Use @env for environment variables in texinfo manuals

It renders the same as @code, so in many cases this change is entirely cosmetic.

* doc/emacs/misc.texi (Gnus Startup):
* doc/lispref/files.texi, doc/lispref/frames.texi:
* doc/lispref/loading.texi, doc/lispref/os.texi, doc/lispref/processes.texi:
Use @env for environment variables.

doc/emacs/ChangeLog

@@ -1,3 +1,7 @@
+2012-04-08  Glenn Morris  <rgm@gnu.org>
+
+	* misc.texi (Gnus Startup): Use @env for environment variables.
+
 2012-04-07  Glenn Morris  <rgm@gnu.org>
 
 	* Makefile.in: Replace non-portable use of $< in ordinary rules.

doc/emacs/misc.texi

@@ -92,7 +92,7 @@ file named @file{.newsrc} in your home directory which lists your
 Usenet newsgroups and subscriptions (this file is not unique to Gnus;
 it is used by many other newsreader programs).  It then tries to
 contact the system's default news server, which is typically specified
-by the @samp{NNTPSERVER} environment variable.
+by the @env{NNTPSERVER} environment variable.
 
   If your system does not have a default news server, or if you wish
 to use Gnus for reading email, then before invoking @kbd{M-x gnus} you

doc/lispref/ChangeLog

@@ -1,3 +1,8 @@
+2012-04-08  Glenn Morris  <rgm@gnu.org>
+
+	* files.texi, frames.texi, loading.texi, os.texi, processes.texi:
+	Use @env for environment variables.
+
 2012-04-07  Glenn Morris  <rgm@gnu.org>
 
 	* Makefile.in: Replace non-portable use of $< in ordinary rules.

doc/lispref/files.texi

@@ -2154,7 +2154,7 @@ double all @samp{$} characters to prevent subsequent incorrect
 results.
 
 @c Wordy to avoid overfull hbox.  --rjc 15mar92
-Here we assume that the environment variable @code{HOME}, which holds
+Here we assume that the environment variable @env{HOME}, which holds
 the user's home directory name, has value @samp{/xcssun/users/rms}.
 
 @example
@@ -2239,9 +2239,9 @@ non-@code{nil}.  To use it, you should expand the prefix against
 the proper directory before calling @code{make-temp-file}.
 
 @defopt temporary-file-directory
-@cindex @code{TMPDIR} environment variable
-@cindex @code{TMP} environment variable
-@cindex @code{TEMP} environment variable
+@cindex @env{TMPDIR} environment variable
+@cindex @env{TMP} environment variable
+@cindex @env{TEMP} environment variable
 This variable specifies the directory name for creating temporary files.
 Its value should be a directory name (@pxref{Directory Names}), but it
 is good for Lisp programs to cope if the value is a directory's file
@@ -2249,7 +2249,7 @@ name instead.  Using the value as the second argument to
 @code{expand-file-name} is a good way to achieve that.
 
 The default value is determined in a reasonable way for your operating
-system; it is based on the @code{TMPDIR}, @code{TMP} and @code{TEMP}
+system; it is based on the @env{TMPDIR}, @env{TMP} and @env{TEMP}
 environment variables, with a fall-back to a system-dependent name if
 none of these variables is defined.
 

doc/lispref/frames.texi

@@ -488,7 +488,7 @@ frame.  @code{title} and @code{name} are meaningful on all terminals.
 @item display
 The display on which to open this frame.  It should be a string of the
 form @code{"@var{host}:@var{dpy}.@var{screen}"}, just like the
-@code{DISPLAY} environment variable.
+@env{DISPLAY} environment variable.
 
 @vindex display-type, a frame parameter
 @item display-type

doc/lispref/loading.texi

@@ -235,7 +235,7 @@ it skips the latter group.
 in a list of directories specified by the variable @code{load-path}.
 
 @defvar load-path
-@cindex @code{EMACSLOADPATH} environment variable
+@cindex @env{EMACSLOADPATH} environment variable
 The value of this variable is a list of directories to search when
 loading files with @code{load}.  Each element is a string (which must be
 a directory name) or @code{nil} (which stands for the current working

doc/lispref/os.texi

@@ -89,7 +89,7 @@ that Emacs is being initialized.
 @c set-locale-environment
 @item
 It sets the language environment and the terminal coding system,
-if requested by environment variables such as @code{LANG}.
+if requested by environment variables such as @env{LANG}.
 
 @item
 It does some basic parsing of the command-line arguments.
@@ -352,8 +352,8 @@ control whether and where to find the init file; @samp{-q} (and the
 stronger @samp{-Q}) says not to load an init file, while @samp{-u
 @var{user}} says to load @var{user}'s init file instead of yours.
 @xref{Entering Emacs,,, emacs, The GNU Emacs Manual}.  If neither
-option is specified, Emacs uses the @code{LOGNAME} environment
-variable, or the @code{USER} (most systems) or @code{USERNAME} (MS
+option is specified, Emacs uses the @env{LOGNAME} environment
+variable, or the @env{USER} (most systems) or @env{USERNAME} (MS
 systems) variable, to find your home directory and thus your init
 file; this way, even if you have su'd, Emacs still loads your own init
 file.  If those environment variables are absent, though, Emacs uses
@@ -430,7 +430,7 @@ This variable holds the name of the @file{.emacs.d} directory.  It is
   Each terminal type can have its own Lisp library that Emacs loads when
 run on that type of terminal.  The library's name is constructed by
 concatenating the value of the variable @code{term-file-prefix} and the
-terminal type (specified by the environment variable @code{TERM}).
+terminal type (specified by the environment variable @env{TERM}).
 Normally, @code{term-file-prefix} has the value
 @code{"term/"}; changing this is not recommended.  Emacs finds the file
 in the normal manner, by searching the @code{load-path} directories, and
@@ -468,7 +468,7 @@ use this hook to define initializations for terminals that do not
 have their own libraries.  @xref{Hooks}.
 
 @defvar term-file-prefix
-@cindex @code{TERM} environment variable
+@cindex @env{TERM} environment variable
 If the value of this variable is non-@code{nil}, Emacs loads a
 terminal-specific initialization file as follows:
 
@@ -481,7 +481,7 @@ You may set the @code{term-file-prefix} variable to @code{nil} in your
 init file if you do not wish to load the
 terminal-initialization file.
 
-On MS-DOS, Emacs sets the @code{TERM} environment variable to @samp{internal}.
+On MS-DOS, Emacs sets the @env{TERM} environment variable to @samp{internal}.
 @end defvar
 
 @defvar term-setup-hook
@@ -1010,7 +1010,7 @@ value is @code{":"} for Unix and GNU systems, and @code{";"} for MS systems.
 
 @defun parse-colon-path path
 This function takes a search path string such as the value of
-the @code{PATH} environment variable, and splits it at the separators,
+the @env{PATH} environment variable, and splits it at the separators,
 returning a list of directory names.  @code{nil} in this list means
 the current directory.  Although the function's name says
 ``colon'', it actually uses the value of @code{path-separator}.
@@ -1113,7 +1113,7 @@ want to use the default value.
 
 @defun user-login-name &optional uid
 This function returns the name under which the user is logged in.
-It uses the environment variables @code{LOGNAME} or @code{USER} if
+It uses the environment variables @env{LOGNAME} or @env{USER} if
 either is set.  Otherwise, the value is based on the effective
 @acronym{UID}, not the real @acronym{UID}.
 
@@ -1124,12 +1124,12 @@ corresponds to @var{uid}, or @code{nil} if there is no such user.
 @defun user-real-login-name
 This function returns the user name corresponding to Emacs's real
 @acronym{UID}.  This ignores the effective @acronym{UID}, and the
-environment variables @code{LOGNAME} and @code{USER}.
+environment variables @env{LOGNAME} and @env{USER}.
 @end defun
 
 @defun user-full-name &optional uid
 This function returns the full name of the logged-in user---or the value
-of the environment variable @code{NAME}, if that is set.
+of the environment variable @env{NAME}, if that is set.
 
 If the Emacs process's user-id does not correspond to any known user (and
 provided @code{NAME} is not set), the result is @code{"unknown"}.
@@ -1249,9 +1249,9 @@ The argument @var{time-value}, if given, specifies a time (represented
 as a list of integers) to analyze instead of the current time.
 @end defun
 
-The current time zone is determined by the @samp{TZ} environment
+The current time zone is determined by the @env{TZ} environment
 variable.  @xref{System Environment}.  For example, you can tell Emacs
-to use universal time with @code{(setenv "TZ" "UTC0")}.  If @samp{TZ}
+to use universal time with @code{(setenv "TZ" "UTC0")}.  If @env{TZ}
 is not in the environment, Emacs uses a platform-dependent default
 time zone.
 
@@ -1325,7 +1325,7 @@ yourself before you call @code{encode-time}.
 The optional argument @var{zone} defaults to the current time zone and
 its daylight saving time rules.  If specified, it can be either a list
 (as you would get from @code{current-time-zone}), a string as in the
-@code{TZ} environment variable, @code{t} for Universal Time, or an
+@env{TZ} environment variable, @code{t} for Universal Time, or an
 integer (as you would get from @code{decode-time}).  The specified
 zone is used without any further alteration for daylight saving time.
 

doc/lispref/processes.texi

@@ -77,14 +77,14 @@ sections.  Since the three functions are all called in a similar
 fashion, their common arguments are described here.
 
 @cindex execute program
-@cindex @code{PATH} environment variable
-@cindex @code{HOME} environment variable
+@cindex @env{PATH} environment variable
+@cindex @env{HOME} environment variable
   In all cases, the function's @var{program} argument specifies the
 program to be run.  An error is signaled if the file is not found or
 cannot be executed.  If the file name is relative, the variable
 @code{exec-path} contains a list of directories to search.  Emacs
 initializes @code{exec-path} when it starts up, based on the value of
-the environment variable @code{PATH}.  The standard file name
+the environment variable @env{PATH}.  The standard file name
 constructs, @samp{~}, @samp{.}, and @samp{..}, are interpreted as
 usual in @code{exec-path}, but environment variable substitutions
 (@samp{$HOME}, etc.) are not recognized; use