Date: Tue, 29 Aug 2017 08:20:14 -0400 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: getopt() not exposing __optpos - shell needs it On Tue, Aug 29, 2017 at 01:32:01PM +0200, Denys Vlasenko wrote: > On Mon, Aug 28, 2017 at 5:28 PM, Rich Felker <dalias@...c.org> wrote: > > On Mon, Aug 28, 2017 at 12:18:57PM +0200, Denys Vlasenko wrote: > >> I am using getopt() in busybox hush shell. > >> "unset" builtin, for example: it takes -v and -f options. > >> This works fine. > >> > >> However, POSIX requires that shells has a "getopts" builtin: > >> http://pubs.opengroup.org/onlinepubs/9699919799/utilities/getopts.html > >> > >> It is basically an API binding to access getopt() in the shell code: > >> it uses OPTIND and (in bash) OPTERR on entry, returns a single-char > >> variable on return and updates OPTIND and OPTARG. Sounds familiar, right? > >> > >> When I try to do that (use getopt() to implement "getopts"), it hits a snag. > >> Unlike normal getopt() usage in C programs, where it is called in a loop > >> with the same argv array until parsing is finished, > >> when it is used from "getopts", each successive call will (usually) have > >> the same argv CONTENTS, but not the ADDRESSES. > >> (The reason is in how shell works: it re-creates command arguments just before > >> running a command, since there can be variable substitution, globbing, etc). > > > > First, some background out of the spec to establish what is supposed > > to work and what's not: > > > > If the application sets OPTIND to the value 1, a new set of > > parameters can be used: either the current positional parameters > > or new arg values. Any other attempt to invoke getopts multiple > > times in a single shell execution environment with parameters > > (positional parameters or arg operands) that are not the same in > > all invocations, or with an OPTIND value modified to be a value > > other than 1, produces unspecified results. > > > > What this means is that, when you use getopts(1), you need to either > > use the exact same arguments (as you said, *string contents*, not > > likely to be the same argv pointers) or reset it with OPTIND=1. > > > > It seems to me that the easiest, fully-portable fix is just the > > obvious quadratic-time solution: on each run of getopts(1), reset > > getopt(3) to the start and call it ++N times. > > This has several problems: > It prints multiple messages "invalid option -q" > when there are options which are not in optstring. opterr=0; Either leave it 0 and always do your own error printing, or set it nonzero just before the last call (for the current option) so that only that one prints an error. > It mangles optarg if an option without argument follows > an option with an argument. Maybe I'm missing what you're trying to say, but all the state is clobbered; I don't see how optarg is a problem specifically. You can clear or set it to a sentinel value before the relevant call if you're trying to determine if the call set it. Across other calls (not the one for the current option) I don't see why it matters at all what happens to it. Rich
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