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Re: Inconsistent arithmetic evaluation of parameters


From: Chet Ramey
Subject: Re: Inconsistent arithmetic evaluation of parameters
Date: Wed, 2 Sep 2015 10:06:28 -0400
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:38.0) Gecko/20100101 Thunderbird/38.2.0

On 9/1/15 12:50 AM, Clint Hepner wrote:

> Bash Version: 4.3
> Patch Level: 42
> Release Status: release
> 
> Description:
> 
> Parameter names are recursively evaluated in an arithmetic expression, but 
> this
> is not done consistently.

Parameter names are expanded and treated as expressions where they need to
be evaluated as a number, and as identifiers when they are the subject of
assignment.  This is the usual way to handle context-dependent evaluation.

> Repeat-By:
> 
>     foo=bar
>     bar=5
>     echo $(( foo ))    # produces 5
>     echo $(( foo++ ))  # produces 5
>     echo $foo          # produces 6, not bar
>     echo $bar          # produces 5, not 6

Consider this equivalent expression:

        oldfoo=foo,foo=foo+1,oldfoo

Would you claim that the foo on the lhs of the assignment statement should
be expanded to `bar'?  How would assignments ever be performed if it were?

-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU    chet@case.edu    http://cnswww.cns.cwru.edu/~chet/



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