Regex 文字 クラス リファレンス

Shorthand Classes

Regular expressions provide shorthand escapes for common character sets. The lowercase escapes match character classes while the uppercase escapes match their complements. These shorthands are affected by the Unicode and case-insensitive flags, expanding or contracting their membership. Using shorthands instead of explicit ranges improves readability and handles locale-specific characters correctly.

\d

Digit, equivalent to [0-9]

\d+ matches 123

\w

Word char: letter, digit, underscore

\w+ matches foo_bar

\s

Whitespace: space, tab, newline

\s+ matches spaces

\D \W \S

Complements of the above

\D matches non-digits

.

Any char except newline (unless dotall)

a.b matches aXb

Custom Ranges

Square brackets define a custom character class containing any of the listed characters or ranges. A hyphen between two characters creates a range based on code point order. The caret at the start negates the class. Ranges should be used carefully with Unicode because code point order does not reflect natural language order. Escaping metacharacters inside a class is simpler than outside: only the closing bracket, backslash, and caret at start need escaping.

Unicode Effects

The Unicode flag u changes how shorthands and ranges behave. With the flag, \w matches all Unicode word characters including letters from non-Latin scripts, not just ASCII. Ranges like a-z still only cover the specified code points, but the flag enables surrogate pair handling. The v flag adds set operations to character classes, allowing subtraction and intersection. Always specify the intended flag to avoid surprising matches on international text.