Re: Does declaring an array variable initialize it?

[Chet Ramey]

On 3/20/14 12:41 AM, Richard Tollerton wrote:
> 
> Old behavior, bash 4.2.45:
> 
> $ bash -c 'set -u; echo ${#arr1[@]}'; \
> bash -c 'set -u; declare var1; echo ${#var1}'; \
> bash -c 'set -u; declare -a arr2; echo ${#arr2[@]}'
> bash: arr1: unbound variable
> bash: var1: unbound variable
> 0
> 
> New behavior, bash 4.3:
> 
> $ bash -c 'set -u; echo ${#arr1[@]}'; \
> bash -c 'set -u; declare var1; echo ${#var1}'; \
> bash -c 'set -u; declare -a arr2; echo ${#arr2[@]}'
> bash: arr1: unbound variable
> bash: var1: unbound variable
> bash: arr2: unbound variable
> 
> I suppose that this change in behavior makes array variables more
> consistent with normal variables, but I couldn't find anything in
> CHANGES which obviously relates to this, so I'm not sure if this is a
> bug or not.

There is this, in the list of changes in bash-4.3-beta:

f.  Fixed several cases where `invisible' variables (variables with attributes
    but no values, which are technically unset) were treated incorrectly.


> Was I always mistaken in figuring that declaring an array also
> initialized it?

A variable is not set until it has been assigned a value.  This was always
true, and always supposed to apply to array variables as it did to scalars.
bash-4.2 had a number of inconsistencies here, and I fixed some number of
those.  I'm sure some still remain.

This topic has come up several times in the past, most recently a couple
of weeks ago:

http://lists.gnu.org/archive/html/bug-bash/2013-01/msg00068.html
http://lists.gnu.org/archive/html/bug-bash/2013-11/msg00000.html
http://lists.gnu.org/archive/html/bug-bash/2014-03/msg00052.html

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