Using wildcards, special characters, and regular expressions in filters

The host(), match(), and program() filter functions accept regular expressions as parameters. The exact type of the regular expression to use can be specified with the type() option. By default, AxoSyslog uses PCRE regular expressions.

In regular expressions, the asterisk (\) character means 0, 1, or any number of the previous expression. For example, in the f\*ilter expression the asterisk means 0 or more f letters. This expression matches for the following strings: ilter, filter, ffilter, and so on. To achieve the wildcard functionality commonly represented by the asterisk character in other applications, use .\ in your expressions, for example, f.\*ilter.

Alternatively, if you do not need regular expressions, only wildcards, use type(glob) in your filter:

Example: Filtering with widcards

The following filter matches on hostnames starting with the myhost string, for example, on myhost-1, myhost-2, and so on.

   filter f_wildcard {host("myhost*" type(glob));};

For details on using regular expressions in AxoSyslog, see Using wildcards, special characters, and regular expressions in filters.

To filter for special control characters like the carriage return (CR), use the \\r escape prefix in AxoSyslog version 3.0 and 3.1. In AxoSyslog 3.2 and later, you can also use the \\x escape prefix and the ASCII code of the character. For example, to filter on carriage returns, use the following filter:

   filter f_carriage_return {match("\x0d" value ("MESSAGE"));};