Is there a "standard" format for command line/shell help text?

If not, is there a de facto standard? Basically I'm writing a command line help text like so:

usage: app_name [options] required_input required_input2
  options:
    -a, --argument     Does something
    -b required     Does something with "required"
    -c, --command required     Something else
    -d [optlistitem1 optlistitem 2 ... ]     Something with list

I made that from basically just reading the help text of various tools, but is there a list of guidelines or something? For example, do I use square brackets or parentheses? How to use spacing? What if the argument is a list?

Typically, your help output should include:

• Description of what the app does
• Usage syntax, which:
  • Uses [options] to indicate where the options go
  • arg_name for a required, singular arg
  • [arg_name] for an optional, singular arg
  • arg_name... for a required arg of which there can be many (this is rare)
  • [arg_name...] for an arg for which any number can be supplied
  • note that arg_name should be a descriptive, short name, in lower, snake case
• A nicely-formatted list of options, each:
  • having a short description
  • showing the default value, if there is one
  • showing the possible values, if that applies
  • Note that if an option can accept a short form (e.g. -l) or a long form (e.g. --list), include them together on the same line, as their descriptions will be the same
• Brief indicator of the location of config files or environment variables that might be the source of command line arguments, e.g. GREP_OPTS
• If there is a man page, indicate as such, otherwise, a brief indicator of where more detailed help can be found

Note further that it's good form to accept both -h and --help to trigger this message and that you should show this message if the user messes up the command-line syntax, e.g. omits a required argument.