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Processing All Files in a Directory

Problem

You want to do something to each file in a particular directory.

Solution

Use PltScheme's standard function directory-list to retrieve the contents in a directory and do something with them.

(for-each do-something-with-the-contents
          (map (lambda (f)
                 (string-append path "/" f))
               (directory-list path)))

You just have to take in account that directory-list returns a list of all files and directories in the directory specified by path. If path is omitted, a list of files and directories in the current directory is returned.

If you need to process the files only. We can define a new procedure that only retrieves the files in a directory like this:

(require (lib "1.ss" "srfi"));; to use the filter procedure

;; directory-list-files: String -> (listof String)
;; Obtains a list with the files (only) in the specified path
(define (directory-list-files path)
  (filter (lambda (v)
            (file-exists? (string-append path "/" v)))
          (directory-list path)))

So our first code will turn into

(for-each do-something-with-the-contents
          (map (lambda (f)
                 (string-append path "/" f))
               (directory-list-files path)))

Finally, in the previous examples we used the for-each procedure, that applies a procedure to each element in a list, but returns void. If you want to return a value you may want to use the map procedure instead of for-each.

Discussion

Comments about this recipe

Contributors

-- IvanHernandez - 03 Jun 2004