Extract file extension from file path

Question

How can I extract the extension of a file given a file path as a character? I know I can do this via regular expression regexpr(\"\\\\.([[:alnum:]]+)$\", x), b

Answer 1

The regexpr above fails if the extension contains non-alnum (see e.g. https://en.wikipedia.org/wiki/List_of_filename_extensions) As an altenative one may use the following function:

getFileNameExtension <- function (fn) {
# remove a path
splitted    <- strsplit(x=fn, split='/')[[1]]   
# or use .Platform$file.sep in stead of '/'
fn          <- splitted [length(splitted)]
ext         <- ''
splitted    <- strsplit(x=fn, split='\\.')[[1]]
l           <-length (splitted)
if (l > 1 && sum(splitted[1:(l-1)] != ''))  ext <-splitted [l] 
# the extention must be the suffix of a non-empty name    
ext

}