I agree that it was not what was expected but it does fulfill the criteria as stated. The answer was probably supposed to be this as noted elsewhere:

$[

The index of the first element in an array, and of the first character
+ in a substring. Default is 0, but you could theoretically set it to 
+1 to make Perl behave more like awk (or Fortran) when subscripting an
+d when evaluating the index() and substr() functions. (Mnemonic: [ be
+gins subscripts.) 
As of release 5 of Perl, assignment to $[ is treated as a compiler dir
+ective, and cannot influence the behavior of any other file. --> Its 
+use is highly discouraged :-)


$[ = 1;
$x[0] = 1;
show();
$x[0] = 2;
show();
$x[1] = 3;
show();
sub show { print "\$x[$_] = $x[$_]\n" for 0..$#x; }
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