proxycheck(1) on Linux
The text 601304ec4047, as Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch) shipped it.
open proxy server checker
Flags it lists
-
-D -
-M -
-a -
-b -
-h -
-i -
-m -
-n -
-p -
-s -
-t -
-v -
-x