On 05/13/2014 11:44 AM, Markus Armbruster wrote:
>> But when I try to put this in a function to avoid repeating:
>>
>> function _no_dump_exec()
>> {
>> (ulimit -c 0; exec "$@")
>> }
>>
>> _no_dump_exec $QEMU_IO -c "write -P 0x5a 0 512" -c "abort" "$TEST_IMG")
>> | _filter_qemu_io
>>
>> it doesn't work:
>>
>> 039 1s ... - output mismatch (see 039.out.bad)
>> --- 039.out 2014-05-13 12:10:39.248866480 +0800
>> +++ 039.out.bad 2014-05-13 17:19:46.161986618 +0800
>> @@ -9,6 +9,7 @@
>>
>> == Creating a dirty image file ==
>> Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=134217728
>> +./039: line 51: 10517 Aborted "$@"
>> wrote 512/512 bytes at offset 0
>> 512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
>> incompatible_features 0x1
>>
>> Any idea what the difference is here?
>
At least in bash, the shell does error reporting any time the last
command in a pipeline exits via a signal. By factoring things into a
function, you've changed from a 2-command pipeline where the abort was
on the left to a (trivial one-command) pipeline; therefore, now that the
shell is executing a pipeline that exits via signal, it gets verbose.
dash, on the other hand, reports an abort no matter where in the
pipeline it occurs:
$ cat foo.c
#include <stdlib.h>
int main(void) { abort(); }
$ bash -c './foo;:'
bash: line 1: 5706 Aborted (core dumped) ./foo
$ bash -c './foo|:;:'
$ dash -c './foo;:'
Aborted (core dumped)
$ dash -c './foo|:;:'
Aborted (core dumped)
>
> It goes away when I redirect the output *within* the function:
>
> function _no_dump_exec()
> {
> "$@" | cat
> }
Yes, for bash, because that once again puts your command on the left of
the pipeline, with the right side no longer exiting via a signal. But
unless this script is specifically running on bash, you are not portable
to dash unless you manually redirect the expected stderr blurb from the
shell to /dev/null.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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