How do I read data from stdin to gnuplot and plot same data twice

Question

I have a program that generates data with a couple of input arguments and spits it out to stdout, I pipe this data to gnuplot and plot it (in my case I don't have an intermediate file):

$ cat sample_data.dat | gnuplot plot_script.gp

sample_data.dat:

plot_script.gp

#!/usr/bin/gnuplot
set terminal wxt size 700,524 enhanced font 'Verdana,10' persist

set style line 1 lc rgb '#0060ad' pt 7 lt 1 lw 0.5 # circle blue thin line
set style line 2 lc rgb '#949599' lt 1 lw 1 # --- grey

plot "<cat" using 1:2 w lp ls 1 notitle

what I want to accomplish is something like this

 plot "<cat" using 1:2 w l ls 2 notitle, \
      "" using 1:2 w p ls 1 notitle

That is, I want the line in one colour and the dots in another. I just can figure out a solution for this.

Could I read the stdin to a variable to store it so I could plot it twice?

There are some close questions on stackoverflow but nothing that I could really use to figure out to fit my problem, gnuplot-plot-two-data-set-from-stdin and pipe-plot-data-to-gnuplot-script

Edit:

I have now tried this as well:

plot for[col=2:3] "<awk '{print $1,$2,$2}'" using 1:col w lp ls col notitle

Christoph · Accepted Answer · 2015-03-10 07:45:17Z

3

You must duplicate your data before you send it to gnuplot. A way to to this on Unix-like systems is

$ cat sample_data.dat | cat - <(echo 'e') | tee - | gnuplot script.gp

and using the script which you already have, like

plot '<cat' w l, '' w p

In gnuplot 5 one could also use some trickery inside of gnuplot like

data = system('cat -')
set print $db
print data
unset print
plot $db w l, $db w p

and call this script just with

gnuplot plot_script.gp < sample_data.dat

answered Mar 10, 2015 at 7:45

Christoph

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1 Comment

Sparx Over a year ago

Thanks for your answer. I don't have access to gnuplot 5 so can't try it. But I have some issues running the code you provided. The output does not seem to be deterministic. I get different sorting of the doubled data points randomly, and when I manually copy to the right structure I get the error warning: Skipping data file with no valid points

Carl Ponder · Accepted Answer · 2022-08-01 14:10:02Z

0

As old as this thread is, I found the information useful in solving my own problem. For what it's worth, I expect gnuplot 5 to be accessible on most systems now. Here's a script I wrote with it:

#!/usr/bin/gnuplot -c
set term x11 persist  # Allow script to exit without closing plot-window.
set xlabel ARG1       # Axis labels passed-in as parameters.
set ylabel ARG2
plot "/dev/stdin" with points              # Read points from input-pipe.

I can just pipe-in two columns of data and generate the chart:

cat POINTS | plot.points "X-axis label" "Y-axis label"

answered Aug 1, 2022 at 14:10

Carl Ponder

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