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The option parser.
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Clive lets you easily create command line interfaces, from simply checking for the presence of a few flags to multiple command behemoths.


Install with:

$ gem install clive


NOTE: Throughout I will be using the new 1.9 {a: b} hash syntax, obviously the old {:a => b} syntax still works and can be used if you want or where 1.8 compatibility is needed.

Clive is generally used by creating a class to hold your command line interface as shown in the example below.

# my_app.rb
require 'clive'

module MyApp
  VERSION = "0.1.4"

  # some code

  class CLI < Clive
    config name: 'myapp'

    opt :v, :version, 'Display the current version' do
      puts MyApp::Version
      exit 0

result =

Then run with my_app.rb --version to display the version for MyApp. By default #run will use ARGV as the input, but you can pass something else if necessary.

.run returns an instance of Clive::StructHash by default, this is a hybrid hash and struct allowing you to access keys by calling them or using #[]. It also stores any extra arguments that may have been passed which can be accessed with #args or #[:args].

class CLI
  opt :n, :name, args: '<first> <last>'
  opt :age, arg: '<age>', as: Integer

result = %w(--name John Doe --age 23 "I like coding!")

bio  = result.args #=> "I like coding!"
name = #=> ['John', 'Doe']
age  = result.age  #=> 23

This simple example shows how Clive can handle multiple arguments, casting to types (Integer in this case) and how extra arguments are stored in #args.


Options are defined using #opt and/or #option they can have short (-a) or long names (--abc) and can also have arguments. The description can be given as an argument to #opt or can be defined before it using #desc (or #description).

opt :v, :version, 'Display the current version' do
  # ...

# is equivalent to

desc 'Display the current version'
opt :v, :version do
  # ...

Longer option names, containing _s are called by replacing the _ with a - so

opt :longer_name_than_expected

would be called with --longer-name-than-expected.

Boolean Options

Boolean options are options which can be called with a no- prefix, which then passes false to the block/state. For example,

bool :a, :auto

Can be called with -a or --auto which would set :auto to true, or --no-auto which sets :auto to false. If a block is given you can retrieve the truth by adding block parameters or using the truth variable which is automatically set.

bool :a, :auto do |t|
  puts t

# OR

bool :a, :auto do
  puts truth

Boolean options must have a long name.


Commands are defined using #command. They can be used to group related Options together acting like a namespace, but Commands are fully featured Options so can also take arguments. Commands can be created with multiple names.

desc 'Create a new project'
command :new, :create, arg: '<dir>', as: Pathname do

  # Set the default type to use
  set :type, :basic

  desc 'Select type of template to use'
  opt :type, arg: '<choice>', in: %w(basic complex custom), as: Symbol

  bool :force, 'Force overwrite'

  action do
    puts "Creating #{get :type} in #{dir}"
    # do writing

The above example also shows using the #set and #get methods, these allow you to set and get values from the state. Also note how the logic for executing the new command is given to #action, this is because the block passed to #command is used for option definition.


As previously talked about Options and Commands can take arguments by passing a hash with the key :arg or :args.

opt :size, args: '<height> <width>'

The option --size takes two arguments. These would be saved to state as an array, for instance running with --size 10 40 would set :size to ['10', '40'].

Arguments can be made optional by enclosing one or more arguments with [ and ]:

# both required
opt :size, args: '<h> <w>'
# --size 10   #=> Error

# first required
opt :size, args: '<h> [<w>]'
# --size 10   #=> [10, nil]

# second required
opt :size, args: '[<h>] <w>'
# --size 10   #=> [nil, 10]

# neither required
opt :size, args: '[<h> <w>]'
# --size 10   #=> [10, nil]

You can make an argument 'infinite' by appending the name with ..., like <arg>.... Optional-ness is respected so <arg>... expects at least one argument whereas [<arg>...] takes 0 or more arguments. Infinite arguments also play well with standard arguments, and will return arrays of items even if only one argument was passed.

opt :items, :arg => '<thing>...'
# --items            #=> Error
# --items iPad       #=> ['iPad']
# --items iPad iPod  #=> ['iPad', 'iPod']

opt :items, :arg => '[<thing>...]'
# --items            #=> []
# and same as previously in other cases

opt :items, :arg => '<amount> <thing>...', :as => [Integer, nil]
# --items 5 iPad iMac  #=> [5, 'iPad', 'iMac']

There are also various options that can be passed to constrain or change the arguments. If one of the below is passed to an option with :arg or :args a generic argument called <arg> will be added.

Types (:types, :type, :kind or :as)

An argument will be checked if it matches how the type should look, then converts it to that type. For more information see lib/clive/type/definitions.rb.

opt :list, as: Array

This accepts a comma delimited list of items, --list a,b,c and sets :list to ['a', 'b', 'c'].

Matches (:matches or :match)

Allows you to say that an argument must match a regular expression (or any object which responds to #match).

opt :word, match: /^\w+$/

This accepts --word hello but not --word 123.

Withins (:withins, :within or :in)

Allows you to say that an argument must be within a passed Array, Set or Range (any object which responds to #include?).

opt :num, in: "1".."100"

This accepts --num 50 but not --num 900. The example above had to use a range of Strings because that is what is passed, you can use this with :type to use Integers.

opt :num, as: Integer, in: 1..100

Would work in the same way as the one above but return an Integer.

Defaults (:defaults or :default)

Allows you to give a default value that should be used if an argument is not given.

opt :type, default: 'house'

So --type would set :type to 'house', but --type shed would set :type to 'shed'. The default value is only set if the option is used. To set a value regardless of whether the option is used use #set in the class or commands body.

set :type, 'house'
opt :type

Would always set :type to 'house' even when --type is not used.

Constraints (:constraint or :constraint)

Allows you to constrain the argument using a Proc, this is to cover the very few events where the above options do not satisfy the requirements.

opt :long_word, constraint: -> i { i.size >= 7 }

Accepts --long-word eventually but not --long-word event. You can also pass a symbol which will have #to_proc called on it.

opt :odd, as: Integer, constraint: :odd?

This only accepts odd Integers.


All blocks passed to options or given to a command's action are run in the Runner class. This provides a few shortcuts to make life easier. Here is a quick run down with examples.

Argument Referencing

You can reference an options or commands arguments directly by name without having to use block parameters.

opt :size, args: '<height> <width>', as: [Float, Float] do # no params!
  puts "Area = #{height} * #{width} = #{height * width}"

As shown earlier the truthiness of a boolean option is set to the value truth.

Working with the State

Four fundamental methods are defined for working with the state, #get, #set, #update and #has?.

#get allows you to get values previously set.

opt :get_some_key do
  puts get(:some_key) #=> value set for :some_key

#set allows you to set values in the state.

opt :set_some_key, arg: '<value>' do
  set :some_key, value

#update allows you to modify a value in the state.

set :list, []
opt :add, arg: '<item>' do
  update :list, :<<, item

  # or using a block
  update(:list) {|l| l << item }

#has? tells you whether a value has been set for the key.

opt :has_some_key do
  puts has?(:some_key)

Help Formatters

Clive comes with two help formatters, one with colour and the other without. To use the plain formatter (colour is default), use

class CLI < Clive
  config formatter:

  # ...

To create your own formatter take a look at lib/clive/formatter.rb.


clive/output contains various monkey patches on String that allow you to easily colourise output.

puts "I'm blue".blue                     # will print blue text
puts "I'm green and bold".green.bold     # will print green and bold text
puts "Crazy".blue.l_yellow_bg.underline
# etc

Colours available: white, green, red, magenta, yellow, blue, cyan, black. Effects available: bold, underline, blink, reverse.

Light versions can be used by prepending the name with l_, ie. l_red, the light version of black is called grey.

All colours can be used as backgrounds by appending _bg, ie. red_bg, light backgrounds are as expected, l_red_bg.


Copyright (c) 2010-12 Joshua Hawxwell. See LICENSE for details.

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