Re: [Qemu-devel] [PATCH] tests: Handle $RANDOM not being supported by the shell

[Eric Blake <eblake@redhat.com>]

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On 07/14/2017 06:27 AM, Kamil Rytarowski wrote:
> On 14.07.2017 12:45, Peter Maydell wrote:
>> In various places in our test makefiles and scripts we use the
>> shell $RANDOM to create a random number. This is a bash
>> specific extension, and doesn't work on other shells.
> 
> This is supported on other shells like ksh (Korn Shell), but still as an
> extension.
> 
>> With dash the shell doesn't complain, it just effectively
>> always evaluates $RANDOM to 0:
>>   echo $((RANDOM + 32768))     => 32768
>>
>> However, on NetBSD the shell will complain:
>>   "-sh: arith: syntax error: "RANDOM + 32768"
>>
> 
> I will make sure whether this behavior is correct in our sh(1).

The question is what your shell does for:

unset foo
echo $(( foo % 255 ))

if it reliably prints 0, then it would do the same when RANDOM is an
undefined (and not a magic) variable.  Presumably, where sh is going
wrong is that it is treating an undefined variable not as 0, but as a
syntax error, and you'd get that behavior regardless of whether RANDOM
is in the mix.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org


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