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Re: [Libguestfs] [PATCH] supermin: Die with an error if no kernels found (RHBZ#539746).



Richard W.M. Jones wrote:

> On Wed, Nov 25, 2009 at 09:25:37AM +0100, Jim Meyering wrote:
>> First, on this kernels-assigning line,
>>
>>     kernels=$(ls -1vr /boot/vmlinuz-*.$arch* 2>/dev/null | grep -v xen; ls -1vr /boot/vmlinuz-* 2>/dev/null | grep -v xen)
>>
>> if you add ls' -d option, that will prevent a false-positive match
>> if /boot/vmlinuz-* ever matches a directory containing something whose
>> name includes "xen".
>>
>> Also, you can avoid duplicating the "2>/dev/null | grep -v xen" part
>> by using a single invocatin of ls, and then I noticed that the expansion
>> of the second glob, /boot/vmlinuz-*, would include anything matched by
>> the first one, so this is adequate:
>>
>>     kernels=$(ls -1dvr /boot/vmlinuz-* 2>/dev/null | grep -v xen)
>
> On rereading this, I understand the mistake.
>
> The order that the kernels is presented in is significant, which is
> why we first search for $arch-specific kernels, and secondly for
> general kernels (in both cases avoiding Xen PV kernels).

Ahh.. good point.  I hadn't looked at how $kernels was used.

Keeping the two globs, you can still use only one ls invocation,
(adding ls's -U (don't sort) option):

  kernels=$(ls -1duvr /boot/vmlinuz-*.$arch* /boot/vmlinuz-* 2>/dev/null \
            | grep -v xen)

Does it matter that ls's -v (version sort) option is relatively new?
It was added in coreutils-7.0 (2008-10-05).


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