Consider the output of "uptime"

$ uptime
11:19:07 up 7 days, 23:46, 1 user, load average: 0.12, 0.41, 0.34

You could use, cut, grep etc etc to pull out the 5 minute average value.

$ uptime | awk -F' ' '{print substr($10, 1, length($10)-1)}'
0.12

This takes the value of the 10th field starting at the 1st character, then take the length of field 10 and removes the last character.