From: Jilles Tjoelker <jilles@stack.nl>
To: Dan Muresan <danmbox@gmail.com>, dash@vger.kernel.org
Subject: Re: shift "fatal error"
Date: Tue, 15 Mar 2011 22:31:16 +0100 [thread overview]
Message-ID: <20110315213116.GA53303@stack.nl> (raw)
In-Reply-To: <20110310192333.GE3948@wopr.local.invalid>
On Thu, Mar 10, 2011 at 08:23:33PM +0100, Guido Berhoerster wrote:
> * Dan Muresan <danmbox@gmail.com> [2011-03-10 19:41]:
> > Hi, is there some consensus on whether shift should cause a "fatal
> > error" as reported by Herbert against bash:
> >
> > http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=252378
> >
> > # doesn't print anything
> > dash -c 'shift 2; echo hi'
> >
> > My copy of SUSv3 doesn't seem to imply any "fatal error" handling
> > requirement for shift:
> >
> > --- 8-X ---
> > EXIT STATUS
> >
> > The exit status is >0 if n>$#; otherwise, it is zero.
> >
> > CONSEQUENCES OF ERRORS
> >
> > Default.
> > --- 8-X ---
> For IEEE Std 1003.1-2008 see section 2.8.1 "Consequences of
> Shell Errors": a "utility syntax error (option or operand error)"
> with special built-ins shall cause the shell to exit. That's what
> dash, ksh93, and pdksh do.
That may have been the intention (considering that it matches the real
Bourne shell in addition to various flavours of Korn shell), but that is
not how I would interpret it. A too high shift count still seems
syntactically valid to me.
A statement about the exit status in a particular error situation also
usually indicates that the shell shall not abort.
Examples of shift commands that I think shall cause the shell to abort:
shift -S # unless a -S option is supported as an extension
shift x # unless arithmetic expressions are accepted as an extension
shift @ # unless there is some strange extension
The FreeBSD sh shift special builtin behaves this way (a too high shift
count is not fatal but a syntactically invalid number is). This was done
a few years ago when the syntax-error property of special builtins was
implemented, as making a too high shift count fatal caused a configure
script in the FreeBSD base system to fail.
I would not encourage the extension of accepting arithmetic expressions
because that requires a subtly different kind of arithmetic expression
without octal constants. POSIX is clear that 'shift 010' should shift
ten positions, not eight, while 'shift $((010))' should shift eight
positions.
--
Jilles Tjoelker
next prev parent reply other threads:[~2011-03-15 21:31 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-10 18:40 shift "fatal error" Dan Muresan
2011-03-10 19:23 ` Guido Berhoerster
2011-03-15 21:31 ` Jilles Tjoelker [this message]
2011-03-26 7:11 ` Dan Muresan
2011-03-26 7:27 ` Jonathan Nieder
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