Cisco Cisco Firepower Management Center 2000

Protection

Character classes include alphabetic characters, numeric characters, alphanumeric characters, and white 
space characters. While you can create your own character classes within brackets (see 

), you can use the predefined classes as shortcuts for different types of character types. When 

used without additional qualifiers, a character class matches a single digit or character.

The following table describes and provides examples of the predefined character classes accepted by 
PCRE.

Protection

()

Groups expressions.

(abc)+

 matches 

abc

, 

abcabc

, 

abcabcabc

 and so on.

{}

Specifies a limit for the number of matches for a 
character or expression. If you want to set a lower 
and upper limit, separate the lower limit and upper 
limit with a comma. 

a{4,6}

 matches 

aaaa

, 

aaaaa

, or 

aaaaaa

.

(ab){2}

 matches 

abab

.

[]

Allows you to define character classes, and 
matches any character or combination of characters 
described in the set. 

[abc123]

 matches 

a

 or 

b

 or 

c

, and so on.

^

Matches content at the beginning of a string. Also 
used for negation, if used within a character class.

^in

 matches the “in” in 

info

, but not in 

bin

. 

[^a]

 

matches anything that does not contain 

a

.

$

Matches content at the end of a string.

ce$

 matches the “

ce

” in 

announce

, but not 

cent

.

|

Indicates an OR expression.

(MAILTO|HELP)

 matches 

MAILTO

 or 

HELP

.

\

Allows you to use metacharacters as actual 
characters and is also used to specify a predefined 
character class.

\.

 matches a period, 

\*

 matches an asterisk, 

\\

 

matches a backslash and so on. 

\d

 matches the 

numeric characters, 

\w

 matches alphanumeric 

characters, and so on. See 

 for more information about using 

character classes in PCRE.

\d

Matches a numeric character (“digit”).

[0-9]

\D

Matches anything that is not an numeric character.

[^0-9]

\w

Matches an alphanumeric character (“word”).

[a-zA-Z0-9_]

\W

Matches anything that is not an alphanumeric character.

[^a-zA-Z0-9_]

\s

Matches white space characters, including spaces, carriage returns, tabs, 
newlines, and form feeds.

[ \r\t\n\f]

\S

Matches anything that is not a white space character.

[^ \r\t\n\f]