If you need a simple command-line tool for making charts, Gnuplot is a great choice.

Table of Contents

Starting Gnuplot

You can run a script file (gnuplot script.gp) or use the interactive mode. For this tutorial, I am going to use the interactive mode.

$ gnuplot

	G N U P L O T
	Version 5.4 patchlevel 2    last modified 2021-06-01 

	Copyright (C) 1986-1993, 1998, 2004, 2007-2021
	Thomas Williams, Colin Kelley and many others

	gnuplot home:     http://www.gnuplot.info
	faq, bugs, etc:   type "help FAQ"
	immediate help:   type "help"  (plot window: hit 'h')

Terminal type is now 'qt'
gnuplot>

Close Gnuplot by typing quit.

Set terminal

You can set how to output the plots with set terminal. By default, it will show a GUI window. Gnuplot default terminal

# Show plots directly in the terminal window
set terminal dumb

# Output as a PNG, you can define a width in pixels
set terminal png size 600

In case you want to output plots as files, you must specify the file name.

set output 'image.png'

Set datafile separator

Define what character separates the fields with set datafile separator '<character>'.

set datafile separator ','

Define data format

Set data from an axis to be dates by typing set xdata|ydata time.

set xdata time

Then, define the date-time format of the data with set timefmt '<format>'.

set timefmt '%Y-%m-%d %H:%M:%S'

Create a plot

Finally, create a plot with plot '<file>' using <col-number-x>:<col-number-y> with dots|lines|points.

plot 'test.csv' using 1:3 with points
  • You can specify more options like title "myplot" or smooth bezier (check gnuplot help).

More options

Set plot title

set title 'My plot'

Set title based on file data

Following command causes the first entry in each column of input data to be interpreted as a text string and used as a title for the corresponding plot.

set key autotitle columnheader

Set axis ranges

Set minimum and maximum value on every axis with set xrange|yrange [min:max]. You can use * to set autoscaling in one of the range limits.

set yrange [0:200]

set yrange [*:1200]

Add axis labels

Add labels for every axis with set xlabel|ylabel 'mylabel'

set xlabel 'Year'

Disable the legend

set key off

Add grid

set grid

Show statistics

stats 'data.csv'
  • You can add using <colx:coly> (or only one column).
  • After this command, stats are available as variables: STATS_mean_y, STATS_mean_x (or STATS_mean if only one command were used when running stats), STATS_min_x, etc.

Add more lines

After running stats data.csv using 2, you can add the ‘mean’ line to the plot:

plot 'saldo-cuenta.csv' using 1:2 with lines, '' using 1:(STATS_mean) with lines

Unset

Options defined with set can be returned to their default state by the corresponding unset command.

unset xrange

Tricks

Pipe a command output to gnuplot

First, create a gnuplot script (e.g.: test.gp), then type your plot options (including set datafile separator if it’s needed) and make sure your plot command refers to '<cat' (instead of a data file):

plot '<cat' using 1:2 with lines

Now you can pipe the output of a command to gnuplot. For example:

sqlite3 -csv -header database.db 'select col1, col2 from table1' | gnuplot test.gp

Get help

You can type help inside Gnuplot to get more info. Inside help, press Enter to go through a help page. At the end, it will show you a list of subpages: you can type the name of the subpage or press Enter again to go to the parent page or exit (you can also press Ctrl + C to exit from help menu).

You can also check official documentation (PDF).

If you have any suggestion, feel free to contact me via social media or email.