[getopt-sig] commands on the command line

[A.T. Hofkamp]

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Hello all,

I've been thinking about commands on the command line. For example in cvs:

cvs [cvs-options] command [command-options-and-arguments]

Currently, we don't consider commands. However, that didn't feel right to me....


The basic idea that I thought is that a command is not very different from an
option. Both are a single words that we must recognize.
The only difference between options and commands is that occurrence of the
latter may cause a change in which options and commands we recognize.
That is, it should be possible to modify the recognition of options and
commands while processing. I didn't see any fundamental obstacles to this
approach. The longer I thought about it, the better it became, so it was worth
an experiment, which turned out very nicely if I may say so:

As an experiment, I have a list of options and a list of commands that we
'currently' recognize in a class Parser.
The parser gets options and arguments from a Generator class, similar to the
argparser code (I didn't have that code nearby, so I wrote my own version).
The parser offers words from the generator to the 'current' options and
commands using an ismatch() method.
* Options can retrieve the option argument through a 'getargument()' method.
  Also, they should store the match, etc, what argtools, Optik, and other option
  processing packages currently do. (Since I wasn't interested in that part, my
  options just print '--spam detected'.)
* Commands can use 'setopts()' and 'setcmds()' of the parser to modify the
  recognized options respectively commands. (There is no fundamental reason why
  an option could not modify options and/or commands, but I haven't yet seen any
  need for that.)

See also the attached code.

The example understands

opts.py [-v] [--verbose] [-oFILE] [--output=FILE] commit [-c]
opts.py [-v] [--verbose] [-oFILE] [--output=FILE] status [--brief]
opts.py [-v] [--verbose] [-oFILE] [--output=FILE] version

although it only prints recognized options.


Leveling the playing field to recognize any piece of text is quite an
improvement in my opinion. The ability to modify the recognized commands and
options is extremely powerful, it should cover most of our needs.

Also, it makes a new step in making the option-processing package more modular,
which is always good (ok, I'll settle for 'almost always' :-) ).
For example, the "--" which used to be a bit special, is trivial now. Just
consider it a command that throws away all options.
(actuallly, that is what the hard-coded version in the parser object is doing now).


No doubt there are other nice features that I have forgotten now, but they will
pop up in the discussion.

TTFN,
Albert
-- 
Constructing a computer program is like writing a painting

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