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➠ Website of David Bryant Copeland

Introducing Methadone, the Awesome Command-Line Library

I’ve spent the last year writing a book on building awesome command-line applications in Ruby. Over the course of writing it, I’ve used a lot of Ruby libraries for building command-line apps, and none of them work quite right. In my book, I spent significant time on OptionParser, since it’s builtin, and GLI, since I wrote it (and since it’s actually very fully-featured compare to the alternatives).

I just finished up an appendix where I showed alternate implementations of the running examples using main, thor, and trollop. I did this for a few reasons:

  • These tools are popular, and people have asked if they’d be included
  • They are, by and large, very different from how OptionParser and GLI work
  • I wanted to give them a real shakedown

I also surveyed many other tools, but, alas, I couldn’t include everything. Each of these tools have a common theme, which is to avoid the boilerplate of OptionParser, and make it really easy to parse command-line arguments. They all have done this, but at a cost. All of them are less powerful and extensible than OptionParser, and only slightly more compact (or, in the case of main, more verbose).

Enter methadone, which has all of OptionParser’s power, but the compactness of these other frameworks.

Another command-line option parser?

Yes and no. Methadone isn’t a re-implementation of command-line option parsing. It’s barely a DSL, making use of almost no meta-programming, class_eval, or other craziness. It’s a plain Ruby proxy to OptionParser, with some helper methods. It makes idiomatic option parsing and command-line app design as seemless as possible, but doesn’t force any of itself on you. In this post, I’ll derive its syntax while showing you the basics of how to structure a simple command-line app.
You’ll have to buy the book to dig deeper1.

Basic Command-line App Structure

Most command-line apps start off with parsing the command-line with OptionParser (which typically consists of setting values into some Hash), defining a few helper methods, and then, at the end, implementing the main logic of the program:

Typical Command-Line App Structure
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#!/usr/bin/env ruby

require 'optparse'

options = {}

parser = OptionParser.new do |opts|
  opts.banner 'My awesome app'

  opts.on("-u USERNAME","--username","The username") do |user|
    options[:username] = user
  end

  opts.on("-v","--verbose","Be verbose") do
    options[:verbose] = true
  end

  # etc.

end

parser.parse!

def some_helper_method
end

def some_other_helper_method

puts "Starting program" if options[:verbose]

# etc, the main logic of your program

Yuck. The boilerplate option parsing is bad enough, but the structure is all wrong. The interesting stuff is all the way at the bottom; you have to read the thing in the wrong order. At the very least, you should extract the core logic into a main method, put that at the top, and call it at the end.

Extracting Logic to a Main Method
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#!/usr/bin/env ruby

require 'optparse'

def main(args)
  # main logic of your app
  0 # or return nonzero if something went wrong
end

def some_helper_method
end

def some_other_helper_method

puts "Starting program" if options[:verbose]

options = {}

parser = OptionParser.new do |opts|
  opts.banner 'My awesome app'

  opts.on("-u USERNAME","--username","The username") do |user|
    options[:username] = user
  end

  opts.on("-v","--verbose","Be verbose") do
    options[:verbose] = true
  end

  # etc.

end

parser.parse!

exit main(ARGV)

Now, we can see, immediately upon opening the file, the main thing this app is doing. Of course, an exception might be raised. We may even do it on purpose, but we can’t have the app vomiting a stack trace to the user, so we wrap our call to main in a begin..rescue block:

Handling Exceptions
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begin
  exit main(ARGV)
rescue => ex
  STDERR.puts ex.message
  exit 1
end

Methadone’s Main Method

The structure we just saw is pretty decent, and gives us, and future contributors, an easy way to follow the code. Users also get a pretty decent experience and never have to see a backtrace.

This brings us to the first feature of methadone. Instead of including this boilerplate every time, we extract it into a module, Methadone::Main, which gives us two methods: main and go!.

main takes a block that represents our main method from before. go! calls that block, handling the exceptions for us. Our app now looks like so:

Methadone’s Boilerplate Removal
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#!/usr/bin/env ruby

require 'methadone'

include Methadone::Main

main do |args,go,here|
  # main logic
  # raise exceptions at will
end

# declare options and helper methods as before

go!

go! will extract the contents of ARGV leftover after parsing and pass them to the block. Since they’re passed as individual arguments, you don’t have to call shift a bunch of times on some array. Just name your parameters whatever, and Metahdone takes care of it. If your main block raises an exception, go! will handle catching it, messaging the user without a backtrace, and exiting nonzero2.

Parse Options with no Loss of Power

Notice how we can still safely use OptionParser. Methadone doesn’t hide that. As we’ll see, it provides some more features to make option parsing even easier. First, we can get rid of the options Hash as well as the actual creation of the OptionParser instance.

Methadone provides two methods: options and opts. options provides access to a Hash that we can use inside our main block. opts provides access to the underlying OptionParser instance that is automatically created. We can now remove a few lines of code, losing no functionality:

Methadone Provides an OptionParser and Options Hash for You
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opts.banner 'My awesome app'

opts.on("-u USERNAME","--username","The username") do |user|
  options[:username] = user
end

opts.on("-v","--verbose","Be verbose") do
  options[:verbose] = true
end

Given that opts is baked in, there’s no need to even use that for our cases, because Methadone provides a method on that proxies to the underlying OptionParser. You can still use opts to access anything else, but for declaring command-line options, just call on directly:

The on Method Proxies to OptionParser
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opts.banner 'My awesome app'

on("-u USERNAME","--username","The username") do |user|
  options[:username] = user
end

on("-v","--verbose","Be verbose") do
  options[:verbose] = true
end

You can see, as we peel off layers of boilerplate, Methadone hides nothing; it’s just making commonly-written code easier to write. At any time, you can abandon it and go back to the old way.

So far, we’ve only saved a few lines of code and a couple of characters. That’s because we haven’t seen the true power of the on method. on is more than just a proxy to OptionParser. It does one additional thing for us: it we omit the block, Methadone will provide one for us. That Methadone-provided block simply sets the value from the command-line in the options Hash automatically. Meaning that the above code is equivalent to this:

The on Method Provides Idiomatic Behavior
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opts.banner 'My awesome app'

on("-u USERNAME","--username","The username")
on("-v","--verbose","Be verbose")

Not bad! This means that all we need to do, assuming we’re doing things idiomatically, is to give on the names of our options and their descriptions. Note, however, this still proxies to OptionParser’s on method. Suppose we only allowed usernames with all lower-case characters? In Methadone, as in OptionParser, you pass in a Regexp:

Validation using Regular Expressions
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on("-u USERNAME","--username","The username",/^[a-z]+$/)
on("-v","--verbose","Be verbose")

Suppose you want the value type-converted for you? We have access to the underlying OptinParser, so we can set that up easily:

Custom Type Conversions
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opts.accept(User) do |username|
  User.find_by_name(username)
end

on("-u USERNAME","--username","The username",User)
on("-v","--verbose","Be verbose")

Do the Right Thing

You’ve noticed that we are still setting our banner manually. You’ve also noticed our banner is kinda lame; It doesn’t say what our app does nor does it give an overview of how to use it. It should look like so:

$ awesome_app.rb --help
Does so many awesome things, you won't believe it.

Usage:  awesome_app.rb [options] thing other_thing [optional_thing]

Since Methadone knows that our app takes options (by virtue of us having declared them), and it knows the name of our app, we just need to tell it what our app does, and it will assemble the banner for us3.

Automatically Generate the Banner
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main do |thing,other_thing,optional_thing|
  # logic
end

on("-u USER","--username","The user name")
on("-v","--verbose","Be verbose")

description "Does so many awesome things, you won't believe it."

go!

Finally, you’ll note that our main block takes three arguments. Methadone provides the method arg that allows us to name them (in the language the user will understand) and indicate which are required and which are optional. Methadone will put this information into the banner, and will fail if any required arguments are missing:

Describing the Arguments
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main do |thing,other_thing,optional_thing|
  # logic
end

on("-u USER","--username","The user name")
on("-v","--verbose","Be verbose")

description "Does so many awesome things, you won't believe it."

arg :thing
arg :other_thing
arg :optional_thing, :optional

go!

Now, the banner looks like we’d like it, and we didn’t have to do much more than describe our program. You can even bootstrap your app using the methadone command-line app. It will create an empty app, using this structure, with some helpful comments to let you describe your UI easily and quickly. But it won’t prevent you from doing any sort of crazy thing with OptionParser that you need to.

Sweet, Sweet Sugar

But wait! There’s more! Complex programs start to look like this:

Complex, Annoying Code
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if have_connection
  # puts "got a connection"
  file = request_data
  puts "Got data"
  if file.nil?
    STDERR.puts "Data was nil?"
  end
end
# puts "Moving on"

You’ve got a mix of commented-out debug statements, informational messages and tediously long statements sending error messages to the standard error. Methadone includes a special Logger instance, along with some helper methods, that does away with all this:

Cleaner Messaging
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include Methdone::CLILogging # sets up Logger, provides helper methods

if have_connection
  debug "got a connection"   # Calls logger.debug 
  file = request_data
  info "Got data"            # Calls logger.info
  if file.nil?
    error "Data was nil?"    # Calls logger.error
  end
end
debug "Moving on"            # Calls logger.debug

The logger is set up as follows:

  • debug messages don’t go anywhere.
  • info goes to the standard output.
  • warn, error, and fatal go to the standard error.
  • Log messages are unformatted when logged to a TTY
  • Log messages are formatted with timestampes, levels, etc, when logged to a file

This means that for command-line use, the user sees messages formatted for them, and not horrible Maven-style enterprise logging. As soon as you use your app in cron, however, the logger senses the absence of a TTY and switches its format to this style, so that the log files do have that valuable information.

You have complete access to the logger via logger and logger=, so you can ultimatley do whatever you want.

Methdone::CLILogging is included in Methdone::Main, so, if you followed the structure above, you have access to the logger and these methods.

Is there more?

In addition to all of this, Methadone provides some Cucumber step definitions, based on Aruba that allow you to test-drive your command-line app. When you bootstrap your app using methadone, this will be set up for you.

I’m planning a few more things before v1.0.0, so checkout the roadmap for more info.

And, don’t forget the buy the book


  1. Never fear, if you don’t like Methadone, it only takes up a few scant pages at the end.
  2. You can, of course, set DEBUG in the environment and a methadone-powered app will dump the stack on an exception.
  3. Of course, you can continue to use opts.banner= to set your own if you like.