From: Bart Schaefer <schaefer@brasslantern.com>
To: Zsh hackers list <zsh-workers@sunsite.dk>
Subject: Re: multios and unnecessary processes
Date: Mon, 10 Jan 2005 16:53:25 +0000 [thread overview]
Message-ID: <1050110165325.ZM26928@candle.brasslantern.com> (raw)
In-Reply-To: <20050110094918.GA4432@sc>
On Jan 10, 9:49am, Stephane Chazelas wrote:
} Subject: Re: multios and unnecessary processes
}
} > I don't know offhand why multios would behave differently when
} > the shell is interactive.
} [...]
}
} That's because of the -g option to lsof (process group $$, and
} lsof is run in a different process group in interactive mode),
Ah, I should have thought of that.
} > The right way to write multios-independent code is to wrap things in
} > curly braces, e.g.: { lsof -ag $$ -d0-2,10-15 >&2 } >&2
}
} Thanks for the
}
} { { cmd 2>&1 >&3 3>&-; } | cmd2 3>&-; } 3>&-
}
} ~$ zsh -c '{ { lsof -ag $$ -d 0-2,10-15 2>&1 >&3 3>&-; } | tr a b 3>&-; } 3>&1'
} But that's still one more process compared to:
}
} ~$ zsh -o nomultios -c '{ lsof -ag $$ -d 0-2,10-15 2>&1 >&3 3>&- | tr a b 3>&-; } 3>&1'
If the number of processes spawned is important, you have to know when
to use curly braces and when to force a subshell with parens. Curly
braces imply that the parent zsh sticks around and waits, whereas a
subshell with parens can simply do an exec.
zsh -fc '{ ( lsof -ag $$ -d 0-2,10-15 2>&1 >&3 3>&-; ) | tr a b 3>&-; } 3>&1'
COMMAND PID PGRP USER FD TYPE DEVICE SIZE NODE NAME
tr 26811 26811 schaefer 0r FIFO 0,0 72995 pipe
tr 26811 26811 schaefer 1u CHR 136,7 9 /dev/pts/7
tr 26811 26811 schaefer 2u CHR 136,7 9 /dev/pts/7
lsof 26822 26811 schaefer 0u CHR 136,7 9 /dev/pts/7
lsof 26822 26811 schaefer 1u CHR 136,7 9 /dev/pts/7
lsof 26822 26811 schaefer 2w FIFO 0,0 72995 pipe
next prev parent reply other threads:[~2005-01-10 16:54 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-01-09 16:47 Stephane Chazelas
2005-01-09 20:32 ` Bart Schaefer
2005-01-10 9:49 ` Stephane Chazelas
2005-01-10 16:53 ` Bart Schaefer [this message]
2005-01-10 17:11 ` Stephane Chazelas
2005-01-10 19:20 ` Bart Schaefer
2005-01-10 19:48 ` Peter Stephenson
2005-01-11 9:07 ` Stephane Chazelas
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