isdirectory

ISDIRECTORY True if argument is a directory.

   ISDIRECTORY(DIR) returns 1 if DIR is a directory and 0 otherwise.
   [T, NEWDIR] = ISDIRECTORY(DIR) also returns the name of the directory as
   returned by CD.  NEWDIR is empty if DIR is not a directory.

   Using EXIST(DIR, 'dir') is too unreliable.  For instance, under Windows
   it returns false if DIR is 'c:' (where c: is an existing drive) and it
   returns false and if DIR is a directory which is in the path but does
   not exist.