Re: Inconsistent arithmetic evaluation of parameters

From	Chet Ramey <chet.ramey@case.edu>
Newsgroups	gnu.bash.bug
Subject	Re: Inconsistent arithmetic evaluation of parameters
Date	2015-09-02 10:23 -0400
Message-ID	<mailman.394.1441203851.19560.bug-bash@gnu.org> (permalink)
References	<61895190-83A6-4D62-B90E-65023D5E966B@gmail.com> <20150901175030.GP4309@eeg.ccf.org> <CANaoh6LNi_YyOOB56ZMR3P8thRSMfoTcDCGyW8S921nVoP1H7Q@mail.gmail.com> <20150901202308.GR4309@eeg.ccf.org> <CANaoh6+kxLMGGAO8GR37xriYh8j3AZgUDNs4uL+Qjvz5bxT_Ww@mail.gmail.com>

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On 9/1/15 5:05 PM, Dennis Williamson wrote:

> It's the line above those two where I demonstrate the failure in the
> indirection and equivalency.
> 
> $ echo $((foo))  # expansion succeeds, indirection fails
> dash: 4: Illegal number: bar

Because `foo' is expanded, but the value is not treated as an expression.
The dash arithmetic evaluator never treats values resulting from expansion
as expressions, only as constants.

> $ echo $(($foo))  # both expansion and indirection succeed
> 5

Because the arithmetic evaluator sees $(( bar )).  The word expansion that
happens before arithmetic evaluation expands $foo.

http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_06_04

is the Posix specification for arithmetic evaluation.
-- 
``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 10:23 -0400

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