What are regex capture groups?

Capture groups allow you to extract specific parts of a regex match for later use.

Basic capture groups:

Parentheses create capture groups:

• (\d{3})-(\d{4}) matches phone numbers and captures area code and number separately
• First group captures \d{3}, second group captures \d{4}

Accessing captured values:

After matching, you can access each group:

• In JavaScript: match[1], match[2], etc.
• In Python: match.group(1), match.group(2), etc.
• Group 0 is always the full match

Named capture groups:

Modern regex supports named groups for better readability:

• (?<area>\d{3})-(?<number>\d{4}) creates named groups
• Access by name: match.groups.area in JavaScript

Non-capturing groups:

Sometimes you need grouping without capturing:

• (?:abc)+ groups "abc" for repetition but doesn't create a capture
• Useful for performance when you don't need the captured value

Common use cases:

• Extracting data from structured text (prices, dates, IDs)
• Parsing HTML or XML without a full parser
• Reformatting text by swapping captured groups
• Validating and extracting parts of user input

Capture groups are essential for web scraping when you need to extract multiple values from a single pattern match.