Traversing a directory tree

Question

i am trying to traverse a given directory and create a list of files ending in .jpg.

(setq files (list ))

(defun jpg-list(directory)  
  (dolist (node (directory-files directory t ) )
      (if (file-directory-p node)      
          (if (not 
           (string= (substring node (- (string-width node) 1)) "."))
             (jpg-list node))
    (if (string-match ".jpg" node)
        (setq files (cons node files)))))
  files)

i would like to do this without using an external variable (files). What is the idiomatic way of doing this in elisp?

Answer 1

Your best bet is use 'directory-files full interface and just use:

(directory-files directory t ".jpg$")

The bigger question was how to avoid the top-level variable, which is usually solved by a 'let statement, e.g.

(defun jpg-list (directory)
  (let ((files))
    ...do something with files...
    files))

Answer 2

Here's my functional solution:

(defun jpg-list (dir)
  (if (file-directory-p dir)
      (append
       (directory-files dir t ".jpg$")
       (apply 'append (mapcar 'jpg-list (directory-files dir t "[^.]+"))))))