GNU bug report logs - #32751
split does not break on error from tar

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Alexander Fieroch <alexander.fieroch <at> mpi-dortmund.mpg.de>
To: <bug-coreutils <at> gnu.org>
Subject: split does not break on error from tar
Date: Mon, 17 Sep 2018 10:38:27 +0200

[Message part 1 (text/plain, inline)]

Hi all,

I found a bug in "split".
I want to tar some files but some of them have wrong permissions. tar 
puts out an exit code 2 "Cannot open: Permission denied". That is good 
because in my script I can catch this error and react to this.

$ tar -c -f /tmp/test.tar -C /media/testpath testfile ; echo $?
tar: testfile: Cannot open: Permission denied
tar: Exiting with failure status due to previous errors
2

Unfortunately my tar directory is too big to save it in one file on my 
filesystem that I have to split the archive but doing this "split" does 
not get the error code 2 from tar and does not break as it should:

$ tar -c -f - -C /media/testpath testfile | split - ; echo $?
tar: testfile: Cannot open: Permission denied
tar: Exiting with failure status due to previous errors
0

In the end I got a tar file without files that have no permissions and 
my script does not break because of error code 0.

Thanks!

----
Ubuntu 18.04.1
tar 1.29b
coreutils 8.28
----

Best regards,
Alexander

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Message #8 received at 32751 <at> debbugs.gnu.org (full text, mbox):

From: "Rainer M. Canavan" <coreutils <at> canavan.de>
To: alexander.fieroch <at> mpi-dortmund.mpg.de
Cc: 32751 <at> debbugs.gnu.org
Subject: Re: bug#32751: split does not break on error from tar
Date: Mon, 17 Sep 2018 21:10:31 +0200 (CEST)

Alexander Fieroch <alexander.fieroch <at> mpi-dortmund.mpg.de> wrote:
> Hi all,
> 
> I found a bug in "split".
> I want to tar some files but some of them have wrong permissions. tar 
> puts out an exit code 2 "Cannot open: Permission denied". That is good 
> because in my script I can catch this error and react to this.
> 
> $ tar -c -f /tmp/test.tar -C /media/testpath testfile ; echo $?
> tar: testfile: Cannot open: Permission denied
> tar: Exiting with failure status due to previous errors
> 2
> 
> Unfortunately my tar directory is too big to save it in one file on my 
> filesystem that I have to split the archive but doing this "split" does 
> not get the error code 2 from tar and does not break as it should:
> 
> $ tar -c -f - -C /media/testpath testfile | split - ; echo $?
> tar: testfile: Cannot open: Permission denied
> tar: Exiting with failure status due to previous errors
> 0
> 
> In the end I got a tar file without files that have no permissions and 
> my script does not break because of error code 0.


As far as I can tell, this is not a bug, but the way pipelines work, 
i.e. the  result of a pipeline (here the combination of tar and 
split) is the result of the last command in the pipeline. If you 
want the combination to fail if tar fails, you can use e.g. 
set -o pipefail in bash or read PIPESTATUS. For other shells,
see e.g. http://cfajohnson.com/shell/cus-faq-2.html#Q11


Rainer

Message #11 received at 32751 <at> debbugs.gnu.org (full text, mbox):

From: Alexander Fieroch <alexander.fieroch <at> mpi-dortmund.mpg.de>
To: "Rainer M. Canavan" <coreutils <at> canavan.de>
Cc: 32751 <at> debbugs.gnu.org
Subject: Re: bug#32751: split does not break on error from tar
Date: Tue, 18 Sep 2018 09:59:32 +0200

[Message part 1 (text/plain, inline)]

> As far as I can tell, this is not a bug, but the way pipelines work,
> i.e. the  result of a pipeline (here the combination of tar and
> split) is the result of the last command in the pipeline. If you
> want the combination to fail if tar fails, you can use e.g.
> set -o pipefail in bash or read PIPESTATUS. For other shells,
> see e.g. http://cfajohnson.com/shell/cus-faq-2.html#Q11
> 
> 
> Rainer

Thanks Rainer, that is a very good hint and is working for me!
But why is this not a bug? In what case is it useful to ignore a 
non-zero exit code in a pipeline?

Thanks!

Best regards,
Alexander

[smime.p7s (application/pkcs7-signature, attachment)]

Message #14 received at 32751 <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: Alexander Fieroch <alexander.fieroch <at> mpi-dortmund.mpg.de>,
 "Rainer M. Canavan" <coreutils <at> canavan.de>
Cc: 32751 <at> debbugs.gnu.org
Subject: Re: bug#32751: split does not break on error from tar
Date: Tue, 18 Sep 2018 01:06:24 -0700

tag 32751 notabug
close 32751
stop

On 18/09/18 00:59, Alexander Fieroch wrote:
>> As far as I can tell, this is not a bug, but the way pipelines work,
>> i.e. the  result of a pipeline (here the combination of tar and
>> split) is the result of the last command in the pipeline. If you
>> want the combination to fail if tar fails, you can use e.g.
>> set -o pipefail in bash or read PIPESTATUS. For other shells,
>> see e.g. http://cfajohnson.com/shell/cus-faq-2.html#Q11
>>
>>
>> Rainer
> 
> Thanks Rainer, that is a very good hint and is working for me!
> But why is this not a bug? In what case is it useful to ignore a 
> non-zero exit code in a pipeline?

Well that's been the shell behavior since the beginning,
and lot's of scripts depend on that,
and so it can't be changed.

As for split, it just sees the end of input
and exits without error.

thanks,
Pádraig

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