Regular Expressions: Exceptions in a Character Set

You can easily search for all characters except those in square brackets by putting a caret (^) as the first character after the left square bracket ([). To match all characters except lowercase vowels, use [^aeiou].

Like the anchors in places that can't be considered an anchor, the right square bracket (]) and dash (-) do not have a special meaning if they directly follow a [. Table 32-2 has some examples.

Table 32-2. Regular expression character set examples

Regular expression	Matches
`[0-9]`	Any digit
`[^0-9]`	Any character other than a digit
`[-0-9]`	Any digit or a `-`
`[0-9-]`	Any digit or a `-`
`[^-0-9]`	Any character except a digit or a `-`
`[ ]0-9]`	Any digit or a `]`
`[0-9]]`	Any digit followed by a `]`
`[0-99-z]`	Any digit or any character between 9 and z
`[ ]0-9-]`	Any digit, a `-`, or a `]`

Many languages have adopted the Perl regular expression syntax for ranges; for example, \w is equivalent to "any word character" or [A-Za-z0-9_], while \W matches anything but a word character. See the perlre(1) manual page for more details.