Patterns for common data Updated November 2026

Regex for whitespace

\s matches any whitespace character: space, tab, newline, carriage return, form feed and Unicode spaces such as the non-breaking space. Use \s+ for runs, ^\s+|\s+$ to trim, and \S for non-whitespace. To collapse repeated spaces, replace \s+ with a single space.

Syntax

\s  (one whitespace character)   \S  (one non-whitespace character)

Examples

"  hello   world  ".replace(/^\s+|\s+$/g, "")

Result: "hello world"

Trim both ends; the same as .trim(). Inner spaces are untouched.

"a   b \t c\nd".replace(/\s+/g, " ")

Result: "a b c d"

Collapse any run of whitespace, including tabs and newlines, to one space.

"one two  three".split(/\s+/)

Result: ["one", "two", "three"]

["no_spaces", "has space", "   "].map(s => /^\s*$/.test(s))

Result: [false, false, true]

^\s*$ detects empty or blank-only strings.

Common mistakes

Using a literal space instead of \s, which misses tabs and newlines.
Calling replace(/\s/, "") without the g flag, which removes only the first whitespace character.
Splitting on \s+ without trimming first: " a b".split(/\s+/) returns an empty first element.
Assuming \s is ASCII-only: in JavaScript it also matches the non-breaking space (U+00A0) and other Unicode spaces, which is usually what you want.

Practice Regex for whitespace

These drills check your answer on live data, free, no account needed.

Trim whitespaceReplace to remove all whitespace at the start and end of each line, leaving inner spacing alone. Every occurrence must be replaced, so think about the g flag.
Collapse repeated spacesReplace every run of two or more spaces with a single space.
Character class: gray or greyThe whole line must match. Match both spellings, gray and grey, and nothing else.

Questions

How do I match a tab in regex?

\t matches a tab. [ \t] matches a space or tab but not newlines, which is useful when you want to stay on one line.

What is the regex for an empty or whitespace-only string?

^\s*$ matches an empty string or one made only of whitespace. Use \S to test that a string has at least one visible character.

Does \s match a newline?

Yes, \s includes \n and \r. To match horizontal whitespace only, use [ \t] or, in engines that support it, \h.

Regex for numbers onlyThe ^\d+$ pattern for digits-only strings, stripping everything that is not a digit, extracting numbers from text, and patterns for signed and decimal values.
Character classesWhat a character class matches, how ranges and negation work, what \d \w \s and their uppercase opposites mean, and what the dot does and does not match.
Dot and newlineWhy . does not match line breaks by default, the s flag in JavaScript and re.DOTALL in Python, the portable [\s\S] trick, and how s differs from m.
Escaping special charactersThe regex metacharacters that must be escaped, how to match a literal dot, dollar, plus or slash, what changes inside brackets, and how to escape user input.