Re: $((expr)) allows the hexadecimal constant "0x"

[Steffen Nurpmeso]

Koichi Murase wrote in
 <CAFLRLk_btwbPzzTRMp9OL21-2AG7i9KAXiXC7tQocSay3VKaJw@mail.gmail.com>:
 |2023年12月10日(日) 15:58 Koichi Murase <myoga.murase@gmail.com>:
 |> 2023年12月10日(日) 14:13 Martin D Kealey <martin@kurahaupo.gen.nz>:
 ...
 |> I'm not a big fan of `10#[-+]digits' and invalidating `10#' either
 ...
 |I checked the behaviors of different shells because I was interested
 |in them.  They seem to vary more than I expected.
 |
 || $((10#)) | $((2*10#-1)) | $((2*10#- 1))
 |----------|----------|--------------|---------------
 |bash-5.0  | 0        | -1           | -1
 |bash-5.1  | error    | error        | error
 |ksh93u    | 0        | -2           | -1
 |ksh93v    | error    | error        | error
 |mksh      | 0        | -1           | -1
 |zsh       | 0        | -2           | error
 |
 |ksh93u is tested with "Version AJM 93u+m/1.0.3 2022-08-25" and
 |"Version AJM 93u+ 2012-08-01". ksh93v is tested with "Version A
 |2020.0.0" (strictly speaking, this is not 93v but developed based on
 |93v).  $((2*10# -1)) was the same as $((2*10#-1)). $((2*10# - 1)) was
 |the same as $((2*10#- 1)).

It is totally off-topic, but please let me add the results for the
MUA i maintain (ie the next version that includes $(()), but the
cold is now over a year old):

  ? echo $((10#))
  .. Bad $(()) substitution: unknown operator: 10#: stop near: 10#

Derived from the ISO C standard, i thought when 0x is 0 rest x,
then that is 10 rest #, and that is not a valid arithmetic
expression.  $((10#    8)) would echo "8" for my one, as below.

  ? echo $((2*10#-1))
  -2
  ? echo $((2*10#- 1))
  ..: Bad $(()) substitution: unknown operator: 2*10#- 1: stop near: 10#- 1

This is because field padding is not supported: "- 1" is not
a negative value, but a hyphen-minus, a space, and a positive
decimal.

  ? echo $((2*10#  -1))
  -2

As above, $(()) uses a convenience mode

  /*! Relaxed \a{base} 0 convenience: if the input used \c{BASE#number} number 
sign syntax,
   * then the scan will be restarted anew with the given base.
   * Like this an UI can be permissive and support \c{s='  -008'; eval 10#\$s} 
out of the box
   * (it would require a lot of logic otherwise). */
  su_IDEC_MODE_BASE0_NUMSIG_RESCAN = 1u<<3,

I thought this would be a good idea, and i like it in practice.
Here it is local to $(()) in addition.

--steffen
|
|Der Kragenbaer,                The moon bear,
|der holt sich munter           he cheerfully and one by one
|einen nach dem anderen runter  wa.ks himself off
|(By Robert Gernhardt)
|
| Only in December: lightful Dubai COP28 Narendra Modi quote:
|  A small part of humanity has ruthlessly exploited nature.
|  But the entire humanity is bearing the cost of it,
|  especially the inhabitants of the Global South.
|  The selfishness of a few will lead the world into darkness,
|  not just for themselves but for the entire world.
|  [Christians might think of Revelation 11:18
|    The nations were angry, and your wrath has come[.]
|    [.]for destroying those who destroy the earth.
|   But i find the above more kind, and much friendlier]