Raspberry Pi 3 wifi access-point-setup (AP) and internet sharing over ethernet

rPi3-ap-setup.sh

#!/bin/bash
#
# This version uses September 2017 august stretch image, please use this image
#

if [ "$EUID" -ne 0 ]
	then echo "Must be root"
	exit
fi

if [[ $# -lt 1 ]]; 
	then echo "You need to pass a password!"
	echo "Usage:"
	echo "sudo $0 yourChosenPassword [apName]"
	exit
fi

APPASS="$1"
APSSID="rPi3"

if [[ $# -eq 2 ]]; then
	APSSID=$2
fi

apt-get remove --purge hostapd -yqq
apt-get update -yqq
apt-get upgrade -yqq
apt-get install hostapd dnsmasq -yqq

cat > /etc/dnsmasq.conf <<EOF
interface=wlan0
dhcp-range=10.0.0.2,10.0.0.5,255.255.255.0,12h
EOF

cat > /etc/hostapd/hostapd.conf <<EOF
interface=wlan0
hw_mode=g
channel=4
auth_algs=1
wpa=2
wpa_key_mgmt=WPA-PSK
wpa_pairwise=CCMP
rsn_pairwise=CCMP
wpa_passphrase=$APPASS
ssid=$APSSID
ieee80211n=1
wmm_enabled=1
ht_capab=[HT40][SHORT-GI-20][DSSS_CCK-40]
EOF

sed -i -- 's/allow-hotplug wlan0//g' /etc/network/interfaces
sed -i -- 's/iface wlan0 inet manual//g' /etc/network/interfaces
sed -i -- 's/    wpa-conf \/etc\/wpa_supplicant\/wpa_supplicant.conf//g' /etc/network/interfaces
sed -i -- 's/#DAEMON_CONF=""/DAEMON_CONF="\/etc\/hostapd\/hostapd.conf"/g' /etc/default/hostapd

cat >> /etc/network/interfaces <<EOF
# Added by rPi Access Point Setup
allow-hotplug wlan0
iface wlan0 inet static
	address 10.0.0.1
	netmask 255.255.255.0
	network 10.0.0.0
	broadcast 10.0.0.255

EOF

echo "denyinterfaces wlan0" >> /etc/dhcpcd.conf

systemctl enable hostapd
systemctl enable dnsmasq

sudo service hostapd start
sudo service dnsmasq start

#
# Set up IP forwarding
#

ADAPTER="eth0"

# Allow overriding from eth0 by passing in a single argument
if [ $# -eq 1 ]; then
    ADAPTER="$1"
fi

#Uncomment net.ipv4.ip_forward
sed -i -- 's/#net.ipv4.ip_forward/net.ipv4.ip_forward/g' /etc/sysctl.conf
#Change value of net.ipv4.ip_forward if not already 1
sed -i -- 's/net.ipv4.ip_forward=0/net.ipv4.ip_forward=1/g' /etc/sysctl.conf
#Activate on current system
echo 1 > /proc/sys/net/ipv4/ip_forward

iptables -t nat -A POSTROUTING -o $ADAPTER -j MASQUERADE  
iptables -A FORWARD -i $ADAPTER -o wlan0 -m state --state RELATED,ESTABLISHED -j ACCEPT  
iptables -A FORWARD -i wlan0 -o $ADAPTER -j ACCEPT

# Save it for reboot
sh -c "iptables-save > /etc/iptables.ipv4.nat"
echo "iptables-restore < /etc/iptables.ipv4.nat" > /lib/dhcpcd/dhcpcd-hooks/70-ipv4-nat

echo "All done! Please reboot"