Hello,
I was wondering, is it possible to write to a .txt file just one of the steps of a DC sweep and not all values?

 

Say what? You can write anything you want into a text file. If you want to use it for some useful purpose or with a particular software package you need to supply a bit more information. Helps us out here; we are not mind readers contrary to popular expectations.

 

in ngspice, I want to write the calculated voltages and currents, in different txt files, one for each voltage step. I use dc sweep, e.g. I run for 0 to 500 V with a voltage step of 1V and I want to have at the end 501 txt files, including all voltages and currents for each timestep. does this make sense?

 

AFIK, LTSpice has two ways to do it. Both are in the help file. Look at these topics:

Exporting Waveform Data

and

.MEASURE

 

ngspice ≠ LTSPICE

That is probably why I had trouble reading the original post.

 

MikeML offered the correct option ... Exporting data ...

Why not visit http://ngspice.sourceforge.net/docs.html and get the manual for NGSpice and see what it states about exporting data.

Of course almost every program has a HELP feature.