$ perl -MDevel::Peek -e " my $a = q!1234!; Dump $a; "
SV = PV(0x3f6d74) at 0x9ba724
  REFCNT = 1
  FLAGS = (PADMY,POK,pPOK)
  PV = 0x9bf9fc "1234"\0
  CUR = 4
  LEN = 8

$ perl -MDevel::Peek -e " my $a = q!1234!; substr$a,0,2,q!!; Dump $a; "
SV = PV(0x3f6d8c) at 0x9ba764
  REFCNT = 1
  FLAGS = (PADMY,POK,OOK,pPOK)
  OFFSET = 2
  PV = 0x9bfa4e ( "1\002" . ) "34"\0
  CUR = 2
  LEN = 6

$ perl -MDevel::Peek -e " my $a = q!1234!; substr($a,0,2)=q!!; Dump $a; "
SV = PV(0x3f6d8c) at 0x9ba764
  REFCNT = 2
  FLAGS = (PADMY,POK,OOK,pPOK)
  OFFSET = 2
  PV = 0x9bfa4e ( "1\002" . ) "34"\0
  CUR = 2
  LEN = 6

$ perl -MDevel::Peek -e " my $a = q!1234!; substr($a,0,2)=q!!; substr$a,0,2,q!!; Dump $a; "
SV = PV(0x3f6d8c) at 0x9ba77c
  REFCNT = 2
  FLAGS = (PADMY,POK,OOK,pPOK)
  OFFSET = 4
  PV = 0x9bfa58 ( "1\0023\4" . ) ""\0
  CUR = 0
  LEN = 4

$ perl -MDevel::Peek -e " my $a = q!1234!; substr$a,0,2,q!!; substr($a,0,2)=q!!; Dump $a; "
SV = PV(0x3f6d8c) at 0x9ba77c
  REFCNT = 2
  FLAGS = (PADMY,POK,OOK,pPOK)
  OFFSET = 4
  PV = 0x9bfa58 ( "1\0023\4" . ) ""\0
  CUR = 0
  LEN = 4