Re: static vs. dynamic scoping

[Chris F.A. Johnson]

On Tue, 9 Nov 2010, Eric Blake wrote:

> On the Austin Group mailing list, David Korn (of ksh93 fame)
> complained[1] that bash's 'local' uses dynamic scoping, but that ksh's
> 'typeset' uses static scoping, and argued that static scoping is saner
> since it matches the behavior of declarative languages like C and Java
> (dynamic scoping mainly matters in functional languages like lisp):
>
> [1]
> https://www.opengroup.org/sophocles/show_mail.tpl?CALLER=show_archive.tpl&source=L&listname=austin-group-l&id=14951
>
> I'm trying to standardize the notion of local variables for the next
> revision of POSIX, but before I can do so, I need some feedback on two
> general aspects:
...
> 2. User aspect:
>  Is anyone aware of a script that intentionally uses the full power of
> dynamic scoping available through 'local' which would break if scoping
> switched to static?  In particular, I know that the bash-completion
> project has fought with local variable scoping issues; would it help or
> hurt to switch to static scoping?
>
> Here's a sample shell script that illustrates the difference between the
> two scoping methods.
>
> $ ksh -c 'function f1 { typeset a=local; f2; echo $a; };
>  function f2 { echo $a; a=changed; };
>  a=global; f1; echo $a'
> global
> local
> changed
>
> $ bash --posix -c 'function f1 { typeset a=local; f2; echo $a; };
>  function f2 { echo $a; a=changed; };
>  a=global; f1; echo $a'
> local
> changed
> global
...

   I find the bash behaviour more logical, and I do use it in scripts.

--
   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)