knock(1) on Linux
The text 2e455c4e3b9a, as Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch) shipped it.
port-knock client
Flags it lists
-
--delay -
--help -
--udp -
--verbose -
--version -
-V -
-d -
-h -
-u -
-v