From: Paul Jackson <pj@sgi•com>
To: Linus Torvalds <torvalds@osdl•org>
Cc: git@vger•kernel.org, pasky@ucw•cz
Subject: Re: How to get bash to shut up about SIGPIPE?
Date: Fri, 29 Apr 2005 23:29:22 -0700 [thread overview]
Message-ID: <20050429232922.03057aba.pj@sgi.com> (raw)
In-Reply-To: <Pine.LNX.4.58.0504291956030.2296@ppc970.osdl.org>
Linus replied to pj:
> > Code Sample 2:
> > ...
> Didn't change anything for me. Same thing.
I don't believe you did what I did.
The source code for bash, both 2.x and 3.x versions, clearly displays a
simpler error message (no line number or redisplay of your script
commands) in the case that you set a trap. And I tested both shells on
a multiprocessor, to verify that they behaved as I expected, running
these silly little scripts.
To labour the point, just now on a multiprocessor near me, the following
six line script:
======================== begin ========================
#!/usr/people/pj/etc/bash/bash-3.0/bash
for x in 1 2
do
trap continue PIPE # reduce broken pipe screeching
cat /etc/termcap # a big text file
done | sed 1q
========================= end =========================
produced the following three lines of output:
======================== begin ========================
######## TERMINAL TYPE DESCRIPTIONS SOURCE FILE
Broken pipe
Broken pipe
========================= end =========================
whereas the following five line script (no trap):
======================== begin ========================
#!/usr/people/pj/etc/bash/bash-3.0/bash
for x in 1 2
do
cat /etc/termcap # a big text file
done | sed 1q
========================= end =========================
produced the following three __noisier__ lines of output:
======================== begin ========================
######## TERMINAL TYPE DESCRIPTIONS SOURCE FILE
foo: line 2: 11663 Broken pipe cat /etc/termcap
foo: line 2: 11665 Broken pipe cat /etc/termcap
========================= end =========================
> > just that noise, leaving whatever else was on stdout and/or stderr
> > unscathed:
>
> It will also grep out any occurrence of "Broken pipe", so if we're talking
> about a kernel changelog, where we fix a pipe bug...
No no no. You didn't read the code or the comment ;). That or my code
and comment were both unclear ... far more likely.
The following line noise is not plagarized from last years Obfuscated
Perl Contest:
( ( (
...
) 1>&3 ) 2>&1 | grep -vxF 'Broken pipe' 1>&2 ) 3>&1
It's the magic shell incantation to run grep only on the stderr stream,
while passing through the stdout stream untouched. Even on the stderr
stream, it only zaps lines that are exactly the eleven characters
'Broken pipe' (plus newline).
> I don't know why the bash people have that stupid pipe reporting in the
Now there we agree. I might speculate that they were trying to get an
early lead in the Linus Git of the Year contest. But this is relatively
mild compared to some of the crap I've seen on other projects I won't
name here. So I too am at a loss to know why.
--
I won't rest till it's the best ...
Programmer, Linux Scalability
Paul Jackson <pj@engr•sgi.com> 1.650.933.1373, 1.925.600.0401
next prev parent reply other threads:[~2005-04-30 6:24 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-04-28 18:28 How to get bash to shut up about SIGPIPE? Linus Torvalds
2005-04-28 19:03 ` Rene Scharfe
2005-04-28 19:21 ` Linus Torvalds
2005-04-28 20:13 ` Rene Scharfe
2005-04-28 20:27 ` Ryan Anderson
2005-04-28 20:47 ` Linus Torvalds
2005-05-01 12:07 ` Herbert Xu
2005-05-01 15:51 ` David A. Wheeler
2005-05-02 16:10 ` Paul Jackson
2005-05-04 2:30 ` David A. Wheeler
2005-05-04 2:50 ` Linus Torvalds
2005-05-04 8:26 ` Herbert Xu
2005-04-28 21:31 ` Edgar Toernig
2005-04-28 22:16 ` Linus Torvalds
2005-04-29 1:00 ` Joshua T. Corbin
2005-04-30 0:22 ` Paul Jackson
2005-04-30 2:59 ` Linus Torvalds
2005-04-30 6:29 ` Paul Jackson [this message]
2005-04-30 11:04 ` Rene Scharfe
2005-05-02 22:17 ` Paul Jackson
2005-05-02 23:17 ` Petr Baudis
2005-05-03 1:44 ` Paul Jackson
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