Re: [PATCH 1/2] docs: korn shells can have $? > 256 for signal-terminated children

[Peter Rosin]

Hi Stefano!

Some nits inlined...

Cheers,
Peter

Stefano Lattarini wrote On 2011-09-29 10:51:
> Some Korn shells, when a child process die due to signal number
> n, can leave in $? an exit status of 256+n, instead of the "more
> standard" 128+n.  See also Austin Group issue 0000051:
>   <http://www.austingroupbugs.net/view.php?id=51>
> 
> * doc/autoconf.texi (Signal handling): Document the described Korn
> Shell behaviour, and some of its possible shortcomings.
> 
> Suggestion by Eric Blake.
> ---
>  ChangeLog         |   14 +++++++----
>  doc/autoconf.texi |   61 
> +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 70 insertions(+), 5 deletions(-)
> 
> diff --git a/ChangeLog b/ChangeLog
> index be019f5..cb6416c 100644
> --- a/ChangeLog
> +++ b/ChangeLog
> @@ -1,9 +1,13 @@
> -2011-09-26  Eric Blake  <address@hidden>
> -
> -     docs: relax documentation license by dropping cover text
> -     * doc/autoconf.texi (copying): Drop front- and back-cover texts.
> -     * NEWS: Document this.
> -     Reported by Brian Gough.
> +2011-09-29  Stefano Lattarini  <address@hidden>
> +
> +     docs: korn shells can have $? > 256 for signal-terminated children
> +     Some Korn shells, when a child process die due to signal number
> +     n, can leave in $? an exit status of 256+n, instead of the "more
> +     standard" 128+n.  See also Austin Group issue 0000051:

Perhaps more common instead of "more standard"? Once more below.

> +       <http://www.austingroupbugs.net/view.php?id=51>
> +     * doc/autoconf.texi (Signal handling): Document the described Korn
> +     Shell behaviour, and some of its possible shortcomings.
> +     Suggestion by Eric Blake.
>  
>  2011-09-13  Stefano Lattarini  <address@hidden>
>  
> diff --git a/doc/autoconf.texi b/doc/autoconf.texi
> index 91bb50a..2f74072 100644
> --- a/doc/autoconf.texi
> +++ b/doc/autoconf.texi
> @@ -15610,6 +15610,67 @@ and @code{/usr/xpg4/bin/sh} will proceed to exit 
> with status 130 (i.e.,
>  128 + 2). In any case, if there is an active trap associated with
>  @code{SIGINT}, those shells will correctly execute it.
>  
> +Some Korn shells, when a child process die due receiving a signal with

dies due to?

> +signal number @var{n}, can leave in @samp{$?} an exit status of
> address@hidden instead of the ``more standard'' address@hidden  Observe the
> +difference between AT&T @code{ksh93} (2011) and @code{bash} 4.1.5 on
> +Debian:
> +
> address@hidden
> +$ @kbd{/bin/ksh -c 'sh -c "kill -1 \$\$"; echo $?'}
> +/bin/ksh: line 1: 7837: Hangup
> +257
> +$ @kbd{/bin/bash -c 'sh -c "kill -1 \$\$"; echo $?'}
> +/bin/bash: line 1:  7861 Hangup        (sh -c "kill -1 \$\$")
> +129
> address@hidden example
> +
> address@hidden
> +This @command{ksh} behaviour is allowed by POSIX, if implemented with
> +due care; see this @uref{http://www.austingroupbugs.net/view.php?id=51,
> +Austin Group discussion} for more background.  However, if it is not
> +implemented with proper care, such a behaviour might can cause problems

"in" is missing here (between "problems" and "some").

and

might or can, not both :-)

> +some corner cases.  To see why, assume we have a ``wrapper'' script
> +like this:
> +
> address@hidden
> +#!/bin/sh
> +# Ignore some signals in the shell only, not in its child processes.
> +trap : 1 2 13 15
> +wrapped_command "$@@"
> +ret=$?
> +other_command
> +exit $ret
> address@hidden example
> +
> address@hidden
> +If @command{wrapped_command} is interrupted by a @code{SIGHUP} (which
> +has signal number 1), @code{ret} will be set to 257.  Unless the
> address@hidden shell builtin is smart enough to understand that such
> +a value can only have been originated from a signal, and adjust the
> +final wait status of the shell appropriately, the value 257 will just
> +get truncated to 1 by the closing @code{exit} call, so that a caller
> +of the script will have no way to determine that termination by a
> +signal was involved.  Observe the different behaviour of AT&T
> address@hidden (2011) and @code{bash} 4.1.5 on Debian:
> +
> address@hidden
> +$ @kbd{cat > foo.sh}
> +#!/bin/sh
> +sh -c 'kill -1 $$'
> +ret=$?
> +echo $ret
> +exit $ret
> +$ @kbd{/bin/ksh foo.sh; echo $?}
> +foo.sh: line 2: 12479: Hangup
> +257
> +1
> +$ @kbd{/bin/bash foo.sh; echo $?}
> +foo.sh: line 2: 12487 Hangup        (sh -c 'kill -1 $$')
> +129
> +129
> address@hidden example
> +
>  @node File System Conventions
>  @section File System Conventions
>  @cindex File system conventions