                                SHELL

    SHELL=[d1:][pathname1]filename1[.ext1] [d2:][pathname2] /P [/E:nn]
							[/MSG]	[new DOS 4.0]

[d1:][pathname1]filename1[.ext1] is the name and pathname of the program to 
    be loaded at system startup time to respond to (process) command lines 
    entered from the keyboard, sometimes called the command processor. The
    program is usually COMMAND.COM. On a system with a hard disk, C:\ is
    typically the pathname used, and A:\ is typically the pathname on a 
    system with diskettes only. 

[d2:][pathname2] is the pathname to be used after system startup if the program
    needs to be reloaded from disk into memory. An environment variable COMSPEC
    is created in the DOS environment space to save this path. If the program
    is to be reloaded from a virtual disk, don't use this. Instead, COPY it
    to the virtual disk in AUTOEXEC.BAT, and follow the COPY with a SET COMPSEC
    command.

/P keeps the program from trying to unload itself when EXIT is entered from
   the keyboard, or when AUTOEXEC.BAT terminates (if it is executed, which
   may not happen without the /P option). Not required, but should be.

/E specifies the size of the DOS environment space where SET variables are
    stored. For DOS 3.1, nn is the number of 16-character paragraphs to be
    allocated (maximum of 62, default is 10). For later levels of DOS, it is
    the number of characters to allocate (minimum of 160, maximum of 32767, 
    default is 620).

/MSG causes error messages to be read into memory at boot time for later
    display on the screen, rather than being read in from disk as needed.

The SHELL line permits you to write and install your own program to process  
command lines. The options described above assume that the program used is
some version of COMMAND.COM. A more frequent use of the SHELL line is to expand
the DOS environment space with the /E option so that a long PATH can coexist 
with several environment variables. 
