adding to pf rules dynamically via a script

[rance at frontiernet.net]

could someone be so kind as to point to an example I can study as to  
how to add pf rules via a log monitoring script Im trying to port from  
linux.

I know it can be done, but none of the docs I'm reading show how.

I think I'm understanding that this is done with an anchor.

but I'm having trouble finding a documented example I can study and  
learn from.

Anybody know of a good doc on this, or have a well documented example  
they woulnt mind sharing?