Blog - Command-line interface description language in Perl5

I released to CPAN! is perl port of [docopt].

docopt helps you: analyze SYNOPSIS section in your CLI tool's pod! When you write SYNOPSIS to describe CLI tools usage, then you got a working code.

docopt is based on conventions that are used for decades in help messages and man pages for program interface description. Interface description in docopt is such a help message, but formalized. Here is an example:

Naval Fate.

  naval_fate ship new <name>...
  naval_fate ship <name> move <x> <y> [--speed=<kn>]
  naval_fate ship shoot <x> <y>
  naval_fate mine (set|remove) <x> <y> [--moored|--drifting]
  naval_fate -h | --help
  naval_fate --version

  -h --help     Show this screen.
  --version     Show version.
  --speed=<kn>  Speed in knots [default: 10].
  --moored      Moored (anchored) mine.
  --drifting    Drifting mine.

The example describes interface of executable naval_fate, which can be invoked with different combinations of commands (ship, new, move, etc.), options (-h, --help, --speed=, etc.) and positional arguments (, , ).

Example uses brackets "[ ]", parens "( )", pipes "|" and ellipsis "..." to describe optional, required, mutually exclusive, and repeating elements. Together, these elements form valid usage patterns, each starting with program's name naval_fate.

Below the usage patterns, there is a list of options with descriptions. They describe whether an option has short/long forms (-h, --help), whether an option has an argument (--speed=), and whether that argument has a default value ([default: 10]).

docopt implementation will extract all that information and generate a command-line arguments parser, with text of the example above being the help message, which is shown to a user when the program is invoked with -h or --help options.