@c This is part of the Emacs manual.
@c Copyright (C) 1985, 86, 87, 93, 94, 95, 1996 Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node MS-DOS, Manifesto, Antinews, Top
@appendix MS-DOS Issues
@cindex MS-DOG
@cindex MS-DOS peculiarities

  This section briefly describes the peculiarities of using Emacs under
the MS-DOS ``operating system'' (also known as ``MS-DOG'').  If you
build Emacs for MS-DOS, the binary will also run on Windows 3, Windows
NT, Windows 95, or OS-2 as a DOS application; the information in this
chapter applies for all of those systems, if you use an Emacs that was
built for MS-DOS.

  Note that it is possible to build Emacs specifically for Windows NT or
Windows 95.  If you do that, most of this chapter does not apply;
instead, you get behavior much closer to what is documented in the rest
of the manual, including support for long file names, multiple frames,
scroll bars, mouse menus, and subprocesses.  However, the section on
text files and binary files does still apply.  There are also two
sections at the end of this chapter which apply specifically for Windows
NT and 95.

@menu
* Keyboard and Mouse on MS-DOS::
* Display on MS-DOS::
* File Names on MS-DOS::
* Text and Binary::
* Printing and MS-DOS::
* Subprocesses on MS-DOS::
* Windows Subprocesses::
* System Menu on Windows::
@end menu

@node Keyboard and Mouse on MS-DOS
@section Keyboard and Mouse on MS-DOS

@cindex Meta (under MS-DOS)
@cindex Hyper (under MS-DOS)
@cindex Super (under MS-DOS)
@vindex dos-super-key
@vindex dos-hyper-key
  The PC keyboard maps use the left @key{Alt} key as the @key{META}
key.  You have two choices for emulating the @key{SUPER} and
@key{HYPER} keys: either the right @key{CONTROL} key or the right
@key{ALT} key by setting the variables @code{dos-hyper-key} and
@code{dos-super-key} to 1 or 2 respectively.

@kindex LFD (MS-DOS)
@vindex dos-keypad-mode
  The variable @code{dos-keypad-mode} is a flag variable which controls
what key codes are returned by keys in the numeric keypad.  There is
no dedicated @key{LFD} key; use @kbd{C-j} instead.  You can also
define the @key{kp-enter} key to act as @key{LFD}, by putting the
following line into your @file{_emacs} file:

@smallexample
;; Make the Enter key from the Numeric keypad act as LFD.
(define-key function-key-map [kp-enter] [?\C-j])
@end smallexample

@kindex DEL (MS-DOS)
@kindex BS (MS-DOS)
  The key which is called @key{DEL} in Emacs (because that's how it is
designated on most workstations) is known as @key{BS} (backspace) on a
PC.  That is why the PC-specific terminal initialization remaps the
@key{BS} key to act as @key{DEL}; the @key{DEL} key is remapped to act
as @kbd{C-d} for the same reasons.

@cindex mouse support under MS-DOS
  Emacs on MS-DOS supports a mouse (on the default terminal only).
The mouse commands work as documented, including those that use menus
and the menu bar (@pxref{Menu Bars}).  Scroll bars don't work in
MS-DOS Emacs.  PC mice usually have only two buttons; these act as
@kbd{Mouse-1} and @kbd{Mouse-2}, but if you press both of them
together, that has the effect of @kbd{Mouse-3}.

@cindex Windows clipboard support
  Emacs built for MS-DOS supports clipboard operations when it runs on
MS-Windows.  Commands which put text on the kill ring and yank text from
the ring, check the Windows clipboard first, just like Emacs does on X
(@pxref{Mouse Commands}).  Only the primary selection and the cut buffer
are supported by MS-DOS Emacs on MS-Windows, secondary selection always
appears as empty.  Due to the way clipboard access is implemented by
MS-Windows, the length of text you can put into the clipboard is limited
by the amount of free DOS memory that is available to Emacs.  Usually,
up to 620KB of text can be put into the clipboard, but this limit
depends on the system configuration and will be lower if you run Emacs
as a subprocess of another program.  If the killed text is too long to
fit into the available DOS memory, Emacs will print a message in the
echo area to that effect and won't put the text into the clipboard.

@vindex dos-display-scancodes
  The variable @code{dos-display-scancodes}, when non-@code{nil},
directs Emacs to display the ASCII value and the keyboard scan code of
each keystroke; this feature serves as a complement to the
@code{view-lossage} command, for debugging.

@node Display on MS-DOS
@section Display on MS-DOS
@cindex faces under MS-DOS
@cindex fonts, emulating under MS-DOS

  Display on MS-DOS cannot use multiple fonts, but it does support
multiple faces, each of which can specify a foreground and a background
color.  Therefore, you can get the full functionality of Emacs
packages which use fonts (such as @code{font-lock}, Enriched Text
mode, and others) by defining the relevant faces to use different
colors.  Use the @code{list-colors-display} and
@code{list-faces-display} commands (@pxref{Modifying Faces}) to see
what colors and faces are available and what they look like.

@cindex frames on MS-DOS
  Multiple frames (@pxref{Frames}) are supported on MS-DOS, but they all
overlap, so you only see a single frame at any given moment.  That
single visible frame occupies the entire screen.  When you run Emacs
under Windows version 3, you can make the visible frame smaller than
the full screen, but Emacs still cannot display more than a single
frame at a time.

@cindex frame size under MS-DOS
@findex mode4350
@findex mode25
  The @code{mode4350} command switches the display to 43 or 50
lines, depending on your hardware; the @code{mode25} command switches
to the default 80x25 screen size.

  By default, Emacs only knows how to set screen sizes of 80 columns by
25 or 43/50 rows.  However, if your video adapter has special video
modes that will switch the display to other sizes, you can have Emacs
support those too.  When you ask Emacs to switch the frame to @var{n}
rows by @var{m} cols dimensions, it checks if there is a variable called
@code{screen-dimensions-@var{n}x@var{m}}, and if so, uses its value
(which must be an integer) as the video mode to switch to.  (Emacs
switches to that video mode by calling the BIOS @code{Set Video Mode}
function with the value of @code{screen-dimensions-@var{n}x@var{m}} in
the @code{AL} register.)  For example, suppose your adapter will switch
to 66x80 dimensions when put into video mode 85.  Then you can make
Emacs support this screen size by putting the following into your
@file{_emacs} file:

@example
(setq screen-dimensions-66x80 85)
@end example

  Since Emacs on MS-DOS can only set the frame size to specific
supported dimensions, it cannot honor every possible frame resizing
request.  When an unsupported size is requested, Emacs chooses the next
larger supported size beyond the specified size.  For example, if you
ask for 36x80 frame, you will get 50x80 instead.

  The variables @code{screen-dimensions-@var{n}x@var{m}} are used only
when they exactly match the specified size; the search for the next
larger supported size ignores them.  In the above example, even if your
VGA supports 44x80 dimensions and you define a variable
@code{screen-dimensions-44x80} with a suitable value, you will still get
50x80 screen when you ask for a 36x80 frame.  If you want to get the
44x80 size in this case, you can do it by setting the variable named
@code{screen-dimensions-36x80} with the same video mode value as
@code{screen-dimensions-44x80}.

  Changing frame dimensions on MS-DOS has the effect of changing all the
other frames to the new dimensions.

@node File Names on MS-DOS
@section File Names on MS-DOS
@cindex file names under MS-DOS
@cindex init file, default name under MS-DOS

  MS-DOS normally uses a backslash, @samp{\}, to separate name units
within a file name, instead of the slash used on other systems.  Emacs
on MS-DOS permits use of either slash or backslash, and also knows
about drive letters in file names.

  On MS-DOS, file names are case-insensitive and limited to eight
characters, plus optionally a period and three more characters.  Emacs
knows enough about these limitations to handle file names that were
meant for other operating systems.  For instance, leading dots
@samp{.} in file names are invalid in MS-DOS, so Emacs transparently
converts them to underscores @samp{_}; thus your default init file
(@pxref{Init File}) is called @file{_emacs} on MS-DOS.  Excess
characters before or after the period are generally ignored by MS-DOS
itself, so if you, e.g., visit a file
@file{LongFileName.EvenLongerExtension}, you will silently get
@file{longfile.eve}; but Emacs will still display the long file name
on the mode line.  Other than that, it's up to you to specify file
names which are valid under MS-DOS; the transparent conversion as
described above only works on file names built into Emacs.

@cindex backup file names on MS-DOS
  The above restrictions on the file names on MS-DOS make it almost
impossible to construct the name of a backup file (@pxref{Backup
Names}) without losing some of the original file name characters.  For
example, the name of a backup file for @file{docs.txt} is
@file{docs.tx~} even if single backup is used.

@cindex file names under Windows 95/NT
@cindex long file names on MS-DOS under Windows 95/NT
  If you run Emacs as a DOS application under Windows 95 or NT, you can
turn on support for long file names.  If you do that, Emacs doesn't
truncate file names or convert them to lower case; instead, it uses the
file names that you specify, verbatim.  To enable long file name
support, set the environment variable @code{LFN} to @samp{y} before
starting Emacs.

@cindex @code{HOME} directory under MS-DOS
  MS-DOS has no notion of home directory, so Emacs on MS-DOS pretends
that the directory where it is installed is the value of @code{HOME}
environment variable.  That is, if your Emacs binary,
@file{emacs.exe}, is in the directory @file{c:/utils/emacs/bin}, then
Emacs acts as if @code{HOME} were set to @samp{c:/utils/emacs}.  In
particular, that is where Emacs looks for the init file @file{_emacs}.
With this in mind, you can use @samp{~} in file names as an alias for
the home directory, as you would in Unix.  You can also set @code{HOME}
variable in the environment before starting Emacs; its value will then
override the above default behavior.

@node Text and Binary
@section Text Files and Binary Files
@cindex text and binary files on MS-DOS

@vindex file-name-buffer-file-type-alist
  Emacs on MS-DOS distinguishes between text and binary files.  This
distinction is not part of MS-DOS; it is made by Emacs only.  Emacs
treats files of human-readable text (including program source code) as
text files, and treats executable programs, compressed archives, etc.,
as binary files.  Emacs uses the file name to decide whether to treat
a file as text or binary: the variable
@code{file-name-buffer-file-type-alist} defines the file name patterns
which denote binary files.

  Emacs reads and writes binary files verbatim.  Text files use a two
character sequence to end a line: carriage-return (control-m) followed
by newline (control-j).  When you visit a text file, Emacs strips off
these control-m characters; when you write a text file to disk, Emacs
puts them back in.  Thus, the text appears within Emacs with just a
newline character at the end of each line.

  You can tell whether Emacs considers the visited file as text or
binary based on the mode line (@pxref{Mode Line}).  Text files have a
@samp{T:} marker prefixed to the major mode name; binary files have a
@samp{B:} prefix.

@cindex cursor location, under MS-DOS
@cindex point location, under MS-DOS
@findex what-cursor-position (@r{MS-DOS})
  One consequence of this special format-conversion of text files is
that character positions as reported by Emacs (@pxref{Position Info})
do not agree with the file size information known to the operating
system.

@node Printing and MS-DOS
@section Printing and MS-DOS

  Printing commands, such as @code{lpr-buffer} (@pxref{Hardcopy}) and
@code{ps-print-buffer} (@pxref{Postscript}) can work in MS-DOS by
sending the output to one of the printer ports, if a Unix-style @code{lpr}
program is unavailable.  A few DOS-specific variables control how this
works.

@vindex dos-printer
  If you want to use your local printer, printing on it in the usual DOS
manner, then set the Lisp variable @code{dos-printer} to the name of the
printer port---for example. @code{"PRN"}, the usual local printer port
(that's the default), or @code{"LPT2"} or @code{"COM1"} for a serial
printer.  You can also set @code{dos-printer} to a file name, in which
case ``printed'' output is actually appended to that file.  If you set
@code{dos-printer} to @code{"NUL"}, printed output is silently
discarded.

  If you set @code{dos-printer} to a file name, it's best to use an
absolute file name.  Emacs changes the working directory according to
the default directory of the current buffer, so if the file name in
@code{dos-printer} is relative, you will end up with several such files,
each one in the directory of the buffer from which the printing was
done.

@findex print-buffer, under MS-DOS
@findex print-region, under MS-DOS
@vindex lpr-headers-switches, under MS-DOS
  The commands @code{print-buffer} and @code{print-region} call the
@code{pr} program, or use special switches to the @code{lpr} program, to
produce headers on each printed page.  MS-DOS doesn't normally have
these programs, so by default, the variable @code{lpr-headers-switches}
is set so that the requests to print page headers are silently ignored.
Thus, @code{print-buffer} and @code{print-region} produce the same
output as @code{lpr-buffer} and @code{lpr-region}, respectively.  If you
do have a suitable @code{pr} program (e.g., from GNU Textutils), set
@code{lpr-headers-switches} to @code{nil}; Emacs will then call
@code{pr} to produce the page headers, and print the resulting output as
specified by @code{dos-printer}.

@vindex print-region-function under MS-DOS
@cindex lpr usage under MS-DOS
@vindex lpr-command, under MS-DOS
@vindex lpr-switches, under MS-DOS
  Finally, if you do have an @code{lpr} work-alike, you can set
@code{print-region-function} to @code{nil}.  Then Emacs uses @code{lpr}
for printing, as on other systems.  (If the name of the program isn't
@code{lpr}, set the @code{lpr-command} variable to specify where to find
it.)

@findex ps-print-buffer, under MS-DOS
@findex ps-print-buffer-with-faces, under MS-DOS
@findex ps-print-region, under MS-DOS
@findex ps-print-region-with-faces, under MS-DOS
@findex ps-spool-buffer, under MS-DOS
@findex ps-spool-buffer-with-faces, under MS-DOS
@findex ps-spool-region, under MS-DOS
@findex ps-spool-region-with-faces, under MS-DOS
@vindex dos-ps-printer
@vindex ps-lpr-command, under MS-DOS
@vindex ps-lpr-switches, under MS-DOS
  A separate variable, @code{dos-ps-printer}, defines how PostScript
files should be printed.  If its value is a string, it is used as the
name of the device (or file) to which PostScript output is sent, just as
@code{dos-printer} is used for non-PostScript printing.  (These are two
distinct variables in case you have two printers attached to two
different ports, and only one of them is a PostScript printer.)  If the
value of @code{dos-ps-printer} is not a string, then the variables
@code{ps-lpr-command} and @code{ps-lpr-switches} (@pxref{Postscript})
control how to print PostScript files.  Thus, if you have a
non-PostScript printer, you can set these variables to the name and the
switches appropriate for a PostScript interpreter program (e.g.,
Ghostscript).

  For example, to use Ghostscript for printing on an Epson printer
connected to @samp{LPT2} port, put this on your @file{.emacs} file:

@example
(setq dos-ps-printer t)  ; @r{Anything but a string.}
(setq ps-lpr-command "c:/gs/gs386")
(setq ps-lpr-switches '("-q" "-dNOPAUSE"
			"-sDEVICE=epson"
			"-r240x72"
			"-sOutputFile=LPT2"
			"-Ic:/gs"
			"-"))
@end example

@noindent
(This assumes that Ghostscript is installed in the @file{"c:/gs"}
directory.)

@node Subprocesses on MS-DOS
@section Subprocesses on MS-DOS

@cindex compilation under MS-DOS
@cindex inferior processes under MS-DOS
@findex compile (@r{MS-DOS})
@findex grep (@r{MS-DOS})
  Because MS-DOS is a single-process ``operating system'',
asynchronous subprocesses are not available.  In particular, Shell
mode and its variants do not work.  Most Emacs features that use
asynchronous subprocesses also don't work on MS-DOS, including
spelling correction and GUD.  When in doubt, try and see; commands that
don't work print an error message saying that asynchronous processes
aren't supported.

  Compilation under Emacs with @kbd{M-x compile} and grep with
@kbd{M-x grep} do work, by running the inferior processes synchronously.
This means you cannot do any more editing until the compilation or the
grep process finishes.

@cindex printing under MS-DOS
  Printing commands, such as @code{lpr-buffer} (@pxref{Hardcopy}) and
@code{ps-print-buffer} (@pxref{Postscript}), work in MS-DOS by sending
the output to one of the printer ports.  @xref{Printing and MS-DOS}.

  When you run a subprocess synchronously on MS-DOS, make sure the
program terminates and does not try to read keyboard input.  If the
program does not terminate on its own, you will be unable to terminate
it, because MS-DOS provides no general way to terminate a process.

  Accessing files on other machines is not supported on MS-DOS.  Other
network-oriented commands such as sending mail, Web browsing, remote
login, etc., don't work either, unless network access is built into
MS-DOS with some network redirector.

@cindex directory listing on MS-DOS
@vindex dired-listing-switches (@r{MS-DOS})
  Dired on MS-DOS uses the @code{ls-lisp} package where other
platforms use the system @code{ls} command.  Therefore, Dired on
MS-DOS supports only some of the possible options you can mention in
the @code{dired-listing-switches} variable.  The options that work are
@samp{-A}, @samp{-a}, @samp{-c}, @samp{-i}, @samp{-r}, @samp{-S},
@samp{-s}, @samp{-t}, and @samp{-u}.

@node Windows Subprocesses
@section Subprocesses on Windows 95 and Windows NT

Subprocesses, both synchronous and asynchronous, work fine on both
Windows 95 and Windows NT as long as you run only 32-bit Windows
applications.  However, when you run a DOS application in a subprocess,
you may encounter problems or be unable to run the application at all;
and if you run two DOS applications at the same time in two
subprocesses, you may have to reboot your system.

Since the standard command interpreter (and most command line utilities)
on Windows 95 are DOS applications, these problems are significant when
using that system.  But there's nothing we can do about them; only
Microsoft can fix them.

If you run just one DOS application subprocess, the subprocess should
work as expected as long as it is ``well-behaved'' and does not perform
direct screen access or other unusual actions.  If you have a CPU
monitor application, your machine will appear to be 100% busy even when
the DOS application is idle, but this is only an artifact of the way CPU
monitors processor load.

You must terminate the DOS application before you start any other DOS
application in a different subprocess.  Emacs is unable to interrupt or
terminate a DOS subprocess.  The only way you can terminate such a
subprocess is by giving it a command that tells its program to exit.

If you attempt to run two DOS applications at the same time in separate
subprocesses, the second one that is started will be suspended until the
first one finishes, even if either or both of them are asynchronous.

If you can go to the first subprocess, and tell it to exit, the second
subprocess should continue normally.  However, if the second subprocess
is synchronous, Emacs itself will be hung until the first subprocess
finishes.  If it will not finish without user input, then you have no
choice but to reboot if you are running on Windows 95.  If you are
running on Windows NT, you can use a process viewer application to kill
the appropriate instance of ntvdm instead (this will terminate both DOS
subprocesses).

If you have to reboot Windows 95 in this situation, do not use the
@code{Shutdown} command on the @code{Start} menu; that usually hangs the
system.  Instead, type @kbd{CTL-ALT-@key{DEL}} and then choose
@code{Shutdown}.  That usually works, although it may take a few minutes
to do its job.

@node System Menu on Windows
@section Using the System Menu on Windows

Emacs normally turns off the Windows feature that tapping the @key{ALT}
key invokes the Windows menu.  The reason is that the @key{ALT} also
serves as @key{META} in Emacs.  When using Emacs, users often press the
@key{META} key temporarily and then change their minds; if this has the
effect of bringing up the Windows menu, it alters the meaning of
subsequent commands.  Many users find this frustrating. 

@vindex win32-pass-alt-to-system
You can reenable Windows's default handling of tapping the @key{ALT} key
by setting @code{win32-pass-alt-to-system} to a non-@code{nil} value.

