>perl -MDevel::Peek -e"my $x='abcdef'; Dump($x); substr($x,0,1)=''; Dump($x);"
SV = PV(0x226104) at 0x2252e8
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,POK,pPOK)
  PV = 0x182ca64 "abcdef"\0
  CUR = 6
  LEN = 8
SV = PVIV(0x227134) at 0x2252e8
  REFCNT = 2
  FLAGS = (PADBUSY,PADMY,POK,OOK,pPOK)
  IV = 1  (OFFSET)
  PV = 0x182ca65 ( "a" . ) "bcdef"\0
  CUR = 5
  LEN = 7