Filters

Filters perform log routing inside syslog-ng. You can write a boolean expression using internal functions, which has to evaluate to true for the message to pass.

Filters have also a uniquely identifying name, so you can refer to filters in your log statements. Syntax for the filter statement:
	  filter <identifier> { expression; };
	
An expression may contain the operators "and", "or" and "not", and any of the functions listed below.

Example 2-2. A filter statement finding the messages containing the word deny coming from the host blurp

	  filter f_blurp_deny { host("blurp") and match("deny"); };
	

Table 2-3. Available filter functions in syslog-ng

FunctionDescription
facility()Selects messages based on their facility code
level() or priority()Selects messages based on their priority
program()Tries to match a regular expression to the program name field of log messages
host()Tries to match a regular expression to the hostname field of log messages
match()Tries to match a regular expression to the message itself.

For a complete description on the above functions, see the Reference chapter.