Gnuplot in a Nutshell

Plot

plot sin(2*pi*x) $\rightarrow$ most important functions are built in.
plot "measurement.dat" $\rightarrow$ first and second column of the file measurement.dat are taken as the x and y values of the points to plot.
plot [20:80][10:] "measurement.dat" $\rightarrow$ the x axis extends from 20 to 80, the y axis from 10 to a value chosen by gnuplot to present all data.
plot "measurement.dat" using 1:3 title "second run" with linepoints $\rightarrow$ first and third column will be used, point are connected with a line, the legend reads: second run.
plot "measurement.dat" u 1:3 t "second run" w lp $\rightarrow$ does the same.
plot "measurement.dat" u 0:1 $\rightarrow$ the row number will be used as x-value.
plot "measurement.dat" u 1:2:3 w yerrorbars $\rightarrow$ with y errorbars from the third column..
plot "measurement.dat" u ($1/$4):($2*0.17) $\rightarrow$ the x-value is the ratio of the first and the fourth column, the y-value is 0.17 times the second column.
plot "measurement.dat" w lines linewidth 2 $\rightarrow$ line is drawn with double width.
plot "measurement.dat" , "theory.dat" $\rightarrow$ more curves to plot are separated by commas.

Fit

f(x) = a*x**2 + b*x + c $\rightarrow$ define a fit function:
a = 1, b = 1, c = 0 $\rightarrow$ initialize fit variables with reasonable values..
fit f(x) "measurement.dat" via a,b,c $\rightarrow$ is fit to the data in measurement.dat. The file fit.log contains all details of the fit result..
fit [0:10] f(x) "measurement.dat" u 1:4 via a,b,c $\rightarrow$ the fit is limited to the x-intervall 0 to 10, the y-values are taken from the fourth column.

set terminal post enhanced color solid "Helvetica" 21 $\rightarrow$ output driver is postscript, enhanced driver option are switched on, the plot is color and with solid lines, font is Helvetica 21 points.
set out "plot_name.ps" $\rightarrow$ save result as as plot_name.ps.
plot "measurement.dat" with points integer
Choice of symbols:

integer Symbol integer Symbol

65 $\circ$ 7 $\bullet$

64 $\square$ 5 $\blacksquare$

66 $\vartriangle$ 9 $\blacktriangle$

67 $\triangledown$ 11 $\blacktriangledown$

68 $\lozenge$ 63 $\blacklozenge$
replot $\rightarrow$ repeat last plot command..
set terminal x 11 $\rightarrow$ after postscript file is finished: switch output back to screen!

set xlabel "This will be the x-label"
set ylabel "And this is written on the y-axis."
set title "Here comes the plot title"
set key bottom left $\rightarrow$ legende goes to the bottom left part of the graph..
set xtics 0, 15, 90 $\rightarrow$ set tics on x-axis between 0 and 90 with spacing 15.
set arrow from 0,0 to 70,70 $\rightarrow$ draw an arrow
set samples 4000 $\rightarrow$ use 4000 points to plot a function (default is sometimes to low with 100)
set encoding iso_8859_1 $\rightarrow$ enables umlauts.
set term post enhanced:
- {/Symbol m} produces $\mu$
- x_i creates
- x{-2} creates $x^{-2}$
- /usr/share/doc/packages/gnuplot/doc/ps_guide.ps has more examples..