Non-patch: Option arguments

[Peter Stephenson <pws@csr.com>]

I've rewritten the option handling for builtins to improve the currently
woeful handling of arguments to options.  As I didn't see fit to
maintain compatibility with the current broken form, this changes
everything involving options.  So the patch is huge and unless anyone
screams I will commit it without posting it from home, where I've been
writing it, in the next couple of days.

The syntax for option arguments uses a trailing `:' for a mandatory
argument, as usual, a trailing `::' for an optional argument (one which
must occur in the same word or will be assumed not to be present), which
seems to be how the GNU getopts library function works, and I've
invented `:%' for an optional integer argument, which is different
because `-i 10' and `-i10' are both allowed.  Maybe someone knows some
more standard conventions.

I have't seen fit to provide compatibility for the following current
weirdnesses:
- in `read -k num', num is actually the first argument to `read', not an
  option argument at all (undocumented).
- in print and read, -u0 can be specified as -0u, -u -0, etc.  However,
  I have written a special case for -up (equivalent to -p) which,
  although undocumented, is at least half-way logical.
- `fc -e' was silently allowed as meaning `fc', even though -e
  supposedly had a mandatory argument.
- (Still to do) `cd' has non-standard option handling, so that
  `cd -' and `cd -3' work.  However, this is probably best handled as a
  special case in the option parsing code rather than in cd.  One
  current oddity is that cd is limited to two arguments including any
  options:
    % cd -P -P -P
    cd: too many arguments

  However, there is also the fact that `cd -directory' doesn't try to
  parse options though `cd -sPL' does.  As `cd -- -directory' doesn't
  work at the moment, there's no way of standardizing this without
  creating an incompatibility.  So I may quietly forget about cd for the
  moment.  Note, however, that other shells use standard option handling
  with cd, so I think'll we'll have to fix it and maybe just take the
  hit with the (rare) case of directories beginning with a `-' working
  differently from now on.

  P.S.: I hate cd.

Not addressed in this patch, but may want looking at:
- Some modules advertise builtins with options which instead of normal
  arguments take `the first non-option argument'.  Many of these might
  be less confusing if they were real option arguments.  (This doesn't
  apply to `-m' pattern arguments which tend to alter the meaning of
  real arguments instead of the option taking an argument.)
- Some commands which handle their own options may now work with
  standard option handling, although it's still complicated with things
  like `kill'.
- It would not be that difficult to add handling of repeated options
  as a linked list, e.g. -o opt1 -o opt2 creates a linked list of
  strings instead of a single string for the option argument.
  If the option argument becomes a union, handling of integer arguments
  can be standardised, too (currently they get converted from a string
  at the point of use resulting in multiple bits of code that issue
  similar `this isn't an integer, idiot' error messages).
- Something else I've forgotten but may remember later on.

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR Ltd., Science Park, Milton Road,
Cambridge, CB4 0WH, UK                          Tel: +44 (0)1223 692070


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