$ perl -MDevel::Peek -e " Dump($!); $!=20; stat 1; printf qq[%d %s %d\n], $!,$!,-$!; Dump($!);  "
SV = PVMG(0x9b3adc) at 0x9ba5ac
  REFCNT = 1
  FLAGS = (GMG,SMG)
  IV = 0
  NV = 0
  PV = 0
  MAGIC = 0x9c6d9c
    MG_VIRTUAL = &PL_vtbl_sv
    MG_TYPE = PERL_MAGIC_sv(\0)
    MG_OBJ = 0x9ba59c
    MG_LEN = 1
    MG_PTR = 0x9c2b7c "!"
2 No such file or directory -20
SV = PVMG(0x9b3adc) at 0x9ba5ac
  REFCNT = 1
  FLAGS = (GMG,SMG,pNOK,pPOK)
  IV = 20
  NV = 2
  PV = 0x3ffed4 "No such file or directory"\0
  CUR = 25
  LEN = 28
  MAGIC = 0x9c6d9c
    MG_VIRTUAL = &PL_vtbl_sv
    MG_TYPE = PERL_MAGIC_sv(\0)
    MG_OBJ = 0x9ba59c
    MG_LEN = 1
    MG_PTR = 0x9c2b7c "!"