OptionParser

Developer Documentation (not for RDoc output)

Class tree

• OptionParser:: front end
• OptionParser::Switch:: each switches
• OptionParser::List:: options list
• OptionParser::ParseError:: errors on parsing
  • OptionParser::AmbiguousOption
  • OptionParser::NeedlessArgument
  • OptionParser::MissingArgument
  • OptionParser::InvalidOption
  • OptionParser::InvalidArgument
    • OptionParser::AmbiguousArgument

Object relationship diagram

  +--------------+
  | OptionParser |<>-----+
  +--------------+       |                      +--------+
                         |                    ,-| Switch |
       on_head -------->+---------------+    /  +--------+
       accept/reject -->| List          |<|>-
                        |               |<|>-  +----------+
       on ------------->+---------------+    `-| argument |
                          :           :        |  class   |
                        +---------------+      |==========|
       on_tail -------->|               |      |pattern   |
                        +---------------+      |----------|
  OptionParser.accept ->| DefaultList   |      |converter |
               reject   |(shared between|      +----------+
                        | all instances)|
                        +---------------+

OptionParser

Introduction

OptionParser is a class for command-line option analysis. It is much more advanced, yet also easier to use, than GetoptLong, and is a more Ruby-oriented solution.

Features

1. The argument specification and the code to handle it are written in the same place.
2. It can output an option summary; you don‘t need to maintain this string separately.
3. Optional and mandatory arguments are specified very gracefully.
4. Arguments can be automatically converted to a specified class.
5. Arguments can be restricted to a certain set.

All of these features are demonstrated in the examples below.

Minimal example

  require 'optparse'

  options = {}
  OptionParser.new do |opts|
    opts.banner = "Usage: example.rb [options]"

    opts.on("-v", "--[no-]verbose", "Run verbosely") do |v|
      options[:verbose] = v
    end
  end.parse!

  p options
  p ARGV

Complete example

The following example is a complete Ruby program. You can run it and see the effect of specifying various options. This is probably the best way to learn the features of optparse.

  require 'optparse'
  require 'optparse/time'
  require 'ostruct'
  require 'pp'

  class OptparseExample

    CODES = %w[iso-2022-jp shift_jis euc-jp utf8 binary]
    CODE_ALIASES = { "jis" => "iso-2022-jp", "sjis" => "shift_jis" }

    #
    # Return a structure describing the options.
    #
    def self.parse(args)
      # The options specified on the command line will be collected in *options*.
      # We set default values here.
      options = OpenStruct.new
      options.library = []
      options.inplace = false
      options.encoding = "utf8"
      options.transfer_type = :auto
      options.verbose = false

      opts = OptionParser.new do |opts|
        opts.banner = "Usage: example.rb [options]"

        opts.separator ""
        opts.separator "Specific options:"

        # Mandatory argument.
        opts.on("-r", "--require LIBRARY",
                "Require the LIBRARY before executing your script") do |lib|
          options.library << lib
        end

        # Optional argument; multi-line description.
        opts.on("-i", "--inplace [EXTENSION]",
                "Edit ARGV files in place",
                "  (make backup if EXTENSION supplied)") do |ext|
          options.inplace = true
          options.extension = ext || ''
          options.extension.sub!(/\A\.?(?=.)/, ".")  # Ensure extension begins with dot.
        end

        # Cast 'delay' argument to a Float.
        opts.on("--delay N", Float, "Delay N seconds before executing") do |n|
          options.delay = n
        end

        # Cast 'time' argument to a Time object.
        opts.on("-t", "--time [TIME]", Time, "Begin execution at given time") do |time|
          options.time = time
        end

        # Cast to octal integer.
        opts.on("-F", "--irs [OCTAL]", OptionParser::OctalInteger,
                "Specify record separator (default \\0)") do |rs|
          options.record_separator = rs
        end

        # List of arguments.
        opts.on("--list x,y,z", Array, "Example 'list' of arguments") do |list|
          options.list = list
        end

        # Keyword completion.  We are specifying a specific set of arguments (CODES
        # and CODE_ALIASES - notice the latter is a Hash), and the user may provide
        # the shortest unambiguous text.
        code_list = (CODE_ALIASES.keys + CODES).join(',')
        opts.on("--code CODE", CODES, CODE_ALIASES, "Select encoding",
                "  (#{code_list})") do |encoding|
          options.encoding = encoding
        end

        # Optional argument with keyword completion.
        opts.on("--type [TYPE]", [:text, :binary, :auto],
                "Select transfer type (text, binary, auto)") do |t|
          options.transfer_type = t
        end

        # Boolean switch.
        opts.on("-v", "--[no-]verbose", "Run verbosely") do |v|
          options.verbose = v
        end

        opts.separator ""
        opts.separator "Common options:"

        # No argument, shows at tail.  This will print an options summary.
        # Try it and see!
        opts.on_tail("-h", "--help", "Show this message") do
          puts opts
          exit
        end

        # Another typical switch to print the version.
        opts.on_tail("--version", "Show version") do
          puts OptionParser::Version.join('.')
          exit
        end
      end

      opts.parse!(args)
      options
    end  # parse()

  end  # class OptparseExample

  options = OptparseExample.parse(ARGV)
  pp options

Further documentation

The above examples should be enough to learn how to use this class. If you have any questions, email me (gsinclair@soyabean.com.au) and I will update this document.