Re: [Gnuplot-info] Using GNUplot, plot data and show that graph into web browser.

[Richard H. <r.h...@rl...>]

jimineep wrote:

> 
> I've just done it in perl/cgi so I don't see why php couldnt do it!
> 
> I did it by saving off the data to a temporary .dat file, then running
> gnuplot from my script using this file, saving the output to a png file
> (jpeg might be possible...probably something like set term jpeg) and then
> getting my script to write an html output displaying this .png file. Im no
> expert in perl or gnuplot but it wasnt too tricky.
> 
> A question for anyone who might know........is it possible for me to by
> pass saving off the temporary file and instead keeping a 2d array in
> memory and sending it straight to gnuplot
> 

yes; one method is to write and read from stdin/stdout.
the code below (untested) uses this technique.

however, you should read up on piping to stdin reading from
stdout with perl: there are a number of issues to consider.
In addition, one must give consideration to security when 
deploying gnuplot on a webserver.

hope this helps,
r,

--begin code example--

#
# call gnuplot into existence and render the commands, returning a binary blob 
# from gnuplot. we use bidirectional communication.
# this has a problem in that we can't garentee to receive a result from our process
# in a timely manner.
# In short, if something goes wrong with gnuplot input, we will have to wait till
# apache kills the session. hopefully.
#
    my $gnuplotCommands = "set term png; plot sin(x)";
    #&errmsg("commands = '$gnuplotCommands'");
    my $pid = open2(*Reader, *Writer, " gnuplot " ) or die "could not open $gnuplot: $!";
    select *Writer;
    $| = 1;  # flush all writes down the pipe.
    print Writer $gnuplotCommands or die "Could not write data to $gnuplot: $!";
    close Writer or die "Ploblem closing $gnuplot, status=$?";

    select STDOUT;
    binmode(Reader);
    my $buffer = "";
    my $binaryPic = "";
    while (read Reader, $buffer, 1024) {
        $binaryPic .= $buffer;
    }
    close Reader or die "Problem closing $gnuplot, status=$?";
    print 'Content-type: image/png; name"testfile"\n';
    print 'Content-Disposition: filename="testfile.png';
    print "\n\n";
    print $binaryPic;

--end code example--