Date: Tue, 29 Aug 2017 13:32:01 +0200 From: Denys Vlasenko <vda.linux@...glemail.com> To: musl <musl@...ts.openwall.com>, Rich Felker <dalias@...c.org> Subject: Re: getopt() not exposing __optpos - shell needs it 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. It mangles optarg if an option without argument follows an option with an argument.
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