A simple bash script that monitors the CPU temp using cron and controls a fan accordingly. No python required!
Download all the files then chmod +x and run installer.sh in the same directory as tempmon.sh and gettemp.sh, then follow the onscreen instructions.
I used 2 minute intervals and a maximum temp of 40°C. Rerun the installer if you want to change the time and temperature variables after installation.
Run rm -r ~/.scripts && rm /usr/bin/gettemp to remove all the scripts.
Also note that pin 11 refers to GPIO11, which is pin 23 on the board. Because the Pi works at 3.3v logic level, I used an NPN transistor to control the fan and powered it straight from the 5V rails because these come directly from the USB power supply, so no worries about damaging the Pi by drawing too much current.