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Perl Language Reference Manual
by Larry Wall and others
Paperback (6"x9"), 724 pages
ISBN 9781906966027
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13.3 Bracketed Character Classes

The third form of character class you can use in Perl regular expressions is the bracketed form. In its simplest form, it lists the characters that may be matched, surrounded by square brackets, like this: [aeiou]. This matches one of a, e, i, o or u. Like the other character classes, exactly one character will be matched. To match a longer string consisting of characters mentioned in the character class, follow the character class with a quantifier. For instance, [aeiou]+ matches a string of one or more lowercase ASCII vowels.

Repeating a character in a character class has no effect; it's considered to be in the set only once.

Examples:

"e"  =~  /[aeiou]/        # Match, as "e" is listed in the class.
"p"  =~  /[aeiou]/        # No match, "p" is not listed in the class.
"ae" =~  /^[aeiou]$/      # No match, a character class only matches
                          # a single character.
"ae" =~  /^[aeiou]+$/     # Match, due to the quantifier.
ISBN 9781906966027Perl Language Reference ManualSee the print edition