Groups and Capturing

Use parentheses to group patterns and capture matched text.

Basic Capturing Group

(\d{3})-(\d{4})

Matches: 555-1234

• Group 1: 555
• Group 2: 1234

Non-Capturing Group

(?:Mr|Mrs|Ms)\.?\s+([A-Z][a-z]+)

Matches: Mr. Smith, Mrs Jones

• Doesn't capture title, only captures name

Named Capturing Groups

(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})

Matches: 2025-11-09

• Named group year: 2025
• Named group month: 11
• Named group day: 09

Backreferences

(\w+)\s+\1

Matches repeated words: hello hello, test test

• \1 refers back to first captured group

Multiple Groups

^(\w+)@(\w+)\.(\w+)$

Matches: user@example.com

• Group 1: user
• Group 2: example
• Group 3: com

Alternation in Groups

(cat|dog|bird)

Matches: cat, dog, or bird

Nested Groups

((Mr|Mrs|Ms)\.?\s+)?([A-Z][a-z]+)

Matches: Mr. Smith or just Smith

• Group 1: Optional title with space
• Group 2: Title only
• Group 3: Last name

Backreference for Quotes

(['"])(.+?)\1

Matches quoted strings with same quote type:

• "hello" ✓
• 'world' ✓
• "mixed' ✗

Conditional Groups

(\d{3})-?(\d{4})

Matches phone numbers with or without dash:

• 555-1234 ✓
• 5551234 ✓

Group for Replacement

When using regex in JavaScript:

const text = "John Smith";
const result = text.replace(/(\w+)\s+(\w+)/, "$2, $1");
// Result: "Smith, John"

Complex Email Pattern with Groups

^(?<username>[a-zA-Z0-9._%+-]+)@(?<domain>[a-zA-Z0-9.-]+)\.(?<tld>[a-zA-Z]{2,})$

Matches: user.name@example.co.uk

• username: user.name
• domain: example.co
• tld: uk