Fftp(1) is a program for generating Fourier spectra from evenly sampled
real and complex ASCII data sets.  Fftp(1) will perform Welch's
smoothing method on large data files and optionally use the Chirp Z
Transform to efficiently zoom into portions of the frequency spectrum. 

Fffp(1) is a classic command-line UNIX program.  Fftp(1) handles
windowing, conversion to single-sided spectrum, and DC-level
correction/nulling.  Many hours of corner case testing has been done to
ensure that when you need an FFT, you can quickly get an accurate
analysis without having to open up a textbook. 

Fftp(1) outputs the resulting spectrum-analyzer data as an ASCII file
ready for plotting in pdplot, gnuplot, or other graphing package.

FFtp(1) is self-contained, using only stdio.h, stdlib.h and math.h.  Just
type "make" and then "make install".