Re: Passing variables by reference conflicts with local

[Chet Ramey]

On 5/3/10 3:30 PM, Freddy Vulto wrote:
> On 100503 08:57, Chet Ramey wrote:
>>> On Sat, May 01, 2010 at 04:26:16AM -0500, Dennis Williamson wrote:
>>>> I prefer to avoid using eval by using declare, but declare inside a
>>>> function makes the variable local. Wouldn't it be nice to have a
>>>> global flag (declare -g) like zsh's typeset -g.
> 
>> I am planning a feature like this for a future release.  It may end up
>> in bash-4.2.
> 
> What I'm happily exploiting in this thread (and trying to get consent
> for) is the fact that declaring a global within a function does NOT
> automatically make the variable global, but instead allows one to pass
> variables between functions.  In this light I also find the term
> "global" misleading.

Think of a chain of variable scopes corresponding to a chain of function
calls.  When you look for a variable, you proceed "up" the scope
chain to the "root", returning the first instance you find.  The requested
`declare -g' feature would create a variable at the global scope, rather
than the scope corresponding to the current function.

> This thread is still leaving me with the feeling I'm doing something
> wrong.  Is this a documented and maintained bash feature?  Can we safely
> apply this feature to the bash-completion package?  Will a `declare -g'
> preserve the existing behaviour in say bash-4.2?

Unless you use it, `declare -g' won't matter.  If you use it, the
proposed `declare -g' will declare variables at the global scope, as
if the declare had not been supplied.

> In other words: is it safe to exploit the behaviour below - 'a=A b=B'
> not becoming global?

That doesn't have anything to do with any proposed -g option to declare,
since you are not and won't be using it.  Your code declares local
variables at one function scope and accesses them in a called function.
Bash variable scoping is dynamic.  It will continue to work this way.

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/