diff --git a/nhentai/cmdline.py b/nhentai/cmdline.py
index 7621715..624b9ab 100644
--- a/nhentai/cmdline.py
+++ b/nhentai/cmdline.py
@@ -30,9 +30,12 @@ def banner():
 
 
 def cmd_parser():
-    parser = OptionParser()
-    parser.add_option('--download', dest='is_download', action='store_true', help='download doujinshi or not')
-    parser.add_option('--show-info', dest='is_show', action='store_true', help='just show the doujinshi information.')
+    parser = OptionParser('\nnhentai --search [keyword] --download'
+                          '\nNHENTAI=http://h.loli.club nhentai --id [ID ...]'
+                          '\n\nEnvironment Variable:\n'
+                          'NHENTAI                 nhentai mirror url')
+    parser.add_option('--download', dest='is_download', action='store_true', help='download doujinshi (for search result)')
+    parser.add_option('--show-info', dest='is_show', action='store_true', help='just show the doujinshi information')
     parser.add_option('--id', type='string', dest='id', action='store', help='doujinshi ids set, e.g. 1,2,3')
     parser.add_option('--search', type='string', dest='keyword', action='store', help='search doujinshi by keyword')
     parser.add_option('--page', type='int', dest='page', action='store', default=1,
diff --git a/nhentai/downloader.py b/nhentai/downloader.py
index c46c5e6..737a409 100644
--- a/nhentai/downloader.py
+++ b/nhentai/downloader.py
@@ -31,6 +31,8 @@ class Downloader(Singleton):
         try:
             with open(os.path.join(folder, base_filename.zfill(3) + extension), "wb") as f:
                 response = request('get', url, stream=True, timeout=self.timeout)
+                if response.status_code != 200:
+                    logger.warning('Warning: url: {} return status code 404'.format(url))
                 length = response.headers.get('content-length')
                 if length is None:
                     f.write(response.content)