$sym = "${callpack}::$sym" unless $sym =~ /::/;
*$sym =
(  $ch eq "\$" ? \$$sym
 : $ch eq "\@" ? \@$sym
 : $ch eq "\%" ? \%$sym
 : $ch eq "\*" ? \*$sym
 : $ch eq "\&" ? \&$sym 
 : do {
	 require Carp;
	 Carp::croak("'$_' is not a valid variable name");
 });

##</code><code>##

perl -Mstrict -Wle 'BEGIN { *main::x = \$main::x; } $x = 42;'

##</code><code>##

Variable "$x" is not imported at -e line 1.
Global symbol "$x" requires explicit package name at -e line 1.
Execution of -e aborted due to compilation errors.

##</code><code>##

perl -Mstrict -Wle 'BEGIN { package ARBITRARY_PACKAGE_NAME; *main::x = \$main::x; } $x = 42;'