Ask HN: Best Practices for CLI sub-command, argument, option, flag, etc. design?

I am looking for any insights or resources on best practices surrounding cli application design. There is a lot of variance out there in how tools use sub-commands, arguments, options, flags, etc. Some tools like git use nested sub-commands to distinguish between operations, while others like curl use options to accomplish the same purpose. Sometimes flags are mnemonic, but many times that's not possible because of the sheer number of flags. Some tools keep "long option" names short ("--list") while others may have multiple words ("--list-software-updates"). There's more but, I'll stop now to keep from rambling.

I did a cursory search and found a few seemingly universal guidelines, though none of them spoke to how arguments and options should be used.

* use stdout and stderr appropriately (i.e., don't write messages to the user to stdout) * use exit codes to indicate success / failure cases * ensure output is consistent and easily parsed by other cli tools

What do you like? What do you hate? I would love to hear your thoughts on what style choices make for a more ergonomic cli tool.