gnuplot how to give column number to plot dynamically?

Question

I am automating a task to create small graphs using gnuplot. And I need to pass the column number from the datafile that is to be plotted

pfile=system(\"echo         


        

Answer 1

You could also pass the column number via command line

gnuplot -e "colnum=$colnum" script.gp

and your script.gp contains

plot pfile using 4:(column(colnum))

Answer 2

This is an alternative to @EWCZ's answer. Any variable initialized using the system command is treated as a string: in your case, colnum="2" (with quotes). You can transform it to an integer by adding zero:

# first option
plot pfile using 4:(column(colnum+0))

# second option
colnum = system("echo $colnum") + 0
plot pfile using 4:(column(colnum))

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As a side note, your task could be more flexible (easier to automate) by using @Christoph's answer; better if you have gnuplot 5.0 because you can pass arguments to a gnuplot script directly

Answer 3

it seems that one has to do colnum=int(system("echo $colnum")) so that the variable colnum is interpreted as an integer and not a string