:D expanded when var set
true
TRUE
:U expanded when var undef
true
TRUE
:D skipped if var undef

:U skipped when var set
is set
:? only lhs when value true
true
TRUE
:? only rhs when value false
false
FALSE
do not evaluate or expand :? if discarding
is set
year=2016 month=04 day=01
date=20160401
Version=123.456.789 == 123456789
Literal=3.4.5 == 3004005
We have target specific vars
exit status 0