Cri

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

Usage

The central concept in Cri is the command, which has option definitions as well as code for actually executing itself. In Cri, the commandline 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   :m, :more,  'do even more stuff'
  option :s, :stuff, 'specify stuff to do', :argument => :required

  run do |opts, args, cmd|
    stuff = opts[: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 commandline tool itself), the command could be called like this:

command.run(ARGS)

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
    -m --more      do even more stuff
    -s --stuff     specify stuff to do

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 commandline 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.

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   :m, :more,  'do even more stuff'
option :s, :stuff, 'specify stuff to do', :argument => :required

Options can be defined using the following methods:

• Cri::CommandDSL#option or Cri::CommandDSL#opt
• Cri::CommandDSL#flag (implies forbidden argument)
• Cri::CommandDSL#required (implies required argument)
• Cri::CommandDSL#optional (implies optional argument)

Each of the above methods also take a block, which will be executed when the option is found. The argument to the block are the option value (true in case the option does not have an argument) and the command.

The last part of the command defines the execution itself:

run do |opts, args, cmd|
  stuff = opts[: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.

Commands can have subcommands. For example, the git commandline 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

Contributors

(In alphabetical order)

• Toon Willems

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