How do you specify a required switch (not argument) with Ruby OptionParser?

Question

I\'m writing a script and I want to require a --host switch with value, but if the --host switch isn\'t specified, I want the option parsing to fai

Answer 1

I came up with a clear and concise solution that sums up your contributions. It raises an OptionParser::MissingArgument exception with the missing arguments as a message. This exception is catched in the rescue block along with the rest of exceptions coming from OptionParser.

#!/usr/bin/env ruby
require 'optparse'

options = {}

optparse = OptionParser.new do |opts|
  opts.on('-h', '--host hostname', "Host name") do |host|
    options[:host] = host
  end
end

begin
  optparse.parse!
  mandatory = [:host]
  missing = mandatory.select{ |param| options[param].nil? }
  raise OptionParser::MissingArgument, missing.join(', ') unless missing.empty?
rescue OptionParser::ParseError => e
  puts e
  puts optparse
  exit
end

Running this example:

 ./program            
missing argument: host
Usage: program [options]
    -h, --host hostname              Host name