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

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  Re: set -e ignored in subshell if part of command list Ángel <angel@debian.16bits.net> - 2019-11-15 00:02 +0100

#15597 — Re: set -e ignored in subshell if part of command list

On 2019-11-13 at 11:30 -0500, Chet Ramey wrote:
> 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 would say that the confusing part is that the behavior of the subshell
is dependant on *where* it is being executed in the parent.

In general terms, I would expect
  ( <code> )
to be roughly equivalent to 
  bash -c "<code>"

i.e. <code> being executed on its own context and unable to affect the
parent

but the provided case shows that 
  ( set -e; false; echo here ) && echo bar
behaves differently than
  bash -c "set -e; false; echo here" && echo there

since the initial subshell has an advanced knowledge that there will be
a later command joined by an and.

And the fact that reversing the order
  echo hello && ( set -e; false; echo here )

gives a different result, as it is now the *final* element of the &&
list.

The joys of set -e
https://mywiki.wooledge.org/BashFAQ/105, already mentioned in the thread
gives a «funny» read of these things.

Kind regards

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