extracting data from a log file and plotting it using Gnuplot

Question

I have a logfile with the following data in it:

Sat Sep 20 11:25:01 BST 2014 -- temp=53.0'C -- message from script /usr/src/scripts/wifi_test_2.sh
Sat Sep 20 11:26:01 BST 2014 -- temp=53.0'C -- message from script /usr/src/scripts/wifi_test_2.sh
Sat Sep 20 11:27:01 BST 2014 -- temp=53.0'C -- message from script /usr/src/scripts/wifi_test_2.sh

There are many more logs but I've shown only 3.

I have a script with the following commands in it, but the data is not in the correct format for GNUplot to work.

SCRIPT:

set terminal png size 400,300
set output '/usr/src/scripts/plots/core_temp_data/output.png'
plot "/var/log/rebootlogfile.log" using 4:8 with lines

Is it possible to plot 11:25:01 against 53.0 with a gnu command,or gnu and awk, or do I have to strip out the log file of unnecessary data?

Answer 1

There may be better ways to do this, but the following accurately generated a graph based on the data, with string values on the time axis.

#Process log data into compatible format. plotdata is Just a copy/paste of your sample data
awk -F" -- " '{print $2,$1}' plotdata | while read temp date; do echo $(date --date="$date" '+%R') $(echo $temp | grep -o "[0-9\.]*"); done > plotdataout; 
#Run the script on the converted data
gnuplot gnuplotscript

Then below is the gnuplot script with string labels:

set term png 
set output "plotdata.png"
set title "Temp Data"
set xlabel "Time (s)"
set ylabel "Temp (F)"
set grid
plot "plotdataout" using 2:xticlabels(1) with lines