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Perl Language Reference Manual
by Larry Wall and others
Paperback (6"x9"), 724 pages
ISBN 9781906966027
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13.3.3 Negation

It is also possible to instead list the characters you do not want to match. You can do so by using a caret (^) as the first character in the character class. For instance, [^a-z] matches a character that is not a lowercase ASCII letter.

This syntax makes the caret a special character inside a bracketed character class, but only if it is the first character of the class. So if you want to have the caret as one of the characters you want to match, you either have to escape the caret, or not list it first.

Examples:

"e"  =~  /[^aeiou]/   #  No match, the 'e' is listed.
"x"  =~  /[^aeiou]/   #  Match, as 'x' isn't a lowercase vowel.
"^"  =~  /[^^]/       #  No match, matches anything that isn't a caret.
"^"  =~  /[x^]/       #  Match, caret is not special here.
ISBN 9781906966027Perl Language Reference ManualSee the print edition