From: Peter Stephenson <pws@csr.com>
To: zsh-users@sunsite.dk
Cc: dominik.vogt@gmx.de
Subject: Re: why does "jobs | wc" not work?
Date: Tue, 26 Nov 2002 12:08:16 +0000 [thread overview]
Message-ID: <14578.1038312496@csr.com> (raw)
In-Reply-To: "Dominik Vogt"'s message of "Tue, 26 Nov 2002 12:42:22 +0100." <20021126114222.GG1937@gmx.de>
Dominik Vogt wrote:
> > In zsh
> >
> > jobs | anything
> >
> > causes the shell to fork for the left hand side of the pipeline.
>
> Um, why must builtin commands run in a subshell? I would have
> naively thought commands like "echo something | ..." would just
> run in the current shell. Spawning a subshell sounds a bit
> inefficient.
That's how all pipes work in all shells and scripting languages in all
variants of UNIX: one process feeds its output to another process, so
one side of the pipe has to be forked as a separate process. The only
question is which bits are forked off.
The only obvious alternative is the horrible method which used to be
used in MSDOS: fake separate processes by switching between the two
tasks; but we are certainly never going to have a task manager in the
shell when we have a proper multiprocessor operating system to do the
job more efficiently.
> > In 4.1, we use the obvious workaround: remember that we're in a subshell
> > of an interactive shell and keep a fossilized list of the jobs.
>
> Obvious, maybe, but it still sounds wrong in my ears.
Just in case my explanation above hasn't made this remark obvious:
wrong in what way? It's either that or no output at all.
--
Peter Stephenson <pws@csr.com> Software Engineer
CSR Ltd., Science Park, Milton Road,
Cambridge, CB4 0WH, UK Tel: +44 (0)1223 692070
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next prev parent reply other threads:[~2002-11-26 12:09 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-11-26 10:49 Dominik Vogt
2002-11-26 10:56 ` Vincent Lefevre
2002-11-26 11:09 ` Peter Stephenson
2002-11-26 11:17 ` Vincent Lefevre
2002-11-26 11:27 ` Peter Stephenson
2002-11-26 11:42 ` Dominik Vogt
2002-11-26 11:59 ` Vincent Lefevre
2002-11-26 12:08 ` Peter Stephenson [this message]
2002-11-26 12:48 ` Dominik Vogt
2002-11-26 13:05 ` Peter Stephenson
2002-11-26 13:33 ` Dominik Vogt
2002-11-26 17:20 ` Danek Duvall
2002-11-26 13:13 ` Vincent Lefevre
2002-11-26 11:24 ` Stephane Chazelas
2002-11-26 17:11 Borzenkov Andrey
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