What is the regex for subdomain extraction?

The regex pattern for subdomain extraction is `^(?:https?:\/\/)?([a-zA-Z0-9](?:[a-zA-Z0-9-]*[a-zA-Z0-9])?)\.(?:[a-zA-Z0-9-]+\.)+[a-zA-Z]{2,}`. This pattern validates extracts the subdomain from a url or domain name.

How do I use this regex in JavaScript?

In JavaScript, create the regex with `const regex = /^(?:https?:\\/\\/)?([a-zA-Z0-9](?:[a-zA-Z0-9-]*[a-zA-Z0-9])?)\.(?:[a-zA-Z0-9-]+\.)+[a-zA-Z]{2,}/;` and test with `regex.test(yourValue)`. It returns `true` if the value matches.

How do I use this regex in Python?

In Python, use `import re; re.match(r'^(?:https?:\/\/)?([a-zA-Z0-9](?:[a-zA-Z0-9-]*[a-zA-Z0-9])?)\.(?:[a-zA-Z0-9-]+\.)+[a-zA-Z]{2,}', value)`. The raw string prefix (`r`) prevents Python from interpreting backslashes as escape characters.

Is this regex case-sensitive?

This pattern explicitly handles both uppercase and lowercase via the character classes. No additional flags needed.

Regex for Subdomain Extraction

Regex Pattern

^(?:https?:\/\/)?([a-zA-Z0-9](?:[a-zA-Z0-9-]*[a-zA-Z0-9])?)\.(?:[a-zA-Z0-9-]+\.)+[a-zA-Z]{2,}

Extracts the subdomain from a URL or domain name

Quick Answer

The regex pattern for subdomain extraction is `^(?:https?:\/\/)?([a-zA-Z0-9](?:[a-zA-Z0-9-]*[a-zA-Z0-9])?)\.(?:[a-zA-Z0-9-]+\.)+[a-zA-Z]{2,}`. Extracts the subdomain from a URL or domain name. This works in JavaScript, Python, Ruby, PHP, Java, and most regex engines that support PCRE syntax.

Test Examples

Input	Result
api.example.com	✓ Matches
https://blog.example.co.uk	✓ Matches
cdn.static.example.com	✓ Matches
example.com	✗ No match
http://example.com	✗ No match
localhost	✗ No match

Code Examples

javascript

const regex = /^(?:https?:\\/\\/)?([a-zA-Z0-9](?:[a-zA-Z0-9-]*[a-zA-Z0-9])?)\.(?:[a-zA-Z0-9-]+\.)+[a-zA-Z]{2,}/;
const isValid = regex.test(value);

python

import re
pattern = r'^(?:https?:\/\/)?([a-zA-Z0-9](?:[a-zA-Z0-9-]*[a-zA-Z0-9])?)\.(?:[a-zA-Z0-9-]+\.)+[a-zA-Z]{2,}'
if re.match(pattern, value):
    print("valid")

ruby

pattern = /^(?:https?:\/\/)?([a-zA-Z0-9](?:[a-zA-Z0-9-]*[a-zA-Z0-9])?)\.(?:[a-zA-Z0-9-]+\.)+[a-zA-Z]{2,}/
if value =~ pattern
  puts "valid"
end

php

if (preg_match('/^(?:https?:\\/\\/)?([a-zA-Z0-9](?:[a-zA-Z0-9-]*[a-zA-Z0-9])?)\.(?:[a-zA-Z0-9-]+\.)+[a-zA-Z]{2,}/', $value)) {
    echo "valid";
}

java

String pattern = "^(?:https?:\\/\\/)?([a-zA-Z0-9](?:[a-zA-Z0-9-]*[a-zA-Z0-9])?)\\.(?:[a-zA-Z0-9-]+\\.)+[a-zA-Z]{2,}";
boolean isValid = value.matches(pattern);

Frequently Asked Questions

Related Regex Patterns

Protocol Detection

Detects and captures the protocol from a URL

Port Number

Extracts port number from a URL or host string

Query Parameter

Extracts key-value pairs from URL query strings

HTTP vs HTTPS URL

Matches HTTP or HTTPS URLs and captures the protocol

Data URL

Matches data: URL scheme with optional MIME type and base64 encoding

WebSocket URL

WebSocket URL starting with ws:// or wss://