use Data::Dumper;

$x{a}     = "bare a";
$x{"a.b"} = "quoted a.b";
$x{a.b}   = "unquoted a.b";
print Dumper(\%x);'

__DATA__
$VAR1 = {
          'ab' => 'unquoted a.b',
          'a.b' => 'quoted a.b',
          'a' => 'bare a'
        };