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

Network interface with multiple IP's

/etc/network/interfaces

auto lo

iface lo inet loopback
auto eth0
iface eth0 inet dhcp

auto eth0:0
iface eth0:0 inet static 
      address 192.168.1.42 
      netmask 255.255.255.0

allow-hotplug wlan0
iface wlan0 inet manual
wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
iface default inet dhcp