Running /bin/uptime may be a more portable way of determining load average.
But in case you hadn't seen it: Under Linux there is a proc pseudo file /proc/loadavg that you can read for this purpose.

man 5 proc
loadavg
The load average numbers give the number of jobs in the run queue (state R) or waiting for disk I/O (state D) averaged over 1, 5, and 15 minutes. They are the same as the load average numbers given by uptime(1) and other programs.

Staunch