OptionParse with no arguments show banner

optionparser, ruby

Solution

Just add the -h key to the ARGV, when it is empty, so you may to do something like this:

require 'optparse'

ARGV << '-h' if ARGV.empty?

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

  opts.on("-l", "--length L", Integer, "Length") { |l| options[:length] = l }
  opts.on("-w", "--width W", Integer, "Width") { |w| options[:width] = w }

  opts.on_tail("-h", "--help", "Show this message") do
    puts opts
    exit
  end
end.parse!

Problem

I'm using `OptionParser` with Ruby. I other languages such as C, Python, etc., there are similar command-line parameters parsers and they often provide a way to show help message when no parameters are provided or parameters are wrong. ``` options = {} OptionParser.new do |opts| opts.banner = "Usage: calc.rb [options]" opts.on("-l", "--length L", Integer, "Length") { |l| options[:length] = l } opts.on("-w", "--width W", Integer, "Width") { |w| options[:width] = w } opts.on_tail("-h", "--help", "Show this message") do puts opts exit end end.parse! ``` Questions: - Is there a way to set that by default show `help` message if no parameters were passed (`ruby calc.rb`)? - What about if a required parameter is not given or is invalid? Suppose `length` is a REQUIRED parameter and user do not pass it or pass something wrong like `-l FOO`?

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