fswalk_new

 SYNOPSIS
  Create an object to walk the filesystem tree

 USAGE
  obj = fswalk_new (Ref_Type enterdir_func, Ref_Type file_func[, Ref_Type leavedir_func]; qualifiers)

 DESCRIPTION
  The `fswalk_new' function creates an object that is useful
  for exploring a filesystem tree.  It requires at least two arguments that
  are references to functions to be called when a directory or file is
  encountered. The third argument (`leavedir_func') is optional.
  Each of these functions is passed at least two
  arguments: the name of the file or directory (including leading path
  elements relative to the directory where processing started), and
  the stat structure of the file or directory.  Qualifiers may
  be used to specify additional arguments.

  The object's `walk' method is the one that actually walks the
  filesystem.

  The `enterdir_func' callback function is called when a
  directory is encountered.  It must return an integer value that
  indicates how it should be processed.  If the function returns 0,
  then the directory will be skipped (pruned).  A positive value
  indicates that the directory will processed.  If the function
  returns a negative value, then no further processing by the walk
  function will take place and control will pass back to the caller.  The
  value of this function may be NULL.

  The `file_func' callback function must return an integer that
  indicates how processing should continue.  If it returns a positive
  value, then additional files in the corresponding directory will be
  processed.  If it returns 0, then no further files or subdirectories
  of the directory will be processed, and processing will continue to
  take place in the parent directory.  Otherwise, the return value is
  negative, which indicates that processing should be stopped and
  control will pass back to the caller.  The value of this function
  may be NULL.

  If the `leavedir_func' has been specified and is non-NULL, then
  it will be called after the directory has been processed.  It must
  return an integer.  A return value of -1 is used to indicate that an
  error has occurred, and that further processing should stop.

 QUALIFIERS
  The following qualifiers are supported:

   dargs={args...}

    `dargs' is a list of additional arguments that will be added when
    calling the `enterdir_func' callback.

   fargs={args...}

    `fargs' is a list of additional arguments that will be added when
    calling the `file_func' callback function.

   largs={args...}

    `largs' is a list of additional arguments that will be added when
    calling the `leavedir_func' callback.

   followlinks[=val]

    The `followlinks' qualifier may be used to indicate whether
    or not directories that are symbolic links are to be followed.  By
    default, they are not.  If `followlinks' is present with no
    value, or has a non-zero value, then symbolic links will be
    followed.  Otherwise, if `followlinks' is not present, or is
    set to 0, then directories that are symbolic links will be skipped.

 METHODS

   .walk (String_Type top_dir)

    The `.walk' function walks the filesystem starting at the
    specified top-level directory calling the directory and file
    callback functions as it goes.

 EXAMPLE
  Print a list of all files containing a `.png' extension under
  the current directory:

     private define file_callback (name, st)
     {
        if (".png" == path_extname (name))
          message (name);
        return 1;
     }
     variable w = fswalk_new (NULL, &file_callback);
     w.walk (".");


  Get a list of all directories that are symbolic links under /usr.

     private define dir_callback (name, st, list)
     {
        st = lstat_file (name);
        if (stat_is ("lnk", st.st_mode))
          {
            list_append (list, name);
            return 0;
          }
        return 1;
     }

     define get_symdir_list (top)
     {
        variable list = {};
        variable w = fswalk_new (&dir_callback, NULL
                                 ;dargs={list}, followlinks);
        w.walk (top);
        return list;
     }
     symdirlist = get_symdir_list ("/usr");

  Note that in this example, the dir_callback function returns 0 if
  the directory corresponds to a symbolic link.  This causes the link
  to not be followed.

  Get a list of dangling symbolic links:

     private define file_callback (name, st, list)
     {
        if (stat_is ("lnk", st.st_mode))
          {
             if ((NULL == stat_file (name))
                 && (errno == ENOENT))
               list_append (list, name);
          }
        return 1;
     }

     define get_badlinks (top)
     {
        variable list = {};
        variable w = fswalk_new (NULL, &file_callback ;fargs={list});
        w.walk (top);
        return list;
     }


 SEE ALSO
  glob, stat_file, lstat_file, listdir;

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