[command-line] How to pass command line argument to gnuplot?

I want to use gnuplot to draw figure from data file, say foo.data. Currently, I hardcoded the data file name in the command file, say foo.plt, and run command gnuplot foo.plg to plot data. However, I want to pass the data file name as a command argument, e.g. running command gnuplot foo.plg foo.data. How to parse the command line arguments in gnuplot script file? Thanks.

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

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.

@vagoberto's answer seems the best IMHO if you need positional arguments, and I have a small improvement to add.

vagoberto's suggestion:

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

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

which gets called by:

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

for those lazy typers like myself, one could make the script executable (chmod 755 script.gp)

then use the following:

#!/usr/bin/env gnuplot -c

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

and execute it as:

$ ./imb.plot a b c d
script name        : ./imb.plot
first argument     : a
third argument     : c
number of arguments: 4

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.

Yet another way is this:

You have a gnuplot script named scriptname.gp:

#!/usr/bin/gnuplot -p
# This code is in the file 'scriptname.gp'
EPATH = $0
FILENAME = $1 

plot FILENAME

Now you can call the gnuplot script scriptname.gp by this convoluted peace of syntax:

echo "call \"scriptname.gp\" \"'.'\" \"'data.dat'\"" | gnuplot 

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)

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 may use trick in unix/linux environment:

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

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

In the shell write

gnuplot -persist -e "plot filename1.dat,filename2.dat"

and consecutively the files you want. -persist is used to make the gnuplot screen stay as long as the user doesn't exit it manually.