Character sets: `[abc]`

When a predefined class like \d or \w is not enough, you can define a custom character set with square brackets [...]. Inside the brackets, each character is an alternative: the regex matches one of any of the listed elements.

Pattern: [aeiou]
Sample:  ciao mondo
         ^   ^^  ^^

Each vowel is a match on its own. Brackets match exactly one character (unless quantified): [aeiou]+ matches a contiguous sequence of vowels.

Special characters inside brackets

Inside [...] most meta-characters lose their special meaning:

• . inside [.] matches a literal dot (no escape needed).
• *, +, ?, (, ), {, } are literal.
• \ ] ^ instead remain special and must be escaped or carefully positioned.

Pattern: [.,;:]
Match: any punctuation mark among dot, comma, semicolon, colon.

Special characters inside square brackets

Most regex meta-characters (., *, +, ?, etc.) lose their special meaning inside brackets and are treated as literal characters. Only the dash -, the caret ^ at the start, and the backslash \\ retain operational meanings.

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