I have a data file a.dat that is updated every few seconds. I wish to plot it in gnuplot every few seconds to see the changes
plot "a.dat"
What is the easiest way to do it? Thanks.
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3 Answers
Make a script with a loop:
while (1) {
plot "a.dat"
pause 1 # waiting time in seconds
}
Execute it with gnuplot script.gp.
For purposes of code structure and debugging, you might prefer the following alternative:
plot "a.dat"
while (1) {
replot
pause 1
}
This has the advantage that you do not have to put a complicated plot command inside the loop and do not suffer from incorrect line numbers for the plot command in error messages (that happen in at least some version of Gnuplot).
Finally, if your Gnuplot is so old that it does not yet support loops, there is the alternative:
plot "a.dat"
pause 1
reread
With reread making the script interpreter jump to the beginning of the file again.
2 Comments
Marcel
This solution has the disadvantage that gnuplot may sometimes read incomplete input from a.dat when it happens to read the file exactly while it is written by the other application.
lnostdal
Marcel: you must swap the file atomically. Most OS'es can do this. Here's how I do this from Clojure: gist.github.com/lnostdal/cc956e2a80dc49d8097b7c950f7213bd
If gnuplot is called with plot commands in the command line (option -e) instead of a command script file, only the version
gnuplot -e "...plot command(s)...; while (1) { pause 1; replot; }"
worked in my case, the other version
gnuplot -e "...plot command(s)...; pause 1; reread;"
did not.
On windows 10, I have to kill the gnuplot task in the task manager, because if I close the gnuplot window with the close-window-button, the window opens again after one second latest. Does anybody have an idea of how to handle this in a more comfortable way?
Comments
The accepted solution, of a script with a loop, works for me on a Ubuntu computer. To resolve the problem mjavu raised, which was needing a clean method to stop the script and associated task running, Ctrl-C in the terminal window works fine.
Comments
