:~$ perl -MDevel::Peek -E'"42"=~/(\d+)/; say $1; Dump $1; $a=$1+1; Dump $1'
42
SV = PVMG(0x5d60b28468a0) at 0x5d60b2868a50
  REFCNT = 1
  FLAGS = (GMG,SMG,POK,pPOK)
  IV = 0
  NV = 0
  PV = 0x5d60b283f5f0 "42"\0
  CUR = 2
  LEN = 16
  MAGIC = 0x5d60b286f0e0
    MG_VIRTUAL = &PL_vtbl_sv
    MG_TYPE = PERL_MAGIC_sv(\0)
    MG_OBJ = 0x5d60b2868a38
    MG_LEN = 1
SV = PVMG(0x5d60b28468a0) at 0x5d60b2868a50
  REFCNT = 1
  FLAGS = (GMG,SMG,IOK,POK,pIOK,pPOK)
  IV = 42                                             #<--- Caching
  NV = 0
  PV = 0x5d60b283f5f0 "42"\0
  CUR = 2
  LEN = 16
  MAGIC = 0x5d60b286f0e0
    MG_VIRTUAL = &PL_vtbl_sv
    MG_TYPE = PERL_MAGIC_sv(\0)
    MG_OBJ = 0x5d60b2868a38
    MG_LEN = 1
:~$