Download & install XQuartz 2.7.3 (X11 server), Xcode 4.5, & MacPorts 2.1.2.
Had to clear out the old ports.
Had to run sudo xcodebuild -license to accept an Xcode license.
Install gnuplot.
% sudo port install gnuplot
2018-09-21
Gnuplot still working on iMac with PS output. Terminal output doesn’t seem to work.