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

[Arfrever Frehtes Taifersar Arahesis]

2014-05-05 17:18 Chet Ramey napisał(a):
> On 5/3/14, 7:22 PM, Arfrever Frehtes Taifersar Arahesis wrote:
> > 'local -x VARIABLE' (without assignment of value) does not clear variable 
> > for subprocesses.
> > It is regression in bash 4.3.
> 
> It's not actually a regression; it's a bug fix.  It's worth having the
> discussion again, though.
> 
> A variable isn't set until it's assigned a value.  A statement like
> `local x' or `export x' doesn't actually create a variable.  It creates
> a `placeholder' so that a subsequent assignment will instantiate a
> variable with the right attributes, or change the behavior when a value
> is assigned, but does not assign a value itself.  This means that
> something like
> 
> export x
> echo ${x-unset}
> printenv x
> 
> will display `unset'.
> 
> The idea behind the bash-4.3 behavior is that the placeholder local
> variable isn't set, and doesn't really exist.  It doesn't shadow a
> global variable with the same name until it gets a value.  The bash-4.2
> behavior was inconsistent: variables with attributes but without values
> weren't quite set (value == 0x0, but still visible) and weren't quite
> unset.

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

bash 4.2.47:

$ 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:
declare -x VAR1
declare -x VAR2
### Subshell:
declare -x VAR1
declare -x VAR2
### Non-subshell subprocess:
bash: line 0: declare: VAR1: not found
bash: line 0: declare: VAR2: not found

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"


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

--
Arfrever Frehtes Taifersar Arahesis

signature.asc
Description: This is a digitally signed message part.