This thread is getting a bit complicated here. 

I didn't think I would have to play with the source code to have a
script running. I taught there was already a mechanism in amanda to
permit so.

I had read somewhere that 'amdump' looks for a file called "hold" and
waits for the file to disapear befor begining to dump.  That would
have worked (of cours, I wouls still need to know when amdump has
finished to restart oracle)

Otherwise, I don't see how to use a "wrapper" to gnu tar or
ufsdump/dump.  For that, I would have to know WHAT parameters dump or
gnu tar expects. Anyway, I think it's overly complicated.