Is there a "list all files" procedure in scheme?

Question

Is there a racket/scheme procedure that returns a list (or vector) of the names of all user accesible files?
The output needs to be a list or vector for applying a "filter", like so:

(filter pred list-of-all-files)

The intended application is a text-based, user-friendly "librarian" program.

Are you asking for something like the shell command `ls` (limited to a specific directory) but filtered to be only files that the user can read or something more like a list of _every single file_ on-disk that the user can read? — Lazerbeak12345, Jul 10 '20 at 16:24
I was looking for the latter, but in the former, do you mean terminal shell or racket shell? I haven't of `ls` before now. — Flowerfist.rkt, Jul 12 '20 at 21:48

score 4 · Answer 1 · answered Jul 13 '20 at 02:29

The relevant procedures you are looking for are directory-list and in-directory.

Using directory-list, you can retrieve a list of all files and directories in the directory specified by some path (similar to the shell command ls).

;; ls /some/path
(directory-list "/some/path")

On the other hand, in-directory returns a sequence that produces all of the paths for files, directories, and links within a directory, traversing nested subdirectories recursively (which seems to be what you are primarily looking for).

For example, to return the names of all user readable files and directories under "/some/path", you can do:

(for/list ([f (in-directory "/some/path"
                            (lambda (p)
                              (member 'read (file-or-directory-permissions p))))])
  f)

You can use path->string to produce the file names in string format instead. So, to create your list-all-files procedure:

(define (list-all-files path)
  (define (user-readable? f)
    (member 'read (file-or-directory-permissions f)))
  (for/list ([f (in-directory path user-readable?)])
    (path->string f)))

Then, you can filter the generated list using any predicate pred:

(filter pred (list-all-files "/some/path"))

There might be a built-in function that does this better, but one could use that example with `in-directory` along with a recursive utility function to traverse the directory tree. This might be closer to what @Flowerfist.rkt is looking for — Lazerbeak12345, Jul 13 '20 at 17:38

Is there a "list all files" procedure in scheme?

1 Answers1