custom_route.sh

#!/bin/bash

# don't use this if all your need is a route that goes through your ISP router
# instead of an openvpn tunnel. OpenVPN has this as a built-in feature!

if [ "$EUID" -ne 0 ]
  then echo "Please run as root"
    exit 1
fi

TARGET="$1"
INTERFACE="$2"

LOG="/tmp/custom_route.log"

# for debugging
#set -x

# first check whether route exist already
if [[ $(ip route show ${TARGET} | wc -c) -ne 0 ]]; then
  #echo "DBG: Route exists!"
  echo "`date -Iseconds` Route to ${TARGET} via ${INTERFACE} exists already." >>${LOG}
  exit 0 # all good

else
  #echo "DBG: Route missing..."
  # then find out the default gateway which must be via $INTERFACE
  if [[ $(ip route show dev eth0 | grep default | cut -d" " -f3 | wc -c) -ne 0 ]]; then
    GATEWAY=$(ip route show dev eth0 | grep default | cut -d" " -f3)
    # echo "YEAH: now need to run: ip route add ${TARGET} via ${GATEWAY} dev ${INTERFACE} proto static"
    echo "`date -Iseconds` Trying to add route to ${TARGET} via ${GATEWAY} on ${INTERFACE} now." >>${LOG}
    ip route add ${TARGET} via ${GATEWAY} dev ${INTERFACE} proto static >/dev/null 2>&1
    exit 0

  else
    #echo "DBG: else"
    echo "`date -Iseconds` Unable to add route ${TARGET} via ${INTERFACE}!" >>${LOG}
    exit 1
  fi

fi

# EOF