A: This question has 
turned out a bit more complicated than I first
thought. There are several methods, each with some catch. The 
first
is trying to open the name as a file and observing the IOResult. 
The
ISDIRFN function in ftp://garbo.uwasa.fi/pc/ts/tspa3470.zip TPU 
unit
TSUNTJ.TPU is based on this method. Unfortunately it is not 
always
stable. I have been reported problems in connection with DRDOS 
by
Richard Breuer (ricki@pool.informatik.rwth-aachen.de) who has
tested these routines.
  The second method (ISDIR2FN) is based on the fact that the file
NUL exists in a directory if the directory exists.
  The thrid method (ISDIR3FN) is a brute force method. It is given
below, since it is quite an instructive little exercise of Turbo
Pascal programming.
  (* Search recursively through a drive's directories.
     Auxiliary, recursive procedure for ISDIR3FN *)
  procedure SEARCHDR (Path, FileSpec : string;
                      name           : string;
                      var found      : boolean);
  var FileInfo : SearchRec;
  begin
    FindFirst (Path + '*.*', Directory, FileInfo);
    while DosError = 0 do
      begin
        if ((FileInfo.Attr and Directory) > 0) and
            (FileInfo.Name <> '.') and
            (FileInfo.Name <> '..') then
              begin
                SEARCHDR (Path + FileInfo.Name + '\',
                          FileSpec,
                          name,
                          found);
                if Path + FileInfo.Name + '\' = name then
                  found := true;
              end;
        FindNext (FileInfo);
      end; {while}
  end;  (* searchdr *)

  (* Does a name refer to 
a directory *)
  function ISDIR3FN (name : string) : boolean;
  var drive : char;
      found : boolean;
  begin
    {... Default value ...}
    isdir3fn := false;
    {... Discard empty names ...}
    if name = '' then exit;
    {... Expand into a fully qualified name, makes it uppercase ...}
    name := FExpand (name);
    if name[Length(name)] <> '\' then name := name + '\';
    {... Extract the drive letter from the name ...}
    drive := UpCase (name[1]);
    {... Check first for the root ...}
    if drive + ':\' = name then
      begin isdir3fn := true; exit; end;
    {... Check the rest of the directories recursively ...}
    found := false;
    SEARCHDR (drive + ':\', '*.*', name, found);
    isdir3fn := found;
  end;  (* isdir3fn *)

-Date: Mon, 13 Jun 1994 
00:13:05 +0000 (GMT)
-From: JEROEN SCHIPPER <JSCHIPPER@HUT.NL>
-To: ts@uwasa.fi (Timo Salmi)
-Subject: Is a name a directory in TP

The method I use is 
simply checking the attribute bit, as this small
program will demonstrate:
  program isdir;
  uses dos;
  var s:string;
      attr:word;
      f:file;
  begin
    repeat
      readln(s);
      if s = '' then break;
      assign(f,s);
      getfattr(f,attr);
      if doserror <> 0 then
        writeln('DOS error code = ', doserror)
      else
      begin
        if attr and directory <> 0 then
          writeln(S,' is a directory')
        else
          writeln(S,' is a not directory')

      end;
    until false;
  end.
The methods you mention in your faq are far more complicated, 
but
why? Is there are catch why the method above won't work? I guess
don't really understand the problem here.
Jeroen.

 A2: This has turned out 
to be a tricky FAQ. There are some
additional suggestions and comments from the gentle readers. 
You can
track them from ftp://garbo.uwasa.fi/pc/ts/tspost00.zip index.