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Re: 'local -x VARIABLE' does not clear variable for subprocesses

From: Chet Ramey
Subject: Re: 'local -x VARIABLE' does not clear variable for subprocesses
Date: Mon, 05 May 2014 16:12:54 -0400
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On 5/5/14, 1:13 PM, Arfrever Frehtes Taifersar Arahesis wrote:

> Behavior of bash 4.3 is inconsistent between non-subshell subprocesses and 
> other places:

> bash 4.3.11:
> $ export VAR{1,2}=abc
> $ f() { local VAR1; local -x VAR2; echo "### Normal scope:"; declare -p 
> VAR{1,2}; echo "### Subshell:"; (declare -p VAR{1,2}); echo "### Non-subshell 
> subprocess:"; bash -c 'declare -p VAR{1,2}'; }
> $ f
> ### Normal scope:
> bash: declare: VAR1: not found
> bash: declare: VAR2: not found
> ### Subshell:
> bash: declare: VAR1: not found
> bash: declare: VAR2: not found
> ### Non-subshell subprocess:
> declare -x VAR1="abc"
> declare -x VAR2="abc"

A subshell is created as an exact copy of the parent shell, so the state
of local variables in the subshell is the same as in the parent, and I
would expect the behavior to be the same in both cases.  You can argue
whether or not the behavior is correct -- I would argue that in this case
the behavior is incorrect.

A `non-subshell subprocess', as you've termed it, can only propagate
variables via the environment.  So-called placeholder variables aren't
added to the environment.

I am thinking that as a general rule, variable lookups should not `find'
placeholder variables; assignments should.  Implementing that general rule,
though, will take some close reading of the code.

> Ability to locally unset a variable also for subprocesses would be preferable 
> solution.

OK.  I'm not sure exactly what this means.  Can you give me an example?
How would you use this in a situation where `unset' or `declare +x' are

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