[R] get absolute file path

[Sebastian Gibb]

Hello,

I get a value which stores a relative file name. (I get it from another 
function, which I don't want to change.)
e.g.
> fileName <- "../data/2010-08.csv";

Is it possible to get the absolute file path out of this value?
(e.g. /home/sebastian/documents/data/2010-08.csv)

Kind regards,

Sebastian