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Re: Inconsistent arithmetic evaluation of parameters

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On 9/1/15 4:13 PM, Dennis Williamson wrote:

> The version of dash I have handy (0.5.7) has math support which IMHO is broken:
> 
> $ foo=bar 
> $ bar=5
> $ echo $foo
> bar
> $ echo $((foo))
> dash: 4: Illegal number: bar
> $ echo $(($foo))
> 5
> $ echo $((bar))
> 5
> $ echo $(($bar))
> 5

Dash does the minimum that Posix requires for $(( )) and no more.

The stuff between $(( and )) is expanded and the result is treated as an
arithmetic expression.  When there is something that looks like an
identifier (e.g., `foo') remaining after expansion, it's treated as a
shell variable whose value is assumed to be an integer constant, not an
expression.  Since foo expands to `bar', and `bar' is not an integer, dash
throws an error.

> 
> Note the inconsistency in support of omitting the inner dollar sign. Also
> post increment produces an error and pre increment produces no error and no
> action:

Posix allows implementations to omit support for prefix and postfix ++ and
--.  If you don't implement prefix ++ and --, they are unary plus and
minus operators that happen to `stack'.

-- 
``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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Re: Inconsistent arithmetic evaluation of parameters Chet Ramey <chet.ramey@case.edu> - 2015-09-02 10:18 -0400

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