Codice:

#!/bin/bash

USER="username"
PASS="password"
IP_ROUTER="192.168.1.1"
CURL="/usr/bin/curl"
INDIRIZZI=(1 2 3 4 5)
LIMITE=${#INDIRIZZI[@]}

IP=$($CURL -s "http://checkip.dyndns.org/ " | grep -o "[[:digit:].]\+")
echo "Ip pubblico corrente $IP"
MY_IP_1=$(echo "$IP" | cut -d '.' -f1)
MY_IP_2=$(echo "$IP" | cut -d '.' -f2)
MY_IP_3=$(echo "$IP" | cut -d '.' -f3)
MY_IP_4=$(echo "$IP" | cut -d '.' -f4)

INDICE=0

#echo "Elementi: $LIMITE"
for (( i = 0 ; i < $LIMITE ; i++ ))
do
#    echo "Elemento [$i]: ${INDIRIZZI[$i]}"
    if [ ${INDIRIZZI[$i]} -eq $MY_IP_4 ] ;  then
   INDICE=$i
    fi
done

INDICE=$(expr $INDICE + 1)
if [ $INDICE -eq $LIMITE ] ; then
    INDICE=0
fi

MY_IP_4=${INDIRIZZI[$INDICE]}
echo "Nuovo indirizzo: $MY_IP_1.$MY_IP_2.$MY_IP_3.$MY_IP_4"

$CURL "http://$USER:$PASS@$IP_ROUTER/apply.cgi" -d "index&action=ApplyTake&change_action=& submit_type=&now_proto=static&dhcp_dnsmasq=1&dns_dnsmasq=1&auth_dnsmasq=1& fullswitch=0&ppp_mlppp=0&lan_ipaddr=4&wan_proto=static&wan_ipaddr=4& wan_ipaddr_0=$MY_IP_1&wan_ipaddr_1=$MY_IP_2&wan_ipaddr_2=$MY_IP_3& wan_ipaddr_3=$MY_IP_4&wan_netmask=4&wan_netmask_0=255&wan_netmask_1=255& wan_netmask_2=255&wan_netmask_3=248&wan_gateway=4&wan_gateway_0=gw1& wan_gateway_1=gw2&wan_gateway_2=gw3&wan_gateway_3=gw4&wan_dns=4&wan_dns0_0=8& wan_dns0_1=8&wan_dns0_2=8&wan_dns0_3=8&wan_dns1_0=8&wan_dns1_1=8&wan_dns1_2=4& wan_dns1_3=4&wan_dns2_0=208&wan_dns2_1=67&wan_dns2_2=222&wan_dns2_3=222& lan_stp=0&router_name=link&wan_hostname=link&wan_domain=&mtu_enable=0& lan_ipaddr_0=192&lan_ipaddr_1=168&lan_ipaddr_2=1&lan_ipaddr_3=1&lan_netmask=4& lan_netmask_0=255&lan_netmask_1=255&lan_netmask_2=255&lan_netmask_3=0& lan_gateway=4&lan_gateway_0=0&lan_gateway_1=0&lan_gateway_2=0&lan_gateway_3=0& sv_localdns=4&sv_localdns_0=0&sv_localdns_1=0&sv_localdns_2=0&sv_localdns_3=0& dhcpfwd_enable=0&lan_proto=dhcp&dhcp_check=&dhcp_start=100&dhcp_num=50& dhcp_lease=1440&wan_wins=4&wan_wins_0=0&wan_wins_1=0&wan_wins_2=0&wan_wins_3=0& _dhcp_dnsmasq=1&_dns_dnsmasq=1&_auth_dnsmasq=1&ntp_enable=1&time_zone=CET- 1CEST%2CM3.5.0%2F2%2CM10.5.0%2F3&ntp_server=ntp1.inrim.it"
echo "Indirizzo cambiato, aspetto 10 secondi per la verifica..."
sleep 10
IP=$($CURL -s "http://checkip.dyndns.org/ " | grep -o "[[:digit:].]\+")
echo "Indirizzo corrente $IP"