Regex Replace

Replace matches using the engine's own template syntax and compare the text before and after.

Replace matches; see before and after

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Workspace actions
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.

To run: enter a regex; enter a test text; enter a replacement (or use an empty one).

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Verified Fixture FX-R11

What it does

Replace matches using the selected engine’s own template syntax and compare the text before and after.

How to use it

  1. Write the regex that finds what to replace.
  2. Write the replacement in the engine’s template syntax, or switch to literal text.
  3. Compare the before and after text; chain further steps if needed.

Verified example

Example

Text "a b\tc"

JavaScript · This browser
[ \t]+

Result: " ", "\t"

Python re · Local WASM
[ \t]+

Result: " ", "\t"

PCRE2-8 · Local WASM
[ \t]+

Result: " ", "\t"

Go regexp · Local WASM
[ \t]+

Result: " ", "\t"

Counterexample

Text "abc"

JavaScript · This browser
[ \t]+

Result: no match

Python re · Local WASM
[ \t]+

Result: no match

PCRE2-8 · Local WASM
[ \t]+

Result: no match

Go regexp · Local WASM
[ \t]+

Result: no match

Recorded by running fixture FX-R11 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