Regular Expression - Matching a URL

A regex, which is short for regular expression, is a sequence of characters that defines a specific search pattern. When included in code or search algorithms, regular expressions can be used to find certain patterns of characters within a string, or to find and replace a character or sequence of characters within a string. They are also frequently used to validate input. In this article we'll see how to use a regex to match a URL.

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

Let's break down the components of this regular expression used to match and validate URLs.

🌻 Regex Components

◾ Anchors

The URL matching regex starts with the ^ (caret) symbol and ends with the $ (dollar) symbol. These anchors define that the entire string must match the pattern between them, ensuring that the regex matches the complete URL and not just a part of it.

• The caret anchor indicates that the string to be examined must include the characters following it. It is important to note that the regular expression is case-sensitive.

• The dollar sign anchor indicates that the string to be examined includes the characters preceding it.

◾ Quantifiers

Quantifiers used to quantify how many times a part of your regular expression should be repeated.

• * (zero or more occurrences)

• + (one or more occurrences)

• ? (zero or one occurrence)

• {} (specifying a specific range of occurrences).

◾ Grouping Constructs

The parentheses grouping constructs () in regular expressions are used to group commands together to determine the order of processing.

◾ Bracket Expressions

Bracket Expressions [] match any one of a set of characters specified within square brackets. For example, [abc] matches any single character that is either a, b, or c.

🌻 Matching a URL

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

🟡 Protocol

This part of our regex https?:\/\/ matches the protocol of a URL, such as "http://" or "https://". The ? makes the 's' character optional, allowing URLs with both HTTP and HTTPS protocols to match.

🟡 Domain Name

This section [\da-z.-]+ matches the domain name in the URL. It allows for alphanumeric characters (including digits), hyphens, and dots.

• www.example

🟡 Top-Level Domain

This section [a-z.]{2,6} matches the top-level domain part of the URL. It typically includes domain extensions like .com, .net, .org, etc. The {2,6} specifies that it can consist of 2 to 6 characters.

• .com

• .org

🟡 Path and File Name

This segment [/\w .-]* matches the path and file name portion of the URL(represents the specific location or resource on the web server). It allows forward slashes, word characters, spaces, dots, and hyphens.

• /page1.html

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Conclusion

Regular expressions offer a powerful way to search, manipulate, and validate text data in programming. With practice, regex can become an indispensable part of your programming toolkit.