Re: optparse question: how to warn of missing positional arguments

After the option parser has completed parsing arguments, it will leave any
non-option arguments in the argument array.  You can check that the array
is empty and then print the help message and exit.  The key is to preserve
a reference to the parser object so that you can call #to_s on it later to
emit the usage output when needed.  Below is an example largely lifted from
the documentation for the optparse library which will do what I believe you
are asking about:

example.rb
-------------------------------------------
require 'optparse'

option = false

parser = OptionParser.new do |opts|
  opts.banner = 'Usage example.rb [options] REQUIRED_ARG'
  opts.separator ''

  opts.on('-a', '--an-option', 'An example option') do |val|
    option = val
  end

  opts.on('-h', '--help', 'Prints this help') do
    puts opts
    exit
  end
end
parser.parse!

if ARGV.empty?
  puts parser
  exit 1
end

p option
p ARGV


-Jeremy


On Fri, Mar 22, 2019 at 2:49 PM Artie Ziff <[email protected]> wrote:

> Hello,
>
> My goal is to force a display of the banner (usage string) when a
> positional parameter is not present; in the sense of ARGV[1] == nil
>
> An possible way would be to force the OptionParse.new block parse to fail
> if ARGV[1] == nil. How to do this properly in Ruby?
>
> I love Ruby so much! Thx all!
> az
>
>
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