Syntax Updated November 2026

Dot and newline

By default the dot matches any character except line terminators (\n, \r and, in JavaScript, \u2028 and \u2029). To make it match newlines too, add the s flag (dotAll) in JavaScript or re.S / re.DOTALL in Python, or use [\s\S], which works in every engine.

Syntax

/a.b/s      [\s\S]      Python: re.compile(p, re.S)

Examples

/start.*end/.test("start\nend")

Result: false

/start.*end/s.test("start\nend")

Result: true

The s flag lets the dot cross the line break.

/start[\s\S]*end/.test("start\nend")

Result: true

[\s\S] is whitespace or non-whitespace, so anything at all.

"<p>a\nb</p>".match(/<p>(.*?)<\/p>/s)[1]

Result: "a\nb"

Common mistakes

Wondering why a multi-line block never matches: the dot stopped at the first newline. Add the s flag.
Confusing m with s: m changes what ^ and $ match, s changes what the dot matches.
Writing (.|\n)* to cross lines, which backtracks badly on long input; use [\s\S]* or the s flag.
Using the s flag in an engine that lacks it (older browsers before 2018, some SQL dialects); [\s\S] is the portable fallback.

Practice Dot and newline

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

The dot matches one characterThe whole line must match. Match three-character lines that start with h and end with t, with any single character in the middle.
Multiline flag: TODO linesEach test is a block of several lines. Capture the text after TODO: on every line that starts with TODO: (TODO, colon, space).
Lazy vs greedy: the first quoted textCapture the text inside the first pair of double quotes on the line in group 1. It can be empty.

Questions

What does the s flag do in regex?

It makes the dot match every character, including \n and \r. JavaScript calls it dotAll and exposes it as regex.dotAll.

How do I match across multiple lines in Python?

Pass re.S (or re.DOTALL): re.search(r"start.*end", text, re.S). Without it, the dot stops at each newline.

Does the dot match \r?

No. Carriage return is a line terminator, so a Windows line ending (\r\n) stops the dot twice. The s flag or [\s\S] handles both.

Regex flagsWhat each JavaScript regex flag does (case-insensitive, global, multiline, dotAll, unicode, sticky), how to set them, and the lastIndex trap with g and test.
Lazy vs greedyHow greedy quantifiers overshoot, how adding ? makes them lazy, why a negated class is often better than .*?, and the performance and newline traps.
Regex for whitespaceHow \s matches spaces, tabs and newlines, trimming leading and trailing whitespace, collapsing repeated spaces, splitting on whitespace, and detecting blanks.
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.