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

Question

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.

Take a look at docopt. It is a formal standard for documenting (and automatically parsing) command line arguments.

For example...

Usage:
  my_program command --option <argument>
  my_program [<optional-argument>]
  my_program --another-option=<with-argument>
  my_program (--either-that-option | <or-this-argument>)
  my_program <repeating-argument> <repeating-argument>...

I think there is no standard syntax for command line usage, but most use this convention:

Microsoft Command-Line Syntax, IBM has similar Command-Line Syntax

---

• Text without brackets or braces

  Items you must type as shown
  
  

• <Text inside angle brackets>

  Placeholder for which you must supply a value
  
  

• [Text inside square brackets]

  Optional items
  
  

• {Text inside braces}

  Set of required items; choose one
  
  

• Vertical bar {a|b}

  Separator for mutually exclusive items; choose one
  
  

• Ellipsis <file> …

  Items that can be repeated
  
  

We are running Linux, a mostly POSIX-compliant OS. POSIX standards it should be: Utility Argument Syntax.

• An option is a hyphen followed by a single alphanumeric character, like this: -o.
• An option may require an argument (which must appear immediately after the option); for example, -o argument or -oargument.
• Options that do not require arguments can be grouped after a hyphen, so, for example, -lst is equivalent to -t -l -s.
• Options can appear in any order; thus -lst is equivalent to -tls.
• Options can appear multiple times.
• Options precede other nonoption arguments: -lst nonoption.
• The -- argument terminates options.
• The - option is typically used to represent one of the standard input streams.

The GNU Coding Standard is a good reference for things like this. This section deals with the output of --help. In this case it is not very specific. You probably can't go wrong with printing a table showing the short and long options and a succinct description. Try to get the spacing between all arguments right for readability. You probably want to provide a man page (and possibly an info manual) for your tool to provide a more elaborate explanation.

Microsoft has their own Command Line Standard specification:

This document is focused at developers of command line utilities. Collectively, our goal is to present a consistent, composable command line user experience. Achieving that allows a user to learn a core set of concepts (syntax, naming, behaviors, etc) and then be able to translate that knowledge into working with a large set of commands. Those commands should be able to output standardized streams of data in a standardized format to allow easy composition without the burden of parsing streams of output text. This document is written to be independent of any specific implementation of a shell, set of utilities or command creation technologies; however, Appendix J - Using Windows Powershell to implement the Microsoft Command Line Standard shows how using Windows PowerShell will provide implementation of many of these guidelines for free.