Character Classes
Example C-1
tested against letters and numbers, but there are many
ways to do that. [a-z]
is a good way
to test for lowercase letters in English, but many languages use
characters outside of that range. Regular expression character classes
let you create sets of characters as well as use predefined groups of
characters to identify what you want to target.
To create your own character class, use the square braces:
[
and ]
. Within the square braces, you can either
list the characters you want, or create a set of characters with the
hyphen. To match all the (guaranteed) English vowels in lowercase, you
would write:
/[aeiou]/
If you wanted to match both upper- and lowercase vowels, you could write:
/[aeiouAEIOU]/
(If you wanted to ignore case entirely in your search, you could
also use the i
modifier described
earlier: /[aeiou]/i
.)
You can also mix character classes in with other parts of a search:
/[Rr][aeiou]by/
That would match Ruby
, ruby
, raby
,
roby
, and a lot of other variations
with upper- or lowercase R
, followed
by a lowercase vowel, followed by by
.
Sometimes listing all the characters in a class is a hassle. Regular expressions are difficult enough to read without huge chunks of characters in classes. So instead of:
/[abcdefghijklmnopqrstuvwxyz]/
you can just write:
/[a-z]/
As long as the characters you want to match form a single range, thatâs simpleâthe hyphen just means âeverything in between.â
Thereâs also a ânotâ option available, in the ^
character. ...
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