Hi. 2010/9/26, Loïc Minier <l...@dooz.org>: > On Sat, Sep 25, 2010, Jilles Tjoelker wrote: >> You are certainly right that POSIX requires this to be handled >> differently, but there are various other shells that are non-compliant >> in the same way as dash and it is easy to avoid the behaviour, so I >> would not recommend depending on it. > > I don't know why it was put there in the first place, but my first > reaction was to send patch to remove the use of exit in the trap > handler: > http://lists.gnu.org/archive/html/qemu-devel/2010-09/msg01803.html -trap "rm -f $TMPC $TMPO $TMPE ; exit" EXIT INT QUIT TERM +# NB: do not call "exit" in the trap handler; this is buggy with some shells; +# see <addr...@hidden> +trap "rm -f $TMPC $TMPO $TMPE" EXIT INT QUIT TERM > but the discussion led me to report this bug against dash
1) IMHO doing cleaning in a `trap` is bad coding style in the first place. Here i think about, how much one allowed to do in signal handlers in C? The `trap` for me is like *try / catch* exception handling: trap 'echo "unexpected error in script block xyz, please send console messages and log files to d...@example.org"' EXIT # critical part script block xyz trap "" EXIT # ordinary part .... 2) So, when "fine POSIX" changes rules of `exit` inside `trap`, this is even worse game playing style. While `dash` doesn't do much about stepping over POSIX, this case shows, that standards are inflexible, to say least, and `dash` went its own way here. 3) After dealing with 1), 2) and pipes, conclusion is that exit status code is a very weak information source. For example, when program is failing to free (e.g. TMP) resources, this *is* another problem, like checking errno after close() in C -- somebody cares, the most don't. Thus, like in many good scripts, I would have do_exit() with all kinds of cleanup (console, files, logs etc.). And `trap` lines would have `echo “unexpected error #xyz” ; catch_xyz || do_exit 1` > Thanks for your detailed reply! Am I also expected to log this issue > somewhere for tracking? Tracking what? After many years, I think, `dash` will remain such features unchanged. -- sed 'sed && sh + olecom = love' << '' -o--=O`C #oo'L O <___=E M -- To unsubscribe from this list: send the line "unsubscribe dash" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
