Hmmmm.... For me it works. Here a complete program to demonstrate the concept:

use strict;
use warnings;
my $var1=35;
my $var2=undef;
foreach my $name ('$var1','$var2') {
  $_=eval($name);
  print(defined $_ ? ("$name=[$_]") : "$name is undefined","\n");
}
[download]

$var1=[35]
$var2 is undefined
[download]