Improvement: better command line API

[vaab]

The current command line API has lots of thing left to be desired.

• Name are not easy to remember
  • does it start with get- (get-values and values) ?
  • does it take a "s" (get-value and get-values) ?
• Which ACTION can I use on which type ?
• The final -0 seems like a bad smell, why not a separate option ? -0

Some others concerns raised:

• Would be nice to have more choice that stdin as input and stdout as output. it would be a great idea if you pass a file as parameter... #11
• order of KEY and ACTION could be inverted, as we first browse, then think to
  what we'd like to do with the target.
  • get-value ACTION could then be the default action and be removed.
  • and a separate optional [--get-keys | --get-values | --get-key-values | --get-type] could be
    enough for all remaining ACTIONs.

Some deeper reflection on these subject might help to get further:

• . (dot) is the get-value action in some ways. Why not put all in the KEY and remove the need of
  ACTION. KEY would be a way to map a YAML entry into a list of YAML (possibly a list of 1 element).
  • This would require special chars to map to meanings as current keys, values.
  • how to differentiate between a list in one YAML entry and a list of YAML separated entries ?

[vaab]

I'm inclined to go towards these changements::

shyaml KEY [--get-keys | --get-values | --get-key-values | --get-type] [-0] [--default DEFAULT]

With these rules:

• all the --get-* are mutually exclusive and optional (choose one of them or none of them), and
  • they work on the YAML value currently targetted by KEY
  • if they finish with a s, then they'll output a list of values that requires a separator, by default
    this separator is \n, but can be changed to \0 thanks to -0 option.
  • if it mentions key then it works only on struct. --get-values on struct only return list of values.

Optionally we could also have:

• [--input FILE | -i FILE] and [--output FILE | -o FILE] to read/write from files, supporting - as
  being stdin/stdout, and defaulted to those if not specified. it would be a great idea if you pass a file as parameter... #11

Any comments ?