Regex Cheatsheet

Regular expressions (regex) describe patterns for searching and manipulating text. This cheatsheet covers the core syntax used across most languages.

Character Classes

Match categories of characters.

.        any character (except newline)
\d       a digit (0-9)
\D       a non-digit
\w       word character (a-z, A-Z, 0-9, _)
\W       non-word character
\s       whitespace
\S       non-whitespace

Custom Sets

Define your own character groups.

[abc]      a, b, or c
[^abc]     not a, b, or c
[a-z]      any lowercase letter
[0-9]      any digit
[A-Za-z]   any letter

Quantifiers

Specify how many times.

*        zero or more
+        one or more
?        zero or one (optional)
{3}      exactly 3
{2,4}    between 2 and 4
{2,}     2 or more

Anchors

Match positions, not characters.

^        start of string/line
$        end of string/line
\b       word boundary
\B       non-word boundary

Groups & Alternation

Capture and choose.

(abc)      capture group
(?:abc)    non-capturing group
(a|b)      a or b
\1         backreference to group 1

Common Patterns

Ready-to-use examples.

\d{3}-\d{4}                    phone: 555-1234
[\w.-]+@[\w.-]+\.\w+           basic email
^https?://                       starts with http(s)
\b\d{4}-\d{2}-\d{2}\b          date: 2026-01-31

Flags

Change matching behavior.

g        global (all matches)
i        case-insensitive
m        multiline (^ and $ per line)
s        dotall (. matches newline)

In JavaScript

Use regex in code.

const re = /\d+/g;
"a1b2".match(re);          // ['1', '2']
"a1b2".replace(re, "#");   // 'a#b#'
/^\d+$/.test("123");       // true

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Regex is a compact, powerful tool for text processing. Start with character classes and quantifiers, and test patterns interactively before using them.

For an interactive tester, see https://regex101.com/