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Re: some problems with scope of fds in process substitution

From: Stephane Chazelas
Subject: Re: some problems with scope of fds in process substitution
Date: Sun, 3 Dec 2017 23:07:22 +0000
User-agent: Mutt/1.5.24 (2015-08-30)

2017-12-03 17:31:00 -0500, Chet Ramey:
> On 12/1/17 2:00 PM, Stephane Chazelas wrote:
> > Also, there's a lot of problems reported at
> > unix.stackexchange.com at least that are caused by bash not
> > waiting for the processes started by process substitutions,
> > especially the >(...) form.
> Bash always reaps these processes. Do you mean waiting for them
> to terminate before executing the next command?

Hi Chet,

yes, that's what I meant as in:

$ rm -f a; bash -c 'echo test > >(cat > a); cat a'


cmd1 <(cmd2)

It's usually OK not to wait for cmd2, same as

cmd2 | cmd1

where not all shells wait for cmd2 (before running cmd3).

as cmd1 will generally wait for cmd2 by virtue of it waiting on
eof on the pipe but in:

cmd1 >(cmd2)

It's more cmd2 that would be waiting for cmd1. So when cmd1
returns, often, cmd2 has not finished yet, and if cmd3 needs
something produced by cmd2, that's where we run into problems.

See the link I gave (https://unix.stackexchange.com/a/403788)
for more details including the situation with other shells that
implement process substitution (ksh, zsh, rc, es).


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