* admin/notes/bug-triage: Fix bug priorities. Explain colors in debbugs-gnu.

[emacs.git] / doc / emacs / msdos-xtra.texi

@c This is part of the Emacs manual.
@c Copyright (C) 2004-2016 Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@c
@c This file is included either in emacs-xtra.texi (when producing the
@c printed version) or in the main Emacs manual (for the on-line version).
@node MS-DOS
@section Emacs and MS-DOS
@cindex MS-DOS peculiarities

  This section briefly describes the peculiarities of using Emacs on
MS-DOS.
@iftex
Information about Emacs and Microsoft's current operating system
Windows is in the main Emacs manual
(@pxref{Microsoft Windows,,, emacs, the Emacs Manual}).
@end iftex
@ifnottex
Information about peculiarities common to MS-DOS and Microsoft's
current operating systems Windows is in
@ref{Microsoft Windows}.
@end ifnottex

  If you build Emacs for MS-DOS, the binary will also run on Windows
3.X, Windows NT, Windows 9X/ME, Windows 2000/XP, or OS/2 as a DOS
application; all of this chapter applies for all of those systems, if
you use an Emacs that was built for MS-DOS.

@iftex
  @xref{Text and Binary,,,emacs, the Emacs Manual}, for information
@end iftex
@ifnottex
  @xref{Text and Binary}, for information
@end ifnottex
about Emacs's special handling of text files under MS-DOS (and Windows).

@menu
* Keyboard: MS-DOS Keyboard.   Keyboard conventions on MS-DOS.
* Mouse: MS-DOS Mouse.         Mouse conventions on MS-DOS.
* Display: MS-DOS Display.     Fonts, frames and display size on MS-DOS.
* Files: MS-DOS File Names.    File name conventions on MS-DOS.
* Printing: MS-DOS Printing.   Printing specifics on MS-DOS.
* I18N: MS-DOS and MULE.       Support for internationalization on MS-DOS.
* Processes: MS-DOS Processes. Running subprocesses on MS-DOS.
@end menu

@node MS-DOS Keyboard
@subsection Keyboard Usage on MS-DOS

@kindex DEL @r{(MS-DOS)}
@kindex BS @r{(MS-DOS)}
  The key that 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{Delete} key is remapped to act
as @kbd{C-d} for the same reasons.

@kindex C-g @r{(MS-DOS)}
@kindex C-Break @r{(MS-DOS)}
@cindex quitting on MS-DOS
  Emacs built for MS-DOS recognizes @kbd{C-@key{Break}} as a quit
character, just like @kbd{C-g}.  This is because Emacs cannot detect
that you have typed @kbd{C-g} until it is ready for more input.  As a
consequence, you cannot use @kbd{C-g} to stop a running command
@iftex
(@pxref{Quitting,,,emacs, the Emacs Manual}).
@end iftex
@ifnottex
(@pxref{Quitting}).
@end ifnottex
By contrast, @kbd{C-@key{Break}} @emph{is} detected as soon as you
type it (as @kbd{C-g} is on other systems), so it can be used to stop
a running command and for emergency escape
@iftex
(@pxref{Emergency Escape,,,emacs, the Emacs Manual}).
@end iftex
@ifnottex
(@pxref{Emergency Escape}).
@end ifnottex

@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:
choose either the right @key{Ctrl} 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.  If neither @code{dos-super-key} nor
@code{dos-hyper-key} is 1, then by default the right @key{Alt} key is
also mapped to the @key{META} key.  However, if the MS-DOS international
keyboard support program @file{KEYB.COM} is installed, Emacs will
@emph{not} map the right @key{Alt} to @key{META}, since it is used for
accessing characters like @kbd{~} and @kbd{@@} on non-US keyboard
layouts; in this case, you may only use the left @key{Alt} as @key{META}
key.

@kindex C-j @r{(MS-DOS)}
@vindex dos-keypad-mode
  The variable @code{dos-keypad-mode} is a flag variable that controls
what key codes are returned by keys in the numeric keypad.  You can also
define the keypad @key{ENTER} key to act like @kbd{C-j}, by putting the
following line into your @file{_emacs} file:

@smallexample
;; @r{Make the @key{ENTER} key from the numeric keypad act as @kbd{C-j}.}
(define-key function-key-map [kp-enter] [?\C-j])
@end smallexample

@node MS-DOS Mouse
@subsection Mouse Usage on MS-DOS

@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
@iftex
(@pxref{Menu Bar,,,emacs, the Emacs Manual}).
@end iftex
@ifnottex
(@pxref{Menu Bar}).
@end ifnottex
 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}.  If
the mouse does have 3 buttons, Emacs detects that at startup, and all
the 3 buttons function normally, as on X.

  Help strings for menu-bar and pop-up menus are displayed in the echo
area when the mouse pointer moves across the menu items.  Highlighting
of mouse-sensitive text
@iftex
(@pxref{Mouse References,,,emacs, the Emacs Manual})
@end iftex
@ifnottex
(@pxref{Mouse References})
@end ifnottex
is also supported.

@cindex mouse, set number of buttons
@findex msdos-set-mouse-buttons
  Some versions of mouse drivers don't report the number of mouse
buttons correctly.  For example, mice with a wheel report that they
have 3 buttons, but only 2 of them are passed to Emacs; the clicks on
the wheel, which serves as the middle button, are not passed.  In
these cases, you can use the @kbd{M-x msdos-set-mouse-buttons} command
to tell Emacs how many mouse buttons to expect.  You could make such a
setting permanent by adding this fragment to your @file{_emacs} init
file:

@example
;; @r{Treat the mouse like a 2-button mouse.}
(msdos-set-mouse-buttons 2)
@end example

@cindex Windows clipboard support
  Emacs built for MS-DOS supports clipboard operations when it runs on
Windows.  Commands that put text on the kill ring, or yank text from
the ring, check the Windows clipboard first, just as Emacs does on the
X Window System
@iftex
(@pxref{Mouse Commands,,,emacs, the Emacs Manual}).
@end iftex
@ifnottex
(@pxref{Mouse Commands}).
@end ifnottex
Only the primary selection and the cut buffer are supported by MS-DOS
Emacs on Windows; the secondary selection always appears as empty.

  Due to the way clipboard access is implemented by 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 is lower if you run Emacs as a subprocess of
another program.  If the killed text does not fit, Emacs outputs a
message saying so, and does not put the text into the clipboard.

  Null characters also cannot be put into the Windows clipboard.  If the
killed text includes null characters, Emacs does not put such text into
the clipboard, and displays in the echo area a message to that effect.

@vindex dos-display-scancodes
  The variable @code{dos-display-scancodes}, when non-@code{nil},
directs Emacs to display the @acronym{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 MS-DOS Display
@subsection Display on MS-DOS
@cindex faces under MS-DOS
@cindex fonts, emulating under MS-DOS

  Display on MS-DOS cannot use font variants, like bold or italic, 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 that 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} command
@iftex
(@pxref{Colors,,,emacs, the Emacs Manual})
@end iftex
@ifnottex
(@pxref{Colors})
@end ifnottex
and the @code{list-faces-display} command
@iftex
(@pxref{Faces,,,emacs, the Emacs Manual})
@end iftex
@ifnottex
(@pxref{Faces})
@end ifnottex
to see what colors and faces are available and what they look like.

  @xref{MS-DOS and MULE}, later in this chapter, for information on
how Emacs displays glyphs and characters that aren't supported by the
native font built into the DOS display.

@cindex cursor shape on MS-DOS
  When Emacs starts, it changes the cursor shape to a solid box.  This
is for compatibility with other systems, where the box cursor is the
default in Emacs.  This default shape can be changed to a bar by
specifying the @code{cursor-type} parameter in the variable
@code{default-frame-alist}
@iftex
(@pxref{Creating Frames,,,emacs, the Emacs Manual}).
@end iftex
@ifnottex
(@pxref{Creating Frames}).
@end ifnottex
The MS-DOS terminal doesn't support a vertical-bar cursor,
so the bar cursor is horizontal, and the @code{@var{width}} parameter,
if specified by the frame parameters, actually determines its height.
For this reason, the @code{bar} and @code{hbar} cursor types produce
the same effect on MS-DOS@.  As an extension, the bar cursor
specification can include the starting scan line of the cursor as well
as its width, like this:

@example
 '(cursor-type bar @var{width} . @var{start})
@end example

@noindent
In addition, if the @var{width} parameter is negative, the cursor bar
begins at the top of the character cell.

@cindex frames on MS-DOS
  The MS-DOS terminal can only display a single frame at a time.  The
Emacs frame facilities work on MS-DOS much as they do on text
terminals
@iftex
(@pxref{Frames,,,emacs, the Emacs Manual}).
@end iftex
@ifnottex
(@pxref{Frames}).
@end ifnottex
When you run Emacs from a DOS window on MS-Windows, 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 dos-mode4350
@findex dos-mode25
  The @code{dos-mode4350} command switches the display to 43 or 50
lines, depending on your hardware; the @code{dos-mode25} command switches
to the default 80x25 screen size.

  By default, Emacs only knows how to set screen sizes of 80 columns by
25, 28, 35, 40, 43 or 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} columns 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 40x80 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 38x80 dimensions and you define a variable
@code{screen-dimensions-38x80} with a suitable value, you will still get
40x80 screen when you ask for a 36x80 frame.  If you want to get the
38x80 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-38x80}.

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

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

  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
@iftex
(@pxref{Init File,,,emacs, the Emacs Manual})
@end iftex
@ifnottex
(@pxref{Init File})
@end ifnottex
is called @file{_emacs} on MS-DOS@.  Excess characters before or after
the period are generally ignored by MS-DOS itself; thus, if you visit
the 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
@iftex
(@pxref{Backup Names,,,emacs, the Emacs Manual})
@end iftex
@ifnottex
(@pxref{Backup Names})
@end ifnottex
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 in DOS box under Windows 95/NT
  If you run Emacs as a DOS application under Windows 9X, Windows ME, or
Windows 2000/XP, 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 @env{LFN} to
@samp{y} before starting Emacs.  Unfortunately, Windows NT doesn't allow
DOS programs to access long file names, so Emacs built for MS-DOS will
only see their short 8+3 aliases.

@cindex 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 the @env{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 @env{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 on GNU or Unix.  You can also set
@env{HOME} variable in the environment before starting Emacs; its
value will then override the above default behavior.

  Emacs on MS-DOS handles the directory name @file{/dev} specially,
because of a feature in the emulator libraries of DJGPP that pretends
I/O devices have names in that directory.  We recommend that you avoid
using an actual directory named @file{/dev} on any disk.

@node MS-DOS Printing
@subsection Printing and MS-DOS

  Printing commands, such as @code{lpr-buffer}
@iftex
(@pxref{Printing,,,emacs, the Emacs Manual}) and @code{ps-print-buffer}
(@pxref{PostScript,,,emacs, the Emacs Manual})
@end iftex
@ifnottex
(@pxref{Printing}) and @code{ps-print-buffer} (@pxref{PostScript})
@end ifnottex
can work on MS-DOS by sending the output to one of the printer ports,
if a Posix-style @code{lpr} program is unavailable.  The same Emacs
variables control printing on all systems, but in some cases they have
different default values on MS-DOS.

@iftex
@xref{Windows Printing,,,emacs, the Emacs Manual},
@end iftex
@ifnottex
@xref{Windows Printing},
@end ifnottex
for details about setting up printing to a networked printer.

  Some printers expect DOS codepage encoding of non-@acronym{ASCII} text, even
though they are connected to a Windows machine that uses a different
encoding for the same locale.  For example, in the Latin-1 locale, DOS
uses codepage 850 whereas Windows uses codepage 1252.  @xref{MS-DOS and
MULE}.  When you print to such printers from Windows, you can use the
@kbd{C-x @key{RET} c} (@code{universal-coding-system-argument}) command
before @kbd{M-x lpr-buffer}; Emacs will then convert the text to the DOS
codepage that you specify.  For example,
@kbd{C-x @key{RET} c cp850-dos @key{RET} M-x lpr-region @key{RET}}
will print the region while converting it to the codepage 850 encoding.

@vindex dos-printer
@vindex dos-ps-printer
  For backwards compatibility, the value of @code{dos-printer}
(@code{dos-ps-printer}), if it has a value, overrides the value of
@code{printer-name} (@code{ps-printer-name}), on MS-DOS.


@node MS-DOS and MULE
@subsection International Support on MS-DOS
@cindex international support @r{(MS-DOS)}

  Emacs on MS-DOS supports the same international character sets as it
does on GNU, Unix and other platforms
@iftex
(@pxref{International,,,emacs, the Emacs Manual}),
@end iftex
@ifnottex
(@pxref{International}),
@end ifnottex
including coding systems for converting between the different
character sets.  However, due to incompatibilities between
MS-DOS/MS-Windows and other systems, there are several DOS-specific
aspects of this support that you should be aware of.  This section
describes these aspects.

  The description below is largely specific to the MS-DOS port of
Emacs, especially where it talks about practical implications for
Emacs users.

@table @kbd
@item M-x dos-codepage-setup
Set up Emacs display and coding systems as appropriate for the current
DOS codepage.
@end table

@cindex codepage, MS-DOS
@cindex DOS codepages
  MS-DOS is designed to support one character set of 256 characters at
any given time, but gives you a variety of character sets to choose
from.  The alternative character sets are known as @dfn{DOS codepages}.
Each codepage includes all 128 @acronym{ASCII} characters, but the other 128
characters (codes 128 through 255) vary from one codepage to another.
Each DOS codepage is identified by a 3-digit number, such as 850, 862,
etc.

  In contrast to X, which lets you use several fonts at the same time,
MS-DOS normally doesn't allow use of several codepages in a single
session.  MS-DOS was designed to load a single codepage at system
startup, and require you to reboot in order to change
it@footnote{Normally, one particular codepage is burnt into the
display memory, while other codepages can be installed by modifying
system configuration files, such as @file{CONFIG.SYS}, and rebooting.
While there is third-party software that allows changing the codepage
without rebooting, we describe here how a stock MS-DOS system
behaves.}.  Much the same limitation applies when you run DOS
executables on other systems such as MS-Windows.

@vindex dos-codepage
  For multibyte operation on MS-DOS, Emacs needs to know which
characters the chosen DOS codepage can display.  So it queries the
system shortly after startup to get the chosen codepage number, and
stores the number in the variable @code{dos-codepage}.  Some systems
return the default value 437 for the current codepage, even though the
actual codepage is different.  (This typically happens when you use the
codepage built into the display hardware.)  You can specify a different
codepage for Emacs to use by setting the variable @code{dos-codepage} in
your init file.

@cindex language environment, automatic selection on @r{MS-DOS}
  Multibyte Emacs supports only certain DOS codepages: those which can
display Far-Eastern scripts, like the Japanese codepage 932, and those
that encode a single ISO 8859 character set.

  The Far-Eastern codepages can directly display one of the MULE
character sets for these countries, so Emacs simply sets up to use the
appropriate terminal coding system that is supported by the codepage.
The special features described in the rest of this section mostly
pertain to codepages that encode ISO 8859 character sets.

  For the codepages that correspond to one of the ISO character sets,
Emacs knows the character set based on the codepage number.  Emacs
automatically creates a coding system to support reading and writing
files that use the current codepage, and uses this coding system by
default.  The name of this coding system is @code{cp@var{nnn}}, where
@var{nnn} is the codepage number.@footnote{The standard Emacs coding
systems for ISO 8859 are not quite right for the purpose, because
typically the DOS codepage does not match the standard ISO character
codes.  For example, the letter @samp{@,{c}} (@samp{c} with cedilla) has
code 231 in the standard Latin-1 character set, but the corresponding
DOS codepage 850 uses code 135 for this glyph.}

@cindex mode line @r{(MS-DOS)}
  All the @code{cp@var{nnn}} coding systems use the letter @samp{D}
(for ``DOS'') as their mode-line mnemonic.  Since both the terminal
coding system and the default coding system for file I/O are set to
the proper @code{cp@var{nnn}} coding system at startup, it is normal
for the mode line on MS-DOS to begin with @samp{-DD\-}.
@iftex
@xref{Mode Line,,,emacs, the Emacs Manual}.
@end iftex
@ifnottex
@xref{Mode Line}.
@end ifnottex
Far-Eastern DOS terminals do not use the @code{cp@var{nnn}} coding
systems, and thus their initial mode line looks like the Emacs
default.

  Since the codepage number also indicates which script you are using,
Emacs automatically runs @code{set-language-environment} to select the
language environment for that script
@iftex
(@pxref{Language Environments,,,emacs, the Emacs Manual}).
@end iftex
@ifnottex
(@pxref{Language Environments}).
@end ifnottex

  If a buffer contains a character belonging to some other ISO 8859
character set, not the one that the chosen DOS codepage supports, Emacs
displays it using a sequence of @acronym{ASCII} characters.  For example, if the
current codepage doesn't have a glyph for the letter @samp{@`o} (small
@samp{o} with a grave accent), it is displayed as @samp{@{`o@}}, where
the braces serve as a visual indication that this is a single character.
(This may look awkward for some non-Latin characters, such as those from
Greek or Hebrew alphabets, but it is still readable by a person who
knows the language.)  Even though the character may occupy several
columns on the screen, it is really still just a single character, and
all Emacs commands treat it as one.

@cindex MS-Windows codepages
  MS-Windows provides its own codepages, which are different from the
DOS codepages for the same locale.  For example, DOS codepage 850
supports the same character set as Windows codepage 1252; DOS codepage
855 supports the same character set as Windows codepage 1251, etc.
The MS-Windows version of Emacs uses the current codepage for display
when invoked with the @samp{-nw} option.

@node MS-DOS Processes
@subsection 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
Shell mode and GUD@.  When in doubt, try and see; commands that
don't work output an error message saying that asynchronous processes
aren't supported.

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

  Spell checking also works, by means of special support for synchronous
invocation of the @code{ispell} program.  This is slower than the
asynchronous invocation on other platforms

  Instead of the Shell mode, which doesn't work on MS-DOS, you can use
the @kbd{M-x eshell} command.  This invokes the Eshell package that
implements a Posix-like shell entirely in Emacs Lisp.

  By contrast, Emacs compiled as a native Windows application
@strong{does} support asynchronous subprocesses.
@iftex
@xref{Windows Processes,,,emacs, the Emacs Manual}.
@end iftex
@ifnottex
@xref{Windows Processes}.
@end ifnottex

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

  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.
Pressing @kbd{C-c} or @kbd{C-@key{Break}} might sometimes help in these
cases.

  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
@iftex
(@pxref{ls in Lisp,,,emacs, the Emacs Manual}).
@end iftex
@ifnottex
(@pxref{ls in Lisp}).
@end ifnottex
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}.