Firewall [Debian]

#!/bin/bash

# Funcao 1

# Firewall
firewall()
{
        if [[ -f /usr/local/bin/firewall.sh ]]
        then
                echo "Arquivo ja existente"
        else
                echo "#!/bin/bash" > /usr/local/bin/firewall.sh
        echo "# Limpar todas as regras pré existentes" >> /usr/local/bin/firewall.sh
        echo "iptables -F" >> /usr/local/bin/firewall.sh
        echo "iptables -t nat -F" >> /usr/local/bin/firewall.sh
        echo "iptables -t mangle -F" >> /usr/local/bin/firewall.sh

        echo "# A linha abaixo ativa o módulo do netfilter que evita ataques DoS" >> /usr/local/bin/firewall.sh
        echo "echo 1 > /proc/sys/net/ipv4/tcp_syncookies" >> /usr/local/bin/firewall.sh

        echo "# Liberar portas dos serviços necessários" >> /usr/local/bin/firewall.sh
        echo "iptables -A INPUT -p tcp --dport 22 -j ACCEPT" >> /usr/local/bin/firewall.sh
        echo "iptables -A INPUT -p tcp --dport 80 -j ACCEPT" >> /usr/local/bin/firewall.sh
        echo "iptables -A INPUT -p tcp --dport 443 -j ACCEPT" >> /usr/local/bin/firewall.sh
        echo "iptables -A INPUT -p tcp --dport 3306 -j ACCEPT" >> /usr/local/bin/firewall.sh

        echo "# Bloqueio de PING" >> /usr/local/bin/firewall.sh
        echo "iptables -I INPUT -p ICMP -j DROP" >> /usr/local/bin/firewall.sh

        echo "# A linha abaixo faz o bloqueio de conexões nas demais portas" >> /usr/local/bin/firewall.sh
        echo "iptables -A INPUT -p tcp --syn -j DROP" >> /usr/local/bin/firewall.sh

                chmod +x /usr/local/bin/firewall.sh

                echo "Script 'firewall.sh' criado"
        fi
}

# Servico do Firewall
firewall_service()
{
        if [[ -f /etc/systemd/system/firewall.service ]]
        then
                echo "Arquivo ja existente"

        else
                echo "[Unit]" >> /etc/systemd/system/firewall.service
                echo "Description=Firewall" >> /etc/systemd/system/firewall.service

        echo "[Service]" >> /etc/systemd/system/firewall.service
                echo "ExecStart=/usr/local/bin/firewall.sh start" >> /etc/systemd/system/firewall.service
                echo "ExecStop=/usr/local/bin/firewall.sh stop" >> /etc/systemd/system/firewall.service
                echo "ExecReload=/usr/local/bin/firewall.sh restart" >> /etc/systemd/system/firewall.service

                echo "[Install]" >> /etc/systemd/system/firewall.service
                echo "WantebBy=multi-user.target" >> /etc/systemd/system/firewall.service

                echo "Servico 'firewall.service' criado"
        fi
}

# Exclusao de Arquivos
deletar_arquivo()
{
        if [[ -f /etc/systemd/system/firewall.service || -f /usr/local/bin/firewall.sh ]]
        then
                rm -rf /usr/local/bin/firewall.sh
                rm -rf /etc/systemd/system/firewall.service

                echo "Arquivos excluidos"

        else
                echo "Arquivos nao existem"
        fi
}

# Execucao de Comandos
executar()
{
        /usr/local/bin/firewall.sh
        systemctl daemon-reload
        systemctl enable firewall
        systemctl start firewall
        systemctl status firewall
}

############
# Programa #
############

i=1
while(( $i == 1 ))
do
    clear
    echo "Programa Firewall"
        echo ""
        echo "Tarefas Agendadas"
        echo "[1] Criar arquivos de regras de Firewall"
        echo "[2] Executar junto ao sistema"
        echo "[3] Deletar Arquivo de Regras de Firewall [ICMP]"
        echo "[4] Sair"
        echo ""
        echo -n "Resp: "
        read resp

        if (( $resp == 1 ))
        then
                firewall
                firewall_service
        echo ""
        echo "--- Pressione qualquer tecla ---"
        read

        elif (( $resp == 2))
        then
                executar
        echo ""
        echo "Pressione qualquer tecla"
        read

        elif (( $resp == 3 ))
        then
                deletar_arquivo
        echo ""
        echo "--- Pressione qualquer tecla ---"
        read

        else
                i=2
                clear
        fi
done