$s = undef;
@a = ();
%h = ();
####
undef $s;
undef @a;
undef %h;
##
##
$ perl -MDevel::Peek -e'
$s = "abc"; Dump $s;
$s = undef; Dump $s;
undef $s; Dump $s;
'
SV = PV(0x814fb00) at 0x814f69c
REFCNT = 1
FLAGS = (POK,pPOK) <-- Var contains a string
PV = 0x81651b8 "abc"\0
CUR = 3
LEN = 4
SV = PV(0x814fb00) at 0x814f69c
REFCNT = 1
FLAGS = () <-- Var is undefined
PV = 0x81651b8 "abc"\0 <-- String buffer still
CUR = 3 allocated after clearing
LEN = 4
SV = PV(0x814fb00) at 0x814f69c
REFCNT = 1
FLAGS = () <-- Var is undefined
PV = 0 <-- undef freed the buffer