any word character equivalent to [a-zA-Z0-9_] \. = matches the character . - = matches the character -

Character Classes

Symbol	Description	Code in Regex
\d	Matches a single character that is a digit.	([\da-z\.-]+)
\w	Matches any word character. Alphanumeric charatcer plus underscore.	[\/\w \.-]

Character Escapes

Symbol	Description	Code in Regex
\d	Matches a single character that is a digit.	([\da-z\.-]+)
\w	Matches any word character. Alphanumeric charatcer plus underscore.	[\/\w \.-]

Author

Savannah Fortson, student in web development.

• GitHub: https://github.com/SavannahF