GNUplot

It is often highly convenient to make a quick plot of a function or data right from the command line. The gnuplot utility provides this. If desired, one can make high-quality plots as well. However, I recommend using python for plots made regularly or for serious presentations or publications, and using gnuplot for on-the-spot analysis.

Plot a function

To plot functions, such as the Coulomb and Lennard-Jones potentials, type gnuplot to enter the interactive interpreter mode, then enter the following:

p -1/x t 'Coulomb', 1/x**12 - 2/x**6 t 'LJ'
set xr[0:8]
set yr[-1:1]
rep

I have adopted the fast but terse style allowed by gnuplot. You could also use the following:

plot -1/x title 'Coulomb', 1/x**12 - 2/x**6 title 'LJ'
set xrange[0:8]
set yrange[-1:1]
replot

Plot a data file

Suppose instead of an analytic function, you have a simple text file containing data you want to plot, perhaps generated using awk or something similar. You could plot such a file using (w p denotes with points, and the default used above is with lines):

p 'file' u 1:2 w p, '' u 1:3 w p, '' u 1:4 w p