Why can't I use a Perl variable's value to access a lexical variable name?

Question

Why does this print 42:

$answer = 42;
$variable = "answer";

print ${$variable} . "\n";

but this doesn't:

my $answer = 42;
my $variable = "answer";

print ${$variable} . "\n";

Answer 1

Only package variables (the kind declared in your first example) can be targeted via symbolic references. Lexical (my) variables, cannot be, which is why your second example fails.

See the excellent article Coping with Scoping for how the two separate variable systems in Perl operate. And see the also excellent Why it's stupid to use a variable variable name for why that's stupid. :)