Re: $OPTIND varibale value is different from sh

[Greg Wooledge]

On Wed, Jun 20, 2018 at 05:16:48PM +0900, Hyunho Cho wrote:
> set -- -a -bc hello world
> 
> echo $OPTIND                    # sh, bash  = 1
> 
> getopts abc opt "$@"  
> echo $opt, $OPTIND           # sh, bash = a, 2
> 
> getopts abc opt "$@"          # bash  = b, 2                  <------ 
> different from "sh"
> echo $opt, $OPTIND            # sh      = b, 3        

(There is no "sh".  There are just differing implementations of the POSIX
standard.  If you meant "dash", then yes, I get the same results as you
using bash and dash.)

POSIX says,

  Each time it is invoked, the getopts utility shall place the value of
  the next option in the shell variable specified by the name operand
  and the index of the next argument to be processed in the shell
  variable OPTIND.

After your second call to getops, the second argument is only half-way
processed.  Your third call to getopts will still be processing the
second argument.  So, it's unclear what OPTIND should contain at that
point.

Since POSIX doesn't say anything about what OPTIND should contain
when you're in the middle of processing an argument with multiple
concatenated options inside it, I'd say that this falls into the
realm of "unspecified behavior", and shells can do anything they
want.  So, not a bug in bash.  Or in dash.  Or in ksh, which by the
way does the same thing as bash.

I really don't understand what you're doing here, either.  The only
use of OPTIND is after the final call to getopts, when there are no
more options to process.  At that point, OPTIND tells you how many
times you have to "shift" to get rid of all the options that were
processed.  (And you have to subtract 1, because legacy historical
reasons.)

Any attempt to use OPTIND in the middle of the loop seems pointless
and hazardous to me.

If you want the option-argument of an option that takes one, it's in
the OPTARG variable.  You use that inside the while getopts loop.
(Your example didn't have any options with arguments, so I'm still
puzzled as to what you're actually trying to do.)