Match Selected File Extensions

Match file names that end in .csv or .json; other extensions are left out on purpose.

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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-R06

What it does

Match file names that end in .csv or .json.

How to use it

  1. Load the example or paste file names, one per line with the line-by-line scope.
  2. Check the counterexample.
  3. Add further extensions to the group if you need them.

Verified example

Example

Text "report.csv"

JavaScript · This browser
\.(?:csv|json)$

Result: ".csv"

Python re · Local WASM
\.(?:csv|json)$

Result: ".csv"

PCRE2-8 · Local WASM
\.(?:csv|json)$

Result: ".csv"

Go regexp · Local WASM
\.(?:csv|json)$

Result: ".csv"

Counterexample

Text "report.csv.bak"

JavaScript · This browser
\.(?:csv|json)$

Result: no match

Python re · Local WASM
\.(?:csv|json)$

Result: no match

PCRE2-8 · Local WASM
\.(?:csv|json)$

Result: no match

Go regexp · Local WASM
\.(?:csv|json)$

Result: no match

Recorded by running fixture FX-R06 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.

Engines

Limits