Re: [Help-bash] set -u in an arithmetic context

[Eric Blake]

On 04/26/2012 03:59 PM, Bill Gradwohl wrote:
> On Thu, Apr 26, 2012 at 11:01 AM, Eric Blake <address@hidden> wrote:
> 
>> Especially since 'set -u' _does_ affect arithmetic expansion (although I
>> couldn't quickly find such a requirement in POSIX, so we may have a hole
>> in the standard):
>>
>>
> 
> We're on the same bash level.
> 
> I question the notion of "expansion" in this case. Without the $ or ${}
> wrappers is there "expansion" going on?

In the fact that $((x)) sees 'x', and checks for a shell variable of the
same name, and uses the numeric value of the contents of that shell
variable.

> 
> Man bash says that set -u work as part of "parameter expansion". Without
> the $ or ${} wrappers, isn't it just taking whatever the value is an using
> it as is with no expansion?

There is expansion going on.  POSIX requires $((x)) and $(($x)) to give
the same output when x is set; so logically, it should require 'set -u'
to cause the same error when x is unset.

-- 
Eric Blake   address@hidden    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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