Add support for exit codes.

[hildjj]

Fixes #435.
Fixes #188.

[SomeKittens]

Broken tests, can you fix those up?

[zhiyelee]

@SomeKittens I'm not sure whether we need that

[zhiyelee]

Also that would be break change to change default code from 1 to 64.

[hildjj]

Sorry, thought I had gotten all of the tests fixed up. I think there's a legitimate discussion to be had about what exit code to use when the user asks for help with --help vs. when they supply invalid arguments. I would be fine with --help returning 0, if you prefer.

[hildjj]

Oh, and I'm also happy to change the defaults so that the interface doesn't change, and only the people that want 64-exits get them.

[zhiyelee]

@hildjj Thank you! I'm not sure 64 is convention for such error. I have checked wget and git with unknown option, they give 2 and 129 respectively.

I am open to allow user set custom exit code.

[SomeKittens]

@zhiyelee good checking - I'm ok with user-set as well.

[roman-vanesyan]

@zhiyelee is it still necessary?

[shadowspawn]

I have added this pull request to a triage collection of exit related issues for future reference.

This pull request has not had any activity in over six months. It isn't likely to get acted on due to this report.

Feel free to open a new issue if it comes up again, with new information and renewed interest.

Thank you for your contributions.