gnuplot

Summary

Hello_World.plt

#!/bin/gnuplot
set term postscript eps enhanced color 25
set output 'Hello_World.eps'
set xlabel 'x (m)'
set ylabel 'y (kg)'
set title 'Hello World Title'
plot cos(x) title 'Hello World curve'

Ouput Hello_World.eps:

fit.plt

#!/bin/gnuplot
f(x)=a*x+b
fit f 'data_file' via a,b
set output 'data_file_fit.eps'
set term postscript eps enhanced color 25
plot [0:] 'data_file', f

Ouput data_file_fit.eps:

Suggested way: wrap perl script into a bash script. Example:
fit