RPi

Setup as output

echo "23" > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpio23/direction

echo "1" > /sys/class/gpio/gpio23/value
echo "0" > /sys/class/gpio/gpio23/value

Setup as input

echo "23" > /sys/class/gpio/export
echo "in" > /sys/class/gpio/gpio23/direction

cat /sys/class/gpio/gpio23/value

echo "23" > /sys/class/gpio/unexport

Or:

gpio -g mode 23 out
gpio -g write 23 1
gpio -g write 23 0