Re: Expanding an undefined array

[Chet Ramey]

Bernd Eggink wrote:
> Is the following difference intentional, a bug, or do I miss something?
> 
>   unset a
>   set -- "${a[@]}"
>   echo $#
> 
> Output: 0

This is correct.

>   typeset a
>   set -- "${a[@]}"
>   echo $#
> 
> Output: 1

The question is how to treat the variable created by `typeset'.  Bash
has traditionally treated `typeset a' as equivalent to `typeset a=""'
instead of creating a `placeholder' variable that exists in a sort of
limbo.  That's different from things like `export a' or `readonly a',
and probably inconsistent enough to be worth changing for bash-4.0.
That's the difference between the examples, not the expansion of
"${a[@]}".

Chet

Chet
> 
> The man page says, "If the word is double-quoted, ... ${name[@]} expands
> each element of name to a separate word. When there are no array
> members, ${name[@]} expands  to  nothing." It doesn't mention a
> difference between an empty and an unset variable in this context. As a
> quoted 'nothing' normally counts 1 word, the 'nothing' in the first
> example appears to be some kind of 'super-nothing'.
> 
> Regards,
> Bernd
> 


-- 
``The lyf so short, the craft so long to lerne.'' - Chaucer

Chet Ramey, ITS, CWRU    chet@case.edu    http://cnswww.cns.cwru.edu/~chet/