Re: Local variables overriding global constants

[Chris F.A. Johnson]

On Wed, 3 Apr 2013, Pierre Gaston wrote:

> On Wed, Apr 3, 2013 at 11:03 AM, Chris Down <chris@chrisdown.name> wrote:
>
> > On 2013-04-03 11:00, Nikolai Kondrashov wrote:
> > > > > > It doesn't work because you are trying to redefine an existing
> > > > > > readonly variable.
> > > > >
> > > > > Yes, but I'm explicitly redefining it locally, only for this function.
> > > > > And this works for variables previously defined in the calling
> > function.
> > > > You're not redefining it locally, you are unsuccessfully trying to
> > override a
> > > > global.
> Still Nikolai has a point.
> It's not clear why readonly variable can be overridden when the variable is
> declared readonly in the scope of an englobing function but not if it is
> declared readonly in the global scope.

   If it's declared readonly in a function, the variable doesn't exist
   outside of that function, so it's not readonly there.


> $ bash -c 'a() {  v=2;echo "$v"; }; b () { declare -r v=1; a; echo "$v"; };
> b'
> bash: v: readonly variable
>
> The variable is locale to b, but the readonly flag is preserved in a
>
> $ bash -c 'a() { declare -r v=2;echo "$v"; }; b () { declare -r v=1; a;
> echo "$v"; }; b'
> 2
> 1
>
> The variable is locale to b, but you can redeclare it  locale to a even if
> it has the readonly flag
>
> $ bash -c 'declare -r v=2; b () { declare -r v=1; echo "$v"; }; b'
> bash: line 0: declare: v: readonly variable
> 2
>
> it looks like the same as the first case except that the variable is
> declared readonly in the global scope.
>
> (Also readonly defers from declare -r:
> bash -c 'a() { declare -r v=2;echo "$v"; }; b () { readonly v=1; a; echo
> "$v"; }; b; v=2'
> $ bash -c 'a() { declare -r v=2;echo "$v"; }; b () { readonly v=1; a; echo
> "$v"; }; b; v=2'
> bash: line 0: declare: v: readonly variable
> 1
> 1
> bash: v: readonly variable.
>
> I seem to recall this has been discussed on this list at some point)

--
   Chris F.A. Johnson, <http://cfajohnson.com/>
   Author:
   Pro Bash Programming: Scripting the GNU/Linux Shell (2009, Apress)
   Shell Scripting Recipes: A Problem-Solution Approach (2005, Apress)