gnuplot with texshop in osx - latex

Question

I have installed gnuplot through macports but when i compile my latex document in texshop it doesn't show the plots and I get these errors in the log file:
Package pgf Warning: Plot data file `tutorial.x.table' not found. on input line
17.
Package pgf Warning: Plot data file `tutorial.sin.table' not found. on input li
ne 19.
Package pgf Warning: Plot data file `tutorial.exp.table' not found. on input li
ne 21.
I'm just trying to compile this basic example:
% Author: Till Tantau
% Source: The PGF/TikZ manual
\documentclass{article}
\usepackage[latin1]{inputenc}
\usepackage{tikz}
% GNUPLOT required
\begin{document}
\pagestyle{empty}
\begin{tikzpicture}[domain=0:4]
\draw[very thin,color=gray] (-0.1,-1.1) grid (3.9,3.9);
\draw[->] (-0.2,0) -- (4.2,0) node[right] {$x$};
\draw[->] (0,-1.2) -- (0,4.2) node[above] {$f(x)$};
\draw[color=red] plot[id=x] function{x}
node[right] {$f(x) =x$};
\draw[color=blue] plot[id=sin] function{sin(x)}
node[right] {$f(x) = \sin x$};
\draw[color=orange] plot[id=exp] function{0.05*exp(x)}
node[right] {$f(x) = \frac{1}{20} \mathrm e^x$};
\end{tikzpicture}
\end{document}

Answer 1

Yes, you need to turn the .gnuplot files that tikz creates into the tables files. You have two choices for this:
you can run (pdf)latex with the additional command line switch --shell-escape, sometimes also called --enable-write-18, then gnuplot is run automatically for you. (You might not be comfortable with allowing arbitrary programs to be starte from within pdflatex, though.)
you can run gnuplot yourself on the test.exp.gnuplot, test.sin.gnuplot, test.x.gnuplot etc. files. Simply gnuplot test.exp.gnuplot should do it. (Can't verify here, since my gnuplot version is too old.)