Cri

Cri is a library for building easy-to-use command-line tools with support for nested commands.

Requirements

Cri requires Ruby 2.5 or newer (including Ruby 3.x).

Compatibility policy

Cri is guaranteed to be supported on any officially supported Ruby version, as well as the version of Ruby that comes by default on

• the last two Ubuntu LTS releases
• the last two major macOS releases

Usage

The central concept in Cri is the command, which has option definitions as well as code for actually executing itself. In Cri, the command-line tool itself is a command as well.

Here’s a sample command definition:

command = Cri::Command.define do
  name        'dostuff'
  usage       'dostuff [options]'
  aliases     :ds, :stuff
  summary     'does stuff'
  description 'This command does a lot of stuff. I really mean a lot.'

  flag   :h,  :help,  'show help for this command' do |value, cmd|
    puts cmd.help
    exit 0
  end
  flag   nil, :more,  'do even more stuff'
  option :s,  :stuff, 'specify stuff to do', argument: :required

  run do |opts, args, cmd|
    stuff = opts.fetch(:stuff, 'generic stuff')
    puts "Doing #{stuff}!"

    if opts[:more]
      puts 'Doing it even more!'
    end
  end
end

To run this command, invoke the #run method with the raw arguments. For example, for a root command (the command-line tool itself), the command could be called like this:

command.run(ARGV)

Each command has automatically generated help. This help can be printed using Cri::Command#help; something like this will be shown:

usage: dostuff [options]

does stuff

    This command does a lot of stuff. I really mean a lot.

options:

    -h --help      show help for this command
       --more      do even more stuff
    -s --stuff     specify stuff to do

General command metadata

Let’s disect the command definition and start with the first five lines:

name        'dostuff'
usage       'dostuff [options]'
aliases     :ds, :stuff
summary     'does stuff'
description 'This command does a lot of stuff. I really mean a lot.'

These lines of the command definition specify the name of the command (or the command-line tool, if the command is the root command), the usage, a list of aliases that can be used to call this command, a one-line summary and a (long) description. The usage should not include a “usage:” prefix nor the name of the supercommand, because the latter will be automatically prepended.

Aliases don’t make sense for root commands, but for subcommands they do.

Command-line options

The next few lines contain the command’s option definitions:

flag   :h,  :help,  'show help for this command' do |value, cmd|
  puts cmd.help
  exit 0
end
flag   nil, :more,  'do even more stuff'
option :s,  :stuff, 'specify stuff to do', argument: :required

The most generic way of definition an option is using either #option or #opt. It takes the following arguments:

1. a short option name
2. a long option name
3. a description
4. optional extra parameters
   • argument: (default: :forbidden)
   • transform:
   • default:
   • multiple: (default: false)
5. optionally, a block

In more detail:

• The short option name is a symbol containing one character, to be used in single-dash options, e.g. :f (corresponds to -f). The long option name is a symbol containing a string, to be used in double-dash options, e.g. :force (corresponds to --force). Either the short or the long option name can be nil, but not both.

• The description is a short, one-line text that shows up in the command’s help. For example, the -v/--version option might have the description show version information and quit.

• The extra parameters, argument:, multiple:, default:, and transform:, are described in the sections below.

• The block, if given, will be executed when the option is found. The arguments to the block are the option value (true in case the option does not have an argument) and the command.

There are several convenience methods that are alternatives to #option/#opt:

• #flag sets argument: to :forbidden
• (deprecated) #required sets argument: to :required -- deprecated because #required suggests that the option is required, wich is incorrect; the argument is required.)
• (deprecated) #optional sets argument: to :optional -- deprecated because #optional looks too similar to #option.

Forbidden, required, and optional arguments (argument:)

The :argument parameter can be set to :forbidden, :required, or :optional.

• :forbidden means that when the option is present, the value will be set to true, and false otherwise. For example:

  option :f, :force, 'push with force', argument: :forbidden
  
  run do |opts, args, cmd|
    puts "Force? #{opts[:force]}"
  end

  % ./push mypackage.zip
  Force? false
  
  % ./push --force mypackage.zip
  Force? true

  :argument is set to :forbidden by default.

• :required means that the option must be followed by an argument, which will then be treated as the value for the option. It does not mean that the option itself is required. For example:

  option :o, :output, 'specify output file', argument: :required
  option :f, :fast, 'fetch faster', argument: :forbidden
  
  run do |opts, args, cmd|
    puts "Output file: #{opts[:output]}"
  end

  % ./fetch http://example.com/source.zip
  Output file: nil
  
  % ./fetch --output example.zip http://example.com/source.zip
  Output file: example.zip
  
  % ./fetch http://example.com/source.zip --output
  fetch: option requires an argument -- output
  
  % ./fetch --output --fast http://example.com/source.zip
  fetch: option requires an argument -- output

• :optional means that the option can be followed by an argument. If it is, then the argument is treated as the value for the option; if it isn’t, the value for the option will be true. For example:

  option :o, :output, 'specify output file', argument: :optional
  option :f, :fast, 'fetch faster', argument: :forbidden
  
  run do |opts, args, cmd|
    puts "Output file: #{opts[:output]}"
  end

  % ./fetch http://example.com/source.zip
  Output file: nil
  
  % ./fetch --output example.zip http://example.com/source.zip
  Output file: example.zip
  
  % ./fetch http://example.com/source.zip --output
  Output file: true
  
  % ./fetch --output --fast http://example.com/source.zip
  Output file: true

Transforming options (transform:)

The :transform parameter specifies how the value should be transformed. It takes any object that responds to #call:

option :p, :port, 'set port', argument: :required,
  transform: -> (x) { Integer(x) }

The following example uses #Integer to transform a string into an integer:

option :p, :port, 'set port', argument: :required, transform: method(:Integer)

The following example uses a custom object to perform transformation, as well as validation:

class PortTransformer
  def call(str)
    raise ArgumentError unless str.is_a?(String)
    Integer(str).tap do |int|
      raise unless (0x0001..0xffff).include?(int)
    end
  end
end

option :p, :port, 'set port', argument: :required, transform: PortTransformer.new

Default values are not transformed:

option :p, :port, 'set port', argument: :required, default: 8080, transform: PortTransformer.new

Options with default values (default:)

The :default parameter sets the option value that will be used if the option is passed without an argument or isn't passed at all:

option :a, :animal, 'add animal', default: 'giraffe', argument: :optional

In the example above, the value for the --animal option will be the string "giraffe", unless otherwise specified:

OPTIONS
    -a --animal[=<value>]      add animal (default: giraffe)

If the option is not given on the command line, the options hash will not have key for this option, but will still have a default value:

option :a, :animal, 'add animal', default: 'giraffe', argument: :required

run do |opts, args, cmd|
  puts "Animal = #{opts[:animal]}"
  puts "Option given? #{opts.key?(:animal)}"
end

% ./run --animal=donkey
Animal = donkey
Option given? true

% ./run --animal=giraffe
Animal = giraffe
Option given? true

% ./run
Animal = giraffe
Option given? false

This can be useful to distinguish between an explicitly-passed-in value and a default value. In the example above, the animal option is set to giraffe in the second and third cases, but it is possible to detect whether the value is a default or not.

Multivalued options (multiple:)

The :multiple parameter allows an option to be specified more than once on the command line. When set to true, multiple option valus are accepted, and the option values will be stored in an array.

For example, to parse the command line options string -o foo.txt -o bar.txt into an array, so that options[:output] contains [ 'foo.txt', 'bar.txt' ], you can use an option definition like this:

option :o, :output, 'specify output paths', argument: :required, multiple: true

This can also be used for flags (options without arguments). In this case, the length of the options array is relevant.

For example, you can allow setting the verbosity level using -v -v -v. The value of options[:verbose].size would then be the verbosity level (three in this example). The option definition would then look like this:

flag :v, :verbose, 'be verbose (use up to three times)', multiple: true

Skipping option parsing

If you want to skip option parsing for your command or subcommand, you can add the skip_option_parsing method to your command definition and everything on your command line after the command name will be passed to your command as arguments.

command = Cri::Command.define do
  name        'dostuff'
  usage       'dostuff [args]'
  aliases     :ds, :stuff
  summary     'does stuff'
  description 'This command does a lot of stuff, but not option parsing.'

  skip_option_parsing

  run do |opts, args, cmd|
    puts args.inspect
  end
end

When executing this command with dostuff --some=value -f yes, the opts hash that is passed to your run block will be empty and the args array will be ["--some=value", "-f", "yes"].

Argument parsing

Cri supports parsing arguments, as well as parsing options. To define the parameters of a command, use #param, which takes a symbol containing the name of the parameter. For example:

command = Cri::Command.define do
  name        'publish'
  usage       'publish filename'
  summary     'publishes the given file'
  description 'This command does a lot of stuff, but not option parsing.'

  flag :q, :quick, 'publish quicker'
  param :filename

  run do |opts, args, cmd|
    puts "Publishing #{args[:filename]}…"
  end
end

The command in this example has one parameter named filename. This means that the command takes a single argument, named filename.

As with options, parameter definitions take transform:, which can be used for transforming and validating arguments:

param :port, transform: method(:Integer)

(Why the distinction between argument and parameter? A parameter is a name, e.g. filename, while an argument is a value for a parameter, e.g. kitten.jpg.)

Allowing arbitrary arguments

If no parameters are specified, Cri performs no argument parsing or validation; any number of arguments is allowed.

command = Cri::Command.define do
  name        'publish'
  usage       'publish [filename...]'
  summary     'publishes the given file(s)'
  description 'This command does a lot of stuff, but not option parsing.'

  flag :q, :quick, 'publish quicker'

  run do |opts, args, cmd|
    args.each do |arg|
      puts "Publishing #{arg}…"
    end
  end
end

% my-tool publish foo.zip bar.zip
Publishing foo.zip…
Publishing bar.zip…
%

Forbidding any arguments

To explicitly specify that a command has no parameters, use #no_params:

name        'reset'
usage       'reset'
summary     'resets the site'
description '…'
no_params

run do |opts, args, cmd|
  puts "Resetting…"
end

% my-tool reset x
reset: incorrect number of arguments given: expected 0, but got 1
% my-tool reset
Resetting…
%

A future version of Cri will likely make #no_params the default behavior.

The run block

The last part of the command defines the execution itself:

run do |opts, args, cmd|
  stuff = opts.fetch(:stuff, 'generic stuff')
  puts "Doing #{stuff}!"

  if opts[:more]
    puts 'Doing it even more!'
  end
end

The +Cri::CommandDSL#run+ method takes a block with the actual code to execute. This block takes three arguments: the options, any arguments passed to the command, and the command itself.

The command runner

Instead of defining a run block, it is possible to declare a class, the command runner class that will perform the actual execution of the command. This makes it easier to break up large run blocks into manageable pieces.

name 'push'
option :f, :force, 'force'
param :filename

class MyRunner < Cri::CommandRunner
  def run
    puts "Pushing #{arguments[:filename]}…"
    puts "… with force!" if options[:force]
  end
end

runner MyRunner

To create a command runner, subclass Cri::CommandRunner, and define a #run method with no params. Inside the #run block, you can access options and arguments. Lastly, to connect the command to the command runner, call #runner with the class of the command runner.

Here is an example interaction with the example command, defined above:

% push
push: incorrect number of arguments given: expected 1, but got 0

% push a
Pushing a…

% push -f
push: incorrect number of arguments given: expected 1, but got 0

% push -f a
Pushing a…
… with force!

Subcommands

Commands can have subcommands. For example, the git command-line tool would be represented by a command that has subcommands named commit, add, and so on. Commands with subcommands do not use a run block; execution will always be dispatched to a subcommand (or none, if no subcommand is found).

To add a command as a subcommand to another command, use the Cri::Command#add_command method, like this:

root_cmd.add_command(cmd_add)
root_cmd.add_command(cmd_commit)
root_cmd.add_command(cmd_init)

You can also define a subcommand on the fly without creating a class first using Cri::Command#define_command (name can be skipped if you set it inside the block instead):

root_cmd.define_command('add') do
  # option ...
  run do |opts, args, cmd|
    # ...
  end
end

You can specify a default subcommand. This subcommand will be executed when the command has subcommands, and no subcommands are otherwise explicitly specified:

default_subcommand 'compile'

Loading commands from separate files

You can use Cri::Command.load_file to load a command from a file.

For example, given the file commands/check.rb with the following contents:

name        'check'
usage       'check'
summary     'runs all checks'
description '…'

run do |opts, args, cmd|
  puts "Running checks…"
end

To load this command:

Cri::Command.load_file('commands/check.rb')

Cri::Command.load_file expects the file to be in UTF-8.

You can also use it to load subcommands:

root_cmd = Cri::Command.load_file('commands/nanoc.rb')
root_cmd.add_command(Cri::Command.load_file('commands/comile.rb'))
root_cmd.add_command(Cri::Command.load_file('commands/view.rb'))
root_cmd.add_command(Cri::Command.load_file('commands/check.rb'))

Automatically inferring command names

Pass infer_name: true to Cri::Command.load_file to use the file basename as the name of the command.

For example, given a file commands/check.rb with the following contents:

usage       'check'
summary     'runs all checks'
description '…'

run do |opts, args, cmd|
  puts "Running checks…"
end

To load this command and infer the name:

cmd = Cri::Command.load_file('commands/check.rb', infer_name: true)

cmd.name will be check, derived from the filename.

Contributors

• Bart Mesuere
• Ken Coar
• Tim Sharpe
• Toon Willems

Thanks for Lee “injekt” Jarvis for Slop, which has inspired the design of Cri 2.0.