R environment variable

which R environmen variable can be used to point to
x1.R so that it can be sourced in any directory?

I don't think there is such a thing.  source() looks in the current
working directory, it doesn't use environment variables to do a wider
search.

Of course, you can always make up your own variable, and then do
something like

source(paste(getenv('MYDIR'),'/x1.R',sep=''))

and that will work from anywhere if MYDIR is defined properly.

Duncan Murdoch