C:\test>perl -MDevel::Peek=Dump -E"
$s = 'fred'; 
$r = \substr $s, 1, 2; 
$$r = 'oo'; 
say $s; 
Dump $_ for $s, $r; 
$$r = 'eu'; 
say $s;  
Dump $_ for $s, $r
"

food
SV = PV(0x16d6f0) at 0x97b60
  REFCNT = 3
  FLAGS = (POK,pPOK)
  PV = 0x16b3b8 "food"\0
  CUR = 4
  LEN = 8
SV = RV(0x97be8) at 0x97bd8
  REFCNT = 2
  FLAGS = (ROK)
  RV = 0x97c80
  SV = PVLV(0xe2c48) at 0x97c80
    REFCNT = 2
    FLAGS = (PADMY,GMG,SMG,pPOK)
    IV = 0
    NV = 0
    PV = 0x16b478 "oo"\0
    CUR = 2
    LEN = 8
    MAGIC = 0x103708
      MG_VIRTUAL = &PL_vtbl_substr
      MG_TYPE = PERL_MAGIC_substr(x)
    TYPE = x
    TARGOFF = 1
    TARGLEN = 2
    TARG = 0x97b60
    SV = PV(0x16d6f0) at 0x97b60
      REFCNT = 2
      FLAGS = (POK,pPOK)
      PV = 0x16b3b8 "food"\0
      CUR = 4
      LEN = 8
feud
SV = PV(0x16d6f0) at 0x97b60
  REFCNT = 3
  FLAGS = (POK,pPOK)
  PV = 0x16b3b8 "feud"\0
  CUR = 4
  LEN = 8
SV = RV(0x97be8) at 0x97bd8
  REFCNT = 2
  FLAGS = (ROK)
  RV = 0x97c80
  SV = PVLV(0xe2c48) at 0x97c80
    REFCNT = 2
    FLAGS = (PADMY,GMG,SMG,pPOK)
    IV = 0
    NV = 0
    PV = 0x16b478 "eu"\0
    CUR = 2
    LEN = 8
    MAGIC = 0x103708
      MG_VIRTUAL = &PL_vtbl_substr
      MG_TYPE = PERL_MAGIC_substr(x)
    TYPE = x
    TARGOFF = 1
    TARGLEN = 2
    TARG = 0x97b60
    SV = PV(0x16d6f0) at 0x97b60
      REFCNT = 2
      FLAGS = (POK,pPOK)
      PV = 0x16b3b8 "feud"\0
      CUR = 4
      LEN = 8