These variables are used only on particular configurations:
On MS-DOS and MS-Windows, the name of the command interpreter to use
when invoking batch files and commands internal to the shell. On MS-DOS
this is also used to make a default value for the
On MS-DOS, this variable defaults to the value of the
On MS-DOS, this specifies a file to use to log the operation of the internal terminal emulator. This feature is useful for submitting bug reports.
On MS-DOS, this specifies the screen colors. It is useful to set them this way, since otherwise Emacs would display the default colors momentarily when it starts up.
The value of this variable should be the two-character encoding of the foreground (the first character) and the background (the second character) colors of the default face. Each character should be the hexadecimal code for the desired color on a standard PC text-mode display. For example, to get blue text on a light gray background, specify ‘EMACSCOLORS=17’, since 1 is the code of the blue color and 7 is the code of the light gray color.
The PC display usually supports only eight background colors. However, Emacs switches the DOS display to a mode where all 16 colors can be used for the background, so all four bits of the background color are actually used.
On MS-Windows, if you set this variable, Emacs will load and initialize the network library at startup, instead of waiting until the first time it is required.
emacs_dir is a special environment variable, which
indicates the full path of the directory in which Emacs is installed.
If Emacs is installed in the standard directory structure, it
calculates this value automatically. It is not much use setting this
variable yourself unless your installation is non-standard, since
unlike other environment variables, it will be overridden by Emacs at
startup. When setting other environment variables, such as
EMACSLOADPATH, you may find it useful to use
rather than hard-coding an absolute path. This allows multiple
versions of Emacs to share the same environment variable settings, and
it allows you to move the Emacs installation directory, without
changing any environment or registry settings.