Control a General GPIO:

echo 18 > /sys/class/gpio/export     // Export gpio 18 so we can use it
echo "high" > /sys/class/gpio/gpio18/direction   //  Set direction to out and
set level to high. Use "low" to set direction to output and level to low

echo 0 > /sys/class/gpio/gpio18/value    // Set output to 0 or 1
echo "in" > /sys/class/gpio/gpio18/direction  // Set GPIO18 as input

cat  /sys/class/gpio/gpio18/value  // Get GPIO18 value if set input

Control a GPIO already exported as SYSTEM LEDs .
echo 1 > /sys/class/leds/dragino2\:red\:system/brightness  // Turn On LED dragino2:red:system
echo 0 > /sys/class/leds/dragino2\:red\:system/brightness  // Turn off LED dragino2:red:system