The answer to the &quot;knowing what options are&quot; is auto-complete [0], [1]. (Almost) nobody knows all the commands by heart.<p>[0] <a href="http:&#x2F;&#x2F;www.cisco.com&#x2F;c&#x2F;en&#x2F;us&#x2F;td&#x2F;docs&#x2F;security&#x2F;fwsm&#x2F;fwsm31&#x2F;command&#x2F;reference&#x2F;fwsm_ref&#x2F;usecli.html#wp1046291" rel="nofollow">http:&#x2F;&#x2F;www.cisco.com&#x2F;c&#x2F;en&#x2F;us&#x2F;td&#x2F;docs&#x2F;security&#x2F;fwsm&#x2F;fwsm31&#x2F;co...</a><p>[1] <a href="http:&#x2F;&#x2F;zsh.sourceforge.net&#x2F;Doc&#x2F;Release&#x2F;Completion-System.html" rel="nofollow">http:&#x2F;&#x2F;zsh.sourceforge.net&#x2F;Doc&#x2F;Release&#x2F;Completion-System.htm...</a>