use strict;
use warnings;
use Devel::Peek;

sub p1 {
    my $n1 = @_;
    print "1. Parameters to the sub p1 $n1\n";
    print \$_,"\n" for @_;
    Dump $_ for @_;
}
p1 $ARGV[0], undef;

__END__
1. Parameters to the sub p1 2
SCALAR(0x604f80)
SCALAR(0x604160)
SV = PVLV(0x67eba0) at 0x604290
  REFCNT = 3
  FLAGS = (GMG,SMG)
  IV = 0
  NV = 0
  PV = 0
  MAGIC = 0x62f2a0
    MG_VIRTUAL = &PL_vtbl_defelem
    MG_TYPE = PERL_MAGIC_defelem(y)
  TYPE = y
  TARGOFF = 0
  TARGLEN = 0
  TARG = 0x604f80
  SV = NULL(0x0) at 0x604f80
    REFCNT = 2
    FLAGS = ()
SV = NULL(0x0) at 0x604160
  REFCNT = 2
  FLAGS = ()