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? Thanks!