How to disable a src.conf on command-line

[M. Warner Losh]

In message: <4489E354.5070201 at bitfreak.org>
            Darren Pilgrim <darren.pilgrim at bitfreak.org> writes:
: M. Warner Losh wrote:
: > So if you make WITH_SSP off by default, then having WITH_SSP in the
: > src.conf can't be overridden.  If you have it on by default, having
: > WITHOUT_SSP in the src.conf file can't be overriden.  this appears to
: > be an unintended flaw with the with/without stuff.  I'm not sure the
: > right way to compensate.
: 
: I can't speak for the "right" way, but if you specify the variable in 
: src.conf/make.conf with ?= instead of =, you can override it on the 
: command-line:
: 
: # grep KERNCONF /etc/make.conf
: KERNCONF?=TTPWEB
: # make -V KERNCONF
: TTPWEB
: # env KERNCONF=SOMETHING_ELSE make -V KERNCONF
: SOMETHING_ELSE

?= doesn't mesh well with WITH/WITHOUT because then it will always be
defined, thus defeating its purpose.

Warner