$ perl -MDevel::Peek -e \
'my $toes = "potatoes"; substr($toes, 0, 4, ""); Dump($toes);'
SV = PVIV(0x1801a20) at 0x1801434
  REFCNT = 1
  FLAGS = (PADBUSY,PADMY,POK,OOK,pPOK)
  IV = 4  (OFFSET)
  PV = 0x300b64 ( "pota" . ) "toes"\0
  CUR = 4
  LEN = 5