Fix gravityDB check

piholeFTL exposes configuration to relocate/rename gravityDB so
we cannot just check a hard coded location. This commit greps
pihole-FTL.conf for a custom location. Since pihole-FTL.conf
will eventually be replaced by TOML, some verbosity is added to
denote what config file is being checked and what location it
ultimately ended up checking.

Signed-off-by: D.Rect <48034372+DistractionRectangle@users.noreply.github.com>

s6/debian-root/etc/cont-init.d/20-start.sh

@@ -14,9 +14,19 @@ $bashCmd /start.sh
 if [ -n "$PYTEST" ]; then
     sed -i 's/^gravity_spinup$/#gravity_spinup # DISABLED FOR PYTEST/g' "$(which gravity.sh)"
 fi
-if [ -z "$SKIPGRAVITYONBOOT" ] || [ ! -f /etc/pihole/gravity.db ]; then
+
+gravityDBfile="/etc/pihole/gravity.db"
+config_file="/etc/pihole/pihole-FTL.conf"
+# make a point to mention which config file we're checking, as breadcrumb to revisit if/when pihole-FTL.conf is succeeded by TOML
+echo "  Checking if custom gravity.db is set in ${config_file}"
+if [[ -f "${config_file}" ]]; then
+    gravityDBfile="$(grep --color=never -Po "^GRAVITYDB=\K.*" "${config_file}" 2> /dev/null || echo "/etc/pihole/gravity.db")"
+fi
+
+
+if [ -z "$SKIPGRAVITYONBOOT" ] || [ ! -e "${gravityDBfile}" ]; then
     if [ -n "$SKIPGRAVITYONBOOT" ];then
-        echo "  SKIPGRAVITYONBOOT is set, however no gravity.db exists (Likely due to a fresh volume). This is a required file for Pi-hole to operate."
+        echo "  SKIPGRAVITYONBOOT is set, however ${gravityDBfile} does not exist (Likely due to a fresh volume). This is a required file for Pi-hole to operate."
         echo "  Ignoring SKIPGRAVITYONBOOT on this occaision."
     fi