Command doesn't allow specification of an "end of flags" marker

[hugoduncan]

Some programs take option like arguments (i.e. options starting with --) as data. In other option processing libraries, -- can be used to explicitly mark the end of options to be processed.

While we can workaround this by manually splitting the argument list before passing it to Command.run, it would be great to see support for this in Command.

[avsm]

Yes, this came up in earlier discussions about supporting "-" as a valid filename. It can be current be written by using the Command.Spec.escape flag (which can only be passed once) to escape the parser and pass through all remaining arguments.

It's worth considering if -- should be the default escape flag, which is present unless another escape flag supersedes it.

-anil

On 4 Sep 2013, at 11:39, Hugo Duncan notifications@github.com wrote:

Some programs take option like arguments (i.e. options starting with --) as data. In other option processing libraries, -- can be used to explicitly mark the end of options to be processed.

While we can workaround this by manually splitting the argument list before passing it to Command.run, it would be great to see support for this in Command.

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[hugoduncan]

Thanks for pointing to escape. I'm trying to use it but don't seem to be getting it right - would you have an example (I can't see one in the examples/command/main.ml)?

You have to create a parameter named "--". For instance:

open Core.Std

let main args () =
  let args = Option.value args ~default:[] in
  List.iter args ~f:print_endline
;;

let () =
  let spec =
    Command.Spec.(empty
                  +> flag "--" escape ~doc:" stop processing command line arguments")
  in
  Command.run (Command.basic ~summary:"Blah." spec main)

$ ./foo -- a -b c
a
-b
c

[hugoduncan]

Ahh, the escape flag returns the anon arguments - I was assuming it would be returning () and an +> anon would still be necessary. I actually have a couple of anon arguments, so would loose that ability when using the -- flag.

When invoking the above without -- I get errors however:

$ ./foo a b c
...
too many anonymous arguments

My assumption was that ./foo a b c and ./foo -- a b c would be equivalent.