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 fail.

I can't seem to figure out how to do that. The docs seem to only specify how to make the argument value mandatory, not the switch itself.

Answer 1

An approach using optparse that provides friendly output on missing switches:

#!/usr/bin/env ruby require 'optparse'  options = {}  optparse = OptionParser.new do |opts|   opts.on('-f', '--from SENDER', 'username of sender') do |sender|     options[:from] = sender   end    opts.on('-t', '--to RECIPIENTS', 'comma separated list of recipients') do |recipients|     options[:to] = recipients   end    options[:number_of_files] = 1   opts.on('-n', '--num_files NUMBER', Integer, "number of files to send (default #{options[:number_of_files]})") do |number_of_files|     options[:number_of_files] = number_of_files   end    opts.on('-h', '--help', 'Display this screen') do     puts opts     exit   end end  begin   optparse.parse!   mandatory = [:from, :to]                                         # Enforce the presence of   missing = mandatory.select{ |param| options[param].nil? }        # the -t and -f switches   unless missing.empty?                                            #     raise OptionParser::MissingArgument.new(missing.join(', '))    #   end                                                              # rescue OptionParser::InvalidOption, OptionParser::MissingArgument      #   puts $!.to_s                                                           # Friendly output when parsing fails   puts optparse                                                          #   exit                                                                   # end                                                                      #  puts "Performing task with options: #{options.inspect}" 

Running without the -t or -f switches shows the following output:

Missing options: from, to Usage: test_script [options]     -f, --from SENDER                username of sender     -t, --to RECIPIENTS              comma separated list of recipients     -n, --num_files NUMBER           number of files to send (default 1)     -h, --help 

Running the parse method in a begin/rescue clause allows friendly formatting upon other failures such as missing arguments or invalid switch values, for instance, try passing a string for the -n switch.