[R] How to check if file is on a drive?

[Sergey Goriatchev]

Hello, everyone

How would I check in R if a particular file (Excel file) is in a
particular folder on a particular drive?
I am writing a piece of code around that file, using xls.open() in
xlsReadWritePro to open the file in memory and use it. But before I
try to open the file I want to catch the possibility of the file not
being on the drive.

Thank you in advance!

SG