[TUHS] Systematic approach to command-line interfaces

Adam Thornton athornton at gmail.com
Sun Aug 1 00:25:24 AEST 2021

Digressing a bit (but only a bit) talking about IPC: Powershell and CMS
PIPELINES both take the approach of more structured pipelines, where pipe
contents are not just streams of bytes but can be structured records.  This
offers a lot of power, but it also inhibits the ability to arbitrarily
compose pipe stages, because you've effectively introduced a type system.

On the other hand you can certainly argue that stream-of-bytes pipes ALSO
introduce a type system, it's just a completely ad-hoc, undocumented, and
fragile one that relies on the cooperation of both ends of the pipe to work
at all, and you'd be right.

In practice...well, I'd rather use stream-of-bytes, but I am more
comfortable in Unix-like environments than Powershell, and my CMS PIPELINES
skills are quite rusty now.

On Sat, Jul 31, 2021 at 7:21 AM Adam Thornton <athornton at gmail.com> wrote:

> On Jul 31, 2021, at 5:25 AM, Michael Siegel <msi at malbolge.net> wrote:
> 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.
> I see that Dan Halbert beat me to mentioning "click."
> The trick with shell is that unless you write the parser in shell, which
> is going to be miserable, you’re doing it in a command in a subshell, and
> therefore your return values have to be a structured stream of bytes on
> stdout, which the parent shell is going to have to interpret.  An eval-able
> shell fragment, where you have a convention of what the variables you get
> from the option parser will be, is probably the easiest way, since from the
> parent that would look like:
> $(parse_my_opts $*)
> # Magic variables spring to life
> if [ “$OPT_SUBCOMMAND_0” == “burninate” ]; then ….
> Adam
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