Bash, tar, and broken pipe

[heinz at cc.univie.ac.at]

In <1991May15.155040.19078 at ssd.kodak.com> weimer at garden.ssd.kodak.com (Gary Weimer (253-7796)) writes:


>In article <586 at kepler1.kepler.com>, jwu at kepler.com (Jasper Wu) writes:
>|> 
>|> I have some problem when using pipelined tar in bash and hope someone
>|> can help me find out why.
>|> 
>|> When I do    
>|>            zcat foo.tar.Z | tar tvfB -
>|>     or     uncompress < foo.tar.Z | tar tvfB -
>|> 
>|> it gives me the table of contents correctly but reports an error
>|> message "Broken pipe" to stderr when it finishes.   However, if i add 
>|> a "cat" to the pipeline as
>|>            cat foo.tar.Z | uncompress | tar tvfB -
>|> 
>|> then it works fine (i.e., no error message).  All commands above work fine
>|> in csh or sh.

>In csh I use:

>   uncompress -c foo.tar.Z | tar tvf -
>              ^^

>(I've never had a problem not using B for tar). I don't know if this
>will fix your problem or not.

This does *not* fix the problem. I've been using bash for quite a
long time  now,  and have made the same experience as Jasper. For
bash, it doesn't make any difference whether  you  use  'compress
-c'  or  'zcat'  (because  it's  the  same program anyway - zcat,
compress and uncompress are links to the same  program),  and  it
doesn't make any difference whether you use 'tar' with -B or not.

I'm sorry I can't give a solution to the problem  -  all  that  I
know  is  that bash reports a broken pipe if one of the processes
making up the pipe is killed or terminated abnormally  (well,  it
doesn't  have  to  be  terminated abnormally, it only needs to be
just  terminated).   As  I  didn't   have   time   to  look  into
bash's  source code  yet,  I don't  know if the actual problem is
a bug in  bash or an abnormal behaviour of zcat which  isn't  re-
vealed  by the other  shells.  It  also  might be a 'timing prob-
lem' as zcat  surely terminates before tar, and  this  may  cause
bash to report the pipe as being broken.
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---/     Heinz M. Herbeck                    /    Trust me, I know    /       /-
--/     heinz at sophie.pri.univie.ac.at       /    what I'm doing !    /       /--
-/     Vienna University, Austria          /    (Sledge Hammer)     /       /---
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