From: Stefano Crocco <stefano.crocco@...>
Date: 2008-10-19T03:33:18+09:00
Subject: Re: Handling invalid options with OptionParser

Alle Saturday 18 October 2008, Adam Penny ha scritto:
> Hi there,
>
> I wrote my own Wake on Lan Script in ruby that uses a Plist to look up
> either target Mac address by selected printer or target MAC address by
> server and I use option parser for this.
>
> It all works fine if the arguments are input correctly, but if the
> arguments are off you get something like this. -x is not declared in my
> options and was a test to see how it did when it got something that it
> didn't recognize.
>
> ruby test.rb -x
> /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/opt
>parse.rb:1443:in `complete': invalid option: -x
> (OptionParser::InvalidOption)
>   from
> /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/opt
>parse.rb:1441:in `catch'
>   from
> /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/opt
>parse.rb:1441:in `complete'
>   from
> /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/opt
>parse.rb:1280:in `parse_in_order'
>   from
> /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/opt
>parse.rb:1247:in `catch'
>   from
> /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/opt
>parse.rb:1247:in `parse_in_order'
>   from
> /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/opt
>parse.rb:1241:in `order!'
>   from
> /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/opt
>parse.rb:1332:in `permute!'
>   from
> /System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib/ruby/1.8/opt
>parse.rb:1353:in `parse!'
>   from test.rb:4
>
> It's not the end of the world as if the options are wrong then it won't
> do anything anyway, but I was wondering if anyone could tell me if
> there's any method in the class or extra thing I could do to catch dodgy
> arguments and output the help file or the banner rather than this
> inelegant list of errors?
>
> Thanks in advance.

I guess you can enclose the call to OptionParser#parse! in a begin/rescue 
expression, rescuing OptionParser::InvalidOption or OptionParser::ParseError 
(which is the parent of InvalidOption) and display an error message. Here's a 
simple example of how you can do it:

require 'optparse'

o = OptionParser.new do |o|
  o.banner  = "test usage: test [OPTIONS]"
  o.on('-o', '--option', 'this option does nothing '){}
end

begin o.parse! ARGV
rescue OptionParser::InvalidOption => e
  puts e
  puts o
  exit 1
end

the line

puts e

will display a message like 

invalid option -a

(where -a is the invalid option passed to the script). The line

puts o

will display the usage message.

exit 1

will make the script exit with the error code 1.

I hope this helps

Stefano