Share 4g Internet by using your wlan0 or usb0 trough a raspberry

share4GTroughRaspbian.sh

#!/bin/bash
#CommonPart
iptables -F INPUT
iptables -F FORWARD
iptables -F OUTPUT
iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT
iptables -P FORWARD ACCEPT
echo 1 > /proc/sys/net/ipv4/ip_forward

INTERFACES="usb0 wlan0"
configuredFlag="no"

function configureInterfaces
{
  for INET in $INTERFACES
  do
     echo Configuring $INET
     INETIP="$(ifconfig $INET | sed -n '/inet addr/{s/.*addr://;s/ .*//;p}')"
     echo " iptables -t nat -A POSTROUTING -o $INET -j SNAT --to-source $INETIP "
     iptables -t nat -A POSTROUTING -o $INET -j SNAT --to-source $INETIP
     if [ ! -z $INETIP ];then
       configuredFlag="yes"
       echo "Configured $configured"
       break
     fi
  done
  if [ $configuredFlag = "no" ];then
     echo "configuredFlag $configuredFlag, sleeping"
     sleep 30
     configureInterfaces
  fi
}
configureInterfaces

Its intentended to get connected from wlan or usb. then It shares internet by using other routers devices attached. I get stick with an older router by using this

some recursion that way If Its not reacheable It would retry in 30seconds.
as a plus If I call this script at /etc/rc.local . On every restart It will keep on listening for sharing internet.