8.4.3. Comparing macro values in filters

Starting with syslog-ng OSE version 3.2, it is also possible to compare macro values and templates as numerical and string values. String comparison is alphabetical: it determines if a string is alphabetically greater or equal to another string. Use the following syntax to compare macro values or templates. For details on macros and templates, see Section 11.1, Customizing message format using macros and templates.

filter <filter-id>
        {"<macro-or-template>" operator "<value-or-macro-or-template>"};
Example 8.12. Comparing macro values in filters

The following expression selects log messages containing a PID (that is, ${PID} macro is not empty):

filter f_pid {"${PID}" !=""};

The following expression selects log messages that do not contain a PID. Also, it uses a template as the left argument of the operator and compares the values as strings:

filter f_pid {"${HOST}${PID}" eq "${HOST}"};

The following example selects messages with priority level 4 or higher.

filter f_level {"${LEVEL_NUM}" > "5"};

Note that:

  • The macro or template must be enclosed in double-quotes.

  • The $ character must be used before macros.

  • Using comparator operators can be equivalent to using filter functions, but is somewhat slower. For example, using "${HOST}" eq "myhost" is equivalent to using host("myhost" type(string)).

  • You can use any macro in the expression, including user-defined macros from parsers and results of pattern database classifications.

  • The results of filter functions are boolean values, so they cannot be compared to other values.

  • You can use boolean operators to combine comparison expressions.

The following operators are available:

Numerical operatorString operatorMeaning
==eqEquals
!=neNot equal to
>gtGreater than
<ltLess than
>=geGreater than or equal
=<leLess than or equal

Table 8.2. Numerical and string comparison operators