mkdir -p /tmp/test/{aaa,bbb,ccc,ddd}

mkdir -p /tmp/test/{aaa,bbb,ccc,ddd}/{eee,fff}

mkdir -p /tmp/test/{2008,2009,2010,2011}/{01,02,03,04,05,06,07,08,09,10,11,12}/{1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30}