Working with Raspberry Pi

Below is an example /etc/network/interfaces for Debian based distros on Raspberry Pi 1/2

This particular example allows you to forward DHCP traffic to wlan0, so that you can push internet through eth0

auto lo
iface lo inet loopback

auto eth0
allow-hotplug eth0
iface eth0 inet manual

auto wlan0
allow-hotplug wlan0
iface wlan0 inet dhcp
   wpa-ssid "<SSID>"
   wpa-psk "<password>"
wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf
   post-up /usr/sbin/parprouted eth0 wlan0
   post-down /usr/bin/killall /usr/sbin/parprouted
   # clone the dhcp-allocated IP to eth0 so dhcp-relay will relay for the correct subnet
   post-up /sbin/ip addr add $(/sbin/ip addr show wlan0 | perl -wne 'm|^\s+inet (.*)/| && print $1')/32 dev eth0
   post-down /sbin/ifdown eth0

auto wlan1
allow-hotplug wlan1
iface wlan1 inet manual
wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf