User Guide

REGULAR EXPRESSION CHARACTER TABLE
CHAPTER 13: URL FILTERS 291
/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 “.*”.
Note — You must enclose regular expressions that contain blank spaces or non-alphanumeric
characters in ASCII quotation marks.
Regular Expression Character Table
Table 13-5 describes characters that are commonly used to form regular expressions:
Table 13-5 Regular Expression Character Descriptions
Character Description
. 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