@User I have this in a control block:

.control

save all

* op

* tran 1n 300n

dc vvcc 1 4 0.01

set appendwrite

write cmos_example.raw

.endc

and everytime i run a simulation the cmos_example.raw file grows. Simulation results are appended. Ensure the 'set appendwrite' is before the write command. You also can place a 'quit' command in the control block, so ngspice exits automatically. Also ensure you run ngspice in interactive mode (

ngspice -i circuit.spice -a

) and not in batch mode (

ngspice -b -r circuit.raw circuit.spice

)