[Gnuplot-py-users] Help with gnuplot and php

Hello people, I'm working with a simple php program. I'm suppossed to 
send some variables to gnuplot and wait for it to plot what I want. The 
problem is that I must be doing it really bad, since no plot appears at 
all. I'll explain better: I'm using the "exec" instruction, but I don't 
know how to tell my program that gnuplot must open. I directly write:
       
        exec(""set title \"Evolucion de las SMTU en el tiempo\"");
        exec("set format y \"%.3f\"");
        exec("set xlabel \"Fecha\"");
        exec("set ylabel ".$ejey);
        exec("set yrange [:]");
        exec("set xdata time");
        exec("set ytics 0.25");
        exec("set xtics");
        exec("set nomx2tics");
        exec("set nomy2tics");
        exec("set grid");
        exec("set size 2");
        exec("set lmargin 7");
        exec("set rmargin 2");
        exec("set tmargin 3");
        exec("set bmargin 3");
        exec("set boxwidth 10");
        exec("set output \"salida_gnuplot.png\"");
        exec("set terminal png");
           
        exec("plot '-' with linespoints, '-' with linespoints, '-' with 
linespoints);
            (and here, I star a bucle to send all the values like this:
               3
                4
                6
                0
.... and so on)

Another problem I have is that my xaxis is a date, and I don't 
understand very well how this structure of plot '-' works with dates.

No error message appears on my screen, but neither the plot appears.

thank you very much if you could help me!!