5.6.2.1. 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 empty parentheses 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`).

Example 5.8. Passing arguments to blocks

The following sample defines a file source block, which can receive the name of the file as a parameter. If no parameter is set, it reads messages from the /var/log/messages file.

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. 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));
};
Example 5.9. Using arguments in blocks

The following example is the code of the pacct() source driver, which is actually a block that can optionally receive two arguments.

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