How to pass command line argument to gnuplot?

Question

You can input variables via switch -e

$ gnuplot -e "filename='foo.data'" foo.plg

In foo.plg you can then use that variable

$ cat foo.plg 
plot filename
pause -1

To make "foo.plg" a bit more generic, use a conditional:

if (!exists("filename")) filename='default.dat'
plot filename
pause -1

Note that -e has to precede the filename otherwise the file runs before the -e statements. In particular, running a shebang gnuplot #!/usr/bin/env gnuplot with ./foo.plg -e ... CLI arguments will ignore use the arguments provided.

You can pass arguments to a gnuplot script since version 5.0, with the flag -c. These arguments are accessed through the variables ARG0 to ARG9, ARG0 being the script, and ARG1 to ARG9 string variables. The number of arguments is given by ARGC.

For example, the following script ("script.gp")

#!/usr/local/bin/gnuplot --persist

THIRD=ARG3
print "script name        : ", ARG0
print "first argument     : ", ARG1
print "third argument     : ", THIRD 
print "number of arguments: ", ARGC 

can be called as:

$ gnuplot -c script.gp one two three four five
script name        : script.gp
first argument     : one
third argument     : three
number of arguments: 5

or within gnuplot as

gnuplot> call 'script.gp' one two three four five
script name        : script.gp
first argument     : one
third argument     : three
number of arguments: 5

---

In gnuplot 4.6.6 and earlier, there exists a call mechanism with a different (now deprecated) syntax. The arguments are accessed through $#, $0,...,$9. For example, the same script above looks like:

#!/usr/bin/gnuplot --persist

THIRD="$2"
print "first argument     : ", "$0"
print "second argument    : ", "$1"
print "third argument     : ", THIRD
print "number of arguments: ", "$#"

and it is called within gnuplot as (remember, version <4.6.6)

gnuplot> call 'script4.gp' one two three four five
first argument     : one
second argument    : two
third argument     : three
number of arguments: 5

Notice there is no variable for the script name, so $0 is the first argument, and the variables are called within quotes. There is no way to use this directly from the command line, only through tricks as the one suggested by @con-fu-se.

You can also pass information in through the environment as is suggested here. The example by Ismail Amin is repeated here:

In the shell:

export name=plot_data_file

In a Gnuplot script:

#! /usr/bin/gnuplot

name=system("echo $name")
set title name
plot name using ($16 * 8):20 with linespoints notitle
pause -1

The answer of Jari Laamanen is the best solution. I want just explain how to use more than 1 input parameter with shell variables:

output=test1.png
data=foo.data
gnuplot -e "datafile='${data}'; outputname='${output}'" foo.plg

and foo.plg:

set terminal png
set outputname 
f(x) = sin(x)
plot datafile

As you can see,more parameters are passed with semi colons (like in bash scripts), but string variables NEED to be encapsuled with ' ' (gnuplot syntax, NOT Bash syntax)

You may use trick in unix/linux environment:

1. in gnuplot program: plot "/dev/stdin" ...

2. In command line: gnuplot program.plot < data.dat

This question is well answered but I think I can find a niche to fill here regardless, if only to reduce the workload on somebody googling this like I did. The answer from vagoberto gave me what I needed to solve my version of this problem and so I'll share my solution here.

I developed a plot script in an up-to-date environment which allowed me to do:

#!/usr/bin/gnuplot -c 
set terminal png truecolor transparent crop
set output ARG1
set size 1, 0.2
rrLower = ARG2
rrUpper = ARG3
rrSD = ARG4
resultx = ARG5+0 # Type coercion required for data series
resulty = 0.02 # fixed
# etc.

This executes perfectly well from command-line in an environment with a recent gnuplot (5.0.3 in my case).

$ ./plotStuff.gp 'output.png' 2.3 6.7 4.3 7

When uploaded to my server and executed, it failed because the server version was 4.6.4 (current on Ubuntu 14.04 LTS). The below shim solved this problem without requiring any change to the original script.

#!/bin/bash
# GPlot v<4.6.6 doesn't support direct command line arguments.
#This script backfills the functionality transparently.
SCRIPT="plotStuff.gp"
ARG1=$1
ARG2=$2
ARG3=$3
ARG4=$4
ARG5=$5
ARG6=$6

gnuplot -e "ARG1='${ARG1}'; ARG2='${ARG2}'; ARG3='${ARG3}'; ARG4='${ARG4}'; ARG5='${ARG5}'; ARG6='${ARG6}'" $SCRIPT

The combination of these two scripts allows parameters to be passed from bash to gnuplot scripts without regard to the gnuplot version and in basically any *nix.

You could even do some shell magic, e.g. like this:

#!/bin/bash
inputfile="${1}" #you could even do some getopt magic here...

################################################################################
## generate a gnuplotscript, strip off bash header
gnuplotscript=$(mktemp /tmp/gnuplot_cmd_$(basename "${0}").XXXXXX.gnuplot)

firstline=$(grep -m 1 -n "^#!/usr/bin/gnuplot" "${0}")
firstline=${firstline%%:*} #remove everything after the colon
sed -e "1,${firstline}d" < "${0}" > "${gnuplotscript}"


################################################################################
## run gnuplot
/usr/bin/gnuplot -e "inputfile=\"${inputfile}\"" "${gnuplotscript}"
status=$?
if [[ ${status} -ne 0 ]] ; then
  echo "ERROR: gnuplot returned with exit status $?"
fi

################################################################################
## cleanup and exit
rm -f "${gnuplotscript}"
exit ${status}

#!/usr/bin/gnuplot
plot inputfile using 1:4 with linespoints
#... or whatever you want

My implementation is a bit more complex (e.g. replacing some magic tokens in the sed call, while I am already at it...), but I simplified this example for better understanding. You could also make it even simpler.... YMMV.