To do it automatically with a shell script

echo "Configure: /etc/hostapd/hostapd.conf"                                                     | tee -a ${log_file} 
if [ ! -f /etc/hostapd/hostapd.conf ]; then
# -f = True if FILE exists and is a regular file. !-f = file does not exist
	touch /etc/hostapd/hostapd.conf    
#The touch command is the easiest way to create new, empty files. 
fi
	
echo "interface=$NIC"                                    >  /etc/hostapd/hostapd.conf
#echo "something" > file  Erase the file and add a line

echo "ssid=${AP_SSID}"                                   >> /etc/hostapd/hostapd.conf
#echo "something" >> file  Append the file and add a line


echo "channel=${AP_CHANNEL}"                             >> /etc/hostapd/hostapd.conf
echo "# WPA and WPA2 configuration"                      >> /etc/hostapd/hostapd.conf
echo "macaddr_acl=0"                                     >> /etc/hostapd/hostapd.conf
echo "auth_algs=1"                                       >> /etc/hostapd/hostapd.conf
echo "ignore_broadcast_ssid=0"                           >> /etc/hostapd/hostapd.conf
echo "wpa=2"                                             >> /etc/hostapd/hostapd.conf
echo "wpa_passphrase=${AP_WPA_PASSPHRASE}"               >> /etc/hostapd/hostapd.conf
echo "wpa_key_mgmt=WPA-PSK"                              >> /etc/hostapd/hostapd.conf
echo "wpa_pairwise=TKIP"                                 >> /etc/hostapd/hostapd.conf
echo "rsn_pairwise=CCMP"                                 >> /etc/hostapd/hostapd.conf
echo "# Hardware configuration"                          >> /etc/hostapd/hostapd.conf

#Setting required for config files for hostapd, dhcp-server and iptables Based on tutorial here: http://raspberry-at-home.com/hotspot-wifi-access-point/

sudo apt-get update
sudo apt-get install hostapd isc-dhcp-server iptables

sudo nano /etc/hostapd/hostapd.conf

interface=wlan0
ssid=WaterScopi3
hw_mode=g
channel=6
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=2
wpa_passphrase=waterscope
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP

sudo nano /etc/default/hostapd add

DAEMON_CONF="/etc/hostapd/hostapd.conf"

sudo nano /etc/dhcp/dhcpd.conf

ddns-update-style none;
default-lease-time 600;
max-lease-time 7200;
authoritative;
log-facility local7;

subnet 10.0.0.0 netmask 255.255.255.0 {
  range 10.0.0.5 10.0.0.55;
  option broadcast-address 10.0.0.255;
  option routers 10.0.0.1;
  default-lease-time 600;
  max-lease-time 7200;
  option domain-name "local";
  option domain-name-servers 8.8.8.8, 8.8.4.4;
}

sudo nano /etc/udhcpd.conf

INTERFACES="wlan0"

sudo nano /etc/network/interfaces

allow-hotplug wlan0
iface wlan0 inet static
address 10.0.0.1
netmask 255.255.255.0

up iptables-restore < /etc/iptables.ipv4.nat

sudo nano /etc/sysctl.conf

net.ipv4.ip_forward=1

Finally

sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
sudo iptables -A FORWARD -i eth0 -o wlan0 -m state --state RELATED,ESTABLISHED -j ACCEPT
sudo iptables -A FORWARD -i wlan0 -o eth0 -j ACCEPT  
sh -c "iptables-save > /etc/iptables.ipv4.nat"
sudo update-rc.d hostapd enable
sudo update-rc.d isc-dhcp-server enable