my $var3 = 1;

##</code><code>##

my $var |= 1;
my $var2 ||= 1;

##</code><code>##

my $var;
$var = $var | 1;
       ^^^^
       Known to be undef since it was just created.

my $var2;
$var2 = $var2 || 1;
        ^^^^^
        Known to be undef since it was just created.