@Usermy suggestions: • put

.save all

before the

.dc

line • After the

.dc

line put the following 3 lines, if you are using ngspice in interactive mode. •

.control

•

write inverter_tt.raw

•

.endc

That said, for my simulations i almost never use an external wave viewer, since xschem can now display waveforms by itself. See this tutorial