The syslog-ng 3.0 Administrator Guide

The syslog-ng application can dynamically create filenames, directories, or names of database tables using macros that help you organize your log messages. Macros refer to a property or a part of the log message, for example, the $HOST macro refers to the name or IP address of the client that sent the log message, while $DAY is the day of the month when syslog-ng has received the message. Using these macros in the path of the destination log files allows you for example to collect the logs of every host into separate files for every day.

A set of macros can be defined as a template object and used in multiple destinations.

Another use of macros and templates is to customize the format of the syslog message, for example to add elements of the message header to the message text. Note that if a message uses the IETF-syslog format, only the text of the message can be customized, the structure of the header is fixed.

For details on using templates and macros, see Section 3.7, “Templates and macros” and Section 8.5, “Macros”.