diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index dbff044..2cc4e03 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,3 +1,8 @@
+2009-07-01  Sean O'Rourke  <address@hidden>
+
+	* os.texi (System Environment): document null-device,
+	shell-file-name, and shell-command-switch.
+
 2009-06-24  Chong Yidong  <address@hidden>
 
 	* display.texi (Window Systems): Add ns to the list.
diff --git a/doc/lispref/os.texi b/doc/lispref/os.texi
index 07ae1a0..ff415a8 100644
--- a/doc/lispref/os.texi
+++ b/doc/lispref/os.texi
@@ -991,6 +991,21 @@ in the system's terminal driver, before Emacs was started.
 The value is @code{nil} if Emacs is running under a window system.
 @end defvar
 
address@hidden null-device
+This variable holds the name of the system's null ouput device, used
+to discard a program's output.  Use this variable instead of
address@hidden/dev/null} or @file{NUL}.
address@hidden defvar
+
address@hidden shell-file-name
+This variable holds the name of the system shell.
address@hidden defvar
+
address@hidden shell-command-switch
+This variable holds the switch used to have the shell execute its
+command line argument.
address@hidden defvar
+
 @node User Identification
 @section User Identification
 @cindex user identification