sub new{

    my ($class,$logpath) = @_;

    unless ( ref $singleton eq 'Log' ) {
        $singleton = {};
        bless( $singleton, $class );
        $singleton->create_path($logpath);
    }

    return $singleton; 
}
[download]

There's a couple of things I'd change:

package Log;
my $instance = undef;

sub new {
    shift; 
    unless ($instance){
       $instance={};
       bless $instance,"Log";
    }
    return $instasnce;
}
[download]

You would not need the get_log_instance sub since

| handwaving here
my $log=new Log();
|
[download]

would either return the instance in play already or create a new one it there wasn't one in play. Creating a singleton is something I do all the time. Especially for my logging module. :-)