Variables and namespaces

As we already said when describing the configuration files, the PICA central executable begins by preprocessing and reading pica.conf. After that, hosts.conf is parsed. Here, the program finds out about the machines, their attributes, variables and such. Then, and once for each host, PICA preprocess and reads objects.conf. Obviously, as the file is preprocessed once for each machine, the result can be different, because the preprocessor namespace is, in general, distinct. That way, we can define different distribution files, or in different ways, for each machine. Thus, we can:

1. Make the host definition depend on command line definitions,
2. Make the objects definition depend on command line and host variables; and
3. Make the contents of the objects depend on almost everything

Understanding this is very important to understand PICA behaviour. Once you get the hang of it, you will know how to make PICA do what you want.