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Regular expressions

Character classes, anchors, repetition, groups and practical patterns—with the regex engine made explicit.

30 entries

Characters and classes

Literal sequence: /atlas/
Looks for that exact sequence. [2][1]
Any ordinary character: /./
Excludes line terminators unless dotAll is enabled. [2][1]
ASCII digit: /\d/
Matches 0 through 9 in JavaScript. [2][1]
Nondigit: /\D/
Complements the digit class. [2][1]
Word character: /\w/
Primarily ASCII letters, digits and underscore; not a universal alphabet class. [2][1]
Whitespace: /\s/
Includes more than an ordinary space. [2][1]
One of these characters: /[abc]/
Matches exactly one listed character. [2][1]
Not one of these: /[^abc]/
Negates the character class. [2][1]
ASCII lowercase range: /[a-z]/
Does not cover accented letters. [2][1]
Literal dot: /\./
Escapes the dot's special meaning. [2][1]

Zero or more: /ab*/
Repeats b, not the whole ab sequence. [3][1]
One or more: /ab+/
Requires at least one b. [3][1]
Optional character: /colou?r/
Accepts color or colour. [3][1]
Exact count: /\d{4}/
Requires four consecutive digits, not necessarily the whole input. [3][1]
Bounded count: /\d{2,4}/
Matches between two and four digits. [3][1]
Lazy repetition: /a.*?b/
Chooses the shortest successful expansion. [3][1]
Start anchor: /^atlas/
Requires the match at input start without the m flag. [3][1]
End anchor: /atlas$/
JavaScript permits some line-ending behavior; validate full-input needs carefully. [3][1]
Word boundary: /\bcat\b/
Boundaries follow the engine's word-character rules. [3][1]
Whole ASCII digits: /^\d+$/
A simple nonnegative-integer shape, not a complete numeric parser. [3][1]

Alternation: /cat|dog/
Either alternative may match. [4][1]
Capture a group: /(ab)+/
Captures the repeated group. [4][1]
Group without capturing: /(?:ab)+/
Groups repetition without creating a capture slot. [4][1]
Named capture: /(?<year>\d{4})/
Reads the capture through groups.year after a successful match. [4][1]
Repeated word: /\b(\w+)\s+\1\b/
Backreference repeats the captured characters. [4][1]
Ignore case: /atlas/i
Case behavior depends on Unicode and engine rules. [4][1]
Find all matches: [...'a1 b2'.matchAll(/\d/g)]
matchAll requires a global regex argument. [4][1]
Test for a match: /\d/.test('item 2')
Returns a boolean. [4][1]
Replace matches: 'a1 b2'.replace(/\d/g, '#')
Produces a# b#. [4][1]
Split on comma spacing: 'a, b,c'.split(/,\s*/)
Produces three text fields for this simple input. [4][1]

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Updated 2026-10-19JavaScript RegExp · common modern features

cheatsheetatlas.com/sheets/regex/ · Updated 2026-10-19 · JavaScript RegExp · common modern features