Cisco Cisco Email Security Appliance C170 Guia Do Utilizador

Message filter rules with regular expressions can be created through the content filter GUI, or using a 
text editor to generate a file that is then imported into the system. For more information, see 

 and 

It is important to begin a regular expression with a caret (

^

) and end it with a dollar sign (

$

) whenever 

you want to exactly match a string and not a prefix. 

When matching an empty string, do not use 

“”

 as that actually matches all strings. Instead use 

“^$”

. For 

an example, see the second example in 

.

It is also important to remember that if you want to match a literal period, you must use an escaped period 
in the regular expression. For example, the regular expression 

sun.com

 matches the string 

thegodsunocommando

, but the regular expression 

^sun\.com$

 only matched the string 

sun.com.

Technically, the style of regular expressions used are Python re Module style regular expressions. For 
a more detailed discussion of Python style regular expressions, consult the Python Regular Expression 
HOWTO, accessible from

:

http://www.python.org/doc/howto/

In some languages, the concepts of a word or word boundary, or case do not exist. 

Complex regular expressions that depend on concepts like what is or is not a character that would 
compose a word (represented as “

\w

” in regex syntax) cause problems when the locale is unknown or if 

the encoding is not known for certain. 

Regular expressions can be tested for matching using the sequence 

==

 and for non-matching using the 

sequence 

!=

. For example: 

Unless otherwise noted, regular expressions are case-sensitive. Thus, if your regular expression is 
searching for 

foo

, it does not match the pattern 

FOO

 or even 

Foo

.

rcpt-to == "^goober@dev\\.null\\....$" (matching)

rcpt-to != "^goober@dev\\.null\\....$" (non-matching)