gnuplot> plot '< tail -n 40 c:/test/bitgbp1.dat'  using 3:2:((delta_v($2) > 0.0) ? 1 : -1 )with impulses lw 2 palette
                                                                                                              ^
         warning: Skipping data file with no valid points
                                                                                                                     ^
         x range is invalid

##</code><code>##

gnuplot> pause 10
{"success":false,"error":"Service temporarily unavailable"}
gnuplot>
gnuplot> reread
gnuplot>
gnuplot> replot;
         ^
         no previous plot

##</code><code>##

#!/usr/bin/perl -w
use LWP::Simple;
use Fcntl qw(:DEFAULT :flock);

my $interval = 30; # seconds between calls
my $url='http://www.cryptonator.com/api/ticker/btc-gbp';

# {"success":false,"error":"Service temporarily unavailable"}
sub fetch{

    print"ok3\n";
    my $replie = get($url);
    print"$replie \n";
    my($a,$b,$c,$d)= $replie  =~ /^.+?(\d+\.\d+).+?(\d+\.\d+)?.+?(\d+\.\d+).+?(\d+).*$/;
    $a="not defined" unless defined($a);
    $b="not defined" unless defined($b);
    $c="not defined" unless defined($c);
    $d="not defined" unless defined($d);
        open(OUT,">>","c:/test/bitgbp1.dat") or die "BIT File open error $!\n";
        unless (flock(OUT, LOCK_EX|LOCK_NB))
        {
            warn "can't immediately write-lock the file ($!), blocking ...";
            unless (flock(OUT, LOCK_EX))
            {
                die "can't get write-lock on numfile: $!";
            }
        }
        print OUT "$c,$a,$d\n";
        flock(OUT, LOCK_UN) or die  "cant unlock file\n";
        close(OUT);
        #print  "$c,$a,$d\n";

    alarm($interval);
};

$|++;
$SIG{TERM}=sub{print "ok1\n";alarm(0);exit;};
fetch();

my $pid = fork;

if($pid == 0) {
    my $pid1 = open(CHILD, "|-", "C:/Downloaded/gp45-winbin/gnuplot/binary/gnuplot.exe -persist ") or die "Couldn't fork: $!\n";
    local $/=undef;
    my $plot=<DATA>;
    print CHILD "$plot\n";
    close(CHILD);
    print"forking\n";
    exit;
}

$SIG{ALRM}=\&fetch;

print"ok2\n";

sleep;

__DATA__
reset
delta_v(x) = ( vD = x - old_v, old_v = x, vD)
old_v = NaN
unset key
set xtics border in scale 0,0 nomirror rotate by -90  offset character 0,0  autojustify
set datafile separator ','
set bmargin at screen 0.15
#set palette defined (100 "red", 200 "green", 300 "blue")
set palette defined (-1 "red", 1 "#1B6821")
#set palette model RGB defined ( -1 'red', 1 '#006400', 0 'black' )
set cbrange [-1:1]
set grid
set yrange [*:*]
unset colorbox
set style fill solid noborder
#set xrange [1446061653-946684800:1446064653-946684800]
set xdata time
set timefmt "%s"
set format x "%H:%M"     # or anything else
set xlabel "time"
set xtics autofreq
data=system("tail -n 1 c:/test/bitgbp1.dat")
print delta_v(2)
plot '< tail -n 40 c:/test/bitgbp1.dat'  using 3:2:((delta_v($2) > 0.0) ? 1 : -1 )with impulses lw 2 palette
pause 10
reread
replot;