new file mode 100644
--- /dev/null
+++ b/scripts/io/is_valid_file_id.m
@@ -0,0 +1,38 @@
+## Copyright (C) 2010 John W. Eaton
+##
+## This file is part of Octave.
+##
+## Octave is free software; you can redistribute it and/or modify it
+## under the terms of the GNU General Public License as published by
+## the Free Software Foundation; either version 3 of the License, or (at
+## your option) any later version.
+##
+## Octave is distributed in the hope that it will be useful, but
+## WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+## General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with Octave; see the file COPYING.  If not, see
+## <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} {} is_valid_file_id (@var{fid})
+## Return true if @var{fid} refers to an open file.
+## @seealso{fopen}
+## @end deftypefn
+
+function retval = is_valid_file_id (fid)
+
+  retval = false;
+
+  if (nargin == 1)
+    try
+      [file, mode, arch] = fopen (fid);
+      retval = ! isempty (file);
+    end_try_catch
+  else
+    print_usage ();
+  endif
+
+endfunction