C:\>perl -MO=Deparse -wMstrict -e "{package foo; *::x=\$a} $x++"
Variable "$x" is not imported at -e line 1.
Global symbol "$x" requires explicit package name (did you forget to declare "my
 $x"?) at -e line 1.
-e had compilation errors.
BEGIN { $^W = 1; }
use strict;
{
    package foo;
    *main::x = \$a;
}
$main::x++;