Local and global at the same time?

[newbie01 perl]

Hi all,

If I declare a variable x1 outside of the sub that makes it global, right?
Now the question is can I have the same variable x1 as a local variable of a
sub, i.e. will the following work?

$x1 = "cat";

sub sample()
{
   my $x1="dog";
   ...
   ...
}

Just trying to work out some guidelines on using variables, i.e. using
local, my or global and some naming converntion stuff ...

Is there some good links on such guidelines?