Bash hotspot creation script - has some bugs but i use internally when needed.

create_hotspot.sh

#!/bin/bash

if (( $(id -u) != 0 )); then
	echo "Non root user detected - need to run with root privileges. Exiting..."
	exit 99
fi 

### start functions

function _clean(){
	graceful_exit 5
	rm "${ERR_FIFO}" "${LOG_DIR}" -r &>/dev/null
	exec 2>&-
	exec 3<&-
}

function _out(){
	echo "$@"
}

function _debug(){
	[[ "${DEBUG,,}" == "true" ]] &&  _out "[DEBUG] $@"
}

function _info(){
	_out "[INFO] $@"
}

function _warn(){
	_out "[WARN] $@"
}

function _error(){
	_out "[ERROR] $@"
}

function print_err(){
	echo -e "\n\n!!! Error Dump !!!\n"
	sleep 1
	cat <$ERR_FIFO
	echo -e "\n!!! End Dump !!!\n"
	exit 99
}

function _pause(){
	sleep 0.5
}

graceful_exit() {
	echo "Exit requested..."

	_debug "closing ${HS_INTERFACE}"
	iw dev ${HS_INTERFACE} del

	_debug "bringing OG wifi interface back online"
	ip l set up dev wlan0 

	_pause

	local timeout=${1:-4}
	local list=""
	for c in $(ps -o pid= --ppid $$); do
		# request children shutdown
		kill -0 ${c} 2>/dev/null && kill -TERM ${c} && list="$list $c" || true
	done
	if [ -n "$list" ]; then
		# schedule hard kill after timeout
		(sleep ${timeout}; kill -9 ${list} 2>/dev/null || true) &
		local killer=${!}
		wait ${list} 2>/dev/null || true
		# children exited gracfully - cancel timer
		sleep 0.5 && kill -9 ${killer} 2>/dev/null && list="" || true
	fi
	
	[ -z "$list" ] && echo "Exit Gracefully (0)" && exit 0 || echo "Dirty Exit (1)" && exit 1
}

### end functions

## trap exit

trap exit INT TERM ERR
trap _clean EXIT 

# make fifo for stderr hiding
ERR_FIFO=/tmp/hotspot_setup.stderr
exec 3<>$ERR_FIFO
exec 2>&1 

DEBUG=true
LOG_DIR=$(mktemp -d)
declare -a PIDS

# interface bindings
SRC_DEVICE=phy0
HS_INTERFACE=hotspot0
BR_INTERFACES=()
USE_BRIDGE=""

# check that the interface supports ap mode 
if ! iw phy | head -n +$(iw phy | grep -n 'Band 1:' | cut -d':' -f1) | tail -n +$(iw phy | grep -n 'Supported interface modes:' | cut -d':' -f1) | grep -E '^[[:space:]]*\* AP$' &>/dev/null ; then
	echo "no interface that is compatible with AP mode found. Exiting..."
	exit 99
fi

# check if the user wants a bridge wrapped on the interface
if  [ -z "${USE_BRIDGE}" ]; then
	read -p "Do you want to bind the interface to a bridge (alternative to routing) ( default: false ): " yn
	case ${yn,,} in
		y*)
			USE_BRIDGE=true
			;;
		n*)
			USE_BRIDGE=false
			;;
		*) 
			USE_BRIDGE=false
			;;
	esac

	if [[ "${USE_BRIDGE}" == "true" ]]; then	
		# enter a name for the bridge interface (if no default)
		if [ -z "${BRIDGE_INTERFACE}" ]; then
			read -p "Enter an alternate name for the bridge interface ( default: hotspot_br0 ): " BRIDGE_INTERFACE
			if [ -z "${BRIDGE_INTERFACE}" ]; then
				BRIDGE_INTERFACE=hotspot_br0
			fi
		fi

		# interfaces to bridge
		while read -p "Enter additional interfaces to bind to bridge (leave blank to continue): " INT && [ ! -z "${INT}" ] ; do
			if ip -o l | sed -E 's/^[0-9]+: ([a-zA-Z0-9-]+):.*$/\1/' | grep ${INT} &>/dev/null; then
				# interface on host
				BR_INTERFACES+="${INT}"
			else
				# interface not present on host
				echo "Interface '${INT}' doesnt exist - try again"
			fi 
		done
	fi
fi 


echo "Ready to deploy "

cat <<EOF 

Creating hotspot:
	physical device: ${SRC_DEVICE} 
	interface: ${HS_INTERFACE}
	using bridge: ${USE_BRIDGE}
EOF

if [[ "${USE_BRIDGE,,}" == "true" ]]; then 
	cat <<EOF
Creating Bridge:
	interface: ${BRIDGE_INTERFACE}
	slaves interfaces: ${HS_INTERFACE} ${BR_INTERFACES[@]}
EOF
fi
 
### actual configuration of interfaces ###

# create interface 
_debug "making secondary wireless interface after disabling primary"
ip l set down wlan0 2>&1 >&3 || print_err
_pause

iw phy ${SRC_DEVICE} interface add ${HS_INTERFACE} type __ap >&3 || print_err
_pause

_debug "setting to managed mode to get around bug with master mode not being able to set 4addr"
iwconfig ${HS_INTERFACE} mode managed
_pause

_debug "configuring interface to use 4addr settings on wireless"
iw dev ${HS_INTERFACE} set 4addr on >&3 || print_err
_pause

if [[ "${USE_BRIDGE,,}" == "true" ]]; then
	_debug "adding bridge interface"
	ip l add ${BRIDGE_INTERFACE} type bridge >&3 || print_err
	
	_debug "setting hotspot interface as slave to bridge"
	ip l set master ${BRIDGE_INTERFACE} ${HS_INTERFACE} >&3 || print_err
	for INT in ${BR_INTERFACES}; do 
		_debug "setting interface '${INT}' as slave to bridge"
		ip l set master ${BRIDGE_INTERFACE} ${INT} >&3 || print_err
	done 
	
	_debug "bring bridge up"
	ip l set up ${DRIDGE_INTERFACE} >&3 || print_err
	
fi

_debug "compiling configuration file for hostapd" 
cat <<EOF > hostapd.conf
interface=${HS_INTERFACE}
driver=nl80211
ssid=${AP_SSID:-cs-2-go}
channel=5
hw_mode=g
wme_enabled=1
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=2
wpa_passphrase=${AP_PASSWORD:-mypassword}
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP
EOF

_debug "Bringing interface ${HS_INTERFACE} up now"
ip l set up dev ${HS_INTERFACE}
_pause

if [[ "${USE_BRIDGE,,}" != "true" ]]; then
	_debug "Not using bridge therefore starting instance of dhcp server on interface ${HS_INTERFACE}"
	if [ ! -f /etc/dhcp/dhcpd.conf ]; then
		_err "not able to find dhcpd configuration in /etc/dhcp/dhcpd.conf - not running dhcp server"
	else
		_debug "Using current DHCPd configuration in '/etc/dhcp/dhcpd.conf'"
		_debug "Setting ip on ${HS_INTERFACE} to match dhcpd configuration"
		IP_ADDR=$( grep router /etc/dhcp/dhcpd.conf | sed -E 's/^.*[[:space:]](([0-9]{1,3}.?){4});$/\1/')
		if ! echo "${IP_ADDR}" | grep -E '^([0-9]{1,3}.?){4}$' &>/dev/null; then
			_err "not able to locate a valid ip for the interface in the dhcpd.conf file - skipping"
		else
			ip a add ${IP_ADDR}/24 dev ${HS_INTERFACE}
			echo "" > /var/lib/dhcp/dhcpd.lease
			_pause
		
			_debug "Starting DHCPd server..." 
			dhcpd -f -cf /etc/dhcp/dhcpd.conf ${HS_INTERFACE} &>"${LOG_DIR}/dhcpd.log" &
			PIDS+=($!)
			_pause
		fi
	fi
fi

_debug "Starting hostapd - CTRL+c to exit..."
_pause
hostapd hostapd.conf &>"${LOG_DIR}/hostapd.log" &
PIDS+=($!)
_pause

tail -vf "${LOG_DIR}"/*.log