1 1.1 apb 2 1.2 sjg :D expanded when var set 3 1.3 sjg true 4 1.3 sjg TRUE 5 1.2 sjg :U expanded when var undef 6 1.3 sjg true 7 1.3 sjg TRUE 8 1.2 sjg :D skipped if var undef 9 1.2 sjg 10 1.2 sjg :U skipped when var set 11 1.2 sjg is set 12 1.2 sjg :? only lhs when value true 13 1.3 sjg true 14 1.3 sjg TRUE 15 1.2 sjg :? only rhs when value false 16 1.3 sjg false 17 1.3 sjg FALSE 18 1.4 sjg do not evaluate or expand :? if discarding 19 1.4 sjg is set 20 1.1 apb exit status 0 21