{ 2 * $^x }         # or
-> $x { 2 * $x }    # or
sub ($x) { 2 * $x } # or
sub { 2 * $_[0] }

##</code><code>##

$sub(3);      # or
$sub.(3);     # All except the last one can also be called using:
$sub(x => 3); # or
$sub.(x => 3);