file.path(..., fsep = .Platform$file.sep)fsep if all arguments have positive length;
otherwise, an empty character vector (unlike paste).
paste) as this function is used extensively in R itself. It can also be used for environment paths such as PATH and
R_LIBS with fsep = .Platform$path.sep.
Trailing path separators are invalid for Windows file paths apart from
/ and d:/ (although some functions/utilities do accept
them), so as from R 3.1.0 a trailing / or \ is
removed.