The fourier command performs Fourier analysis.
fourier fundamental_frequency [value ...]The command initiates a fourier analysis of each of the given values, using the first 10 multiples of the fundamental frequency (or the first nfreqs, if that variable is set). The values may be any valid expression. They are interpolated onto a fixed-space grid with the number of points given by the fourgridsize variable, or 200 if it is not set. The interpolation will be of degree polydegree if that variable is set, or 1. If polydegree is 0, then no interpolation will be done. This is likely to give erroneous results if the time scale is not monotonic. This command is executed when a .four line is present in the input file and WRspice is being run in batch mode.