script to setup wifi access point for raspbian os

rpi-wifi-setup.sh

#!/bin/bash

function backup () {
  if [ -e $1 -a ! -e $1.bak ]; then
    cp $1{,.bak}
  fi
}

function restore () {
  cp $1{.bak,}
}

if [ $(whoami) != "root" ]; then
  echo "root authentication is required"
  exit 1
fi

if [[ $# -lt 1 ]]; then
  echo "Usage:"
  echo "  $0 passphrase [apName]"
  exit 1
fi

APPASS="$1"
APSSID="rpi-develop-wifi"

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

# install packages
apt-get update -y
apt-get install -y hostapd dnsmasq

# dhcpcd
backup /etc/dhcpcd.conf
restore /etc/dhcpcd.conf
echo "denyinterfaces wlan0" >> /etc/dhcpcd.conf

cat <<EOF > /etc/network/interfaces.d/wlan0
allow-hotplug wlan0
iface wlan0 inet static
    address 172.24.1.1
    netmask 255.255.255.0
    network 172.24.1.0
    broadcast 172.24.1.255
EOF

systemctl daemon-reload
service dhcpcd restart
/etc/init.d/networking restart

# hostapd
cat <<EOF > /etc/hostapd/hostapd.conf
interface=wlan0
hw_mode=g
channel=10
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

backup /etc/default/hostapd
restore /etc/default/hostapd
echo "DAEMON_CONF=\"/etc/hostapd/hostapd.conf\"" >> /etc/default/hostapd

# dnsmasq
backup /etc/dnsmasq.conf
restore /etc/dnsmasq.conf
cat <<EOF > /etc/dnsmasq.conf
interface=wlan0
listen-address=172.24.1.1
server=8.8.8.8
dhcp-range=172.24.1.2,172.24.1.50,12h
EOF

# sysctl
backup /etc/sysctl.conf
restore /etc/sysctl.conf
sed -i -r 's/#(net.ipv4.ip_forward)/\1/' /etc/sysctl.conf

echo 1 > /proc/sys/net/ipv4/ip_forward

# iptables
iptables -t nat -F
iptables -F
iptables -X
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -i eth0 -o wlan0 -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i wlan0 -o eth0 -j ACCEPT

iptables-save > /etc/iptables.ipv4.nat

# rc.local
backup /etc/rc.local
restore /etc/rc.local
sed -i -r 's/^exit 0/iptables-restore < \/etc\/iptables.ipv4.nat\nexit 0/' /etc/rc.local

service hostapd restart
service dnsmasq restart