docopt.cr

docopt for crystal-lang: command-line interfaces declared as help text, with everything that grows on top of them.

A fork of the original docopt.cr by chenkovsky, conformant with the official docopt test suite, that grew:

• compile-time parsing (Docopt.compile, Docopt.compile_config)
• working bash, fish and zsh completion generation, including subcommand-aware completion for dispatch tools
• the configuration layer (require "docopt/config"): YAML config files and environment variables under CLI precedence
• subcommand dispatch (require "docopt/dispatch"): git-style command trees with help, typo suggestions and exit codes
• both together (require "docopt/dispatch_config"): every command's options resolved through the full precedence chain

See the changelog for release history.

Installation

Add this to your application's shard.yml:

dependencies:
  docopt:
    github: ralsina/docopt.cr
    version: "~> 1.0"

Usage

Declare your interface as its own help text; docopt parses argv against it and hands you the values:

require "docopt"

doc = <<-DOC
  Naval Fate.

  Usage:
    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

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

options = Docopt.docopt(doc, ARGV)
if options["--version"]
  puts "naval_fate 1.0"
elsif options["ship"] && options["move"]
  speed = options["--speed"].as(String)
  puts "Moving #{options["<name>"]} to #{options["<x>"]},#{options["<y>"]} at #{speed} knots"
end

Flags parse as booleans, options with arguments as strings, repeated elements as arrays and counting flags as integers; unmatched argv prints the usage and exits (or raises Docopt::DocoptExit with exit: false).

Error Messages

Failed matches explain what went wrong instead of only dumping the usage: unknown options and unexpected arguments are named, and close typos get a "did you mean" hint computed against the declared options and commands.

$ prog --verbso
Unknown option --verbso. Did you mean --verbose?
Usage:
  prog [--verbose] [--version]
  ...

The matcher behind the hints is public and domain independent: Docopt.suggestions_for(attempted, candidates) returns the close matches (closest first, ties alphabetically, at most four, within a distance of max(size // 3, 2)).

Typed Access

Instead of .as(String) casts and their generic failures, ask the result for the type you want; a wrong ask raises a TypeMismatchError naming the option, the value and its actual type.

options = Docopt.docopt(doc, ARGV)
speed = options.string("--speed")
count = options.int("-v")              # counting flags are integers
names = options.array("<name>")
shout = options.bool("--shout")
quiet = options.string?("--output")    # nil when not given

The same questions work on ConfigOptions from the configuration layer (after precedence) and on a dispatch command's options. Note that counting flags (-vv) are Int32, not Bool.

Compile-time parsing

Docopt.docopt parses the usage text on every run, which for a program with a couple of dozen options costs a few milliseconds of startup. The usage text is almost always a constant, so it can be parsed while compiling instead:

require "docopt"

USAGE = <<-DOC
  Usage: prog [-v] <file>...

  Options:
    -v  Verbose.
  DOC

COMPILED = Docopt.compile(USAGE)
options = Docopt.match(COMPILED, ARGV)

Docopt.compile is a macro. It takes a string literal, or a constant assigned one, parses it at compile time and embeds the resulting pattern in the binary, so at runtime only the argument matching runs. An invalid usage text becomes a compilation error instead of a runtime one. Docopt.match accepts the same help, version, options_first and exit arguments as Docopt.docopt and returns the same hash.

For a 17-line usage text with 21 options, Docopt.docopt costs about 1.6 ms per call and Docopt.match on the compiled pattern about 0.02 ms.

The two halves are also available at runtime as Docopt.parse(doc), which returns a Docopt::Compiled, and Docopt.match(compiled, argv), for programs that match many argument vectors against one usage text.

A Compiled pattern also exposes what the doc declares, so layered tools (configuration files, environment variables, subcommand dispatchers) never need to re-parse the doc:

• compiled.defaults — the value every declared option parses to when absent from argv: its [default: ...] value (an array for repeated options), false for flags, nil otherwise.
• compiled.without_defaults — a copy of the pattern with declared defaults neutralized, so matching tells "given on the command line" apart from "fell back to the default". Equivalent to matching the same doc with the [default: ...] annotations stripped.

compiled = Docopt.parse(USAGE)
given = Docopt.match(compiled.without_defaults, ARGV, exit: false)
speed = given["--speed"]? || compiled.defaults["--speed"]

Configuration Layer

require "docopt/config" layers YAML configuration files and environment variables under docopt's command-line parsing, with the precedence CLI > environment > config file > docopt defaults:

require "docopt/config"

options = Docopt.docopt_config(USAGE,
  argv: ARGV,
  config_file_path: "config.yml",
  env_prefix: "MYAPP"
)

options["--verbose"] # CLI value when given, else env, else file, else default

Config keys map to options in any of three shapes (verbose, --verbose, input_file for --input-file); values are coerced to the type docopt would produce (booleans for flags, arrays for repeatable options). Environment variables map from MYAPP_INPUT_FILE-style names with the same coercion, and --print-config-style flags can dump the fully-resolved configuration as a working config file.

The usage text can be parsed once at compile time, like the core:

CONFIG = Docopt.compile_config(USAGE)
options = Docopt.docopt_config(CONFIG, argv: ARGV, env_prefix: "MYAPP")

See the docopt-config shard's README for the full tier semantics; the code and tests now live here.

Subcommand Dispatch

require "docopt/dispatch" builds git-style tools where every subcommand has its own complete docopt help text:

require "docopt/dispatch"

struct Hello < Docopt::Dispatch::Command
  @@name = "hello"
  @@doc = <<-HELP
    Says hello to the world

    Usage:
      say hello [--shout]

    Options:
      --shout  SHOUT IT
    HELP

  def run : Int32
    puts(options["--shout"] ? "HELLO WORLD" : "hello world")
    0
  end
end

Hello.register

exit(Docopt::Dispatch.main("say", ARGV))

Dispatch handles the help [COMMAND] command, -h/--help, git-style "most similar command" suggestions for typos, and exit codes (commands propagate their run return value; errors exit 1). Each command's doc is parsed once and cached (Command.compiled), so dispatching is a plain argv match. Help requests are not honored after a -- separator. This layer grew out of the polydocopt shard; its README has the full behavior table.

Dispatch composes with the completion generators: one script covers the whole command tree, with each command's options and arguments coming from its own doc, and custom completions keyed by command path ("say_hello"):

puts Docopt::Dispatch.bash_completion("say")
puts Docopt::Dispatch.fish_completion("say", {"say_hello" => "world mars"})
puts Docopt::Dispatch.zsh_completion("say")

The typo machinery is reusable: Dispatch.suggestions_for(attempted, candidates) returns the close matches for any word list (closest first, ties alphabetically, at most four, within a distance of max(size // 3, 2)), defaulting to the registered commands.

Dispatch also composes with the configuration layer: require "docopt/dispatch_config" adds Dispatch.config_main, which resolves every command's options through the full precedence chain (CLI > environment > config file > docopt defaults) before run sees them — commands keep reading options["-p"] unchanged — and supports a per-command --print-config flag:

exit(Docopt::Dispatch.config_main("say", ARGV,
  config_file_path: "~/.config/say/config.yml",
  env_prefix: "SAY",
  print_config_option: "--print-config"))

See examples/dispatch for a complete tool with completion flags.

Shell Completion Generation

docopt.cr can generate shell completion scripts for bash, fish, and zsh so that when you TAB while writing a command it will show you the possible options.

Bash Completion

The code to create a bash completion looks like this for the classic naval_fate example:

    bash_completion = Docopt.bash_completion("naval_fate", doc)

To make this available to the user you could have something like a naval_fate --completion-bash in your usage instructions and either tell the user to put this in their .bashrc:

    naval_fate --completion-bash >> ~/.bashrc

Or write it to a file and put it in /etc/bash_completion.d/:

    naval_fate --completion-bash > /etc/bash_completion.d/naval_fate

Fish Completion

For fish shell completion:

    fish_completion = Docopt.fish_completion("naval_fate", doc)

Users can install fish completions by adding to their config:

    naval_fate --completion-fish > ~/.config/fish/completions/naval_fate.fish

ZSH Completion

For zsh shell completion:

    zsh_completion = Docopt.zsh_completion("naval_fate", doc)

Users can install zsh completions by adding:

    naval_fate --completion-zsh > ~/.local/share/zsh/site-functions/_naval_fate

Or system-wide:

    naval_fate --completion-zsh > /usr/share/zsh/site-functions/_naval_fate

Custom Completions

Usually the suggestions provided by the completions are limited to flags options and files, which may not be the right thing.

Suppose you want the naval_fate ship new command to be completed with just the names from a list of famous ships. You can do that using the custom_completions argument:

    bash_completion = Docopt.bash_completion(
      "naval_fate", 
      doc, 
      {"naval_fate_ship_new" => %("Titanic 'Queen Mary' 'USS Enterprise')}
    )

The key is the name of the command and any subcommands, joined by _ (underscore). In this case, the command is naval_fate ship new.

The completion should be provided as a list of space-separated strings, and if any of them contain spaces, they should be single-quoted.

It can be made more dynamic by using instead the output of a command. For example, if the command naval_fate ship list existed, we could do this using bash ability to run commands inside other commands:

    bash_completion = Docopt.bash_completion(
      "naval_fate", 
      doc, 
      {"naval_fate_ship_new" => "$(naval_fate ship list)"}
    )

And the completion for naval_fate ship new would be the output of naval_fate ship list.

Options that take an argument have their own custom completions, keyed by the option name: after --speed (or --speed=) the values are offered, and in bash the attached form completes --speed=5-style words.

completions = {"--speed" => "5 10 15 20"}

Without a custom, the value of an option with an argument completes with file names.

Custom Completions for All Shells

The custom completion system works consistently across all three shells:

    # Define custom completions once
    completions = {
      "naval_fate_ship_new" => "$(naval_fate ship list)",
      "naval_fate_mine_set" => %("anchored drifting")
    }

    # Use with any shell
    bash_completion = Docopt.bash_completion("naval_fate", doc, completions)
    fish_completion = Docopt.fish_completion("naval_fate", doc, completions)
    zsh_completion = Docopt.zsh_completion("naval_fate", doc, completions)

This ensures consistent completion behavior regardless of which shell the user prefers.

Man Pages

If the doc is the single source of truth, it is also the manual: Docopt.man_page turns it into a roff page — the description becomes NAME and DESCRIPTION, the usage section SYNOPSIS, the declared options OPTIONS with their defaults.

puts Docopt.man_page("naval_fate", doc, version: VERSION)

A typical wiring is a --man flag writing it to stdout, or an install target putting it in share/man/man1. The output is deterministic; dates and versions come only from what you pass.

Colored Help

Help and usage output can be colored through a hook: set Docopt.colorizer to any Proc(String, String) and it runs on help text and usage-in-errors — only on terminals, and only when NO_COLOR (https://no-color.org) is unset. Docopt.colorize(text, io) applies the same gating to your own output.

For tartrazine-grade coloring, tartrazine itself ships the integration — its docopt lexer highlights the help, in-process:

require "docopt"
require "tartrazine/docopt_color"   # from the tartrazine shard

Docopt.use_tartrazine_color            # or use_tartrazine_color("gruvbox-dark")
options = Docopt.docopt(doc, ARGV)

Examples

Both are built by shards build and installed in CI; see examples/README.md.

Naval Fate CLI

The classic docopt example, with completion generation for the three shells and custom completions with dynamic content:

./bin/naval_fate --help
./bin/naval_fate --completion-bash > ~/.bash_completion.d/naval_fate

say

A subcommand-oriented tool built from the dispatch and completion layers: each command carries its own doc, and one completion script covers the whole tree:

./bin/say help
./bin/say hello --shout -p mars
./bin/say --completion-bash

Development

shards build  # Builds both examples
crystal spec  # 353 examples: unit, reference, conformance and real-shell completion tests
ameba         # Lint

The spec suite runs the official docopt conformance cases (spec/fixtures/testcases.docopt), a port of the reference unit tests, and executes generated completion scripts through real bash (fish and zsh when installed).

Contributing

1. Fork it ( https://github.com/ralsina/docopt.cr/fork )
2. Create your feature branch (git checkout -b my-new-feature)
3. Commit your changes using conventional commit messages (feat:, fix:, chore:, ...) — the changelog is generated from them
4. Push to the branch (git push origin my-new-feature)
5. Create a new Pull Request

Contributors

• chenkovsky chenkovsky.chen - creator, maintainer
• ralsina Roberto Alsina - fork maintainer