[R] install.packages() for a local file

[Jeff Gentry]

Hello ...

I see that on Windows one can specify a filename as the "pkgs" argument
and then set CRAN=NULL when calling install.packages() for a local
file.  Is there a way to do this on unix?  It doesn't appear to be
possible, but perhaps I am missing something here.  

Also, if indeed there is no method to do this on unix, is there a reason
behind it or has it just never been implemented?