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), but wondering if there's a built-in function to deal with this?

Answer 1

This is the sort of thing that easily found with R basic tools. E.g.: ??path.

Anyway, load the tools package and read ?file_ext .

Answer 2

Let me extend a little bit great answer from https://stackoverflow.com/users/680068/zx8754

Here is the simple code snippet

  # 1. Load library 'tools'
  library("tools")

  # 2. Get extension for file 'test.txt'
  file_ext("test.txt")

The result should be 'txt'.

Answer 3

simple function with no package to load :

getExtension <- function(file){ 
    ex <- strsplit(basename(file), split="\\.")[[1]]
    return(ex[-1])
} 

Answer 4

This function uses pipes:

library(magrittr)

file_ext <- function(f_name) {
  f_name %>%
    strsplit(".", fixed = TRUE) %>%
    unlist %>%
    extract(2)
 }

 file_ext("test.txt")
 # [1] "txt"

Answer 5

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

}