Date: Thu, 14 Aug 2014 10:36:51 -0400 From: Rick Miller <vmiller@hostileadmin.com> To: Arthur Chance <freebsd@qeng-ho.org> Cc: FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: /bin/sh script not behaving as expected Message-ID: <CAHzLAVHH1t0WN8=BOzVsm=e0SMoqi9CCE75=EaOFSLz=ns_wpA@mail.gmail.com> In-Reply-To: <53ECC716.2020106@qeng-ho.org> References: <CAHzLAVE1E8hZvZEnDko8-7cfx6JYypezi3oxs4vKKjxDzSzZnw@mail.gmail.com> <53ECC716.2020106@qeng-ho.org>
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On Thu, Aug 14, 2014 at 10:26 AM, Arthur Chance <freebsd@qeng-ho.org> wrote=
:
> On 14/08/2014 15:13, Rick Miller wrote:
>
>> Hi all,
>>
>> I have shell code whose purpose is to determine the first disk in the
>> system where FreeBSD is to be installed. The code is not behaving as
>> expected and I=E2=80=99m hoping that fresh pairs of eyes might help me i=
dentify
>> the
>> problem.
>>
>> Here is the script along with an explanation of the implementation and
>> description of the problem:
>>
>> #! /bin/sh
>>
>> disks=3D"da2 da1 da0";
>>
>> for d in ${disks}; do
>> if [ -z "${disk}" -o "${disk}" '>' "${d}" ]; then
>> : ${disk:=3D${d}};
>> fi
>> done
>>
>>
>> echo $disk;
>>
>>
>> [ snip ]
>>
>>
> Your problem is in
>
> : ${disk:=3D${d}};
>
> From man sh
>
> ${parameter:=3Dword}
> Assign Default Values. If parameter is unset or null, the expan=
=E2=80=90
> sion of word is assigned to parameter. In all cases, the final
> value of parameter is substituted. Quoting inside word does not
> prevent field splitting or pathname expansion. Only variables,
> not positional parameters or special parameters, can be assigned
> in this way.
>
> Once $disk has been set this form won't reset it.
>
> You should have
>
> disk=3D"$d"
>
Excellent, thanks! My understanding of parameter expansion was flawed. I
appreciate the info.
--=20
Take care
Rick Miller
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