use Devel::Peek;
$_ = 'blah';
while(/./g){
    Dump $_;
    for ('foo'){      # implicit localization of $_
        pos($_) = 2;
        Dump $_;
    }
    Dump $_;
    last;
}
__END__
output:

SV = PVMG(0x8102ff8) at 0x80e72ac
  REFCNT = 1
  FLAGS = (SMG,POK,pPOK)
  IV = 0
  NV = 0
  PV = 0x80f4d78 "blah"\0
  CUR = 4
  LEN = 5
  MAGIC = 0x80f35d0
    MG_VIRTUAL = &PL_vtbl_mglob
    MG_TYPE = 'g'
    MG_LEN = 1
SV = PVMG(0x8103018) at 0x80f90f0
  REFCNT = 3
  FLAGS = (SMG,POK,READONLY,pPOK)
  IV = 0
  NV = 0
  PV = 0x80f38e8 "foo"\0
  CUR = 3
  LEN = 4
  MAGIC = 0x80f1cb0
    MG_VIRTUAL = &PL_vtbl_mglob
    MG_TYPE = 'g'
    MG_LEN = 2
SV = PVMG(0x8102ff8) at 0x80e72ac
  REFCNT = 1
  FLAGS = (SMG,POK,pPOK)
  IV = 0
  NV = 0
  PV = 0x80f4d78 "blah"\0
  CUR = 4
  LEN = 5
  MAGIC = 0x80f35d0
    MG_VIRTUAL = &PL_vtbl_mglob
    MG_TYPE = 'g'
    MG_LEN = 1