>perl -E"$foo=\'foo'; say $$foo;"
foo

>perl -E"$foo=\'foo'; say $foo->;"
syntax error at -e line 1, near "->;"
Execution of -e aborted due to compilation errors.

##</code><code>##

>perl -e"$foo=sub{}; $foo->();"

>perl -e"$foo=sub{}; $$foo();"
syntax error at -e line 1, near "$foo("
Execution of -e aborted due to compilation errors.