get network address

gistfile1.sh

#!/bin/sh
DEFAULTIF="eth0"
IPADDR=`/sbin/ifconfig $DEFAULTIF | grep "inet addr" | awk '{ print $2 }' | sed 's/addr://'`
NETMASK=`/sbin/ifconfig $DEFAULTIF | grep "inet addr" | awk '{ print $4 }' | sed 's/Mask://'`
NETADDR=`ipcalc -n "$IPADDR" "$NETMASK" | sed 's/NETWORK=//'`

echo "ip:   $IPADDR"
echo "mask: $NETMASK"
echo "net:  $NETADDR"