@goto _beg

The dos set command always converts variables to uppercase.
The 3.x and 9x windir and winbootdir are lowercase variables.
The set command cannot change them b/c they are lowercase,
therefore, if these still exist, then they were set by the
Windows OS, and decisions can be made based on this concept.

Sean Blankenship <seanb/at/writeme/dot/com>

:_beg
	@echo off
:_set
	:: use the lowercase trick to clear any chance of
	:: existing variables.
	set windir=
	set windbootdir=
:_mod
	:: winNT is explicit and obvious
	if [%OS%]==[Windows_NT] goto _nt
	:: dos does not have windir but win3x does
	if [%windir%]==[]       goto _dos
	:: win3x has windir but not winbootdir
	if [%winbootdir%]==[]   goto _3x
	:: if winbootdir exists, it must be either 9x or NT
	:: we have already checked for NT
	goto _9x
:_dos
	set xOS=DOS
	goto _rep
:_3x
	set xOS=3x
	goto _rep
:_9x
	set xOS=9x
	goto _rep
:_nt
	:: may be able to check for 2k variables like system root
	:: or system drive, etc...
	if     exist "c:\documents and settings\" set XOS=2k
	if not exist "c:\documents and settings\" set XOS=40
	goto _rep
:_rep
	:: return XOS
	echo Running OS: %xOS%
	goto _end
:_end