syslog-ng Open Source Edition 3.33 - Administration Guide

Mandatory parameters

You can express in block definitons that a parameter is mandatory by defining it with empty brackets (). In this case, the parameter must be overridden in the reference block. Failing to do so will result in an error message and initialization failure.

To make a parameter expand into nothing (for example, because it has no default value, like hook-commands() or tls()), insert a pair of double quote marks inside the empty brackets: ("")

block source my_tcp_source(localport() flags("")) {
    network(port(`localport`) transport(tcp) flags(`flags`));
};

my_tcp_source(localport(8080))

network(port(8080) transport(tcp) flags());

Passing arguments to configuration blocks

Configuration blocks can receive arguments as well. The parameters the block can receive must be specified when the block is defined, using the following syntax:

block type block_name(argument1(<default-value-of-the-argument>) argument2(<default-value-of-the-argument>) argument3())

If an argument does not have a default value, use an empty double quote bracket pair ("") after the name of the argument. To refer the value of the argument in the block, use the name of the argument between backticks (for example, `argument1`).

block source s_logfile (filename("messages")) {
    file("/var/log/`filename`" );
};

source s_example {
    s_logfile(filename("logfile.log"));
};

If you reference the block with more arguments then specified in its definition, you can use these additional arguments as a single argument-list within the block. That way, you can use a variable number of optional arguments in your block. This can be useful when passing arguments to a template, or optional arguments to an underlying driver.

The three dots (…) at the end of the argument list refer to any additional parameters. It tells syslog-ng OSE that this macro accepts `__VARARGS__`, therefore any name-value pair can be passed without validation. To reference this argument-list, insert `__VARARGS__` to the place in the block where you want to insert the argument-list. Note that you can use this only once in a block.

The following definition extends the logfile block from the previous example, and passes the optional arguments (follow-freq(1) flags(no-parse)) to the file() source.

block source s_logfile(filename("messages") ...) {
    file("/var/log/`filename`" `__VARARGS__`);
};

source s_example {
    s_logfile(
        filename("logfile.log")
        follow-freq(1)
        flags(no-parse)
    );
};

block source pacct(file("/var/log/account/pacct") follow-freq(1) ...) {
    file("`file`" follow-freq(`follow-freq`) format("pacct") tags(".pacct") `__VARARGS__`);
};

block options setup-dns(use-dns()) {
    keep-hostname(no);
    use-dns(`use-dns`);
    use-fqdn(`use-dns`);
dns-cache(`use-dns`);
};

options {
    setup-dns(use-dns(yes));
};