Path: csiph.com!optima2.xanadu-bbs.net!xanadu-bbs.net!news.glorb.com!usenet.stanford.edu!not-for-mail From: Chet Ramey Newsgroups: gnu.bash.bug Subject: Re: Inconsistent arithmetic evaluation of parameters Date: Wed, 2 Sep 2015 10:18:25 -0400 Lines: 40 Approved: bug-bash@gnu.org Message-ID: References: <61895190-83A6-4D62-B90E-65023D5E966B@gmail.com> <20150901175030.GP4309@eeg.ccf.org> Reply-To: chet.ramey@case.edu NNTP-Posting-Host: lists.gnu.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Trace: usenet.stanford.edu 1441203540 29653 208.118.235.17 (2 Sep 2015 14:19:00 GMT) X-Complaints-To: action@cs.stanford.edu Cc: "bug-bash@gnu.org" , Clint Hepner , chet.ramey@case.edu To: Dennis Williamson , Greg Wooledge Envelope-to: bug-bash@gnu.org X-Enigmail-Draft-Status: N1110 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 In-Reply-To: X-Junkmail-Status: score=10/60, host=mpv5.cwru.edu X-Junkmail-Whitelist: YES (by domain whitelist at mpv1.tis.cwru.edu) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.4.x-2.6.x [generic] X-Received-From: 129.22.105.36 X-BeenThere: bug-bash@gnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Bug reports for the GNU Bourne Again SHell List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Xref: csiph.com gnu.bash.bug:11461 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/