http://souptonuts.sourceforge.net/how_to_linux_and_open_source.htm

This software is ideal for printing graphs.

gnuplot> set term png
gnuplot> set output 'testcos.png'
gnuplot> plot cos(x)*sin(x)
gnuplot> exit

Or the following command can be put into "file"

$ cat > file
set term png
set output 'testcos.png'
plot cos(x)*sin(x)
exit
^D

Then, run as follows:

$ gnuplot file

Or, suppose you have the following file "/home/chirico/data". Comments
with "#" are not read by gnuplot.

# File /home/chirico/data
#
2005-07-26  1    2.3    3
2005-07-27  2    3.4    5
2005-07-28  3    4    6.6
2005-07-29  4    6    2.5

And you have the following new "file"

set term png
set xdata time
set timefmt "%Y-%m-%d "
set format x "%Y/%m/%d"
set output '/var/www/html/chirico/gnuplot/data.png'
plot '/home/chirico/data' using 1:2 w linespoints  title '1st col', \
'/home/chirico/data' using 1:3 w linespoints  title '2nd col', \
'/home/chirico/data' using 1:4 w linespoints  title '3rd col'
exit

You can now get a graph of this data running the following:

$ gnuplot file