cvs commit: src/usr.sbin/portsnap/portsnap portsnap.sh

[Brian Somers]

On Sat, 13 Aug 2005 21:06:35 -0500 Bob Willcox <bob at immure.com> wrote:
> On Sat, Aug 13, 2005 at 02:47:19PM -0700, Colin Percival wrote:
> > Colin Percival wrote:
> > >   This bug was caused by the astonishing interaction of "return" and
> > >   pipelines; in the following code, the "return" does not exit the
> > >   function, but instead exits the subshell which was spawned for the last
> > >   element of the pipeline; consequently, the output produced is "foo".
> > >   
> > >   foo() {
> > >           echo bar | while read baz; do
> > >                   if [ ${baz} = "bar" ]; then
> > >                           return 1
> > >                   fi
> > >           done
> > >   
> > >           echo foo
> > >   }
> > 
> > For what it's worth, I don't know if the behaviour of our sh(1) is correct
> > here.  IEEE 1003.1, 2004 Ed. says
> > 
> > "The return utility shall cause the shell to stop executing the current function
> > or dot script. If the shell is not currently executing a function or dot script,
> > the results are unspecified."
> > 
> > and I don't see any mention of not returning from a function just because we
> > happen to be inside a subshell.
> 
> I tried this on a some different shells. Turns out that bash & pdksh
> behave similar to the FreeBSD shell, but with ksh93 the return exits the
> function. So maybe ksh93 is the only one working correctly--or it's the
> only one that's broke.

No.  ksh93, aka the original ksh, is documented to execute the last
command in a pipeline inline.  Other shells don't.  This is great for
doing things like ``echo $line | read a b c'', and also avoids the
unexpected return/exit not returning or exiting problems that Colin
has seen.

However, traditional Bourne shell scripts have to just handle this sort
of weirdness with constructs like

    get input | while read line
    do
        important command || exit 1
        other important command || exit 1
    done || exit 1

AFAIK POSIX doesn't explicitly say what's right here, but not having
the POSIX spec handy, treat that with a pinch of salt!!

-- 
Brian Somers                                          <brian at Awfulhak.org>
Don't _EVER_ lose your sense of humour !               <brian at FreeBSD.org>