dhcpcd-hooks/29-lookup-hostname

# Lookup the hostname in DNS if not set

lookup_hostname()
{
	[ -z "$new_ip_address" ] && return 1
	local h=
	# Silly ISC programs love to send error text to stdout
	if type dig >/dev/null 2>&1; then
		h=$(dig +short -x $new_ip_address)
		if [ $? = 0 ]; then
			echo "$h" | sed 's/\.$//'
			return 0
		fi
	elif type host >/dev/null 2>&1; then
		h=$(host $new_ip_address)
		if [ $? = 0 ]; then 
			echo "$h" \
			| sed 's/.* domain name pointer \(.*\)./\1/'
			return 0
		fi
	fi
	return 1
}

set_hostname()
{
	if [ -z "$new_host_name" -a -z "$new_fqdn_name" ]; then
		export new_host_name="$(lookup_hostname)"
	fi
}

if $if_up; then
	set_hostname
fi