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comp.lang.ruby

OptionParser question

Jos Backus

3/15/2005 1:49:00 AM

OptionParser is still a mystery to me. In the example below, how do I
distinguish between a -c flag without an argument (which is a fatal syntax
error) and no -c flag at all? In both cases client equals nil. There doesn't
seem to be a way to intercept the `missing argument' message, or if there is,
I can't seem to find it in the documentation :-/

require 'optparse'

client = nil
ARGV.options do |opt|
opt.on("-c CLIENT", String) do |s|
puts "client: #{s}"
client = s
end
opt.parse!
end

puts "client is #{client}" if client

puts "done"

Running the example yields:

lizzy:~% ruby op -c foo
client: foo
client is foo
done
lizzy:~% ruby op -c
op: missing argument: -c
done
lizzy:~% ruby op
done
lizzy:~%

--
Jos Backus
jos at catnook.com
6 Answers

Jonathan Paisley

3/15/2005 8:50:00 AM

0

On Tue, 15 Mar 2005 10:48:36 +0900, Jos Backus wrote:

> OptionParser is still a mystery to me. In the example below, how do I
> distinguish between a -c flag without an argument (which is a fatal syntax
> error) and no -c flag at all? In both cases client equals nil. There doesn't
> seem to be a way to intercept the `missing argument' message, or if there is,
> I can't seem to find it in the documentation :-/

opt.parse! returns the remaining non-option arguments (which is in fact
just ARGV at this stage, with options removed), or nil upon failure. This
is propagated to the return value of ARGV.options. A common idiom seems to
be:

ARGV.options do |opt|
...
...
opt.parse!
end or exit 1
# ^^^^^^^^^

Wybo Dekker

3/15/2005 10:51:00 AM

0

Jos Backus

3/15/2005 8:10:00 PM

0

On Tue, Mar 15, 2005 at 07:51:16PM +0900, Wybo Dekker wrote:
> On Tue, 15 Mar 2005, Jos Backus wrote:
> Try [CLIENT] instead of CLIENT:
>
> require 'optparse'
>
> client = nil
> ARGV.options do |opt|
> opt.on("-c [CLIENT]", String) do |s|
> puts "client: #{s}"
> client = s
> end
> opt.parse!
> end
>
> puts "client is #{client}" if client
>
> puts "done"

Thanks, but the problem with this is that when one adds the line

opt.on("-h") do puts opt; exit 64 end

to the example, the help message will show `-c [CLIENT]', suggesting that the
CLIENT value is optional because of the brackets.

--
Jos Backus
jos at catnook.com

Jos Backus

3/15/2005 8:46:00 PM

0

On Tue, Mar 15, 2005 at 11:02:21PM +0900, Jonathan Paisley wrote:
> opt.parse! returns the remaining non-option arguments (which is in fact
> just ARGV at this stage, with options removed), or nil upon failure. This
> is propagated to the return value of ARGV.options. A common idiom seems to
> be:
>
> ARGV.options do |opt|
> ...
> ...
> opt.parse!
> end or exit 1
> # ^^^^^^^^^

I might use this. The downside here is that one doesn't know which option
failed so it's hard to give a more specific error message. Perhaps the author
will address this issue in due time.

Thanks!

--
Jos Backus
jos at catnook.com

nobu.nokada

3/15/2005 11:58:00 PM

0

Hi,

At Wed, 16 Mar 2005 05:46:04 +0900,
Jos Backus wrote in [ruby-talk:133774]:
> > opt.parse! returns the remaining non-option arguments (which is in fact
> > just ARGV at this stage, with options removed), or nil upon failure. This
> > is propagated to the return value of ARGV.options. A common idiom seems to
> > be:
> >
> > ARGV.options do |opt|
> > ...
> > ...
> > opt.parse!
> > end or exit 1
> > # ^^^^^^^^^
>
> I might use this. The downside here is that one doesn't know which option
> failed so it's hard to give a more specific error message. Perhaps the author
> will address this issue in due time.

Actually, #parse! just raises a exception, subclass of
OptionParser::Error, and ARGV.options does rescue it in the
given block and converts to nil.

require 'optparse'

client = nil
ARGV.options do |opt|
opt.on("-c CLIENT", String) do |s|
puts "client: #{s}"
client = s
end
begin
opt.parse!
rescue OptionParser::MissingArgument
p $!.args # => "-c"
abort
end
end

puts "client is #{client}" if client

puts "done"

--
Nobu Nakada

Jos Backus

3/16/2005 6:29:00 AM

0

Hello,

On Wed, Mar 16, 2005 at 08:57:35AM +0900, nobu.nokada@softhome.net wrote:
> Actually, #parse! just raises a exception, subclass of
> OptionParser::Error, and ARGV.options does rescue it in the
> given block and converts to nil.
[example snipped]

Neat. I would never have figured that one out :-/

Thanks for the example, Nobu, that's the type of control I'm looking for.
Maybe this can be added to the examples in the documentation...

Cheers,
--
Jos Backus
jos at catnook.com