Multiple execution of a transformation: write to log

Hi,
I run hundreds of tranformations, executing the same transf and passing them some parameters.
I need a way to visualize which parameter has been passed (for debug purpose).
I try to add a "write to log" step at the very beginning of my transformation and setting this message to log
"--------------> ${FILE}"

But running my job i don't see the output and I don't know which file has errors.

Can you please suggest to me how to display my params passed to my transformation?

thank you very much,
nicola