I have a simple widget to display free memory:
myFreeMemory = awful.widget.watch(\'bash -c "free -h | awk \\\'/^Mem:/ {print $3}\\\'"\', 1) <
myFreeMemory = awful.widget.watch(\'bash -c "free -h | awk \\\'/^Mem:/ {print $3}\\\'"\', 1)