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

Jon Steinhart jon at fourwinds.com
Sun Aug 1 05:20:02 AEST 2021

Michael Siegel writes:
> Hello,
> I've recently started to implement a set of helper functions and
> procedures for parsing Unix-like command-line interfaces (i.e., POSIX +
> GNU-style long options, in this case) in Ada.
> While doing that, I learned that there is a better way to approach
> this problem – beyond using getopt(s) (which never really made sense to
> me) and having to write case statements in loops every time: Define a
> grammar, let a pre-built parser do the work, and have the parser
> provide the results to the program.
> Now, defining such a grammar requires a thoroughly systematic approach
> to the design of command-line interfaces. One problem with that is
> whether that grammar should allow for sub-commands. And that leads to
> the question of how task-specific tool sets should be designed. These
> seem to be a relatively new phenomenon in Unix-like systems that POSIX
> doesn't say anything about, as far as I can see.
> So, I've prepared a bit of a write-up, pondering on the pros and cons
> of two different ways of having task-specific tool sets
> (non-hierarchical command sets vs. sub-commands) that is available at
>   https://www.msiism.org/files/doc/unix-like_command-line_interfaces.html
> I tend to think the sub-command approach is better. But I'm neither a UI
> nor a Unix expert and have no formal training in computer things. So, I
> thought this would be a good place to ask for comment (and get some
> historical perspective).
> This is all just my pro-hobbyist attempt to make some people's lives
> easier, especially mine. I mean, currently, the "Unix" command line is
> quite a zoo, and not in a positive sense. Also, the number of
> well-thought-out command-line interfaces doesn't seem to be a growing
> one. But I guess that could be changed by providing truly easy ways to
> make good interfaces.
> --
> Michael

Well, don't let me discourage you from doing what you want.  But, in my
opinion, it doesn't add value to do something that's already been done
but differently; it detracts from value because now there's yet another
competing way to do something.

I'm actually surprised that the format of commands was as consistent as
it was for as long as it was.  Sure, I never liked the way that things
like tar were inconsistent, but it was mostly good for a long time.  I
see two reasons for the more recent messiness.

 o  Minimal learning of history by newer practicioners resulting in
    doing things in a way that they're familiar instead of learning
    the behavior of the target environment and fitting in.  It's what
    I call the "Ugly American Tourist" model; I'm in your country so
    you should speak English; why would I learn your language?

 o  The endless pile of --gnu-long-option-names.

On one hand, I sort of understand the long option names because so many
commands have so many options that there's no way to have one-character
mnemonics.  But, I would make the argument that if one has that many
options it's a sign that the command is trying to do too much stuff.
For example, I don't care for the compression options on tar.  These are
actually just invoking separate programs in a pipeline, which to me is
the job of the shell.  Sure, it can be convenient, but again, one of the
advantages of the shell is that I can make scripts for anything that I'm
doing so often that the convenience would be nice.  And without restarting
an old flame war, separate programs are more stylisticly in line and more
useful than many of the cat options.

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.


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