INT 2E - DOS 2+ - PASS COMMAND TO COMMAND INTERPRETER FOR EXECUTION
DS:SI -> commandline to execute (see below)
Return: all registers except CS:IP destroyed
AX = status (4DOS v4.0)
0000h successful
FFFFh error before processing command (not enough memory, etc)
other error number returned by command
Notes:  this call allows execution of arbitrary commands (including COMMAND.COM
internal commands) without loading another copy of COMMAND.COM
if COMMAND.COM is the user's command interpreter, the primary copy
executes the command; this allows the master environment to be
modified by issuing a "SET" command, but changes in the master
environment will not become effective until all programs descended
from the primary COMMAND.COM terminate
since COMMAND.COM processes the string as if typed from the keyboard,
the transient portion needs to be present, and the calling program
must ensure that sufficient memory to load the transient portion can
be allocated by DOS if necessary
results are unpredictable if invoked by a program run from a batch file
because this call is not reentrant and COMMAND.COM uses the same
internal variables when processing a batch file
hooked but ignored by 4DOS v3.0 COMMAND.COM replacement unless SHELL2E
has been loaded
the MSDOS 5 Programmer's Reference calls this "Reload Transient"

Format of commandline:
Offset  Size    Description
00h    BYTE    length of command string, not counting trailing CR
01h    var     command string
N     BYTE    0Dh (CR)


2E - DOS 2+ - PASS COMMAND TO COMMAND INTERPRETER FOR EXECUTION