Construct the path to a file from components in a platform-independent way.

the path separator to use.

A character vector of the arguments concatenated term-by-term and separated by fsep if all arguments have positive length; otherwise, an empty character vector (unlike paste).

The implementation is designed to be fast (faster than 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 a trailing / or \ is removed.