One quick place to look for information on *printf is man 3 printf. It's the C manpage on printf, but perl implements it more or less just like in C. You'll probably find it very helpful in the future for printing anything in the format you like.

I think I'll write a comprehensive tutorial on *printf at some point, unless someone knows about a good one already out there. At least in my version of perldocs, the printf page just says 'just like in C'.