Character Classes

A character class [abc] matches any one character from the set inside the brackets. You can use ranges for convenience: [a-z] matches any lowercase letter, [0-9] any digit, [A-Za-z] any letter.

Prefixing with ^ inside the brackets negates the class: [^0-9] matches any character that is NOT a digit.

Shorthand classes are common shortcuts: - \d — digit, same as [0-9] - \w — word character: letters, digits, underscore [A-Za-z0-9_] - \s — whitespace: space, tab, newline - . — any character except newline (no backslash needed)

For the negated versions, use uppercase: \D, \W, \S match the opposite.