Command line variables

Let us use undefined variables FILE and COLUMN in the gnuplot script

plot FILE using 1:COLUMN with lines

They can be defined at execution:

gnuplot -e "FILE='data.txt'; COLUMN=2"

CSV files

Support CSV files:

set datafile separator ","

Use the first CSV row as title:

set key autotitle columnhead noenhanced

noenhanced is to disable (LaTeX-like) subcripting with underscore.

Second axis

set ylabel "First Y axis"
set y2tics # Enable second axis
set ytics nomirror # Don't copy tics on second axis
set y2label "Second Y axis"
plot "filename" using 1:2 with lines, "" using 1:3 with lines axis x1y2