use strict;
use warnings;
use Devel::Peek;

{
    my $foo;
    print '$foo is ', (defined($foo) ? 'defined' : 'undef'), "\n";
    Dump($foo);
}
print "\n\n";


{
    my $foo;
    print '$foo eq $foo: $foo is stringwise ', ($foo eq $foo ? 'equal' : 'unequal'), "\n";
    Dump($foo);
}
print "\n\n";

{
    my $foo;
    print '$foo == $foo: $foo is numerically ', ($foo == $foo ? 'equal' : 'unequal'), "\n";
    Dump($foo);
}

##</code><code>##

$foo is undef
SV = NULL(0x0) at 0x1275f40
  REFCNT = 1
  FLAGS = ()


Use of uninitialized value $foo in string eq at mytest.pl line 17.
Use of uninitialized value $foo in string eq at mytest.pl line 17.
$foo eq $foo: $foo is stringwise equal
SV = PV(0x1252e70) at 0x12a0470
  REFCNT = 1
  FLAGS = ()
  PV = 0


Use of uninitialized value $foo in numeric eq (==) at mytest.pl line 24.
Use of uninitialized value $foo in numeric eq (==) at mytest.pl line 24.
$foo == $foo: $foo is numerically equal
SV = PVNV(0x12510f0) at 0x12a0608
  REFCNT = 1
  FLAGS = ()
  IV = 0
  NV = 0
  PV = 0