SteamCMD does not have a “list all” command to get all command options within SteamCMD. Instead you have to use find . This script outputs all the commands available and saves it to a file.
Simply download the script and run it.
wget https://raw.githubusercontent.com/dgibbs64/SteamCMD-Commands-List/master/steamcmdcommands.sh;chmod +x steamcmdcommands.sh;./steamcmdcommands.sh List
You can get the output without using the script.
My server now checks daily for updates and posts them to this repo. So this list will always be up-to-date.