use Win32::TieRegistry (Delimiter => '/');
my $version=2.1;

my $key_single = 'HKEY_LOCAL_MACHINE/Software/SPS/$version';
my $key_double = "HKEY_LOCAL_MACHINE/Software/SPS/$version";

print "Single quotes: <$key_single>\n";
print "Double quotes: <$key_double>\n";