Cisco Cisco Email Security Appliance C190 Guida Utente

The backslash character escapes special characters. 
Thus the sequence

 \. 

only matches a literal period, 

the sequence

 \$

 only matches a literal dollar sign, and 

the sequence 

\^

 only matches a literal caret symbol. 

The backslash character also begins tokens, such as 

\d

. 

Important Note: The backslash is also a special 
escape character for the parser. As a result, if you 
want to include a backslash in your regular 
expression, you must use two backslashes — so that 
after parsing, only one “real” backslash remains, 
which is then passed to the regular expression system. 

Token that matches a digit (

0

-

9

). To match more than 

one digit, enter an integer in 

{}

 to define the length of 

the number.

For example, 

\d

 matches only a single digit such as 

5

, 

but not 

55

. Using 

\d{2}

 matches a number consisting 

of two digits, such as 

55

, but not 

5

.

The regular expression notation that indicates the 
number of repetitions of the previous token is 
supported. 

For example, the expression “

\d{8}

” matches 

12345678

 and 

11223344

 but not 

8

.

Alternation, or the “or” operator. If A and B are 
regular expressions, the expression “

A|B

” will match 

any string that matches either “A” or “B.” Can be used 
to combine number patterns in a regular expression.

For example, the expression “

foo|bar

” will match 

either 

foo

 or 

bar

, but not 

foobar

.