+ DEFVAR_CONST_LISP ("null-device", &Vnull_device /*
+Name of the null device, which differs from system to system.
+The null device is a filename that acts as a sink for arbitrary amounts of
+data, which is discarded, or as a source for a zero-length file.
+It is available on all the systems that we currently support, but with
+different names (typically either `/dev/null' or `nul').
+
+Note that there is also a /dev/zero on most modern Unix versions (including
+Cygwin), which acts like /dev/null when used as a sink, but as a source
+it sends a non-ending stream of zero bytes. It's used most often along
+with memory-mapping. We don't provide a Lisp variable for this because
+the operations needing this are lower level than what ELisp programs
+typically do, and in any case no equivalent exists under native MS Windows.
+*/ );
+ Vnull_device = build_string (NULL_DEVICE);
+