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Re: set -e ignored in subshell if part of command list


From: Chet Ramey
Subject: Re: set -e ignored in subshell if part of command list
Date: Wed, 13 Nov 2019 11:30:05 -0500
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:68.0) Gecko/20100101 Thunderbird/68.2.2

On 11/13/19 10:59 AM, Shaun Crampton wrote:
But the commands in the subshell execute inside a different shell
execution context so they shouldn't have
their own set -e context (Section 2.12)?

Why? That section says the only thing that changes in the subshell environment is signal dispositions.

In fact, the example in the set builtin description explicitly assumes
the subshell inherits the errexit setting. The only thing the standard
requires here is that setting -e in the subshell doesn't change the
parent's setting.

But that's not exactly the point. The shell is "executing any command of an
AND-OR list other than the last" so errexit is ignored.


I don't see where the spec says that the subshell has to inherit the
and/or list-ness of the
parent context.  Section 2.12 doesn't mention that as being one of the
things that a subshell inherits
(and unless I'm missing a good use-case, it seems like a pretty
useless thing to inherit in a subshell
or a function that happens to be called on the LHS of an and/or).

"A subshell environment shall be created as a duplicate of the shell
environment, except that signal traps that are not being ignored shall be
set to the default action. "

It's an exact duplicate of the shell environment. It's easier to list the
exceptions rather than the long list of things it inherits (more than the
list earlier in that section).

In any event, it's how existing shells behave, and the standard is
attempting to match existing practice. In fact, part of the proposed
language from 2009, when this was debated at length, was "The -e option is
ignored and cannot be enabled by any command run by these lists" but that
was considered unnecessary.

--
``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    address@hidden    http://tiswww.cwru.edu/~chet/



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