Re: Unsetting Array

[Stephane Chazelas <Stephane_Chazelas@xxxxxxxx>]

On Tue, Dec 09, 2008 at 02:18:34PM +0000, Peter Stephenson wrote:
> "Jerry Rocteur" wrote:
> > I'm using ZSH_VERION 4.2.6 on Redhat 5 to test some Korn shell scripts.
> > 
> > Note that /usr/bin/ksh is a link to /bin/zsh
> > 
> > I am unsetting an array like this unset variable[$i] and get
> >..
> > What is the correct way to unset an array element.
> 
> You can't strictly *unset* an element to an array.  In zsh, an array is
> always a set of strings that has a particular length.  So what you can
> do is limited to changing the length of the array or setting an element
> of the array to be an empty string.  The latter is probably nearest to
> what you want, but (in places where it makes a difference) the shell
> will always treat the empty element as a string with zero length, not as
> an unset parameter.  The syntax for that is
> 
>   variable[$i]=
[...]

Yes, contrary to ksh, zsh arrays are not sparse arrays but
normal arrays as for instance in C (though indices start at 1,
not 0). You could implement a sparse array with an associative
array.

Another thing to be aware of is that $array in zsh expands to
the non-empty elements of the array.

~$ a[5]=foo
~$ printf '<%s>\n' $a
<foo>
~$ printf '<%s>\n' "$a[@]"
<>
<>
<>
<>
<foo>

a[100000]=

declares an array of 100000 elements, all of them empty.

But you could do:

typeset -A a
a[100000]=

Which would declare an associative array with only one element
of key "100000" (beware 100000 is a string)

"$a[@]" would then expand to the list of values (here only one
empty value) but beware that you cannot guarantee the order in
which the values will be displayed.

-- 
Stéphane