route-update.sh: add --help with detailed parameter descriptions

router/route-update.sh

@@ -6,6 +6,7 @@
 #        route-update.sh --add IP|DOMAIN GROUP
 #        route-update.sh --del IP|DOMAIN GROUP
 #        route-update.sh --flush GROUP
+#        route-update.sh --help
 
 cd "$(dirname "$(realpath "$0")")" || exit
 
@@ -27,6 +28,61 @@ ADD_DEL_TARGET=
 ADD_DEL_GROUP=
 FLUSH_GROUP=
 
+show_help()
+{
+    cat <<'HELP'
+route-update.sh — declarative policy routing via directory-based config
+
+Reads routes.d/ (IPv4) and routes6.d/ (IPv6) directories. Each subdirectory
+is a route group containing gateway, table, and .list symlink files.
+
+MODES OF OPERATION:
+  (no args)       Process all groups, skip unchanged (default mode).
+                  Detects changes via MD5 hash of .list + gateway + table files.
+                  Automatically reloads groups if ip rules/routes are lost
+                  or route count drops more than 1% from expected.
+
+  --resolve       Re-resolve DNS in all groups. Routes are reloaded only
+                  if resolved IPs actually changed.
+
+  --force         Reload all groups unconditionally (flush + reload).
+
+  --show          Dry-run: show what would be done without making changes.
+                  Can be combined with other flags.
+
+  --set-rules     Only create ip rules for all groups (no route loading).
+                  Useful after network restart to restore rules quickly.
+
+  --flush GROUP   Flush all routes in the specified group's table and exit.
+
+  --add IP|DOMAIN GROUP
+                  Add a route for IP or domain to the group immediately.
+                  Domains are resolved to IPs first. Does not modify .list files.
+
+  --del IP|DOMAIN GROUP
+                  Remove a route for IP or domain from the group's table.
+
+  --verbose, -v   Show detailed progress: hashes, route counts, skip reasons.
+                  Can be combined with any mode.
+
+  --help, -h      Show this help and exit.
+
+DIRECTORY STRUCTURE:
+  routes.d/GROUP/gateway    Gateway IP(s), one per line. "default" = default gw.
+                            Multiple lines = multipath (per-flow balancing).
+  routes.d/GROUP/table      Routing table number. ip rule pref = table × 10.
+  routes.d/GROUP/*.list     Symlinks to files with IPs, subnets, or domains.
+  routes6.d/                Same structure for IPv6 groups.
+
+EXAMPLES:
+  ./route-update.sh                    # normal run
+  ./route-update.sh --resolve -v       # re-resolve DNS, verbose
+  ./route-update.sh --add example.com egw
+  ./route-update.sh --flush ogw
+HELP
+    exit 0
+}
+
 while [ -n "$1" ] ; do
     case "$1" in
         --force)     FORCE=1 ;;
@@ -34,6 +90,7 @@ while [ -n "$1" ] ; do
         --show)      SHOW=1 ;;
         --set-rules) SET_RULES=1 ;;
         --verbose|-v) VERBOSE=1 ;;
+        --help|-h)   show_help ;;
         --flush)     FLUSH_GROUP="$2" ; shift ;;
         --add)       ACTION=add ; ADD_DEL_TARGET="$2" ; ADD_DEL_GROUP="$3" ; shift 2 ;;
         --del)       ACTION=del ; ADD_DEL_TARGET="$2" ; ADD_DEL_GROUP="$3" ; shift 2 ;;