Create an array @x such that changing $x[0] ...

@x=(\$_,\$_);
my $initial_value = $x[0];
$_=10;
print "\$x[$_] = ${$x[$_]}\n" for 0..$#x;
die "But \$x[0] did not change.\n" if $x[0] eq $initial_value;
$_=20;
print "\$x[$_] = ${$x[$_]}\n" for 0..$#x;
die "But \$x[0] did not change.\n" if $x[0] eq $initial_value;
[download]

You're really printing the wrong thing.

print "\$x[$_] = ${$x[$_]}\n" for 0..$#x;
                 ^^      ^
LHS is $foo, RHS is $$foo. The output is very misleading.

print "\${\$x[$_]} = ${$x[$_]}\n" for 0..$#x;

LHS is $$foo and RHS is $$foo. But we're interested in $foo.

print "\$x[$_] = $x[$_]\n" for 0..$#x;

LHS is $foo and RHS is $foo. Output is correct and shows that the need
+ed change did not happen.
[download]

You're changing the variable that is refered to by the references in $x[0] and $x[1], but you're not actually changing the value in the container that is named $x[0].

Clearer would be: "so that assigning to $x[0] also changes ...", but as said, we're against sanity.

Juerd # { site => 'juerd.nl', plp_site => 'plp.juerd.nl', do_not_use => 'spamtrap' }