$ perl -e 'my @arr=(1,2,3); $arr[-1]=4; print join " ", @arr, "\n";'
1 2 4
$

##</code><code>##

$ perl -e 'my @arr; $arr[-1]=4; print join " ", @arr, "\n";'
Modification of non-creatable array value attempted, subscript -1 at -e line 1.
$