As an electrical/computer engineering student, I make Bode plots from time to time. I found this article at http://www.ecet.vtc.edu/~scolwell/elt2040/homework/ELT2040_Homework02.pdf that explains how to make Bode plots with gnuplot. I haven’t tested this out myself as I don’t currently need to do this.
N.B. I didn’t provide an actual link above so I don’t hotlink.
Mac OS X coding 