How can I "URL decode" a string in Emacs Lisp?

Question

I've got a string like "foo%20bar" and I want "foo bar" out of it.

I know there's got to be a built-in function to decode a URL-encoded string (query string) in Emacs Lisp, but for the life of me I can't find it today, either in my lisp/ folder or with Google.

What is it called?

Answer 1

url-unhex-string

Answer 2

In my case I needed to do this interactively. The previous answers gave me the right functions to call, then it was just a matter of wrapping it a little to make them interactive:

(defun func-region (start end func)
  "run a function over the region between START and END in current buffer."
  (save-excursion
    (let ((text (delete-and-extract-region start end)))
      (insert (funcall func text)))))

(defun hex-region (start end)
  "urlencode the region between START and END in current buffer."
  (interactive "r")
  (func-region start end #'url-hexify-string))

(defun unhex-region (start end)
  "de-urlencode the region between START and END in current buffer."
  (interactive "r")
  (func-region start end #'url-unhex-string))

Add salt, I mean bind to keys according to taste.

Answer 3

Emacs is shipped with a URL library that provides a bunch of URL parsing functions—as huaiyuan and Charlie Martin already pointed out. Here is a small example that'd give you an idea how to use it:

(let ((url "http://www.google.hu/search?q=elisp+decode+url&btnG=Google+keres%E9s&meta="))
  ;; Return list of arguments and values
  (url-parse-query-string
   ;; Decode hexas
   (url-unhex-string
    ;; Retrieve argument list
    (url-filename
     ;; Parse URL, return a struct
     (url-generic-parse-url url)))))
=> (("meta" "") ("btnG" "Google+keresés") ("/search?q" "elisp+decode+url"))

I think is better to rely on it rather than Org-mode as it is its main purpose to parse a URL.