Here's a dummy data source. In reality, this could take input from anything that outputs a time and a value.

#!/usr/bin/perl -w

use strict;
use POSIX qw(strftime);

my $value=rand(100);

$|=1;

while(1) {
    sleep(1);
    print strftime("%H:%M:%S",localtime),",$value\n";
    # jitter the value
    $value+=rand(2)-1;
}
[download]

Here's the actual gnuplot-calling code. This assumes gnuplot is on your path, and that you have File::Temp installed.

If you don't have File::Temp, it should be simple to adjust the script to use a fixed file name.

#!/usr/bin/perl -w

use strict;
use File::Temp qw(tempfile tempdir);
use IO::Handle;

my $tempdir=tempdir(CLEANUP=>1);
my ($plotFh, $plotFilename)=tempfile(DIR=>$tempdir);

# replace this with whatever the real data src is if needed
open(DATASRC,"perl dataSrc.pl|") or die "Can't run data source, error 
+$!";

open(GNUPLOT,"|gnuplot");

$plotFh->autoflush(1);

select GNUPLOT;
$|=1;

# set up plot options for time series graph
print GNUPLOT "set xdata time\n";
print GNUPLOT q(set timefmt "%H:%M:%S"),qq(\n);

my $prevTime="";
my $prevValue=0;

while(<DATASRC>) {
    chomp;
    my ($time, $value)=split /,/;

    if($time ne $prevTime) {
        if($prevTime ne "") {
            print $plotFh "$prevTime $prevValue\n";
            print GNUPLOT "plot '$plotFilename' using 1:2\n";
        }
        $prevTime=$time;
    }
    $prevValue=$value;
}
[download]