You use character
classes to specify a list of characters to match one position in the
regular expression. You define character classes with square brackets
(
[
and
]
). For example, the
following regular expression defines a character class that matches
bag
,
beg
,
big
,
bog
,
or
bug
:
/b[aeiou]g/
Escape sequences in character classes
Most metacharacters
and metasequences that normally have special meanings in a regular
expression
do not
have those same meanings inside a character
class. For example, in a regular expression, the asterisk is used
for repetition, but this is not the case when the asterisk appears
in a character class. The following character class matches the
asterisk literally, along with any of the other characters listed:
/[abc*123]/
However,
the three characters listed in the following table do function as metacharacters,
with special meaning, in character classes:
|
Metacharacter
|
Meaning in character classes
|
|
]
|
Defines the end of the character class.
|
|
-
|
Defines a range of characters (see the following
section “Ranges of characters in character classes”).
|
|
\
|
Defines metasequences and undoes the special
meaning of metacharacters.
|
For any of these characters to be recognized
as literal characters (without the special metacharacter meaning),
you must precede the character with the backslash escape character.
For example, the following regular expression includes a character
class that matches any one of four symbols (
$
,
\
,
]
,
or
-
):
/[$\\\]\-]/
In
addition to the metacharacters that retain their special meanings,
the following metasequences function as metasequences within character
classes:
|
Metasequence
|
Meaning in character classes
|
|
\n
|
Matches a newline character.
|
|
\r
|
Matches a return character.
|
|
\t
|
Matches a tab character.
|
|
\u
nnnn
|
Matches the character with the specified
Unicode code point value (as defined by the hexadecimal number
nnnn
).
|
|
\\x
nn
|
Matches the character with the specified
ASCII value (as defined by the hexadecimal number
nn
).
|
Other regular expression metasequences
and metacharacters are treated as normal characters within a character
class.
Ranges of characters in character classes
Use the hyphen to specify a range
of characters, such as
A-Z
,
a-z
,
or
0-9
. These characters must constitute a valid
range in the character set. For example, the following character
class matches any one of the characters in the range
a-z
or any
digit:
/[a-z0-9]/
You
can also use the
\\x
nn
ASCII character code
to specify a range by ASCII value. For example, the following character
class matches any character from a set of extended ASCII characters
(such as
é
and
ê
):
\\x
Negated character classes
When you use a caret (
^
)
character at the beginning of a character class, it negates that
class—any character not listed is considered a match. The following character
class matches any character
except
for a lowercase letter
(
az
–) or a digit:
/[^a-z0-9]/
You
must type the caret (
^
) character at the
beginning
of
a character class to indicate negation. Otherwise, you are simply
adding the caret character to the characters in the character class.
For example, the following character class matches any one of a
number of symbol characters, including the caret:
/[!.,#+*%$&^]/
