[TUHS] Systematic approach to command-line interfaces [ meta issues ]

Jon Steinhart jon at fourwinds.com
Sun Aug 1 08:16:58 AEST 2021

Bakul Shah writes:
> On Jul 31, 2021, at 12:20 PM, Jon Steinhart <jon at fourwinds.com> wrote:
> > 
> > So I never got getopt().  One of my rules is that I don't use a library
> > in cases where the number of lines of gunk that that it takes to use a
> > library function is >= the number of lines to just write it myself.  Yeah,
> > I know the "but the library has more eyeballs and is debugged" argument
> > but in reality libraries are the source of many bugs.  I've always taken
> > the approach that I would never hire someone who had to use a library to
> > implement a singly-linked list.
> getopt() is perhaps the wrong solution but consider something like MH,
> whose commands all follow a common pattern. Consider:
>   - options (switches) all start with a single '-'
>   - they may be abbreviated to a unique prefix.
>   - Boolean options may be inverted by prepending -no (e.g. -nolist)
>   - value options may also have -no format to remove a previous (or default) value
>   - options may appear anywhere and the last instance wins
> But different commands take different options. It would make sense to factor
> out common parsing, help etc. for a consistent treatment. In my Go code for
> parsing MH like options I used Go's flag package as a model.
> Personally I vastly prefer MH style option processing to either single char
> options or --very-long-names which can't be abbreviated. Never mind options for
> commands like gcc, who can even remember 40+ ls options?
> But I haven't thought about how to extend this for shell scripts, or
> exposing these so that shells like zsh can do command completion. To specify
> these you need a vector of tuples (name, type, default, brief-help) but that
> is painful to do in a shell.

Ah, well, you've given away the secret of real UNIX geezers, we're on both
this mailing list and the nmh list :-)

Yes, I'm mostly happy with the way that nmh does options.

I guess that I would look more kindly on getopt if it had existed much earlier
so that people writing new commands would be encouraged to use the same format.
Not as happy with it as an afterthought.

Once again, I have to go back to the meatspace locality of reference issues.
Sure, it would be nice to be able to factor out common parsing, for example
if a related set of programs shared the same option set.  But unless it's
something huge, I'd just put it in it's own file and use it for multiple
programs; I wouldn't put it in a library.  My point is that the code that
does the actual parsing is really trivial, and not necessarily the best
use of a library.

As far as help goes, I don't expect help built into command line programs;
I expect to look up error messages on the manual pages.  I'm happy with a
generic usage error as most "helpful" output that I get from programs is
not actually helpful.

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