ip=xx.xx.xx.xx
cat /etc/file.conf | sed 's/^IP.*/IPADDRESS=$ip/g' > /etc/file.conf2 && mv /etc/file.conf2 /etc/file.conf
IPADDRESS=$ip
IPADDRESS=xx.xx.xx.xx
sed -i "s/^IP.*/IPADDRESS=$ip/g" /etc/file.conf
sed -i 's/^IP.*/IPADDRESS='$ip'/g' /etc/file.conf
sed "s/^IP.*/IPADDRESS=$ip/g" /etc/file.conf > /etc/file.conf2 && mv /etc/file.conf2 /etc/file.conf