Re: why does "jobs | wc" not work?

[Peter Stephenson <pws@xxxxxxx>]

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@xxxxxxx>                  Software Engineer
CSR Ltd., Science Park, Milton Road,
Cambridge, CB4 0WH, UK                          Tel: +44 (0)1223 692070


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