diff --git a/nhentai/cmdline.py b/nhentai/cmdline.py
index 9687d71..6a171b1 100644
--- a/nhentai/cmdline.py
+++ b/nhentai/cmdline.py
@@ -213,7 +213,7 @@ def cmd_parser():
             _ = [i.strip() for i in f.readlines()]
             args.id = set(int(i) for i in _ if i.isdigit())
 
-    if (args.is_download or args.is_show) and not args.id and not args.keyword and not args.favorites:
+    if (args.is_download or args.is_show) and not args.id and not args.keyword and not args.favorites and not args.artist:
         logger.critical('Doujinshi id(s) are required for downloading')
         parser.print_help()
         sys.exit(1)
diff --git a/nhentai/utils.py b/nhentai/utils.py
index bedaaea..434bcb0 100644
--- a/nhentai/utils.py
+++ b/nhentai/utils.py
@@ -166,6 +166,9 @@ def generate_main_html(output_dir='./'):
 def generate_cbz(output_dir='.', doujinshi_obj=None, rm_origin_dir=False, write_comic_info=True, move_to_folder=False):
     if doujinshi_obj is not None:
         doujinshi_dir = os.path.join(output_dir, doujinshi_obj.filename)
+        if os.path.exists(doujinshi_dir+".cbz"):
+            logger.warning(f'Comic Book CBZ file exists, skip "{doujinshi_dir}"')
+            return
         if write_comic_info:
             serialize_comic_xml(doujinshi_obj, doujinshi_dir)
         cbz_filename = os.path.join(os.path.join(doujinshi_dir, '..'), f'{doujinshi_obj.filename}.cbz')