switch_forward.sh

#!/bin/bash

# Test if script has root privileges, exit otherwise
id=$(id -u)
if [ "${id}" -ne 0 ]; then
    echo "You need to run this with sudo or as root."
	exit 1
fi
# Define the lines to insert, using actual tab characters instead of \t
FORWARD_ACCEPT="        iptables -P FORWARD ACCEPT"
DOCKER_FORWARD="        iptables -I FORWARD -i docker0 -j ACCEPT\n        iptables -I FORWARD -o docker0 -j ACCEPT"

# File to edit
file="/var/packages/ContainerManager/scripts/start-stop-status"

if grep -q 'iptables -P FORWARD ACCEPT' "${file}"; then

    # this has the FORWARD ACCEPT rule in place.
    echo "Found FORWARD ACCEPT policy in start-stop-status script..."
    echo "Switching to docker FORWARD rules"
    match="^[[:space:]]*iptables -P FORWARD ACCEPT"
    # Use sed to replace the line with the DOCKER_FORWARD line
    sed -i "/${match}/c\\${DOCKER_FORWARD}" "${file}"
    echo "Modified FORWARD ACCEPT line with docker FORWARD rules"
	echo
	echo "To avoid a restart of docker, applying the rules now. This should automatically apply"
	echo "  with the next docker restart"
	iptables -I FORWARD -i docker0 -j ACCEPT
    iptables -I FORWARD -o docker0 -j ACCEPT

elif grep -q 'iptables -I FORWARD -i docker0 -j ACCEPT' "${file}"; then

    # this already has the DOCKER rules applied.
    echo "Found FORWARD rules for docker interface in start-stop-status script..."
    echo "Switching to FORWARD ACCEPT policy"
    match="^[[:space:]]*iptables -I FORWARD -i docker0 -j ACCEPT"
    # Use sed to replace both lines with FORWARD ACCEPT
    sed -i "/${match}/{N;s/.*\n.*/${FORWARD_ACCEPT}/}" "${file}"
    echo " Restored FORWARD ACCEPT line"
	echo
	echo "To avoid a restart of docker, applying the rules now. This should automatically apply"
	echo "  with the next docker restart"
    # Remove the iptables rules that were previously inserted
    iptables -D FORWARD -i docker0 -j ACCEPT
    iptables -D FORWARD -o docker0 -j ACCEPT

    # Reset default policy
    iptables -P FORWARD ACCEPT

else
    echo "No IP FORWARD rules found in ${file}."
fi