Slop is a simple option parser with an easy to remember syntax and friendly API. API Documentation is available here.

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opts = Slop.parse do
  banner 'Usage: foo.rb [options]'

  on 'name=', 'Your name'
  on 'p', 'password', 'An optional password', argument: :optional
  on 'v', 'verbose', 'Enable verbose mode'

# if ARGV is `--name Lee -v`
opts.verbose?  #=> true
opts.password? #=> false
opts[:name]    #=> 'lee'
opts.to_hash   #=> {:name=>"Lee", :password=>nil, :verbose=>true}


gem install slop

Printing Help

Slop attempts to build a good looking help string to print to your users. You can see this by calling or simply puts opts.

Configuration Options

All of these options can be sent to or Slop.parse in Hash form.

  • strict - Enable strict mode. When processing unknown options, Slop will raise an InvalidOptionError. default: false.
  • help - Automatically add the --help option. default: false.
  • banner - Set this options banner text. default: nil.
  • ignore_case - When enabled, -A will look for the -a option if -A does not exist. default: false.
  • autocreate - Autocreate options on the fly. default: false.
  • arguments - Force all options to expect arguments. default: false.
  • optional_arguments - Force all options to accept optional arguments. default: false.
  • multiple_switches - When disabled, Slop will parse -abc as the option a with the argument bc rather than 3 separate options. default: true.
  • longest_flag - The longest string flag, used to aid configuring help text. default: 0.


opts = Slop.parse do
  on :list=, as: Array
# ruby run.rb --list one,two
opts[:list] #=> ["one", "two"]
# ruby run.rb --list one,two --list three
opts[:list] #=> ["one", "two", "three"]

You can also specify a delimiter and limit.

opts = Slop.parse do
  on :list=, as: Array, delimiter: ':', limit: 2
# ruby run.rb --list one:two:three
opts[:list] #=> ["one", "two:three"]


opts = Slop.parse do
  on :range=, as: Range
# ruby run.rb --range 1..10
opts[:range] #=> 1..10
# ruby run.rb --range 1...10
opts[:range] #=> 1...10
# ruby run.rb --range 1-10
opts[:range] #=> 1..10
# ruby run.rb --range 1,10
opts[:range] #=> 1..10


Slop has an 'autocreate' feature. This feature is intended to create options on the fly, without having to specify them yourself. In some case, uses this code could be all you need in your application:

# ruby run.rb --foo bar --baz --name lee
opts = Slop.parse(autocreate: true)
opts.to_hash #=> {:foo=>"bar", :baz=>true, :name=>"lee"}
opts.fetch_option(:name).expects_argument? #=> true


Slop supports git style sub-commands, like so:

opts = Slop.parse do
  on '-v', 'Print the version' do
    puts "Version 1.0"

  command 'add' do
    on :v, :verbose, 'Enable verbose mode'
    on :name, 'Your name'

    run do |opts, args|
      puts "You ran 'add' with options #{opts.to_hash} and args: #{args.inspect}"

# ruby run.rb -v
#=> Version 1.0
# ruby run.rb add -v foo --name Lee
#=> You ran 'add' with options {:verbose=>true,:name=>"Lee"} and args ["foo"]
opts.to_hash(true) # Pass true to tell Slop to merge sub-command option values.
# => { :v => nil, :add => { :v => true, :name => "Lee" } }

Woah woah, why you hating on OptionParser?

I'm not, honestly! I love OptionParser. I really do, it's a fantastic library. So why did I build Slop? Well, I find myself using OptionParser to simply gather a bunch of key/value options, usually you would do something like this:

require 'optparse'

things = {}

opt = do |opt|
  opt.on('-n', '--name NAME', 'Your name') do |name|
    things[:name] = name

  opt.on('-a', '--age AGE', 'Your age') do |age|
    things[:age] = age.to_i

  # you get the point

things #=> { :name => 'lee', :age => 105 }

Which is all great and stuff, but it can lead to some repetition. The same thing in Slop:

require 'slop'

opts = Slop.parse do
  on :n, :name=, 'Your name'
  on :a, :age=, 'Your age', :as => :int

opts.to_hash #=> { :name => 'lee', :age => 105 }