On 02/06/2015 00:10, Jilles Tjoelker wrote:
On Mon, Jun 01, 2015 at 07:30:46PM +0200, Harald van Dijk wrote:
On 01/06/2015 08:29, Herbert Xu wrote:
On Fri, May 29, 2015 at 07:50:09AM +0200, Harald van Dijk wrote:
But the test script in this thread does invoke getopts with
parameters that are the same in all invocations, and without
modifying OPTIND. I don't see anything else in the normative
sections that would make the result undefined or unspecified either.
I do think the script is valid, and the results in dash should match
those of other shells.
The bash behaviour makes it impossible to call shell functions
that invoke getopts while in the middle of an getopts loop.
IMHO the dash behaviour makes a lot more sense since a function
always brings with it a new set of parameters. That plus the
fact that this behaviour has been there since day one makes me
reluctant to change it since the POSIX wording is not all that
clear.
True. Given that almost no shell supports that anyway, there can't be
too many scripts that rely on it, but I did warn about the risk of
breaking another type of existing scripts as well, I agree that's a real
concern.
FreeBSD sh inherits similar code from ash and likewise has per-function
getopts state. Various shell scripts in the FreeBSD base system use
getopts in functions without setting OPTIND=1.
Yikes. That's an unfortunate effect of writing scripts that only get run
on a single shell: things like that don't even show up as a possible
problem. It's similar to how many bashisms sneak into supposedly
portable shell scripts.
One thing that doesn't really make sense, though: if the getopts
internal state is local to a function, then OPTIND and OPTARG really
should be too. Because they aren't, nested getopts loops already don't
really work in a useful way in dash, because the inner loop overwrites
the OPTIND and OPTARG variables. While OPTARG will typically be checked
right at the start of the loop, before any inner loop executes, OPTIND
is typically used at the end of the loop, in combination with the shift
command. The current behaviour makes the OPTIND value in that case
unreliable.
First, note that the OPTARG and OPTIND shell variables are not an input
to getopts, except for an assignment OPTIND=1 (restoring an OPTIND local
at function return does not reset getopts), and that getopts writes
OPTIND no matter whether getopts's internal optind changed in this
invocation.
With that, the value of OPTIND generally used in scripts is not
unreliable. OPTIND is generally only checked after getopts returned
false (end of options), in the sequence
while getopts ...; do
...
done
shift "$((OPTIND - 1))"
Ah, you're right, I missed that there will usually be another execution
of getopts before OPTIND is used. Thanks for clearing that up. In that
case, I agree, the situations in which the values of OPTIND and OPTARG
are unreliable are only situations in which scripts usually don't bother
checking their values.
So either way, I think something should change. But if you prefer to get
clarification first about the intended meaning of the POSIX wording,
that certainly seems reasonable to me.
I think the POSIX wording is clear enough, but it may not be desirable
to change getopts to work that way.
It was Herbert Xu who felt the POSIX wording was unclear, and he is the
dash maintainer, so his opinion on whether the wording is clear is the
one that matters.
If it is clear or clarified what POSIX requires, and that POSIX allows
the current implementation, then I see no need either to change the dash
behaviour. It could still be useful to make OPTIND and OPTARG local, but
you've convinced at least me that it's only a minor problem.
If it is clear or clarified what POSIX requires, and that POSIX
disallows the current implementation, and the current implementation is
deemed too desirable to drop, then it might make sense to support both
alternatives, with an option at configure time to switch between them.
As far as I know, dash does still aim to conform to POSIX, so even if a
conscious decision is made to deviate from POSIX by default, I think an
option to conform to it would be nice for those who care about it. I
would be happy to create a patch, if this approach would be more agreeable.
Cheers,
Harald van Dijk
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