error out if there are extra command line options

CHANGES

+5157.	[bug]		Nslookup now errors out if there are extra command
+			line arguments. [GL #207]
+
 	--- 9.13.6 released ---
 5156.	[doc]		Extended and refined the section of the ARM describing

bin/dig/nslookup.c

@@ -879,6 +879,23 @@ get_next_command(void) {
 	isc_mem_free(mctx, buf);
 }
 
+ISC_PLATFORM_NORETURN_PRE static void
+usage(void) ISC_PLATFORM_NORETURN_POST;
+
+static void
+usage(void) {
+    fprintf(stderr, "Usage:\n");
+    fprintf(stderr,
+"   nslookup [-opt ...]             # interactive mode using default server\n");
+    fprintf(stderr,
+"   nslookup [-opt ...] - server    # interactive mode using 'server'\n");
+    fprintf(stderr,
+"   nslookup [-opt ...] host        # just look up 'host' using default server\n");
+    fprintf(stderr,
+"   nslookup [-opt ...] host server # just look up 'host' using 'server'\n");
+    exit(1);
+}
+
 static void
 parse_args(int argc, char **argv) {
 	bool have_lookup = false;
@@ -900,6 +917,9 @@ parse_args(int argc, char **argv) {
 				in_use = true;
 				addlookup(argv[0]);
 			} else {
+				if (argv[1] != NULL) {
+					usage();
+				}
 				set_nameserver(argv[0]);
 				check_ra = false;
 			}