Perl/shell utilities to drive gnuplot come over and over on HN and Reddit. Gnuplot is _slow_. There's a better (and easier) way to deal with realtime data:

http://www.thregr.org/~wavexx/software/trend/

It's already been used for all kind of stuff (https://projects.ardrone.org/boards/1/topics/show/491, ECG, etc).