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

Question

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?

Answer 1

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

Microsoft Command-Line Syntax (IBM also had similar syntax, but the link is no more valid):

---

• text without brackets or braces for items you must type

  Ex: ls

• <placeholder for a value>

  Ex: cat <file>, <file> should be replace by the path of the file

• [optional]

  Ex: ls [-l] can be ls or ls -l

• {a|b} for mutually exclusive items

  Ex: ip {link|addr} can be ip link or ip addr

• <file> ... for items can be repeated

  Ex: cat <file> ... can be cat a.txt b.txt c.txt

Answer 2

I use the CSS formal notation for this.

Component values may be arranged into property values as follows:

• Several juxtaposed words mean that all of them must occur, in the given order.
• A bar (|) separates two or more alternatives: exactly one of them must occur.
• A double bar (||) separates two or more options: one or more of them must occur, in any order.
• A double ampersand (&&) separates two or more components, all of which must occur, in any order.
• Brackets ([ ]) are for grouping.

Juxtaposition is stronger than the double ampersand, the double ampersand is stronger than the double bar, and the double bar is stronger than the bar. Thus, the following lines are equivalent:

    a b   |   c ||   d &&   e f
  [ a b ] | [ c || [ d && [ e f ]]]

Every type, keyword, or bracketed group may be followed by one of the following modifiers:

• An asterisk (*) indicates that the preceding type, word, or group occurs zero or more times.
• A plus (+) indicates that the preceding type, word, or group occurs one or more times.
• A question mark (?) indicates that the preceding type, word, or group is optional.
• A pair of numbers in curly braces ({A,B}) indicates that the preceding type, word, or group occurs at least A and at most B times.

If you need examples, see Formal definition sections on MDN; here is one for font: https://developer.mozilla.org/en-US/docs/Web/CSS/font#formal_syntax.

And here is a simple example from my own Pandoc's cheat sheet:

$ pandoc <input_file>.md --from [markdown|commonmark_x][-smart]? --to html --standalone --table-of-contents? --number-sections? [--css <style_sheet>.css]? --output <output_file>.html

Answer 3

It may be a bit off-topic, but I once wrote two small tools that make creation and maintenance of command line tools help pages more efficient:

• The MAIN DOCLET that generates an HTML document for the main method of a Java program by processing Javadoc comments in the source code
• The HTML2TXT tool that formats an HTML document as a plain text (which is what we want our help texts)

I integrate these two tools in the MAVEN build process of my programs so they execute automatically on every build.

For example:

• The relevant source file of my ZZFIND tool
• The POM file that builds the project (and runs the two tools mentioned above)
• Example output when ZZFIND is run with the --help command line option

Hope this is useful for others!?

Answer 4

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.

Answer 5

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.

Answer 6

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>...

Answer 7

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.

Answer 8

yes, you're on the right track.

yes, square brackets are the usual indicator for optional items.

Typically, as you have sketched out, there is a commandline summary at the top, followed by details, ideally with samples for each option. (Your example shows lines in between each option description, but I assume that is an editing issue, and that your real program outputs indented option listings with no blank lines in between. This would be the standard to follow in any case.)

A newer trend, (maybe there is a POSIX specification that addresses this?), is the elimination of the man page system for documentation, and including all information that would be in a manpage as part of the program --help output. This extra will include longer descriptions, concepts explained, usage samples, known limitations and bugs, how to report a bug, and possibly a 'see also' section for related commands.

I hope this helps.

Answer 9

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.