If I want to generate a lookup table for an nfet then I would need to perform nested dc simulations of all the transistor ports along with parametric sweeps of 'W' and 'L', is there an simple way to do it in ngspice.

there is a testbench

sky130_tests/test_sweep_mos_w.sch

that sweeps the width of a transistor in a loop and performs dc sims. You can add a second nested loop varying L and collect the data with

wrdata

or

.print

Good sources are the ngspice control language tutorial and the ngspice user manual.