The script below collect the temperature data from the webswitch and saves it in a file. After that the data is plotted with the gnuplot scripts.

The script is named temp_webswitch in the example below.

 #!/bin/bash
 #
 # Small script to read and plot temperature
 # 
 # 1)Save timestamp
 # 2)Retrieve Outdoor temperature
 # 3)Retrieve Indoor Temperature
 # 4)Save time, outdoortemp, indoor temp to file tempdata
 # 5)plot three figures
 #
 DATE=$(date +"%s" )
 UTE=$(curl -s "http://xxxxxx.shacknet.nu:xxxx/temp.egi" | perl -e 'foreach (<>){if(/Current Temp B/){($x)=/Current Temp B.+TD> (.+) C</;print "$x\n";}}')
 INNE=$(curl -s "http://xxxxxx.shacknet.nu:xxxx/temp.egi" | perl -e 'foreach (<>){if(/Current Temp A/){($x)=/Current Temp A.+TD> (.+) C</;print "$x\n";}}')
 echo "$DATE   $UTE    $INNE" >> /home/sm3sgp/temp/tempdata
 /usr/bin/gnuplot "/home/xxxxx/temp/plot.gnu"
 /usr/bin/gnuplot "/home/xxxxx/temp/plot24.gnu"
 /usr/bin/gnuplot "/home/xxxxx/temp/plotweek.gnu"

The scripts plot.gnu, plot24.gnu and plotweek.gnu can be modified to plot a specific time period per figure. It generates a small .png file.

 #
 # Plot the number of lines specified in the tail command below.
 #
 set terminal png
 set output "/home/xxxxx/temp/tempweek.png"
 set grid
 set ytics 5
 set xdata time
 set timefmt "%s"
 set format x "%R"
 set yrange [-10:35]
 plot "< tail -550 /home/xxxxx/temp/tempdata" using 1:2 with lines title "Temperatur utomhus", "< tail -550 /home/xxxxx/temp/tempdata" using 1:3 with lines title "Temperatur inomhus"

Edit the crontab file with command: crontab -e

 # m h  dom mon dow   command
 1-59/2 * * * * /home/xxxxx/temp/temp_webswitch &> /dev/null