Regex: UUID

Flags: i

^

Start of the string.

[0-9a-f]{8}-

Eight hex digits and a dash.

[0-9a-f]{4}-

Four hex digits and a dash.

[1-8][0-9a-f]{3}-

The version digit (1 to 8), three more hex digits, a dash.

[89ab][0-9a-f]{3}-

The variant digit (8, 9, a or b for RFC 9562 UUIDs), three more, a dash.

[0-9a-f]{12}

Twelve hex digits.

$

End of the string. The i flag accepts upper case too.

JavaScript

/^[0-9a-f]{8}-[0-9a-f]{4}-[1-8][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/i

A literal; new RegExp(source, flags) builds the same from a string.

Python

re.compile(r"^[0-9a-f]{8}-[0-9a-f]{4}-[1-8][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$", re.IGNORECASE)

A raw string, so backslashes reach re as written. re.ASCII keeps \d to 0-9, as in JavaScript (Python matches any Unicode digit otherwise). Use re.fullmatch to test a whole string.

Java

Pattern.compile("^[0-9a-f]{8}-[0-9a-f]{4}-[1-8][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$", Pattern.CASE_INSENSITIVE)

A normal string literal, so every backslash is doubled. matcher(s).matches() tests the whole string.

Go

regexp.MustCompile(`(?i)^[0-9a-f]{8}-[0-9a-f]{4}-[1-8][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$`)

A raw string in backticks. RE2 runs in linear time but has no lookaround and no backreferences.

PHP

preg_match('/^[0-9a-f]{8}-[0-9a-f]{4}-[1-8][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/iD', $input)

PCRE with / delimiters inside a single-quoted string. Without the D modifier, $ also matches before a final newline, so it is added to patterns that end in $.

C#

new Regex(@"^[0-9a-f]{8}-[0-9a-f]{4}-[1-8][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$", RegexOptions.IgnoreCase)

A verbatim string: backslashes stay, a quote is doubled. RegexOptions.ECMAScript keeps \d to 0-9, as in JavaScript. $ also matches before a final newline; to reject one, end the pattern with \z instead.