Manually delete Aquaterm if you installed it via dmg file previously from your application.First remove all pre installation of gnuplot and aquaterm, if any:.Here is what I did to do so on both Yosemite and El Capitan MacOS: The best way to use gnuplot on MacOS is to set it to work with aquaterm as opposed to X11. The warning message keeps appearing infinitely if I don't close the terminal. Gnuplot returns these messages : Could not start gnuplot_qt with path '/usr/local/libexec/gnuplot/5.0/gnuplot_qt'Д¬ould not start gnuplot_qt with path '/usr/local/libexec/gnuplot/5.0/gnuplot_qt'Д¬ould not connect to gnuplot_qt ''. So I opened a new terminal shell and typed gnuplot to begin using it (the terminal is automatically set to qt). I could actually visualize the plots and I thought 'great, it works'. The make check command outputs a lot of lines in the shell before testing many gnuplot scripts. With these commands, gnuplot is located in /usr/local/bin/. I followed the installation instructions found in INSTALL.gnu file of the tarball: I ran the configure file and typed make, make check, make install, and make clean. I also installed the Command Line Tools on my OS X 10.7.5 so that I have gcc and make in the /usr/bin folder. I downloaded the source files for gnuplot 5.0.1 (gnuplot-5.0.1.tar.gz) from the source forge page.

Aquaterm homebrew