On 04/21/2015 10:54 AM, Peter Maydell wrote:
> On 21 April 2015 at 17:48, Eric Blake <ebl...@redhat.com> wrote:
>> On 04/21/2015 09:55 AM, Peter Maydell wrote:
>>> If you want pure POSIX shell then it is slightly
>>> uglier as we have to invoke sed:
>>>
>>> argstr=""
>>> for arg in "$@"; do
>>> o=$(printf '%s.\n' "$arg" | sed s/,/,,/g)
>>> argstr=${argstr:+$argstr,}arg=${o%.}
>>> done
>>
>> It's possible to use IFS= and case to avoid the need to fork, while
>> still writing portable shell, but the solution then takes LOTS more
>> lines of code, so I'm not even going to bother to try writing it here.
>>
>> However, one thing this does NOT handle is an argument that is a literal
>> ','. That is, if I pass 'a', ',' and 'b' as my arguments, this script
>> results in $argstr being a,,,,b, which the qemu parser would read as a
>> single argument of 'a,,b' rather than the three intended arguments.
>
> Hmm? You get "arg=a,arg=,,,arg=b". Does the parser not read that
> the way I would expect?D'oh. I missed the 'arg=' insertion. > >> In order to handle that, you'd need some sort of solution that requires >> an unambiguous separation between arguments. For example, >> >> --semihosting-options opt=a,,,,b >> vs. >> --semihosting-options opt=a,opt=,,,opt=b > > The latter is what the script works with (except 'arg' rather > than 'opt'). Indeed, we have an unambiguous representation already, and I just overlooked it. > > Incidentally if you have a better idea for achieving the > desired goal than this messing around with comma-escaping > I would really like to know. I don't like either of the > current two proposals very much :-( Libvirt is already used to doing comma escaping; so while I may not like the resulting syntax, I _do_ like the consistency factor (that is, it's much easier to reuse the same mechanism everywhere than it is to invent yet another mechanism). -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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