Capturing Groups ()

Parentheses () create groups that serve two purposes:

1. Group elements together for quantifiers
2. Capture the matched text for later use

Basic Grouping

The (ha)+ treats "ha" as a unit, matching one or more repetitions.

Grouping for Quantifiers

Without groups, quantifiers only apply to the previous character:

• ab+ = a followed by one or more b's: "ab", "abb", "abbb"
• (ab)+ = one or more "ab" sequences: "ab", "abab", "ababab"

Capturing Text

When you use groups, the regex engine captures what each group matched.

This captures:

• Group 1: "555" and "800"
• Group 2: "1234" and "9999"

Multiple Groups

Nested Groups

Groups can be nested:

Groups are numbered by opening parenthesis position:

• Group 1: "01/15" (outer group)
• Group 2: "01" (first inner)
• Group 3: "15" (second inner)
• Group 4: "2024" (last group)

Practical Examples

Practice Playground

Try capturing:

• \((\d{3})\) - area code
• \$(\d+)\.(\d{2}) - dollars and cents
• (\d{2}):(\d{2}) - hours and minutes

Key Takeaways

• Parentheses () group elements together
• Groups let quantifiers apply to multiple characters
• The matched text in each group is captured
• Groups are numbered left-to-right by opening (
• Nesting creates sub-groups