regex character classes — [...], \d, \w, \s

Q: Special characters inside [...]

Most metacharacters lose their meaning inside [...] . Only ] , \ , ^ , and - need escaping. ``` [.?+*] # matches literal . ? + * (no escaping needed) [\^] # matches literal ^ [\-] # matches literal - (or put it first/last: [-az]) [a\]b] # matches a ] or b ```

Quick Answer

[abc]     match a, b, or c
[a-z]     match any lowercase letter
[A-Za-z0-9]  alphanumeric
[^abc]    match anything except a, b, c

\d    digit       [0-9]
\D    non-digit   [^0-9]
\w    word char   [a-zA-Z0-9_]
\W    non-word
\s    whitespace  [ \t\r\n\f\v]
\S    non-whitespace

Usage

Character classes let you match any one character from a defined set.

Other causes & fixes

Common patterns using character classes

# Match hex color
/#[0-9a-fA-F]{6}/

# Match identifier (starts with letter/underscore)
/[a-zA-Z_]\w*/

# Match one whitespace character
/\s/

# Match a digit sequence
/\d+/

# Strip non-alphanumeric
str.replace(/[^\w\s]/g, '')

Special characters inside [...]

Most metacharacters lose their meaning inside [...]. Only ], \, ^, and - need escaping.

[.?+*]   # matches literal . ? + * (no escaping needed)
[\^]     # matches literal ^
[\-]     # matches literal - (or put it first/last: [-az])
[a\]b]   # matches a ] or b

Unicode property classes (\p{}) — JS and Python

// JavaScript (ES2018+) — /u flag required
/\p{Letter}/u     // any Unicode letter
/\p{Number}/u     // any Unicode number

# Python
import re
re.findall(r'\p{L}+', text)   # requires 'regex' package, not 're'