How to call Gnuplot in a pipe or with a gnuplot-script doesn't produce a plot?

How to call gnuplot in a pipe or with a gnuplot-script doesn't produce a plot?

- Gnuplot can be called by using a perl script.

- Following script illustrates:
#!/usr/local/bin/perl -w
open (GP, "|/usr/local/bin/gnuplot -persist") or die "no gnuplot";
# force the buffer to flush after every write
use FileHandle;
GP->autoflush(1);
print GP,"set term x11;plot '/tmp/data.dat' with lines\n";
close GP