$ perl -MDevel::Peek -e'
    my $x;
    Dump $x;
    Dump $_ for $x;
    Dump grep 1, $x;
    Dump do { $x };
    Dump map $_, $x;
    Dump sub { $x }->();
    Dump eval { $x };
' 2>&1 | grep 'SV ='
SV = NULL(0x0) at 0x814ecdc   # Address of $x
SV = NULL(0x0) at 0x814ecdc   # for  aliases
SV = NULL(0x0) at 0x814ecdc   # grep aliases
SV = NULL(0x0) at 0x814ecdc   # do   aliases
SV = NULL(0x0) at 0x814ed9c   # map  copies
SV = NULL(0x0) at 0x814f7f8   # sub  copies
SV = NULL(0x0) at 0x814ed9c   # eval copies