-o OPTION True if the shell option OPTION is enabled.
-v VAR True if the shell variable VAR is set
+ -R VAR True if the shell variable VAR is set and is a name reference.
! EXPR True if expr is false.
EXPR1 -a EXPR2 True if both expr1 AND expr2 are true.
EXPR1 -o EXPR2 True if either expr1 OR expr2 is true.