Another thing is that octave.app has been prepared to work like you
say, but just putting gnuplot into /Applications - don't know if this
is all that has to be done for that gnuplot package. Try this from
your Terminal.app
bash$ which gnuplot
if it then says something like 'gnuplot not found' then you need to
set up that package somehow different. *Maybe* something like an
'export PATH=$PATH:/<path to your gnuplot binary>' will help?!
It seems the above will not help. The binary inside the package
(gnuplot-version.app/Contents/MacOS/gnupolt-version) does not appear to
be compiled to accept input from stdin. Rather, it launches a console
interface to gnuplot. There is an included binary to pass scripts to
this
app. I tried making this interface binary gnuplot, and calling
plot(y) from Octave, but this only activated the program with the
console and what appeared to be a blank editor page.