This is all about Slop 3 (ruby 1.9 era). Slop 4 has changed the API. See the README And see my new blog post about a Slop 4 example.

One of my favorite features of slop is the automatic help generation. But it’s not intuitive. It doesn’t print out the help when the parsing fails. This isn’t very unix-y. So every time I want to use slop, I have to look up this snippet I saved for myself. So I’m posting it here. This is the only slop example you’ll ever need.

Unix style CLI program in Ruby

require 'slop'

opts = true, help: true) do
  banner 'Usage: slop_test.rb [options]'

  on 'resume=', 'Your resume file', required: true
  on :s, :skill=, 'Skill Name', as: Array, arguments: :optional
  on 'v', 'verbose', 'Enable verbose mode'  # same as adding required: false


  # validation passed
  puts "Here's the data"
  puts opts.to_hash
rescue Slop::Error => e
  puts e.message
  puts opts

Calling it like this will fail:

$ ruby ./slop_test.rb
Missing required option(s): resume
Usage: slop_test.rb [options]
        --resume       Your resume file
    -s, --skill        Skill Name
    -v, --verbose      Enable verbose mode
    -h, --help         Display this help message.

Great! Then using it correctly will do this:

$ ruby slop_test.rb --resume hechicero-del-relámpago.doc
Here's the data
{:resume=>"hechicero-del-relámpago.doc", :skill=>nil, :verbose=>nil, :help=>nil}

The resume flag is the only required one, so in this case that’s how it’s run correctly.

Update: I was very happy that @lee_jarvis (the slop author) accepted my pull request to put this example into the README.