Regex Capture Groups

Learn how capture groups number their parts and keep values as strings.

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Regular expression
Reference

Regex quick reference

^ · $
Start/end; m = lines.
[abc] · \d
Listed character / digit.
* · + · ?
Zero or more, one or more, optional.
(...)
Capture a numbered group.
(?<name>...)
Named capture.
(?=...)
Ahead; lookbehind varies.
i · m · s
Ignore case / line anchors / dot-newline.
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the RegExp of this browser (version not pinned)

Not available in JavaScript · This browser: x · ignore pattern whitespace; a · ASCII-only classes; U · lazy by default; J · duplicate names. u and v cannot be combined.

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Verified Fixture FX-S04

What it does

Parentheses capture: group 1, group 2 and so on keep the text they matched, as strings with leading zeros intact.

How to use it

  1. Load the example.
  2. Open a match to see group 0 (the whole match) and the numbered groups.
  3. Check the counterexample.

Verified example

Example

Text "AB-007"

JavaScript · This browser
([A-Z]{2})-(\d{3})

Result: "AB-007"; groups "AB", "007"

Python re · Local WASM
([A-Z]{2})-(\d{3})

Result: "AB-007"; groups "AB", "007"

PCRE2-8 · Local WASM
([A-Z]{2})-(\d{3})

Result: "AB-007"; groups "AB", "007"

Go regexp · Local WASM
([A-Z]{2})-(\d{3})

Result: "AB-007"; groups "AB", "007"

Counterexample

Text "A-7"

JavaScript · This browser
([A-Z]{2})-(\d{3})

Result: no match

Python re · Local WASM
([A-Z]{2})-(\d{3})

Result: no match

PCRE2-8 · Local WASM
([A-Z]{2})-(\d{3})

Result: no match

Go regexp · Local WASM
([A-Z]{2})-(\d{3})

Result: no match

Recorded by running fixture FX-S04 on : rp.js@1 on Node v24.21.0 (V8), v24.21.0, CPython 3.14.2 (Pyodide 314.0.7), PCRE2 10.48, go1.27.1. JavaScript results come from the rp.js@1 core on Node’s V8; your browser runs the same core.

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