= Welcome to Choice

Choice is a small library for defining and parsing command line options.  It 
works awesomely with Highline[http://highline.rubyforge.org/] or other command 
line interface libraries.

Choice was written by Chris Wanstrath as an exercise in test driving development 
of a DSL.  This project is still an infant: bugs are expected and tattling on them 
is appreciated.  

Installing is easy, with RubyGems.  Give it a shot:
 $ gem install choice

If you are lost, you can find Choice at http://choice.rubyforge.org or 
http://rubyforge.org/projects/choice/.  E-mail inquiries can be directed to
mailto:chris[at]ozmm[dot]org.

Of course, Choice is licensed under the MIT License, which you can find included
in the LICENSE file or by surfing your World Wide Web browser of choice towards 
http://www.opensource.org/licenses/mit-license.php.

== Using Choice

An +examples+ directory is included with Choice, in which some contrived Ruby
programs utilizing the library have been placed.  Here's a snippet:

=== ftpd.rb

  require 'choice'

  PROGRAM_VERSION = 4

  Choice.options do
    header ''
    header 'Specific options:'
  
    option :host do
      short '-h'
      long '--host=HOST'
      desc 'The hostname or ip of the host to bind to (default 127.0.0.1)'
      default '127.0.0.1'
    end

    option :port do
      short '-p'
      long '--port=PORT'
      desc 'The port to listen on (default 21)'
      cast Integer
      default 21
    end
  
    separator ''
    separator 'Common options: '

    option :help do
      long '--help'
      desc 'Show this message'
    end

    option :version do
      short '-v'
      long '--version'
      desc 'Show version'
      action do
        puts "ftpd.rb FTP server v#{PROGRAM_VERSION}"
        exit      
      end
    end
  end

  puts 'port: ' + Choice.choices[:port]

Notice the last line.  For free, you will be given a <tt>Choice.choices</tt> 
hash which contain, at runtime, the options found and their values.

Because we gave option <tt>:port</tt> a default of 21, 
<tt>Choice.choices[:port]</tt> should be 21 if we run ftpd.rb with no options.  
Let's see.

 $ ruby ftpd.rb
 port: 21
 
Cool.  On our system, port 21 is reserved.  Let's use another port.

 $ ruby ftpd.rb -p 2100
 port: 2100
 
Alright.  And, of course, there is the hard way of doing things.

 $ ruby ftpd.rb --port=2100
 port: 2100
 
That <tt>:version</tt> option looks pretty interesting, huh?  I wonder what it 
does...
 
  $ ruby ftpd.rb -v
  ftpd.rb FTP server v4

That's not all, though.  We also get a <tt>--help</tt> option for free.  

  $ ruby ftpd.rb --help
  Usage: ftpd.rb [-hpv]

  Specific options:
      -h, --host=HOST                  The hostname or ip of the host to bind to (default 127.0.0.1)
      -p, --port=PORT                  The port to listen on (default 21)

  Common options: 
          --help                       Show this message
      -v, --version                    Show version
      
      
== The Choice.choices hash

For better or worse, the <tt>Choice.choices</tt> hash is a bit lazy.  It does 
not care how you access it.  Using the above example, assume we have a 
<tt>:port</tt> option and we replace the last line of our program with the 
following three lines:

  puts 'port: ' + Choice.choices[:port]
  puts 'port: ' + Choice.choices['port']
  puts 'port: ' + Choice.choices.port

Now, run it.

  $ ftpd.rb -p 2100
  port: 2100
  port: 2100
  port: 2100

Lazy, huh?

Keep in mind that your option's key in the <tt>Choice.choices</tt> hash is 
defined by the first parameter passed to option statement.  This is perfectly 
legit, albeit somewhat confusing:

  option :name do
    short '-h'
    long '--handle=NAME'
    desc "Your handle."
  end

You can access this option by using <tt>Choice.choices[:name]</tt>, not 
<tt>:handle</tt>.

== Option options

Obviously, Choice revolves around the <tt>option</tt> statement, which receives
a block.  Here are all the, er, options +option+ accepts.  None of them are 
required but +short+ or +long+ must be present for Choice to know what to do.

Options must be defined in the context of a <tt>Choice.options</tt> block, as 
seen above.  This context is assumed for the following explanations.

For the quick learners, here's the list:
* short
* long
* default
* desc
* cast
* valid (takes array)
* validate (takes regex)
* filter (takes a block)
* action (ditto)

You can define these within your option in any order which pleases you.

=== short

Defines the short switch for an option.  Expected to be a dash and a single
character.

  short '-s'

=== long

Defines the long switch for an option.  Expected to be a double dash followed by
a string, an equal sign (or a space), and another string.

There are two variants: longs where a parameter is required and longs where a 
parameter is optional, in which case the value will be +true+ if the option is
present.

*Optional*:
  long '--debug=[LEVEL]'

Assuming our program defines Choices and ends with this line:
  puts 'debug: ' + Choice.choices[:debug]

we can do this:

  $ ruby ftpd.rb --debug
  debug: true
  
  $ ruby ftpd.rb --debug=1
  debug: 1

  $ ruby ftpd.rb --debug 1
  debug: 1

*Required*:
  long '--debug=LEVEL'

Assuming the same as above:

  $ ruby ftpd.rb --debug 1
  debug: 1
  
  $ ruby ftpd.rb --debug
  <help screen printed>

=== long as array

Often you may wish to allow users the ability to pass in multiple arguments and have
them all combined into an array.  You can accomplish this by defining a +long+ and
setting the caps-argument to *ARG.  Like this:
    
  long '--suit *SUITS'

<tt>Choice.choices.suits</tt> will now return an array.  Here's an example of usage:

  $ ruby --suit hearts clubs
  suit: ['hearts', 'clubs']

Check out <tt>examples/gamble.rb</tt> for more information on this cool feature.

=== default

You can define a default value for your option, if you'd like.  If the option
is not present in the argument list, the default will be returned when trying
to access that element of the <tt>Choice.choices</tt> hash.

As with the above, assume our program prints <tt>Choice.choices[:debug]</tt>:

  default 'info'

If we don't pass in <tt>--debug</tt>, the <tt>:debug</tt> element of our hash 
will be 'info.'

  $ ftpd.rb
  debug: info

  $ ftpd.rb --debug warn
  debug: warn

=== desc

The description of this option.  Fairly straightforward, with one little trick:
multiple +desc+ statements in a single option will be considered new desc lines.  
The desc lines will be printed in the order they are defined.  Like this:

  desc "Your hostname."
  desc "(default 'localhost')"

A snippet from your <tt>--help</tt> might then look like this:

  -h, --host=HOST                  Your hostname.
                                   (default 127.0.0.1)


=== cast

By default, all members of the <tt>Choice.choices</tt> hash are strings.  If 
you want something different, like an Integer for a port number, you can use 
the +cast+ statement.

  cast Integer

Currently support +cast+ options:

* Integer
* String
* Float
* Symbol

We'll probably add Date, Time, and DateTime in the future, if people want them.

=== valid

Giving +valid+ an array creates a whitelist of acceptable arguments.

  valid %w[clubs hearts spades diamonds]

If our option is passed anything other than one of the four card suits, the help
screen will be printed.  It might be a good idea to include acceptable arguments in
your option's "desc" value.

  $ ruby gamble.rb -s clubs
  suit: clubs

  $ ruby gamble.rb -s joker
  <help screen printed>

=== validate

The +validate+ statement accepts a regular expression which it will test 
against the value passed.  If the test fails, the <tt>--help</tt> screen will
be printed.  I love ports, so let's stick with that example:

  validate /^\d+$/

Of course, 2100 matches this:

  $ ruby ftpd.rb -p 2100
  port: 2100

I like dogs.  I wish dogs could be ports.  Alas, Choice knows better (once
I've told it so):

  $ ruby ftpd.rb -p labradoodle
  <help screen printed>

=== filter

The +filter+ statement lets you play with a value before it goes into the
<tt>Choice.choices</tt> hash.  If you use +cast+, this will occur post-casting.

In this program we're defining a :name option and saying we don't want any 
crazy characters in it, then printing that element of the 
<tt>Choice.choices</tt>+ hash:

  filter do |value|
    value = value.gsub(/[^\w]/, '')
  end

Now:

  $ ruby ftpd.rb --name=c.hr.is
  name: chris

You can probably think of better uses.  

=== action

A block passed to the +action+ statement will be run if that particular option
is passed.  See the <tt>--version</tt> example earlier.

=== required options

You can specify an option as being required by passing :required => true to the 
option definition.  Choice will then print the help screen if this option is
not present.  Please let your dear users know which options are required.

For example:

  option :card, :required => true do
    short '-c'
    long '--card CARD'
    desc "The card you wish to gamble on.  Required.  Only one, please."
  end

Then:

  $ ruby gamble.rb
  <help screen, -c or --card wasn't passed>

== Other options

These statements are purely aesthetic, used to help make your <tt>--help</tt>
screen a little more digestible.

Passing an empty string to any of these options will print a newline.

=== banner

The banner is the first line printed when your program is called with 
<tt>--help</tt>.  By default, it will be something like this, based on the 
options defined:

  Usage: ftpd.rb [-hpv]

You can pass any string to the +banner+ statement to override what prints.  This
might be useful if you're into ascii art.

  banner "Usage: ftpd.rb"

=== header

The header is what shows up after the banner but before your option definitions
are printed.  Each header call is a newline.  Check out the example above.

  header "ftp is a harsh and unforgiving protocol."

=== separator

As in the example above, you can put separators between options to help display
the logical groupings of your options.  Or whatever.  

  separator "----"

To get a blank line, rock an empty string:

  separator ''

=== footer

The footer is displayed after all your options are displayed.  Nothing new 
here, works like the other options above.

  footer "That's all there is to it!"

== Shorthand

Now that you've gone through all the hard stuff, here's the easy stuff: Choice 
options can be defined with a simple hash if you'd like.  Here's an example,
from the tests:

   Choice.options do
     header "Tell me about yourself?"
     header ""
     options :band => { :short => "-b", :long => "--band=BAND", :cast => String, :desc => "Your favorite band.",
                       :validate => /\w+/ },
             :animal => { :short => "-a", :long => "--animal=ANIMAL", :cast => String, :desc => "Your favorite animal." }
     
     footer ""
     footer "--help This message"
   end

How's that tickle you?  Real nice.

== It looks like poetry

That's it.  Not much, I know.  Maybe this will make handling your command 
line options a bit easier.  You can always use the option parser in the standard 
Ruby library, but DSLs are just so cool.  As one of my non-programmer friends 
said of a Ruby DSL: "It looks like poetry."

== It's totally broken

Okay, I knew this would happen.  Do me a favor, if you have time: run +rake+ 
from the Choice directory and send me the output (mailto:chris[at]ozmm[dot]org).  
This'll run the unit tests.  Also, if you would, send me a bit of information 
on your platform.  Choice was tested on OS X and RHEL with a 2.4 kernel but who 
knows.  Thanks a lot.

== Thanks to

For bug reports, patches, and ideas I'd be honored to thank the following:

- Justin Bailey
- Alexis Li