RESOLVCONF='/etc/resolv.conf'
SEARCH=''
NS1='1.1.1.1'
NS2='4.4.4.4'
NS3='8.8.8.8'

c() {
if [ -n "${SEARCH}" ] && ! grep -q "search ${SEARCH}" "${RESOLVCONF}"; then
return 1
fi
if [ -n "${NS1}" ] && ! grep -q "nameserver ${NS1}" "${RESOLVCONF}"; then
return 1
fi
if [ -n "${NS2}" ] && ! grep -q "nameserver ${NS2}" "${RESOLVCONF}"; then
return 1
fi
if [ -n "${NS3}" ] && ! grep -q "nameserver ${NS3}" "${RESOLVCONF}"; then
return 1
fi
return 0
}

if c
then
{
[ -n "${SEARCH}" ] && printf "search %s\n" "${SEARCH}"
[ -n "${NS1}" ] && printf "nameserver %s\n" "${NS1}"
[ -n "${NS2}" ] && printf "nameserver %s\n" "${NS2}"
[ -n "${NS3}" ] && printf "nameserver %s\n" "${NS3}"
} > "${RESOLVCONF}"
fi