Offline Regex Tester — JS and PCRE

Replacement

JS: $1..$99, $&, $`, $', $$ — PCRE: \\1.., $1.., $&, $`, $', $$

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Examples

Chars: 0 Lines: 0 Ln:1, Col:1 Sel:0 U+—

Replacement preview

Line numbers

0 matches 0 ms Ready

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Cheat Sheet (JS vs PCRE)


• Flags
  JS: i, g, m, s, u, y (indices proposal: d)
  PCRE: i, m, s, x, U, D, A, u

• Groups
  ( ... ) capture, (?: ... ) non-capture, (?<name> ... ) named

• Lookaround
  (?=...), (?!...), (?<=...), (?<!...) — JS supports lookbehind in modern engines.

• Replacement tokens
  JS: $1..$99, $&, $`, $', $$
  PCRE: \1.., $1.., $&, $`, $', $$

• Differences (quick)
  - PCRE supports atomic groups (?>...), possessive quantifiers a++ (JS no)
  - PCRE x (free-spacing) is not in JS; emulate by stripping spaces/comments
  - Anchors: ^, $, \A, \Z (PCRE) — JS lacks \A/\Z
  - Named backref: \k<name> (PCRE) vs \k<name> in JS with u flag

• Safety tips
  Prefer atomic/possessive constructs to avoid catastrophic backtracking.
  Benchmark with a timeout and cap matches for large inputs.