I am currently developing some code for sensors to use with my Raspberry Pi, it came to my interest to get some temperature data from the Pi, a quick search give me a very good result.
Actually there are temperature sensors on the Pi
run
/opt/vc/bin/vcgencmd measure_temp
>temp=42.2’C
Added to cronjob
/opt/vc/bin/vcgencmd measure_temp >> ~/rpi_temp.log
This will append data to the log file.