Cisco Cisco Web Security Appliance S670 User Guide

In the following example, the regular expression matches files ending in 

.exe

, 

.zip

, and .

bin

 in the 

downloads

 directory.

/downloads/.*\.(exe|zip|bin)

Avoid using regular expressions strings that are redundant because they can cause higher CPU usage on 
the Web Security appliance. A redundant regular expression is one that starts or ends with “.*”. 

You must enclose regular expressions that contain blank spaces or non-alphanumeric characters in 
ASCII quotation marks.

 describes characters that are commonly used to form regular expressions: 

.

Matches a single character.

*

Matches zero or more occurrences of the preceding regular expression. 

For example:

[0-9]* matches any number of digits

“.*” matches any arbitrary string of characters

^

Matches the beginning of a line as the first character of a regular expression.

$

Matches the end of a line as the last character of a regular expression.

+

Matches one or more occurrences of the preceding regular expression.

?

Matches zero or one occurrence of the preceding regular expression.

|

Matches the preceding regular expression or the following regular expression. For 
example:

x|y matches either x or y

abc|xyz matches either of the strings abc or xyz

[ ]

Matches the characters or digits that are enclosed within the brackets. 

For example:

[a-z] matches any character between a and z

[r-u] matches any of the characters r, s, t, or u

[0-3] matches any of the single digits 0, 1, 2, 3

{ }

Specifies the number of times to match the previous pattern. 

For example:

D{1,3} matches one to three occurrences of the letter D

( )

Group characters in a regular expression.

For example:

(abc)* matches abc or abcabcabc