If you're interested in GNUplot, especially for the terminal, here is a demo of doing ascii plots with GNUplot (ironically inside a jupyter notebook, but hopefully it makes sense). You can replace the terminal with something sensible (I think Cairo is the usual backend?) and run from the terminal if you want actual graphical plots.

https://gist.github.com/rbitr/7bf79860c92974182bdedce79c7de0...

In practice I use matplotlib for most plotting because the data's already coming from python. I'm not a fan of any of the grammar of graphics plotting packages but some people swear by them.

Also, I miss Matlab.