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

From: Eli Schwartz
Subject: Re: set -e ignored in subshell if part of command list
Date: Thu, 14 Nov 2019 18:16:24 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2

On 11/14/19 6:02 PM, Ángel wrote:
> 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 that's totally wrong for *numerous* reasons.

> 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

What about

var=value; (echo "$var")

which behaves differently from

var=value; bash -c 'echo "$var"'


func() { echo "hi there"; }; (func)

which behaves differently from

func() { echo "hi there"; }; bash -c 'func'

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

An initial subshell has advanced knowledge about lots of things from the
parent shell, it is deeply, worryingly dangerous to write code that
doesn't take this into account. Things will tend to go pretty badly wrong.

Eli Schwartz
Arch Linux Bug Wrangler and Trusted User

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