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Re: Arithmetic expansion with increments and output redirection


From: Andreas Schwab
Subject: Re: Arithmetic expansion with increments and output redirection
Date: Wed, 24 Apr 2019 15:07:53 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.2 (gnu/linux)

On Apr 24 2019, Greg Wooledge <address@hidden> wrote:

> On Wed, Apr 24, 2019 at 06:47:41AM -0600, Ian Neal wrote:
>> At what point is a subshell being invoked? There's no pipeline, command
>> substitution, coprocess, background process, or explicit () subshell here,
>> which are the only cases a subshell should be created. Otherwise, the
>> entire operation should be evaluated by the main shell. Arithmetic
>> expansion is not in that list.
>
> The context got snipped but IIRC it was something like
>
> /bin/true > $((n++))
>
> The /bin/true forces the use of an external command, which means a subshell
> is forked.  The redirection occurs in the forked subshell.

But the expansion isn't required to be performed in the subshell.  I
don't see POSIX having any wording to require one or the other.  Doing
the expansion before the fork looks reasonable, even if only to make it
consistent with builtins.

Andreas.

-- 
Andreas Schwab, address@hidden
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