Pattern for single file lib/script

script.rb

#!/usr/bin/env ruby
#
# Simple pattern for a Ruby script where the command line processing
# is done separately from the rest of the code.  This allows the file
# to be required by other Ruby code without acting as an executable.


class Project
  
  # Defaults to be overridden by command line options
  DefaultHost = "localhost"
  
  # Hard-coded configuration, unlikely to change with each invocation
  ConfigValue = "q"
  
  def initialize(file1, file2, options)
    @file1, @file2 = file1, file2
    @options = options
    @options[:host] ||= DefaultHost
    raise ArgumentError, "No such file: #{@query_file}" unless File.file?(@query_file)
  end
  
  def run
    # Do something clever.
  end
  
end

# The following runs only when this file is executed.
if $PROGRAM_NAME == __FILE__
  require 'optparse'
  
  usage = "Usage: botch.rb [-v] [-h HOST] query_file bval kval"
  options = {}
  OptionParser.new do |opts|
    opts.banner = "Usage: botch.rb [-d] query_file bval kval"

    opts.on("-v", "--verbose", "Verbose output") do |verbose|
      options[:verbose] = verbose
    end
    opts.on("-h", "--host HOST", "The host--") do |host|
      options[:host] = host
    end
  end.parse!
  
  # OptionParser is kind enough to delete its opts from ARGV for us
  file1, file2 = *ARGV
  puts usage and exit unless file2 && file2
  project = Project.new(file1, file2, options)
  project.run
end