Re: multios and unnecessary processes

[Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>]

On Jan 9,  4:47pm, Stephane Chazelas wrote:
} Subject: multios and unnecessary processes
}
} zsh -c 'lsof -ag $$ -d0-2,10-15 >&2 >&- >&2'
} 
} and 
} 
} zsh -c 'lsof -ag $$ -d0-2,10-15 >&2'
} 
} To work the same.

Interesting.  For me, they *do* work the same *if* the command is run
from the shell prompt rather than from "zsh -c".  In fact, I can only
reproduce your results if I use a non-interactive shell.  If I put those
two commands in files and execute the files with "zsh -if" I get (in
both cases):

OMMAND   PID  PGRP     USER   FD   TYPE DEVICE SIZE   NODE NAME
zsh     22683 22683 schaefer    0u   CHR  136,8          10 /dev/pts/8
zsh     22683 22683 schaefer    1u   CHR  136,8          10 /dev/pts/8
zsh     22683 22683 schaefer    2u   CHR  136,8          10 /dev/pts/8
zsh     22683 22683 schaefer   10r   REG    3,1   36 159782 /tmp/lsof1
zsh     22683 22683 schaefer   11u   CHR  136,8          10 /dev/pts/8

But if I leave off the -i I get the extra pipe descriptors in the first
case.  I don't know offhand why multios would behave differently when
the shell is interactive.

} I came accross this while trying to make some code independant
} of the multios setting (hence the >&- to cancel the teed
} redirection).

I'm a little puzzled by that statement, because in your second example
there is no teed redirection.  It's only the doubled >&2 that creates
a teed redirection in the first place.

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
 
} I'm not too sure it's a good idea to make multios the default.

If I had been in Paul Falstad's place 15 years or so ago, I'd have
thought about making the default value of multios follow the the initial
value of interactive; that is, having it on for interactive shells
unless explicitly turned off, and the reverse for non-interactive
shells.  Maybe he did think about it, but that's not what he decided.